Symposium NM01 : Carbon Nanotubes, Graphenes and Related Nanostructures

Over two decades have passed since the discovery and structural elucidation of the carbon nanotube (CNT), and the application of its unique set of properties have yet to reach industry. One of the primary missions of our Center is to do work to promote the development of a CNT industry. We do this through the advancement in high efficiency, high purity, low cost mass production as well as processing technologies to carry the CNT material into functional materials and forms. With this as our motivation, this presentation will provide an overview of our recent progress in the synthesis and application of single-wall carbon nanotubes (SWCNTs) highlighting various milestones and their role in understanding SWCNT synthesis and industrial development.

Bilayer graphene has attracted significant attention from researchers because it holds interesting physical properties such as tunable bandgap, von Hove singularities, etc.[1] Moreover, comparing with monolayer graphene, bilayer graphene is anticipated to have better conductivity and mechanical robustness. Therefore, enable the reliable synthesis of bilayer graphene is very important both for fundamental research and potential applications. Among many synthesis methods, chemical vapor deposition (CVD) is most promising due to its scalability and economic efficiency. In order to break self-limited growth on copper substrate (which gives only monolayer graphene), asymmetric growth is needed to supply carbon atom at graphene/copper interface.[2] Nonetheless, nucleation mechanism at graphene/copper interface is still not well understood. As a result, continuous bilayer graphene is normally grown with multilayer regions (layer number ≥3), which limited the application of this approach.
Here, we report a simple method to control multilayer graphene nucleation by oxidizing copper substrate before the CVD process. Further investigation reveals that copper surface oxygen play double roles on multilayer nucleation. Slightly increasing oxygen level from initial copper foil firstly increase multilayer nucleation density. On the other hand, abundant surface oxygen helps constricting multilayer nuclei, meanwhile, accelerating bilayer growth. After surface oxidization, pure polycrystalline bilayer graphene flake can be obtained as large as 100um in diameter. Moreover, we found surface oxygen is effective on both Bernal bilayer graphene growth and random twist graphene growth. Surprisingly, for bilayer graphene growth using Ni-Cu alloy, effect of surface oxygen is also observed by confirming a more uniform bilayer film. In addition, XPS and XRD studies implies that the decrease of nuclei density is relative to formation of Cu₂O on the surface indicating there exists a limit for surface oxygen level.
In summary, we developed a novel but simple pathway to control multilayer graphene nucleating during bilayer graphene growth. This method opens a door to explore the nucleation mechanism at graphene/copper interface and, to produce high quality, low cost, large area bilayer graphene.


References:
[1] Gao, Zhaoli, et al. "Crystalline Bilayer Graphene with Preferential Stacking from Ni−Cu Gradient Alloy" ACS Nano, 2018, 12(3), 2275-2282
[2] Fang, Wenjing, et al. "Asymmetric Growth of Bilayer Graphene on Copper Enclosures Using Low-Pressure Chemical Vapor Deposition" ACS Nano, 2014, 8(6): 6491-6499

The chemical vapor deposition (CVD) synthesis of millimeter-tall carbon nanotube (CNT) forests using iron catalyst on alumina underlayer has now become established. Many studies have elucidated the role of precursor gases and water vapor, catalyst coarsening, and possible models for growth termination. However, it is well-known to the practitioners that the synthesis is not always fully reproducible and can be affected by tiny amounts of carbon or water vapor present in the reactor, by laboratory temperature or humidity, etc. To solve this problem, we assumed that the key issue is the interface between the catalyst and the alumina underlayer and the subsurface diffusion of iron (catalyst) into alumina (underlayer). We focused on tuning the microstructure of the alumina underlayer and studied how different microstructures would affect CNT growth, keeping all the other process and material parameters constant. We postulated that the issue was the grain size of the underlayer and thus the amount of grain boundaries. Since the iron catalyst subsurface diffusion into the alumina underlayer will strongly be affected by the amount of grain boundaries, with grain boundary diffusion being much faster compared to lattice diffusion, we decided to control the grain size of the alumina. Using electron-beam evaporation, we prepared samples where we heated the substrate at 350 °C during deposition and slowly evaporated the alumina with the goal to obtain large grains in order to minimize the amount of grain boundaries. We also prepared samples where we evaporated the alumina at a fast rate to obtain small grains and to maximize the amount of grain boundaries. We used as reference samples where the alumina was e-beam evaporated at an average rate. After synthesis, we consistently observed tall CNT carpets on the samples where the substrate was heated during deposition and the alumina was evaporated at a low rate. However, the CNT carpets obtained on the other samples were significantly shorter and their height distribution was very wide. We will show statistical distributions of the CNT height obtained from multiple samples. To prove the mechanisms involved in this finding we analyzed the catalyst morphology after annealing of the different samples using atomic force microscopy (AFM) and high-resolution scanning electron microscopy (HRSEM). Using a focused ion beam (FIB), we prepared a lamella for each type of sample and analyzed the alumina nanostructure, iron subsurface diffusion, and overall composition using HRTEM. This study shows how critical it is to consider the microstructure of the alumina underlayer and how by appropriately tuning the deposition conditions, we can obtain samples that will consistently grow millimeter-tall forests of CNTs.

Carbon nanotubes (CNT) had received broad attention in the past decades due to its dramatic physical and chemical performance of individual tubes and became a powerful candidate of future star materials. As synthesis determined the future, in this talk, I will focus on the controlled growth of SWNTs arrays with ultra-high density, high ratio semiconducting properties and special chiral angles. For the SWNTs arrays with ultra-high density, Trojan catalysts (released from substrate) was developed and the density can be as high as 150 tubes/µm. For the SWNTs arrays with semiconducting properties, oxides catalysts with oxygen vacancy, bimetal catalysts and uniform Mo₂C catalyst were used to grow semiconducting SWNTs arrays and ratio of semiconducting tubes can be higher than 95%. For the SWNTs arrays with special chiral angles, it is based on a consideration of nanotube/catalyst interfacial thermodynamics determined by symmetry, and the kinetic growth rates set by the number of kinks. Using these strategies, horizontally aligned metallic ((12, 6), abundance >90%) and semiconducting ((8, 4), abundance >80%) SWNT arrays with an average density higher than 20 tubes/µm and 10 tubes/µm, respectively, were successfully obtained on uniform solid catalysts.

References：
Jin Zhang et. al., Nature, 543(2017), 234-238.
Jin Zhang et. al., Sci. Adv., 2(2016), e1501729.
Jin Zhang et. al., Nat. Commun. 6 (2015), 6099.
Jin Zhang et. al., J. Am. Chem. Soc. 137(28) (2015), 8904-8907.

Although carbon nanotubes have shown a wide range of promising properties [1-3], the inability to fully control their chirality still remains a major impediment factor for their implementation. A few years ago, the community has realized that post-synthesis sorting of carbon nanotubes could be the solution, and so an arsenal of techniques has been developed to reach this goal [4]. Unfortunately, despite their merits, to obtain carbon nanotubes of certain chirality tedious multistep processing must be carried out each time. In this presenation, we would like to show how we have adopted and modified the method of aqueous two-phase extraction [5] to aim for separation of selected carbon nanotube type in a single step [6]. We were able to separate minor chiral species from the CNT mixture with up to 99.7% optical purity without any unnecessary iterations. What is more, we observed emergence of new optical features under certain circumstances.

References:
[1] M.-F. Yu, O. Lourie, M. J. Dyer K. Moloni, T. F. Kelly, R. S. Ruoff, Strength and breaking mechanism of multiwalled carbon nanotubes under tensile load, Science 287, 2000, 637.
[2] A. Lekawa-Raus, T. Gizewski, J. Patmore, L. Kurzepa, K. Koziol, Electrical transport in carbon nanotube fibres, Scripta Materialia 131, 2017, 112.
[3] S. Hong, S. Myung, Nanotube Electronics: A flexible approach to mobility, Nature Nanotechnology 2, 2007, 207.
[4] D. Janas, Towards monochiral carbon nanotubes: a review of progress in the sorting of single-walled carbon nanotubes, Materials Chemistry Frontiers 2, 2018, 36.
[5] J. Fagan, C. Khripin, C. Batista, J. Simpson, E. Haroz, A. Walker, M. Zheng, Isolation of specific small-diameter single-wall carbon nanotube species via aqueous two-phase extraction, Advanced Materials 26, 2014, 2800.
[6] D. Janas, E. Turek, T. Shiraki, T. Shiraishi, T. Shiga, T. Fujigaya, Single-step isolation of optically pure carbon nanotubes, Advanced Functional Materials (submitted)

Since first studies of branched carbon nanotubes (CNTs) with L-, Y- and T- shapes were published in the mid of the 1990 various approaches were presented to grow such structures. Branched carbon nanotubes are of high interest due to their unique electrical properties making them a promising material for advanced nano-electrical devices. However, SWCNTs are not easy to grow in a defined way. Therefore, Y-shaped MWCNTs or CNFs are also examined in order to understand the growth mechanism of branched nanotubes. Beside their potential use as nano-electrical devices, branched CNFs or CNTs are also of interest as a material mimicking hierarchical nanostructures found in nature.

In general, the growth of branched or non-branched CNFs or CNTs is conducted with an elaborate infrastructure relying on a certain amount of process gases and considerable energy input. We present an approach to grow inverted V-shaped or Y-shaped CNFs in an open ethanol flame. Due to their resemblance to the Greek letter lambda we named them Λ- or λ-shaped CNFs depending on their actuals shape. Λ-shaped CNFs consist of two CNFs attached to the substrate with one end and connected to each other with the other end resulting in a free standing lambda-shape. An additional CNF can be grown from the connecting point of the first two CNFs with increasing growth time resulting in λ-shaped CNFs. Our experiments suggest that the connecting point of the lambda-CNFs is the nickel catalyst and that the third CNF growth from that center. The exact growth position of the overall structure on the substrate can be determined through microchannel cantilever spotting (µCS) or dip-pen nanolithography (DPN) via the locally controlled deposition of nickel catalysts. Down-scaling to a spot size that results solely in one single lambda-shaped CNF is demonstrated.

Single-walled carbon nanotubes (SWCNTs) are one-dimensional materials exhibiting unique properties, so they have been anticipated for various electronic devices in future. Presently, catalyst-assisted chemical vapor deposition (CVD) are widely used to obtain high-yield SWCNTs, where alumina buffer layers are used to enhance the catalyst activity. However, the enhancement mechanism of catalyst activity by the alumina buffer layers remains poorly understood. In this study, we preformed SWCNT growth at 600°C by alcohol catalytic CVD using Rh catalysts on different types of alumina buffer layers prepared using different processes, and the effects of oxidation and crystallinity of alumina buffer layers on catalysts activity were investigated.
Five kinds of alumina buffer layers were used to support Rh catalysts; native oxidation of Al layer deposited by electron beam (EB); thermal oxidation of Al layer deposited by EB; EB deposition of Al₂O₃ powder; native oxidation of Al layer deposited by rf-sputtering; thermal oxidation of Al layer deposited by rf-sputtering. After deposition of Rh catalysts (nominal thickness ~ 0.2 nm) on them, we carried out SWCNT growth by alcohol catalytic CVD [1]. The grown SWCNTs were characterized by Raman measurements, FESEM and TEM. The alumina support layers were analyzed by XPS, XANES, AFM, TEM and ellipsometry. Rh particle sizes and subsurface diffusion were characterized by TEM and depth profile using XPS.
Although Rh nanoparticles were formed on all alumina layers, SWCNTs were not grown on the alumina buffer layer in which metallic Al was contained. Depth profile showed that the large inward diffusion of Rh catalysts occurred on the “metallic” alumina buffer layer, resulting in the reduction of SWCNT yield. For the alumina buffer layers prepared by thermal oxidation, diaspore-type alumina polycrystals were formed and that Ostwald ripening of Rh catalysts was enhanced on them, leading to small SWCNT yields. Conversely, on the amorphous alumina layers, Ostwald ripening was suppressed and Rh particles suitable for SWCNT growth were formed. Additionally, the inward diffusion of Rh catalysts was suppressed on the diaspore-type amorphous layers with higher densities. Our results demonstrated that amorphous alumina support layers with high densities are suitable for suppressing both Ostwald ripening and inward diffusion of catalysts, making them favorable for high-density SWCNT growth.
[1] T. Maruyama et al. Carbon 116 (2017) 128.

Raman spectroscopy is an efficient tool giving distinctive features for pristine, damaged and even doped graphene. Typical Raman methods are however limited by their intrinsic microscopic nature, only being able to probe the area exposed to the laser beam (~ 1 μm). Hence, Raman mapping is often used to assess a broader region of graphene samples. Nonetheless, especially when graphene is grown on a polycrystalline substrate, strong discrepancies may appear on a scale larger than the available mapping area (> tens or hundreds of μm). Moreover, in the case of plasma irradiation of graphene, it is essential to understand the impact of the small heterogeneities in pristine graphene (local defects, grain boundaries, etc.) on the resulting graphene structure after treatment. In this context, recent advances in laser technology combined with increased efficiencies of Charge-Coupled Devices (CCD) and the development of efficient Bragg filters opened the road to new Raman imaging methods with reasonable integration time. In particular, hyperspectral Raman Spectroscopy or RIMA (Raman Imaging) is a very powerful method to obtain qualitative as well as quantitative Raman data on a macroscopic scale [1].
In this work, RIMA was used to examine plasma-induced modification of CVD-grown graphene films. Experiments were realized in a low-pressure inductively-coupled plasma. This method is a commonly used post-processing technique to alter materials properties and thus, is a good candidate to tune graphene films. It is however difficult to decouple doping and damage mechanisms. In damage studies of graphene, ions beams are operated at energy above a few tens of eV [2] while ions energy in our plasma conditions is below the energy threshold for atom displacement (T_d = 15-20 eV) [2]. Yet, defects generation by such plasmas are reported in few studies [3] but are not clearly understood.
Graphene films were exposed to an argon plasma and RIMA measurements were performed on different areas to study the sample homogeneity. These results reveal how the initial state of graphene films is a key factor to understand plasma irradiation effects. In addition, the very large number of Raman data (>10⁶) was used to establish links between doping, strain and damage types in both as-grown and plasma-processed graphene films. To further understand plasma-graphene interactions, plasmas conditions were adjusted as to vary ion energy and fluence of plasma-generated species.
[1]: E. Gaufrès, S. Marcet, V. Aymong, N. Y-W. Tang, A. Favron, F.Thouin, C. Allard, D. Rioux, N. Cottenye, M. Verhaegen and R. Martel, J. Raman Spectrosc, 49 (2018)
[2]: O. Lehtinen, J. Kotakoski, A.V. Krasheninnikov, and J. Keinonen, Nanotechnology 22 (2011).
[3]: B. Rousseau, H. Estrade-Szwarckopf, A. L. Thomann, and P. Brault, Appl. Phys. A: Mater. Sci. Process. 77 (2003).

Although significant progress has been made since 25 years, one major obstacle to realization of Single-walled carbon nanotubes (SWNTs)-based nanotechnology has been the lack of control for designing selective synthesis conditions. This is partly due to the incomplete understanding of the physical and chemical effects driving the kind of tubes able to nucleate and grow under given experimental conditions [1].

A way to adress this basic question is to consider SWNT growth from a thermodynamic point of view. To that aim, we have developed a statistical thermodynamics model, valid in the case of a perpendicular growth [2], which has been experimentally proven to yield a near-armchair selectivity [3]. This model relates the stable (n,m) tube structures to the tube/catalyst interfacial energies for zigzag and armchair edges and the temperature [4]. Taking the configurational entropy of the tube edge into account is a central point that explains how chiral tubes become stable at finite temperature, while ground state structures are either zig-zag or armchair. Exploring the parameter set enables one to display temperature dependent chirality maps, locating the most stable tube structure. More precisely, for each set of interfacial energies and temperature, this model yields a probability distribution of (n,m) SWNTs.

With this model in hand and thanks to a scrupulous analysis of our previous results and data of the literature, we will compare in this talk experimental measured and model chirality distributions facing two difficulties. A first notorious difficulty is the experimental evaluation of the chiral distribution of tubes produced in a CVD process, as most of characterization techniques might fail either in the identification of the different kinds of tubes present in a sample or in determining their relative fractions. On the other hand, the model, being purely thermodynamic, does not take into account kinetics and experimental conditions which may impact the tube selectivity such as a possible preferential etching of metallic tubes.
These limits given, we will show the efficiency of the model in understanding the origin of the frequently reported near-armchair selectivity and for accounting for chirality distributions observed under given synthesis conditions. Finally we shall evaluate the potential of the model for providing guidelines for catalyst design and growth condition optimization.
[1] Amara H. and C. Bichara C., Topics in Current Chemistry 375, 55 (2017)
[2] Fiawoo, M.-F. C.et al.Phys. Rev. Lett., 108, 195503 (2012).
[2] He, M. et al.Nanoscale(2018). doi:10.1039/C7NR09539B
[3] Magnin, Y. et al.Entropy driven stability of chiral single-walled carbon nanotubes. Submitted. https://arxiv.org/abs/1803.07350
[5] Ding. F. et al.,Proc. Natl. Acad. Sci.106,2506–2509 (2009)

Two dimensional layered materials (2DLMs) are important candidates of flexible electronics applications, used for health monitors, displays, batteries, and sensors. Despite the significant progress being made in synthesis technologies and in the prototyping of 2DLM flexible electronics, the work in the scalable integration of 2DLMs with flexible polymer substrates has proven, thus far, to be minimal and limited to several specific 2DLMs and polymer substrates. In this work, we demonstrated directly assemble wafer-scale 2DLM film on a polymer substrate through a dynamic energy driven assembly (DEDA) method seamlessly integrating a liquid exfoliation and a new assembly strategy. The DEDA method includes three steps: exfoliation of 2DLM in a designated solvent using sonication, and submerge polymer substrate to process the assembly, and take out the assembled substrate to dry. The principal innovation of DEDA is to control the relative interfacial energy among solvent, 2DLM and polymer substrate such that a relative low-energy 2DLM-polymer interface and a relative high-energy solvent-polymer interface will enable effective assembly of 2DLM on the polymer. Unlike the traditional assembly strategies, which start with a stabilized solution and emphasize good wetting among all components, DEDA theory suggests poor-wetting solvent is the key that determines the assembly quality. As a proof-of-concept, we have successfully used DI water, a non-toxic but poor wetting solvent for PDMS, to exfoliate and then assemble different 2DLMs (graphene, h-BN, and MoS₂) on a PDMS substrate. A uniform film can be formed as short as 10 seconds after immersing PDMS substrate in the solution and by adjusting the solution concentration and assembly time, the thickness of the assembled film can be easily tuned from several nanometers to hundreds of micrometers. It is also interesting to notes, adding 2-propanol into water decreases the assembly efficiency dramatically. This results matching the prediction from DEDA theory where improved wetting between the solution and PDMS diminish the driving force of assembly. In summary, the unique features of this DEDA method are (1) a new interfacial energy driven assembly strategy that has the potential to be generalized broadly to arbitrary 2DLMs and polymers, (2) the usage of the non-equilibrium 2DLMs solution for rapid assembly, and (3) high controllability of the assembly through simple concentration and assembly time controls. This study not only creates a new assembly method for the scalable and hierarchical fabrication of 2DLM flexible electronics but also advances knowledge in nanomaterials assembly and will promote the field of nanomanufacturing.

Due to their extraordinary electrical and mechanical properties, carbon nanotubes (CNTs) and graphene are widely regarded as very attractive nanomaterials. For example, CNT production capacity has rapidly increased worldwide. For commercialization of CNT and graphene-based products, the qualities of CNTs and graphene must be controlled. In this talk, we will show effective methods for quality evaluation of CNTs and graphene.
First, the lengths of CNT are estimated by far-infrared (FIR) spectroscopy.^1-3 Based on the plasmon resonance model, the length of the clean channel (‘effective length') of CNTs can be deduced by the method. The systematic investigations of the relationship between the mechanical and electrical properties of CNT fibers and the effective lengths of the constituent CNTs is discussed.^4,5
Next, lock-in thermography technique is applied for visualizing the network structure of CNTs in composites and evaluation of quality of graphene sheet.^6,7 Detection of Joule heating in a biased device enables local structures to be imaged without the influence of heat broadening in a short acquisition time.
A part of this presentation is based on results obtained from a project (P16010) commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

[1] T. Morimoto, S.-K. Joung, T. Saito, D. N. Futaba, K. Hata, T. Okazaki, ACS Nano, 8, 9897-9904 (2014).
[2] T. Morimoto, T. Okazaki, Appl. Phys. Exp., 8, 055101 (2015).
[3] T. Morimoto, Y. Ikeda, M. Ichida, T. Okazaki, Phys. Rev. B, 93, 195409 (2016).
[4] X. Wu, T. Morimoto, K. Mukai, K. Asaka, T. Okazaki, J. Phys. Chem. C, 120, 20419−20427 (2016).
[5] X. Wu, K. Mukai, K. Asaka, T. Morimoto, T. Okazaki, Appl. Phys. Exp., 10, 055101 (2017).
[6] T. Morimoto, S. Ata, T. Yamada, T. Okazaki, submitted.
[7] H. Nakajima, T. Morimoto, Y. Okigawa, T. Yamada, Y. Ikuta, K. Kawahara, H. Ago, T. Okazaki, submitted.

A gaseous product mixture from Fischer-Tropsch synthesis (FTS-GP) has been utilized as an efficient feedstock for growth of high-quality, well-aligned, single-wall carbon nanotube (SWCNT) carpets of millimeter-scale heights on Fe and (sub) millimeter-scale heights on Co catalysts via chemical vapor deposition (CVD). Growth conducted at optimal temperatures for Co and Fe catalysts yielded predominantly SWCNTs that are largely free of carbon impurities. Growth on Fe is characterized by a growth rate of ~50 μm/min and catalyst lifetime that is longer than 90 min, with the catalyst showing no decay of activity. In contrast, growth on a Co catalyst shows a lifetime of ~60 min, with a slower growth rate of ~7μm/min. Resulting area densities of SWCNT carpets grown on Fe and Co catalysts, determined by the weight-gain method, were 1.0 × 10¹² and 6.0 × 10¹² cm^-2, respectively. The catalyst lifetime and area densities of SWCNTs are among the highest achieved on standard catalysts. Unlike SWCNT carpet growth involving conventional feedstocks (such as C₂H₂, C₂H₄, and CO), growth rate and density of SWCNTs on Fe are less sensitive to the FTS-GP fraction and thus allow for relatively easy optimization and scale-up.

Plasma enhanced chemical vapor deposition (PE-CVD) is the method of choice to fabricate graphene films at temperatures well below 1000°C. Low growth temperatures are of interest e.g., to decrease the production cost, to make the process suitable for roll-to-roll implementation or to facilitate the growth of graphene on other non-catalytic substrates. Although few groups showed nearly defect-free PE-CVD grown graphene at low temperatures, a detailed understanding of the growth mechanism is still missing [1].
In order to study the growth mechanism in PE-CVD we used a commercially available 4” cold wall reactor to fabricate graphene on electrochemically polished high-quality copper foils [2]. A cost-effective DC plasma is applied to dissociate the precursor methane. To suppress unintended vertical graphene growth and ion acceleration to the substrate we introduced a sacrificial Cu foil into the growth chamber. The growth temperature was systematically varied from 1020°C down to 600°C. By varying the growth time at different temperatures two types of samples were prepared: graphene flakes and graphene films. By analyzing the flake areas the growth rate could be determined in dependence of growth time and growth temperature.
Almost defect-free graphene with negligible (I_D/I_G < 0.1) contributions of the D peak in Raman spectroscopy could be prepared even at 600°C. Compared to thermal CVD we found that the activation energy for the growth rate decreases from 4 eV down to 1.8 eV in PE-CVD, indicating efficient precursor dissociation in the plasma. From our studies we conclude that the carbon attachment step is the limiting factor for the PE-CVD growth. During the early stage of growth, we observed crystalline graphene grains surrounded by amorphous carbon in Raman spectroscopy. With increasing growth time graphene flakes grow at the expense of amorphous carbon and eventually merge into an almost defect-free graphene film with a sheet resistance down to 470 Ω/sq.
References
[1] S. Naghdi, K. Y. Rhee, S. J. Park, A catalytic, catalyst-free, and roll-to-roll production of graphene via chemical vapor deposition: Low temperature growth, Carbon 127, 1 (2018)
[2] B. Bekdüz, Y. Beckmann, J. Meier, J. Rest, W. Mertin, G. Bacher, Relation between growth rate and structure of graphene grown in a 4“ showerhead chemical vapor deposition reactor, Nanotechnol. 28, 185601 (2017)

Graphene is one of the atomic layered materials which has interesting physical properties such as mechanical strength, optical transparency, electron and thermal conductivity. The identification of a layer number is necessary for graphene based technology, because these properties strongly depend on a number of layers. Optical microscopy, Raman spectroscopy, scanning electron microscopy and other microscopic techniques are used to image a map of graphene layer. SEM has superior character among these various techniques for its high spatial resolution and large field of view. In order to observe graphene using scanning electron microscopy, it is necessary to detect electrons emitted by the interaction between electron beam, graphene and substrate. When the graphene on substrate are observed with SEM using secondary electrons emitted from not only graphene but also the substrate.
In the present study, the effect of graphene layers on the secondary electrons including elastic and energy loss peaks were investigated using Auger electron microscopy. A carbon-doped poly crystalline nickel foil was heated (up to 900 degree or more) by electrical current supply and cooled rapidly. Through the thermal process, graphene having different number of layers was precipitated on the nickel surface by segregation. SEM observation and reflection electron energy loss spectroscopy (REELS) measurement was performed using a scanning Auger electron microscope (JAMP-9510F, JEOL Ltd.). The accelerating voltage was 1.5 kV. The full width at half maximum of the back scattered electron peak was about 0.9 eV. The angle between the SEM column and electron analyzer was 60 degree. The sample tilting axis of the sample stage was perpendicular to the plane made by SEM beam axis and analyzer collection direction, so called sagittal plane. Therefore, the sample could be set in specular geometry such as the incident and outgoing angle of electrons were the same, by tilting 30 degree. All experiments in this report were performed in the specular condition to get highest intensity for zero-loss and energy loss spectra. At the first, the sample was observed with SEM using out-lens secondary electron detector. The SEM image showed that various layer graphene segregated from the nickel foil. There was the bare nickel region near at the center of the foil ribbon because the center was highly heated by the DC current feed through. The SEM image shows that the layer number of graphene increased along with the ribbon.
The result of REELS measurement is that the intensity of zero-loss peak monotonically decreased depending on the layer number of graphene and the shape of energy loss spectra has specific feature of each layer number of graphene on any kinds of substrate can be determined by using the elastic peak and energy loss spectra.

Chemical vapour deposition (CVD) has emerged as the most promising method for scalable growth of two-dimensional materials (2DM), such as graphene and hexagonal boron nitride (h-BN). To improve growth, the focus has mainly been on fine-tuning the deposition process using a copper (Cu) catalyst. Notable progress has been made regarding the quality of the as-grown 2DM. However, the high vapour pressure of Cu is a source of reactor contamination and its low melting point sets a challenging limit for any process optimization. Furthermore, 2DM are prone to contamination by trace Cu, which is a constraint for CMOS integration.[1] Here we present a holistic approach for CVD of 2DM starting with the choice of the catalyst. Based on considerations including accessible CVD parameter space, ease of CMOS integration, feasibility of growth and strategies for transfer, we have determined platinum (Pt) as the optimal catalyst for growth of graphene and h-BN.
The growth of graphene on Pt is critically dependent on the supply and removal of carbon from the catalyst surface by bulk diffusion. By tuning this kinetic process, it is possible to grow graphene isothermally, by precipitation or through both mechanisms. By careful tuning of the growth conditions, we can achieve continuous single-layer graphene with large domains (>0.1mm), isolated bi-layer graphene domains (>0.05mm) and continuous bilayer graphene.[2] While high-quality graphene alone is sufficient for certain applications, most require a van der Waals (vdW) heterostructure, where graphene is embedded within layers of h-BN. Currently, h-BN is mainly obtained through exfoliation of bulk crystals due to lack of clean methods of transferring CVD grown h-BN. Here, we present an approach to grow high quality h-BN on Pt, with domain sizes exceeding 0.5 mm, and to transfer these layers using a delamination-based process, which avoids the contamination associated with traditional transfer methods. These layers can then be used to sequentially pick up additional layers of h-BN or graphene for scalable fabrication of vdW heterostructures. To demonstrate the feasibility of our approach, we have fabricated devices that outperform existing devices relying on CVD 2DMs.[3]
Based on the in-depth understanding of the CVD growth mechanism and the subsequent integration pathway, we present a new approach to scalable fabrication of 2DM. Instead of additional process optimization, we show how by choosing the optimal catalyst, it is possible to offer solutions to some of the pressing challenges for the scalable manufacture of 2DM. We demonstrate the growth of both graphene and h-BN, with control over layer number, domain size and alignment, and show how these layers can then be cleanly assembled to form vdW heterostructures.

References
[1] S. Hofmann et al., J. Phys. Chem. Lett 14, 2714 (2015)
[2] R. Weatherup & R. Wang et al., In Submission
[3] R. Wang et al., In Submission

In the last few years, a great interest has arisen for thin (with a thickness of less than 100 nm) single-walled carbon nanotube (SWNT) films filled with electron-acceptor molecules [1-4]. They are a macroscopic object and have a transparency of about 90% and a surface resistance of 50 Ω / square [3]. These parameters make them a real candidate for replacing the most popular material for transparent electrodes today - ITO (indium tin oxide). The filling of nanotubes results in their p-type doping, confirmed by the shift of the position of the tangential mode (1592 cm-1) in the Raman spectra and suppression of the E11 and E22 transitions in the optical absorption spectra. The shift of the Fermi level to the valence band was estimated as 1 eV. After doping, the electrical resistance of the tubes decreases by almost an order of magnitude, and the optical transmission increases by 3-5% [2,3]. The effect is more pronounced in the fractions of the tubes, separated by the type of conductivity. The optical properties of hole-doped SWNTs also are also interesting. In photoluminescence (PL) spectra (in contrast to the case of pristine nanotubes), new peaks have been observed. They were assigned to trions, quasiparticles consisting of two holes and one electron. The redistribution of PL intensity between the exciton and trion peaks is demonstrated with an increase in the degree of doping. Pump-probe experiments have revealed the ways of energy transfer in doped SWNTs.
The authors are grateful for the financial support in frames of RFBR projects (16-02-00979 and 17-302-50008). P.A.O. thanks RSF project 17-72-10303.
References
Tonkikh A.A., et al., Physica Status Solidi B 249 (12) (2012), 2454–2459.
Tonkikh A.A., et al., Carbon 94 (2015) 768-774.
Tsebro V.I., et al. Phys. Rev. B 94 (2016) 245438 (1-10).
Eremin T.V., et al.. Phys. Stat. Solidi B 255 (2018) 1700272 (1-4).

When natural rubber is quickly stretched, it gets warm. Conversely, when quickly stretch released, it gets cooled. This effect, called elastocaloric effect (ECE), was discovered in the beginning of 19th century and further observed to occur with several materials. This caloric effect was also observed to happen under the application of other types of stimulus as magnetic or electric fields. Research on ECE and other types of caloric effect has been growing fast because of the interest in the development of new, hazardous chemicals or ozone depletion-free, cooling devices. Recently, the ECE was predicted to be significant in carbon nanotubes (CNTs). Lisenkov and collaborators [Nano Letters 16, 7008−7012 (2016)], showed by means of classical molecular dynamics (MD) simulations, that it is possible to obtain as large as 30 K of variation of temperature when CNTs are subjected to external moderate forces. This finding is, now, motivating the research towards the development of cooling nanodevices. Here, also using tools of MD simulations but differently from the above study, we estimated the ECE performance of CNTs during a complete thermodynamic cycle, similar in the temperature-entropy (TS) diagram to the Otto-cycle but not based on gas compression/expansion, composed by: (1) adiabatic stretch followed by; (2) isobaric thermal equilibration at room temperature; then (3) adiabatic stretch release; and (4) final isobaric thermal equilibration at room temperature. Instead of fixing a load, we fixed the strain rate and stretched the CNT up to 10% of strain. We have obtained temperature variations due to the ECE in CNTs as high as 37 K. We discuss these results and the efficiency of a cooler machine based on the CNTs ECE.

Since 25 years, significant progress has been achieved in the controlled synthesis of Single Walled Carbon Nanotubes (SWNTs), but we are still facing difficult issues concerning the yield and selectivity of their synthesis by Catalytic Chemical Vapor Deposition. The choice of a catalyst is critical, and hitherto made by trial and error. In fact, we don’t know what are the required properties of a “good” catalyst for a selective SWNT growth, partly because currently available models [1,2] did not directly address this issue.
Here, we answer this question by developing a statistical thermodynamics model, that in the case of a perpendicular growth[3,4], relates the stable (n,m) tube structures, to the tube/catalyst interfacial energies for zigzag and armchair edges and the temperature. This model shows that, at low temperature, only zigzag or armchair tubes are stable. Chiral tubes become stable at higher temperature because of the configurational entropy of the tube edge in contact with the catalyst, that is a key element of the model. This enables us to produce chiral stability maps and phase diagrams that relate the catalyst interfacial properties and the temperature with the resulting equilibrium chiral distribution. It explains under which conditions, a near armchair distribution can be obtained, and accounts for the temperature evolution of the chiral distributions reported in a number of experiments. The technical aspects of the model [5] and possible further developments will be discussed.

[1] Ding. F. et al., Proc. Natl. Acad. Sci. 106, 2506–2509 (2009)
[2] Artyukhov, V. I. et al., Nat. Commun. 5, 4892 (2014).
[3] Fiawoo, M.-F. C. et al. Phys. Rev. Lett., 108, 195503 (2012).
[4] He, M. et al. Nanoscale (2018). doi:10.1039/C7NR09539B
[5] Magnin, Y. et al. Entropy driven stability of chiral single-walled carbon nanotubes. Submitted. https://arxiv.org/abs/1803.07350

Graphene and in general all the other 2D materials constitute the building blocks used to engineer vertically stacked structures that yield the desired properties, potentially leading to a new paradigm of metamaterial design and manufacturing. The industrial exploitation of these stacks requires an understanding of the bonding between each of the constituting 2D material surfaces so as to enhance theoretical tractability and assist in experimental design. Specifically, the short-range attractive forces responsible for material adhesion and, in the context of these structures, for the glowing of the different building blocks, are of such fundamental importance to give the name to this construct, i.e, van der Waals heterostructures. Despite the importance of van der Waals forces the effort to directly quantify the strength of such forces has not matched the effort to assess other properties and no measured values found for the most studied of the 2D materials, graphene. Here, we leverage on the successful development of high spatial resolution technique to characterize and robustly quantify the strength of van der Waals forces of graphene. A combination of multimodal AFM and force spectroscopy-based force measurement yields consistent measured values of the Hamaker constant, which effectively accounts for the strength of such forces. Large Hamaker values result in high adhesion and persistent attraction whereas low Hamaker values result in effective inertness. In this work we quantify Hamaker parameters of graphene and show how it scales by a factor of 2 or 3 from single to multiple layers on standard supporting surfaces such as copper of silicon oxide. We furthermore measure suspended graphene to evaluate the Hamaker without the influence of the substrate. Our experimental results are corroborated by first principle calculations and explained in terms of a Lifshitz theory-based analytical model.

The ability to fabricate and manipulate structures down to the level of single atoms has been the ultimate goal of nanotechnology since its inception. The development of such capabilities will have immediate impact in areas such as quantum computing, single spin magnetoelectronic devices, and scalable neuromorphic systems which all need fabrication at the atomic level, for precise positioning of functional dopant atoms and avoidance of even single-atom imperfections, defects, or design deviations in the device’s active region, contacts, and interconnects. Here, we explore the capabilities of a scanning transmission electron microscope (STEM) to alter graphene-based materials on the sub-nanometer and atomic scale. We show precise insertion of individual Si dopants into the graphene lattice as well as controlled movement and assembly of primitive structures through e-beam irradiation. We also demonstrate e-beam-mediated graphene growth, deposition, hole healing and fabrication of graphene nanoribbons and nano-cocoons which can be patterned around inserted dopants. These experiments represent the first steps toward transforming the modern STEM into a fabrication platform capable of tailoring structures down to the level of single atoms.

Structurally analogous to carbon nanotubes (CNTs), boron nitride nanotubes (BNNTs) exhibit similar mechanical and thermal properties. However, BNNTs offer additional features such as greater thermal and chemical properties, electrical resistance, and they absorb radiation. Because of these properties BNNTs have attracted much interest due to the wide range of potential applications in which they could enhance, for instance, fuel efficiency particularly in space applications, thermal management for batteries and devices¹, as tissue engineering scaffolds in biomedical applications, and in applications where strong, lightweight and thermally conductive but electrically insulating materials are required. To date, the exploitation of BNNTs in applications has been hampered by their limited availability.
Although few teams were able to reach yields of up to ca. 20g², the final morphology of the up-scaled BNNT suffers from massive entanglement turning the BNNTs into a felt-like material. Only a very limited number of reports investigating the actual formation of BNNTs are available. In order to produce BNNTs in large quantities, the fundamental science particularly the nucleation and growth of BNNTs must be first understood.
Herein, we report in situ short time reaction studies revealing the formation mechanism of BNNTs and show the nucleation and embryonic stage of BNNTs formation. At the early stages of production large amounts of nanospheres were formed possessing tail-like structures and these were found to be the seed structured of the BNNTs that formed later. ³ Magnesium, a component of the precursor, was found to play a vital role that served to generate the intermediate species and medium for the diffusion of BN species essential for the formation of BNNTs .
Our findings led us to design an experimental set-up that allows the control of three important factors for the formation control; namely (a) B species, (b) N species, and (c) the catalyst. Different morphologies were obtained by controlling the dimension of the catalyst particles. Our theoretical calculations suggested which of the generated species are stable at synthesis conditions, showed the geometrical structure they form, and followed the nucleation process through molecular dynamics simulations. The combined approach of in situ experimental work and theoretical studies paves the way to design efficient production lines for the up-scaling of BNNTs and therefore provides a practical route to the efficient exploitation of BNNTs.

[1] C. Tang, et al. J. Phys. Chem. B, 110, 10354-10357 (2006).
[2] K. S. Kim, et al. ACS nano, 8, 6211-6220 (2014)
[3] J. A. Acapulco Jr, et al. to be submitted

Growth of Carbon Nanotubes (CNTs) to lengths useful in many materials applications is currently limited by a number of factors, the most important of these being Ostwald ripening and subsequent deactivation of the metal catalyst particles from which the CNTs nucleate and grow. Here is proposed and demonstrated a novel method for overcoming this limitation. It is shown that inclusion of refractory, high-melting-point metals in the metallic catalyst used for CNT growth can substantially enhance the lifetimes of the particles of catalytic metals, enabling growth of CNTs to much greater lengths than possible using the pure catalytic metals. This lifetime enhancement occurs because the refractory metal inhibits the surface diffusion of the catalyst metals, slowing the Ostwald ripening of the catalytic particles and allowing them to grow CNTs for greater times, resulting in longer CNTs. This effect has been demonstrated for several catalyst/diffusion-inhibitor systems, and results are presented and discussed here.

Although Carbon nanotube (CNT) thin films are expected as flexible transparent conductive films, the physical origin of their high electric performance remains to be clarified yet due to complexity of nanotube network. This is because that individual variations in nanotube length and chirality are involved in nanotube network and its electrical conductivity also depends on geometrical network structure such as nanotube density and alignment. Therefore, understanding various properties of CNT thin film has been the subject of controversy over the last few years.
In order to understand various properties of CNT thin film, it is essential to understand relation between the network structure with the nanotube densities, alignment, length and diameter, and their electrical transport property. We thus theoretically explored how nanotube alignment affects electrical transport properties of CNT thin films, using a numerical stick-percolation-based model.
In the present study, we investigate electric properties of a CNT films consisted of metallic CNTs. First, we generated two-dimensional random networks in a film. Nanotubes are distributed in a film with the fixed values of the film length of L=5 µm, the film width W=5 µm, nanotube length l_CNT=0.5 µm and the chirality of a nanotube as (10,10) and the angle between the axis of nanotube and x-axis as Θ. The value of Θ takes a uniformly random value in the range -Θ_max<Θ<Θ_max, where 0°<Θ_max<90° (we define Θ_max as nanotube alignment). CNT network is transformed into effective resistor network composed of the resistance R_CNT along an individual CNT and the junction resistance R_j between CNT pairs, using ref [1]-[2]. Then, we apply a nodal analysis method to calculate a current value flowing in a film and calculate the sheet conductance in the film by changing the value of alignment angle Θ_max for several different nanotube area densities σ.
Our simulation reveals two characteristic of CNT thin films. Frist, when exceeds the percolation threshold, the sheet conductance increases, depending on the increase of when Θ_max=90°. Sheet conductance at σ=200 tubes/μm² is 37.6 kΩ/sq, which is in good agreement with the previous experimental work (40.0 kΩ/sq)[3]. Second, when, the sheet conductance exhibits a maximum at a certain nanotube alignment angle while there is a drop of the sheet conductance caused by the function of junction resistance of the (10,10) - (10,10) CNT. This is because of the competition between the decrease in the number of junctions and lengths of the electrical conducting paths. These results would be helpful for understanding electric transport properties of complicated nanotube network structure.
[1] Ishizeki, Keisuke, et al. Physical Review B 96.3 (2017): 035428.
[2] Buldum, Alper, and Jian Ping Lu. Physical Review B 63.16 (2001): 161403.
[3] Scardaci, Vittorio, Richard Coull, and Jonathan N. Coleman. Applied Physics Letters 97.2 (2010): 023114.

Graphite-doped hematite and magnetite nanoparticles systems (~50 nm) were prepared by mechanochemical activation for milling times ranging from 2 to 12 hours. Their structural and magnetic properties were studied by 57Fe Mossbauer spectroscopy. The spectra corresponding to hematite milled samples were analyzed by considering two sextets, corresponding to the incorporation of the carbon atoms into the iron oxide structure. For ball milling time of 12 hours a quadrupole split doublet has been added, representing the contribution of ultrafine particles. The Mossbauer spectra of graphite-doped magnetite were resolved considering a sextet and a magnetic hyperfine field distribution, corresponding to the tetrahedral and octahedral sublattices of magnetite, respectively. A quadrupole split doublet was incorporated in the fitting of the 12-hour milled sample. The recoilless fraction of all samples was determined using our previously developed dual absorber method. It was found that the recoilless fraction of graphite-doped hematite nanoparticles decreases as function of ball milling time. The f factor of graphite-containing magnetite nanoparticles for the tetrahedral sites stays constant, while that of the octahedral sublattice decreases as function of ball milling time. These findings reinforce the idea that carbon atoms exhibit preference for the octahedral sites of magnetite.
Graphene-hematite and graphene magnetite nanoparticles systems were synthesized using mechanochemical activation for time intervals of 2-12 hours. Their structural and magnetic properties were analyzed by Mossbauer spectroscopy. For ball milling times of 2-12 hours, the least-squares fitting revealed the presence of a sextet for hematite (50.84 T), a sextet for carbon-substituted hematite (46.57 T), a broad sextet for iron carbides (29.34 T) and a quadrupole split doublet for iron-containing carbon nanoclusters (0.73 mm/s). Similarly, the Mossbauer spectra of ball-milled graphene and magnetite were consistent with the occurrence of two sextets for the tetrahedral and octahedral positions of magnetite (49.26 and 46.12 T) and the formation of iron carbides (29.5 T) at long milling times (8 and 12 hous ). Also, the appearance of the doublet representing the iron-containing carbon nanoclusters (0.73 mm/s) was manifest at the longest milling times employed. The recoilless fraction was determined from the Mossbauer spectra using our dual absorber method and it could be evidenced that the recoilless fraction exhibits maxima for the occurrence of additional phases at long milling times. If we relate the present results with the previous ones regarding milling graphite and iron oxide nanoparticles, we should note the additional appearance of the iron carbide phases and the occurrence of carbon nanoclusters. This means that graphene is not merely a source of carbon, but exhibits its own reactive properties during mechanochemical activation.

Two-dimensional (2D) materials hold promise for a range of electrochemistry-related applications, including energy storage/conversion and sensing. The tunability of the electronic structure of these materials by their thickness or external stimuli such as electric field or strain suggests a range of opportunities in optoelectronics, electrochemical switching, and photocatalysis [1].
Here, we demonstrate electrochemical tunneling across monolayer and few-layer hexagonal boron nitride (hBN), a wide-gap insulator that has gained interest in device encapsulation and solid-state tunnel field-effect transistors [2]. The electrochemical behavior of tunneling devices based on ~5 µm diameter ultramicroelectrodes is studied using reversible redox mediator systems. Optical microscopy, Raman spectroscopy, and atomic force microscopy, are used to characterize the devices. We show that the tunneling current, electron transfer kinetics, and the breakdown voltage depend on the number of hBN layers between monolayer and bulk. We compare our results to other well-studied tunneling systems, such as alkylthiol chain monolayer or thin-layers of solid-state dielectrics.
Our findings show that varying the thickness of the hBN yields a tunable electrochemical response, which provides fundamental insight into the electrochemical tunneling behavior across atomically-flat insulating materials and could be exploited in applications such as electrochemical switching or surface passivation.

[1] Velický, M. et al., Appl. Mater. Today 8 (2017), 68-103
[2] Britnell, L. et al., Nano Lett. 12 (2012), 1707-1710.

The search for new supercapacitors materials is extreme importance for the development of the future of the energy sector. This is due to the fact that the technology evolution, which demands increasingly alternative devices, fast load, high power and great storage. Thus energy storage devices are currently the focus of several studies, both in the academic and industrial sector, the energy sector depends strongly on the development of the new materials. At the forefront of the materials used for electronic devices, the carbon-based materials such as graphene hybrid system with oxide (GO), carbon nanotubes (CNT) could be significant modified by chemical methods and morphology. These materials are widely used due to low density, high surface area and high load holding capacity. Thus, the objective of this work is to obtain a composite on porous graphene-based 3D structures (like sponge) decorated with nanoparticles like chalcogenides (ZnS, MoS2), transition metal (Ag, Fe, Ni), nickel cobaltite (NiCo2O4), metal oxides (In2O3, SnO2, ZnO), each nanoparticles system were previously grew homogeneously and well dispersed on the multiwalled carbon nanotubes (MWCNTs), under microwave-assisted hydrothermal synthesis (MHS). These hybrid composite display interesting morphology and appropriate electrochemical properties to be applied as electrodes for supercapacitors.

Thermal property of the single-walled carbon nanotube (SWCNT) has been intensively studied because the SWCNT is expected to be an excellent heat transport material. Many measurement methods of thermal conductivity of SWCNTs have been proposed and photoluminescence imaging spectroscopy is one of the powerful methods [1]. In this method, a suspended SWCNT is irradiated by laser, and the spatial distribution of the PL emission energy (E11) along the SWCNT axis is measured by a near-IR 2D camera, which is converted to the temperature distribution. The thermal conductivity is obtained from the temperature distribution. Thus, the accurate conversion of E11 emission energy to temperature is crucial in this method. The temperature dependence of E11 is simply expressed by Varshni’s equation independent of SWCNT chirality (n,m) when SWCNTs are in vacuum. On the other hand, when SWCNTs are located in the ambient air, water molecules adsorb on the outer surface of SWCNTs and they affect the energy of E11 [2]. Elucidation of the temperature dependence of E11 of SWCNTs with water adsorption layer is necessary to measure the thermal conductivity of SWCNTs in the ambient air.
In this study, we measured the temperature dependence of the E11 in suspended SWCNTs with water adsorption. Suspended SWCNT was synthesized by chemical vapor deposition method on a quartz pattern substrate. PL spectra were measured from suspended SWCNTs with different chirality under controlling temperature (220 to 300 K). SWCNTs were exposed to water vapor at 300 K and the water adsorption layer was formed. It was found that the energy shifts of E11 exhibited a complicated temperature dependence depending on chirality in the case of SWCNTs with the adsorption layer. The energy shift was understood as the summation of intrinsic temperature dependence of the band-gap, the strain effect and the change of the dielectric constant of the adsorption layer. When the temperature decreased, axial strain due to the adsorption layer occurred in SWCNT. The strain changed E11 and the change clearly exhibited type-dependence [3]. The dielectric constant of the adsorption layer simply increased with decreasing temperature. Although the interaction between SWCNT and the water adsorption layer is weak, the adsorption layer drastically affected the optical properties of SWCNTs. By taking those effects into account, we could accurately determine the temperature along the tube axis.

[1] K. Yoshino et al., ACS Omega 3 4352 (2018).
[2] Y. Homma et al., Phys. Rev. Lett. 110 157402 (2013).
[3] A. Ozao et al., Jpn. J. Appl. Phys. 54 055102-1-4 (2015).

In a relatively short time, 3D technology has become a new method for manufacturing prototypes and is occuping a first place in terms of research in multiple universities across the world, as well as the searching of new materials with advanced properties suitable for the development of prototypes with 3D printing. In this sense, layered graphene represents one of the most impressive materials for this purpose, due to the combination of its properties like high electrical and thermal conductivity or high mechanical strengh. The main objective of the present research work is to study the impact that graphene has over the properties of the selected polymer when they are integrated in a unique compound forming a nanocomposite. In order to facilitate the integration of both components, graphene and polymer, chemical and structural modification of the layered graphene has been necessary. These modifications of the graphene lead to an improvement in the dispersion of both components, which has shown to be a critical parameter for the stress transfer from the nanoparticles to the matrix. In this way, modified graphene has been synthesized through different chemical processes, what first includes the synthesys of graphene oxide (GO) from graphite and its subsequent chemical reduction with different chemical reducing agents to obtain the reduced graphene oxide (rGO), which has similar properties to graphene. Lyophilization of the resulting graphene samples has been also carried out in order to increase the distance between graphene layers and improve the dispersion. Two different strategies has been employed during the synthesis of the nanocomposites: direct integration of the reduced graphene oxide (rGO) into the matrix of the polymer throught solution in proper solvents (DMF and THF), and reduction in situ of the graphene oxide already integrated into the polymer structure. In both cases it is necessary the complete elimination of the solvent to ensure that the electrical and mechanical properties of the nanocomposite are not affected by the presence of traces of solvent. Polymers most commonly used in 3D printing have been used in this work, including ABS, PCL and PLA filaments. Nanocomposites were prepared with several loads of graphene between 3% and 15%, ir order to compare the mechanical and electrical properties before being use in 3D printing. Graphene loading is also an important factor to take into account since too much loading could hinder the printing process due to the formation of graphene agglomerates. Characterization techniques employed to evaluate the samples have shown that the mechanical reinforcement of the polymeric structures is possible by addition of both GO and rGO. It also been stablish that a well dispersed rGO into the matrix not only improves properties in relation to strength and fracture toughness, but also electrical conductivity of the nanocomposite, which is not possible to get by adding only GO.

