Symposium F.NM03—Nanotubes, Graphene and Related Nanostructures

In the nearly 30 years since the elucidation of the carbon nanotube structure, the reality of mainstream commercial applications, such as touch panels, sealing materials, high performance power sources, etc. are now in the foreseeable future. However, to realize this vision, the practical developmental obstacles need to be resolved. This is precisely the work which is undertaken by the CNT-Application Research Center, AIST. Over the past 15 years, our Center has been working in collaboration with academia and industry to support the establishment of a carbon nanotube industry in Japan by addressing the various stages of research spanning discovery, development, application, scale-up, and commercialization for the general top vital to the development of applications, such as synthesis, processing, and evaluation. In this way, our center works to bring scientific discoveries and bring them to society.
This presentation will provide an overview of our recent progress in the synthesis and application of highly efficient synthesis of millimeter-scale, vertically-aligned single-walled carbon nanotubes using the water-assisted “Super-growth” CVD. In one section of my presentation, I will describe our efforts toward the economical mass-production of single-walled carbon nanotubes (SWCNT). I will then present our progress on the development of commercial applications, and finally I will present some or our work in developing the new technology for the synthetic control of SWCNTs.

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 waste 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 carbon nanotubes (CNTs) and gaseous fuel. To achieve this conversion, a laboratory-scale pyrolytic gasifier was fed with waste plastics including (polyethylene, polypropylene, polyethylene terephthalate, polystyrene, etc.) in an 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 temperatures in the range of 800-1000 °C. The catalytic substrate used for the nanoparticle growth consisted of different grades of stainless steel mesh (SS-304, SS-316 and SS-316L). 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 the mass of the product relative to the mass of feedstock and ranged from 1% to 30%. With the purpose of purification and sorting, the catalysts and the produced CNTs were investigated from synthesis, structure and property characterization by the use of SEM, TEM, AFM, TEM+EDX, HAADF, and TGA. Results showed that the catalyst type, composition and pre-treatment, carrier gas and flowrate as well as the type of waste plastic, are all influential on the yields and physical characteristics of the synthesized CNTs.

This report presents recent results from studies of growth of Carbon Nanotubes (CNTs) by CVD using metal catalyst particles doped with heavy refractory metals. In such growth, the heavy metal acts as a diffusion inhibitor to prevent erosion and Ostwald ripening of the catalyst particles, extending the lifetime of these particles in the CVD environment and thus allowing the growth of longer carbon nanotubes than would normally result. This effect has been demonstarted in several of our recent studies. Here, we report extension of our results to new reactive systems utilizing new catalyst/inhibitor combinations and new carbon feedstock gases. Implications for the growth of ultra-long (tens of cm or more) CNTs will be discussed.

Driven by the exceptional thermal, electrical, optical, mechanical and fluidic properties of single-walled carbon nanotubes (SWCNT), commercial use of vertically aligned “forests” are on the horizon for applications¹ ranging from optical absorbers and thermal interfaces to selective membranes and advanced fabrics.^2,3 Large-area SWCNT forests with high densities and small diameters are especially important for many applications, yet they are conspicuously absent from the literature due to synthesis challenges.
Here, we demonstrate synthesis of high-density (> 10¹² CNTs/cm²), small-diameter (~ 2 nm) SWCNT forests with structural characteristics that remain uniform over large areas (up to 6-in. diameter)⁴ and, surprisingly, largely unchanged over a wide range of synthesis conditions. We also find that our growth regime enables a record-high carbon conversion efficiency and a stable mass kinetics, both of which are invariant with catalyst type (Fe vs Fe/Mo mixes). To identify the limiting steps in the SWCNT growth kinetics and the factors contributing to the process robustness, we determine the dependence of the reaction rate and carbon conversion efficiency on broad ranges of synthesis parameters. Effects of catalyst area (from 1 × 1 cm² to 6-in wafers), growth pressure (20-790 mbar), gas composition (30-fold acetylene partial pressure, hydrogen-argon ratio), and flowrates (8-fold variation) are presented. The observed growth rate trends can be explained quantitatively with a simple kinetic model in which bulk diffusion of acetylene in gas phase is the limiting step in CNT production and hydrocarbon byproduct formation becomes dominant at high hydrogen partial pressure.
Our demonstration of such robust and reproducible growth of high-density forests over a wide range of synthesis conditions provides valuable insights for future scale-up efforts of SWCNT forest production, which are key for widespread adoption of advanced CNT technologies.

1. R. Rao et al., ACS Nano, 12 (2018) 11756.
2. N. Bui, E. R. Meshot, S. Kim, J. Peña, P. W. Gibson, K. J. Wu, F. Fornasiero, Adv. Mater., 28 (2016) 5871.
3. Y. Li, C. Chen, E. R. Meshot, S. F. Buchsbaum, M. Herbert, R. Zhu, O. Kulikov, B McDonald, N. Bui, M. L. Jue, S. Park, C. Valdez, S. Hok, C. J. Doona, K. J. Wu, T. M. Swager, F. Fornasiero, Adv. Funct. Mater., (2020) 2000258.
4. E. R. Meshot, S. Park, S. F. Buchsbaum, M. L. Jue, T. R. Kuykendall, E. Schaible, L. B. Bayu Aji, S. Kucheyev, K. J. Wu, F. Fornasiero, Carbon, 159 (2020) 236-246.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-797268

Abstract
Boron Nitride Nanotubes (BNNTs) have been of great interest due to their electrically insulating, optically transparent, and biocompatible properties. As we have demonstrated, these properties make BNNTs attractive nanomaterials for novel electronic ^1-3 and biomedical⁴ applications. All these applications require high-quality and high-purity BNNTs. One promising approach is by the use of catalytic chemical vapor deposition (CCVD), where the synthesis of BNNTs are well controlled by the use of catalyst^5-6. Therefore, understanding the catalytic behavior and growth mechanism will enable better control of the quality and purity of BNNTs.
Here we describe the discovery of a new compound Mg_x(SiO₂)_y, as the original catalyst for the growth of BNNTs. Based on the growth-vapor trapping (GVT) approach, we have demonstrated the growth of high-quality BNNTs in a regular tube furnace often use for the synthesis of carbon nanotubes, graphene, and many other two-dimensional (2D) materials.^5-6 Such CCVD approach enable the growth of BNNTs using the boron oxide chemistry without involving dangerous and corrosive materials. We found that MgO powders are the effective “catalyst” for our synthesis. However, our results suggest that MgO will work well only on Si substrates, not on other inert substrates. Detailed experiments and analysis suggest that Mg_x(SiO₂)_y, is the actual catalyst responsible for the growth of high-quality BNNTs. We further compare the synthesis of BNNTs using various Magnesium based compounds, some of which favorite the growth of BNNTs in very small tube diameters. A detailed study of these results will be presented at the meeting.


Acknowledgment
We acknowledge the support from National Science Foundation (Awards numbers 1521057 and 1738466).

References
¹Bhandari, S., et al, “Two-dimensional gold quantum dots with tunable bandgaps”. ACS Nano, 13(4), 4347 (2019).
²Qin, J. K., et al, “Raman response and transport properties of tellurium atomic chains encapsulated in nanotubes”. Nature Electronics, 3(3), 141 (2020).
³Lee, C. H., et al, “Room Temperature Tunneling Behavior of Boron Nitride Nanotubes Functionalized with Gold Quantum Dots”. Advanced Materials, 25(33), 4544 (2013).
⁴