Individual carbon nanotubes (CNTs) are one of the strongest materials in nature. Networks of pristine CNTs, however, do not show similar superior mechanical properties due to weak load transfer between individual CNTs via van-der Waals interaction. Shear load transfer between CNTs can be improved by introducing covalent cross-links between nanotubes by means of ion or electron beam irradiation or chemical functionalization. The goal of this work is to quantify the effect of cross-links on quasi-static and dynamic mechanical properties of CNT network materials like CNT films, fibers, and aerogels in large-scale mesoscopic simulations. In our mesoscopic computational model, every nanotube is represented by a chain of stretchable cylinders. Mesoscopic force field accounts for stretching, bending and buckling of individual nanotubes, van-der Walls interactions, and cross-links between nanotubes. In order to account for the effect of individual cross-links on the load transfer between CNTs, we developed a novel effective bond model. This model is parameterized based on results of atomistic simulations of pulling out of a central CNT from a seven-tube bundle performed in a range of CNT diameters and cross-link linear densities. The developed model is first applied to study the shear load transfer in long CNT bundles. The simulations reveal extremely strong shear lag effect, which sets limits on the ability of cross-links to reinforce nanotube bundles. Next, we perform simulation of quasi-static and dynamic wave loading of CNT films, aerogels, and fibers. The equilibrium networks structures in these materials are obtained in preliminary mesoscopic simulations as a result of self-assembly of dispersed nanotubes into networks of entangled bundles. The cross-links are distributed inside these in-silico generated CNT material samples in order to simulate the process of irradiation or chemical functionalization of pre-existing networks of nanotubes. The simulations show that the dominant mechanisms of non-reversible structural changes in CNT networks under an applied mechanical load strongly depend on the deformation rate. The elastic and inelastic properties of CNT materials, as well as the acoustic speed, are found for materials with various degrees of anisotropy, density, CNT length, and density of cross-links. This work is supported by the NSF CAREER award CMMI-1554589 and NASA Early Stage Innovations program (project NNX16AD99G).

The interaction of carbon and boron nitride nanotubes with metals is significant for a wide variety of applications. For example, the binding of tubes to transition metal nanoparticles plays a role in their catalytic growth, as well as in their nucleation. Similarly, the strength of nanotube-metal composites crucially depends on the interaction strength between the tube and the metal matrix. We performed quantum chemical calculations to investigate the binding strength and geometry of a variety of metals with carbon and boron nitride nanotubes. We examined both, binding by individual metal atoms and the interaction with metallic surfaces to identify possible candidates for the creation of novel metal matrix composites.

Hydrogen peroxide (H₂O₂) is a widely used oxidizer, bleaching agent, and disinfectant in many fields, such as food processing, medicine, and environment. Thus, detecting the trace amount of H₂O₂ is essential for many industrial and biological applications. Electrochemical H₂O₂ sensors, especially nonenzymatic ones, have attracted significant interests because of their relatively simple operation, low cost and fast response. Platinum (Pt) based Electrochemical H₂O₂ sensors demonstrate superior sensing performances, i.e., higher sensitivity, wider detection concentration range and lower detection limit. However, the high mass loading and cost of Pt limits their practical applications. Here, we develop a cathodic polarization treatment method to deposit ultralow mass loading of Pt nanoparticles on a high surface area (385 m²/g) porous carbon composite substrate comprised of reduced graphene oxide (rGO) and carbon nanotubes (CNTs). Using multiple cyclic voltammetry (CV) cycles at the specific potential window (-0.8-0 V vs. standard caramel electrode) in 0.5 M H₂SO₄ electrolyte without Pt precursors, about 3.89 wt.% of Pt nanoparticles were anchored on the rGO-CNT composites with a narrow size distribution around 1–2 nm from a Pt mesh anode. Furthermore, different Pt mass loadings on rGO-CNT composites were obtained by varying the CV cycles and their morphological and physicochemical properties were characterized by SEM/EDS, TEM, and XPS along with H₂O₂ sensing performance to understand the synthesis-structure-property relationships. The optimized Pt/rGO-CNT composite obtained at 3000 CV cycles shows superior H₂O₂ sensing performances with a detection limit of 10 µM, a wide linear range up to 15 mM, and the sensitivity of 2027 µA/mM.cm², which are one of the best among recently reported Pt/carbon composites and commercial 20 wt.% Pt/C catalysts. Further, the Pt/rGO-CNT sensor can also detect trace amount of H₂O₂ in milk and juice samples, demonstrating their excellent practical application potentials.

Anti-corrosion coatings are ubiquitous with an expected market value of $20 billion by 2025. Current innovation is being driven by both demand and regulatory restrictions. (Global Market Insights 2016) A promising option is the incorporation of high aspect ratio nanomaterials (HARNs), such as graphene and boron nitride, as polymer composite coatings. (Liu, et al. 2016)

It has previously been shown that platelet like materials can improve the performance of anti-corrosion coatings. This is typically thought to be due to the creation of a “tortuous path” in which corrosive media (typically water, electrolytes and oxygen) must follow a long path through a network of impermeable filler to reach the metal substrate. (Zheng, et al. 2017) This effect is maximised when the platelets are high aspect ratio and aligned parallel to the metal substrate.

While the concept of such a system is simple there are several complex factors to consider in the production of a working coating. In producing HARNs it is challenging to control morphology and achieve both the large lateral dimensions and the thin sheet sizes desired. Dispersing HARNs in resin also presents challenges as aggregates reduce the effective aspect ratio and risks creating porous structures through which electrolytes can penetrate. Once dispersed the nanomaterial must remain wetted by the resin throughout the cure process to avoid generating voids and an associated decrease in performance. Finally, the coating must remain adhered to the substrate and not delaminate.

In this work we present data on the effect of HARN morphology and surface energy on the barrier performance of a protective coating. Consideration is given to how these variables may affect nanomaterial dispersion quality, porosity and interaction with the metal substrate. Initial results indicate that dispersion quality and HARN surface chemistry both influence performance.

Global Market Insights. 2016. Anti-Corrosion Coatings Market Size By Product (Epoxy, Polyurethane, Acrylic, Alkyd, Zinc, Chlorinated Rubber), By Mode Of Application (Solvent-based, Water-based, Powder), By End Use (Oil & Gas, Shipbuilding, Infrastructure, Industrial markets, Energy, T. Global Market Insights.

Liu, D, W. Zhao, S. Liu, Q Cen, and Q. Xue. 2016. "Comparative tribological and corrosion resistance properties of epoxy composite coatings reinforced with functionalized fullerene C60 and graphene." Surface and Coatings Technology 354-364.

Zheng, H, Y Shao, Y., Meng, G. Wang, and B. Liu. 2017. "Reinforcing the corrosion protection property of epoxy coating by using graphene oxide - poly(urea formaldhyde) composites." Corrosion Science 267-277.

Graphene oxide liquid crystal (GOLC) behavior is very intriguing and powerful phenomenon, especially for simply achieving graphene-based fibers, which have ordered graphene alignments in fiber. Taking advantages of graphene based fiber such as high mechanical strength, electrical conductivity, and supercapacitive behavior, various applications such as energy storage, photovoltaic cell, and chemical sensing have been explosively exploited. Although graphene based fiber have opened up great opportunities for various researches, high graphene density in graphene based fiber is disadvantageous to develop the porous fiber with high meso (2–50 nm) porosity; High porosity is essential for increased surface area and fast gas diffusion and penetration, leading to enhanced detection of toxic chemicals using graphene based fiber. Unfortunately, graphene based fiber is still challenging to detect the ppm level of toxic gas molecules such as nitrogen dioxide (NO₂) because of their poor porosity and low gas reactivity. Therefore, the suggestion of novel platform for the creation of pores on graphene based fiber is significantly desired.

In this work, we propose a facile synthetic route for providing high density of pores in graphene based fiber by employing tunicate cellulose nanofiber (TCNF) engineering. For the first time, by using the liquid crystal (LC) behavior of graphene oxide (GO)-TCNF composite, we successfully develop the ultra-porous GO fibers due to the random distribution of TCNF in GO fiber. Furthermore, by using the super-hydrophilicity of TCNF, TCNF in GO fiber is also used as seed layer for growth of WO₃ nanorods (NRs), leading to formation of porous WO₃ NRs-GO thorn-bush like composite single fiber. Due to its high porosity and heterogeneous junction effect (WO₃ NRs-GO), porous WO₃ NRs-GO showed reversible NO₂ detection capability even at 1 ppm level of NO₂ chemicals.

In the present work, graphite oxide (gO) and graphene oxide (GO) were synthesized utilizing Modified-Hummers method and the effect of ultra-sonication time (2, 4, 6 and 8 h) on their physical properties were studied. SEM and AFM analysis confirm the formation of GO sheets with laminar morphology (width ~2 µm and thickness ~0.7 nm) and the increase in the ultra-sonication time resulted in exfoliation of GO sheets demonstrating the evolution of GO from gO. A left shift of (001) plane from 11.3 (2 h) to 10.7 (8 h) in the diffraction patterns confirms the oxidation and formation of gO and GO. Also, FTIR affirms that all samples possess similar functional groups whereas an increase in the ultra-sonication time widens the O-H band and increases C-H band intensity indicating the reduction of GO. Additionally, Raman analysis shows that the increase in ultra-sonication time increased the ID/IG ratio and decreased the in-plane crystallite size (from 18 to 12 nm) which is due to the defects occurred from additional oxidation and conversion of sp² to sp³ hybridization. Finally, in this work the principal structural and morphological differences between the gO and GO were demonstrated.

Graphene oxide quantum dots (GOQDs) are part of a fascinating class of recently discovered nanocarbons that have both graphene oxide and quantum dots properties. Like carbon quantum dots (CQDs), GOQDs electronic and luminescent properties (e.g. wavelength-tunable emission, excellent photostability and a potential high quantum yield potential) are advantageously combined with chemical stability, water solubility and biocompatibility [1].
Microwave heating is becoming a popular method for fast, efficient and reliable preparation of CQDs, which is usually done in 2 steps (i.e. carbonization, and passivation). Current research is focusing on more sustainable and economical syntheses, greener chemistry and more diversified starting materials. This is why much efforts has been devoted to developing new means of synthesizing CQDs from raw materials such as citrus fruit peels, ground coffee, orange juice, overcooked meat [2-4]. In this context, we report herein the synthesis of GOQDs from various biomass waste materials with the use of a monomode microwave reactor. Various source materials, such as orange peels, date stones and oak acorns were first dried at 60°C for 24 h, then crushed and grounded. The prepared samples were then poured into vials and inserted in the microwave reactor with the required reactants. The accurate verification of temperature, time, pressure and power helps to provide reproducible batches of GOQDs with particles of controlled size. After purification and separation, the prepared GOQDs were then systematically characterized in terms of chemical structure (elemental analysis, TGA and XPS), size (DLS and TEM) and photophysical properties (absorbance and luminescence spectroscopies). Surprisingly, very small GOQDs (≈ 1-2 nm) with identical morphological and photophysical features were elaborated regardless of their biomass waste source. The water soluble particles show excitation-dependent photoluminescence ranging from blue to orange emission wavelength in solution. Interestingly, thin films display white light emission under UV excitation, while aggregation-induced quenching is usually observed in the solid state. This latter observation opens the way to applications in OLED devices that are currently under investigation in our laboratory.
In conclusion, we have been able to set up a fast, reproducible and green microwave-assisted synthetic method to prepare GOQDs. This will undoubtedly lead to new means of upgrading biomass waste as potential photosensitive materials for various applications (optoelectronic devices, energy, biosensors…).
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[2] S. Sahu, B. Behera, T. K. Maiti, S. Mohapatra, Chem. Commun. 2012, 48, 8835-8837.
[3] C. Jiang, H. Wu, X. Song, X. Ma, J. Wang, M. Tan, Talanta 2014, 127, 68–74.
[4] A. Prasannan, T. Imae, Ind. Eng. Chem. Res. 2013, 52, 15673–15678.

For the application of carbon nanotubes (CNTs), a synthesis method which can control its property (e.g. length, diameter and chirality) is required. Catalytic chemical vapor deposition (CCVD) method is the standard way to produce CNTs. In this method, the quality and quantity of CNTs largely depends on the combination of the catalyst and the carbon source. For example when using ethanol as the carbon source, which C-O bond or C-C bond dissociates have effect on CNT growth. In order to develop a better catalyst, it is required to know the mechanism of the dissociation process. In this research, we clarify the difference of ethanol dissociation reaction mechanism by catalyst element from the atomistic viewpoint, using the ab initio molecular dynamics method (AIMD method) and clarify the advantages of using the alloy catalyst and give guidance to new catalyst design.
The dissociation process of ethanol and carbon monoxide on Fe, Co, FeCo catalyst is investigated by AIMD. 30 ethanol molecules and 30 carbon monoxide molecules are placed around the Fe₃₂, Co₃₂, Fe₁₆Co₁₆ clusters, respectively. The dissociation process of 5 ps for ethanol molecules and 2 ps for carbon monoxide molecules is analyzed at 1500 K. C-H bond and C-O bond of ethanol have been observed to dissociate on each catalysts, but C-C bond dissociation is only observed on Fe₁₆Co₁₆ catalyst. Regarding the calculation of carbon monoxide, C-O bond dissociation is only observed on Fe catalyst. We have clarified that bond formation of oxygen and metal atoms is important in dissociation reaction mechanism. Specifically, strong bonds with oxygen as seen with Fe atoms are disadvantageous in C-C bond dissociation but are necessary for C-O bond dissociation in ethanol and CO molecules. From these results, it is possible to design a catalyst that dissociates both C-C bonds and C-O bonds by alloying elements that form strong bonds with oxygen.

Carbon fibers have been of great interest in many industrial applications due to their high specific mechanical properties. The tensile strength of the polyacrylonitrile (PAN)-based commercial carbon fiber is as high as 7 GPa, and the highest tensile modulus is about 600 GPa although the theoretical properties of carbon-carbon bonds are known to be 150 GPa and 1060 GPa, respectively. The property discrepancy is attributed to the defective structures including voids and structural heterogeneity. In addition, carbon fibers are often subjected to extreme environment such as high stress and high temperature, which may change their microstructure and properties. In this study, we have heat-treated commercial carbon fibers as high as 2400 °C without applying external stress, and traced the changes in microstructure using Raman spectroscopy, wide-angle X-ray diffraction, and X-ray photoelectron spectroscopy. The tensile testing and nano-indentation experiment were also conducted to examine the correlation between the microstructural variation and corresponding mechanical properties. The structure-property relationship of carbon fibers upon high temperature heat treatment will be presented.

Single-wall carbon nanotubes (SWCNTs) and polyamidoamine dendrimers (PAMAM) have been proposed for a variety of biomedical applications due to their unique physico-chemical properties. However, toxicological studies have shown that these nanomaterials may exhibit high toxicity in biological environments. In this study we used C2C12 murine cells and membrane model systems to understand the interactions occurring at the bio-nano interface, as well as the possible toxicity exhibited by SWCNT-PAMAM conjugates against to mamalian cells. The results showed that SWCNT-PAMAM and PAMAM inhibited the proliferation and caused DNA damage in C2C12 cells. Flow cytometry analyses revealed a less toxicity in C2C12 cells exposed to SWCNT compared to the other nanomaterials. The toxicity of SWCNT, SWCNT-PAMAM, and PAMAM in C2C12 cells are strongly correlated with the charge of the nanomaterials. The membrane model studies revealed a pronounced incorporation of SWCNT-PAMAM through dipalmitoylphosphatidylcholine (DPPC) monolayers even at high surface pressure values, ~30 mN/m. Therefore, the results confirm that the presence of the nanomaterial affects the packing of the synthetic membrane monolayers. The methodology introduced here may be of great importance for further nanotoxicity studies.

The early detection of biomarkers of renal damage is important because the glomerular filtration rate is reduced before the onset of the signs of renal failure. Cystatin C is a protein that has been identified as the most promising biomarker to acute kidney injury diagnosis in early stages. Here, we introduce a papain-modified graphene oxide field-effect transistor (rGOFET) for the detection of Cystatin C with enhanced sensitivity. The rGOFETs were fabricated using the layer-by-layer (LbL) technique, employing oppositely charged rGO onto interdigitated gold electrodes. Detection of Cystatin C occurred via electrical measurements upon monitoring output and/or transfer curves of rGOFETs. The detection mechanism is based on changes of the charge balance at the electrode surface after the formation of papain/cystatin C complex. Cystatin C could be detected at a concentration range from 5 ng.mL-1 to 100 ng.mL-1 with 0,13 mV/ngmL-1 sensitivity, suggesting that the system may useful for clinical purposes.

Carbon nanotube (CNT) based conductors are candidate light-weight and robust alternatives to conventional metal conductors for a variety of space, defense, and power transmission applications. Although the conductivity of bulk CNT materials is still an order of magnitude less than copper conductors, these demanding applications can benefit from the reduction in weight, increased flexure tolerance, and corrosion resistance provided by CNT conductors. Previously, CNT conductors have been produced from commercially available CNT sheet material, which is rolled into wires of varying diameter. Radial densification and chemical doping with aqueous KAuBr₄ has been used to increase the conductivity of these rolled conductors by an order of magnitude. These works demonstrated the possibilities of CNT conductors along with the effects of densification and chemical doping, but these techniques are limited in scalability due to the batch nature of CNT sheet production. Recently, continuous processes have allowed for the production of CNT yarns available in kilometer lengths, a breakthrough needed for the practical implementation of CNT conductors. With the synthesis of scaled CNT conductors, the operational stability of these materials along with the accompanying chemical doping procedures needs to be explored.

In the present work, densification and chemical doping with KAuBr₄ is shown to improve the conductivity of commercially scaled CNT yarns by 6x, while increasing the current density at failure by 67% to 35 MA/m². A current cycling procedure involving increasing current densities with intermittent rest steps and I-V sweeps is applied to as-received, H₂O densified, and KAuBr₄ doped and densified CNT yarn samples. Analysis of the data allows for changes in resistance, during operation and at low current, as a result of previous current exposure to be determined. The KAuBr₄ doped and densified samples experience no permanent change in resistance at current densities up to ~25 MA/m², exceeding the as-received materials by greater than 3x. Thermogravimetric analysis shows that ~10% of the mass of KAuBr₄ doped and densified CNT yarns oxidizes or desorbs at temperatures lower than 400°C. A series of samples were prepared with varying thermal oxidation and chemical doping treatments to understand how the desorbed or oxidized components affect the electrical properties of the CNT yarns. Analysis on how the thermal stability of KAuBr₄ results in greater electrical stability will be discussed.

With the rapid growth of industrialization, water pollution caused by heavy metals has become one of the most serious environmental problems, and attracted considerable attention. Heavy metals are non-degradable and can accumulate in living tissues, so they must be removed from wastewater. Extraction of heavy metals from wastewater embraces reverse osmosis, chemical precipitation, electrodialysis, organic−inorganic ion exchange, and adsorption. Among these methods, adsorption stand out from the aforementioned methods due to its simple operation and cost-effectiveness. Thus far, the most efficient adsorbent for adsorption heavy metals have high adsorption capacity and removal rate. However, in recent years, the adsorbents designed for the capture of heavy metal have not been suitable for application at wastewater pH. Currently, the design of a suitable wastewater adsorbent shows more promise for the extraction of heavy metals. In this report, we report a facile approach to construct a suitable wastewater pH and large surface area material that polyacrylamide (PAM) covalent grafted onto the surface of GO nanosheets. In the progress, transmission electron microscope (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) were used to determine the effectiveness of the synthesis of GO-PAM composites. Meanwhile, the GO-PAM composites were investigated for adsorption of Cr(VI) from aqueous solution. It is clear that the GO-PAM composites have a high adsorption capacity (q_m= 398.2 mg g^-1, T=298.15 K) at a suitable wastewater pH with a high removal rate (>90%). Based on the FTIR spectroscopy, Zeta potential, and X-ray photoelectron spectroscopy (XPS), a possible adsorption mechanism of Cr(VI) onto GO-PAM composites is revealed. Finally, the result also exhibited outstanding adsorption efficiency and adsorption capacity under the operating conditions for the adsorption-desorption of Cr(VI) from aqueous solution, which indicated a promising potential in the application of the absorbent in wastewater. (This paper is funded by the International Exchange Program of Harbin Engineering University for Innovation-oriented Talents Cultivation.)

Although carbon nanostructures such as carbon nanotubes (CNTs) and graphene have shown promising properties on the electrical [1], thermal [2] and mechanical [3] fronts, their implementation is somewhat restricted because they are incompatible with the most of traditional polymer matrices. The problem is commonly explained by the nature of their surface, which has been considered as highly hydrophobic for many years. The employed main-stream solution is focused on chemical functionalization to introduce certain functional groups to make the surface hydrophilic. We have recently shown that carbon nanotube networks can have unexpectedly high hydrophilic character without any grafting if the films are briefly annealed at high temperature, which does not need to involve oxidation [4,5]. In this contribution, we would like to present an explanation of this effect and mark what are the most immediate applications of this high-performance material.

References:
[1] A. Lekawa-Raus, T. Gizewski, J. Patmore, L. Kurzepa, K. Koziol, Electrical transport in carbon nanotube fibres, Scripta Materialia 131, 2017, 112–118.
[2] K. Koziol, D. Janas, E. Brown, L. Hao, Thermal properties of continuously spun carbon nanotube fibres, Physica E: Low dimensional Systems and Nanostructures 88, 2017, 104-108.
[3] M.-F. Yu, O. Lourie, M. J. Dyer K. Moloni, T. F. Kelly, R. S. Ruoff, Strength and breaking mechanism of multiwalled carbon nanotubes under tensile load, Science 287, 2000, 637-640.
[4] D. Janas, M. Rdest, K. Koziol, Free-standing films from chirality-controlled carbon nanotubes, Materials & Design 121, 2017, 119-125.
[5] D. Janas, G. Stando, Unexpectedly strong hydrophilic character of free-standing thin films from carbon nanotubes, Scientific Reports 7, 2017, 12274.
[5] D. Janas, G. Stando, D. Lukawski, F. Lisiecki, Intrinsic hydrophilic character of carbon nanotube networks, Applied Surface Science (under review)

Graphene has been recognized as a promising material for sensing applications, such as gas detection and biomolecular sensor. Although it has been demonstrated to have good sensing characteristics, some essential aspects such as stability need to be improved for further applications. To conquer these obstacles, different kinds of surface functionalization, for example particle doping, chemical modification, and UV irradiation are used to demonstrate improvements of repeatability and stability with the cost of sensitivity degradation. Following surface functionalization idea, in this work, we used a low-damage oxygen plasma to functionalize a bilayer graphene sheet without high-energy ion bombardment and UV irradiation damage on the graphene structure. This leads to an improved stability of the developed bilayer graphene humidity sensor. Based on the experimental observation of Raman spectroscopy, the D/G ratio showed the result of the low-damage plasma functionalization and the integrity of graphene structure. Utilizing XPS spectra, at the same time, we found the fact that the compositional ratio of C-OH is increased with modified time. Similar observations can also be indicated by wettability enhancement by contact angle measurement. According to these experimental characterizations, one possible scenario is that the upper layer of the bilayer graphene is the one of the functionalization and the lower layer of the bilayer graphene keeps its original 2D structure. Then the developed low-damage bilayer graphene can be experimentally demonstrated as a humidity sensing material. Compared with traditional graphene humidity sensors, the developed low-damage bilayer graphene humidity sensor has less drifting. The drifting response is resulted from the π electron adsorption, which can easily adsorb molecules, including the water molecule and the other air molecules. These adsorbed molecules are difficult to be desorbed from the surface and cause sensor degradations. In our low-damage bilayer graphene, there are high surface ratio of O-H bond introduced by the low-damage oxygen plasma. As a result, the surface with less π-electron helps water molecule to be desorbed from the surface. This results in a stable sensing response to humidity. This work raises a method which potentially helps to functionalize graphene-based sensing materials.

In this work, a partially reduced graphene oxide (GO) biosensor is presented. Mild thermal treatment is used to reduce GO drop-casted on a SiO₂ substrate, after hydrophilization and functionalization. As a result of the reduction, the graphene sp² lattice of GO is gradually restored and its electrical conductivity is enhanced. At the same time, the GO retains functional groups during the course of the reduction, thus facilitating the immobilization of proteins on its surface. To confirm this, Biotinylated Bovine Serum Albumin (b-BSA) was used as a model molecule in protein immobilization experiments. The immobilization of b-BSA was affirmed by inspecting the GO drops under a fluorescence microscope after reaction with the fluorescently labeled streptavidin. Reduced GO biosensors were then constructed by first drop-casting GO on APTES functionalized SiO₂ substrates followed by a mild thermal treatment (heating for 1 h at 180^oC) in order to achieve both protein immobilization and a conductive state. Silver paint conductive adhesive was then used to contact the GO drops.
To test the sensor in the detection of b-BSA immobilization, a plastic frame was placed around the GO drops in order to contain the reaction fluids and prevent short-circuiting while resistance measurements were taken using the following procedure:
a) inserting buffer solution in the frame and over the GO, b) adding different concentrations of b-BSA and monitor its immobilization, c) adding BSA blocking, and d) adding streptavidin at various concentrations. Using this procedure the sensor was capable to detect b-BSA concentrations down to 260 pM.
Based on these initial results the sensor was then used in a medically relevant application which involves the detection of BRCA1 gene. For this experiment the characteristic gene sequence of BRCA1 is amplified and tagged during amplification with a biotin molecule at its end using Recombinase Polymerase Amplification (RPA) at 37°C for 30min. RPA was chosen as it possesses many advantages over other amplifications methods in terms of speed, portability, accessibility, sensitivity and specificity. Next, the GO sensor was prepared by drop-casting and immobilizing streptavidin over the reduced GO through non-covalent binding. Upon insertion, then, of the amplified DNA the biotin end interacts with the immobilized streptavidin. Using this scheme DNA concentrations down to 200pM was detected.
These findings thus demonstrate the ability of the proposed sensor to detect on the one hand the immobilization of biotin on the sensor as well as its usefulness in a real world application. Further work will focus on further optimizing the sensor by introducing DNA probes for label free detection.

[1] E. Tegou et.al, “Immobilization of biomolecules on graphene oxide casted on modified silicon oxide substrates”, 4th International Conference on Bio-Sensing Technology, Lisbon, Portugal, 10-13 May 2015

The formation of the cap structure determines the chirality of the consequent SWCNT and the addition of the last pentagon can turn the SWCNT into one with any possible chiral angle. Therefore, the random formation of the last pentagon during SWCNT nucleation explains the even distribution of chiral angles in most SWNT samples.During the cap formation, an external bias that affects the addition of the last pentagon may lead to the chirality-selected SWCNT growth. Detailed theoretical and experimental study suggests that the growth of (2n,n)-rich SWNT samples can be achieved by catalyst surface symmetry control. Besides the nucleation stage, varying the chirality during SWNT growth is predicted to be another route towards the chirality-specific SWNTs synthesis. Such a predication has been successfully realized by experimental studies and the synthesized SWNTs show exact chirality distribution as predicated theoretically.

Topological insulators (TIs) are an emerging class of materials that host highly robust in-gap boundary states while maintaining an insulating bulk. While most notable scientific advancements in this field have been focused on TIs and related topological crystalline insulators in 2D and 3D, we have shown that 1D symmetry-protected topological phases exist in graphene nanoribbons (GNRs) [1]. Using first-principles and model Hamiltonian calculations, we discover that semiconducting GNRs of different width, edge shape, and terminating unit cells can belong to electronic topological classes characterized by different values of an Z₂ invariant. Interfaces between topologically distinct GNRs characterized by different Z₂ are predicted to support robust in-gap topological interface states which can be utilized as a tool for material engineering.

The experimental realizations of these predictions and rational design of a topologically-engineered GNR superlattice synthesized from molecular precursors have been achieved [2,3]. Such GNR superlattice hosts a 1D array of topological interface states, which generates novel robust electronic bands with desirable properties. We present here the theoretical basis and calculations for these states. The band width and band gap of the topology-induced bands are tunable by the coupling between the adjacent topological interface states, which may be varied for example by varying the segment lengths. This novel manifestation of 1D topological phases presents a new route to band engineering in 1D materials based on precise control of their electronic topology, and is a promising platform for future studies of 1D quantum spin physics.

[1] T. Cao, F. Zhao, and S. G. Louie, "Topological Phases in Graphene Nanoribbons: Junction States, Spin Centers, and Quantum Spin Chains," Phys. Rev. Lett. 119, 076401 (2017).
[2] D. J. Rizzo*, G. Veber*, T. Cao*, C. Bronner, H. Rodriguez, T. Chen, F. Zhao, S. G. Louie, M. F. Crommie, and F. R. Fischer, “Topological Band Engineering of Graphene Nanoribbons,” Nature, in press (2018).
[3] O. Gröning*, S. Wang*, X. Yao*, C. A. Pignedoli, G. B. Barin, C. Daniels, A. Cupo, V. Meunier, X. Feng, A. Narita, K. Müllen, P. Ruffieux, R. Fasel, “Engineering of Robust Topological Quantum Phases in Graphene Nanoribbons,” Nature, in press (2018).

Acknowledgement: This work is supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, and by the National Science Foundation. Computational resources have been provided by DOE at Lawrence Berkeley National Laboratory's NERSC facility. Collaboration with the experimental groups of Professor Michael Crommie and of Professor Felix Fischer is gratefully acknowledged.

The hydrogenation of graphene is a powerful tool to change the carbon hybridization from sp² to sp³, which introduces a finite band gap and generates magnetic moments to make graphene functionalized. Large-scale periodically-hydrogenated graphene, namely with hydrogen atoms chemisorbed in a uniformly-periodic manner, can also be viewed as new kinds of two-dimensional (2D) crystalline materials, e.g. graphane, graphone, and 2D C_xH_y. These new 2D crystals have been predicted to exhibit unique electronic structures beyond graphene, such as large band gap (graphane) and ferromagnetism (graphone). In hydrogenated graphene, however, the electronic properties strongly rely on the distributions of hydrogen atom. Thus, the fabrication of large-scale, periodically-hydrogenated graphene is critical important as the first step towards potential applications.

Here, in a combined investigation of scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), low-energy electron diffraction (LEED), Raman spectroscopy, and density-functional theory (DFT) calculations, we present the formation and anisotropic electronic properties of the single-crystal, millimeter-scale, one third hydrogenated graphene (OTHG) on Ru(0001) substrates. Monolayer graphene (MLG) was firstly synthesized on Ru(0001). The as-fabricated monolayer graphene was then exposed to atomic hydrogen generated by a radio-frequency (RF) atom source for 20 minutes and subsequently annealed to ~1200 K for 20 minutes. After four cycles of hydrogen exposure and subsequent annealing, the sample was characterized by STM and LEED. STM images show that the sample exhibits a moiré pattern with a periodicity of ~2.64 Å. Based on atomic-resolution STM images and LEED pattern, a double-sided √3×√3/R30° hydrogen-adsorbed structure was proposed. Simulated STM images show excellent agreements with experimental observed STM images validating the atomic model. The size and uniformity of the fabricated OTHG were checked by taking LEED patterns and STM images on different locations of the sample. We demonstrate that the single-crystal OTHG sample has areas up to 16 mm² (the size of the Ru substrate). Raman spectra and STS measurement indicate that the interaction between the fabricated OTHG and Ru substrate is weak. DFT calculations using a high-level hybrid functional show that for the new 2D material, OTHG, there are Dirac cones at Fermi level only along one high-symmetry (Γ-M) direction. Energy gaps (~0.6 eV) are opened along other two Γ-M directions due to the hydrogenation, leading to an anisotropic electronic structure. Considering the significant anisotropic electronic structure, novel anisotropic physical properties, such as anisotropic Fermi velocity and directional conductance are expected in OTHG[1].
References:
[1]. H. Chen et al., Adv. Mater., accepted (doi: 10.1002/adma.201801838)

Photoluminescent defect states introduced by low-level covalent functionalization of single wall carbon nanotubes (SWCNTs) are of growing interest as routes to enhanced photoluminescence (PL) quantum yields and new functionality.^1,2 In particular, exciton localization in deep traps at the defect sites gives rise to single photon emission at room temperature that is tunable to telecom wavelengths.^3,4 Control over defect-state emission wavelengths and dynamics is essential for advancing potential applications of these unique emitting states. We present results exploring the role of nanotube structure in determining the range of binding configuration that can occur for functionalizing agents. We show that functionalization occurs at ortho-only binding configurations and that nanotube structural symmetry can lead to a 3-fold decrease in emission wavelength bandwidth for zigzag structural types. Strategies for tailoring the SWCNT environment to extend defect-state PL lifetimes (to nanoseconds) and optimize linewidths will also be presented. Environmental impacts on dephasing times will also be discussed, along with temperature dependent effects on relaxation dynamics.

1. Ghosh, S., et al., Science, 330, 1656 (2010).
2. Piao, Y.M., et al., Nat. Chem., 5, 840 (2013).
3. Ma, X., et al., Nat. Nanotech., 10, 671 (2015).
4. He, X., et al., Nat. Photon., 11, 577 (2017).

Heteroatom doping in graphene leads to bandgap opening and tunable electronic, magnetic and optical properties, which are important for graphene-based electronics applications. In recent years, scalable growth of nitrogen-doped graphene (NG) by chemical vapor deposition (CVD) has been extensively studied because of its potential for practical applications. A phenomenon that occurs exclusively for CVD-grown NG films is the segregation of doping concentration. However, most studies to date are conducted using highly polycrystalline NG films comprising small grain sizes. It is still unknown whether dopant segregation occurs in single crystalline NG domains. Here, we used hexamethylenetetramine ((CH₂)₆N₄) as a single-source solid precursor to grow hexagonal-shaped monolayer NG single crystals of ~20 µm on Cu substrates. The NG single crystals exhibit discrete concentric hexagonal rings comprising N depleted regions as determined by Raman spectroscopy. Supported by scanning tunneling microscopy experiments, we propose that the segregation of N dopants is caused by a competing N attachment mechanism to either zigzag or Klein edges during growth; where the former should result in higher N concentration and the latter with lower N concentration. This work provides critical insights into the growth mechanism of CVD-grown NG and enables new opportunities to engineer the properties of graphene by fabrication of lateral heterostructures.

Since the discovery of carbon nanotubes (CNTs) [1], other carbon allotropes and/or morphologies were obtained. One of these morphologies are coiled carbon nanotubes (CCNTs) [2]. It has been a continuous evolution in the study of the structures as well as properties (electrical, mechanical or thermal) of addition of nanostructured carbon materials (NCMs) to polymers and other host materials, forming all sort of composites. However, the molecular scale mechanisms by which the NCMs interact with the hosts are still not fully understood. Previous studies [3-5] used theoretical simulations to address the interaction of NCMs with polymers, and a recent review also illustrated the use of simulations on the study of graphene and hexagonal boron nitride polymer nanocomposites [6]. Inspired by these studies, we investigated the mechanical properties of pristine CCNTs as well as composites formed with CCNTs and paraffins (C₃₆H₇₄). The methodology involves the use of fully atomistic reactive molecular dynamics simulations using the ReaxFF force field within charge optimized many-body potential included in the LAMMPS open source simulation package. Besides standard tensile and compression strain analyses, we also considered torsional deformations (clockwise and counterclockwise). For pristine systems, all the coils are left-handed: a) the stress response to tension shows a complex behavior and for some structures the stress reaches ~7-8 GPa with a strain 20-30%; b) from the compression analysis the elastic regime persist up to 4-5GPa in stress and strain range 16-18%; c) under counterclockwise torsion the systems start to exhibit failure point (symmetry breaking) within (3/8-1/2) of a turn; d) under clockwise deformation the systems evolve to a compact coiled and tube collapsed. For composite systems (CCNTs and paraffin) we observed a significant alignment of paraffin molecules with the main axis tubes. The mechanical behavior is very similar to the one for pristine systems, but as expected, at different deformation rates and/or ranges.

[1] S. Iijima, Nature, v354, 56 (1991).
[2] S. Amelinckx, X. B. Zhang, D. Bernaerts, X. F. Zhang, V. Ivanov, J. B. Nagy, Science v265, 635 (1994).
[3] V. V. Mokashi, D. Qian, Y. Liu, Comp Sci Technol, v67, 530, (2007)
[4] Q. Zheng, D. Xia, Q. Xue, K. Yan, X. Gao, Q. Li, Appl Surf Sci, v255,3534 (2009)
[5] J. Wang, T. Kemper, T. Liang, S. B. Sinnott, Carbon, v50, 968 (2012)
[6] H. Wang, X. Li, G. Gao, Y. Li, Y. Ma, WIREs Comput Mol Sci, v8, e1346 (2018)
[7] H. Babaei, P. Keblinski, J. M. Khodadadi, WIREs Int. Jour. of Heat and Mass Transfer, v58209 (2013)

Single-walled carbon nanotubes have outstanding electronic and optical properties including ballistic transport and tunable infrared light emission. These properties arise from the delocalized π electrons of the sp² carbon structure and confinement effects around the nanotube circumference. There has been a long-standing need to controllably tailor single-walled nanotubes through the covalent attachment of functional groups. We recently introduced a novel way of nanotube functionalization using triazine anchors that preserves the π electrons of single-walled carbon nanotubes.[1] Infrared light emission from the optically active E₁₁ exciton was observed even at high degree of functionalization (4% of the carbon atoms).

Here, we present functional hybrids that are built using the triazine groups to anchor functional units on single-walled carbon nanotubes. We show how our platform provides routes toward controlled doping in carbon nanotubes. Nanotube luminescence is tailored by the attachment of molecular switches and enhancing plasmonic gold nanostructures. The molecular switch spiropyran reproducibly introduces blinking in single-walled carbon nanotubes after switching into its open merocyanine form. This makes carbon nanotubes that are covalently functionalized with merocyanine promising markers for ultra-high resolution imaging in the infrared.

[1] Preserving π-conjugation in covalently functionalized carbon nanotubes for optoelectronic applications, A. Setaro, M. Adeli, M. Gläske, D. Przyrembel, T. Bisswanger, G. Gordeev, F. Maschietto, A. Faghani, B. Paulus, M. Weinelt, R. Arenal, R. Haag, and S. Reich, Nat. Comm. 8, 14281 (2017).

Holey graphene (HG) is a particular form of structurally defective nanoporous graphene where the holes are introduced during the fabrication process. A HG matrix is a vertical stacking of multiple HG sheets with inter-stack separation of several nanometers. This structure affords generation of a massive ion-accessible graphene surface area and has ben employed for applications such as fabrication of supercapacitors, oxygen reduction, nitrogen adsorption, Li-ion batteries, etc. Here we would present our research on the use of molecular dynamics (MD) simulation to probe the capillarity-driven interaction of a water drop with the HG. We consider appropriate functionalization of the edges of the holes of the HG. We recover highly interesting transportation behavior of water through the HG matrix where in presence of an applied force water is transported faster in HG with hydrophobic functionalization of the hole edges and Darcy’s law is violated at a weak force where capillarity dominates. Secondly for cases where the force is applied for a duration less than that needed to make the water escape the HG matrix, our simulations reveal a development of novel transient and equilibrated water-graphene wetting states that ensure an attainment of enhanced water-graphene wetted area in a most facile manner. Finally, we study the motion of ion-rich drop through the HG matrix, only to reveal that an appropriate analysis would necessitate addressing the hitherto untracked problem of the role of ions in modifying the capillary waves at the air-water interface.

The graphene quantum dots (GQDs), a zero-dimensional graphene quantum structure, have triggered an intense research worldwide. GQDs possess unique optical, chemical and physical properties as compared to conventional quantum dots (QDs), such as low toxicity, biocompatibility, optical stability, chemical inertness, high photostability and good water-solubility and therefore hold great application potential in biomedical, optoelectronics and energy storage devices. The doping of GQDs with heteroatoms is one of the most effective ways to tune their photoluminescence emission and to increase quantum yield. In this study, we developed a novel approach to synthesize high-quality Nitrogen-doped graphene quantum dots (N-GQDs) with high quantum yield, via irradiation of s-triazene in a solution with benzene by using pulsed laser. The TEM, HRTEM, XPS, XRD, Raman spectroscopy and FTIR were carried out to observe the morphology, size distribution, crystalline structure and to prove successful doping of GQDs with nitrogen atoms. To observe optical properties of as synthesized N-GQDs, the UV-vis and Photoluminescence measurements were carried out. The as-synthesized NGQDs exhibit high quality crystalline structure of graphene with an average size of about 3.7 nm. A high quantum yield was exhibited by the obtained N-GQDs as compare to the pristine GQDs. The obtained N-GQDs with oxygen-rich functional groups exhibit a strong emission. These outcomes result in an ample opportunity for the biomedical and optoelectronic applications.

Controlling the structure and arrangement of single-walled carbon nanotubes (SWCNTs) directly during their growth constitutes a central bottleneck for the applications of SWCNTS in numerous fields including optics and microelectronics. Catalytic chemical vapor deposition (CCVD) is currently the most popular method for synthesizing SWCNTs because it offers more defined and versatile growth conditions, thus allowing to grow SWCNTs with a better control of their structure, orientation, surface density and purity. Although many groups reported catalyst systems and growth conditions yielding high selectivity for specific diameters or chiralities, a profound understanding of the processes impacting the structural distribution of SWCNTs is still missing. Two main reasons can explain the difficulty to experimentally correlate growth mechanism and structural features: 1) monitoring the growth of individual SWCNTs still remain very challenging, 2) determining SWCNT structure is usually complex and requires a combination of methods.
In this contribution, we will show how optical methods of spectroscopy and microscopy can help addressing this issue. First, we will present in situ and ex situ Raman measurements used to study the dynamics of the different populations of SWCNTs during their growth by CCVD [1]. Importantly, this study reveals that the nanotube diameter distribution strongly evolves during SWCNT growth but in dissimilar ways depending on the growth conditions. The origins of these evolutions will be discussed. Second, we will show how polarization-based optical methods can be used to monitor the growth of individual SWCNTs on substrates [2]. We will notably show that individual SWCNTs on substrate can be imaged during their growth with time resolution of 5-50 ms. Third, we will propose a general modeling of the polarized optical spectra of individual SWCNTs including the influence of the multi-layer substrate and of coherent and non-coherent depolarization by the optics. We will show that this model allows one to extract both the real and imaginary parts of the nanotube susceptibility and to improve the methodology of chirality assignment [3].

References
[1] Navas et al, ACS Nano 2017, 11, 3081−3088.
[2] Tran, Monniello, Jourdain et al., in preparation.
[3] Monniello, Tran, Jourdain et al., in preparation.

The public concern regarding possible toxicities of carbon nanotubes (CNTs) has attracted many attentions. Because CNTs would be mainly entrapped by macrophages when CNTs entered into the living body, the investigation of the degradation of CNTs and the resulted cytotoxicity after uptake by macrophage would be crucially important. In this study, we quantitatively investigated the intracellular degradation of CNTs by macrophages using an optical absorption method [1] and studied the toxicity changes of CNT during degradation. We have found that the intercellular degradations of CNTs by both primary cells and cultured macrophages were happened in the beginning 3 days after uptake and almost no degradation by the longer period incubation. The cell viability and cell total protein amount did not change during the degradation, and the amount of ROS generated by macrophage decreased with the degradation. These results indicated that the degradation of CNTs by macrophages followed the oxygen-depended mechanism and the residues of un-degraded CNTs persisted in macrophages without toxicity. In addition, through investigation of over 8-types of CNTs, we have found that the degradation rates of CNTs were dependent on their diameters, which would be helpful to predict the degradation characteristics of CNTs from their physical and chemical properties.

[1] M. Zhang et al. Small, 8, 2524 (2012).

Defect engineering through irradiation processes and chemical functionalization of graphene are promising routes for fabrication of carbon nanostructures and 2D metamaterials with unique properties and function. In previous computational studies, we reproduced experimentally observed structures of electron-irradiated graphene sheets through introduction of random distributions of vacancies in the graphene lattice and proper structural relaxation. We found that a vacancy-induced amorphization transition in graphene occurs for an inserted vacancy concentration between 5% and 10%. This order-to-disorder transition is accompanied by a brittle-to-ductile transition in the fracture mechanism upon uniaxial tensile straining as well as a transition in the lattice thermal transport mechanism in these irradiated graphene sheets.

Here, based on molecular-dynamics (MD) simulations in conjunction with first-principles density functional theory (DFT) calculations, we report results for the electronic structure of irradiated and irradiation-induced amorphized graphene. We find that localized states appear at the Fermi level upon irradiation and the corresponding local density of states increases with increasing inserted vacancy concentration. Furthermore, electronic band structure calculations show that band flattening occurs due to electron localization in the vicinity of irradiation-induced defects and reduces the charge carrier mobility. This band flattening effect becomes stronger with increasing vacancy concentration inducing an increasing number of flat bands near the Fermi level. Moreover, we present electron wave functions (as frontier orbitals) and charge density distributions, which provide clear evidence of carrier localization near the irradiation-induced carbon dangling bonds. Passivating these bonds with hydrogen atoms leads to delocalization of the charge density, hence increasing the carrier mobility, which also is seen in the reduced density of states observed at the Fermi level and the increased band dispersion with increasing inserted vacancy concentration. We find these spatially localized states to be spin polarized, which gives rise to a net local magnetic moment. Passivation of these states can cause the complete removal of these induced local magnetic moments. Our studies provide the fundamental understanding required to design electronic 2D materials for specific applications using irradiated graphene and passivated irradiated graphene as templates.

Single-walled carbon nanotubes (SWCNTs) are fundamentally interesting and technologically relevant materials with size-tunable absorption and emission across visible and near infrared wavelengths. However, several important aspects of SWCNT photophysical properties defy even simple physical explanation. For example, we found using variable temperature photoluminescence excitation spectroscopy that a sideband located approximately 130 meV away from the bright S₁₁ exciton peak relating to the K-momentum dark exciton state, called X₁, decreased in intensity five-fold as the nanotubes were cooled. Direct optical excitation of this dark state is nominally forbidden, thus calling into question how the state is populated, why it is so prominent in the photoluminescence spectrum, and what causes its strong temperature dependence. Interestingly, the ratio of the integrated photoluminescence intensities of X₁ to S₁₁ scales with a Boltzmann factor completely unrelated to the phonon that is thought to be responsible for depopulating the K-momentum dark exciton state: an in-plane transverse optical phonon, A₁’. Furthermore, photoluminescence spectra from individual nanotubes show that only a small fraction exhibit the X₁feature, with varying oscillator strength, thus suggesting that intrinsic processes such as phonon scattering are not responsible for populating the dark state. Alternatively, we suggest that populating the K-momentum dark exciton state requires scattering from defects, which is consistent with the increased magnitude of the X₁ feature for samples with increased sample purification and processing. Thus, the presence of an X₁ peak in photoluminescence is an extremely sensitive spectroscopic indicator of defects on single-walled carbon nanotubes.

Recent advances in material science provoked a new wave of researches in a thermoacoustic process induced by Joule heating. Mainly due to very low heat capacity per unit area (HCPUA) of the modern materials. Here, we present the state-of-the-art performance of free-standing single walled carbon nanotubes (SWCNTs) thin films as thermoacoustic sound generators. The SWCNT films synthesized by an aerosol chemical vapor deposition (CVD) method showed record sound pressure level of 101 dB with a frequency of 100 kHz at the distance of 3 cm and the input power of 1 W. Such performance was caused by extremely low HCPUA of the films 0.35 * 10^-3.
The research was performed with the films of different thicknesses in the sound range from 1 kHz to 100 kHz. The importance of aerogel structure of the materials for thermoacoustic generation researched theoretically and with experiments of densification and vacuum annealing. Full theoretical model of thermoacoustic free-standing films, which included effects of diffraction and finiteness of heat capacity per unit area was derived. Theoretical model was checked numerically in 3D by solving full system of coupled Linearized Navier Stokes and Helmholtz differential equations.
This work was supported by Skoltech NGP Program (Skoltech-MIT joint project).

Carbon nanotubes have recently been used as the building blocks of thermoelectric materials that enables the construction of wearable electronics and power modules. In this context, air- and thermally-stable doped, i.e. n-type materials are highly desired not only for the development of practical PN series thermoelectric modules but also for the optimal tuning of thermoelectric transport. In this presentation, I will talk about the preparation of air- and thermally-stable p- and n-type carbon nanotubes, and their application in thermoelectric transport studies [1-6]. Supramolecular (electro-) chemistry is introduced to improve, and quantify doping efficiency and stability. A recent progress on the power factor enhancement is also presented.

[1] Y. Nonoguchi, K. Ohashi, R. Kanazawa, K. Ashiba, K. Hata, T. Nakagawa, C. Adachi, T. Tanase, T. Kawai, Sci. Rep. 3, 3344 (2013).
[2] Y. Nonoguchi, M. Nakano, T. Murayama, H. Hagino, K. Miyazaki, R. Matsubara, M. Nakamura, T. Kawai, Adv. Funct. Mater. 26, 3021 (2016).
[3] Y. Nonoguchi, A. Tani, T. Ikeda, C. Goto, N. Tanifuji, R. M. Uda, T. Kawai, Small, 13, 1603420 (2017).
[4] M. Nakano, T. Nakashima, T. Kawai, Y. Nonoguchi, Small, 13, 1700804 (2017).
[5] Y. Nonoguchi, S. Sudo, A. Tani, T. Murayama, Y. Nishiyama, R. M. Uda, T. Kawai, Chem. Commun., 53, 10259 (2017).
[6] Y. Nonoguchi, K. Kojiyama, T. Kawai, J. Mater. Chem. A, doi: 10.1039/C8TA03948H (2018).

Weak interlayer coupling in 2-dimensional layered materials such as graphite gives rise to rich mechanical and electronic properties in particular in the case where the two atomic lattices at the interface are rotated with respect to one another. A lack of crystal symmetry leads to anti-correlations and cancellations of the p_z orbital interactions across the twisted interface, which gives rise to low friction behavior and low interlayer electrical transport. Using our recent nanomanipulation technology¹, based on atomic force microscopy, we studied the interlayer electrical conductivity as a function of twist angle between two misoriented graphene layers with unprecedented angular resolution of ~ 0.1 deg. The angular dependence indicates that the electrical transport across the interface is dominated by a phonon assisted channel which conserve the momentum of conduction band electrons, tunnelling across the twisted Dirac bands. Most intriguingly, the conduction is significantly enhanced within a narrow angular range of less than 0.5 deg at pseudo-commensurate angles of 21.8 and 38.2 degrees. This provides the first experimental evidence for the existence of a 2-dimensional interface state originating from the coherent coupling of electronic states in the twisted sheets due to commensurate superlattices². Finally, we show that combined electro-mechanical characterization techniques of mesoscopic graphite structures can be uniquely address open fundamental question related to the dielectric interlayer interactions and electronic charge transport through stacking faulted structures³.



References


E. Koren et al., Science, 6235 (2015) 679.
E. Koren et al., Nature Nanotech., 9 (2016) 752.
E. Koren et al., Nature Comm., 5 (2014) 5837.

The physics governing the adsorption of ions onto metallic or semimetallic surfaces underpins future technological developments in many areas. Specifically for graphene-based technology new emerging applications for example in energy storage or water filtration require a precise understanding of the relative stability of ions at the graphene surface and surface wetting properties. [1] However,many questions about the atomic structure of the electrolyte/graphene interface remain challenging to answer since the characterization of the interface proved to be elusive largely because the experimental techniques have not allowed direct observation of the behaviour of the ions. [2]
The driving force for the ion interfacial adsorption is a complex mix of enthalpic and entropic contributions, but molecular dynamics (MD) simulations of the electrolyte interface with both air and unstructured hydrophobic surfaces have demonstrated that it is mainly related to the stability of the ion’s solvation shell and its propensity to dehydrate. [3]For a semi-metallic surface, such as graphene, the proximity of an ion induces a further effect associated with polarization of the surface itself, which strongly affects the interfacial attraction/repulsion of the ions. In order to capture these important phenomena, we recently developed a novel molecular model that can include the polarizability of all the species involved and allow the prediction of the specific relative adsorption of ions on the graphene surface for electrolyte concentrations comparable to the experimental ones. [4]
In this talk we will show that this new model predicts that in a 1 M electrolyte solutions, cations are adsorbed onto the graphene surface with a trend (Li⁺ < Na⁺ < K⁺) opposite to that predicted by the gas-phase calculations and different than from that obtained from the single-ion simulations and with an energy of adsorption now validated by microscopy and electrochemistry experiments. [5] We will discuss how these findings are relevant for the graphene exfoliation process and wetting properties of the surface.

References
[1] Abraham, K. S. Vasu,C. D. Williams, K. Gopinadhan, Y. Su, C. Cherian, J. Dix, I. V. Grigorieva, P. Carbone, Geim, A. K. , Nair, R. R.Nat. Nanotech., 2017, 12, 546
[2] D. L. McCaffrey, et al.Proc. Natl. Acad. Sci.2017, 114, 13369
[3] Horinek, D.; Netz, R. R. Phys. Rev. Lett. 2007,99(22), 226104.
[4] C. Williams, J. Dix, A. Troisi, P. Carbone, J. Phys. Chem. Lett, 2017, 8, 703
[5] M. Ricci, W. Trewby, C. Cafolla, C. Voïtchovsky, Sci. Rep.2017, 7,43234

Thin films of single-walled carbon nanotubes (SWCNT) have many attractive opto-electronic features such as tunable conductivity and visible light transmission that make them of interest for a variety of applications. We present a characterization method that employs multi-angle spectroscopic ellipsometry spanning a wide spectral range from the ultraviolet to the terahertz (210 nm – 3 mm) that is capable of simultaneously determining a variety of opto-electronic properties in a contactless manner. In particular, SWCNT films are prepared in both “de-doped” (i.e. heat treated) and heavily nitric acid doped states and measured in both ex-situ and in-situ modes. The ex-situ measurements fully leverage the wealth of spectral features present in the wide spectral range while the in-situ mode allows for tracking of changes in real time as the film properties change due to atmospheric exposure. This frequency domain spectroscopic measurement is one of the only known techniques sensitive to the optical effects arising from electrical anisotropy between the in-plane and out-of-plane directions. Comparison to direct electrical measurements sampling the in-plane electrical properties confirms accuracy. Such electrical anisotropy arises from the fact that, despite no intentional alignment of the nanotubes being made, the nanotubes tend to lie flat on the substrate surface. Nitric acid doping is shown to decrease the film resistivity by factors of ~4 and ~100 in the in-plane and out-of-plane directions, respectively. This capability of determining electrical anisotropy is particularly relevant for incorporation of SWCNT films into devices where the desired direction for conduction is a consideration. Measurement of real-time changes to the film through the in-situ measurements are of interest for SWCNT films used in sensor applications. Additionally, the influence of doping on optical features arising from metallic and semiconducting transitions is determined.

The Berry phase is a geometrical phase that is known to provide the essential physics behind several intriguing materials properties such as the electric polarization, anomalous Hall effect, orbital magnetization, etc. It is expected that this geometrical phase also reflects the intrinsic topological properties of one-dimensional (1D) insulators, because the 1D Brillouin zone (BZ) integral forms a natural loop in the k-space. In this work, we study the system of gapped graphene nanoribbons (GNRs) with spatial symmetries (e.g., inversion) and show that a symmetry-protected Z₂ topological phase exists. Although the Berry phase turns out to be -quantized in the presence of the chiral symmetry, it does not provide the correct Z₂ correspondence as expected. It is found that only the origin-independent part of the Berry phase gives the correct bulk-boundary correspondence by its -quantized values, with the relevant Z₂ invariant dependent on the choice of the bulk unit cell (namely, ribbon truncation) and connected to the symmetry eigenvalues of the wave functions at the center and boundary of the BZ. Using the cove-edged GRNs as examples, we demonstrate the existence of localized states at the end of some GNR segments and at the junction between two GNRs based on topological analysis. The current results are expected to shed light on the design of electronic devices based on GNRs as well as the understanding of the topological features in 1D systems.

Novel nanocarbon-metal composites called covetics have the potential to improve significantly upon the mechanical, thermal, and electrical properties of common metals and alloys, including Al. Electric current applied to the melt containing a C precursor is believed to ionize carbon atoms and cause nanoscale graphitic ribbons and chains to form within the resulting Al lattice. Despite the potential of nanocarbon incorporation to improve desirable properties of Al alloys, critical for aerospace, structural, and power transmission applications, the atomic-scale mechanism is not yet completely understood.

In this work, the effects of current density and residence time on the uniformity and extent of carbon conversion to nano-graphite are explored in order to provide further insight into the conversion process. We characterize the structural and chemical features of nanocarbon-Al covetics using Raman spectroscopy, TEM imaging, electron energy loss spectroscopy (EELS), and X-ray photoelectron spectroscopy (XPS). Raman and EEL spectra are localized to within a few µm of a selected region of interest, as guided by fiducial marks milled using a focused ion beam tool before collection of the spectrum images (SIs). The Raman and EELS SIs are subjected to nonlinear iterative fitting and hyperspectral decomposition using machine learning techniques to reveal features indicating nanocrystalline graphite embedded within the Al lattice. The Raman G and D peak intensities and shifts are found to depend on the current parameters, with greater exposure corresponding to greater graphitic order. Evidence of sp² carbon bonding and Al-C bonding is seen by EELS and XPS. Local mechanical (nano-indentation) and electrical conductivity measurements will also be taken and related to processing conditions and local structure.

This work is based upon work supported by the U. S. Department of Energy under Award No. DE-EE0008313. Dr. David Forrest is the Project Technology Manager and Debbie Schultheis is the Project Officer/Manager.

Graphene and graphene oxide (GO) are arguably some of the most interesting materials to have emerged in the past decade. Their unique features, such as mechanical strength, electrical, thermal, and optical properties have brought them to the forefront of technology; from basic science research, to applications in electronic devices, athletic equipment and biodevices.^1,2 Research in the field is focusing towards the development of large scale manufacturing processes, suitable for industrial production.³ One of the key prerequisites for the industrial use of graphene and GO is their rapid, reliable and cost-effective characterization and quality control via a method suitable for operation in an industrial production line. Currently, most laboratory techniques employed for the characterization of 2D materials rely on the description of their chemical, mechanical and electronic properties. Electron and scanning probe microscopy imaging offers the most direct characterization approach;⁴ however, these typically require long imaging times and oftentimes complicated sample preparation. They are, therefore, unsuitable for routine screening and quality control of a large number of samples. On the other hand, conventional optical microscopy, even though simple and time-effective, has a theoretical resolution limit too large for the characterization of 2D materials.
Here we present the development of a novel imaging technique based on optical microscopy, suitable for the characterization of atomically and molecularly thin materials. Utilizing the property of negative refractive index media to enhance the normally undetectable evanescent waves,⁵ a microsphere objective lens was manufactured and integrated in a simple optical microscope, ultimately improving significantly the resolution limit and allowing the observation of features as small as 50 nm in the lateral direction.⁶ The developed technique was verified by imaging GO flakes. Bypassing any need for complicated sample preparation, it was possible to reproducibly and rapidly observe topographical features of the flakes, as well as monolayers and GO agglomerates.
Using light microscopy we were able to observe topographical features of a 2D material at high lateral resolution for the first time. Our technique allows the implementation of such measurements both under well controlled laboratory conditions and alongside an industrial production line, at a high throughput rate and without requiring complicated sample preparation, enabling rapid and detailed characterization of atomically and molecularly thin materials.
References:
1.Novoselov, K. S., Fal'Ko, V. S. et al. Nature 490, 192–200 (2012)
2.Choi, W., Lahiri, I.et al. Crit. Rev. Solid State Mater. Sci. 35, 52–71 (2010)
3.Wang, G. et al. Carbon N. Y. 47, 3242–3246 (2009)
4.Lee, J., Zheng, et al. Diam. Relat. Mater. 54, 64–73 (2015)
5.Pendry, J. B. Phys. Rev. Lett. 85, 3966–3969 (2000)
6.Wang, Z., Guo, W. et al. Nat. Commun. 2, 216–218 (2011)

Single cell analysis is an emerging technology that can provide a mechanistic understanding of the complex biological systems and cell heterogeneity (1). Any disruption of its activity can be monitored through interfacial bioelectrochemistry. In this emerging technology it is necessary to have high spatial and temporal resolution over an extended period of time that has been seldom achieved in the adopted analytical measurements. This problem has been solved in the present work by using an electrochemical technique such as differential pulse voltammetry (DPV) carried out with carbon nanotube pipette electrode that is laden with graphene quantum dots (20 nm-50 nm) (2). This modification gives rise to a sensitive electrode material for high temporal resolution through idealizing the DPV parameters. The in-vitro experiments carried out in understanding oxidative stress produced by p-aminophenol (PAP) that results in membrane disruption suggest that molecular attachment of PAP to graphene is higher than the pipette electrodes (amorphous carbon) as indicated by the signal strengths being several orders of magnitude higher than with nanotube pipette electrode. The shape and features of the current-voltage curves that are recorded can be idealized as nanotube electrode arrays acting as an ensemble in harmony. As the electric field known to influence the cells, the electric field produced during the detection of an electroactive species by this ensemble has been simulated for practical usage for in-vivo studies. The new electrode opens up an approach at observing the electroactive neurotransmitter during its functioning in chronic diseases.

1. H. R. Rees, S.E. Anderson, E. Privman, H.H. Bau, and B. J. Venton, Anal. Chem., 87, 3849, (2015).
2. P. Wong, K.S.V. Santhanam, and S. Kandlikar, J. Electrochemical Society, 165, B232 (2018)

Electrochemical (re)activity of graphene and graphene-based ‘hybrid’ nanomaterials is crucial for food, energy and water sustainability applications, which requires delicate control over its geometric and electronic structures. We demonstrate that precise control of the density of defects, hierarchical porosity, and topological interconnectedness, invoked in hydrothermally synthesized graphene aerogel integrated with multi-walled carbon nanotubes that can finely tune mesoporosity and enhance the electrochemical heterogeneous electron transfer rate (k_ET). We prepared range of three-dimensional solid network of graphene-based ‘hybrid’ scaffolds (i.e. aerogel) and their nitrogenated counterparts with varying graphene-carbon nanotube compositions using two schemes (approach 1 and approach 2). This study allows us to correlate quantitatively between number defect density determined (via Raman spectroscopy; RS) and heterogeneous electron transfer rate (via scanning electrochemical microscopy; SECM). RS provides nanoscale phononics characterization revealing collective atomic/molecular motions and localized vibrations. The first- and second-order phonon modes are analyzed in terms of Raman intensity, band position (intrinsic mechanical strain) and intensity ratio (structural disorder, number defect density), distinct localized π electronic states were found in photoluminescence excitation (PLE) spectra reflecting carbon atoms around oxygenated and nitrogenated species. The role of carbonyl (C=O), epoxy (C-O-C) and nitrogen (pryridinic-N and graphitic/pyrrolic-N) surface functionalities and corresponding bonding configurations besides hierarchical mesoporosity are emphasized in view of understanding the improved physicochemical properties for electrochemical energy, water desalination and sensing applications. The engineered defect density induced increase in finite electronic density of states (DOS) near Fermi level revealed using density functional theory (DFT) calculations and decrease in room temperature electrical conductivity, heled in establishing optimal defect density for moderate heterogeneous rate as a critical state such that the whole system becomes electronically activated while maintained structural integrity. Moreover, it enlarges the overlap between DOS for graphene-based aerogels and redox probe couple, which signifies the experimental correlation establishments.

Extensive research is being conducted on graphene-based composite films to explore their potential in actuation mechanisms stimulated by electrical, thermal, mechanical or optical energy sources owing to its extra-ordinary electrical and mechanical properties.¹ In this study, we report the use of all graphene based functionally graded, bilayer free-standing films as mechanical actuators triggered by adsorption of moisture at the film interface. The bilayer films were fabricated by a single-step doctor blade coating technique and dried at controlled temperature and humidity conditions. The reduction mechanism of Graphene Oxide into rGO was implemented through metal substrate-assisted reduction², which involves coating GO paste on an active metal like Aluminum that possess a high oxidation potential.³ The internal architecture of the films was tuned as per requirement by changing the initial process parameters like the concentration and pH of GO and the surrounding humidity and temperature. Selective reduction of Graphene Oxide into desired intricate patterns was also demonstrated, through usage of masks during film coating and deposition.
The functional grading of the films, where one side is electrically-conducting GO while the other being insulating rGO was confirmed by SEM, Raman, XRD, FTIR and XPS analyses. SEM revealed an overall understanding of the porous nature of the film throughout the cross section whereas Raman Spectroscopy showed an increase in (Id/Ig) ratio from GO to rGO face, denoting gradual restoration of sp² hybridized hexagonal carbon structure. XRD, FTIR and XPS results also confirmed the functional grading throughout the thickness of the film post-reduction. The bilayer film, which is composed of Graphene Oxide and Reduced Graphene Oxide on either side, is shown to exhibit selective bending mechanism in humid environments, due to the affinity of Graphene Oxide towards polar molecules like water. Reduced Graphene Oxide being immiscible in water shows repulsive nature towards humidified surroundings, thus triggering a differential bending mechanism in the individual bilayer film. The Hygromorphic behavior¹ exhibited by the robust and flexible functionally graded graphene films, can intrigue a variety of applications in mechanical actuation, robotics and gas sensing systems.
References:
1. Cheng, H.; Liu, J.; Zhao, Y.; Hu, C.; Zhang, Z.; Chen, N.; Jiang, L.; Qu, L., Graphene fibers with predetermined deformation as moisture-triggered actuators and robots. Angewandte Chemie International Edition 2013, 52 (40), 10482-10486.
2. Hu, C.; Zhai, X.; Liu, L.; Zhao, Y.; Jiang, L.; Qu, L., Spontaneous reduction and assembly of graphene oxide into three-dimensional graphene network on arbitrary conductive substrates. Sci Rep 2013, 3, 2065.
3. Liu, Q.; He, M.; Xu, X.; Zhang, L.; Yu, J., Self-assembly of graphene oxide on the surface of aluminum foil. New Journal of Chemistry 2013, 37 (1), 181-187.

The mechanics of triply periodic minimal surfaces (TPMSs) with three-dimensional (3D) graphene foams are systematically studied to understand the effects of structure and size on the mechanical properties, e.g., elasticity, strength, and fracture. The design of lightweight open-shell porous solid materials with TPMSs has shown excellent and tunable load-bearing properties. However, filure mechanisms and their relations with surface topologies are largely unknown. Utilizing reactive molecular dynamics simulations, here we investigate the elastic and fracture properties of three different surface topologies with 3D graphene foams: P (primitive), D (diamond), and G (gyroid). Models with different lattice sizes are utilized to derive power laws, which can connect the properties along different sizes to shed light on the multiscale mechanics of 3D graphene with TPMSs. Our study provides a systematic understanding of the relation between TPMS topologies and their mechanical properties, including failure mechanisms of graphene foams, opening opportunities to explore designable complex structures with tailored properties.

Graphene has excellent mechanical, thermal and electrical properties. However, there are limitations in utilizing monolayers of graphene for mechanical engineering applications due to its atomic thickness and lack of bending rigidity. Synthesizing graphene aerogels or foams is one approach to utilize graphene in three-dimensional bulk forms. The structures of graphene foams can be idealized with the triply periodic minimal surface (TPMS):P (primitive), D (diamond), and G (gyroid). Here, we investigate the thermal conductivity of three different surface topologies with 3D graphene foams by using full-atom molecular dynamics simulations. We derive a scaling law showing how the different TPMSs have different trends. Our analysis shows that the trend of the thermal conductivities can be attributed to defects and curvatures of graphene. Our study shows that three-dimensional porous graphene has potential that may be utilized in designing new lightweight structural materials with low and density-insensitive thermal properties and superior mechanical strength.

In this study, we have designed and engineered polymer blends as an improvement of the thermal diffusion structure for polymer materials. In our system, poly (lactic acid) (PLA) was used as a second phase reorganizer of the Poly (butylene adipate-co-butylene terephthalate) (PBAT)/graphene composites. Two different types of graphene, H-5 and C-750, were used in this study to guarantee the thermal conductivity of the composites. According to the contact angle measurements and the calculation of the interfacial tension between polymers and graphene, we observed that graphene will be more stable in the PBAT phase than in the PLA one. Therefore, in our blends system, PBAT was designed as the polymer matrix, while the PLA was considered as the minor phase with a comparatively lower concentration. Because the size of H-5 (average around 5 ) is larger than the PLA domain size (around 3 ), H-5 can disperse perfectly in PBAT matrix and form continuous thermal diffusion paths. With 20% of graphene H-5, the thermal conductivity of PBAT/PLA blend can achieve a 26% enhancement, as compared with the sample without PLA. Moreover, we discovered that the incorporation of C-750, unfortunately, failed in promoting the thermal conductivity of the PBAT/PLA blend. Since the PLA domain size is much larger than the size of C-750 (average around 750 nm), it can hardly help drive the dispersion of the C-750 in a preferential orientation in the PBAT matrix and makes the formation of the thermal diffusion path even harder.

Over the past decade, comprehensive investigations have been conducted to develop graphene based two-dimensional (2D) materials to harness their excellent and unprecedented properties such as high electrical conductivity, optical transparency, mechanical strength, and flexibility. To fully utilize these functionalities, a number of methods including chemical vapor deposition, liquid shear exfoliation, sonication, ball milling, electrochemical exfoliation and the recently conceived compressible flow exfoliation (CFE) have been successfully studied. However, these methods can introduce significant amount of defects during exfoliation into the graphene crystal structures that have a strong influence on their properties. This study is designed to compare the defect and flake quality between CFE and bath or probe sonication process for producing high-performance conductive ink from exfoliated graphene.
In our CFE process, graphite is rapidly jettisoned through a small orifice using high-pressure gases without the need for any time-based treatment, unlike other shear-based liquid processes. Shear-induced exfoliation occurs due to the high velocities that expanding and accelerating gases can achieve in small orifices coupled with viscous friction effects resulting in a high shear rate (γ>10⁵ s^-1) experienced by the graphite particles. In contrast, in the sonication methods, an ultrasonic transducer is used to induce unstable cavitation bubbles in a liquid medium, which upon their inevitable collapse emanate a shock wave. The energy of this shockwave is sufficient to fragment nearby bulk graphite powders into smaller lengths as well as thickness along the weak, secondary c-axis. But when the bulk particle is fragmented into smaller flakes, a good number of edge and basal plane defects are introduced into the flakes. The defect population increases as the time for sonication rises. The occurrence of a disorder-activated D peak at 1330 cm^-1 in the Raman spectra of graphene is indicative of defects, in particular, those which disrupt the sp² hybridization. Such defects can be interpreted to be the creation of new edges, vacancies or substitutions, with the ratio between the peaks intensities of the D to G peak (I_D/I_G) providing a qualitative indication of their population. In our study, we found the ratio of D peak to G peak is significantly less in CFE than that of bath sonicated graphene-I_D/I_G=0.66 for CFE graphene and I_D/I_G=1.1 for bath sonicated graphene. In contrast, the bulk graphite powder had I_D/I_G ratio of 0.62. The increased quantity of defects in bath sonication may be attributed to the prolonged sonication time which is well known to be responsible for reducing the flake length and hence, introducing more edges. The flake quality of exfoliated graphene was also verified using atomic force microscope (AFM) and transmission electron microscope (TEM).

Graphene is bustlingly exploited as a linker layer in surface plasmon resonance (SPR) biosensing for advanced biomolecule-recognition due to its intriguing plasmonic properties. However, the chemical nature of pristine graphene limits the binding of receptor biomolecules to physisorption and π-π stacking. Therefore, chemically exfoliated graphene oxide (GO) and reduced graphene oxide (rGO) are used instead for covalent immobilization of receptor biomolecules, since they possess various functional groups on the carbon basal plane and concurrently preserve the carbon-lattice as pristine graphene within nanoscale size. In this work, we investigated the sensing performances of Au/glass SPR chips with GO and rGO thin films as functional layers. As a proof-of-concept we applied a lectin Concanavalin A (ConA) binding assay with prostate cancer-specific antigen (PSA) as receptors. The results demonstrated stronger surface plasmon resonance effects for biomolecule recognition with rGO functional layers, whilst the average intensity of surface plasmons and signal-to-noise ratio were 1.7 and 3 times higher compared to the GO as functional layers. More remarkably, taking advantage of the bipolar property of the rGO thin films, it was possible to further enhance the surface plasmon intensity by applying bias voltages to the rGO thin films. The limit of detection ConA target molecules was 0.01 µg/ml. Such tunable SPR platforms based on rGO thin films lighten up a wider road for diverse surface functionalization, adjustable sensing regimes and improved sensitivity in the field of SPR biosensing.

Single-walled carbon nanotubes (SWCNTs) have been anticipated for applications in a lot of future nanodevices. However, there still remain several problems for realizing the SWCNT devices, and one of the most significant issues is high-yield growth of semiconducting SWCNTs. So far, to grow SWCNTs with high-yield, Al₂O₃ buffer layers are widely used, because they prevent migration of catalysts on the substrate surface at growth temperature and aggregation of catalyst particles are suppressed [1]. In this study, we attempted to grow SWCNTs using Ir catalysts without Al₂O₃ buffer layers, which have never been used as catalysts in SWCNT growth.
After deposition of Ir catalysts on SiO₂/Si substrates, SWCNT growth was carried out using alcohol gas source method in a high vacuum [2]. Growth Temperature and growth time were set at 800°C and 1 h, respectively. The ethanol pressure was varied between 1×10^-3 and 1×10^-1 Pa. The grown SWNTs were characterized by FE-SEM, TEM and Raman spectroscopy.
SEM and Raman results showed that, as the ethanol pressure increased, the SWCNT yield became higher and the SWCNT diameter became narrower. When the ethanol pressure was 1×10^-1 Pa, high-density vertically aligned SWCNTs were grown, whose lengths were about 2 μm. Raman measurement showed that SWCNT diameter were distributed between 0.83 and 1.13 nm. In addition, Raman spectra showed that semiconducting SWCNTs were dominantly grown from Ir catalysts. This study is the first report to grow SWCNTs from Ir catalysts, and our results indicated that Ir catalysts are effective to obtain high-density vertically aligned and small diameter SWCNTs using no Al₂O₃ buffer layers.
[1] K. Hata et al. Science 306 (2004) 1362.
[2] T. Maruyama et al. Carbon 116 (2017) 128.

Heterojunctions of nanomaterials have attractive attention due to interesting electrical and optical characteristics. One of the interesting materials is graphene, which has Dirac-cone band structure. Utilizing this band structure and other contacting semiconductor nanomaterials, diode and transistor behaviors can be controlled by applying a global back gate voltage. However, due to vertical integration of this heterojunction, each band structure cannot be separately controlled to observe different functions. Furthermore, although the barrier height as a function of gate voltage has been studied, detail band alignment has yet to be studied due to difficulties of gate voltage separation between graphene and other nanomaterial. To address these challenges, we demonstrate a graphene-carbon nanotube (CNT) junction device laterally integrated with local gate electrodes for graphene and CNT. Furthermore, barrier height dependence is also investigated as a function of local gate voltages.
CVD-grown monolayer graphene was transferred onto a Si/SiO₂ substrate with Au source and drain electrodes. After graphene was patterned by an oxygen plasma, semiconductor-enriched CNT networks were deposited by modifying the surface of graphene and SiO₂ surfaces with poly-L-lysine. SiO_x/Al₂O₃/SiO_x dielectric layers were deposited over the substrate, followed by Al gate electrode deposition. To apply the gate bias at graphene, CNT, and junction of them, multi-gate stack structure was fabricated by repeating the gate dielectric and electrode deposition.
Uniform formation of Graphene, CNT, and junctions were confirmed using Raman spectroscopy and AFM. Dirac point of graphene was about -3 V, and ambipolar behavior of CNT/graphene transistor was observed. When graphene voltage from -6 V to 3 V was applied, threshold voltage is modulated from 0 V to 0.24 V. These mobilities are 7.0±1.6 cm²/Vs and 1.1±0.2 cm²/Vs for p-type and n-type behaviors, respectively. After analyzing the device as a function of temperature, thermal and tunnel emission probabilities were calculated. At the transition between thermal and tunnel emission, barrier heights were extracted at different local gate bias of graphene. Based on the results, barrier heights were linearly changed by changing the gate voltage, which is in good agreement with our expectation due to the Fermi level movement. The barrier heights are varied from ~84.5 meV to ~69 meV for n-type and ~85.5 meV to ~71.5 meV for p-type depending on the graphene gate voltage. The values are slightly lower than that of vertically integrated graphene/TMD materials. This may be caused by the multiple junctions with defects to the Fermi level of graphene due to solution process of CNT network formation.
In summary, we could successfully fabricate the locally gate controllable graphene/CNT junction transistor and analyzed the barrier height at different local gate voltage corresponding to the Fermi level movement.

Carbon nanotubes (CNTs) is one of the most promising material because of their superior electronic, thermal and mechanical properties. Single-walled carbon nanotubes(SWNTs) have a hollow space of about several nm in diameter. It is possible to encapsulate various functional molecules in hollow space and expected new functions by encapsulation.
One of the polycyclic aromatic hydrocarbon (PAH) molecules, coronene has been reported to exhibit interesting fluorescent properties depending on the local structure. The unique luminescence properties of columnar stacked coronene encapsulated in SWNTs have been also reported.In this study, molecular dynamics simulation was performed to clarify the local structure and properties of various kinds of PAH molecules encapsulated in SWNTs systematically.
We will report the detailed results of SWNT chirality dependence of encapsulated structures of PAH molecules.

Owing to the energy needs of the modern world, numerous studies have been performed in order to develop new materials with advanced electrical properties to be applied in energy storage devices, especially capacitors and supercapacitors. Accordingly, carbon-based materials such as carbon nanotubes (CNT) and reduced graphene oxide (rGO) are regarded as great alternatives to be used in the clean energy industry. Also, the possibility of the development of nanocomposites with carbon-based materials, metallic nanoparticles and metal oxides becomes interesting for electrochemical applications, such as energy storage devices, capacitors, gas sensors and others, and is the main focus of many researches in the last few years. A potential candidate to be used in the surface modification of CNT’s is the indium tin oxide (ITO), since it presents very interesting electrical properties and is studied for several applications. In the present work, nanocomposites of CNT/ITO have been prepared using a microwave-assisted hydrothermal synthesis (MHS), with posterior annealing of 400 °C and 600 °C, in inert atmosphere, to obtain crystalline ITO. Hydroxylated (CNTOH) and carboxylated (CNTCOOH) multiwalled carbon nanotubes-MWCNT (30% w/w), indium nitrate and tin chloride were used as precursors. The obtained powder was investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical properties were evaluated by cyclic voltammetry, electrochemical impedance spectroscopy e galvanostatic charge-discharge, using a two electrode cell with current collectors made of 304 stainless steel, KOH 6 mol L-1 as electrolyte and filter paper as separator. The measurements were performed in a sourcemeter Keithley model 2651A and a potentiostat IVIUM -Compactstat.e. XRD results showed that the sample annealed at 400 °C, the phase obtained was rombohedral, while at 600 °C was formed the cubic phase. Charge-discharge results showed values of 3.2 F/g and 1.4 F/g for CNTOH/ITO-400 and CNTOH/ITO-600, respectively, and 5.1 F/g and 0.3 F/g for CNTCOOH/ITO-400 and CNTCOOH/ITO-600, respectively. It is possible to observe that the specific capacitance of the samples with rhombohedral ITO was higher than for cubic, which can be explained by a degradation of nanotubes structure when submitted to higher temperatures. However, these findings require further characterization, such as Raman spectroscopy and FEG-SEM images, for example.

Two-dimensional materials have attracted attention in recent years because of their excellent electrical properties and can develop innovative devices [1-3]. In particular, single-layer graphene with the high carrier mobility and saturation velocity could push the limit of high-frequency devices [4]. In this work, we focus on fabrication and electrical characterization of gate tunable graphene lateral tunnel diodes to realize optical rectennas which receive and convert optical frequency electromagnetic radiation into DC output with high-efficiency and low-cost [5].

The gate tunable graphene lateral tunnel diodes have been fabricated using monolayer graphene grown by chemical vapor deposition (CVD) on Cu foil and later transferred on 83-nm-thick SiO₂/n⁺-Si substrates. Tunnel regions between adjacent graphene layers were defined by using electron beam lithography, and the tunnel length ranged from 60 to 150 nm. Tunnel dielectric consists of plasma Si₃N₄ and Al₂O₃. The Al₂O₃ layer was formed by atomic layer deposition on the native oxide of Al thin film. Metal electrodes (anode and cathode) were formed by electron beam evaporation of Ti/Pd/Au (0.5/20/100 nm) right after an oxygen plasma treatment to reduce contact resistance between graphene and electrodes. Top and back gate electrodes were formed by Ti/Au (20/80 nm) and Al (100 nm), respectively.

Typical current-voltage (I-V) characteristics of the fabricated devices showed rectifying characteristics at a low voltage below 1 V. The on-state current of the lateral diodes increased with reducing the tunnel length. The lateral diodes have p-type rectifying characteristics for positive gate voltages and n-type rectifying characteristics for negative gate voltages. This result indicated that the tunnel barrier height could be controlled by applying gate voltage. We also measure the rectifying characteristics as a function of the back gate voltage to confirm the tunneling transport. The devices exhibited steep subthreshold slope (SS) of 40 mV/decade, which was lower than the theoretical limit of MOSFETs at room temperature indicating the devices were tunnel diodes.

References
[1] M. Chhowalla et al, Nature Reviews Materials, 1, 16052 (2016).
[2] T. Uchino, et al, Appl. Phys. Lett, 103, 193111 (2013).
[3] T. Uchino, et al, Electrochemical Solid-State Lett, 14, pp. K21-K23 (2011).
[4] E. Guerriero, et al, Scientific Reports 7, 2419 (2017).
[5] A. Sharma, et al, Nature Nanotechnology 10, pp. 1027–1032 (2015).

Many papers have clarified that the healing of crystalline defects in materials improves various properties. In this study, we demonstrate a new approach for healing crystalline in single wall carbon nanotubes (SWCNTs) based on simultaneously applying electrical current and heat. In this way, we succeeded in improving the graphitization without inducing other changes to the structure, in particular diameter and wall number. To achieve this we designed and constructed a specialized treatment device capable independently applying current (∼240 A cm^-2) and heating (room temperature to 2000 ^oC). Our examination found that at 800 ^oC, 150 A cm^-2 for 1 min, we could achieve a 3.2-times increase in crystallinity as indicated by an increase in Raman G- to D-band ratio, a 3.1-times increase in electrical conductivity (from 25.2 to 78.1 S cm^-1), and a 3.7-times increase in thermal conductivity (from 3.5 to 12.8 W m^-1 K^-1). The simultaneous increase in electrical and thermal conductivities stems directly from defect healing, and importantly we observed no additional change in diameter or wall number. The simultaneous application of current is essential in maintaining the initial CNT structure (diameter and wall number) as demonstrated in a reference test where CNTs were treated without an applied current. Further studies have demonstrated the scalability of this process in achieving similar improvement (~3-fold) in both thermal and electrical conductivities, which results indicate the fundamentally scalable towards larger scale (i.e. gram-level or more) amounts of SWCNT.
In addition, due to a fundamental similarity in composition and structure, we applied this re-graphitization process to few-layer, free-standing exfoliated graphene. We achieved this by applying the electrical current (current density: ∼900 A cm⁻²) in conjunction with heating (∼900 °C) in-plane of an “exfoliated graphene sheet” with the original sample holder in an argon ambient. After treatment at 900 °C and 545 A cm⁻² for 1 min, we observed a significant increase in graphitization as exhibited by a ~10-times increase in the Raman G- to D-band ratio (2.84 to 36.7) and no observed change in interlayer separation, i.e. (002) reflection by x-ray diffraction. Furthermore, we observed a~2.0-times increase in electrical conductivity (from 1088 to 2275 S cm⁻¹). These results demonstrate the use of a post-synthesis process to nanocarbon materials to improve crystallinity and the difference between its application towards SWCNTs and graphene. Therefore, we believe strongly that this process overcomes one of the major limitations of SWCNT and graphene (other 2D-materials) toward real applications.

Targeted tuning of the structure and properties of carbon nanotubes (CNT) using ion irradiation is very attractive for technological applications. To understand the damage formation and evolution due to ion irradiation in multiwalled (MW) CNT, we used 25 keV Ne⁺ and He⁺ ion irradiation with controlled fluences in the range of 10¹⁴ to 10¹⁸ ions/cm² and subsequently investigated the irradiated areas by TEM imaging and Raman spectroscopy. A new methodology involving Au TEM grids was developed to ensure compatibility across the different techniques and to preclude the Raman contribution coming from the amorphous carbon support of typical TEM grids. The experimental results indicate a significant difference in the damage evolution between He⁺ and Ne⁺ irradiation. Furthermore, the sample thickness was found to play an important role in determining the extent of damage. TEM imaging suggests that the thicker areas are significantly amorphized, while thin areas (t < 10 nm) were found to be relatively undamaged with only very minor changes in comparison to pristine samples. For He⁺ and Ne⁺ irradiation, damage formation evolves differently, with a change in the trend of the ratio of D to G peak in the Raman spectra being observed for He⁺ but not for Ne⁺. The experimental results were then compared with the Monte-Carlo (MC) simulations of ion-solid interaction by approximating the sample to a thin carbon membrane. Due to the small thickness of the MWCNTs, sputtering has been observed for the top and bottom side of the samples. Depending on thickness and ion species, the sputter yield is significantly higher for the bottom than the top side.
In this presentation, we will describe the new correlative methodology that was developed for this study and discuss the experimental results from correlative TEM-Raman analysis of MWCNT under He⁺ and Ne⁺ irradiation together with insights drawn from MC simulations using SDTRIMSP.

Semiconducting single-walled carbon nanotubes (SWNTs), which have one-dimensional cylindrical structures with a graphene wall, show near infrared (NIR) photoluminescence (PL). As an interesting feature of SWNTs, the PL properties are sensitively changed by effects of microenvironments that are composed of surfactants and solvent molecules. Therein, physical properties of microenvironments such as polarity and polarizability could affect coulumb interactions between electron - electron or electron - hole in the tubes [1].
In recent studies, local chemical functionalization of SWNTs is reported to produce novel PL properties [2][3]; The locally functionalized SWNTs (lf-SWNTs) emit new PL (E₁₁*) whose wavelength are red-shifted over 100 meV from the original PL (E₁₁) of the pristine SWNTs and their quantum yields increase largely. These properties arise from electronic structure variation introduced by the functionalization and exciton trapping at the functionalized sites, respectively. Actually, we experimentally revealed that energy levels of the HOMO and LUMO shifted at the local functionalized sites with dependence on the chemical structures of the functionalized groups [4].
In this study, we examine microenvironment effects on the E₁₁* PL of lf-SWNTs in order to compare excitonic properties at the local functionalized sites and the pristine sites. Herein, we synthesized nitroaryl-functionalized SWNTs (lf-SWNTs-NO₂) that were solubilized in D₂O containing sodium dodecylbenzenesulfonate (SDBS). For microenvironment creation of an organic solvent [5], o-dichlorobenzene (oDCB), which was immiscible in water, was poured into the lf-SWNTs-NO₂ solution and vigorously shaken, then the separated aqueous layer was collected for measurements. After the experimental process, PL peaks of E₁₁* and E₁₁ were red-shifted, indicating that oDCB permeated into the hydrophobic regions between the nanotubes and the coating SDBS micelles. Interestingly, the shifted energy value of E₁₁* was larger than that of E₁₁. The result indicates that interactions of oDCB on the nanotubes might be varied at the local functionalized sites and the pristine sites. Details including the effects of other solvents will be discussed in this presentation.
References
[1] Y. Miyauchi, J. Mater. Chem. C, 2013, 1, 6499.
[2] Y. Piao, B. Meany, L. R. Powell., N. Valley. H. Kwon., G. C. Schats., Y. Wang., Nat. Chem. 2013, 5, 840.
[3] H. Onitsuka, T. Fujigaya, N. Nakashima, T. Shiraki, Chem. Eur. J. 2018, in press. DOI: 10.1002/chem.201800904.
[4] T. Shiraishi, T. Shiraki, N. Nakashima, Nanoscale. 2017, 9, 16900.
[5] C. A. Silvera-Batista, R. K. Wang, P. Weinberg, K. J. Ziegler, Phys. Chem. Chem. Phys. 2010, 12, 6990.

Herein, we report a diverse and simple method that enables stabilization and transcription of protein - derived nano - sized superstructure. It is known that ß-lactoglobulin used to forms aggregates by controlling specific protein concentrations and solution pH, ionic concentlation and heating temperature, however in this study, by precisely controlling the pH, we also succeeded in controlling the size of the protein spherical aggregates. In addition, we investigated stabilization of supermolecular structures and morphological transcription by performing π-conjugated polymer coating on this protein spherical aggregate (PNS) and report it. We used 1,5-dihydroxynaphthalene and 1,3,5-trimethyl-1,3,5-triazinane as raw material monomers to the PNS aqueous solution and polymerized at room temperature and as obtained a π-conjugated polymer-coated protein spherical aggregate (PPNS). Subsequently, the obtained PPNS was carbonized at mild temperature to obtain carbon-like nano spherical aggregates (CPNS). PNS and PPNS were confirmed for their morphology and shape by transmission electron microscopy (TEM) and dynamic light scattering (DLS) techniques. From the results of TEM observation and DLS analysis, it was found that the PNS diameter can be controlled from tens of nm to submicron by changing the pH. As a result of conducting reaction monitoring of polymer coating by ultraviolet-visible spectroscopy (UV-Vis) and fluorescence spectrophotometer (FL), it was confirmed that reaction intermediates decreased with increasing reaction time. By cross-section analysis of PPNS by field emission scanning electron microscope (FE-SEM), it was possible to confirm the polymer layer on the surface of the spherical aggregate, maintaining the spherical shape even after polymer coating, so it was thought that we succeeded in morphological transcription. Furthermore, CPNS after high temperature carbonization also maintained spherical shape with nano-sized carbon-shell. It was also possible to confirm the morphological stabilization of the superstructure before and after polymer coating under alkaline conditions. Prepared CPNS is expected to be used in fields such as nanosensor, drug delivery, and adsorbent. In addition, this method is expected to be used as a method for preparing and functionalizing carbon nanostructures, which is convenient and versatile than ever before.

In the past few years there have been many exciting achievements in the synthesis of large-size and high-quality monolayer graphene (MLG) using the chemical vapor deposition (CVD) method¹ on Cu substrates. During the MLG growth, accompanying adlayers occur and remain a broad interest to researchers for a deep understanding of the graphene mechanism. When methane is used as the precursors, it is believed that the adlayers are grown underneath the previous layer,^2,3 whereas when ethanol or other precursors with stronger reactivity is used, adlayer growth follows a layer-by-layer regime.^4,5 In this work, we studied the growth mechanism of graphene adlayers using carbon isotope labelling of the precursors and Raman spectroscopy. Results show that when methane is used, the growth of the adlayers exhibits several different modes. For most of the adlayers, they maintain their AB-stacked or twist structures with the upper layer during the growth since their nucleation, but for some of them these stacking structures can suddenly change during the growth. Moreover, we also observed that the adlayers can nucleate tens of minutes later during the growth (not together with the first layer), with an AB-stacking with the upper layer. We also compared the results with previously reported work using ethanol, whose epitaxial nucleation of the second layer is mainly due to the active CH₃ radicals with the presence of a monolayer-graphene-covered Cu surface. We believe that this study will help clarify more growth mechanism of graphene by CVD process, and lead to many new strategies for scalable synthesis of graphene with more controllable structures and numbers of layers.

References
1. Li, X.; Cai, W.; An, J.; Kim, S.; Nah, J.; Yang, D.; Piner, R.;Velamakanni, A.; Jung, I.; Tutuc, E.; et al. Large-Area Synthesis of High-Quality and Uniform Graphene Films on Copper Foils. Science 2009, 324, 1312.
2. Li, Q.; Chou, H.; Zhong, J.-H.; Liu, J.-Y.; Dolocan, A.; Zhang, J.; Zhou, Y.; Ruoff, R. S.; Chen, S.; Cai, W. Growth of Adlayer Graphene on Cu Studied by Carbon Isotope Labeling. Nano Lett. 2013, 13, 486.
3. Fang, W.; Hsu, A. L.; Caudillo, R.; Song, Y.; Birdwell, A. G.; Zakar, E.; Kalbac, M.; Dubey, M.; Palacios, T.; Dresselhaus, M. S.; et al. Rapid Identification of Stacking Orientation in Isotopically Labeled Chemical-Vapor Grown Bilayer Graphene by Raman Spectroscopy. Nano Lett. 2013, 13, 1541.
4. Zhao, P.; Kim, S.; Chen, X.; Einarsson, E.; Wang, M.; et al. Equilibrium chemical vapor deposition growth of bernal-stacked bilayer graphene. ACS Nano 2014, 8, 11631.
5. Song, Y.; Zhang, J.; Song, M.; Yin, S.; Cheng, Y.; et al. Epitaxial nucleation of CVD bilayer graphene on copper. Nanoscale 2016, 8, 20001.

Transition metal oxides (TMOs) are regarded as alternative anode materials due to their high theoretical capacity, nontoxic and low cost. However, it is unable to take into account of high capacity and stable cycling performance which hinder their practical applications. Here, we improve both specific capacity and stability of transition metal oxides by following two aspects: 1) composing with CNTs through a hierarchical coaxial nanostructure, and 2) introducing with massive oxygen vacancies.
The synergistic reaction between TMOs (shell) and CNTs (core) through a hierarchical coaxial nanostructure can effectively enhance conductivity and reduce the Li⁺ diffusion distance, and consequently improve the rate performance, cycling stability and specific capacity. We develop an unique three-dimensional sponge-like CNT bulk material with excellent conductivity, high porosity and stable compressibility, which can be used as an ideal current-collector. Titanium dioxide (TiO₂) is directly deposited onto the CNT sponge as a coaxial structure, forming a highly porous composite sponge electrode without any redundant additives (such as conducting agent and binder). As an anode for LIBs, TiO₂@CNT sponge exhibit stable charging/discharging plateau voltages, higher capacity, better stability and rate performance comparing with pure TiO₂ electrodes.
Moreover, due to the TMOs are directly deposited onto the CNT sponge, the morphology of electrodes are determined by the CNT sponge. We fabricate a 1D porous electrode by depositing CNT sponges on a single carbon fiber (CF) and then deposit manganese dioxide (MnO₂) onto the CNT sponge and obtain a MnO₂@CNT@CF fiber-shaped electrode for LIBs.
Massive oxygen vacancies are introduced into TMOs to further improve the performance of LIBs. An unique electric field assistant annealing method is developed to treat TiO₂@CNT sponges. Under the combined function of the temperature and electric field, oxygen vacancies are rapidly formed and migrated through TiO₂, forming an amorphous TiO_2-x@CNT sponge with a large number of oxygen vacancies (~45%) uniformly distributed in the hole TiO_2-x. As an anode for LIBs, TiO_2-x@CNT exhibits a capacity as 604 mAh/g which is much higher than theoretical capacity of TiO₂ (335 mAh/g). Even under high rate condition (10000 mA/g), the capacity is stable as 110 mAh/g. This extraordinary performance is originated from the massive uniformly distributed oxygen vacancies which significantly enhance the conductivity and Li⁺ diffusion ability of TiO_2-x. Using this electric field assistant annealing method, massive oxygen vacancies can be introduced into many other TMOs (such as MnO₂ and SnO₂).
In conclusion, we efficiently improve the lithium storage performances of TMO electrodes by composing CNT sponge with a coaxial structure and introducing massive oxygen vacancies uniformly. Our work has a prospect in achieving advanced LIB anodes with stable and high rate capacities for many practical applications.

A new classification of carbon allotropes called, Novamene is the first release in a series which fall into an entirely new class of carbon in 2016¹. The basis of this new classification resides on the concept of combining hexagonal diamond (sp³ bonded carbon − lonsdaleite) and ring carbon (sp² bonded carbon − graphene), provides the basis for the new carbon allotropes, whose properties have been found to be superior to graphene that has been introduced by Nobel Laureates Andrea Geim and Konstantin Novoselov in 2010. Since hexagonal diamond acts as an insulator and sp² bonded rings act as conductors, these predicted materials can transform the electronic industry and have potential applications for transistors, other electronic components such as quantum computers and even energy applications. Following up the debut of Novamene, another new carbon allotrope named Protomene has been also introduced as a family of Novamene recently. It turns out that Protomene exhibits surprisingly outstanding electronic/optical/thermal properties compared to Novamene.² As for the comparison with diamond and other carbon allotropes, thermal properties of Protomene can be differentiated. Since thermal expansion behaviors of Protomene are associated with interplane bonding, Protomene may experience structural phase change which can lead to a more rapid change in energy band gap and thermal expansion compared with diamond and silicon.
We will present our efforts of on-going development of fabrication techniques for new carbon allotropes including Novamene and Protomene based on both top-down and bottom-up approaches and modeling activities by means of Density Functional Theory (DFT) simulations.
References
1. L. A Burchfield, M. Al Fahim, R. S Wittman, F. Delodovici, N. Manini, "Novamene: A new class of carbon allotropes" Heliyon 3, e00242 (2017).
2. F. Delodovici, N. Manini, R. Wittman, D. Choi, M. Al Fahim, and L. Burchfield, “Protomene: A new carbon allotrope”, Carbon, 126, pp574-579 (2018).

Recently [1], a new class of carbon allotrope, called protomene, was proposed. This new structure is composed of sp2 and sp3 carbon-bonds. Topologically, protomene can be considered as a carbon sp3 structure (~80% of this bond type) doped by sp2 carbons. First-principles simulations have shown that protomene presents an electronic bandgap of ~3.4 eV [1]. However, up to now its mechanical properties have not been investigated. In this work, we have investigated protomene mechanical behavior under compressive/tensile strains through fully atomistic reactive molecular dynamics simulations. We used the ReaxFF force field as available in the LAMMPS code. Our results [2] show that the protomene are very stable, up to very high temperatures (> 1000 K). The obtained ultimate strength and ultimate stress show an anisotropic material; the highest ultimate strength was obtained for x direction, with a value of ~102 GPa. As for the ultimate strain, the highest one was for z direction ( 27% of strain) before protomene mechanical failure (fracture).

Acknowledgments:
We would like to thank the Brazilian agency FAPESP (Grants 2013/08293-7 and 2016/18499-0) for financial support.

References:
[1] F. Delodovici, N. Manini, R. S. Wittman, D. S. Choi, M. Al Fahim,and L. A. Burchfield, Carbon, 126, 574-579 (2018)
[2] E. F. Oliveira, P. A. S. Autreto, C. F. Woellner, and D. S. Galvao, Submitted.

Graphene quantum dots (GQDs) [1], a carbon nanomaterial, has emerged as a promising material with unique optical and electronic properties due to their quantum confinement and edge effects. They are highly fluorescent, non-toxic and can be produced in large scale, which makes them attractive candidates for optoelectronics devices, sensing and biological applications. Controlling the shapes and sizes of GQDs as well as controlling the surface functional groups can tune their optical and electronic properties which make them attractive materials for optoelectronic devices and bio-imaging. As GQDs emit primarily in UV or blue region, they are harmful for living cells.
In the current work, we have demonstrated that controlling the surface functional groups present on the surface of the GQDs by thermal treatment significantly changes the photoluminescent (PL) emission properties which are very important for optoelectronics and bio-imaging applications. Also, with increasing annealing temperature, transition from positive thermal quenching (PTQ) to negative thermal quenching (NTQ) has been observed.
GQDs were prepared by oxidative cutting of graphene oxide (prepared by modified Hummer’s method [2] and subsequent thermal reduction. Transmission electron microscopy was utilized to measure the lateral dimension of the as prepared GQDs. The as synthesized sample was drop casted on substrates and annealed at different temperatures viz. 100 °C, 200 °C and 300 °C. Evolutions of different functional groups were studied by X-ray photoelectron spectroscopy (XPS). Red shifting of the peak PL emission was observed with increasing anneal temperature. In temperature dependent PL spectroscopy, as-synthesized sample exhibited PTQ behavior while the sample annealed at 300 °C showed NTQ phenomenon with crossover at intermediate temperatures. This phenomenon has been explained using a multi-level model proposed by Shibata in 1998 [3]. The changes observed in emission properties have been correlated with evolution of surface functional groups.
References:
[1] M. Bacon, S.J. Bradley, T. Nann, Graphene quantum dots, Part. Part. Syst. Charact. 31 (2014) 415–428. doi:10.1002/ppsc.201300252.
[2] D. Pan, J. Zhang, Z. Li, M. Wu, Hydrothermal route for cutting graphene sheets into blue-luminescent graphene quantum dots, Adv. Mater. 22 (2010) 734–738. doi:10.1002/adma.200902825.
[3] H. Shibata, J.I. Pankove, E.W.W. and H.B. Bebb, E.H.B. and H.B. Bebb, M.S. and E.G. D. Bimberg, F.E.W. and H. Eyring, S.F. and M.S. T. Yokogawa, T. Taguchi, T.K. and K.S. I. Aksenov, M. Matsui, Negative Thermal Quenching Curves in Photoluminescence of Solids, Jpn. J. Appl. Phys. 37 (1998) 550–553. doi:10.1143/JJAP.37.550.

Nitrogen-doped carbon nanomaterials are emerging as metal-free, low-cost, and high-durable catalysts for oxygen reduction reaction (ORR) at the cathode of polymer electrolyte fuel cells. According to the recent theoretical studies, the nitrogen doping alters the electronic property of carbon nanomaterials and hence provides the ORR catalytic activity. However, in experimental approaches, the role of nitrogen doping on the ORR catalytic activity has not been understood comprehensively. In addition, the relation between electronic property and ORR catalytic activity of carbon nanomaterials has not been investigated experimentally. Here, we synthesized nitrogen-doped single-walled carbon nanotubes (SWCNTs) by a combination of defluorination-assisted post-doping process and high-temperature annealing treatment, and evaluated their ORR catalytic activities in an acid electrolyte. In addition, their electronic properties including work function, carrier type, and conductivity were measured and correlated with their ORR catalytic activity for understanding the catalytic mechanism of the ORR on nitrogen-doped SWCNTs.
Highly crystalline SWCNTs (hc-SWCNTs) were prepared by the arc-discharge method. The hc-SWCNTs were fluorinated at 250 °C using 20% F₂ / N₂ gas for 4 h. Then fluorinated SWCNTs were heated at 500 °C for 30 min in a gas flow of 1% NH₃ / N₂. The resulting sample (N-SWCNTs) was further annealed at 1000 °C for 3 h in a N₂ flow to prepare AN-SWCNTs. The products were characterized by X-ray photoelectron spectroscopy, transmission electron microscopy, and Raman scattering spectroscopy. In addition, we evaluated the ORR catalytic activity by electrochemical measurement using the RDE technique in 0.5 M H₂SO₄ electrolyte. Work function measurement was conducted using ultraviolet photoelectron spectroscopy. The carrier type and conductivity of the sample films were determined and measured by thermopower measurement and four probe method, respectively.
The N-SWCNTs contained 2.4 at% nitrogen with enriched Py-N species, while the AN-SWCNTs contained 0.8 at% nitrogen with about 50% of Gr-N species to the total nitrogen species. This result indicates that the type of nitrogen species can be controlled by the annealing treatment. Judged from the onset potential, oxygen reduction current density at half-wave potential, and numbers of electrons transferred per oxygen molecule in the ORR, the AN-SWCNTs exhibited superior ORR catalytic activity to the N-SWCNTs. The work function of the AN-SWCNTs was lower than that of the N-SWCNTs, and the carrier type of the AN-SWCNT film was obviously n-type even in air. The conductivity of the AN-SWCNT film was higher than that of the N-SWCNT film. These results suggest that the low work function and high conductivity observed in the AN-SWCNTs can promote the ORR catalytic activity.

Chemical Vapour Deposition (CVD) has become the dominant technique for the growth of graphene and related 2D materials, driven by the emerging industrial demand for ‘electronic-grade’ materials that are consistent over large areas. Significant progress has been made using heterogeneous catalysis[1], and among the most widely used substrates is polycrystalline copper foil. A fundamental challenge in devising a CVD process that consistently results in homogeneous single crystal graphene is the initial substrate: which has varying concentrations of different trace impurities that can affect the growth process. It has been shown that a simple oxidative pre-treatment of the Cu catalyst to remove residual carbon results in a significant reduction in nucleation density, allowing for a much larger graphene domain size to be achieved[2].There is still a compromise between fast growth rates and reducing sources of defects such as grain boundaries. Further to this, adequate characterisation of large area monolayer graphene films has become a significant challenge on its own.

Here we report how these compromises in controlled graphene growth can be addressed by systematically studying modifications of the Cu catalyst. The effects of adding oxygen to the Cu bulk on graphene nucleation density, morphology, growth rate and quality are closely examined. The epitaxial relationship of graphene on different Cu textures is quantitatively analysed and the capability to significantly enlarge Cu grains and recrystallize the foil is demonstrated. By leveraging the epitaxial alignment seen on specific Cu facets, single crystal graphene films can be rapidly grown, paving the way for films with improved homogeneity. In addition, a novel method to characterise graphene quality on a larger scale is introduced based on a modification of established Raman characterisation strategies.

[1] Hofmann et al J. Phys. Chem. Lett. 6, 2714 (2015).
[2] Braeuninger-Weimer et al. Chem. Mat. 28, 8905 (2016).

The magnetorheological (MR) performance of suspensions based on the Fe₃O₄-deposited carbon nanotubes (CNTs) was investigated by using a vibrating sample magnetometer (VSM) and a rotational rheometer. The Fe₃O₄-deposited CNTs were synthesized by the reduction process in which nano-Fe₃O₄ nanoparticles were generated and adsorbed on the surface of CNTs. All tested suspensions displayed excellentMR behaviors with high yield strengths. The important parameter which determined the MR performance was the surface density of Fe₃O₄ on the CNT surface. The morphology was observed by scanning electron microscope (SEM) and transmission electron microscope (TEM). Most Fe₃O₄ particles adsorbed on the surface of PS/Fe₃O₄ particles to make the surface topology bumpy and rough which decreased the particle sedimentation velocity. Finally, Turbiscan apparatus was used to examine the sedimentation properties of Fe₃O₄-deposited CNTs suspensions. The suspensions showed excellent stability against sedimentation, much better than bare Fe₃O₄ particle suspension due to the inherent low density of CNT and its inside pore which can reduce the density mismatch between the nanoparticles and the carrier medium as well as the surface topology change due to the adsorption of Fe₃O₄.

Gas Cluster Ion Beams (GCIB) is a powerful tool for surface modification of various materials and theoretically and experimentally demonstrated the ability to create defects in ultrathin graphene-like films. In this study GCIB of Ar with acceleration energy E = 30 kV (Exogenesis, MA, USA) and total fluences ranged from 1x10⁹ to 1x10¹³ ions/cm² is used to produce defects in ultrathin films such as graphene, graphene oxide, MoS₂ and Si, HOPG as a reference.
GCIB irradiated ultrathin films were characterized by NEXAFS and Raman spectroscopy, scanning electron and atomic force microscopy. The Raman spectroscopy (Horiba) study of the irradiated samples was conducted by a 632 nm laser wavelengths and 100x objective with a laser spot size of ~1 μm, 2 mW power and atomic force microscopy (AIST NT) measurements were carried out in a tapping mode by SUPERSHARPSILICON™ AFM probes for high resolution. NEXAFS spectroscopy measurements were carried out at the NewSUBARU BL09A beamline of the New SUBARU SR LASTI facility at the University of Hyogo, using total-electron yield (TEY) method and without uncompleted correction of energy.
Density functional theory (DFT) calculations have been performed to study the Raman spectra of pristine and graphene with vacancy defects. Large-scale parallel molecular dynamics (MD) simulations (LAMMPS) were employed for studying interactions of accelerated cluster ions with ultrathin films, such as graphene, MoS₂, HOPG, and BN. The MD results showed formation of uniform holes, with the diameters of 10-20 nm, in the ultrathin films, and were used for optimization of the experimental fabrication of holes in 2D-films.
The DFT and MD simulations provides fundamental understanding of the argon bombardment of ultrathin films and its influence on Raman spectra of graphene.

Single-walled carbon nanotubes (SWCNTs) are seamless cylinders of graphene that have been at the forefront of nanotechnology research for the past two decades. While mass-produced SWCNT powders are adequate for some applications, many emerging applications require stricter control over SWCNT properties and architectures, necessitating targeted growth, i.e. tailoring the physical properties of the SWCNTs (diameter, orientation/architecture, etc.).
This work attempts to prove the key role of the graphene properties and the metal - catalyst interaction in the relation between catalyst size and nanotube diameter. We work on the assumption that the curvature energy is one of the most influential factors in the graphene film formation and a crucial constraint to determine the stable diameter of the nanotube during the growth. The calculation of interlayer binding energies using density functional theory (DFT) and pseudopotential functions has been valuable to find the transition diameter between fullerene and tube. Additionally, we propose a new model that links statistical mechanics theory with the possible strain energy states and allows the calculation of the expected or most probable diameter. This is just the first step to bring light to the yet undiscovered reigning principle for the nanotube’s diameter stability during nucleation.

Printed electronics is a burgeoning field that has received intense research interest and is beginning to experience commercial successes. Single-walled carbon nanotubes (SWNTs) are a unique and promising building block for incorporation into next generation superfast electronic devices. SWNTs have very high carrier mobilites, with band gaps compatible for integration into logic circuits. Their excellent mechanical flexibility allows for potential incorporation into flexible printed electronics, enabling fully-printed transistors and circuits with performances that support low cost, large area fabrication. Progress in incorporating SWNTs into commercial devices has been hindered by the presence of metallic SWNTs, which are produced alongside semiconducting SWNTs during synthesis, and negatively impact device performance. Fabrication of ambipolar SWNT organic thin film transistors (OTFTs) with high carrier mobilities and high on/off ratios remains particularly challenging; many examples in the literature required high temperature, expensive and energy-demanding processes.
Since the initial discovery of conjugated polymer-assisted dispersion and purification of SWNTs in 2008, several polymer families have been successfully shown to selectively disperse semiconducting SWNTs. However, only a relatively small number of these supramolecular complexes have been incorporated into OTFTs. We used a novel conjugated polymer to exclusively disperse semiconducting SWNTs. The dispersal procedure requires a simple sonication and centrifugation, during which the metallic SWNTs sediment out. Solution purity was evaluated using UV-Vis-NIR and Raman spectroscopies. The resulting dispersions are amenable to solution processing techniques such drop casting and spin coating, allowing for the potential for large area device fabrication at room temperature. Ambipolar OTFTs were fabricated under ambient conditions using this solution and tested in both air and under inert atmosphere. The presence of excess conjugated polymer, solution deposition techniques, SWNT density, surface treatment, and post-fabrication treatment were all investigated to determine which parameters facilitated the production of OTFTs with high mobilities (>20 cm²V^-1s^-1), high on/off ratios (10⁶-10⁸), negligeble hysteresis, controlled threshold voltages, and high bias stability.

Concussions in sports and sudden other accidental cases occur very regularly. Often times concussions leads to chronic traumatic encephalopathy (CTE) and eventual death. Polydimethylsiloxane(PDMS)-based nanomaterial are gaining widespread attention in this regard. Here we report a unique bubble tunable graphene reinforced PDMS nanocomposites as a vibration dampening and possibly concussion resistant material. PDMS based nanocomposite was prepared by solvent swelling of the PDMS (Sylgard 184 from Dow Crowing Company) in chloroform/TEOS (4:1 ratio) mixture followed by ultrasonication of the graphene nanoplatelets in the solvent that swells the polymer. Various nanocomposite structures with and without bubbles were prepared. We studied the mechanical properties of PDMS-graphene nanocomposite as a function of temperature, pressure, nanoparticle size, solvent percentage, curing agent and filler concentration. The effect of different concentrations of graphene in the nanocomposite with/without bubble formation were measured and analyzed using dynamic mechanical analyzer (DMA) and impact testing. Physical interaction of PDMS adsorptions on the graphene were computed using
molecular dynamic (MD) simulation. The influence of a-well controlled bubble structure on the energy absorption behavior of the nanocomposite was explored. Stiffness of the nanocomposites increased with the loading of graphene. The role of bubble and bubble-graded nanocomposites is underway.

Investigation of the structure and properties of the intercalated molecules between interfaces of two-dimensional layers or of a layered material and a substrate is a subject of great interest. Formation of crystalline patterns as well as induction of chemical reactions under two-dimensional covers are two of the main drivers behind this interest. One recent study by Reinke and collaborators [Nano Letters 15, 7421−7430 (2015)], showed the formation of amorphous and crystalline structures of C₆₀ intercalated between graphene and a copper substrate. They further reported the existence of more or less strained graphene wrinkles, as well as detached graphene from substrate depending on the concentration or distance between the intercalated C₆₀ molecules. Motivated by this work, we investigated the formation and thermal stability of graphene wrinkles as well as graphene attachment and detachment from substrate on previously distributed C₆₀ and carbon nanotube molecules on cooper substrate. We performed fully atomistic reactive molecular dynamics (MD) simulations using the third generation of the charge optimized many-body potential as available in the LAMMPS computational package. As the timeframe of spontaneous intercalation of C₆₀ molecules between graphene and the substrate is too high to be feasibly simulated by MD methods, we simulated the “blanketing” of graphene on different concentrations of C₆₀s and carbon nanotubes previously laid on the substrate. We tested both fixed and non-fixed structures, i.e., we predicted the change in the height of graphene, fullerene, and substrate when the fullerenes are not fixed. We then verified that graphene attaches to the substrate when the distance between the fullerenes is at least 6 nm. Below that distance, graphene becomes locally suspended and low strain is verified. While such studies of intercalation of molecules on interfaces formed by graphene-substrate are motivated by finding out ways to control wrinkling and strain in graphene, this work reveals the role of stability and wrinkling as well as the shape and structure of intercalated molecules under the action of graphene on the final structure and its properties.

In this work, we present a study regarding the interaction between molecular hydrogen (H₂) and graphene field effect transistor with different metals and contact geometries. We demonstrate that this interaction is strongly dependent on the characteristics of the graphene-metal contact interface. Three different contacts were probed: pure Au, Au/ Cr and Au/ Cr₂O₃ contacts. Interestingly, we observed that only for Au/Cr₂O₃ contact devices the emergence of a second charge neutrality point (CNP) in the resistance as function of gate voltage curves (“M-shape”) due the H₂ exposure. This is the first time that such behavior (“M-shape”) is found due to a gas interaction with graphene devices. This effect was observed for different conditions of temperatures (25°C-200°C) and H₂ concentrations (0.5%-50%) and it is totally reversible. Previous works about graphene-contact interaction, demonstrated that the difference of the work function between both materials generate a local p-type or n-type doping [1]. Added to the electrostatic doping generated by the back gate voltage, a pn junction is formed. Also, Cadore et al. verified that the H₂ can modulate these pn junctions in graphene devices with Au / Cr or Au contacts [2]. Thus, the formation of the two CNP that appear on devices with Au/Cr₂O₃ contacts can be explained by the fact that the charge density of the graphene under the electrodes and in the channel can be modulated by back gate voltage application. That is, two CNP appear without pinning the work functions, and the difference between the Fermi level in both regions generates the two CNP [3]. Also, we believe that the thin layer of oxide formed (Cr₂O₃) may be responsible for a catalystic process and facilites the hydrogen flow inside the interface contact-graphene, hence increasing the influence from such regions of during the electrical measurements. In other words, our findings suggest a way of inducing the decoupling of the work function between the metallic electrodes and graphene by the use of contacts Au/Cr₂O₃ and hydrogen gas exposure. Additionally, we demonstrate that the high variation of the resistance generated by the emergence of the second peak and the low time of response to hydrogen provides a system that is very promising for H₂ sensor applications. This work was supported by CAPES, Fapemig (Rede 2D), CNPq and INCT/Nanomaterias de Carbono. References:
[1] G. Giovannetti, et al. Physical Review Letters, vol. 101, n. 026803 , pp. 1-4, 2008.
[2] A. R. Cadore, et al. Applied Physics Letters 109, n. 033109, pp. 1-5, 2016.
[3] S. M. Song e B. J. Cho, Carbon Letters, vol. 14, n. 3, pp. 162-170, 2013.

Low-cost piezoresistive strain/pressure sensors with large working range, at the same time able to reliably detect ultralow strain (≤0.1%) and pressure (≤1 Pa), are one of the challenges that have still to be overcome for flexible piezoeresistive materials towards personalized health-monitoring applications.

Here, we report on unprecedented, simultaneous detection of ultrasmall strain (0.1%, i.e. 10 µm displacement over 10 mm) and subtle pressure (20 Pa, i.e. a force of only 2 mN over an area of 1cm²) in compression-mode, coupled with a large working range (i.e., up to 60% for strain – 6 mm in displacement - and 50 kPa for pressure) using piezoeresistive, flexible three-dimensional (3D) macroporous PDMS (pPDMS) foams decorated with pristine multi-walled CNTs.¹
pPDMS/CNTs foams with pore size up to 500 µm (i.e. twice the size of those of commonly used foams, at least) and porosity of 77%, decorated with a nanostructured surface-network of CNTs at densities ranging from 7.5 to 37 mg/cm³ are prepared using a low-cost and up-scalable process, through replica molding of sacrificial sugar templates and subsequent drop-casting of CNT ink. A thorough characterization shows that piezoresistive properties of the foams can be finely tuned by controlling the CNT density, and reach an optimum at a CNT density of 25 mg/cm³, for which a maximum change of the material resistivity (e.g., ρ₀/ρ₅₀=4 at 50% strain) is achieved under compression. Further static and dynamic characterization of the pPDMS/CNTs foams with 25 mg/cm³ of CNTs highlights a detection limit for strain and pressure of 0.03% (3 µm displacement over 10 mm) and 6 Pa (0.6 mN over an area of 1 cm2), respectively; moreover, good stability and limited hysteresis are apparent by cycling the foams with 255 compression-release cycles over the strain range 0-60%, at different strain rates up to 10 mm/min.
Our results on piezoresistive, flexible pPDMS/CNT foams pave the way towards breakthrough applications for personalized health care, though not limited to, which were not fully addressable to date with flexible strain/stress sensors.

[1] R. Iglio, S. Mariani, V. Robbiano, L. Strambini, G. Barillaro, Flexible Polydimethylsiloxane Foams Decorated with Multi–Walled Carbon Nanotubes Enable Unprecedented Detection of Ultralow Strain And Pressure Coupled With Large Working Range, ACS Applied Materials and Interface, 10, 13877-13885 (2018)

A small amount of chemical modification of single-walled carbon nanotubes (SWNTs) has been reported to create modified sites with narrower band gaps on the tubes. The resultant locally functionalized SWNTs (lf-SWNTs) show new photoluminescence (PL) with red-shifted wavelengths and high quantum yields (E₁₁*) compared to that of pristine SWNTs (E₁₁)[1]. We have reported largely red-shifted PL (E₁₁²*) than E₁₁* through the local functionalization using bis-aryldiazonium salts[2]. Therein, we experimentally revealed that differences in the methylene spacer lengths connecting two aryldiazonium groups induced wavelength variation of E₁₁²* and the theoretical calculations indicated that the E₁₁²* wavelengths were also influenced by the differences in the connected position of the second aryl groups. Recently, Doorn et al. reported that such secondary reacted positions related to spectral shifts of E₁₁*[3]. In this study, we newly design bis-aryldiazonium salts that have two aryldiazonium groups connected by methylene spacers at the meta positions, which are different from our previous molecular design using the methylene linkage at the para positions.
The used SWNTs were (6,5) chirality-rich tubes (CoMoCAT) and they were solubilized in D₂O containing sodium dodecylsulfate through sonication followed by ultracentrifugation. Chemical modification of SWNTs was conducted by mixing the solubilized SWNTs and synthesized meta-linked bis-aryldiazonium salts. When the meta-linked bis-aryldiazonium salt having the spacer of five methylene units (mC5-Dz) was reacted with SWNTs (mC5-lf-SWNTs), very slight changes were observed in the UV/vis/NIR absorption spectrum in comparison to that of the pristine SWNTs, indicating that local chemical functionalization occurred. In sharp contrast, in the PL spectrum of mC5-lf-SWNTs, a new PL peak appeared at 1246 nm that was largely red-shifted from typical E₁₁* and was the different wavelength value from the E₁₁²* of the previously reported lf-SWNTs using the para-linked bis-aryldiazonium salts. These results indicate that the structural difference between meta- and para-linked bis-aryldiazonium salts may induce unique spectral changes of E₁₁²* for the lf-SWNTs. Other structural factors will be discussed in the meeting.

References
[1] Y. Piao, B. Meany, L. R. Powell, N. Valley, H. Kwon, G. C. Schatz, Y. Wang, Nat. Chem. 2013, 5, 840.
[2] T. Shiraki, T. Shiraishi, G. Juhasz, N. Nakashima, Sci. Rep. 2016, 6, 28393.
[3] B. J. Gifford, S. Kilina, H. Htoon, S. K. Doorn, S. Tretiak, J. Phys. Chem. C. 2018, 122, 1828.

Since the first reports of its isolation in 2004, graphene has received unprecedented interest from the scientific community. This is due to its remarkable properties such as high electron mobility, thermal conductivity and mechanical strength.¹ However, in spite of this huge potential, a number of hurdles have existed which hinder graphene’s wholesale uptake by commercial applications. One of these is the need to improve the processability of graphene materials by improving their dispersibility in a range of aqueous and non-aqueous solvent.² A wide range of approaches have been employed to try to improve the dispersibility of graphene in many solvents such as covalent functionalization of graphene sheet, aiming to enhance dispersibility by improving interaction with the solvent.³ The downside to all covalent modification techniques is that the presence of additional chemical functionalities disrupts the sp² matrix of the graphene sheets by introducing defect sites which can have a significant negative effect on the properties of the material.⁴ Surfactants have been used which adsorb non-covalently to the surface of the graphene sheets improving their dispersibility.⁵ However, residual surfactant molecules can have a negative impact on the properties of the graphene prepared and can be difficult to remove.
Herein, we have developed a method for improving the dispersibility of graphene and its related materials in commonly used, and low boiling solvents by making use of prior dispersion in good solvents (such as N-methyl-2-pyrrolidone (NMP) and dimethylformamide (DMF)). This method allows reduced graphene oxide (rGO) to be dispersed in water at concentrations of up to 20 μg ml^-1 which is over a six-fold improvement compared to dispersion of untreated rGO prepared under the same conditions. Predispersion of rGO in NMP can produce NMPrGO which forms a stable dispersion in water, with less than 0.3% residual NMP, confirmed by the experimental characterizations. Furthermore, molecular dynamics (MD) simulations have been used to exploit how the dispersion process is facilitated by the organic solvent treatment (NMP and DMF in this study), and investigate graphene and solvents interactions, and solvent geometry and orientation with respect to the graphene sheet. Additionally, DFT calculations have been used to study the electrical properties and charge distribution upon organic solvent adsorption on the graphene surface, in order to rationalize the improved dispersibility in water and ethanol.


(1) Allen, M. J. et al., Chem. Rev. 2010, 110 (1), 132-145.
(2) Johnson, D. W. et al., Curr. Opin. Colloid Interface Sci 2015, 20 (5), 367-382.
(3) Lomeda, J. R. et al., J. Am. Chem. Soc. 2008, 130 (48), 16201-16206.
(4) Eigler, S. et al., Carbon 2012, 50 (10), 3666-3673.
(5) Lotya, M. et al., ACS Nano 2010, 4 (6), 3155-3162.

Carbon nanotubes (CNTs) hold great theoretical promise as electrical conductors due to a combination of high conductivity, flexure tolerance, tensile strength, and a low thermal coefficient of resistivity (TCR). However, translating these nanoscale properties into bulk structures has proven difficult. The relatively weak van der Waals forces that hold bundles of CNTs together lead to issues with the alignment and packing of individual nanotubes, creating highly resistive junctions in bulk conductors. One strategy currently under investigation to alleviate these issues is to integrate CNTs with traditional metallic conductors to combine the metal’s high conductivity with the low density and TCR of CNTs.
In this study, site-selective copper nanometal seeding through chemical vapor deposition (CVD) is demonstrated as a viable method in concert with solution electrodeposition of bulk Cu to enhance the electrical conductivity of a low-density (0.12 g/cm³, ~9 mg/m) CNT roving. An electrical bias applied directly to the CNT roving causes Joule heating which provides the thermal energy necessary for the decomposition of a bis(t-butylacetoacetato) copper (Cu(tBAOAC)₂) precursor. Localized changes in the resistance within a bulk CNT conductor due to differences in junction density may be used to selectively deposit the precursor at thermally active sites. The deposition varies from localized Cu deposits at applied currents producing average temperatures of ~225°C to a consistent deposition of 50 nm Cu particles at applied currents producing average temperatures >300°C. Scanning electron microscopy of a cross-section of the sample reveals Cu depositions on the interior of the sample, demonstrating the penetration of the vapor into the CNT network. The deposition mass can be controlled up to and exceeding 50% w/w of the composite mass through control of the vacuum environment and the reaction time. A commercial acid-based Cu electroplating solution was used to deposit bulk Cu onto as-prepared and CVD seeded CNT wires, followed by planar densification and H₂/Ar annealing. The finished conductors with Cu loadings from ~30-95% w/w which combine CVD Cu seeding and electrodeposition result in specific conductivity 3-5X higher than Cu-CNT conductors produced by electrodeposition alone. Ultimately, a CNT hybrid conductor with 94.2% w/w Cu, achieved a specific conductivity of 5632 S*m²/kg and electrical conductivity of 28.1 MS/m; which is among the best of recent results from the literature at equivalent loadings. The measured TCR for the Cu-CNT hybrid was 3.55×10^-3 K^-1 (compared to 3.9×10^-3 K^-1 for bulk Cu) illustrating the benefit for high temperature applications. Overall, the present results demonstrate the potential of Joule-heating-driven-CVD towards both seeding metal prior to electroplating and as a possible method towards the enhanced nanometal interconnection of carbon conductors (NICCs).

Graphene quantum dots have emerged as functional material for myriads applications due to their unique properties such as deep ultraviolet and blue to green luminescence, two-photon induced fluorescence, minimal to no toxicity, chemical- photo-stability, and biocompatibility. These attractive properties of graphene quantum dots are mainly due to the bandgap opening of two-dimensional graphene quantum confinement effects, edge effects, surface functionalization, and doping. We present our results on the effect of both p- and n-doping on the absorption properties and correlate the results with the diameters to explore electronic and phonon confinement effects.

Nanocomposite membranes made with multiwalled carbon nanotubes (MWCNTs) and aromatic polyamide (PA) have been studied do their superior performance, that combines high permeation, high salt rejection, good chlorine resistance, and low-fouling behavior. We have used a combination of experimental techniques, such as cross-flow filtration, microscopy and spectroscopy, whereas molecular dynamics studies were carried out to understand the membrane at the atomic level. MWCNT-PA nanocomposite membranes were prepared by interfacial polymerization using an aqueous phase containing MWCNTs and an organic phase. Membranes were then evaluated under cross-flow and studied by x-ray photoelectron spectroscopy, fourier transformed infrared spectroscopy, and electron microscopy. Organic fouling was studied using a protein (bovine serum albumin) solution, whereas scaling was produced using a mixture of calcium chloride and sodium bicarbonate that precipitates calcium carbonate. During these studies, the fouling of the membrane was followed in situ using fluorescence optical microscopy using an acrylic-made transparent cross-flow cell. The protein was labeled with fluorescein while calcein was added in the scaling study to render the calcium scales fluorescent. MWCNT-PA nanocomposite membranes showed consistently lower organic fouling and less scaling. Our findings show that the observed antiscaling and antifouling nature of the MWCNT−PA membranes is the result of several factors, among them: a smooth membrane surface morphology, a lower surface charge, an interfacial layer of water, and lower mobility of the membrane molecules. These results are important for the design and development of promising low-fouling RO membranes for water treatment. Regarding the water diffusion across the membrane, our studies shown that instead of flowing inside the MWCNTs, an oriented diffusion mechanism explains the high water permeation of these membranes. MWCNTs reduce the diffusion path of water molecules across the membranes by providing a lower energy path. The proposed water diffusion mechanism offers an alternative and most likely explanation for the high permeation phenomena observed in CNTs and PA nanocomposite membranes, and its understanding is key to improve the performance of the nanocomposite reverse osmosis desalination membranes.

Exploiting an electrolyte-based gate dielectric that relies on direct migration of ions allows design of unconventional transistor architecture.¹ For example, the current density of a transistor channel can be modulated using a gate electrode that is not located directly on top/below the channel but placed apart from the channel as long as the electrode is bridged with the channel through the electrolyte– which we refer to as the remote gating. For effective remote gating, the electric double layer at both the electrolyte/channel and the electrolyte/gate interfaces has to be formed promptly. However, the promptness of the electric double layer formation relies on the distance between the channel and the gate. This indicates that the dynamic characteristics of a remote-gated transistors degrades with this distance. Here we present new device architecture to maintain the dynamic characteristics of a graphene transistor, even if its channel is gated remotely. The new structure employs multiple coplanar floating gates bridged through short ionic dielectric layers. Unlike the dynamic characteristics of a remote-gated graphene transistor employing a single, extended electrolyte layer, the devices with multiple, short electrolyte layers could operate promptly even when they are gated from a distance. We confirmed that the effective current modulation of graphene transistor can be achieved at 1 kHz, even when the gate electrode is located 1700 μm apart from the channel, which were comparable to the dynamic characteristics of a device using a gate located 200 μm apart. The results indicate that the distance-dependence degradation on the dynamic characteristics of the remote-gated graphene transistors can be eliminated. The new device architecture provided here shows new opportunities to exploit graphene transistors.

Reference
1. Kim, B. J.; Lee, S. -K.; Kang, M. S.; Ahn, J. -H.; Cho, J. H. ACS Nano 2012, 6, (10), 8646-8651.

The energy storage systems applied on wearable electronic devices should exhibit mechanical robustness, high cost efficiency, and high electrochemical activity in various human body motion. To solve these requirements, we introduce all-carbon-based large-area nanocomposites for freely-deformable electrochemical capacitors. Three-dimensionally incorporated all-carbon-based self-supported nanocomposites are composed of activated carbons (ACs) dispersed in carbon nanotube (CNT) sheets derived by direct spinning method without additives such as conductive agents and polymeric binders. On account of the synergetic effects from immensely porous AC particles providing large number of active sites, high electrical conductivity of CNTs, and facile ion accessibility in aqueous electrolyte solution utilized by the acid treatment, the nanocomposites show a greatly improved specific capacitance compared to that of conventional electrodes used metallic current collectors in terms of total mass of the electrodes. We also fabricated the deformable all-carbon-based electrochemical capacitors that showed excellent durability and electrochemical performances under extreme mechanical deformations of bending, folding, twisting, and stretching.

Carbon nanotubes (CNTs) have attracted great interest for many potential applications. To realize such applications, low-cost production of high quality CNTs is highly demanded. Fluidized-bed chemical vapor deposition (CVD) is one of the candidates for the realization of mass production [1]. We previously reported fluidized-bed CVD synthesis and easy separation of submillimeter-long CNTs on/from ceramic beads with smooth surface [2]. Our previous reports revealed that the preparation of catalyst is important for CNT growth. Two methods have been examined for the preparation: ex situ sputtering and in situ CVD methods. Fe/AlO_x catalyst by ex situ sputtering yields single-wall CNTs [3]. On the other hand, in situ CVD method enables the fast catalyst deposition in a few minutes [2,4]. Other methods including impregnation have been introduced for the catalyst preparation [5]. However, all these methods still have limitations. For the case of sputtering and impregnation, they take long time. In situ CVD is quick but uneasy to make fine control of catalyst for single-wall CNTs. Therefore, in order to increase the productivity, it is required to find a method which realizes both the easy control of the catalyst and the short preparation time.
Here we report a fast solution-based catalyst preparation on ceramic beads for CNTs. We coated catalyst on beads by gas-pressurized filtration of ethanol solution of Fe(CH₃COO)₂ and Al(OC₃H₇)₃ in a vertical tube for a few minutes. We then synthesized CNTs on the beads. The beads yielded CNTs with submillimeter length but on a part of the bead surface due to the non-uniform catalyst deposition. After the separation of CNTs from the beads, the beads were reused to reduce the cost. The beads with re-coated catalyst yielded CNTs with higher coverage with increasing number of reuse, resulting in improved yield of CNTs. We will discuss the catalyst condition on the structure of the resulting CNTs.

References:
[1] Q. Zhang, et al., Carbon nanotube mass production: principles and processes ChemSusChem 4, 864–889 (2011).
[2] D.Y. Kim, et al., Sub-millimeter-long carbon nanotubes repeatedly grown on and separated from ceramic beads in a single fluidized bed reactor, Carbon 49, 1972–1979 (2011).
[3] D.Y. Kim, et al., Fluidized-bed synthesis of sub-millimeter-long single walled carbon nanotube arrays, Carbon 50, 1538–1545 (2012).
[4] Z. Chen, et al., Over 99.6 wt%-pure, sub-millimeter-long carbon nanotubes realized by fluidized-bed with careful control of the catalyst and carbon feeds, Carbon 80, 339–350 (2014).
[5] Q. Zhang, et al., Mass production of aligned carbon nanotube arrays by fluidized bed catalytic chemical vapor deposition, Carbon 48, 1196–1209 (2010).

In-situ transmission electron microscopy (TEM) method is powerful in a way that it can directly correlate the atomic structure with physical and chemical properties. By using the homemade in-situ TEM holders, the properties at nanoscale under various physical stimuli have been studied, including mechanical, electrical, and optical properties. For example, the physical properties of individual carbon nanotubes with known chirality have been reported previously. For this work, the real-time imaging of solid state electrochemical processes at atomic scale has been carried out by in-situ TEM. In this presentation, we will review our progress on the studies of phase transition mechanism of the two-dimensional layered transition metal dichalcogenides (TMDs) by alkali metal intercalation.

The optical properties of single-wall carbon nanotubes (SWCNTs) are extremely sensitive to their external and internal environment. For example, filling the endohedral cavity with water molecules results in characteristic shifts and broadening of both the SWCNTs’ radial breathing mode vibrational frequency and their optical (electronic) transitions, as well as a quenching of their emission.[1] Although mostly ignored in literature, solvent ingestion effects are substantial, and can also be used to passivate the nanotube interior, by controlled manipulation of the endohedral environment prior to dispersion.[2]
In this work, specific and tunable modification of the optical properties of SWCNTs is demonstrated through the direct encapsulation of guest molecules with widely varying dielectric constants. Over 30 different compounds with static dielectric constant varying from 1.8 to 109 have been encapsulated inside the SWCNTs and their spectroscopic analysis, in comparison to unfilled (empty) SWCNTs, demonstrates for the first time experimentally that the general effect of filler static dielectric on the nanotube optical properties corresponds to a monotonic energy reduction (red-shifting) of the optical transitions with increased magnitude for higher dielectric constants.
Systematic two-dimensional fitting of the fluorescence-excitation spectra enables the direct comparison of this red shifting as a function of nanotube diameter, modulus and chirality. In addition to these spectral shifts, the filling with dielectric molecules also reveals a general increase of fluorescence intensity with lower dielectric constants, with some fillers approaching the emission efficiencies of empty SWCNTs.
Our investigation hence demonstrates a new degree of modulation of the SWCNTs’ optical properties by simple endohedral ingestion of various guest molecules.


[1] S. Cambré et al. Phys. Rev. Lett. 104, 207401 (2010); W. Wenseleers et al. Adv. Mater. 19, 2274 (2007); S. Cambré et al. ACS Nano 6, 2649 (2012)
[2] J. Campo et al Nanoscale Horizons 1, 317 (2016)

The discovery and development of carbon based nanomaterials have played a significant role in shaping the landscape of nanotechnology. Although basic science in the area has progressed significantly, there are still challenges related to engineering and integration of these nanomaterials and their architectures into applications and commercial products. This talk will discuss some of the challenges and opportunities in this field. Our group has made pioneering contributions to the field and a synopsis of our recent work in the area will be presented. The talk will discuss aspects related to synthesis, processing, chemistry and engineering of carbon nanostructures into larger meso- and macro-scale architectures using simple processes. Creation of hybrid structures and composites using nanotubes and graphene will be discussed and how properties can be engineered to produce the next generation of carbon materials with interesting properties. Various architectures and dimensionalities of made from nanocarbon building blocks will be described and applications of these relating to electrical, electrochemical, mechanical and other miscellaneous behaviour will be discussed.

The fabrication of three dimensional (3D) architectures (such as sponges, aerogels, etc.) from graphene and its related materials is recently an extensively studied field due to the broad range of applications in the areas of electronics, energy storage, healthcare, or catalysis [1]. However, the utilization of such materials and their extraordinary properties, like the high tensile strength of 63 GPa for carbon nanotubes (CNTs) or graphene’s lowest electrical resistance, is typically limited by the lack of advanced structural design [1]. In this study, a versatile, highly porous (up to 98%) ceramic template [2] material is introduced for the 3D assembly of low-D nanomaterials, such as graphene and CNTs into hierarchical macroscopic (cm³ scale) networks. Using a simple wet chemical infiltration process, the sacrificial template can be homogenously coated with 1D and 2D nanomaterials [3]. The following removal of the template results in free-standing, highly porous and lightweight 3D nanoarchitectures consisting of interconnected hollow microtubes with nanoscopic wall thickness, being composed of individual nanoparticles (e.g. CNTs, graphene oxide and exfoliated graphene). Even though no cross-linking agent is used the nanoparticles form a stable 3D architecture that can be tuned in its mechanical and electrical properties. Therefore, this approach offers the possibility for effective utilization of nanoscopic functionalities in 3D. Furthermore, the utilization of a template allows for a high degree of fabrication flexibility (e.g. tuning of pore size, pore interconnectivity and density). Combination of different nanomaterials can be easily achieved by wet chemical infiltration with different nanomaterial dispersions, leading to complex 3D composite architectures with tailored properties suitable for applications such as cell scaffolding, gas sensing, and next generation batteries.


Acknowledgements
The authors gratefully acknowledge financial support from the Deutsche Forschungsgemeinschaft (DFG) in the framework of the GRK 2154, and support from the European Commission in the framework of the Graphene Flagship.

References
[1] Shehzad, K. et al. Chem. Soc. Rev. 45 (2016) 5541-5588
[2] Mishra, Y.K. et al. Materials Today (2017), In Press
[3] Schütt, F. et al. Nat. Comm. 8 (2017) 1215

High-quality channel layer is required for next-generation flexible electronic devices. Graphene is a good candidate due to its high carrier mobility and unique ambipolar transport characteristics but typically shows a low on/off ratio caused by gapless band structure. Here we propose a graphene/MoSe₂ channel layer with high-k ion-gel gate dielectric. The graphene/MoSe₂ device shows both high on/off ratio and carrier mobility. Most importantly, it reveals ambipolar behaviors which are controlled by external bias, although such ambipolarity has never been previously reported in graphene/semiconductor barristor structures. Therefore, our graphene/MoSe₂ barristor with ion-gel gate dielectric can offer various with high performances. Here we make a contact of graphene and MoSe_2. The graphene/ MoSe₂ barristor exhibits high on/off ratio of 10⁵ and high mobility. The modulation of graphene’s Fermi level (E_F) by applying gate voltage (V_g) is confirmed by the change in Schottky barrier height at the graphene/MoSe₂ junction. Such field effects including ambipolar behaviors are locally investigated by using scanning photocurrent microscopy (SPCM). We have shown that graphene/MoSe₂ barristor can be created to obtain highly efficient photocurrent generation and photodetection. Therefore, our graphene/MoSe2 barristor with ion-gel gate dielectric can be a suitable candidate for a ambipolar transistor (with high mobility and on/off ratio) and gate tunable broad-area photodetector (with high EQE and responsivity).

Porous 3D networks of graphene have potential applications in battery electrodes, chemical sensors, oil adsorption and catalysis. These networks exhibit high surface area and unique mechanical and electrical properties, depending on their preparation method, chemical composition, and morphology. In this work, a low temperature sol-gel technique was used to prepare graphene aerogels from graphene oxide (GO) nanosheets. Through this method, GO nanosheets simultaneously undergo reduction and crosslinking in presence of ammonia to form a hydrogel. The Critical point drying was performed on the hydrogels, and they were annealed at higher temperatures to produce graphene aerogels. Our studies indicated that the GO/ammonia ratio affects the reduction pathway and crosslinking of the nanosheets, which in turn determine the packing density and pore size distribution in the final aerogels. The nature of the covalent bonds and the inter-sheet “bridges” observed in the SEM images were investigated using various spectroscopic techniques. These aerogels possessed considerably high surface areas in the range of 900-1500 m2/g and electrical conductivities comparable to those of copper and silver.

Nanosheets morphology and aspect ratio is another factor that determines the morphology and properties of GO aerogels. To study the effect of theses parameters, we have used semi-spherical crumpled graphene oxide (cGO) particles as the precursor for aerogel preparation. cGO particles were produced by spray drying aqueous GO dispersions. During this process, the 2D nanosheets are crumpled into 3D semispherical particles. Usage of these cGO particles instead of flat GO nanosheets led to a higher degree of crosslinking and packing density in a 100% cGO aerogel. A slight increase in the surface area (1600 m2/g) was also observed in this sample. The synergistic effects of mixed GO/cGO precursors on the structure and properties of aerogels were also explored and characterized.

Establishing a 3D electrically percolating network in an insulating matrix is key to numerous engineering and functional applications including energy storage and conversion, sensing devices, and telecommunication. To this end, using hydrophobic carbon nanofillers like graphene or carbon nanotubes is tempting, but still results in suboptimal performance due to processing challenges including colloidal instabilities in aqueous media.
Here, we demonstrate how natural cellulose nanofibers (1) can be in situ transformed into graphene-like sheets connected to a 3D network enhancing both the transport and the mechanical properties of sintered engineering ceramics (2). The advantage presented here is the colloidal processing in water of CNF hydrogels with ceramic powder slurries, which guarantees uniform and homogeneous properties from the bulk scale down to the nanoscale (3). The network architecture of the few-layered graphene (FLG) sheets also permits the decoupling of electrical and thermal conductivities, which represents a major obstacle in attaining efficient thermoelectric materials.
In this communication we present how cellulose nanofibers are converted into FLG during spark plasma sintering within Al₂O₃ and yttria-stabilized ZrO₂ (YSZ) matrices, respectively. The microstructure of the resulting materials was characterized by electron microscopy and spectroscopy (STEM/EELS), while the electrical and dielectrical properties were analyzed by impedance spectroscopy. The materials showed high electrical conductivity at only 2 % initial CNF content, while the FLG-YSZ nanocomposites exhibited mixed ionic-electronic conduction at ≤1% CNF, which is interesting for electrode materials in solid-oxide fuel cells. Besides the transport properties, the incorporated cellulose nanofibers largely improve the mechanical properties and also enable the use of technologically important machining methods for electro-conductive ceramics.
We envisage that our results can advance the processing science and technology to provide the improved hierarchical graphene composite materials needed for advanced applications in fields like energy and telecommunications.

References
(1) Wicklein et al. Nature Nanotechnology 2015, 10, 277.
(2) Kocjan et al. Nanoscale, 2018, DOI: 10.1039/c8nr00717a.
(3) Kocjan, Wicklein, Ruiz-Hitzky, Patent PCT/EP2017/078239.

Most of good material properties of carbon nanotube (CNT), including thermal and electrical conductivities, and tensile strength and modulus, appear in the direction of long axis of CNT. Therefore, to derive CNT properties into applications, alignment degree is one of the important structural parameters. In this study, aligned CNT sheet preforms were prepared by dry spinning from CNT forests. The aligned CNTs were mixed with epoxy or polyamide resin. A hot-melt method of the CNT sheet with the resin film enabled high CNT volume fraction up to 49 %. We investigated thermal and electrical conductivity of the high CNT content composites. Spin-capable CNT array was synthesized by chloride mediated thermal chemical vapor deposition (CM-CVD). Dimensions of CNT are 30 nm in diameter and > 1mm in length. By stacking the CNT webs, a CNT sheet was formed. Then, aligned CNT/polymer composite films were prepared by hot-pressing the CNT sheet and a polymer sheet simultaneously. We used a thermosetting polymer of B-stage epoxy and thermoplastic one of polyamide. Since polymer was impregnated in the the CNT preform, uniformly dispersed composites were obtained with a high Vf of 49 % in epoxy. With increasing Vf, thermal conductivity was increased monotonically up to 80 W/m/K. Similar increase was observed for CNT/PA. For both composites, uniform dispersion of CNTs in polymer matrix was observed. Electrical conductivity increased with increasing Vf as well as thermal conductivity, and it reached to 700 S/cm. We found that both conductivities are influenced by CNT Vf but by polymer materials.

Printing has drawn a lot of attention as a means of low per-unit cost, high throughput and additive patterning of graphene inks for scaled-up functional thin-form factor device manufacturing. However, the traditional printing processes typically require a flat surface and hence the current graphene printing methods are incapable of achieving patterning onto arbitrarily-shaped objects such as 3D printed parts and even on human skin.

Here, we present a conformal printing method to deliver conductive graphene patterns on to arbitrarily-shaped 3D objects using a sacrificial layer. We first formulate a water-insoluble conductive graphene ink and print it on to an ultrathin polyvinyl alcohol (PVA) film using conventional printing processes. The printed graphene patterns are then floated onto water, allowing the dissolution of PVA, while retaining the graphene patterns. This allows transfer of the conductive graphene patterns directly onto arbitrarily-shaped 3D objects with high resolution. I will present the formulation process and the parameters vital to achieving this and demonstrate this process onto a variety of irregularly-shaped 3D objects. Using this approach, I will also demonstrate multilayered device fabrication/transfer, including simple 2D material based electric circuits and components as well as resistive and capacitive strain sensors, without requiring post deposition processing.

In this talk, I will present first our current understanding of structure-defined DNA-carbon nanotube hybrids, then a description of the DNA sequence selection problem, and finally utility of DNA-carbon nanotube hybrids in molecular sensing. An artificial perception system, i.e. molecular perceptron, is proposed to take full advantage of the structure diversity of DNA-carbon nanotube hybrids.

Functionalization aims at granting compounds with additional features. This is achieved by typically attaching novel groups to the original systems. The aftermath of such process yields complexes whose charcteristics often result in more than just the mere sum of the initial products. The specific character of the functionalized structure, moreover, depends upon the way the functionalization strategy has been pursued.

We will focus on the carbon nanotubes functionalization through perylene, an aromatic molecule emitting in the excitation window of most single-walled nanotubes commercially available. We have previously shown that the perylene core of custom surfactants was able to attach though pi-pi stacking interactions onto the sidewall of CNTs while ensuring efficient excitation transfer to the tubes [1,2]. Here we will show how starting from the same elements (perylene and nanotubes) and pursuing different functionalization routines, we achieve systems with different features and functions. In particular, we will compare the characteristics of perylene-comprising polymers wrapped around the tubes [3] with the peculiarities of perylene covalently attached to the nanotubes following a novel conjugation-preserving routine we recently developed [4]. We will highlight the difference among the properties of the final products as well as the applications they would be suitable for.

[1] F Ernst et al., Adv. Funct. Mat. 2012, 22, 3921.
[2] F Ernst et al., Appl. Phys. Lett. 2013, 102, 233105.
[3] K. Huth et al, Small (2018), DOI 10.1002/smll.201800796.
[4] A Setaro et al. Nat. Comm. 2017, 8, 14281.

The molecular recognition of carbohydrates remains a major challenge due to their inherent structural complexity and low affinity for most substrates despite its importance in biological systems. Natural and synthetic lectins have been broadly studied and comprised the majority of molecular recognition strategies to date. However, in this work, we explore a class of specific polymers that adopt a unique 3D configuration and exhibit highly specific carbohydrate binding when adsorbed at the surface of a carbon nanotube. A compositionally diverse polymer library based on reversible addition-fragmentation chain-transfer (RAFT) polymerization of ortho-, meta-, and para-phenyl boronic acids (PBA) with acrylic, methyl acrylic, vinyl benzoic, and maleimidopropionic monomers, forming alternating, random, and block co-polymer variations is evaluated for the ability to selectively bind various monosaccharides and sugar alcohols. When adsorbed as a solubilizing corona phase onto single walled carbon nanotubes (SWNT), we demonstrate several examples, including a meta-(PBA maleic anhydride) co-polymer that enables dulcitol over mannitol and sorbitol recognition despite differing by only one or two cis/trans hydroxyl(s). We also identify a meta-(PBA 3-maleoimido-proponic acid) co-polymer selective for D-(-)-arabinose over all other aldopentoses including L-arabinose. This corona phase molecular recognition represents the first synthetic systems capable of specific, chiral saccharide recognition, which satisfies the demand for high precision assays, chemical sensors, catalysts, and biological probes for difficult to detect carbohydrates.

We propose a conceptually new structure, in which mono- or few-layer hexagonal BN seamlessly wrap around a single-walled carbon nanotube (SWCNT), and result in an atomically smooth coaxial tube consisting two different materials, SWCNT@BNNT. The structure is synthesized by chemical vapor deposition (CVD), and the length of the coaxial tubes can reach up to micrometers. As the reaction occurs on outer surface of the existing SWCNTs, we name this process conformal CVD. Various SWCNTs, e.g. vertically aligned array, horizontally aligned arrays, suspended SWCNTs, random networks and films, are employed as the starting material, and successful coating are achieved on all of them. TEM-EELS clearly demonstrated the BN-SWCNT coaxial structure in individual tube scale, while Raman, optical absorption, and cathode luminance spectra clearly confirm the existence of this structure in large scale. After coating, the SWCNTs can be fully coated and thermal stability significantly increases.
Our characterizations confirm that the outside BN coating started locally on the wall of a SWCNT and then merged into a BN nanotube on the curved surface of the SWCNT which served as a template. The thinnest inner SWCNT that can support the BN layer growth is found to be 0.6-0.7 nm. The number of walls can be tuned from 1 to few by controlling the CVD condition. The structure of inside SWCNTs are almost not effected by the conformal CVD, as evidenced by Raman and many other characterizations. The crystallization and cleanness of the starting SWCNT template are believed to be critical for the successful fabrication of outside walls. This structure is expected to have a broad interest and impact in many fields, which include but not limited in investigating the intrinsic optical properties of environment-isolated SWCNTs, fabricating BN-protected or gated SWCNT devices, and building more sophisticated 1D material systems.
Part of this work was supported by JSPS KAKENHI Grant Numbers JP25107002 and JP15H05760.

Single-walled carbon nanotubes (SWCNTs) are expected to have high thermal conductivity along the tube axis. However, experimentally obtained values of the thermal conductivity vary widely because of the difficulties in the thermal conductivity measurements as well as the characterization of SWCNTs. We have recently developed a novel method for measuring thermal conductivity using photoluminescence (PL) imaging spectroscopy [1]. We use a long SWCNT individually suspended between quartz pillars, and evaluate the chirality of SWCNT by PL and crystallinity by Raman spectroscopy. Because the measurements are done for chirality-assigned and isolated (not bundled) SWCNTs, the obtained conductivities are highly reliable. For (9, 8) SWCNTs with 10−12 μm in length, the thermal conductivity was 1166 ± 243 Wm^-1K^-1 at 400 K. We can also obtain the temperature dependence of thermal conductivity from the temperature distribution along the tube axis. We will discuss the accuracy of the measurement based on the data for multiple chiralities.
This work was partially supported by a MEXT Grant-in-Aid for Scientific Research on Innovative Areas “Science of hybrid quantum systems” (grant no. 15H05869).

[1] K. Yoshino, T. Kato, Y. Saito, J. Shitaba, T. Hanashima, K. Nagano, S. Chiashi, and Y. Homma, ACS Omega, 3, 4352-4356 (2018).

Membranes incorporating vertically aligned carbon nanotubes (CNTs) as through-pores have been shown to transport fluids at rates orders-of-magnitude faster than predicted by theory, offering promise as highly permeable membranes for applications as diverse as breathable yet protective garments, desalination membranes, and highly efficient filters.¹ However, there is a need for cost-effective and scalable solutions for fabricating large-area vertically aligned nanotube membranes, ideally starting from bulk nanotubes.² Here, we describe a new, solution-based fabrication technique for creating polymer composite membranes using electric-field alignment and electrophoretic concentration of CNTs initially dispersed in a solvent. The solvent is then replaced with a UV-curable oligomer, which is cured to controlled thickness to form a membrane with vertically aligned carbon nanotubes. After etching to open CNT pores, the pore size and total open area are assessed with He-N₂ flowrate ratios, size-exclusion tests and aqueous KCl conductance measurements. By comparing to theory, a pressure-driven gas-flow enhancement factor of 200 - 300× is found for flow through the small-diameter nanotube pores, which is consistent with reports in the literature for membrane fabricated from CVD-grown aligned nanotube forests. We conclude by describing recent progress in significantly increasing nanotube number density and membrane permeability, and the remaining challenges for ultimate roll-to-roll fabrication of vertically aligned nanotube membranes.

1) N. Bui, E. R. Meshot, S. Kim, J. Peña, P. W. Gibson, K. J. Wu, F. Fornasiero, Adv. Mat. (2016)
2) R. J. Castellano, C. Akin, G. Giraldo, S. Kim, F. Fornasiero, J. W. Shan, J. Applied Physics. (2015)

Graphene (G), Graphene Oxide (GO), and Reduced Graphene Oxide (rGO) have had an explosive growth in their applications ranging from electronic devices to biomedical applications. The use of lithographic and non-lithographic patterning methods have enabled the unique applications of such materials in electronics, display devices, flexible electronics, sensors, etc.. This talk will highlight the preparation of patterned surfaces via templating and photo masking shows the versatility of GO electrochemistry and photochemistry in unique film applications. We also demonstrate their use in improving anti-microbial properties against known classes of pathogens. The use of silver nanoparticles and other metal particles for antimicrobials has been the dominant additive for coatings, textiles, and other devices. Here we demonstrate the use of GO and rGO additives for anti-microbial activity such as E. Coli and B. subtilis including mitigation biofilm formation on a host of substrates. These properties were observed on solution preparation, coatings, and electrodes that have been modified by polymer-GO composites including preparation as fibers. Modification of graphene oxide further provides chemical functionality that is able to capture heavy metals for separations processes.

Atomically-thin two-dimensional semiconducting materials including graphene and MoS₂ are practically ideal for the development of Hall magnetic sensor due to its high carrier mobility, tunable carrier density and ultrathin channel properties. With the help of large area synthesis technique and photo-lithography, they could be patterend in the shape of Hall sensor array which might be applicable in the fabrication of large-area wafer-scale mass-production processes. The proto-type graphene Hall sensor array shows the extremely high current-normalized sensitivity of ~ 2000 V/AT [1] by the employment of large-area hexagonal BN layer as a substrate for graphene. This sensitivity could be improved a lot up to the level of ~ 3000 V/AT [2] by the replacement of large-area synthesized graphene with exfoliated MoS₂ flake, but the level of applied current for such a high sensitivity regime is too small. Therefore, we further examine the possibility of electrolyte gating in the graphene Hall sensor configurations with the usage of commercially available chemical-vapor-deposition grown graphene layer without hexagonal BN. Due to the suppressed charge-impurity scattering in the electrolyte,, the current-normalized sensitivity can reach to the value of > 3000 V/AT with moderate current levels and noises. In addition, the choice of operating conditions for the source-drain and gate voltage biases is to be systematically discussed, while the way of predicting it without a real test under the magnetic field is introduced from the analytical model. Low voltage operation (~ 0.5V) of the electrolyte-gating graphene Hall sensor is the additional advantage for the applications in the mobile devices.

[1] M.-K. Joo et al., ACS Nano 10 (9), pp 8803–8811 (2016)
[2] M.-K. Joo et al., 2D Materials 4 (2), 021029 (2017)

Reduced graphene oxide (rGO) has attracted a great deal of research attention in the fields of energy storage, electronics, photonics, catalysis, environmental engineering, etc. Currently, the most popular way to prepare rGO is to reduce graphene oxide, which is obtained by modified Hummer methods using tedious treatments in a harsh environment, to rGO flakes. Industrial applications demand advanced preparation methods that can mass produce highly uniform rGO sheets on arbitrary substrates. In this work, a one-step growth process is introduced that utilizes cellulose acetate as a precursor, without any catalysts, to produce uniform ultrathin rGO films on various substrates and free-standing rGO powders. Systematic spectroscopic and microscopic studies on the resulting rGO are performed. Prototypes of electronic and optoelectronic devices, such as field effect transistors (FETs), photodetectors, and humidity sensors, are fabricated and tested, demonstrating the intriguing applications of our rGO materials across a wide range of fields.

Non-crystalline carbon nanotubes (NC-CNTs) were synthesized by chemical decomposition in vapor phase using nanoporous anodized aluminum oxide (AAO) membranes as templates. In the present work a study of the influence of temperature of synthesis, the flow of the carbon precursor gas and doping with hetero-atoms, like the nitrogen, in the electrical conductivity of the NC-CNTs-N is shown.
To evaluate the influence of the synthesis temperature and the flux of the carbon precursor gas, experiments were performed between 600 and 800 ^oC, with concentrations of carbon precursors between 2-15 % with respect to an argon atmosphere. It was observed that, with increasing temperature the thickness of the walls of the NC-CNTs were higher and that it was possible to reduce the resistivity of the NC-CNTs synthesized in five orders of magnitude, from 2 MΩ (NC-CNTs-650^oC) to 24 Ω (NC-CNTs-800^oC). This result could indicate that there is a structural organization of the coal deposit, allowing CNTs greater mobility of the load carriers.
To evaluate the effect of doping with nitrogen, experiments were performed with thin-walled CNTs, which were then carbon-nitrogen deposited (C-N). It was observed that doping the CNTs with nitrogen reduced the resistivity by five orders of magnitude, from 2 MΩ (NC-CNTs-650^oC) to 13 Ω (NC-CNTs-N-650^oC). This phenomenon occurs because nitrogen introduces free electrons to the π conjugation system of carbon atoms.

GaN-on-diamond device cooling can be enhanced by reducing the thermal boundary resistance (TBR_{eff, Dia/GaN}) of the GaN/diamond interface. One limiting factor of TBR_{eff, Dia/GaN} is the dielectric layer type at the GaN to diamond interface. The thermal properties of this interface and the polycrystalline diamond grown onto GaN using SiN and AlN dielectric layers under same growth conditions are investigated and systematically compared for the first time. Using a combination of time-domain thermoreflectance (TDTR) measurement, adhesion evaluation and microstructural analysis, the TBR_eff,Dia/GaN of GaN-on-diamond wafers is shown to be dominated by dielectric layer type for diamond growth seeding, with additional impacts from the diamond nucleation surface. By changing the type of dielectric layer(AlN,SiN)，TBR_{eff, Dia/GaN} can be significantly reduced, and a TBR_{eff, Dia/GaN} of GaN-on-diamond wafers as low as 36~41m²K/GW is demonstrated when the dielectric layer is SiNx. This makes it possible to significantly reduce the thermal resistance of GaN / diamond transistors.

Carbon nanomaterials have been promising elements for a variety of future applications in electronics. Since the contact interfaces between carbon nanomaterials and metal electrodes influence the properties of assembled structures, the extensive studies on the interfaces have been conducted. The atomic configuration and electrical properties of the interfaces have been investigated to elucidate the conduction mechanism [1]. In situ transmission electron microscopy (TEM) using nanotip operation techniques allows the simultaneous observation of the structures and electrical properties of the junction of a carbon nanocapsule (CNC) and metal electrodes [2]. In this study, we applied in situ TEM to investigate the relationship of the structure and electrical resistivity of the interfaces between a CNC and metal electrodes.
CNCs were dispersed in ethanol and were dropped on the edge surfaces of a gold (Au) nanotip. This nanotip and another bare nanotip were inserted in a transmission electron microscope. Single nanoparticle junctions (SNPJs) were assembled using the CNCs and the two Au nanotips (electrodes) by piezomanipulation inside the microscope. After the preparation of SNPJs, their configuration was controlled by using piezomanipulation and was observed in situ at an atomic scale. Simultaneously, the conductance of SNPJs was measured by a two-terminal method while applying bias voltages. These process of observations and electrical measurements were performed at room temperature in a vacuum of 1 × 10⁻⁵ Pa. The observed high-resolution TEM images and currents were analyzed.
We could observe several interfaces and measure their contact resistivity. Consequently, it was found that the contact resistivity depended on the orientational relationships of the interfaces.
[1] F. Xia, V. Perebeinos, Y. Lin, Y. Wu, and P. Avouris, Nat. Nanotechnol. 6, 179 (2011).
[2] M. Tezura and T. Kizuka, Sci. Rep. 6, 29708 (2016).

Polyamide/polyethersulfone (PA/PES) membranes containing carbon nano-onions (NOs) were fabricated for the application in reverse osmosis (RO) membrane with enhanced antibacterial properties. The PA/PES membranes were prepared by interfacial polymerization between m-phenylenediamine (MPD) and trimesoyl chloride (TMC) on the surface of PES as support membrane. Then, the resulting PA/PES membranes were incorporated with the NOs to give antibacterial activities and use as RO membrane. The PA/PES membranes containing NOs were prepared in two variants; one contains aminated NO (NO-NH₂) and another contains acyl chloride-terminated NO (NO-COCl). Each functional group in both NOs was reacted with MPD or TMC in the PA membranes, resulted in grafting NO with PA membrane. The formation of PA membranes containing NOs was confirmed by some analyses including FT-IR, XPS, FE-SEM and TGA. The PA/PES/NO-NH₂ membrane exhibited better antibacterial properties compared with the PA/PES/NO-COCl composite membrane. In addition, the PA/PES/NO-NH₂ membrane showed high water flux without a loss in salt rejection. Thus, the excellent performances of PA/PES/NO-NH₂ membrane make its potential applications as an effective RO membrane.

Aliphatic polyketone (PK) composites containing PK grafted multi-walled carbon nanotubes (PK-g-MWCNTs) were prepared and their physical properties containing interfacial adhesion between PK and multi-walled carbon nanotubes (MWCNTs) and mechanical strength of the composite were examined. To fabricate PK-g-MWCNTs, 1-pyrenylmethylmagnesium bromide (PMgBr) was absorbed on the MWCNT surface by physisorption and then reacted with PK. During this procedure, Grignard reagent in the PMgBr reacted with ketone groups in the repeat unit of PK, resulting in grafting PK with MWCNTs. The formation of PK-g-MWCNT was explored by spectroscopy, electron microscopy, and thermal analysis. The interfacial adhesion energy between PK and PK-g-MWCNT was the highest value that can be achieved with PK and modified MWCNTs. The PK/PK-g-MWCNT composite exhibited better MWCNT dispersion compared with PK/pristine MWCNT composite. As a result, the PK/PK-g-MWCNT composite showed the highest mechanical strength among the composite examined owing to the improved interfacial adhesion and MWCNT dispersion.

Carbon materials have great potential for advanced nanotechnology. They exist in various allotropes in several dimensions, such as 0D of C60 family and graphene quantum dots, 1D of carbon nanotube (CNT), graphene nanoribbon (GNR) and carbon fiber (CF), and 2D of graphene relate materials. Each of these allotropes shows unique and interesting properties making them representative nano-materials. Recently, hybrid system of those different carbon allotropes has great attentions to achieve an improved and synergetic properties. Making 3D hybrid structure gives many enhanced properties, such as high integrity, interconnectivity, porosity, conductivity and mechanical strength. New strategy to connect different carbon allotropes with covalent bonding allows us to fabricate more advanced structure which was not possible previously and to understand novel properties of materials. After first research about seamlessly connected graphene and carbon nanotube hybrid structure (G/CNT) has been reported, it has attracted great attentions due to its high surface area, excellent electrical and mechanical properties. In this presentation, several researches derived from G/CNT structure will be introduced. such as patterning, mechanical strength at the junction and energy storage application, and its powerful possibility will be discussed.

Use of environmentally friendly solid polymer electrolytes is important for battery technology. This work aims at investigating effect of lithium in chitosan-graphene films which can be useful for energy storage applications. Lithium ion are small in size. Lithium salts conduct electricity under electric field due to the mobile lithium ions which can easily migrate. Chitosan is an abundantly available biopolymer. It has good film forming ability. However chitosan films do not have good conductivity. Graphene-based functional materials have caused great interests in electronic, medical, environmental applications due to its large surface area, high electrical conductivity and high mechanical strength. H5 Graphene was purchased from XG Sciences, USA. The graphene platelets have approximate thickness of 15 nm and length of 5 micro meter. Chitosan solution was prepared by adding 1% (w/v) of chitosan powder, 1.5% (w/v) of acetic acid and 100ml of double distilled water. The solution was stirred for 30-40 minutes to form a transparent thick solution. A part of this solution was transferred to a plastic dish to form a film at room temperature. To proportionate amount of chitosan solution 33, 66 and 100% (weight with respect to chitosan) of lithium perchlorate (LiClO₄) was added. To a part of the chitosan lithium solution 5% of graphene (weight with respect to chitosan) was added. The solution was stirred and heated for 30 min. This solution was poured on a plastic dish and dried at room temperature in order to obtain chitosan–graphene-lithium nanocomposites. The thickness of the nanocomposite films varied between 50-200 micro meter. Dielectric studies such as conductivity, dielectric constant, dissipation factor and impedance were measured using impedance spectrometer. The conductivity ranges from 10^-8 to 10^-4 S/cm for graphene-chitosan lithium system. The conductivity of chitosan was lowest. In the absence of graphene the conductivity increases with increasing LiClO₄ concentration. Conductivity (at 100 Hz) for Chitosan, Chitosan 33% LiClO₄, Chitosan 66% LiClO₄, Chitosan 100% LiClO₄ films are 6x10^-8, 2x10^-6, 2x10^-4 and 3.5x10^-4 S/Cm respectively. Conductivity (at 100 Hz) for Chitosan 5%H5, Chitosan 5%H5 33% LiClO₄, Chitosan 5%H5 66% LiClO₄ and Chitosan 5%H5 100% LiClO₄ are 3.5x10^-7, 5x10^-5, 1.5x10^-4 and 3.5x10^-5 S/Cm respectively. The conductivity measurements show that incorporation of graphene decreases the conductivity for films with 66 and 100% LiClO₄. This indicates that graphene induces crystallization of Lithium salts thereby reducing the conductivity. SEM image shows that graphene affects the crystallization of LiClO₄. Both LiClO₄ and graphene increased the dielectric constant of the nanocomposites. Dissipation factor analysis showed that the relaxation behavior is affected due to incorporation of graphene. The dissipation was also relatively low (similar to chitosan), indicating that the nanocomposites do not have much heat loss.

Graphene, a one-atomic-thick material with honeycomb structure built from carbon atoms, which can be considered as a monolayer of graphite, is the most representative two-dimensional material. It has drawn tremendous attention due to fascinating electronic and mechanical properties. Graphene with no defect is believed to be the strongest material. Through all synthesis methods, chemical vapor deposition (CVD) is a facile approach to grow large-scale monolayer graphene, which is polycrystalline with inevitable defects and boundaries. Thus, the study on mechanics of graphene, particularly fracture behavior, is essential from both fundamental interest and technological importance. Numerous studies on fracture mechanics of graphene are emerging. The fracture toughness and crack propagation of graphene have been investigated by means of in situ methods and simulations. In these studies, fragmentation of graphene tends to initiate randomly at pre-existing defect locations, resulting in irregular morphology and is considered as a limitation in applications.
However, ordered fragmentation can be utilized in nanostructuring. Here, our works propose and demonstrate a facile method on controlling the fragmentation of graphene to fabricate ordered graphene nanoribbon arrays with sharp edges by taking the advantage of strong localized strain existing at the neck front during polymer cold-drawing process. For the thermoplastic polymer, a neck will form locally during a stretch. This necking phenomenon results from the mechanical instabilities of the polymer and will propagate along the entire length of polymer, which is called cold-drawing. The neck front moves uniaxially with strong localized strain while the deformation of after-necking areas ceases. We harness this strong localized yet moving strain to fragment graphene and show the fabrication of finely ordered graphene nanoribbons. The CVD grown monolayer graphene is transferred to polycarbonate substrate and then mounted on a linear travel stage. After the following cold-drawing process of the polycarbonate substrate, monolayer graphene nanoribbon arrays are fabricated. The structure and morphology of obtained monolayer graphene nanoribbons are systematically investigated using various microscopic and spectroscopic measurements. Moreover, the potential applications for both chemical and physical sensing are explored. Future work will be conducted to investigate the fragmentation via polymer cold-drawing on multilayer graphene.

Recent research works have employed a wide range of materials with different structures to improve actuators’ performance and extend their application prospect. Among all the reported actuators, graphene oxide (GO) based actuators have shown superior ability in responding to various stimuli because of their lightweight, high thermal conductivity, and good mechanical properties. However, almost all the reported GO-based actuators are based on composites, whose fabrication process are quite complicated. Moreover, these reported actuators always need direct contact with strong external stimuli, which will potentially restrict their application area and reduce their service life. Additionally, noticing that most objects will bear charges because of electrification, a lightweight GO film can be easily driven by the electrostatic force to achieve contactless control. In this work, we will report a flexible contactless actuator based on GO film strip prepared by one-step solvent evaporation process. This actuator can be contactlessly controlled by electric force offered by a wide range of charged objects. And it shows a fast and reversible response to a weak electric force variation. In addition, a smart ‘radar’ based on GO film strip array is demonstrated for motion tracking.
GO dispersion with a concentration of 0.9 mg/mL is prepared by modified Hummer’s method. 50 mL GO dispersion is transfer into a glass petri dish and then dried under 323 K for 24 h. The GO film is cut in to strip (18.6mm * 2 mm) after peeled off from the dish. SEM, AFM, XRD and FTIR spectrometer are used to characterize the GO film. Results show that the GO film has a thickness of 4 micrometer and a layer distance of approximately 0.8 nm and it contains alkoxy, epoxy, and hydroxy groups. To study the behavior of the GO film strip based actuator, a PS petri dish is placed above the actuator to make it bend at a certain angle. Results show that the actuator is very sensitive to almost all the charged objects such as tweezers, gloves, human fingers, and polymer films. Also, the actuator shows fast and reversible actuation within 0.56s and good reliability over 15000 cycles. To study its working mechanism, we exclude the effect of humidity and light and put the GO film strip in uniform electric field. Results show that the actuator can be driven even under a charge amount of 1 nC. And the driving force needed is in several micro-Newton range. At last, a smart ‘radar’ consist of 3 * 3 GO film strip array is demonstrated to show its practical application in identifying the position of various objects. This study reveals its application prospect in areas such as motion tracking and small force application.

As-synthesized malic acid carbon dots are found to possess advanced photoblinking properties compared to conventional dyes. Considering their excellent biocompatibility, malic acid carbon dots are suitable for super-resolution fluorescence localization microscopy under a variety of conditions, as we demonstrate in fixed and live trout gill epithelial cells. In addition, during imaging experiments, the so-called “excitation wavelength-dependent” emission was not observed for individual as-made malic acid carbon dots, which motivated us to develop a time-saving and high-throughput separation technique to isolate malic acid carbon dots into fractions of different particle size distributions using C₁₈-reversed phase silica gel column chromatography. This post synthesis separation allowed us to determine how particle size distribution influences the optical properties of malic acid carbon dot fractions, i.e., optical band gap energies and photoluminescence behaviors.

Nanoelectronic systems are perfect testbeds to study and mimic the physicochemical nature of noncovalent interactions which, though weak in nature (~ 100s of meV), form the bedrock of most biological and cellular processes. Furthermore, the ability to electrically tune the charge density (hence the chemical potential) in nanomaterials via electrostatic gating provides another knob to control such interaction. Unfortunately, nearly all existing electronic sensing methodologies are based on charge transfer (covalent interactions) which does not fully represent the interaction between the adsorbed vapor molecules and a pristine nanosurface. Here we present results of electrical probing and tuning of the noncovalent physisorption of both polar and nonpolar molecules on graphene surface by using two different sensing techniques – heterodyne sensing and µColumnFET sensing. Temperature-dependent molecular desorptions for six different polar molecules and five non-polar species were measured in real-time to study the desorption kinetics and extract the binding affinities. Furthermore, we demonstrate electrical tuning of molecule-graphene binding kinetics via electrostatic gating of graphene. Our results not only provide insight into the non-covalent interaction dynamics between graphene and both polar and non-polar molecules, but also pave the way to electrically tailor physisorption dynamics at nanoscale interfaces.

The electronics industry is always looking for new ways of protecting devices from over-voltage, or over-current scenarios. In the present work we will introduce novel low-voltage epoxy-carbon nanotube composites with high non-linearities in resistive devices. Plots of current versus voltage can be fit to powers of voltage >2. Devices of different dimensions were made on single substrates by photolithographic patterning of interdigitated electrode pairs. These devices were tested at different speeds over different voltage ranges, and I-V relationships are compared. From the resulting data, the limiting resistances can be apportioned between injection barriers and bulk nanotube connectivity.

Nylon 6,6 nanocomposites including well-dispersed graphene oxide (GO) and carbon nanotubes (CNTs) were successfully fabricated via in situ interfacial polymerization between two immiscible phases: organic phase assisted by poly(vinylpyrrolidone, PVP) surfactant containing adipoyl chloride with dispersion of GO and CNTs; aqueous phase containing hexamethylenediamine. Prior to the polymerization, GO was functionalized with thionyl chloride, resulting in acyl-chloride-functionalized GO (AGO). The effects of incorporation of AGO and PVP on the state of dispersion were investigated. It was observed that the addition of AGO and PVP reduced particle flocculation, leading to a well-dispersed suspension as verified through dispersion stability analysis and UV–Vis spectroscopy. The interfacial interaction between the carbon nanofillers (AGO, CNTs) and nylon 6,6 chain can be induced via hydrogen and covalent bonding as confirmed using spectroscopic results. According to the analyses of thermal properties, nuclei crystallization in nylon 6,6 nanocomposites was promoted by the strong nucleating behavior of AGO and the thermal stability was improved. Tensile tests of the composite films (nylon 6,6/AGO, CNT) showed 122 and 152% increases in the tensile strength and modulus, respectively, as compared to the neat polymer. This suggests that the interfacial interaction between nylon 6,6 and AGO/CNT contributes to enhanced load transfer in nanocomposites, thus enhancing the mechanical properties.


Acknowledgments

This research was supported by the Nano-Material Technology Development Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning, Korea (Grant No. 2016M3A7B4027697), and the Human Resources Development of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea Government Ministry of Trade Industry and Energy (MOTIE) (No. 20174030201430).

References
[1] E. –Y. Choi, K. Kim, C. –K. Kim & E. Kang, “Reinforcement of nylon 6,6/nylon 6,6 grafted nanodiamond composites by in situ reactive extrusion”, Scientific Reports, 6:37010, (2016)
[2] Evie L. Papadopoulou, F. Pignatelli, S. Marras, L. Marini, A. Davis, A. Athanassiou and Ilker S. Bayer, “Nylon 6,6/graphene nanoplatelet composite films obtained from a new solvent”, RSC Adv., 6, 6823, (2016)

Nonuniform strain fields in graphene have received much attention due to the tight relation between its morphological and electronic properties. In addition to the well–known pseudomagnetic field, another recognized effect induced by a nonuniform strain is a position-dependent Fermi velocity (PDFV) [1]. Pioneering experiments [2], through scanning tunneling spectroscopy (STS), have revealed the existence of a PDFV, but its effects on the graphene physics have been scarcely explored [3].

In this work, we present analytical and numerical studies of the local density of states (LDOS) measured by STS for graphene under a nonuniform strain, either in the absence or in the presence of a uniform magnetic field [4]. The analytical expressions of the LDOS, derived from an effective Dirac model in term of a PDFV, were verified by tight-binding numerical calculations. In consequence, such expressions can be useful to quantify appropriately nonuniform strain effects on STS experiments of strained graphene, including those of Landau level spectroscopy. Finally, our results demonstrate that PDFV effects should be considered in a full description of transport signatures of strain-induced pseudomagnetic fields in graphene.

This work has been partially supported by UNAM-IN106317 and CONACyT-252943. Computations were performed at Miztli of DGTIC, UNAM. M.O.L. acknowledges the postdoctoral fellowship from DGAPA-UNAM.

[1] F. de Juan, M. Sturla, and M. A. H. Vozmediano, “Space dependent Fermi velocity in strained graphene,” Phys. Rev. Lett. 108, 227205 (2012).
[2] W.-J. Jang, et al., “Observation of spatially-varying fermi velocity in strained-graphene directly grown on hexagonal boron nitride,” Carbon 74, 139 (2014).
[3] G. G. Naumis, S. Barraza-Lopez, M. Oliva-Leyva, and H. Terrones, “Electronic and optical properties of strained graphene and other strained 2d materials: a review,” Rep. Prog. Phys. 80, 096501 (2017).
[4] M. Oliva-Leyva, J. E. Barrios-Vargas, and C. Wang, “Fingerprints of a position-dependent Fermi velocity on scanning tunneling spectra of strained graphene,” J. Phys.: Condens. Matter 30, 085702 (2018).

The graphene’s growth directly on germanium surface can be a good route to integrate graphene into nanoelectronic-devices. Several works deal with the syntheses and characterization of the graphene on Ge [1-3]. Graphene/Ge interface interaction is not fully understood. A remarkable aspect that we found was the presence of ripples. The ripples and their characteristics can modify the electronic structure, electron/hole puddle formation and carrier transport in graphene.
The objective of this work is to identify and study how these ripples can modify the local density of states (LDOS) of the graphene growth by CVD on two different germanium crystalline orientations. The samples were characterized by the Raman Spectroscopy and Scanning tunneling microscopy and spectroscopy (STM/STS). Our experimental data shows that the graphene on Ge is strained of compressive biaxial type and such strain is related to the formation of ripples. The characterization by STM reveal the presence of ripples aligned with the Zig-Zag direction and the wavefront parallel to the Armchair direction. STS data showed no band gap in graphene due to the presence of the ripples but a shift on Fermi level.

References

[1] J.H. Lee, E.K. Lee, W.J. Joo, Y. Jang, B.S. Kim, J.Y. Lim, et al., Wafer-scale growth of single-crystal monolayer graphene on reusable hydrogen-terminated germanium, Science 344 (2014) 286–289.
[2] A.M. Scaparro, V. Miseikis, C. Coletti, A. Notargiacomo, M. Pea, M. De Seta, et al., Investigation the CVD synthesis of graphene on Ge(100): toward layer-bylayer growth, ACS Appl. Mater. Interfaces 8 (2016) 33083.
[3] C. D. Mendoza, P. G. Caldas, F. L. Freire Jr. and M. E. H. Maia da Costa, Growth single-layer graphene on Ge(100) by chemical vapor deposition, Applied Surface Science 447 (2018) 816-821.

Carbon nanotubes (CNTs), which have excellent thermal and mechanical properties, are promising materials as ground or space structures. Although there have been many ground-based characterizations of the influence of radiation on CNT, no work has been performed on effect of space radiation. In this study, multi-walled CNT (MWCNT) yarns fabricated by dry spinning method were exposed to the actual space environment on the international space station (ISS) for one or two years. During the flight, ground-based comparison tests, including irradiation of atomic oxygen (AO), electron beam and ultraviolet individually, were performed. For the ground-based comparison tests, significant deterioration in tensile strength was found for AO irradiated MWCNT yarns. Transmission electron microscopy and Raman spectroscopy observations revealed that crystal structure of MWCNT was damaged with showing sharp open edges of graphene. For the actual space test, quite similar damages and decrease of tensile strength were observed.
This study was carried collaborative research project with Obayashi Corp. and Japan Manned Space Systems Corp., which is adopted by project using Exposed Experiment Handrail Attachment Mechanism of Japan Aerospace Exploration Agency.

Gilding is the ancient process of coating intricate geometries with precious thin metal films. Fascinating Egyptian and Chinese sculptures, coated with < 200 nm thin metal leaves by this process, have resisted corrosion and other environmental degradations for thousands of years. Similarly, palladium (Pd) is used as gilding material for its excellent corrosion properties, mechanical performance and of course its silver color. In this work, we enrich the 150 nm thin Pd leaves by doping with a single layer of graphene via low pressure chemical vapor deposition (CVD) processes. Pd leaves are made by hammer forging of micrometer thick foils. During this process, their thickness is reduced to 150 nm while the average grain size exceeds 20 μm. The Pd leaves made by high strain beating are stable at high synthesis temperature, resisting solid state dewetting owing to their extremely low grain triple junctions density (~0.017 µm^-1). Mathematical models of CVD synthesis kinetics on ultrathin metal catalysts guide the development of extremely rapid graphene synthesis conditions, resulting in the formation of high quality uniform graphene monolayer on Pd in less than one minute. Graphene grains growth rate is twice as fast as copper-catalyzed growth. Uniaxial strain testing with Raman spectroscopy reveals the excellent crystallinity of graphene by probing the stress-induced phonon shifts.

Using nanoindentation, we demonstrate the graphene’s ability to significantly strengthen Pd leaves by constraining dislocation motion and bridging grain boundaries and cracks in Pd leaves. The as-grown Pd-Gr composite leaves are indented by a diamond-coated atomic force microscope (AFM) probe with diameter of 100 nm. We found that the effective surface modulus of the Pd-Gr composite leaves is 223.6±23.4 GPa, which is over 2.5-fold of that of the pristine Pd leaves (83.7±14.2 GPa)by coating less than 0.05 wt. % Gr. Moreover, indentation on edge-notched doubly-clamped nanostrip enables the measurement of the critical stress intensity factor in mode I fracture of ultra-thin film materials. We will describe the several systematic experiments on Pd leaves and Pd-Gr composites to reveal the strengthening and toughening mechanisms operating in this new materials. This new nanocomposite material could open exciting opportunities in utilizing high quality 2D materials to coat large structures.

Graphene Quantum Dots (GQDs) is one kind of graphene nanostructure, and it has enormous attention because of their excellent properties originated from the existence of energy bandgap. For synthesizing GQDs, the bottom-up method is required over the top-down approach on synthesis step because it has more potential to control the size and edge status, which is directly related to their optical properties. However, preparation of GQDs using the bottom-up method requires very stringent conditions with specific organic materials after complicated reaction steps. Until now, generating uniform lateral sized GQDs at the synthesis step has not been much successful, although separation of GQDs according to the diameter size have shown marginal success such as stepwise dialysis.
Synthesis of high-quality GQDs with well-controlled size, shape and surface functionalization needs to be further explored. It is still challenging to synthesize the GQDs with clear hexagonal shaped graphitic structure via solution chemistry because the conventional bottom-up processes exhibit low crystallinity and they exhibit broad photoluminescent (PL) spectrum and low quantum yield compare with the top-down method.
Here, we report a novel bottom-up approach not just for the synthesizing single-crystalline graphene quantum dots (GQDs) with hexagonal shape but also discover a new phenomenon that constructing graphitic carbon structure from an understanding of nitrogen site role on graphitization and inducing the catalytic reaction intermediate. In details on selected analysis data, 5 nm lateral sized sample has ~350 pm thickness, and 70 nm lateral sized sample has ~700 pm from atomic force microscopic data and both samples consist of more than 90% carbon species from x-ray photoelectron spectroscopic data. Furthermore, we investigated the origin of luminescence via exciton decay profile through femto-second pulsed laser excitation on various size-controlled GQDs. We discuss the size effect on decay profile to elucidate the origin of luminescence on GQDs by difference core and edge-generated exciton behavior. As the application, we fabricated deep-blue emissive GQDs-light emitting diodes. It shows 2.5 V as turn-on voltage, ~450 cd/m² as max brightness and (0.16, 0.06) as CIE 1931 coordinates.

The graphene grown by chemical vapor deposition method (CVD) has been widely studied for device applications due to scalable growth of CVD. The reduced graphene oxide (rGO) also has attracted huge scientific and industrial interests since it can be easily synthesized in massive quantities. Even CVD-grown graphene as well as rGO show clear hysteresis in IV curves of the devices, mostly due to the inherent or inevitable defects of graphene, which originate from the CVD synthesis itself or the wet process of graphene transfer from the metal substrate to a dielectric substrate. In this work, we have measured workfunction of the graphene and rGO on SiO₂ with varying the gate voltage and the distance of the probe from the source electrode. A spatial dependence mapping of workfunction in graphene and rGO layers from the source electrode (ground) showed different carrier injection with showing the hysteresis similar with that of graphene-based device. The energy shift of Dirac point and the amount of hysteresis in the graphene or rGO devices can be correlated with a crossing point (a neutral point) and the width in spatial and electric mapping of workfunction. Further details will be discussed in the presentation.

Two-dimensional heterointerfaces often provide extraordinary carrier transport as exemplified by superconductivity or excitonic superfluidity. Recently, double-layer graphene separated by few-layered boron nitride demonstrated the Coulomb drag phenomenon: carriers in the active layer drag the carriers in the passive layer. Here, we propose a new switching device operating via Coulomb drag interaction at a graphene (Gr)/MoS₂ heterointerface. The ideal van der Waals distance allows strong coupling of the interlayer electron-hole pairs, whose recombination is largely suppressed by the vertical energy barrier at p-Gr/n-MoS₂ interface via dual-gate, whereas the lateral carrier transport is constructed via Coulomb drag. This device exhibits a high mobility (up to ~3,700 cm²V^-1s^-1) even at room temperature, while maintaining a high on/off current ratio (~10⁸), outperforming those of individual layers. In the electron-electron drag regime, graphene-like Shubnikov-de Haas oscillations are observed at low temperatures. Our Coulomb drag transistor could provide a shortcut for the practical application of quantum-mechanical 2D heterostructures at room temperature.

Thermal interface materials (TIMs) are used for enhancing heat transfer between solid surfaces by creating thermal paths. Their important characteristics are high thermal conductivity and softness for filling the air gaps. Many conventional TIMs consist of the thermal conductive fillers dispersed in polymer matrix, which has disadvantages of low thermal conductivity and poor thermal stability.
Here we propose aerogel TIM replacing polymer matrix with air matrix. Air matrix is released upon pressing and conductive fillers are in direct contact with each other. A soft sponge like self-supporting film can be fabricated using carbon nanotubes (CNTs), and this structure is able to support fillers 100 times larger in weight compared with their own weight [1]. In the case of hybridization with graphite particles, the porosity of the aerogel can be controlled in the range from 20 % to 70 % by changing the amount of CNTs [1]. Moreover, the CNTs do not disturb heat conduction between fillers because CNTs have high thermal conductivity, and the CNT has high thermal stability (500 °C in air).
We selected silver having the highest thermal conductivity among metals as conductive filler. The aerogel TIM was fabricated by hybridizing Ag particles with CNTs. The TIM was self-supporting even when the amount of fillers were 200 times larger than that of CNTs. From the result of steady-state thermal resistance measurement, the thermal resistance of 99.5 wt% Ag-0.5 wt% CNT-TIM between two Cu rods was 60 mm² K/W under 0.8 MPa. Too thick TIM had high bulk thermal conductivity and a too thin one had high contact resistance. In addition, TIM showed lower thermal resistance with lower CNT content. Optimization of the structure is now underway, and the latest results will be reported.

[1] K. Hasegawa and S. Noda, J. Power Sources 321, 155 (2016).

We have engineered a flame retardant ethylene-vinyl acetate (EVA) composite which has the similar mechanical properties as polyvinyl chloride (PVC) and therefore may prove to be an alternative material for cable sheathing. Four composites were studied, EVA with aluminum hydroxide (ATH), EVA with ATH and molybdenum disulfide (MoS2), EVA with ATH and graphene nanoplatelets (GNPs), and EVA with all three components. Tensile testing showed nearly identical results for the EVA/ATH and EVA/ATH/MoS2 compounds, while the EVA/ATH/GNPs compound had higher mechanical properties. The compound containing all three components showed further enhanced mechanical properties, indicating that a synergy was established. This was further confirmed using Scanning Electron Microscopy (SEM) where GNPs were seen to increase the dispersion of the MoS2 and ATH components within the polymer matrix. Cone calorimetry test clearly showed a large decrease in heat release rate when GNPs were added, which was further enhanced by adding GNPs and MoS2 together. Application of the UL-94 test showed that only the compound containing 36 wt% of ATH and 2 wt% each of MoS2 and GNPs can achieve the UL-94 V0 rating.

Alumina is a widely used ceramic material in manufacturing due to its good chemical and thermal stability, light-weight and wear resistance [1-3]. However, the low fracture toughness and conductivity of alumina limit its broader application to build various devices [2]. Carbon nanotubes (CNTs) obtain good mechanical strength and electrical conductivity to reinforce ceramics [4]. Direct ink writing (DIW) is an ideal additive manufacturing method to build ceramics green bodies with the advantages of low cost and free design [5, 6].
In this work, we fabricate CNT-alumina composites to improve the mechanical strength and electrical conductivity. Multi-walled CNT (MWCNT) (6 and 10 wt %), alumina powder (90 and 86 wt %) and Ferro 3134 (4 wt%) were mixed together. 3.7 wt% ammonium polyacrylate (NH₄-PAA) of whole slurry was used as a dispersant and 3.3 wt% polyvinylpyrrolidone (PVP) was used as a binder. 25.9 wt% of deionized (DI) water was used to modify the viscosity of slurry. After 12 hours of ball milling, the well-dispersed slurry ink was used to build the CNT-alumina composites using a modified DIW 3D printer. After drying out for 24 hours, samples were sintered at 1400°C for 3 hours in a high vacuum. Scanning electron microscope (SEM) was used to observe the microstructure of the cross section in both green bodies and sintered samples. SEM images showed the dispersibility of CNT in sintered samples was better than that in green bodies, indicating the effect of sintering to microstructure of ceramics. The density of sintered samples was measured using Archimedes' Method. The density of the composite containing 6 wt% MWCNT was 3.065 g/cm³(80.29% of theoretical density); the density of composite containing 10 wt% MWCNT was 2.875 g/cm³(77.10% of theoretical density), confirming that the density decreased with an increasing amount of CNT [7].
Further study will be focused on the measurement of fracture toughness, compression strength and electric conductivity. We will study the percolation theory for electrical conductivity of composites with different fractions of MWCNT. We will also study various sintering methods, such as spark plasma sintering and hot isostatic pressing.

Reference:
[1] Balani, Kantesh, et al. International Journal of Applied Ceramic Technology 7.6 (2010): 846-855.
[2] Lee, Kyubock, et al. Journal of the American Ceramic Society 94.11 (2011): 3774-3779.
[3] Chen, B., et al. JOM 69.4 (2017): 669-675.
[4] Kasperski, Anne, et al. Scripta Materialia 75 (2014): 46-49.
[5] Rueschhoff, Lisa, et al. International Journal of Applied Ceramic Technology 13.5 (2016): 821-830.
[6] Lewis, Jennifer A., et al. Journal of the American Ceramic Society 89.12 (2006): 3599-3609.
[7] Kim, S. H., et al. Carbon 47.5 (2009): 1297-1302.

Graphene has attracted much attention as a next-generation electronic material for its excellent properties such as ultra-high mobility. Large-size single-crystalline graphene is usually obtained on copper based catalyst with chemical vapor deposition (CVD). However, the property of the graphene is largely deteriorated by the transfer process for device fabrication. Therefore, the direct growth of graphene on the dielectric substrate is studied to overcome the problem.
C-plane sapphire is conventionally used as a substrate for the direct growth of graphene [1]. There are very few studies about the optimization of crystallographic plane of sapphire for the direct growth. In this study, we focus on the use of r-plane sapphire as a substrate, which is sometimes used for the growth of horizontally-aligned carbon nanotubes [2].
Graphene was directly grown on r-plane sapphire using low pressure CVD without metal catalyst. C-plane sapphire was also used for the comparison. Mixture gas of nitrogen (N₂), hydrogen (H₂), and diethylacetylene (C₆H₁₀: 3-Hexyne) was flown to a reactor for the growth of graphene. Growth temperature was systematically changed between 1090 ^oC and 1210 ^oC.
In the case of c-plane sapphire, graphene was found to grow only in the pits of sapphire, which was formed during CVD. This is very similar to the result that Saito et al. reported [3]. They reported Al-rich surface appeared inside the pits and had a catalytic effect. In our experiment, the size of pits enlarged with increasing growth temperature. Also, the growth rate of graphene increased with growth temperature and, then, decreased over 1170 ^oC. On the contrary, in the case of r-plane sapphire, the surface was fully covered with single-layer graphene in all samples. D/G peak intensity ratio and wrinkle density of graphene decreased with increasing growth temperature. On r-plane sapphire, the graphene was found to grow simply in 2D nucleation mode. This is probably because the surface of r-plane sapphire has catalytic effect and enhances the decomposition of growth species. Therefore, the use of r-plane sapphire brings a faster growth rate and smoother surface than those on c-plane sapphire.

Acknowledgement: This work was supported in part by JSPS KAKENHI Grant Numbers 15H03558, 26105002.

Reference
[1] M. A. Fanton et al., ACS Nano 5, 8062 (2011).
[2] N. Ishigami et al., J. Am. Chem. Soc. 130, 17264 (2008).
[3] K. Saito and T. Ogino, J. Phys. Chem. C 118, 5523 (2014).

Carbon nanotube (CNT) has been reported to have high tensile strength of 150 GPa [1]. Since the discovery of dry spinning phenomenon from a CNT forest [2], a dry-spun CNT yarn has been an attractive material as the structural material. One of good things of the dry-spinning is that large-scale and highly aligned CNT structures are uniformly formed. However, since the CNTs are connected by van der Waals force, the spun yarn fails by relative sliding of CNTs, and its mechanical properties are far inferior to those of individual CNT. Moreover, even the relative sliding is suppressed by cross-linking CNTs in the yarn, tensile strength of individual CNT is not so high as expected because of crystal defects, resulting in moderate improvement of strength in the yarn. In this work, in order to reinforce the CNT yarn, CNTs were graphitized at high temperatures. Then CNTs were cross-linked by binder materials. Dry-spin capable MWCNT forests were grown by chlorine mediated CVD using FeCl₂ as catalyst [3]. The yarns were prepared by twisting drawn CNT webs [4]. The yarns were annealed at higher than 2500 °C in inert ambient. The highly graphitized CNT yarns were further reinforced by introducing azide-group cross-linker agent that makes covalent bonding in between CNTs. Mechanical and electrical properties of the reinforced CNT yarns will be reported.

References
[1] B. G. Demczyk et al., Mater. Sci. Eng. A334, 173 (2002).
[2] K. Jiang et al., Nature 419, 801 (2002).
[3] Y. Inoue et al., Appl. Phys. Lett. 92, 213113 (2008).
[4] A. Ghemes et al., Carbon 50, 4579 (2012).

Although there has been a rapid growth of interest in polymer-based nanocomposites, the mechanics of reinforcement in such materials is still not yet fully understood. It has been established by the authors that stress transfer from the matrix to the reinforcement in nanocomposites reinforced by graphene nanoplatelets (GNPs) can be followed from stress-induced Raman band shifts. A detailed study has been undertaken of the mechanisms of stress transfer in a range of polymeric matrices with very different levels of Young’s modulus, E_m, reinforced by graphene nanoplatelets. The matrix materials studies have been natural rubber (E_m ~ 1MPa), thermoplastic elastomers (E_m ~ 10-100 MPa) and polypropylene (E_m ~ 1000 MPa). The microstructure of the nanocomposites has been fully characterised using a range of different advanced analytical techniques that include, Raman imaging, x-ray computer tomography (CT) scans and polarized Raman spectroscopy that give an unprecedented level of information upon their microstructures.
It is found that the addition of the GNPs leads to significant increases in stiffness in each polymer showing high levels of reinforcement are obtained. For each material the effective Young’s modulus of the graphene, E_eff, has been determine using the rule of mixtures and it has been found that this scales with the value of E_m. Additionally the stress-induced Raman bands shifts show different levels of stress transfer from the polymer matrix to the GNPs which again scale with the Young modulus of the matrix. For example, shifts of the order of 1 cm^-1/100% strain are found in the natural rubber matrix nanocomposites compared with ~10 cm^-1/1% strain for the polypropylene matrix nanocomposites with a value of E_m three orders of magnitude higher.
Studies of the mechanics of stress transfer in model composites consisting of single graphene flakes in polymeric matrices have also been undertaken by using Raman spectroscopy to map the strain distribution in the individual flakes. A unifying theory has been developed to predict the stiffness of the bulk nanocomposites from the mechanics of stress transfer from the matrix to the GNP reinforcement based upon these studies of deformation of the individual flakes. Excellent agreement has been found between the measured and predicted values of E_eff, and hence composite Young’s modulus for the bulk nanocomposites. It will be shown that the theory also enables factors such as interfacial bonding, reinforcement geometry and orientation to be taken into account.
Overall it is found that it is only possible to realise the theoretical Young’s modulus of graphene of 1050 GPa for discontinuous flakes as E_m approaches 1 TPa; the effective modulus of the reinforcement will always be less for lower values of E_m. In general it is found that the highest levels of reinforcement will be obtained in nanocomposites with strong graphene-polymer interfaces and optimised reinforcement geometries and orientation.

Two-dimensional (2D) metal oxides have widely studied in various applications due to their intriguing properties, such as super high surface-to-volume ratio, ultra-thin thickness, high meso-porosity and small grain size. However, 2D nanostructures have the tendency to restack, so they can induce the decrease of surface area and amounts of accessible mesopores. In this work, crumpled SnO₂ nanosheets (NSs), crumpled ZnO NSs, and crumpled SnO₂-ZnO composite NSs (C_MO_NSs, MO = SnO₂, ZnO or SnO₂/ZnO) were successfully synthesized by using graphene oxide (GO) sheets as a sacrificial template and used as highly effective 2D oxide gas sensing layers. In detail, GO/metal ion composites were synthesized by dissolving metal precursor and GO in absolute ethanol to allow bonding between GO and the metal ion. And then, by conducting spray pyrolysis of the solution which is composed of dispersed GO/metal ion composites in DI water at 400 ^oC, the crumpled GO/metal oxide composites were fabricated. After calcination of them at 500 ^oC for 1 h, GO were thermally decomposed to form C_MO NSs. Crumpled metal oxide NSs have high surface-to-volume ratio and high distribution of macropores as well as mesopores, which are essential for efficient surface reaction and high gas permeability. Also, ultra-small grain size affects to form complete electron depletion layer for effective modulation of resistance. Additionally, n-n heterojunction from C_SnO₂/ZnO NSs can induce the energy band bending to enhance the gas sensing capability.
The gas sensing performances were proceeded to VOCs (volatile organic compounds) gas species, e.g., CH₃COCH₃, NO, C₇H₈, C₂H₆O, HCHO, H₂S and NO₂. The sensing test results demonstrated that C_MO NSs exhibited enhanced gas sensing performance toward formaldehyde (2.5 times higher response (R_air/R_gas) than that of 2D metal oxide NSs) with high selectivity and fast response/recovery speed. Also, C_SnO₂/ZnO NSs induced the improvement of gas sensing properties due to the creation of heterojunction (3 times higher response (R_air/R_gas) than that of C_MO NSs). This work suggests the facile and effective synthesis method of C_MO NSs templated by the GO for enhanced gas sensor.

Wet spinning process is one of the most common methods of producing polymer microfibers. Wet process has been used in particular for the polymers which can decompose near their melting temperature and thus defy melt spinning process. Poly(acrylonitrile) (PAN), a representative precursor of carbon fibers, belong to this kind of polymers. On the other hand, due to high thermal conductivity and electrical conductivity, carbon nanotubes (CNTs) have been used in PAN fibers to improve the conductivity of carbon fibers. Well-aligned CNTs are known to contribute high electrical conductivity. In this study, we developed high conductive CNT/PAN composite microfibers using a new process, so called current-assisted wet spinning. The current-assisted wet spinning is different from electrospinning which utilizes the electric field to fabricate nanofibers from a charged solution. For the current-assisted spinning, the electrical current is applied to the spinning nozzle of wet spinning system, inducing the interaction of PAN and functional group of CNT and also more packing and alignment of PAN molecules via controlled diffusion between CNT/PAN and coagulation solutions. The electrical and mechanical properties of CNT/PAN fibers fabricated using current-assisted wet spinning were measured by the two-probe method and single fiber tensile test. 2D wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM) were used to characterize the microstructures of CNT/PAN fibers. Nuclear magnetic resonance spectroscopy(NMR) and X-ray photoelectron spectroscopy(XPS) analysis were performed to characterize the chemical bonding of CNT/PAN solutions and fibers. Finally, a mechanism behind high conductivity of CNT/PAN composite microfibers via current-assisted wet spinning was investigated and will be presented in detail at the Conference.

The intercalation of various elements under the buffer layer is an elegant method to produce so-called quasi-freestanding graphene (QFMLG) on SiC substrates. The modification of the graphene/SiC interface changes the electronic properties of QFMLG depending on the choice of the intercalant. Hence, intercalation represents a promising technique to tune graphene’s properties according to the specific application.
So-far three methods for intercalation have been successfully demonstrated to work for different elements. Gaseous species like, e.g., hydrogen [1] or oxygen [2] can be intercalated by annealing in the respective atmosphere. Solids with low vapor pressure such as gold [3] or germanium [4] were intercalated by first depositing the material on top of the buffer layer followed by annealing at a certain temperature in ultra-high vacuum (UHV). On the other hand, solids with high vapor pressure require a different method. Recently it was shown that implantation [5] allows the intercalation of bismuth. In this presentation, using the example of antimony (Sb), we introduce another method to intercalate solid elements with high vapor pressure. The method is based on a reduced rate of sublimation of Sb from the surface when the sample is annealed in argon (Ar) atmosphere rather than in UHV.
To that end, Sb with a thickness of approx. 50 nm was deposited by molecular beam epitaxy on top of the buffer layer and the samples were annealed in 1 bar Ar at an optimized temperature of 550°C. X-ray photoelectron spectroscopy (XPS) and low-energy electron diffraction (LEED) confirmed the intercalation and formation of quasi-freestanding graphene. Both, elemental Sb as well as oxidized Sb were observed at the interface. The latter is caused by the transport of the Sb-covered samples in air which leads to a thin oxide layer on top of the Sb. A two-step annealing process in 1 bar Ar where (i) the oxide is removed by annealing at 400°C and (ii) the intercalation is performed at 550°C leads to the intercalation of purely elemental Sb. Angle-resolved photoelectron spectroscopy (ARPES) reveals a moderate n-type doping of the samples which were intercalated with pure metallic Sb.

[1] C. Riedl et al., Phys. Rev. Lett. 103, 246804 (2009).
[2] M. Ostler et al., Mater. Sci. Forum 717-720, 649 (2012).
[3] I. Gierz et al., Phys. Rev. B 81, 235408 (2010)
[4] K.V. Emtsev et al., Phys. Rev. B 84, 125423 (2011).
[5] A. Stoehr et al., Phys. Rev. B 94, 085431 (2016).

The aim of this study is to promote the ultra-fast, sensitive and real-time monitoring of different clinical cardiac Biomarkers (Myoglobin and Cardiac Troponins) for the diagnosis of the cardiac diseases like Acute Myocardial Infarction (AMI) using the 3D network of 2-ABA functionalized carbon nanotubes in a the Lab-on-a-chip configuration. The development of a rapid and practical immunosensor for detecting Cardiac markers in serum samples (standard as well as spiked) is desirable due to its roles in cardiospecific diagnosis, risk stratification, and assessment. The main objective is to develop a biosensor exploiting microfluidics allowing in-situ self-functionalization. The sensitivity can be adjustable and the device can be used for detection of different cardiac biomarkers. The functionalization takes place in situ and selectively, just before the sensing, keeping the sensing area dry and inactive until the test starts, and conserving the functionality of the device. Also, the reagents and chips are stored separately and may be used before testing, without the need of overnight functionalization process or complex fabrication methods. The monitoring of the signal is performed in real-time and changes in impedance modulus (label-free electrochemical changes) are equivalently recorded by using an alternative and simpler voltage measurement. The label-free electrochemical biosensors are an attractive choice for fast, early diagnostics and monitoring of biological markers due to the direct conversion of a biological event into an electronic read-out signal.

Since the discovery of single-walled carbon nanotube (SWNT), SWNT has attracted with great interest because of their outstanding mechanical and electrical properties. For these reasons, researches for implementation of their electronic applications such as field-effect transistors (FETs), thermoelectric devices and biological imaging have been substantially promoted. However, the co-exsistance of metallic (m-) and semiconducting (sc-) SWNT have disturbed the effective use for electronic applications. In the recent, conjugated polymer wrapping of SWNT has specially aroused great attraction as a method for separation of SWNTs due to their advantages of high selectivity toward sc-SWNT and simple polymer sorting process. Although the π-π interaction between conjugated polymer and wall of SWNTs is related with the selective dispersion of SWNTs, the mechanism how to separate the s-SWNTs remains as issues. In this research, we introduce the pyrene moiety as main chain of conjugated polymer to increase the π-π interaction with s-SWNTs. New pyrene-based conjugated polymers were carefully designed and synthesized via suzuki polymerization. Their dispersion selectivity and diameter of sc-SWNTs enriched by pyrene-based conjugated polymers were characterized by various measurements such as UV-vis absorption spectra, Raman spectroscopy and Photoluminescence excitation/emission analysis. Finally, the sc-SWNTs were employed into FETs as an active layer.

Single-wall carbon nanotube(SWCNT) is excellent material for many applications. Especially, SWCNTs with small diameter and high crystallinity are expected to have better property, however they are more difficult to synthesize which results in high cost (2-100 USD/g). One of the best synthesis methods for high quality CNT is floating catalyst chemical vapor deposition (FCCVD) [1-4]. However, the yield of CNT is still low which stems from the low efficiency of the formation of active catalyst nanoparticles. In the conventional CVD, because the gas which contain the catalyst source is heated gradually by the furnace, most of the catalyst nanoparticles aggregate and deactivate before the nucleation of the CNTs.
In this report, to generate more active catalysts, we designed a new process to control the gas temperature. The catalyst sources (ferrocene and sulfur) are rapidly (i.e., ~ 5 ms) heated to 1300 °C in the narrow flow path (Φ4 mm) to pyrolyze and vaporize efficiently. Then, the iron vapor is mixed with carbon sources (e.g., CH₄, C₂H₄, etc.) and cooled down rapidly to 1150 °C in wide flow path (Φ40 mm), which enables the formation of the catalyst nanoparticles followed by the immediate nucleation and synthesis of the CNTs. The CNT yield was 2.5 mg/min. The TEM observation showed 90% SWCNTs with 10% double-wall CNTs with a diameter of 1.64 ± 0.40 nm. The Raman spectra (excitation wavelength: 488 nm) showed the G-band and D-band peaks at ∼1590 and ∼1350 cm⁻¹, respectively, with the G/D intensity ratio ranging from 40 to 100. The weight ratio of carbon to iron in the carbon products were ~10 by TGA and EDS analysis.

References:
[1] H.M.Chen, et al., Appl. Phys. Lett. 72, 3282 (1998).
[2] P. Nikolaev, et al., Chem. Phys. Lett. 313, 91 (1999).
[3] A.G. Nasibulin, et al., Chem. Phys. Lett. 402, 227 (2005).
[4] T. Saito, et al., J. Phys. Chem. B. 110, 5849 (2006).

Graphene products are obtained by reduction of graphene oxide (GO). A recently chemical procedure for GO synthesis is the Tour method [1]. In this method the GO was synthesized by the oxidation of graphite powder, using KMnO₄ and a 9:1 mixture of H₂SO₄/H₃PO₄, the latter as a protective agent. In this paper a modified Tour method is designed to looking for a simple, easily controlled and an alternative approach for large scale production of GO for solar cell applications. We find that if a mixture of H₂SO₄/H₃BO₃ is used instead of H₃PO₄, then the oxidation time of graphite can be reduced under the same reaction conditions: two hours of oxidation is enough for produce the equal amount of hydrophilic oxidized graphene material as compared to Tour method that requires about seven hours. The reduced graphene oxide (rGO) was prepared by the thermal and chemistry reduction of GO by employing ascorbic acid and ammonia solution at high temperature [2]. The GO and rGO samples were characterized by UV-Visible spectroscopy, FTIR spectroscopy, Raman spectroscopy, SEM, TEM and EDS. It is found that the GO prepared by modified Tour method yields a higher fraction of well-oxidized carbon material and could have the same advantageous in quality for achieving few-layers of graphene sheets for large-scale production than the original Tour method. On the other hands, the results of XRD, EDS and UV-Vis of rGO products reveal that the oxygenated groups that were present in GO products have been widely removed, this can be seen reflected in the atomic ratio C/O of rGO (3.7), it increase close to 70% with respect to the GO (1.3), so that almost 50% of the oxygenated groups were removed. Finally, thin films of GO and rGO were prepared by spin coating method with GO and rGO solutions. Optical and electrical properties of the films are analysed and their potential use as electron or hole transporting layers in perovskite solar cells are discussed. In particular, the presence of the remaining oxygenated groups in rGO reduces the electrical conductivity of the rGO films, and, consequently, the power conversion efficiency of the solar cells. The removal of a higher percentage of oxygenated groups remains as a challenge in the synthesis of graphene products.

With the development of the wearable device industry, there is an increasing interest in conductive textiles, and research on conductive fiber manufacturing is actively being reported. Because carbon black has a high specific surface area, a composite is prepared by mixing with a polymer then a conductive network is formed in a small amount to improve electrical conductivity. In this study, carbon- black/polymer composites composed of polypropylene, polyester, and nylon matrix were prepared and their electrical properties were analyzed. The carbon-black/polyester composite film with good dispersibility showed the highest electrical conductivity and the lowest threshold value among 3 types polymer composites. The nylon composites with high polarity had higher threshold values of conductivity because of aggregation between polymer and carbon black. In order to improve the electrical conductivity, carbon black particles were prepared by 4-aminobenzoyl functionalized carbon black(Ag-ABCB) with silver ions through Friedel-crafts acylation reaction. The electrical conductivity of the fabricated Ag-ABCB/PET fiber was better than the electrical conductivity of origin CB/PET fiber.

hBN layers meet a growing interest for deep UV LED [1], and has become a strategic material for the fabrication of van der Waals heterostructures. Stacked with any other 2D materialit can reveal the best of their physical properties [2]. However, hBN optoelectronic properties remain much less characterized and understood than other 2D materials.

In this talk, we review recent advances made thanks to the development of appropriate spectroscopies in the UV range - cathodoluminescence (CL) at 4K and Raman [3,4], combined with ab initio simulations [5]. Thanks to these tools, a h-BN characterization metrics has been developed on the basis of their original optical properties, governed, in the energy range 5.5 – 6 eV, by strong excitonic effects easily trapped at structural or chemical defects [3]. We shall discuss the interplay between structure, defects and spectroscopic properties and how these properties can be further exploited for sample benchmarking [3].

Beyond this effort, the talk will also address the recent advances made for the understanding of the high luminescence observed although bulk hBN is an indirect band gap material [1,6]. To that aim, the efficiency of radiative recombinations has been measured on a reference single crystal using temperature - dependent CL and compared to that diamond and ZnO [6]. The luminescence of hBN is confirmed to be unusually high and is found to remain constant from 10 to 300K. Enlighting analysis of this behaviour is provided by ab initio calculations of the exciton dispersion in bulk hBN. First, the lowest-energy exciton (iX) is found at 5.97eV and to be indirect, as expected for an indirect band gap, with a binding energy equal to 300 meV. This dispersion behavior accounts for an assignation of the luminescence to phonon assisted recombinations of the indirect exciton as proposed in [7] and for the assignation of the tiny peak observed in CL spectra at 5.956 eV to the zero-phonon radiative recombination of iX [6]. Further iX high binding energy is consistent with the temperature behavior of the luminescence, the high yield being the signature of a strong exciton phonon coupling. Second, calculations also confirm the direct exciton (dX) with a binding energy of 670 meV [6], an energy which turns to be only 100 meV above the indirect one. It comes out that bulk hBN displays a peculiar behavior where luminescence and optical absorption are due to different excitons. This situation totally evolves in the layer, the gap being direct and we could identify the dX line in the CL spectra recorded on very thin hBN layers [6].

[1] K. Watanabe et al Nature Mat, 3 (2004), 404
[2] C. R. Dean et al., Nature Nanotech, 5, 722 (2010).
[3] L. Schué et al., 2D Mat., 4, 015028 (2017)
[4] I. Stenger et al., 2D Mat., 4, 031003 (2017).
[5] L. Sponza, et al, Phys. Rev. B, 97 (2018), 075121
[6] L. Schué et al, arXiv:1803.03766v1 [cond-mat.mtrl-sci]
[7] G. Cassabois et al, Nature Photonics 10, 262 (2016)

Despite their similar crystallographic structures, boron nitride nanotubes (BNNTs) exhibit a range of physical and chemical properties distinct from carbon nanotubes (CNTs), which are mainly attributed to the partial ionic bonding character of BN. Here we present two markedly different properties between BNNTs and CNTs: interlayer mechanics [1] and reduction chemistry [2]. Firstly, we show using van der Waals (vdW) parameterized density functional theory (DFT) that the strong mechanical coupling between the buckled lattices of small-diameter BNNTs greatly elevates the threshold forces and internal friction with respect to the relative motion of BNNT walls. Unlike for CNTs, large difference between relaxed and unrelaxed energy corrugations of BNNTs could yield energy dissipation via the strain-induced anelastic relaxation of interlayer locking, resulting in the experimentally observed ultrahigh interlayer friction of BNNTs. Secondly, through DFT calculations and experimental studies of the covalent alkylation of BNNTs using 1-bromohexane, we demonstrate that the chemical reactivity of BNNTs towards radical molecules can be significantly enhanced via reducing the nanotubes (i.e., negatively charging). Our study predicts that the localization characteristics of the BNNT pi electron system lead the excess electrons to fill the empty p orbitals of boron sites, which promote covalent bond formation with an unpaired electron in radical molecules.

References:
[1] H. Shin, K. S. Kim, B. Simard, and D. D. Klug, Phys. Rev. B 95, 085406 (2017).
[2] H. Shin, J. Guan, M. Z. Zgierski, K. S. Kim, C. T. Kingston, and B. Simard, ACS Nano 9, 12573 (2015).

Compared to carbon, bulk and reduced dimensional forms of pure boron present more complex bonding patterns and atomic-scale geometries. An underlying reason is that boron has the same number of valence orbitals as carbon but has one fewer valence electron (i.e., is “electron deficient”). This means that standard two-center bonding motifs between neighboring atoms in familiar structures, such as hexagonal or triangular networks, are not energetically favorable. This leads to complexity and richness in the phase space of boron structures. This situation has attracted significant scientific attention over the last two decades. While the initial literature consisted of primarily of first principles theoretical studies and predictions, the last few years have witnessed experimental fabrication and characterization of 2D boron sheets which in turn has greatly enhanced interest in these materials.

This talk will provide a brief overview of the initial theoretical predictions in this field followed by a summary of some of the more salient experimental and theoretical performed recently, including some of our work on 2D and nanotubular boron and metal boride nanomaterials. In the process, we will discuss the challenges and opportunities this field may face when attempting to fabricate and use boron nanostructures.

From our theoretical insight into evolutionary selection in synthesis of monocrystal graphene [1], into the paths of back-diffusion in growth of its bilayers [2], and into their possible conversion to monocrystal diamond films like diamane [3,4], we envisage a platform to emerge for design of the point (0D) defects in 2D-media as effective single-photon emitters (SPE) [5]. More diverse basic optics of numerous 2D materials [6] further expands possibilities for SPE realization, where theoretical assessment can guide experimental choices and tests.
[1] I. Vlassiouk, et al. Nature Mater. 17, 318 (2018).
[2] Y. Hao, et al. Nature Nanotech. 11, 426 (2016).
[3] A. Kvashnin, et al. Nano Lett. 14, 676 (2014).
[4] http://terramonstersworldgalaxy.wikia.com/wiki/Diamane
[5] S. Gupta, J.-H. Yang, and B.I.Y., to be published.
[6] S. Gupta, et al. ACS Nano, DOI: 10.1021/acsnano.8b03754 (2018).

Hexagonal boron nitride (h-BN) is structurally like graphite and has continued to gain research interest from synthesis, characterization, to application. Mono and few layered h-BN are now commonly known as boron nitride nanosheets (BNNSs), as one of the emerging two-dimensional (2D) materials. On the other hand, seamless rolls of BNNSs are known as boron nitride nanotubes (BNNTs). BNNTs are meaningful as a role model of materials by design, as they are first predicted by theory and then experimentally realized. Due to the difficulty on the synthesis of BNNTs and BNNSs, their research progress is far slower than the structurally similar carbon nanotubes (CNTs) and graphene. In this invited talk, recent advancement of BNNTs and BNNSs will be discussed, in particular for their application in advanced electronic and biomedical applications. These advancements suggest that BNNTs and BNNSs are important nanomaterials that complement the application of CNTs, graphene, and 2D materials.

Integration of atomic force microscopy and laser spectroscopy traditionally makes possible to obtain more complex information about the studied object: whether it is a living cell, a polymer composite, or nanotubes. In the report are given Various examples of combined AFM and Raman microscope NTGERA Spectra (NT-MDT Spectrum Instruments Co) applications to study both physical properties of the surface (topography, surface potential, magnetic or piezoelectric properties, conductivity, local stiffness) and structural properties measured by Raman spectroscopy will be reported. Normally combined study is done by means of Si cantilevers of top-visual shape to provide optical access to the tip from above by high-resolution objective (100x, 0.7 NA). It is also possible to use metal needles for scanning tunneling microscopy or tuning fork-based feed-back. Measurements can be carried out in a controlled gas or liquid environment, which may be important to maintain the properties of the sample or to eliminate the background low-wavenumbers Raman peaks from the N₂ and O₂ molecules present in air. The design of the spectrometer allows to use either edge filters or notch filters to suppress laser radiation and provide both Stokes and anti-Stokes scattering, including the THz range down to 10 cm-1 from Rayleigh scattering.
The most intriguing possibility that appears when integrating atomic force microscopy and Raman spectroscopy is to overcome the diffraction limit due to local amplification of the field near the tip apex [1]. To achieve strong enhancement of Raman signal in the Tip Enhanced Raman Scattering (TERS) mode, it is necessary to keep the tip at the surface of the sample as close as possible. The mode of nonresonant intermittent-contact microscopy, also known as Hybrid mode [2] allows the probe to be held in contact with the surface up to 70% of time, while eliminating lateral forces during scanning and minimizing the pressure force. In addition, this method is also applicable to keep feedback in the liquid and when the sample is heated, when a significant drift of the cantilever bending is observed.
The presented results, using the example of graphene oxide flakes, show that HybriD mode allows to effectively enhance Raman scattering and, at the same time, significantly reduces the mechanical probe-sample impact during scanning process.

Literature
1. T. Deckert-Gaudig, A. Taguchi, S. Kawata, and V. Deckert, Chem. Soc. Rev., vol. 46, no. 13, pp. 4077–4110, 2017.
2. Patent US 9,110,092 B1.

After the discovery of semi-metallic graphene, layered materials such as hexagonal Boron Nitride (h-BN) and molybdenum disulphide (MoS₂) have attracted a lot of attention. For example, h-BN sheets have become the indispensable underlayers for two dimensional (2D) devices with high electron mobility despite being electrical insulating. On the other hand, the indirect to direct band gap conversion in MoS₂ is due to the quantum confinement effect along the thickness axis of the 2D materials. Here, we present the synthesis and properties of h-BN and MoS₂ quantum dots (QDs) by creating quantum confinement in axes perpendicular to the thickness axis. These QDs offer unique and broad spectra absorption bands for effective photoelectron generation for use in QD-sensitized photovoltaic devices.

A top-down approach was employed to convert h-BN and MoS₂ particles into QDs by using sonication, and solvo-thermal in Dimethylformamide (DMF). The MoS₂ are 2-40 nm in dimension, while the BN QDs are 2-8 nm in dimension. We show that the fluorescent emission from these polydisperse QDs are excitation wavelength dependent. These MoS₂ QDs could absorb a wide spectrum range of light from 320-520 nm to produce fluorescence emission from 385-569 nm. The h-BN QDs can absorb a broader spectra from 300-580 nm with fluorescence emission of 380-620 nm. The broad absorption wavelength range of these QDs would meet the peak of solar irradiation spectrum to enable effective production of photoelectrons from the sun for the applications of photovoltaic devices. Detailed of these results will be discussed in the meeting.

Single-walled carbon nanotubes (CNTs) are one of the most versatile electronic materials ever discovered. Electronically, they can be semiconducting or metallic; mechanically, they are flexible yet have a tensile strength greater than steel; and physically they can be centimeters long to just a few nanometers. For nearly two decades, these diverse properties have excited and motivated researchers pursuing CNTs for electronic applications. However, thus far the versatility of CNTs has also been their greatest obstacle in terms of purification, precise positioning, and so forth. In this talk, I will discuss how the inherent versatility of CNTs can be appropriately harnessed for enabling certain applications. The tremendous progress in solution-phase processing of nanotubes has opened a path for their most suitable, near-term use as printed thin films. Recent advances will be presented in using printed thin films of CNTs for print-in-place additive electronics, sensors for harsh environments, and highly sensitive biosensors. Each of these is made possible by drawing from distinct properties of thin-film CNTs; properties unavailable from any other printable material. Perspectives on stability, reproducibility, and yield will also be offered, with evidence of the impact that printed silver contact morphology has on printed CNT thin-film transistor performance. The unique and reproducible behavior of printed CNT thin films suggests they be given greater consideration from the printed electronics community. In the company of organic semiconducting inks, and even that of non-printed metal-oxide semiconductors, printed films of CNTs are a standout with significant advantages and opportunities.

Stretchable devices have intensively been studied towards a realization of wearable electronics for continuous monitoring of human activity and health condition. Recent works have demonstrated that carbon nanotube thin-film transistors (CNT TFTs) have excellent mechanical flexibility and stretching ability. [1-3] However, they still exhibited a degradation of drain current with applied strain. Another issue to be addressed is high-voltage (a few ten V) operation due to the polymer-based gate dielectric which is flexible and/or stretchable, but of low-dielectric constant. [3] Wrinkled Al₂O₃ gate insulator was proposed for realizing low-voltage and stretchable CNT TFTs, but the degree of tensile strain was limited up to 20%. [2] Here, we have realized low-voltage operable and highly-stretchable all-carbon CNT TFTs by introducing a novel local strain control structure.
We fabricated CNT TFTs composed of a channel of a semiconducting-CNT thin film, transparent electrodes of a CNT thin film, and a 50-nm-thick Al₂O₃ gate dielectric layer on a stretchable poly(dimethylsiloxane) (PDMS) film. The device may exhibit some degree of stretching ability, however, in order to fully suppress the influence of strain on the device characteristics, we formed a local strain control structure with a rather hard polymer material on top of the channel region of a CNT TFT. We also performed the numerical analysis based on the finite element method to design the strain control structure.
The fabricated devices exhibited typical p-type transistor characteristics with a carrier mobility of 7.2 cm²/Vs and on/off ratio of about 10⁵, and was operable at gate voltage of less than 5 V. By introducing the local strain control structure, only 14% of externally applied tensile strain was introduced in the channel region, whereas the CNT electrodes and the other field of the PDMS film were directly stretched. No significant degradation of drain current was observed against tensile strain up to 35%.
[1] D. M. Sun, et al., Nat. Commun. 4 (2013).
[2] S. H. Chae, et al., Nat. Mater. 12, 403 (2013).
[3] S. Wang, et al., Nature 555, 83 (2018).

Semiconducting single-wall carbon nanotubes (sSWCNTs) have been widely used as the channel material for high-performance printed flexible thin-film transistors (TFTs). Due to the absorption of moisture and oxygen in air, the printed sSWCNT TFTs generally exhibit p-type characteristics only. In this paper, we report fully-printed dual-gate sSWCNT TFTs that exhibit almost symmetric ambipolar characteristics. With the applied control gate voltage varying from -60 V to 60 V, a threshold voltage tuning range of 27 V is achieved, allowing the device to be effectively tuned into either predominantly p-type or predominantly n-type. The tunable ambipolar characteristics are found to be very stable over long period of time (4 months). By integrating two printed dual-gate TFTs biased with different control gate voltages, a complementary metal oxide semiconductor (CMOS) inverter with close to rail-to-rail output voltage swing is demonstrated. The use of dual-gate structure for achieving n-type printed carbon nanotube TFTs is much more controllable and repeatable compared to other methods such as chemical doping. Our work shows the feasibility of implementing more sophisticated complementary logic circuits using printed flexible carbon nanotube transistors.

Graphene has a unique broadband absorption from visible to microwave due to its gapless nature. Integrating graphene with microcavities, photonic crystal or surface plasmonic structures can not only increase the strength of light-matter interaction, but also achieve some degree of spectral selectivity for enhanced light absorption around the designed wavelengthes. However, the above-mentioned spectral selectivity results from some forms of resonance structures; therefore once the device is fabricated, the spectral response is fixed at the resonance wavelength for such devices. In our work, we demonstrate an electrically tunable, spectrally distinguishable photoresponse in a graphene-based phototransistor. The device is composed of a 6-nm amorphous silicon tunneling barrier sandwiched by two layers of graphene, one used as the channel and the other as the gate. By applying a sweeping voltage on the graphene gate layer while recording channel layer current, we discover gate-dependent photoresponse curves for different excitation wavelengths. Importantly, this electrical tuning of photoresponse offers a new mechanism for spectrally resolved photodetection with graphene detectors. As a proof-of-concept, we build a responsivity matrix of gate voltage and excitation wavelength by measuring the gate-dependent photoresponse curves for a finite number of wavelengths. Photodetection and spectral reconstruction for mono-color lights were then successfully demonstrated. More detail will be presented at the conference. Our results open the door for on-chip spectrometers free from complex optical setups and may find its applications in technologies such as hyperspectral imaging.

Sheets of unidirectionally oriented carbon nanotubes (CNTs) [1-2], among the various attractive applications, can be employed as transparent and conductive layer for switching but also, interestingly, for aligning liquid crystals (LCs) [3]. Even a single layer, tens of nanometers thick, can be used for applying electric fields strong enough to reorient LC molecules and, at the same time, for serving as an alignment layer for LCs.
The successful implementation of new materials in LC cell geometries is a pre-requisite for future applications in device technology. CNT sheets as aligning electrodes are a relatively new entry that are showing very good performances for LC switching but also, present challenges to face. CNT sheets do not completely adhere to the substrate surface and methods to promote the adhesion, such as chemical treatment of the surfaces or polymer coatings, are needed. As it will be presented, the adhesion of CNTs on different types of underlying polymer films is indeed improved by ethanol treatment but the orientational order parameter of CNT sheets is affected at different extends [4]. The evaluation of the CNT sheet characteristics such as the degree of orientational order of the strands, the film thickness and its uniformity in properties like the electrical conductivity are of importance for the LC passive and active behaviour. However, there are other characteristics that we will describe here, that influence the LC behaviour, connected to the peculiar nature of the CNT sheets being formed by discrete elements, the nanotubes, even if connected in anisotropic networks. To understand the different aspects we investigate the CNT sheets using different techniques. For evaluating the morphology and the uniformity in properties we use electron and atomic force microscopy, profilometry and optical absorption. The electrical characteristics are investigated with and without LCs using DC as well as AC electric fields while monitoring the samples under a polarized optical microscope.

References:

M. Zhang, S. Fang, A. A. Zakhidov, S. B. Lee, A. E. Aliev, C. D. Williams, Ken R. Atkinson,
Ray H. Baughman, Science,2005, 309 (5738), 1215-1219.
[2] K. Truong, Y. Lee, D. Suh, Curr. Appl. Phys. 2016, 16 (9), pp 1250–1258(2016).
[3] W. Fu, L. Liu, K. Jiang, Q. Li, S. Fan. Carbon, 2010, 48, 1876-1879.
[4] M.A. Rahman, H. Agha, J. H. Park, K. Truong, D. Suh, G. Scalia, J. Mol. Liq.,
2017, doi.org/10.1016/j.molliq.2017.12.122

With the aid of advanced electron microscopy, we have established an approach using ED as a means to evaluate the validity of Raman spectroscopy for quantification of concentrations of metallic SWNTs (M%) or of semi-conducting tubes (S-SWNT%) [1]. We have proved that the Raman RBM intensities depend largely on the resonant conditions at certain wavelengths, rather than simply on concentrations. Up to the resonance conditions, some majority nanotube species revealed by electron diffraction measurements induce relatively weak, or even missing RBMs, and vice versa. This certainly leads to an uncertainty over Raman spectroscopy for quantitative assessment of metallic tube concentrations calculating from the relative peak intensities.

Chirality distribution maps of SWNTs produced by CVD methods with Fe nanoparticles as catalysts at various synthesis conditions have been analyzed by electron diffraction technique. As a recent advance [2], we have successfully achieved direct synthesis of single-walled carbon nanotube thin films with various colors using a novel floating-catalyst-CVD process with ferrocene-based iron catalyst particles and CO as the carbon source. The color is tunable by adjusting the reactor conditions, i.e. the temperature and especially the addition of CO₂. Based on unique electron diffraction analysis of individual SWCNTs in our colorful SWCNT thin films, we were able to attribute the colors of the SWCNT thin films to their narrow diameter in certain ranges which give rise to absorption peaks in the visible region. It is demonstrated that the narrow (n, m) chirality distribution also accounts for the display of certain color of a SWCNT thin film.

References
[1] Y. Tian, et. al, Anal. Chem. 90(2018), 2517.
[2] Y.P. Liao, et. al, Submitted to JACS, 2018.

The chemical structure of semiconducting single-walled carbon nanotubes (SWCNTs) results in optical and electronic properties of promise for a wide variety of applications. Until quite recently the presence of metallic SWCNT impurities has hampered efforts to gain a deeper understanding of their true potential, with the additional complication that most commercially available materials contain tens of different chiral species. Significant effort has been devoted to elegant enrichment strategies aimed at extracting tailored semiconducting SWCNT species from the raw soot, from the use of subtly tunable surfactant interactions to the exploitation of specific DNA sequences. However, conjugated polymers, typically based on the fluorene moiety, appear to show the greatest promise with regards to their high selectivity and viability for scalable manufacturing approaches.
Unfortunately, the van de Waals forces between the pi-electron systems of the polymer and SWCNT that enable the selective extraction of semiconducting SWCNTs with high purity also make removal of the polymer difficult. Since these polymers typically have a wide bandgap they act as an insulating coating on the surface of the individual SWCNTs within functional networks, inhibiting the transport of energy in the form of excitons and/or charge carriers.
Here we demonstrate an approach aimed at replacing the strongly-bound polymers with variants that can be removed using simple solution-based chemical strategies, resulting in networks with vastly improved energy transport properties. We show that removal of the polymer results in a significant enhancement of the charge carrier mobility and electrical conductivity. Finally, we extend the approach to samples strongly enriched in a single chiral SWCNT species, which allows us to employ transient spectroscopic techniques to probe energy transfer and exciton transport through the SWCNT network with high spectral fidelity. We show that the efficiency of exciton transport is subtly dependent on the complex interplay between polymer removal and carbon nanotube bundling. Our studies highlight a methodology by which high-performance SWCNT thin films can be prepared that could realize their potential for electronic and optoelectronic applications.

Supramolecular chemistry of carbon nanotubes (CNTs) investigates the non-covalent functionalization of CNTs to preserve their pristine physical properties typically by p-pstacking with aromatic compounds, dispersion of CNTs with surfactants and polymer wrapping surrounding the CNTs for applications such as identification coating for biological sensing based on fluorescence and the use of CNTs for drug delivery. In this context, feasibility to use polymeric spacers as dispersant agents to reduce intratubular van der Walls forces requires adequate comprehension of nature and dynamics of the CNT-polymer interaction that will pave the way to inform on pharmacological carrier ability and biocompatibility linked with specific CNTs functionalization procedures.

In this work, a physico-chemical description of non-covalently functionalized multi wall carbon nanotube (MWCNT) with DiI and dimethyl sulfoxide through high-resolution electron microscopy, Raman and Near Edge X Ray Absorption Fine Structure (NEXAFS) spectroscopy has been employed. NEXAFS is a synchrotron tool capable to reveal molecular sensitivity description at interfaces, therefore, suitable to study non-covalent interactions. Furthermore, combination of experimental and constrained density functional theory simulations of NEXAFS spectra to propose a molecular model to analyze charge exchange at CNTs-dispersants (or loaded biomolecules) interfaces has been also applied.

Our findings suggest that incorporation of fluorescent markers does not change the morphological structure on MWCNTs. CH-p bonding with nearby molecules and Hydrogen bonding with external defects and graphitic lattice has been identified as well. Theoretical modelling suggests non-covalent interaction between dimethyl sulfoxide and CNTs.

An understanding of fluid transport within porous micro-and nanostructured materials is important for their use in microfluidic devices. In this paper we investigate the microfluidic behavior of alumina nanotube-based pathways within hydrophobic CNT barriers. These hybrid systems provide unique benefits toward the potential liquid transport control in porous structures with real-time sensing of those fluids. Specifically, we examine how the alignment of the alumina nanostructures with high internal porosity enables increasing the capillary action. Based on the Lucas and Wasburn model (LW) and modified LW models, the microfluidic behavior of these systems is discussed. The predictions from the models for the time exponent for capillary transport in porous media are ≤ 0.5. The experimental results show that the average capillary rise in nanostructured media driven by capillary force followed the L(t) ∼ t^0.7 law. Integration of electronic and microfluidic functions is also presented, taking advantage of the periodic hydrophilic/electrically insulating (pure alumina part) and hydrophobic/electrically conductive (CNT part) microlayers of the structure.

Surface-enhanced Raman scattering (SERS) spectroscopy attracted much attention for the highly sensitive label-free detection of chemical and biological species. A great research effort has been made to fabricate noble metal (Ag or Au) nanostructures incorporating as much as possible Raman hot spots yielding a huge electromagnetic (EM) field enhancement thanks to the excitation of localized surface plasmons at resonance conditions (LSPR). Moreover, taking advantage of the discovery in 2010 of the graphene-enhanced Raman scattering (GERS), graphene based structures are of great interest for Raman-enhanced (bio) sensing due to the chemical enhancement effect attributed to a charge-transfer (CT) process in synergy with the EM mechanism. The reduced Graphene Oxide (rGO) can be a suitable and low-cost graphene based-material that can be assembled in 3-D networks and allows to exploit different routes of chemical and biochemical functionalization (physisorption or chemisorption). It can take advantage from the presence of the residual oxygen atoms or the possibility to establish p-p non-covalent bonding with the graphene layers. In this work, we report on the synthesis and characterization of a hybrid aerogel based on reduced rGO decorated with silver nanoparticles (AgNPs) exploitable for the SERS detection of biomolecules at very low concentration. Several synthesis conditions were approached by exploiting a one-pot hydrothermal process, starting from commercial GO and adding either AgNO₃ as silver precursor with different additives (such as trisodium citrate) or directly a pre-synthesized Ag colloid. The resulting 3-D porous sponge-like nanoarchitecture provides both a high surface area and a homogeneous spatial distribution of AgNPs arranged in order to maximize the Raman hot spots density and thus allowing to concentrate and adsorb biomolecules from highly diluted solutions. By decorating rGO with AgNPs, the synergy of the EM field and CT enhancements can be exploited. The synthesized AgNPs/rGO aerogels were characterized by means of XRD, BET, XPS, FESEM, and TEM in order to single out the best performing aerogels to be processed for biosensing applications. Promising results were obtained in terms of SERS efficiency by using, as probe molecules, Rhodamine 6G, in the 10^-6 M -10^-12 M concentrations range, and 4-Mercaptobenzoic acid, in the 10^-2 M-10^-7 M concentration range. Optofluidic chip were fabricated by coupling the optimized AgNPs/rGO aerogels to Polydimethylsiloxane (PDMS). Then the devices have been successfully functionalized both by thiol-ended oligos and porphyrin-ended biomolecules. These bioreceptor immobilization routes permit the application of the substrates as versatile SERS biorecognition biochips.

Nano-materials based drug delivery modalities to specific organs and tissue have become one of the critical endeavors in pharmaceutical research. Recently, two dimensional graphene has elicited considerable research interest because of its potential application in drug delivery systems. Here we report, the drug delivery applications of PEGylated nano-graphene oxide (nGO-PEG), complexed with a multiphoton active and anti-cancerous diarylheptanoid drug curcumin. Specifically, graphene derivatives were used as nano vectors for the delivery of the
hydrophobic anticancer drug curcumin due to its high surface area and easy surface functionalization. nGO was synthesized by modified Hummer’s method and confirmed by XRD analysis. The formation of nGO, nGO-PEG and nGO-PEG-Curcumin complex were monitored through UVvis, IR spectroscopy. MTT assay and AO/EB staining found that nGO-PEG-Curcumin complex afforded highly potent cancer cell killing in vitro with a human breast cancer cell line MCF7.

Graphene membranes with nanometer-scale pores could exhibit extremely high permeance and selectivity for the separation of gas mixtures. However, to date, no experimental measurements of gas mixture separation through nanoporous single-layer graphene (SLG) membranes have been reported. Herein, we report the first measurements of the temperature-dependent permeance of gas mixtures in an equimolar mixture feed containing H₂, He, CH₄, CO₂, and SF₆ from 22 to 208 °C through SLG membranes containing nanopores formed spontaneously during graphene synthesis. Five membranes were fabricated by transfer of CVD graphene from catalytic Cu film onto channels framed in impermeabile Ni. Two membranes exhibited gas permeances on the order of 10^-6 to 10^-5 mol m^-2 s^-1 Pa^-1, as well as gas mixture selectivities higher than the Knudsen effusion selectivities predicted by the gas effusion mechanism. We show that a new steric selectivity mechanism explains the permeance data and selectivities. This mechanism predicts a mean pore diameter of 3.0 nm and an areal pore density of 5.5×10¹³ m^-2, which is validated by experimental observations. A third membrane exhibited selectivities lower than the Knudsen effusion selectivities, suggesting a combination of effusion and viscous flow. A fourth membrane exhibited increasing permeance values as functions of temperature from 27 to 200 °C, and a CO₂/SF₆ selectivity of > 20 at 200 °C, suggestive of activated translocation through molecular-sized nanopores. A fifth membrane exhibited no measureable permeance of any gas above the detection limit of our technique, 2 × 10^-7 mol m^-2 s^-1 Pa^-1, indicating essentially a molecularly impermeable barrier. Overall, these data demonstrate that SLG membranes can potentially provide high mixture separation selectivity for gases, with CVD synthesis alone resulting in nanometer-scale pores useful for gas separation. This work also shows that temperature-dependent permeance measurements on SLG can be used to reveal underlying permeation mechanisms.

Graphite, in the bulk, is known to form graphite intercalation compounds (GICs) with certain elemental metals, for example, rare earth and alkali metals. These metals can insert between graphene sheets and alter the magnetic or transport properties of graphite. While intercalation in the bulk of graphite has received much attention, considerably less has been paid to intercalation near the surface of graphite, underneath only one (or a few) graphene layers. First of all, can one embed metals just beneath the graphite surface? Do the surface-intercalated metals adopt different structures compared to their bulk counterparts? What is the driving force for such surface intercalation? These are questions we seek to address.

The presentation will encompass strategies for achieving surface intercalation of metals in graphite. In short, embedding metal atoms just beneath the graphite surface requires two specific conditions: (1) ion-induced defects on the graphite surface, and (2) deposition of metals while holding the graphite substrate at elevated temperature. We find that this synthetic route works for a variety of metals, and the growth temperature is metal-specific. Results on dysprosium, copper and ruthenium will be presented. We use scanning tunneling microscopy to probe and characterize the surface intercalation. Based on experimental results and density functional theory, we find that the intercalated metal atoms at the graphite surface adopt very different structures compared to those in bulk GICs. Furthermore, metals that are not known to form bulk GICs can be encapsulated at the graphite surface. Finally, we find that some of the metals are well protected from atmospheric oxidation by the graphene overlayer. Our synthetic strategy opens up a new avenue for metals to interact with the graphite surface, and to create novel surface nano-structures.

Despite no apparent evidence that the electromagnetic exposure to household mobile communication and other emitting devices poses harm to the general public, excessive electromagnetic radiation is of genuine concern for roentgenologists, radar engineers and pacemaker implanted patients. To alleviate such a concern, electromagnetic shielding clothing for these personnel made with thin steel wires are densely woven into cotton fibers. Here, we report a new method of producing copper-reduced graphene oxide core-shell fibers for the fabrication of lightweight electromagnetic shielding fabrics. Based on a simple electroplating process, a thin layer of copper oxide is coated onto the grooved surface of reduce graphene oxide fibers. After subsequent reduction, copper-coated reduced graphene oxide fibers with high electrical conductivity and high flexibility are obtained. A fabric woven with such fibers can provide comparable electromagnetic shielding to fabrics woven with metal wires, yet is appreciably lower in density.

The liquid phase exfoliated graphene nanoflakes are a high-yield and low-cost synthetic method, but the quality of the graphene nanoflakes is not high due to the presence of functional groups and structural defects. Therefore, the ability to improve the crystal structure of the graphene nanoflakes with excellent electrical properties is desirable for its applications in the field of flexible and printed electronics.[1]
In this talk, I will introduce a approach to structure repairing in electrochemically-exfoliated graphene flakes based on annealing with Ni thin film, accompanied by the laterally stitching of the isolated parts to form a continuous and monolithic film.[2,3] After annealing with Ni film, the graphene flakes-derived film has lower defect density, demonstrating that such a process for the crystal structure improvement is extremely effective. At the same time, the newborn-graphene in the space of the isolated flakes would stitch to form a continuous and monolithic film. After the structural repair, the electrical properties of graphene have been greatly improved, and the carrier mobility of graphene is more than 1000 cm² V^-1 S^-1, nearly 10 times higher than that of the process with Cu or 100 times higher than that of graphene via mere annealing. First-principles calculations on the adsorption of Ni and Cu atoms on different kinds of H-saturated graphene edges reveal that the binding energy depends upon the adsorption site, and the Ni case always gives a value 1.5 eV larger than that for the Cu case which is thus beneficial to the removing of edge saturates and allowing for a faster re-growth process. This approach for the graphene with structural design is promising for electronic and flexible applications. [4]
(Thanks to the support of the JSPS KAKENHI Grant Number JP 17F17337. )
References
[1] X.M. Li, et al., Chemical Society Reviews, 2017, 46, 4417-4449.
[2] X.M. Li*, et al., Chemistry of Materials, 2016, 28, 3360–3366.
[3] X.M. Li*, et al., Chemistry of Materials, 2017, 29, 7808-7815.
[4] X.M. Li*, et al., Adv. Funct. Mater., 2016, 26, 2078-2084.

The electrical resistance of reduced graphene oxide (rGO) was found to increase with increasing relative humidity (RH), due to water absorption into rGO and the swelling of its interlayer spacing. This instability creates significant challenges with using rGO as an electronic material, particularly for sensing applications. In order to control its stability in humidity, the carboxyl groups of rGO were covalently crosslinked with ethylenediamine (EDA), as a means of physically limiting the swelling rGO and thus its water absorption. The crosslinked rGO limited the d-spacing increase to 0.0011 nm at >95% RH and 95°C in comparison to that of 0.0113 nm observed in uncrosslinked rGO. Also, after exposure to 95% RH at 37 °C for 2 days, the relative resistance of crosslinked rGO increased by 52% in comparison to 208% for uncrosslinked rGO. The results suggest that crosslinking provides an effective means of stabilizing the resistance of rGO and enabling its robust use in electronic applications.

Since its discovery in 2004, graphene has received enormous scientific interest due to the remarkable two-dimensional structure, making it highly promising for numerous applications. Electrodes in lithium-ion-batteries (LIBs) are one of these applications that could benefit from mechanical strength, high surface area and electrical conductivity of graphene. For the integration in commercial LIBs, it is important to develop simple, cost effective and scalable methods for the production of graphene-like structures. Due to the good dispersibility in water and other polar solvents, graphene oxide (GO) easily forms multi- and monolayers and therefore offers advantageous properties for a green and simple wet-chemical synthesis.
In this study, GO was synthesized and further processed by liquid and gas phase approaches to obtain GO films via pressure filtration with superior mechanical properties and adjustable thicknesses. These paper-like structures of regularly arranged GO flakes were mechanically stable, scalable to mass production and could be used as flexible ultrathin separators in LIBs given their high electronic insulation. Additionally, the sheet-like structure of GO is expected to suppress the polysulfide shuttle effect in lithium sulfide batteries. Moreover, films of its reduced form (rGO) could additionally be incorporated as cathode or anode material, providing several advantages over traditionally used materials. For instance, if used as anodes, these films facilitated an increased volumetric energy density due to a reduction in weight, as additional battery paste components such as current collector, carbon black and binding agent, were no longer necessary. This was supported by the low preparative effort of the freestanding electrode design. Moreover, nitrogen doping of these graphene-like structures via different approaches had been proven successful to increase the electrical conductivity and storage capacity of anodes. Further investigations focused on the influence of nitrogen-integration in the carbon structure on electrical and electrochemical properties. In terms of cathodes, rGO films served as a highly conductive backbone for lithium sulfide/rGO-composites, in which the active material was well-distributed within the carbon matrix. This prevents the agglomeration of lithium sulfide, buffers the volume change during cycling and offers a good accessibility for charge carriers. In this work, the integration of GO and rGO films into LIB half-cells thus demonstrated their exceptional versatility and high application potential.

Reducing energy and material losses in moving mechanical systems due to friction and wear still remain a significant challenge. A monatomically thin layer of graphene deposited onto a surface is known to reduce friction significantly, but graphene is a brittle material so its wear properties are limited. This study investigates the friction and wear of a lamellar metal-graphene-metal composite. We demonstrate a transfer-free material design comprising of monolayer CVD graphene sandwiched between a Cu substrate and a thin Cu film deposited via physical vapor deposition (Cu-Gr-Cu). A series of scratch tests performed on the free surface of the Cu film shows a considerable decrease in coefficient of friction from 0.4 to ~0.12 and an improved wear resistance for the Cu-Gr-Cu laminate. The reduction in coefficient of friction is proposed to be associated with a lower degree of plastic deformation in the Cu-Gr-Cu laminate suggestive of graphene’s ability to impede the propagation of the plastic zone from the copper film to the underlying copper substrate. Weak Beam Dark field Imaging technique (in TEM) confirm lower density of dislocations present in Cu-Gr-Cu laminate when compared to the Cu-Cu laminate thus indicating the effectiveness of graphene in blocking the propagation of the plastic zone.

The mechanical properties of graphene oxide/polylactic acid (GO/PLA) composites were studied to analyze the effect of GO sheet addition on PLA. GO was synthesized through chemical exfoliation and characterized by using FTIR, Raman spectroscopy and SEM. GO/PLA filaments with various compositions were formed using extruder and the mechanical test specimens were prepared from these filaments by two different methods: injection molding and 3D printing. The mechanical properties of polymer/GO composites which were formed through different techniques and with different compositions were compared.

While doping graphene P type is relatively easy, the typical methods of N doping graphene including electrostatic or chemical methods do not achieve high or persistent N doping of graphene when exposed to air. Diffusion of alkali from a semiconductor onto graphene offers a scalable and low cost way of tunably doping graphene N type and has the potential to improve the electrical properties a large range of devices including solar cells, photodetectors, and supercapacitors. The amount and type of alkali diffused from the semiconductor can be varied which can then tune the fermi level of graphene which alters the graphene semiconductor junction's electrical properties. In this study, we investigate the effect of the diffusion of alkali from the semiconductor Cu(In,Ga)Se2 onto graphene on the electrical properties of a graphene Cu(In,Ga)Se2 schottky junction.

Ever since its discovery in 2004, graphene has been extensively investigated for various applications such as energy storage, environmental barrier, biomedical, electronics, etc. The planar graphene sheet is hydrophobic. However, with the change in topology, i.e., defects, wrinkling, etc., we can tune its interaction with water. By performing Molecular Dynamics (MD) simulation, we discovered that water microdroplets containing graphene nanosheet spontaneously segregate into sack-cargo nanostructures upon drying. These cargo-filled nanosacks are promising for many potential applications where nanoscale materials should be isolated from the environment or biological tissue. Besides this, we considered another situation where water diffuses in between graphene and the underlying substrate during its growth process. The diffused water tends to occupy the empty space of the pre-existing wrinkling of small height and keeps pushing the wrinkling to make it bigger. Upon drying, the wrinkling becomes sharper. Our results show that we can tune the density of diffused water and the magnitude of the initial wrinkles to obtain various wrinkled structures after graphene growth. Our simulation results provide guidelines for the experimentalists for efficient design of the graphene-water systems.

In previous work¹ we have calculated the growth of a graphene monolayer, two models emerged as the most favored: for Ga poor conditions a 3sqr3x3sqr3 graphene structure on top of a 4x4(0001) GaN surface and for Ga rich condition a sqr21xsqr21 graphene structure on top of a 2sqr3x2sqr3 GaN(0001) Gallium double bilayer² with a -1.10% and -0.72% mismatch respectively. The gallium rich model exhibit a magnetic moment of 0.19 Bohr magnetons/cell whereas the stable structure for Ga poor conditions does not presents magnetic behavior. Later we added a second graphene layer with the goal to find defect free epitaxial growth, which could serve as a basis to introduce defects or doping it with the best suited elements in such a way that we will be able to fine tuning a band gap. We also made simulations of scanning tunneling microscope (STM) that revealed a long distance buckling interaction between both layers. Our calculations were based on the plane wave periodic density functional theory and the Tersoff-Hamann formalism for simulating STM images. In this work we are analyzing what is happening when a graphene monolayer approach to the GaN surface and then when a second graphene layer comes closer to the first one, we plot the energy as a function of the interlayer separation distance and the kind of GaN surface. In this fashion we get potential energy surfaces (PES), which allow us to simulate how the graphene monolayer behaves when it is growth in a less than ideal substrate and what happens to the graphene buckling in the grain frontier. The electronic properties of these systems are studied by calculating the band structure and the density of states. The calculations are performed by Density Functional Theory as implemented in the PWscf code of the Quantum ESPRESSO package. The data are not fully analyzed yet as the work is still in progress. Acknowledgments: DGAPA project IN114817. The authors are grateful to A. Rodriguez for his technical assistance. Calculations were performed at the DGCTIC-UNAM under project LANCAD-UNAM-DGTIC-150.
References
1. Espitia-Rico, M.; Rodríguez-Martínez, J.A.; Moreno-Armenta, M.G.; Takeuchi , N., Applied Surface Science 326 (2015) 7–11
2. J.E. Northrup, J. Neugebauer, R.M. Feenstra, A.R. Smith, Phys. Rev. B 61 (2000) 9932.

The Langmuir-Blodgett technique is one of the most controlled methods to deposit monomolecular layers of floating or surface active materials but has lacked the ability to coat truly large area substrates. In our work, by manipulating single layer dispersions of graphene oxide (GO) and other 1D or 2D materials (ex. molybdenum disulfide, reduced graphene oxide, CNTs etc.) into water-immiscible spreading solvents, unlike traditional Langmuir-Blodgett deposition which requires densification achieved by compressing barriers, we demonstrate the ability to control the 2D aggregation and densification behavior of these floating materials without the use of moveable barriers. This is done by controlling the edge-to-edge interactions through modified sub-phase conditions and by utilizing the distance-dependent spreading pressure of the deposition solvent. These phenomena allow substrates to be coated by continuous deposition and substrate withdrawal – enabling roll-to-roll deposition and patterning of large area substrates such as flexible polyethylene terephthalate. The aggregation of GO sheets into 2D domains under various sub-phase conditions were examined by in situ Brewster angle video microscopy. Moreover, by measuring the local spreading pressure using a Langmuir-Adam balance we conclude that the densification phenomenon of deposited sheets is induced by the spreading solvent acting on the floating materials. This allow us to engineer the film density by easily changing the spreading solvent. As an example, the performance of films deposited in this way are assessed as passivation layers for Ag nanowire-based transparent conductors.

Graphene is regarded as a potential material for many application fields due to its unique electrical, mechanical, and thermal properties. Since its first isolation in 2004, growing interest has evolved in the development of facile and scalable synthesis routes. So far, some groups already investigated synthesis techniques towards environmentally-friendly and catalyst-free graphene production from methane or ethanol based on plasma technology, however, the variation carbon precursors is only rudimentarily investigated so far.
In this paper, we present a facile synthesis method for preparing free-standing few-layer-graphene (FLG) by gas-phase pyrolysis carried out in a microwave plasma reactor. This scalable synthesis route can produce highly pure carbonaceous nanostructures with production rates up to several g/h, depending on the precursor used. However, it is still unclear which precursor requirements have to be fulfilled for the formation of high-purity graphene avoiding the formation of byproducts.
Five gaseous and eleven liquid hydrocarbons have been tested in order to identify prerequisites for graphene formation. The materials have also been processed to investigate the growth process and the microstructure of the respective products. The samples have been characterized by X-ray diffraction, Raman-, four-point conductivity measurements, XPS, TEM and BET. The results indicate that the gas-phase generated samples show either FLG, or graphitic particles or soot-like particles or composites containing two or all of them following no straight dependency. However, it was observed that only precursors with certain C:H:O-ratios like ethanol, acetone and isopropanol can deliver graphene in a good quality while oxygen-free precursors with a relatively high C:H-ratio like toluene and acetylene lead primarily to soot-like particles.
All other used precursors with different or same C:H:O- and C:H-ratios tend to produce composites containing besides graphitic particles, FLG and soot-like particles at the same time. The best samples made from ethanol show highly pure surfaces and highly ordered FLG with superior electrical conductivity of more than 4000 S/m.

3-D graphene or graphite foams (GFs) have received immense research attention owing to their superior electrical, mechanical, and thermal properties. Extensive applications of such 3-D GFs have been demonstrated in energy, environment, health, and biomedical research. This work presents an innovative mechanism, the Kirkendall effect, in creating 3-D microporous catalysts with tunable pore sizes for the growth of multilevel porous graphite foams (MPGFs) that offer higher crystallinity, electric conductivity, larger surface area as well as electric invariance to strains compared to conventional GFs. Based on MPGFs, another new type of ramified porous graphite foams (RPGFs) made of strategically created superstructures with covalently-attached diverging microtubes have also been synthesized. Such RPGFs exhibit even higher surface areas than MPGFs, which allows for efficient loading of active pseudocapacitive materials when applied as supercapacitor electrodes. We also integrate the RPGF-based flexible supercapacitors with a nanomotor manipulation system into a portable and self-powered device, which readily compels Au nanomotors to transport along arbitrary trajectories, e.g., tracing letters of “U” and “T”.

Biphenylene carbon (BPC), also called graphenylene, is a hypothetical porous two-dimensional (planar) allotrope carbon [1] that can be obtained from selective dehydrogenation of porous graphene [2]. The BPC molecular geometry consists of an one-atom thickness sheet with regular dodecagonal pores of diameters of 3.2 Å. Its pores resemble typical sieve cavities and/or some kind of zeolites. An open question is if the BPC natural porosity gives a selective permeability property that can lead to promising technological applications, such as gas separation. In this work, we have investigated the permeability and selectivity of natural gases such as CO2, H2, N2, CH4, and CO though BPC membrane. Fully atomistic Molecular Dynamics simulations were performed to predict the gas adsorption and the gas permeability of single components, and separation mechanism of binary gas mixtures. The simulation system is composed of single BPC sheet into contact with a gas reservoir under different thermodynamics conditions (e. g. T, P). We have systematically analyzed the permeability of each gas and the molecular arrangements on the adsorbed layers after the flux is stabilized. The selectivity is also quantified for CO2/H2 (50:50), CO2/N2(15:85), CO2/CH4 (50:50), and CO2/CO (50:50) mixtures and the mechanism of gas diffusion is also discussed. The BPC porosity can be exploited to pressure tune gas selectivity. Our results show that BPC exhibits high H2 selectivity, ideally for hydrogen purification.
[1] R. H. Baughman, H. Eckhardt e M. Kertesz, J. Chem. Phys. 87, 6687 (1987).
[2] G. Brunetto, P. A. S. Autreto, L. D. Machado, B. I. Santos, R. P. B. dos Santos, and D. S. Galvão, J. Phys. Chem. C, 116, 12810−12813 (2012).

Human sensory-mimicking systems, such as electronic brains, tongues, skin, and ears, have been promoted for use in improving social welfare. However, no significant achievements have been made in mimicking the human nose due to the complexity of olfactory sensory neurons. Combinational coding of human olfactory receptors (hORs) is essential for odorant discrimination in mixtures, and the development of hOR-combined multiplexed systems has progressed slowly. Here, we report the first demonstration of an artificial multiplexed superbioelectronic nose (MSB-nose) that mimics the human olfactory sensory system, leading to high-performance odorant discriminatory ability in mixtures. Specifically, portable MSBnoses were constructed using highly uniform graphene micropatterns (GMs) that were conjugated with two different hORs, which were employed as transducers in a liquid-ion gated field-effect transistor (FET). Field-induced signals from the MSB-nose were monitored and provided high sensitivity and selectivity toward target odorants (minimum detectable level: 0.1 fM). More importantly, the potential of the MSB-nose as a tool to encode hOR combinations was demonstrated using principal component analysis.

Recent progress in nanoscale self-assembly has led to the realization of 3D nanostructures with unique optoelectronic properties through a surface tension driven self-folding of diverse 2D graphene patterns. The self-assembly of 2D patterned graphene can yield 3D micro/nanoscale polyhedrons such as closed and open cubic structures with free-standing 2D materials (graphene or graphene oxide) acting as faces of the cube. Self-assembly is a versatile technique that can realize 3D graphene cubes of dimensions ranging from 100 nm to 200 µm. Here, we present simulation and measurement results to study of the optical properties of nanocubes at their plasmon resonance as well as the off-resonance broadband properties of the micro and nanoscale graphene cubes. At a nanoscale, the uniform plasmon coupling in 3D graphene nanocubes gives rise to hybridized modes with strong enhancement of the incident electric (E)-field. The hybrid modes demonstrate large area hotspots of constant field enhancement with a much slower decay of the field away from the surface, giving rise to a volumetric field that is 2 orders of magnitude stronger than that in 2D ribbons. Moreover, even in the absence of plasmon resonance such as in 200 µm sized 3D graphene cubes, the rippled geometry induces a strong absorbance of 2-40% over the entire measured wavelength of 1-10 µm. Fourier transform infrared (FTIR) spectroscopy of the 3D graphene microcubes and Comsol Multiphysics simulations reveal that the angle of incidence, number of graphene layers, and the ripple geometry can be modified to tune the absorbance in 3D graphene over a wider range than in 2D graphene. Thus, the 3D free-standing graphene cubes offer an opportunity to overcome the weak ~3% broadband absorption in 2D planar graphene. The highly confined volumetric field within the nanocubes and strong tunable absorption in graphene microcubes provide an opportunity for the development of non-contact ultrasensitive 3D plasmonic sensors and devices with a larger active area and higher efficiency.

A surface-tension driven self-folding mechanism has led to the realization of diverse self-assembled 3D architectures from patterned 2D ribbons, such as graphene-based pyramids, tube, and cubes. The 3D graphene geometries exhibit distinct plasmon hybridization that cannot be excited in 2D graphene ribbons as a result of plasmon coupling over an extra spatial degree of freedom. However, a detailed systemic study of the plasmon coupling in 3D graphene geometries needs to be performed in order to efficiently utilize the hybrid plasmon modes for desired optoelectronic applications. We have investigated the plasmon coupling and found thathe coupled plasmonic field enhancement in these 3D geometries is strongly dependent on the 3D shape, number of 3D edges, and surface angle of inclination. The uniform coupling in graphene nanocubes gives rise to large circular areas of constant field enhancement. Moreover, if the edges of the nanocubes are spatially separated by nanometer distances, circular field interference patterns are obtained with alternate rings for constructive and destructive coupling. The circular surface enhancement modes in 3D graphene nanocubes can be leveraged for novel optoelectronic applications. In contrast, the square graphene pyramids undergo a strong point enhancement at the apex of the pyramid arising from the inclined tapering faces meeting at the apex. The strong point enhancement propagates throughout the nanopyramid resulting in a volumetric field that is several orders of magnitude higher than in 2D graphene ribbons. Furthermore, as the number of faces and edges are increased to form pentagonal to octagonal pyramids, the point based enhancement can be transformed to uniform surface enhancement at the base of the pyramids. Thus, allowing geometrical parameters in the nanopyramids to be utilized for designing high-sensitivity plasmonic sensors that can assess low concentration analytes in the bulk volume of targeted solution or the molecular surface binding properties at higher analyte concentrations. The graphene tube consisting of only 2 edges existing at the openings of the tube, a virtual hotspot area of extremely high near-field enhancement is created due to radial plasmon coupling at the small opening of the tube. The completely sealed tube demonstrates a strong hotspot, but, the hotspot covers only 13% of the volume of the tube. However, if the nanotubes are fabricated with small slits, the strongly coupled field exists throughout the tube structure giving rise to strong volumetric field. The volumetric field in nanotubes is especially desirable due to their open-ended geometry that can be leveraged for assessing targets flowing through the 3D tube. The self-assembled 3D graphene structures can be varied geometrically to achieve diverse point, edge, surface, and volumetric enhancement modes for achieving plasmonic devices exhibiting increased sensitivity and efficiency, and a high packaging density.

Carbon nanoscrolls (CNSs) are families of carbon-based nanomaterials, where unlike the closed carbon nanotubes, their geometrical aspect is like graphene layers rolling up into a spiral (papyrus-like) form. They have been extensively (theory and experiments) studied [1,2,3]. Due to its open-end topology, where the diameter can be easily varied make them ideal for applications such as hydrogen storage, actuators, tunable water channel, etc. Most of the theoretical works have considered single layer structures; there are only few works on multi-layered scrolls [4]. In this work we have investigated, through fully atomistic reactive (ReaxFF) molecular dynamics simulations, the dynamics formation and structural stability of scrolled structures formed from bi-layer graphene nanoribbons. We have also considered these structures interacting with carbon nanotubes, which has been used as a ‘trigger’ to start the scrolling process [5]. Our results show that stable (up to high temperatures ~1000 K) structures can be obtained. We did not observe the formation of covalent bonds between layers and/or carbon nanotubes for the temperature range investigated.
[1] R. Bacon, J. Appl. Phys. 31, 283 (1960).
[2] D. Xia et al., Small 6, 2010 (2010).
[3] E. Perim, L. D. Machado and D. S. Galvao, Front. Mater. 1, 31 (2014).
[4] A. V. Savin, S. V. Dmitriev, E. A. Korznikova, and A. A. Kistanov, Mater. Phys. & Mech. 35, 155 (2018).
[5] E. Perim, R. Paupitz, and D. S. Galvao, J. Appl. Phys. 113, 054306 (2013).

Over the past few decades, the fiber-based industry has achieved great progress in aerospace, military and many other industrial applications that require light-weight materials with high mechanical strength. As the demand for electronic devices has exponentially risen in recent years, the preparation of highly conductive fibers has become an important subject in the fiber industry. Low dimension carbon fibers such as carbon nanotube and graphene fibers may be an important material in advancing next-generation high-tech applications if their intrinsic mechanical, electrical and thermal properties can be maintained. By strategy of dopamine infiltration, oxidative polymerization and pyrolysis, we successfully fabricate low-dimension carbon composite fibers with remaining their intrinsic properties. The approach described herein presents a novel fabrication process that can enhance both the mechanical and electrical properties of low-dimension carbon based fibers.

We report the dielectrophoresis (DEP)-based deposition and alignment of semiconducting carbon nanotubes and the fabrication of carbon nanotube-based electronic devices. Semiconducting carbon nanotubes, which were dispersed ultrasonically in solutions, were deposited and aligned onto a pair of gold electrodes using the electric-field-directed dielectrophoresis method. The DEP-aligned tubes were further fabricated into carbon nanotube field-transistors (CNTFETs) and CNTFET-based electronic devices such as CNT-based inverters and ring oscillators using the microfabrication techniques. The aligned carbon nanotubes and fabricated devices were imaged using the scanning electron microscope (SEM), and the electrical properties were measured from the fabricated devices using the semiconductor analyzer. The semiconducting CNTs achieved higher yield in the device fabrication, and the fabricated electronic devices demonstrated excellent electrical properties.

Charge carriers in freely suspended graphene can travel very fast (mobility ~200 000 cm²/V-s at 5K), but the reported values for large-area CVD graphene transferred on arbitrary substrate is several orders of magnitude lower, which has been attributed to the polycrystalline nature, surrounding medium, polymer residues, and wrinkles in graphene. The latter two factors were engendered by the polymer-assisted graphene transfer process. Here, we report a new wax-enabled graphene transfer technique that concurrently addresses the polymer residues and graphene wrinkles issues. Compared to poly (methyl methacrylate) (PMMA), the chemical structure of wax is much simpler and does not contain carbonyl (C=O) group, which is reactive to electrophiles or nucleophiles. Our density functional theory calculations further indicate that the adsorption energy of wax is 1.56 kcal/mol times lower than PMMA and wax radicals are not stable while PMMA radicals are stable enough to form covalent bonding with graphene. Remarkably, for graphene transferred with wax support layer, we observe not only much lesser polymer residues, but also a substantial wrinkle reduction in graphene surface, compared to that of PMMA, through atomic force microscopy studies. Field-effect transistors fabricated on wax-assisted transferred graphene shows the Dirac voltage is closer to zero and 2-fold higher electron mobility compared to that of PMMA. In short, wax-assisted transfer process opens a new avenue for the development of graphene-based electronics by minimizing charge carrier scattering centres in graphene (i.e. polymer residues and wrinkles in graphene).

Microcrystals composed of the conjugated organic molecule perylene can be encapsulated beneath single layer graphene using mild conditions. Scanning electron and atomic force microscopy images show that the graphene exists as a conformal coating on top of the crystal. Raman spectroscopy indicates that the graphene is only slightly perturbed by the underlying crystal, probably due to strain. The graphene layer provides complete protection from a variety of solvents and prevents sublimation of the crystal at elevated temperatures. Time-resolved photoluminescence measurements do not detect any quenching of the perylene emission by the graphene layer, although nonradiative energy transfer within a few nanometers of the crystal-graphene interface cannot be ruled out. The ability to encapsulate samples on a glass surface under a graphene monolayer may provide a new way to access and interact with the organic crystal under ambient conditions.

We report behavior of a H₂O molecule inside a heterogeneous carbon nanotube/boron nitride nanotube (CNT/BNNT) structure. We have investigated energetic and electronic properties of our model system using density functional theory calculations. Considering the van der Waals interaction, we used Grimme’s DFT-D2 method implemented in the VASP package. For the model structure, the (7, 7) CNT and BNNT were chosen. The equilibrium distance between a water molecule and the CNT (BNNT) wall was calculated to be 3.3 Å (3.1 Å). In the CNT (BNNT), the energy of the water molecule was 103 meV lower (122 meV lower) at the center of the tube, and was 226 meV lower (257 meV lower) at the equilibrium position in the tube than in vacuum. The potential profile along the tube axis shows a dramatic change around the heterojunction. We plotted the projected density of states (PDOS) of hydrogen and oxygen atoms in the water molecule in the tube to check whether the orbital hybridization changes between the tube wall and the H₂O molecule, depending on the location of H₂O. The PDOS shows ~1 eV downshift in the DOS peaks of O and H atoms to the deeper valence bands when the H₂O molecule is in the (7, 7) BNNT than in the (7, 7) CNT.

Two-dimensional (2D) nanosheets such as those of transition metal di-chalcogenides (TMDs) have become attractive due to the unusual properties associated with their ultrathin structure. Development of applications for these materials have been limited by the lack of a simple method to exfoliate them in single or few-layer flakes in large quantities. In this work, an exfoliation route of 2D materials such as graphotic boron nitride (hBN) using mechanical milling in solid state (cryomilling) and sonication was performed. Materials were cryomilled during 30 min and liquid sonicated. A reduction in particle size of the powders materials after cryomilling was observed and a possible disorder of layers was evident because of the decrease in the intensity of the characteristic peak of the plane (002) in DRX patterns. After sonication process, the incorporation of 2D nanosheets in previously modified polymers by pyrene group, promoted changes in the optical, thermal and mechanical properties of i.e. polypropylene. The thermal diffusivity of thecomposite increased when the non-covalent compatibilizer was incorporated into the polymer even at low level of hBN concentration.

Spintronics is the fusion field of electronics and magnetics, and have attracted much attention from physical and practical viewpoints, because both electric charge and spin of electrons are utilized simultaneously. giant magnetoresistance (GMR) and tunnel magnetoresistance (TMR) effects have been the main principles of spintronics devices such as magnetic heads and magnetic random access memories (MRAM), which use changes in the electrical resistance accompanied by switching between parallel and antiparallel magnetization alignments. These phenomenon are occurred in trilayered spin-valve junctions composed of top and bottom ferromagnetic layers and a nonmagnetic interlayer. Therefore, spin-valves are suitable for investigating the spin-transport potential of interlayer materials due to the simple structure. It is expected that materials composed of light elements possess long spin-transport lengths due to weak spin-orbit interactions. Thus far, we have investigated structurally and electrically investigated ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C:H) composite (UNCD/a-C:H) films. They comprise a large number of nano-sized diamond grains embedded in an a-C:H matrix, and have the following merits: (i) the production of p- and n-type conduction accompanied by enhanced electrical conductivities is possible by boron and nitrogen doping, respectively; (ii) they can be grown on foreign solid substrate; (iii) they can be grown at low temperature even on unheated substrates. Therefore, UNCD/a-C:H prepared by CAPD can be expected as a new candidate for a spin-transport material. Thus far, we have studied artificial lattices and spin-valve junctions comprising ferromagnetic Fe₃Si and semiconducting FeSi₂. In this study, based on experimental techniques in the previous studies, spin-valve junctions comprising B-doped UNCD/a-C:H interlayers and ferromagnetic Fe₃Si and Fe layers were fabricated by a mask method, and they were structurally studied. Fe/B-doped UNCD/Fe₃Si trilayered films were deposited on a p-type Si (111) substrate. The bottom Fe₃Si layer and the top Fe layer were deposited by facing target direct current sputtering (FTDCS) apparatus and B-doped UNCD/a-C:H was deposited by coaxial arc plasma deposition (CAPD) equipped with a 10 at. % B-blended graphite target. The microstructure was investigated by scanning transmittance electron microscopy (STEM). The magnetization curves of the junction measured at room temperature using a vibration sample magnetometer (VSM). From STEM image of the spin-valve junctions, it is confirmed that the UNCD/a-C:H interlayer exists in layer between the Fe and Fe₃Si layers. From magnetization curves, it was observed the shape of the magnetization curve has clear two steps, which implies UNCD/a-C:H layers effectively act as interlayers between the Fe and Fe₃Si layers without interdiffusion. The electrical properties of the spin-valve will be reported at the conference.

Ultrafast fluid transport through the core of single-wall carbon nanotube (SWNT) channels promises to advance membrane applications, from efficient water purification and low-cost separation of high-value components, to next-generation protective garments.¹ As we seek to further enhance the performance of CNT-polymer composite membranes for the latter application, we target vertically-aligned SWNT “forest” growth toward: a) minimizing SWNT diameter to maximize protection via size exclusion; b) maximizing SWNT number density to maximize breathability; and c) scaling up SWNT growth area to eventually incorporate into garments.
We performed low-pressure chemical vapor deposition (CVD) in an AIXTRON^® Black Magic cold-wall furnace, featuring a wafer-scale, local heater stage and gas showerhead. The combination of a low flux of carbon precursors with sub-nm Fe/Mo catalyst films on alumina-coated Si wafers maintains small-diameter SWNTs. High-resolution TEM and X-ray scattering² confirm that our forests contain >99% SWNTs below 4 nm diameter (on wafers up to 4 inches). We combined Rutherford backscattering spectroscopy and AFM to reveal that 8 at% Mo optimally preserves small, densely packed particles, templating growth of forests with high number densities up to 2.2x10¹² cm^-2. Wafer-scale growth from Fe films of equal thickness in the absence of Mo possess SWNT diameter distributions with larger means and tails, which are detrimental to membrane rejection properties. While tuning the Fe thickness down does render smaller diameters, the range of densities grown from these Fe-only films is 0.2-0.6x10¹² cm^-2, regardless of thicknesses studied (0.35-0.65 nm). Furthermore, we explored the catalyst-dependent growth enhancement as a function of H₂O vapor concentration added to the growth ambient (120-1500 ppm) and leverage this understanding to establish robust, uniform wafer-scale growth from Fe/Mo across sequential runs (up to 6).
There remains a currently inaccessible regime of the multi-dimensional parameter space that co-optimizes uniformly large-area growth of small, monodisperse, dense, and sufficiently long SWNTs for high-performance membranes. However, our developments in synthesis represent to our knowledge best-in-class co-optimization of small-diameter, high-density, and large-area SWNT forest growth.
`
1. Bui, N.; Meshot, E. R.; Kim, S.; Peña, J.; Gibson, P. W.; Wu, K. J.; Fornasiero, F., Ultrabreathable and Protective Membranes with Sub-5 nm Carbon Nanotube Pores. Advanced Materials 2016, 28 (28), 5871-5877.
2. Meshot, E.; Zwissler, D. W.; Bui, N.; Kuykendall, T. R.; Wang, C.; Hexemer, A.; Wu, K. J. J.; Fornasiero, F. Quantifying the Hierarchical Order in Self-Aligned Carbon Nanotubes from Atomic to Micrometer Scale. ACS Nano 2017, 11 (6), 5405-5416.

Advanced nanoengineered composites are a promising approach towards improving the mechanical performance of filamentary composites and adding multifunctionality into lightweight structures and vehicles. In particular, the integration of carbon nanotubes into composites through the circumferential growth of radially aligned carbon nanotubes (a-CNTs) onto microfibers has already demonstrated improvements in interlaminar fracture toughness, interlaminar shear strengths, and electrical/thermal conductivities of alumina fiber composites.
However, the implementation of this “fuzzy fiber” reinforced plastic (FFRP) architecture onto high performance carbon fibers (CFs) desired for demanding applications, has been met with microfiber strength loss and effectively trades off in-plane strengths for through-thickness
property improvements. This work presents an approach to growing high yields of CNTs on carbon fabrics to improve interlaminar properties while preserving the carbon fiber properties. Using a low temperature chemical vapor deposition (CVD) approach and a scalable method of catalyst deposition onto filaments, CNTs were directly grown on unidirectional (UD) carbon fabrics to form UD fuzzy CFs plies. Building on previous developments of woven fuzzy carbon fiber reinforced plastic (CFRP) laminates, vacuum assisted resin infusion was used to manufacture UD fuzzy CFRP laminates that have low interlaminar spacings (<15 μm) to increase the CNT fill fraction in the weak interlaminar region, and isolate CNT reinforcement effects. Both UD baseline CFRP and UD fuzzy CFRP were manufactured using a vacuum assisted resin infusion system with interlaminar spacings and laminate quality assessed through X-ray microcomputed
tomography. Transmission and scanning electron microscopies reveal conformal CNT growth around carbon filaments prior to matrix introduction. Thermogravimetric data also shows the removal of the polymeric sizing layer on carbon fibers and the thermoplastic weft (that holds the CF tows together) through CVD processing and consequently informs matrix interface changes as well as process bounds for ensuring ply handleability. Further, short-beam shear testing data of UD fuzzy CFRP are presented, showing a 4% improvement in interlaminar shear strength. Thus, this work is an important step towards realizing hierarchical carbon fiber composites with improved interlaminar properties without compromising in-plane strengths, and provides a platform for future CNT growth optimization that may result in even larger property enhancements.

The fine particles having fluorescent property is currently used as important chemical sensing. However, these materials are synthesized by complicated preparation processes or using precious metals as raw materials. In this paper, we report a simple preparation method of fluorescent nanoparticles based on self-assembling polymerization of aromatic monomers.
The fluorescent polymer particles are prepared using 2,6-dihydroxyanthracene and 1,3,5-trimethylhexahydro-triazinane as monomers by microwave heating process. Solid components were obtained from the reaction solution after an appropriate heating time by centrifugal separation. The obtained particles were spherical in shape, confirmed by Transmission Electron Microscope. The size of particle can be controlled within the range of the nano to submicron scale by changing the reaction conditions. The obtained particles are well dispersed in water. The optical property of particle was evaluated by UV-vis and fluorescent spectra in water at pH7. The particle has specific absorption band around 500 nm, which is not observed in monomer. And the particle shows fluorescent spectra around 600 nm, while the monomer shows in around 450 nm. The storks shift of particles is about 200 nm.
Furthermore, we will also discuss the correlation between chemical structure and particle function in detail from infrared, Nuclear Magnetic Resonance spectroscopy and elemental analysis result.

One of the attractive carbon nanotube (CNT) features is its capability for water transport and purification. Many experimental and theoretical work were dedicated to studying nanofluid delivery via CNTs. However, most conventional methods seem to be inefficient and complicated. The goal of this work is to further develop a new efficient approach for fluid pumping at nanoscale level (i.e., nanopumping) using Rayleigh surface acoustic (traveling) waves propagating on the nanotube walls. In our previous studies [1-4], the nanopumping effect triggered by Rayleigh travelling waves was predicted by molecular dynamic (MD) simulation of simple gases H₂, He, placed inside single layer CNTs. Propagations of surface acoustic waves (SAW) were studied at various frequencies and amplitudes on the CNT walls and interaction of CNT-walls with gas inside the tubes were demonstrated. An average axial velocity of the gas molecules reaching 20 km/s were obtained [1].
In present work, a large scale MD simulation package (LAMMPS) was used to verify that the nanopumping effect also exists in liquid water placed in CNT. Two monolayer graphene sheets with holes consistent with the CNT's diameter were placed in both ends of nanotube along axial direction of the nanotube, preventing water permeation outside of the CNT. Water molecules were placed in a left chamber with a volume of 13500ų containing 1188 water molecules. A TIP3P water model was used in all simulations. The dimensions of simulation box were 44 x 44 x 160 ų and the boundaries were fixed with reflecting walls in all three dimensions. In our simulation, surface acoustic wave propagation was induced by a cosine wave equation.
Our results without SAW showed that water molecules were not experiencing imbibition into CNT. Application of Rayleigh surface travelling waves on CNTs, however, significantly accelerate water motion. The frequencies of SAW applied to CNT walls were varied from tens of MHz to tens of THz. The results of our simulations demonstrated that water molecules passed through CNTs and exited from the other CNT side. The efficiency of the nanopumping model was estimated. Water flow rate defined as a number of water molecules passing through CNT per time and area units, and the total flux of water were calculated depending on the SAW frequency for 100, 300, and 500 Å CNTs lengths.

[1] Z. Insepov, D. Wolf, A. Hassanein, Nanopumping using carbon nanotubes, Nano Lett., Vol. 6, No. 9, 2006
[2] Z Insepov, A Hassanein, Method for nanopumping using carbon nanotubes, US Patent 7,632,482;
[3] Z Insepov, A Hassanein, Method and system for small scale pumping, US Patent 7,651,673.
[4] Z Insepov, R. J Miller, Activation of nanoflows for fuel cells, J. of Nanotechn. in Engin. and Med. 3 (2012) 025201.

Applications of electromechanical probing for wafer testing progressively require smaller pitches, reliable and reproducible manufacturing and lower electrical contact resistances. Current electromechanical testing probes, for instance MEMS based vertical cantilever probes, have fundamental limitations in terms of the shortest pitch that can be achieved, cost and efficiency. The exceptional mechanical and electronic properties of carbon nanotubes (CNTs) make CNTs a promising candidate material for electromechanical probing applications. We synthesise vertically-aligned CNT structures by combining photo-thermal chemical vapour deposition (PTCVD) and photolithography and assemble them into a new type of metal-CNT-Polydimethylsiloxane (PDMS) composite structure for possible probing applications at both wafer-level chip-scale packaging (WLCSP) and wafer-level packaging (WLP) testing. Up to 600 µm tall, CNT-based vertical micro-spring type probes are demonstrated. We propose a design and architecture with a scalable approach, allowing for the assembly of thousands of probes in short manufacturing times, with easy pitch control that can facilitate testing at WLCSP and WLP packaging.
Extra-long (>600 µm), vertically-aligned CNT probes are grown at high process temperatures and pressures, at rates up to 50 µm/min. The CNTs are metallic, multi-wall carbon nanotubes (MWCNTs) and are of good quality (I_D/I_G < 0.3). As-grown CNT probes are transferred to PDMS and metallised with Au, Pd and Cu to form a composite-like probe structure; with CNTs, acting as current carrying channels as well as micro-springs, providing good elasticity without compromising from the electrical conductance and a metal scaffold that stiffens the structure, whilst decreasing the overall contact resistance. Cyclic electromechanical characterisation of CNT-based probes showed reproducible contacts for up to 10,000 cycles, with a 50 µm compliance. For a 200 µm x 200 µm probe cross-sectional area, an average of 0.7 Ω contact resistance is achieved. Low contact resistance is realised by vertically-aligning CNTs, differing the combination of metallisation layers to obtain a good work function matching and wetting at the metal-nanotube interface. In addition, up to 16% compliance is observed and the mechanical failure mechanism is identified as micro-crack induced buckling in the plastic region.
Overall, we demonstrate a scalable CNT-based micro-spring probe design as an alternative candidate to complex MEMS-based vertical cantilever probes for wafer probing applications at wafer level. Fabrication process can easily allow small pitch probes with minimal layout restrictions without compromising from electrical and mechanical properties. In addition, properties such as: stiffness, probe length and probe resistance are tunable via PTCVD deposition and metallisation processes allowing a wider range of probing applications.

Graphene is considered as one of the most promising anti-ballistic materials due to its high strength, stiffness, and low density. While its low-rate behavior has been studied for years, there are few experimental investigations at the high-strain-rate regime. By the observation of micro-spheres penetrating through free-standing graphene membranes in air, Lee and his colleagues (Science 346, 1092 (2014)) directly characterized mechanical properties of multilayer graphene at very high strain rates (~10⁷ /s). Their microscopic ballistic study demonstrated that the specific penetration energy of multilayer graphene was more than 10 times larger than that of steel for 600 m/s impact in the air. Independent numerical studies, however, predicted one order higher specific penetration energy than the experimentally measured value. A thickness effect was brought up to explain this discrepancy, as in modeling, a series of monolayer graphene was more efficient in energy dissipation than multilayer graphene with a same total mass. Moreover, aerodynamic effects of air were also suggested since the numerical simulations were carried out without introducing gases.
For more precise quantification of the high-strain-rate properties of graphene, we have performed the micro-ballistic characterization in vacuum. Since the vacuum level is approximately 1/3,000 of the atmospheric pressure, undesired effects from air, including aerodynamic friction of a projectile and a membrane specimen, become negligible. As a projectile, 3.7 μm diameter silica sphere is accelerated and a suspended graphene membrane is subjected to projectile’s impact. With an ultrafast microscopic imaging system (up to 40 million frame per second), accurate velocities of the projectile before and after penetration are obtained. The specific penetration energy are directly calculated by the ratio of kinetic energy loss of the projectile and the mass of the membrane within the direct impact area of the projectile for different projectile’s velocities (100 – 1,000 m/s) and specimen’s thicknesses (10 – 100 nm). Post-mortem optical micrographs and electron micrographs are taken to measure the total crack length, crack number, and penetration area to explore their relationship with the penetration energy. The fine penetration features near the impact region are mainly examined by scanning electron microscopy.

Micro/nanolenses of alkali metal halides are unique optical components that partially overcome the limitations of existing ones because of their hygroscopicity, solubility in water, tuneable refractive indices, excellent transmittance from UV to infrared, and high mobility of the constituent ions under an electric field. Forming such lenses and arranging them in a well-defined manner, however, remains a challenge. Here we demonstrate selective decoration of array of micro/nanolens along single-walled carbon nanotubes (SWNTs) using various salt species, which can be migrated along exterior of SWNT under an electric field. The lenses are promising for use in both the optical visualization and spectral amplification of underlying individual nanotubes. The lenses help detect molecular species located onto sidewall of a nanotube, such as amorphous carbon and diazonium that are not easily detectable using existing approaches. In addition, molecules dissolved in the solution can be captured within the lenses via exterior transport and then detected by Raman spectroscopy. Such lenses can be easily removed by a simple water rinse without degrading the properties of SWNTs. Thus, our approach will serve as a useful tool for the non-invasive visualization of nanostructures and spectral amplification of various molecular species.

In this study, the exterior of single-walled carbon nanotubes is shown to preferentially migrate cations over a millimeter length scale. Applying an electric field to droplets of NaCl placed at both ends of the nanotubes causes the transport of a cation-enriched solution along the nanotubes in the direction of the electric field, while the anion-enriched solution counter-migrates along the adjacent substrate. This phenomenon is confirmed by Kelvin probe force microscopy and mass spectrometry imaging of individual nanotubes, as well as formation of bright and dark lines along the nanotubes in scanning electron microscopy (SEM). Blocking the exterior of the nanotubes prevents both the bright/dark lines in SEM and flow of current through the nanotubes, confirming the insignificance of interior ion transport and electron current. The cation-preferring transport results in the formation of positively charged salt crystals along the nanotubes (with a cation-to-anion ratio of 0.59:0.41 for KCl) followed by the subsequent shrinkage and growth of crystals in the direction of cation flux. Molecular dynamics simulations shows that cation–π interaction is responsible for such cation-preference observed during transport. The loss of cation-preference upon covalent functionalization of the nanotubes further supports this mechanism. Utilizing the short-range cation–π interaction as a transport mechanism suggests broader applications in areas where charge-specific transport is desired.

The memory resistor, or memristor, was theoretically predicted by Chua in 1971 as the forth fundamental circuit element needed to complete the set of six mathematical equations relating four basic electrical variables: charge, current, voltage and magnetic flux. This idea remained as a missing element until its experimental realization in 2008 as TiO2-based memories. Since then, many researchers have directed their attention and efforts not only to the fabrication of memristors, using different materials, but also to understand the physics behind the switching mechanism, in order to control the processing and structural parameters that allow overcoming some drawbacks to obtain reliable and reproducible memory devices. Two-terminal devices, with the switching material sandwiched between two electrodes, are promising structures for the next generation of non-volatile resistive random access memories, with high speed, low-power consumption and excellent scalability. The two-dimensionality of the insulating graphene oxide sheets makes this material ideal for use in low-dimensional structures in nanoscale devices.
In this work, the transport properties of graphene oxide-based Metal-Insulator-Metal (MIM) structures are addressed. The graphene oxide (GO) was synthesized using an eco-friendly modified Hummers method. The obtained GO sheets were placed between gold electrodes, and the cycling current-voltage curves were measured by applying successive forward and reverse voltage sweeps in a range between -3 and 3V. When the absolute value of the measured current is plotted, in logarithmic scale, versus the applied voltage the typical butterfly-shaped curves are observed, which are better interpreted in terms of their first derivative, or differential conductivity, in order to understand the transport mechanism. A simple model is proposed, whose voltage dependence helps identifying the underlying physics responsible for the bipolar switching mechanism, such as bulk or electrode effects, conducting filament formation or tunneling. The analytical expressions used for the differential conductance for the low resistance state and the high resistance state (LRS and HRS respectively) leads to simple expressions for the I-V curves. The symmetry of the curves after several cycles is lost when compared to those measured on pristine devices, which might indicate the occurrence of filament forming effect, affecting the bipolar switching.

Bilayer graphene (BLG) has attracted enormous interest due to its outstanding mechanical, chemical, electrical and thermal properties with various potential applications. By applying a high ratio of H₂ to CH₄ in chemical vapor deposition (CVD) system, BLG can be synthesized with inversed-cake structures on polycrystalline Cu foils. Bilayer regions show distinct Raman spectra by carbon isotope labeling due to the different compositions of the graphene.
In this work, we studied the growth mechanism of BLG using carbon isotope labeling and Raman spectroscopy. Results show that the growth of BLG reveals several different modes. A new mode of "secondary" nucleation is firstly proposed in the growth of BLG, which means that graphene can be nucleated under the first layer tens of minutes later than the first layer. Moreover, during the BLG growth, the stacking structures of the two layers can suddenly change from AB-stacking to non-AB-stacking, while most of the BLG can still maintain their stacking structures during the whole CVD process. This work enables us to have a deep understanding of graphene growth mechanism as well as the layer control for large scale BLG using CVD.

Although much research has been conducted in the field of epitaxial graphene growth on silicon carbide (SiC), still new phenomena are discovered and need to be investigated in order to fully understand and control graphene synthesis and properties. Usually, during sublimation growth in argon at atmospheric pressure the substrate undergoes strong step bunching [1], which leads to relatively large step heights of multiple SiC unit cells. In contrast, the polymer-assisted sublimation growth (PASG) leads to flat and homogeneous graphene sheets on top of an SiC surface with step heights of mainly one or two SiC-bilayers [2]. This gives rise to a well-developed sequence of alternating SiC surface terminations underneath the graphene, which originate from different crystal truncations within the SiC unit cell at the surface [3].

Recently, scanning tunneling potentiometry measurements on graphene obtained by PASG revealed different values for the sheet resistance for graphene on different SiC terraces. Here, we present our results on PASG graphene investigated by low-energy electron microscopy (LEEM). The termination of the underlying SiC substrate is studied by LEEM bright field and dark field measurements as well as selected area low-energy electron diffraction (µ-LEED) and atomic force microscopy. In addition low-energy electron reflectivity (LEER) spectra reveal slightly different electronic properties of the graphene on different SiC terminations. The relationship between the termination of the SiC substrate and the electronic properties of the PASG graphene as indicated by the LEER spectra is shown. Possible explanations for the local change in sheet resistance and the influence of the substrate are discussed.

[1] K. V. Emtsev et al., Nat. Mater. 8, 203 (2009).
[2] M. Kruskopf et al., 2D Mater. 3 (4), 041002 (2016).
[3] M. Pakdehi et al., ACS Appl. Mater. Interfaces 10 (6), 6039 (2018).

Graphene aerogel, a three dimensionally interconnected porous structure, has gained significant attention due to its fascinating properties, such as high mechanical strength, electrical conductivity, thermal resistance, and ultra-light weight. Incorporation of graphene aerogel into a polymer composite is a promising route for fabrication of ultra-light multifunctional material, which is heavily demanded in various industries.

Recent studies have focused on optimization and alignment of graphene aerogel’s structure, in order to further improve the quality of the aerogel and the corresponding composite. Various methods have been developed for controlling the aerogel structure such as self-assembly, direct printing, and ice templating of graphene flakes. Initially, graphene oxide (GO) flakes was used for fabricating graphene aerogel with aligned structure, due to its abundant surface functional groups, which facilitate both aqueous dispersion and assembly of graphene aerogel. However, those functional groups also act as defects, which severely deteriorate the property of both GO flakes and its aerogel. Therefore, it is highly desired to fabricate graphene aerogel composed of graphene flakes with minimum damage.

Here we report a fabrication method to fabricate graphene aerogel composed only with highly crystalline non-oxidized graphene flakes (NOGFs). Bi-direction freeze casting technique was utilized in order to align the pore walls in two orthogonal directions, vertically and laterally. The graphene aerogel showed low defect concentration and oxygen content of 1.4 % according to Raman and XPS analysis. Due to the synergetic effect of both high quality of NOGFs and the aligned structure, the graphene aerogel exhibited outstanding electrical conductivity of 202.9 S/m, which is the highest value ever reported among carbon nanomaterial based aerogels at similar density. Subsequently, epoxy composite was fabricated by impregnating epoxy resin within the graphene aerogel’s pores with vacuum infiltration method. The epoxy composite showed remarkable fracture resistance of 1.74 MPa m^1/2 at 0.45 vol% and electrical conductivity of 122.6 S/m at 0.27 vol%. Both results are superior to those of epoxy composites based on GO aerogels, which demonstrate that incorporation of NOGFs is a promising approach for fabricating high quality graphene aerogel.

Water splitting is one of the carbon-free hydrogen production methods. Electric power consumption of the hydrogen evolution reaction (HER) depends on the cathode materials. Although Pt is known as the most suitable cathode for HER under acidic conditions, identified resources of platinum are limited in the world. Hence, the development of alternative HER catalysts is required. Currently, MoS₂ presents a promising alternative to Pt due to its low cost and high HER activity. The active sites of MoS₂ are located at the edges, thus it is important to develop a simple synthesis process to obtain edge-rich MoS₂. In previous research, edge-rich MoS₂ of high crystallinity was synthesized under hydrothermal conditions, but the main problem of the process was the long reaction time (24-48 h). MoS₂ synthesis via cathodic electrodeposition is one of the fast and facile processes because the deposited MoS₂ can be applied directly for application. However so far, electrochemically deposited MoS₂ showed low crystallinity and low purity with an amorphous structure.
In order to realize high crystallinity MoS₂ and short processing times, we propose a hydrothermal electrodeposition method to fabricate MoS₂ electrodes. This method enables to synthesize crystalline thin films and to control the composition and morphology of the products by adjusting the operating temperature, pressure, and electrochemical conditions. In this research, we attempted to electrochemically deposit MoS₂ on glassy carbon (GC) under hydrothermal conditions (200 °C, 10 MPa), and the MoS₂/GC electrodes were then applied as HER cathodes.
For the hydrothermal electrodeposition, a high-pressure vessel made of Hastelloy equipped with electrodes was used as a synthesis cell, and potentiostatic measurements were carried out at voltages of –1.5 V for 1-30 min. SEM and TEM images of samples synthesized by 1 min electrolysis revealed the formation of edge-rich MoS₂ deposited on GC, while it seemed that the number of exposed edges of the products decreased with increasing reaction times. XRD patterns of working electrodes realized by electrodeposition for 1 min showed that crystalline MoS₂ was deposited on the GC. From TOF-SIMS measurements, the product was mainly identified as MoS₂, while compounds of molybdenum sulfides and oxides were observed in the case of the electrodes treated at ambient condition. HER catalytic activity measurements showed that products synthesized at hydrothermal condition exhibited higher HER performance than the samples synthesized at ambient conditions. Moreover, edge-rich MoS₂ obtained for an electrolysis time of 1 min had higher activity compared to samples realized by longer electrolysis times, the higher HER activity being attributed to the edge-rich morphology of MoS₂.

As a result of China’s recent ban on the import of most plastic waste, the US and other industrialized countries that have been exporting their plastic waste to China for recycling will need to find new ways to handle the disposal of their wastes as much of it is already starting to pile up in landfills. In research conducted at Northeastern University, plastic wastes have been thermally recycled by pyrolytic gasification to nano-carbons and gaseous fuel. To achieve this conversion, a laboratory-scale pyrolytic gasifier was fed with waste plastics including (polyethylene, polypropylene, polyethylene terephthalate, polystyrene, etc., and combinations of the same) in inert (N₂ or He or Ar or CO₂) atmospheres with different flow rates (0.1-2 l/min). The plastic wastes were gasified in an electrically heated reactor at 600-800 C. Under these conditions, the polymer pyrolyzed into a gaseous mixture of hydrocarbons and hydrogen. The pyrolyzate mixture was then conducted into a separate reactor where it was used as a carbon precursor for chemical vapor deposition process to synthesize carbon nanoparticles. The second reactor was set at 800-1000 C. Different grades of stainless steel wire cloths (SS-304, SS-316 and SS-316L) were used as catalytic substrates for the nanoparticle growth. The wire cloths were used either as-received or upon chemical etching by acid wash and/or heat-treatment in air, nitrogen or helium at 800 C, followed by rapid air quenching. In those cases, the yields were determined, by mass relative to the mass of carbon in the feedstock and ranged from 1% to 30%. With the purpose of purification and sorting, the catalysts and the produced Nano-materials were investigated for synthesis, structure and property characterization by SEM, TEM, AFM, TEM+EDX, HAADF and TGA. Results showed that the catalyst type, composition, and pre-treatment, as well as the type of waste plastic, are all influential on the yields and physical characteristics of the synthesized CNTs.

Keywords: Carbon Nanotube, Waste Plastics, Synthesis, Pyrolysis, Purification and Sorting

Water contaminated with highly toxic long-lived radionuclides is a growing concern in the U.S. These contaminants are introduced into water sources from the legacy wastes of nuclear sites, and from nuclear reactors. Technetium-99 (⁹⁹Tc) is one of the major nuclear waste contributors (~6% yield) generated from thermal neutron fission of uranium-235. It is considered a long-lived radioisotope with a half-life of 2.1x10⁵ years and emits a weak beta with a max energy of 0.29 MeV. ⁹⁹Tc is most prevalent in its oxidized form which predominantly exists as pertechnetate (Tc(VII)O₄^-). This contaminant is of concern in aqueous streams because of its inert nature that allows it to spread at nearly the same rate of water flow. To remediate ⁹⁹Tc, reduction of pertechnetate has been the common approach because ⁹⁹Tc is more reactive and less mobile when in a reduced state. The foundation of this work involved utilizing different functionalized nanomaterials as platforms to investigate the reduction and uptake of ⁹⁹Tc. Titanium dioxide is a promising candidate as it has already shown to be a good material for removing toxic materials from the environment. Furthermore, it has a strong reducing potential and is found to be chemically inert in a variety of environments. Graphene oxide (GO) is an eco-friendly platform with a large surface area that provides tunability due to its functionalization. It is speculated that the combination of these two materials will allow for robust reduction in aqueous solutions. Furthermore, in this study, titanium dioxide and graphene oxide composite nanomaterials were synthesized by a sol-gel method. This study examines the ability of titanium dioxide, graphene oxide, and their composite thereof (TGO) to reduce pertechnetate present in aqueous solutions.

As a building block, graphene possesses intriguing mechanical, electrical, thermal property and chemical stability. Assembling graphene into macro-structures is very appealing, if those unprecedented properties can be inherited. However, it is the physical interaction between graphene nanosheets mainly control the performance of the assembled materials. On the other hand, it should be noted that graphene is probably the most anisotropic material that has even been discovered, as manifested by the prominent contrast of bending modulus (in the order of ~2kT) and tensile modulus (~1 TPa), as well as the ballistic electron transport in-plane and tunneling between-planes. Therefore, it is extremely important to improve the alignment of graphene nanosheets in the same direction and reinforce the interaction between them. Keeping this in mind, we propose to employ mechanical strategies, namely dead-end filtration and centrifugal casting, with the advantages of high efficiency, high yield and universal, to super-align and condense-compact graphene nanosheets, both of which result to materials with outstanding performance [1-3]. Finally, we will also illustrate that the combination of proper rheology properties of graphene oxide based ink and 3D printing technique, materials beyond 2D film with much more complex structures can be obtained.


Reference:
[1] Yu YG, Zhong J*, Liu JD, Zhou GX, Lv LX, Xu CY*, Koratkar N. In-Situ Pressing Synthesis of Densely Compacted Carbon Nanotubes Reinforced Nanocomposites with Outstanding Mechanical Performance. Composites Science and Technology 2017. 146, 7.
[2] Yan Y, Zhong J*, Sun W, Kumar R, Koratkar N*. Solid-State Hybrid Fibrous Supercapacitors Produced by Dead-End Tube Membrane Ultrafiltration. Advanced Functional Materials. 2017. 10.1002/adfm.201606461.
[3] Zhong J, Sun W, Qian X, Cheng H, Ren W. Scalable synthesis of highly aligned and compact 2D nanosheet multifunctional films with record performances. Nature Communications 2018, 9: 3484.

In this work we present a high-throughput first-principles study of elastic properties of bulk and monolayer materials mainly using the vdW-DF-optB88 functional. We discuss the trends on the elastic response with respect to changes in dimensionality. We identify a relation between exfoliation energy and elastic constants for layered materials that can help to guide the search for vdW bonding in materials. We also predicted a few novel materials with auxetic behavior. The uncertainty in structural and elastic properties due to the inclusion of vdW interactions is discussed. We investigated 11 067 bulk and 257 monolayer materials. Lastly, we found that the trends in elastic constants for bulk and their monolayer counterparts can be very different. All the computational results are made publicly available at easy-to-use websites: https://www.ctcms.nist.gov/∼knc6/JVASP.html and https://jarvis.nist.gov/. Our dataset can be used to identify stiff and flexible materials for industrial applications.

In the last two decades, the significant efforts have been made to develop alternative energy sources instead of fossil fuels because of increasing CO₂ emissions and the environmental impacts. Besides; hydrogen has been concerned to be an ideal clean energy carrier among the other renewable energy sources because of its environmental friendliness. However, some challenges have to be addressed before hydrogen will become a conventional and commonly available energy carrier. Carbon-based materials such as graphene and carbon nanotubes have been designed for hydrogen storage due to their large surface area, lightweight, and tunable properties. Recently, we proposed a new strategy in which we considered three pure transition metal (TM) atoms or/and a combination of two TM atoms and one alkali earth metal atom (AEM) with high, medium and low hydrogen adsorption energies. These different metal atoms are used to decorate the Boron doped graphene sheet (BDG) and investigated their performance towards hydrogen storage capacity through spillover mechanism using first-principles calculations. Our results indicate that that the activation energies for H atom diffusion are much smaller, indicating that a fast H diffusion on this proposed surface can be achieved. These TM and AEM atoms decorated BDG surface can have the maximum hydrogen gravimetric capacity of 6.4% for double-sided adsorptions. To further achieve higher gravimetric density, in this study, we have considered Ti atoms decorated on the Boron and Nitrogen co-doped graphene surface (BNDG) because B–N pair is isoelectronic to the C–C pair. However, controlling the binding strength of metal atoms with that of the BNDG surface is an important issue in the application of hydrogen storage. The recent studies have shown that the binding strength between the metal atom and the substrate can be controlled by means of applying an external electric field. Thus, the effects of the external electric field, as well as the effects of applying point charges on the designed medium towards its hydrogen storage capacity, will be discussed. We have also explored the stability of the decoration of metal atoms on BNDG sheet at higher temperatures using molecular dynamics simulations.

Surface area, pore texture and pore distribution have been shown to have a strong influence on capacitance. Therefore, hydrothermal treatment (HT) of the most common carbon source, biomass, prior to carbonization and activation has recently received heightened interest owing to its ability to deliver high surface area carbon nanomaterials with remarkable pore texture via deconstruction of cellulose polymeric network in biomass. Nevertheless, hydrothermal strategies involve high pressure and temperature and thus expensive. This study reports on circumventing HT in preparation of the carbon materials with outstanding mesoporosity for supercapacitor electrodes by use of biogas slurry. The deconstruction of cellulose polymeric network in this case is achieved by bacteria while the carbon source is still in the biodigester for biogas generation. In the study, pore structure and surface chemistry have been modified by altering activation time, temperature and KOH/carbon mass ratio. Mesoporous carbon materials are successively developed as evidenced by type IV isotherms obtained in nitrogen sorption studies. The materials afford BET, micropore and mesopore surface area of 515, 350, and 165 m² g^-1, respectively as well as a narrow pore width distribution of 3-4.5 nm. X-ray photoelectron results confirms the presence of functional groups of oxygen and nitrogen in the samples which facilitates the pseudocapacitance. The materials activated at 700 ^oC, 3:1 KOH to carbon mass ratio, and for 120 min exhibit high specific capacitance of 289 F g^-1 at a scan rate of 5 mV s^-1. Shortening activation time to 30 and 60 min reduces specific capacitance to 163 and 182 F g^-1, in that order. Additionally, at 3:1 KOH to carbon mass ratio and 60 min activation time, specific capacitances of 170 and 210 F g^-1 at 600 and 800 ^oC, respectively are obtained. Moreover, specific capacitance increases with increasing the KOH to carbon mass ratio from 148 F g^-1 for 1:1 to 163 F g^-1 for 3:1 at 700 ^oC. Electrochemical impedance spectroscopy studies demonstrate that the materials have high conductivity. In addition; capacity retention of 96% after 20,000 cycles is attained at a scan rate of 30 mV s^-1. The study shows that high performance electrodes can be designed from biogas slurry thereby eliminating the need for HT to get electrode materials with high surface area and porosity from biomass.

In this presentation, we demonstrate a hierarhical carbon nanostructures for energy-efficient water purification. Specifcally, 2D graphene nanosheets were intercalated with zero-dimensional fullerene nanocrystals, and a fixed interlayer spacing of ~1nm was achieved for tuning water passage. The resultant hybrids were stacked via epoxy adhesive and then the cross-sectional filtration of slaty water was investigated. The as-prepared GO/C60 membrane obtains a high water flux up to 10.85 L h^-1 m^-2 bar^-1 with a salty rejection of 89.66%, which is sufficient to purify brackish water into drinkable water. The energy comsuption is as low as 0.775KWh/L, more than 20-fold less than commercial desaliation process. Such hierarchical GO/C60 membrane exhibits long-term stability, and thus provides a great potential for energy-efficient water desalination.

Single molecule detection has played an important role in monitoring of health and environmental conditions. Health monitoring efficiency depends upon detection of an immune response to pathogen, cell mutation, etc. at its early stages or low concentration. Traditionally, solid state nanopores are fabricated using silicon nitride (SiN_x) membranes. But 20-50nm thick SiN_x membranes makes fabrication and reproduction of 2-5nm pores difficult, hampering detection sensitivity and accuracy. 2D materials with interlayer van der Waals forces, are a good choice for fabricating monolayer thin membranes. Molybdenum disulphide (MoS₂) with surface charge (0.024 C/m²) similar to SiN_x (-0.02C/m²) slows translocation without pore blockage, and also improves resolution. In this work, the advantage of using few layers MoS₂ over monolayer MoS₂ for low-concentration label-free detection has been demonstrated. The strong interlayers coupling creates a potential gradation along the van der Waals separated MoS₂ layers, since the different layers feel different electric potentials. This causes trapping and detrapping of the phosphate groups of DNA with the Molybdenum atoms at the nanopore. The increased negative-positive charge interaction creates an additional electrophoretic pull providing platform for effective capture and detection at very low molecular concentrations, without the usage of any external trapping mechanism.
Here, we have conducted simulation and experiments to compare the detection efficiency of SiN_x and MoS₂ nanopores for dilute samples. We simulated translocation of nucleotide homopolymers in COMSOL Multiphysics. Our simulations show a 30-fold conductance improvement and three times lowering of translocation speed for a 5nm diameter pore on 4 layers (2.6nm) MoS₂ compared to 50nm thick SiN_x, indicating a clear sensitivity improvement. Translocation experiments were conducted using 4E-4% IDT-ACTB1and 60 mM KCl with SiN_x and MoS₂ pores, fabricated by photolithography, etching and TEM drilling. Here the concentration used for detection (4E-4%) implies a 10⁴-fold sensitivity improvement when compared with detection demonstrated in literature (0.1-1%). MoS₂ is seen to detect 102 molecules per minute whereas SiNx detected 20 molecules per minute at the ultra-low concentration without any external trapping mechanism. Moreover, the greatest dwell times obtained in literature for DNA sequencing using 100 mM KCl and monolayer MoS₂ nanopore is ~500 ms whereas dwell times as large as 1100 ms were obtained in our study. MoS₂ (0.3-1.4nA) demonstrates a significantly higher average blockade current as compared to SiN_x (0.08-0.8nA). Simulation and experimental data for all nucleotides will be presented to show inherent capacity of few-layers MoS₂ in improving molecular detection efficiency.

References
1. Nat. Nanotechnol., 2015.
2. Nat. Commun., 2016.

Intriguing electronic properties of graphene related with massless Dirac Fermions have enabled the applications in highly sensitive gas sensors. However, it is widely recognized that the poor gas desorption behavior because gas adsorption occurs defective sites of graphene only. To overcome this insurmountable hurdle, we rationally designed hybrid films including ZnO thin films and CVD-grown graphene in order to combine advantages of ZnO thin films with reliable gas adsorption/desorption related with their gas reaction mechanism and graphene with extremely high gas sensitivity originated from its exceptional electronic structure. The complementary dual channel gas sensor based on roll-allocated graphene-ZnO heterostructures, in which ZnO acts as a gas adsorption channel and graphene plays a role of carrier conducting path, was fabricated by combining atomic layer deposition, chemical vapor deposition, and polymer-assisted wet transfer techniques. The effects of ZnO top-layer thickness on the gas sensing properties of the hybrid films were explored. As a result, NO₂ sensitivity improvement of the optimized hybrid film-based gas sensor was achieved unambiguously as ~40 times higher than that of graphene-based gas sensors. Additionally, we systematically explored the electrical interaction between thickness-controlled ZnO thin films and graphene before and after gas adsorption to explain the correlation between charge transfer and gas sensing properties.

Graphene-based materials have received tremendous attention due to their excellent mechanical and electrical properties. Among them, graphene oxide (GO), which chemically exfoliated from graphite, is possible to solution process in aqueous solutions owing to having oxygen-containing functional groups on its basal plane and edges. Moreover, they have active sites for reduction of GO and covalent functionalization of GO with small organic molecules or inorganic nanomaterials. For these reasons, GO have been researched in many applications such as polymer composites, biomedical, and energy-related materials. In Particular, Reduced graphene oxide (rGO) reduced by functionalized hydrazine from GO is promising alterative material to poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as hole transport layer (HTL) in organic solar cells because it allowed the controllability of electronic properties through versatile functionalization and can improve the long-term stability of solar cells. However, rGO is difficult to apply in inverted organic solar cells because of limited dispersity in alcohol based solvent such as 2-propanol (IPA). The rGO is usually dispersed in dimethylformamide (DMF), which melt the organic active layer. Therefore, more research is required about controlling the dispersibility of rGO while maintaining their electrical properties in order that rGO apply to inverted organic solar cells as a HTL via solution process. In this study, we introduced trifluoromethoxy group on the rGO surface (FMrGO) for controlling the dispersibility of rGO while maintaining their electrical properties. FMrGO is well dispersed in IPA and 2-ethoxyethanol due to the flexible methoxy groups. The structural, optical, and thermal properties of FMrGO was characterized by Infrared spectroscopy, EA, XPS, UV-vis spectroscopy and TGA and their work function was estimated by UPS. Finally, we introduced the FMrGO film as a HTL on the active film through solution process and investigated the effect of FMrGO on device performance and long-term stability of inverted organic solar cells.

Carbon nanotube (CNT), which has one-dimensional atomic structure, is highly accessible to external stimuli because of its high surface area to volume ratio. Thus, electronic configuration of CNT can be strongly influenced by tiny perturbations. The unique interaction between CNT and its surrounding stimuli has been of particular interest over the past decade. A thorough understanding of the interaction enables to develop a wide range of applications, such electrical bio/chemical sensors and actuators with unrivaled performance. Previous researches proved that CNT can generate electrical energy by converting mechanical energy of fluid into electrical energy. The transfer of momentum from the molecules in flowing fluid to the acoustic phonons in the CNT is induced, which in turn drags free charge carriers in the CNT. The driving of free carriers generates a potential difference along the CNT length, but this phenomenon is only realized in low dimensional nano carbon structures. The ability of generating electrical power can be enhanced in highly aligned structures of nanomaterial along the flow direction because this structural characteristic can decrease scattering of dragged charge carriers.
In this work, we investigated the effect of charge carrier dragging in CNT by using more intuitive way of electrostatic induction. A highly aligned, free-standing structure of CNT sheet is used to enhance the charge dragging effect as well as to minimize peripheral influences from a substrate. Up to hundreds of microvolt can be generated, it is affected by sweeping speed, inter-distance between charged object and nanotube sheet, surface charge and number of nanotube sheet layers.
Simple fabrication method of series connection is the most powerful aspect of continuously drawable nanotube sheet, which is simply completed by one-step winding of CNT sheet on the polyethylene terephthalate (PET)/copper foil/PET laminated substrate. As a practical demonstration of the CNT device, we have demonstrated CNT sheet based self-powered motion sensor for tracing finger movements. Coulombic interaction between finger and free charge carriers in CNT sheet induces efficient charge carrier transfer via electrostatic attractive force. Effective motion sensing for moving direction and speed is possible by detecting its electrical output. Motion sensing and energy harvesting are simultaneously available, thus external power source is not needed because of its ability to providing electrical power by itself.
This fundamental studies has great significance in dry-state energy harvesting using nano carbon material which is quietly distinct from previously reported liquid-based energy harvesting studies. Furthermore, suggested self-powered motion sensor can read finger movements (just like a finger commend in a smart phone), requiring no need of touch panels.

Carbon nanotube(CNT) fiber has been substantially realizing the outstanding property of the individual CNT (high strength, light weight, electrical conductivity...) in bulk materials. Due to superb intrinsic properties, CNT fibers are promising for alternative of metal wire. However, there is still challenging for commercialization of CNT fibers. One of major difficulties is CNT-CNT contact resistance, which decreases the electrical conductivity of CNT fibers. To overcome this drawback, nitrogen doping is an effective way to enhance the intrinsic conductivity of CNT fibers by increasing electron carrier density. As for typical doping process, not only quaternary N(N_Q) electron donor but also pyridinic(N_py) and pyrrolic(N_Pyrr) nitrogen types are arbitrarily doped. Since N_Py and N_Pyrr localize electrons resulting in increasing the electrical resistance, controlling the doping site of nitrogen is critical issue. In this study, N_Py and N_Pyrr types were selectively removed by acidic reduction process without oxidation. The acid treated CNTs showed liquid crystalline behaviors, which can be directly spinning of CNT fibers without complex process. We have verified the improved electrical properties of CNT fiber related with bonding types of nitrogen in CNT fibers.

Perfect absorbers have many application in different fields including photovoltaic, antireflective radar absorption coatings for defence, energy harvesting and emissivity control. Here, we design and fabricate a near perfect optical broadband absorber, having absorption capacity of 99.4% from 300 to 2000 nm wavelength range. Etched Silicon wafer is used as base layer to fabricate multilayered optically graded assembly, while carbon nano tubes layer used as a top layer for impedance matching. Subsequent layers are selected as per increasing refractive index and varying micro/nano features for efficient light trapping. Less than 1% of reflectivity in entire range up to 50° beam angle has been observed. Moreover multilayered assembly shows contact angle of more than 160° with roll-off angle of less than 5° which showed that it is not only a near perfect absorber but also a self-cleaning superhydrophobic surface. Conclusively, the properties of multilayered optically graded assembly imparts attractive applications of this superabsorber in the field of photovoltaic.

Linear carbon chains, also known as carbynes, are essentially one-dimensional (1D) systems that present carbon sp hybridization. The research involving linear carbon chains has been a hot topic in recent years mostly due to their unique properties and potential for technological applications. These chains are highly unstable under ambient conditions, but the internal volume of the nanotubes offers ideal conditions for stabilizing such systems. Techniques of encapsulation by DCWNTS and MWCNTs have been successful to produce long linear carbon chains with lengths reaching several hundreds of nanometers. In this work, a systematic investigation has been conducted on linear chains of carbon encapsulated by double- (Cn@DWCNT) and multi-walled carbon nanotubes (Cn@MWCNT). Temperature studies in such materials are important for considering possible applications under extreme conditions (e.g. space and nuclear reactors). Our preliminary studies using low temperature Raman spectroscopy investigations of Cn@MWCNT-Bulk (300K at 20K) showed that the band frequency of the chains (~1,800 cm^-1) increased when the temperature was reduced. However the results seem to indicate an anomaly in the frequency behavior for temperatures below 60K, in which a decrease of the Raman frequency takes place with decreasing the temperature. We also observed that the frequency variations are reversible in the range of temperatures from 4K to 300K.To investigate this effect in detail, these studies will be conducted at the individual level. In other words, both Cn@DWCNTs and Cn@MWCNTs will be isolated and then investigated under low temperature. Dispersion of these materials has been successfully attained and isolated species have been confirmed by Atomic Force microscopy (AFM) measurements and Raman spectral features.

References
1.Leis Shi, Lukas Novotny, Nature Materials, 15,634–639 (2016).
2.Beilstein J. Nanotechnol,6,1708–1711 ( 2015).

Graphene, a one-atom-thick sheet of carbon atoms arranged in a honeycomb-like pattern lattice, has attracted much attention owing to its potential applications in the fields of electricity, conductivity, energy generation, batteries. Intensive recent studies report the wetting transparency of graphene, suggesting that the wettability of graphene is partially governed by the underlying substrate and is more hydrophobic with increasing the number of graphene layers. This infers that its surface energy is decreased with increasing the number of graphene layers. Amongst those studies, the static contact angle measurement is a highly employed method for characterizing the graphene surface wettability; however, this technique requires large scale surface coverage of graphene to contact the milliliter size of water droplet at the solid/liquid interface. This is rather challenging since one cannot precisely control the number of graphene layers at the contact line. This challenge is often ignored despite being the origin of the uncertainty in the measurements that have led to contradictory interpretations. In order to shade light to this controversy, we combine bimodal atomic force microscopy [1] and micro-Raman spectroscopy to measure the surface energy of the graphene surface on different substrates. It is well-known that the number of graphene layers can be determined by the ratio of 2D to G peak in the Raman spectra. Therefore, the graphene sample is fabricated by using a designed two-step chemical vapor deposition method, which has large enough area of monolayer, bilayer and multilayer of graphene on the substrate, respectively. This deposition enables us to precisely measure the same area of graphene sample by using AFM and micro-Raman spectroscopy. Our experimental results show that in contradiction with graphene wettability transparency theory, the derived graphene surface energy increases with increasing the number of graphene layers. We also use density functional theory to directly predict the surface wettability of graphene on different substrate based on [2] and obtain results that qualitatively agree with our AFM experimental characterization.
[1] Lai, Chia-Yun, Sergio Santos, and Matteo Chiesa. "Systematic multidimensional quantification of nanoscale systems from bimodal atomic force microscopy data." ACS nano 10, no. 6 (2016): 6265-6272.
[2] Lu, J. Y., Ge, Q., Li, H., Raza, A., & Zhang, T. (2017). Direct Prediction of Calcite Surface Wettability with First-Principles Quantum Simulation. The Journal of Physical Chemistry Letters, 8(21), 5309-5316.

Thermal management is critical to the continually growing electronics industry to prevent devices from overheating and losing their functionality. As low-cost, lightweight, and highly versatile materials, polymers exhibit great potential for heat exchange applications, but their low thermal conductivity is a barrier to their effectiveness. Additive fillers are usually added into polymers to help enhancing the thermal conductivity.
In this study, we investigated the thermal conductivity of blends of PLA (polylactic acid) and PBAT (polybutylene adipate terephthalate) with graphene nanoplatelets (GNPs) and hexagonal boron nitride (hBN). It is hypothesized that the thermal conductivity of the PLA/PBAT nanocomposite would be elevated when adding the fillers compared to neat polymer blends.
Contact angle measurements between polymer droplets on hBN and GNP layers deposited on a silicon wafers were used to determine the polymers’ relative affinities for the fillers. The calculation of the word of adhesion between fillers and polymers indicates that both hBN and GNP exhibited more affinity for the PBAT phase than the PLA phase, which means the fillers would be interspersed in the PBAT phase. PLA/PBAT blends with various concentrations of hBN powder and GNPs were blended at 180 using a twin-screw mixer at 150 rpm. The thermal conductivity of PLA/PBAT and PBAT blends with hBN alone was tested at the beginning. Slow increase in thermal conductivity with increasing weight fraction of hBN was obtained. To better enhance the thermal conductivity, considering that we have demonstrated that with the larger size of the fillers which meet the size of the domain in the polymer matrix, they will have a better arrangement, we decided to apply Graphene H-5 in the blends to make some new attempts. The results show that as the GNP content of the nanocomposite increased relative to the hBN content, the thermal conductivity increased significantly. Then, the samples were molded into different sizes to test the impact and tensile properties. The mechanical data indicates that although the combination of hBN and Graphene can help increasing the thermal conductivity significantly, it is difficult to maintain the mechanical properties. Therefore, to enhance the thermal conductivity of the polymer blends with relatively high mechanical performance is a new challenge. We did mechanical tests separately with PBAT/PLA/hBN and PBAT/PLA/GNPs and found that hBN can better maintain the mechanical properties. Thus, we tried different ratios of hBN and graphene and kept the total amount of the filler at 30 wt%. The results show that even 3% of hBN can help maintaining the impact toughness at 85.62 J/m, which is pretty high value that meets the demand for most of the applications.

Hydrogen Peroxide (H₂O₂) is a well-known reactive oxygen species produced in various biological phenomena. In various pathological and physiological conditions, higher concentrations of H₂O₂can cause lipid peroxidation, DNA base modification, protein degradation etc. H₂O₂ present in quantities of about 20-50 µM or more can have deleterious effects as it can easily dissolve in aqueous solutions and penetrate biological membranes easily. Hence, sensitive and selective detection of H₂O₂ is important under physiological conditions.
In this work, we report on a non-enzymatic electrochemical method for the facile and sensitive detection of H₂O₂. We explored the approach of conducting polymer-nanocomposite as efficient transducer platform. We synthesizedthree-phase composite polymer system of PEDOT:PSS/GO/MnO2, comprisingpoly(3,4-ethylenedioxythiophene): poly(styrene-sulfonate) (PEDOT:PSS), graphene oxide (GO) and manganese dioxide (MnO₂). On being exposed to H₂O_2,MnO₂undergoes a redox reaction which is responsible for the sensing ability of this material.The composite was prepared using the conventional solution mixing method and then used to modify screen printed electrodes. The physicochemical characterization was carried out Scanning Electron Microscopy, UV- Visible Spectroscopy, Raman Spectroscopy and Fourier Transform Infrared Spectroscopy. Cyclic Voltammetry results showed that the nanocomposite showed high electrochemical activity for the detection of hydrogen peroxide (H₂O₂) in alkaline medium. The PEDOT/GO/ MnO2 based electrode exhibits high sensitivity and selectivity for electrochemical detection of H₂O₂ with a sensitivity of 0.5uM. The present study demonstrates that such this novel nanocomposite is promising for fabrication of non-enzymatic H₂O₂ biosensors. This method can further be explored for Point-Of-Care detection.

Our lab at MIT has been interested in how the 1D and 2D electronic structures of carbon nanotubes and graphene respectively can be utilized to advance new concepts in molecular detection, as well as energy generation. By taking advantage of the exceptional electronic properties of these nano-structures, we continue to discover potential application spaces where carbon can play an important role. For example, we have pioneered a novel technique called Corona Phase Molecular Recognition, or CoPhMoRe, for discovering synthetic, heteropolymer corona phases that form molecular recognition sites at the nanoparticle interface. By screening libraries of synthetic heteropolymers chemically adsorbed onto single-walled carbon nanotubes (SWNT), we have engineered new optical biosensors that exhibit high selective recognition for bio molecules, such as riboflavin, L-thyroxine, dopamine, nitric oxide, sugar alcohols, estradiol, and fibrinogen. These results have significant potential for using SWNT-based sensors to interface to biological systems, allowing monitoring pathways at the sub-cellular, cellular, tissue, and whole-animal scale. I will also highlight our recent efforts in initiating an endeavor we call “Plant Nanobionics”. There we use techniques to deliver and transport functional nanoparticles into living plants to grant them non-native functions. Our goal is to engineer plants to take over many of the functions now performed by electrical devices. I will introduce the nanoparticle co-localization mechanism in a plant, and highlight some of our recent nanobionic plant prototypes including a light-emitting plant. Lastly, I will briefly describe several applications of carbon nanomaterials in the energy space that have come out of our lab. There is a pressing need to find alternatives to conventional energy generation techniques, specifically those that rely on elements in finite global supply. We introduce Asymmetric Doping Cells (ADC), which convert chemical potential to electrical energy by means of spatially selective doping along a nanostructured conduit or particle. These ADCs have applications to energy harvesting from aqueous and organic solvents, as well as electro-catalysis for chemical synthesis. An inverse length-scaling of the maximum power as L^−1.03 that creates specific powers as large as 30.0 kW kg⁻¹ highlights the potential for microscale energy generation. We also introduce carbon materials for what we call thermal resonators that make use of thermal storage elements with high effusivity – the product of the thermal conductivity and heat capacity to the one half power. Thermal resonators base on carbon can harvest energy indefinitely from ambient thermal fluctuations of various frequencies, opening new possibilities for remote applications.

Perovskite solar cells (PSCs) have progressed remarkably through a heated power conversion efficiency (PCE) race. With a surge of research efforts, the certified PCE of the lab scale PSCs increased to 22.7% for last 5 years. Now the research efforts are being focused on enhancing the durability of the devices and reducing the production cost.
PSCs typically require a metal electrode is thermally evaporated on top to serve as a counter electrode. These top metal electrodes, however, are known to substantially increase the process and material cost as expensive gold or silver layers are deposited under high vacuum. Furthermore, the metal electrodes are found to be not robust enough to render long-term stability of the PSCs as the metal ions migrate into the bulk of the device under an operational condition to react with the active materials, thus degrading the device.
As an alternative to the metal electrodes, researchers have incorporated single-walled carbon nanotubes (CNTs) into the PSC system. The CNT is a favorable electrode material, owing to its hydrophobic nature, earth-abundance, and mechanical robustness. The application of CNT realizes CNT-based PSCs with good stability and versatility. Among the reported CNT-used PSCs devices, aerosol-synthesized CNT top electrode (or back electrode) replacing metals in PSCs has shown the most promising potential. The application of CNT as the top electrode substantially enhances the stability of PSCs by removing the ion migration, and drastically reduces the fabrication cost as it can be easily deposited onto devices by a simple mechanical transfer. Despite such advantages, there are three factors limiting the PCE of the CNT top electrode-based PSCs that need to be addressed: 1) the work function of the CNT does not align with the perovskite, leading to loss in potential 2) CNT top electrode is less conductive than the metal counterparts, limiting the fill factor of the devices 3) the CNT back electrode is not reflective that the devices cannot maximize the light harvesting efficiency.
In this work, we addressed those three issues by engineering CNT electrode and photo-active layer. We tuned the work function of CNT electrodes and increased their conductivity by using a vapor-assisted doping of trifluoromethanesulfonic acid (TFMS). Furthermore, by incorporation of Cs-based 2D perovskite-added low bandgap formamidinium perovskite, we enabled the harvesting of long-wavelength light, enhancing the photocurrent of the devices. By combining those technologies all into one device system, CNT electrode-based PSCs produced a PCE of 17.6% with a J_SCof 24.21 mA cm^-2, V_OCof 1.005 V, and FF of 0.72. The obtained PCE is the highest among the values reported from CNT top electrode-based PSCs. Moreover, the resulting CNT-PSCs exhibited higher high-temperature operational stability than those of the devices based on metal electrodes as well as conventional CNT electrodes.

Since the global energy demands are rapidly increasing, energy harvesting from the environment has received much attention. Environmental energy sources such as sunlight, wind, vibration, heat, and flow have been exploited to various extents for electricity generation. Among them, water flow exists in various forms and has potential for developing electricity generators. The interface between flowing water and graphene also shows potential of electricity generation. The energy harvesting by flowing water along the interface of graphene has been studied. The mechanisms proposed to date are still not deterministic, however, surface conditions are key factors for the understanding of the physical mechanism and maximizing the performance. The surface conditions include electrical potential at the phase interface and wettability of graphene, both of which can be tuned by heteroatom doping. In this paper, the role of the surface condition of graphene on flow-induced electricity generation is investigated by heteroatom doping.
Nitrogen-doped graphene was used to investigate the role of surface condition on electricity generation. Characterization of the nitrogen doped graphene was carried out by x-ray photoelectron spectroscopy and Raman spectroscopy. In our typical experiment condition, at least 70 % of the doped nitrogen was graphitic nitrogen. Atomic concentration of nitrogen was approximately 1 %. The electricity was studied with transferred graphene and deionized (DI) water droplets by manually dropping the droplets (0.1 ml). Pristine graphene shows approximately 80 mV and the highest voltage from nitrogen-doped graphene was approximately 380 mV, thus more than 3 times higher voltage generation was observed.
The enhancement of voltage generation by nitrogen doping is explained as follows. The electronic state of the nitrogen-doped sites is considered to have an important role. Nitrogen doping of carbon in various applications acts as an electron donor by providing the unshared electron pair of nitrogen in graphene. The local charge of graphitic nitrogen is positive and that of the surrounding carbon atoms is negative. This is explained by the electron transfer from nitrogen atom. The inside of the droplet sitting on top of graphene is affected by the negative charge on the graphene surface, leading to potential formation at the interface. The induced negative charge reduces electric double layer at the interface, resulting in the formation of steep potential [1].
We have investigated the effect of graphene doping on flow-induced power generation between graphene and water interface and found that the nitrogen-doped graphene shows enhancement of power generation. The surface charge of the nitrogen-doped graphene reduces the electric double layer thickness, resulting in the formation of a steep potential, which contributes to higher power generation.
[1] Okada et al., Applied Physics Letters, 112 (2018) 023902.

Macroscopic assemblies of carbon nanotubes (CNTs) in wire format have been proposed for a variety of applications including power and data transmission for both aerospace and terrestrial scenarios. Wires fabricated from CNTs have demonstrated superior flexure tolerance, weight savings, and corrosion resistance over their traditionally used metal counterparts. Current research is focused on translating the exceptional electrical properties of individual CNTs to bulk CNT wires through fabrication technologies like extrusion and densification, chemical doping, and metal-incorporated hybrids. In this talk, a summary of CNT conductors being advanced from high-purity laser-vaporized single wall carbon nanotubes (SWCNTs) as well as commercial CNT materials will be provided. Acid dispersion and extrusion of SWCNTs into a coagulant bath has been used to fabricate wires, with the coagulation dynamics shown to govern the resulting wire structure leading to electrical conductivities of 5.1 MS/m. Alternative approaches to enhance CNT electrical conductivity have been demonstrated using IBr chemical doping whereby low-dipole moment solvent systems favor the IBr-CNT interaction over the IBr-solvent and the solvent-CNT interactions. Recent work has also utilized densification and chemical doping with KAuBr₄ to improve the conductivity of commercially scaled CNT yarns by 6x, while increasing the current density at failure by 67% to 35 MA/m² in air. The thermal stability of KAuBr₄ is proposed to provide the greater electrical stability at elevated current levels. Lastly, site-selective copper nanometal seeding through chemical vapor deposition (CVD) is demonstrated as a viable method in concert with solution electrodeposition of bulk Cu to enhance the electrical conductivity of a low-density CNT roving. A Cu-CNT hybrid conductor has achieved a specific conductivity of 5632 Sm2/kg and electrical conductivity of 28.1 MS/m. A summary of high-current behavior and limitations to the current carrying capacity of these wires in air due to oxidative failure will be presented. Maximum current densities for SWCNT wires in a helium environment exceed fuse-law behavior for aluminum wires of equivalent diameter. The progress and opportunities for continued advancement of carbon conductors will be highlighted.

Single-walled carbon nanotubes (SWCNTs) are among the strongest candidates for the replacement of commonly used transparent and conductive films (TCFs) based on doped metal oxides, such as indium tin oxide (ITO). SWCNTs possess unique multifunctional nature, which is based on their outstanding combination of mechanical strength and flexibility, chemical stability, exceptional electrical conductivity and optical properties [1]. However, to fully utilize these properties in modern transparent electrode applications, SWCNT-based TCFs have to demonstrate the optoelectronic performance at the level of high-end ITO-based TCFs. This has not been achieved for SWCNT films yet and as a result limit their practical usage.
Using gold chloride as the most effective dopant for the SWCNTs, we improve their optoelectrical characteristics by optimizing the doping solvent and conditions [2]. We examined various solvents to push the optoelectrical performance of the TFCs based on SWCNTs. As a result, we obtained the sheet resistance as low as 40 Ω/sq. at the transmittance of 90% (at 550 nm) using 15 mM HAuCl₄ solution. This optoelectrical performance is better than that of ITO on PET substrates and satisfy most of the requirements for modern applications and relatively stable without additional protection over two years storing under ambient conditions.
Also, we examine the effect of ionic liquid gating and plasma treatement on the electronic structure of the SWCNTs and their optical and electrical properties.
The effect of the presence of catalyst particles on the optoelectronic properties of the SWCNT films is also presented.
This work was supported by the Russian Science Foundation (Project identifier: 17-19-01787).
References:
[1] A. L. Gorkina, A. P. Tsapenko, E. P. Gilshteyn, T. S. Koltsova, T. V. Larionova, A. Talyzin, A. S. Anisimov, I. V. Anoshkin, E. I. Kauppinen, O. V. Tolochko, A. G. Nasibulin, Carbon 100, 501 (2016).
[2] A. P. Tsapenko, A. E. Goldt, E. Shulga, Z. I. Popov, K. I. Maslakov, A. S. Anisimov, E. P. Gilshteyn, P. B. Sorokin, A. G. Nasibulin, Carbon 130, 448 (2018).

Carbon nanotubes are widely regarded as very promising heat conductors. Although that is certainly true for individual carbon nanotubes [1-3], the situation is not that simple for carbon nanotube networks [4,5]. The way the heat is transported through the material is highly dependent on the carbon nanotube alignment, length, purity and other parameters. In fact, the influence is so strong that the spectrum of reported thermal conductivities for carbon nanotube networks ranges from thousands or hundreds of W/mK down to values lower than unity. In this contribution, we would like to show how careful surface modification enabled us to tune the thermal conductivity of the material. Free-standing carbon nanotube films of different composition and microstructure were manufactured and their thermal properties were measured by the previously reported method [6]. The results show a big potential of carbon nanostructures for a wide range of thermal management applications.

References:
[1] P. Kim, L. Shi, A. Majumdar, P. McEuen, Thermal transport measurements of individual multiwalled nanotubes, Physical Review Letters 87, 2001, 215502.
[2] E. Pop, D. Mann, Q. Wang, K. Goodson, H. Dai, Thermal conductance of a individual single-wall carbon nanotube above room temperature, Nano Letters 6, 2006, 96.
[3] A. Marconnet, M. Panzer, K. Goodson, Thermal conduction phenomena in carbon nanotubes and related nanostructured materials, Reviews of Modern Physics 85, 2013, 1295.
[4] B. Kumanek, D. Janas, Thermal conductivity of carbon nanotube networks, Nanoscale (submitted).
[5] B. Kumanek, G. Stando, D. Janas, Thin films from carbon nanotubes of tunable thermal conductivity, Applied Surface Science (submitted).
[6] P. Liu, Z. Fan, A. Mikhalchan, T. Tran. D. Jewell, H. Duong, A. Marconnet, Continuous carbon nanotube-based fibers and films for applications requiring enhanced heat dissipation, ACS Applied Materials & Interfaces 8, 2016, 17461.

Devices and integrated circuits (ICs) with bio-integration capability can significantly expand functions of electronics, which is of growing interest in clinical and biological applications. Generally, intimate and conformal biotic/abiotic interface is an essential. However, as many efforts have been demonstrated for the bio-integration purpose, ICs, the core unit of electronic systems, are still lacking with certain complexity and low power consumption for in situ biological data computation and operation. The presentation will detail carbon nanotube based devices and ICs with both high uniformity and low power consumption that can be transferred onto biological surface, such as plant leaves, person’s wrists and biological polymers, and the wafer-scale platform demonstrated operation on a curved plant leaf. The carbon nanotube transistors exhibited ultralow power consumption with off-current as low as 0.1pAμm⁻¹, a subthreshold swing of 62 mVdec⁻¹, and static power consumption of 2.5 × 10⁻¹³ W was observed in an inverter. Meanwhile, with 80mV standard deviation in threshold voltages, the transistors demonstrated high-uniformity and could be used for IC construction. The most complex carbon nanotube based ICs on flexible substrates, such as a full adder with rail-to-rail outputs and a read-only memory were present driven by a small supplied voltage of 2 V.

Reference
L. Xiang, H. Zhang, G. Dong, D. Zhong, J. Han, X. Liang, Z. Zhang, L. Peng and Y. Hu, Nature Electronics, 2018, 1, 237-245.

We present lightweight copper-matrix carbon nanotube (Cu/CNT) composites [1-3] with electrical performances rivalling that of Cu as promising copper-substitutes. Our Cu/CNT composites, 2/3rd as light as copper, show room-temperature electrical resistivities as low as 3.3 × 10^-6 Ohm cm (~ twice that of Cu). With temperature coefficient of resistivity (TCR) values less than Cu, our Cu/CNT electrical resistivity exhibits higher temperature-stability than copper. The TCR values of our composites range from 4.4 x 10^-4 /K (~10% Cu_TCR) to 1.7 x 10^-3/K (50% Cu_TCR) depending on the CNT-type. Further, the composites also show a higher current-stability (current carrying capacity) than copper. We could fabricate composites with such excellent electrical performances as both microscale pillars as well as macroscopic wires by applying industry-compatible Cu electrodeposition protocols on CNT templates. We believe our high-performance lightweight composites show immense potential to fulfill a growing demand for lightweight electrically conducting Cu-substitutes. The macroscopic Cu/CNT wires could replace heavy copper electrical wiring in aircrafts and automobiles for improved fuel efficiencies. Replacing ~2 Tons of Cu wiring in a commercial aircraft with a material 2/3rd as light translates to 25,000 Tons of fuel-savings and 78,000 Tons of CO₂ emission-cuts per year [4,5]. Our Cu/CNT’s temperature-stable resistivity (low TCR) is specifically favorable for applications requiring reliable conductors operating at high temperatures, like motor windings. Meanwhile, our microscale Cu/CNT pillars with superior current- and temperature-stability could serve as better vertical interconnects than copper in high-power electronics, aiding miniaturization with increased functionality of next-generation devices.

References
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[3] Sundaram R, Yamada T, Hata K, Sekiguchi A. 2018. Jpn. J. Appl. Phys. 57(4), 04FP08.
[4] Ian Moir AS. Design and Development of Aircraft Systems . 2nd ed. Chichester, UK: Wiley; 2013.
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Directed assembly of single walled carbon nanotubes (SWNTs) at the selected of the circuit in a massively parallel fashion is very important for many practical applications of SWNT based devices. Our group have been using AC dielectrophoresis technique for the directed assembly of the SWNTs. In this talk, I will discuss the assembly of individual SWNTs from aqueous solution containing mixed SWNTs and 99% pure semiconducting SWNTs. I will also discuss the assembly of SWNTs in an aligned array with tunable density. Finally, I will discuss the assembly of semiconducting SWNTs as the channel material with metallic SWNTs as electrode. Different parameters relating to the controlling of the DEP assembly will be discussed. Detailed electrical transport properties of the DEP assembled devices will also be discussed.

Wearable sensor devices have the potential to revolutionize preventive medical care and health promotion technologies. Carbon nanotube (CNT) thin films are promising electronic materials for transistors and integrated circuits [1-3], biosensors [4,5], and other passive components to build flexible and stretchable devices with excellent wearability and performance. Recently, high-yield and reproducible fabrication of CNT TFTs have become possible by using purified semiconducting CNTs, leading extensive study on circuit applications. An integration of analog circuits with a sensor is essential for wearable sensor devices to amplify the sensing signal as preventing external noise. A differential amplifier is a fundamental analog amplification circuit used for various sensor devices. In this work, we are focusing on the analog circuit application of CNT TFTs. To design CNT-based analog circuits, circuit simulation tools have been developed with a precise device model which has been built on the basis of electrical characterizations of CNT TFTs. We have realized differential amplifiers on a flexible and transparent plastic film.
Device modelling is indispensable for circuit design. We built the RC-ladder device model based on the charge based model for CNT TFTs, where a correction of pinch off condition was taken into account, considering the contact resistances between CNTs. In order to fit the subthreshold current, the charge equation in weak inversion characteristics was modified. The proposed model well expresses the output characteristics. The frequency dependence of capacitance-voltage characteristic was also built by considering the non-quasi-static effect in the Mayer model. CNT-based analog or analog/digital mixed circuits such as differential amplifiers and analog/digital converters were designed by using the circuit simulation with proposed device model.
We also realized the differential amplifiers on a flexible plastic film. Bottom-gate CNT TFTs with purified semiconducting CNTs were used as the active device. A differential output was obtained with respect to a differential input. Maximum voltage gain of 16.3 (24.3 dB) was achieved for a sinusoidal wave input of 100 mV_pp at 100 Hz with a power source of -12 V. Figure 2 shows the gain as a function of frequency, exhibiting -20 dB/ decay. The voltage gain cut-off frequency was 210 kHz.
Acknowledgments: The semiconducting CNTs were provided by TASC. This work was partially supported by JST/CREST.
[1] Q. Cao et al., Nature 454, 495 (2008).
[2] D.-M. Sun et al., Nat. Nanotechnol. 6, 156 (2011).
[3] D.-M. Sun et al., Nat. Commn. 4, 2302 (2013).
[4] I. Dumitrescu et al., Chem. Commn, 45, 6886 (2009).
[5] W. Harreither et al., Anal. Chem. 85, 7447 (2013).

The field of soft electronics is rapidly progressing as a result of recent advances in functionally generalized, modular device architectures for various applications, including wearable electronics, implantable devices and sensory skins. Various applications in soft electronics could benefit from improvements in light-emitting elements, like fibers and textiles that function as information displays or provide fashionable effects in clothing, sensors that communicate responses optically, and possibly even implantable medical devices that emit light in response to sensor input to release drugs, destroy photochemically sensitized tissue, or communicate to neurons.

Here, we describe and demonstrate light-emitting fibers based on carbon nanotube yarns with a unique planar device concept. The light-emitting fibers are water sensory and easy to be knitted into textiles. The water-polar-electrode-bridged mechanism, light-emitting performance and water sensory properties are discussed. This study may open up a new direction in the development of visual sensing fibers and textiles for the next-generation soft electronics.

Conventional protective garments are passive protection systems that sacrifice breathability (i.e. inhibit water vapor transport) to prevent exposure to harmful agents. This trade-off can lead to overheating in extended wear of protective clothing and severely hinders the duration of their active use. For in-the-field personnel protection from chemical and biological (CB) agents, smart dynamic materials are highly desirable that exhibit a reversible, CB-triggered, rapid transition from a breathable state to a protective state. Materials of this type are expected to be particularly effective in mitigating physiological burden because a less breathable but protective state can be actuated locally and only when needed.
To achieve adaptive protection and simultaneous thermal comfort, we have developed a chemical threat responsive material based on a surface-functionalized carbon-nanotube (CNT)-membrane, in which vertically-aligned CNTs function as the only pores in a polymeric barrier film. Upon exposure to a chemical warfare agent (CWA), responsive polymers grafted at the membrane surface collapse and close the CNT pore entrance to CWA permeation, thus enabling the membrane to switch from a highly breathable state to a protective state.
To demonstrate this concept, we first fabricated membranes with sub 5-nm CNT pores and quantified their breathability and rejection properties before functionalization with CWA-responsive polymers. Our results show that these membranes provide MVTR up to 11,000 gr/m²day, thus exceeding state-of-art breathable fabrics (eVent, GoreTex, etc.) even if the moisture conductive pores are only a few nm wide. Measured water-vapor permeability in 1.9-nm CNT channels under a relative humidity gradient is ~100 times larger than Knudsen diffusion prediction, and this flow enhancement decreases for larger diameter tubes. Complete rejection of 3-nm charged dyes, 5-nm uncharged gold nanoparticles, and ~40-60-nm Dengue virus from aqueous solutions during filtration tests demonstrates that our CNT membranes provide a high degree of protection from bio-threats by size exclusion.¹
Then, we covalently grafted actuating polymers responsive to G-agent simulants to the surface of these CNT membranes.^{2, 3} Upon exposure to simulants, these membranes switch from a breathable state with MVTR> 4,000 gr/m²day to a protective state with MVTR> 1,000 gr/m²day. Permeation tests reveal that simulant transport is reduced by 1-2 orders of magnitude in the protective state. Finally, we demonstrated that a simple base treatment reopens the CNT pores effectively and that regenerated membranes can be re-used for multiple cycles without performance loss.

1. Bui, N.; Meshot, E. R.; Kim, S.; Peña, J.; Gibson, P. W.; Wu, K. J.; Fornasiero, F. Adv. Mater. 2016, 28, 5871-5877.
2. Sha, S.-C.; Zhu, R.; Herbert, M. B.; Kalow, J. A.; Swager, T. M. J. Polym. Sci. A: Polym. Chem. 2017.
3. Belger, C.; Weis, J. G.; Egap, E.; Swager, T. M. Macromolecules 2015, 48, 7990-7994

Based on the recent IEA energy outlook, both solar and wind based energy supply will increase by more than one decade by the year 2040. Such drastic increase requires development of energy storage technologies, as their availability already now is considered forming the bottleneck for further adoption of renewables. Electrochemical water splitting in a membrane electrolysis cell is a promising technology for converting excess electrical energy into chemical bond energy, namely hydrogen bond energy. Hydrogen can serve as an energy carrier and connect energy sector to chemical industry and transportation sectors. In electrolysis cells, the water splitting proceeds via two half reactions: the hydrogen evolution reaction at the cathode (HER: 2H⁺ + 2e^- → H₂) and the oxygen evolution reaction met in the anode (OER: H₂O → 2H⁺ + 2e^- + ½O₂). In acidic membrane cells, scarce platinum group metals (PGMs) are utilized at both the electrodes for electrocatalyzing the above-mentioned reactions.

The cathode is prone to degradation during start up & shut down cycles and consequently, affects the durability of the device. Moreover, it is well recognized the expensive and scarce PGMs cannot cover the foreseen increasing need. Hence, earth-abundant element based durable electrocatalyst for the HER are badly needed.

Carbon nanotubes (CNTs) have several beneficial properties or electrocatalyzing. In addition to high conductivity and good stability, they have appropriate properties for fabricating 3D electrodes. CNTs can function as support for ultra-low-Pt electrocatalysts, or function as a scaffold for synthetizing hybrid electrocatalyst materials comprising only of earth-abundant elements. The latter include doped CNTs as well as transition metal nanoparticles encapsulated in few carbon layers on CNT supports. These materials have inherently different activities towards the HER, but their activity can be also affected by selected synthesis method and starting materials resulting in products with different morphology, surface properties or conductivity, for example. The most active hybrid materials show similar activity to the commercial Pt/C catalyst and excellent durability under the HER conditions. In this presentation, CNT based electrocatalysts promoting the HER are introduced and their properties are discussed. These materials will promote implementation of durable and high-performing electrolyzers.

Recently, we reported that a relativistic Dirac fermion quasicrystal can be realized when the Dirac electrons in a single-layer graphene are incommensurately modulated by another single-layer graphene which is rotated by exact 30° [1]. In this structure, the effective theory for moiré superlattices (i.e., twisted bilayer graphene at angles other than 30°) [3,4] no longer works, since bilayer graphene stacked at 30° gains a 12-fold rotational symmetry which is not compatible with a translation [5].
In this talk, I will discuss the theory of Dirac electrons in a dodecagonal graphene quasicrystal. I will first explain the emergence of the infinite number of Dirac cone replicas in ARPES and the contribution of multiple scattering to the unusually strong scattering signals [1]. Then, I will report a rigorous effective model which can describe the electronic structures of the graphene quasicrystal and show that very unique features, such as the critical states and flat bands arise in this system [6].

[1] S. J. Ahn,* P. Moon,* T.-H. Kim,* H.-W. Kim, H.C. Shin, E. H. Kim, H. W. Cha, S.-J. Kahng, P. Kim, M. Koshino, Y.-W. Son,† C.-W. Yang,† and J. R. Ahn,† Science (2018, in print, dx.doi.org/10.1126/science.aar8412) (*: co-first authors, †: co-corresponding authors).
[2] C. Berger et al., Science 312, 1191 (2006).
[3] J.M.B. Lopes dos Santos, N.M.R. Peres, and A.H. Castro Neto, Phys. Rev. Lett. 99, 256802 (2007).
[4] P. Moon and M. Koshino, Phys. Rev. B 85, 195458 (2012); Phys. Rev. B 87, 205404 (2013).
[5] P. Stampfli, Helv. Phys. Acta 59, 1260 (1986).
[6] P. Moon, M. Koshino, and Y.-W. Son (in preparation).

Mobile gas sensors operating at room temperature with low power consumption, high sensitivity and selectivity are required in many industries as well as in everyday life namely for detecting explosive, combustible and toxic gases, food and air quality monitoring.
The main element of the gas sensor is its’ sensitive material which determines sensors’ sensitivity, selectivity, response time and signal recovery, operation temperature and stability. Single-walled carbon nanotubes (SWCNTs) is a unique material for gas sensors application. Coupled with chemical, thermal and mechanical stability, SWCNTs have large specific surface area with all carbon atoms located on their surface making them exceptionally sensitive for adsorption of gases at room temperatures. In this work we propose a simple approach of SWCNTs low frequency plasma treatment, which on the one hand introduce defects into the structure of nanotubes, which increases gas adsorption and thus increase sensitivity. On the other hand, it allows to obtain different functional groups on SWCNTs surface depending on the plasma atmosphere to increase selectivity of the material.
In this study we investigate SWCNTs conductivity upon adsorption of inorganic gases such like carbon monoxide, nitrogen dioxide and ammonia, and assess the optimal operation temperature and gas concentration detection limits. Particularly, we present the study of oxygen plasma treated SWCNTs with induced defects and oxygen containing groups on its surface which increase SWCNTs sensitivity to such gases as carbon monoxide (respond is 0,5%), nitrogen dioxide (respond is 15%), ammonia (respond is 1.5%), hydrogen disulfide (respond is 0.8%) at room temperature.
The authors acknowledge the Russian Science Foundation (project No. 17-19-01787).

Solution-based device fabrications are now of great interests due to attractive applications of printed flexible and stretchable electronics, which are required to form active components on an amorphous film using deposition and/or printing methods. However, due to difficulties of both p-type and n-type semiconductor formations on a film, most of the studies reported previously are based on Schottky diodes and transistors. To address this bottleneck and challenge, we here propose a solution-based p-n junction diode using developed IZO film and CNT network film formation and integration techniques as n-type and p-type semiconductor materials, respectively. Furthermore, barrier height between IZO and CNT films are also discussed based on the experimental results.
p-n junctions were formed by all solution process on Si/SiO₂ substrates. First, an IZO precursor was spin-coated on the SiO₂ surface with oxygen plasma treatment. After spin coating, it was cured at 300 °C in air ambient. After patterning the IZO film, semiconductor-enriched CNT solution was deposited by using van-der Waals interaction between the chemical-treated SiO₂/IZO surfaces and CNTs. After cleaning the substrate, Ag electrodes were painted on IZO and CNT films. Finally, the samples were annealed at 150 °C in N₂.
Transistor behaviors of I_DS-V_GS using Ag source-drain electrodes and a global back gate were measured. IZO and CNT transistors shows relatively good n-type and p-type behaviors, respectively, with high ON/OFF current ratio of >10⁴. Next, CNT/IZO p-n junction diode was characterized. Based on the results, good rectified behaviors with >10⁴ forward/backward current ratio were observed. After confirming the diode behaviors, barrier height of IZO and CNT was determined by measuring the diode characteristics as a function of temperature. From the experimental results and calculations, the barrier height of them was ~200 meV, which is in good agreement with the theoretical band alignment of CNT and IZO.
In conclusion, we developed p-n junction diode and analyzed the barrier height of CNT and IZO junctions. These material systems will be applied for the flexible devices in near future.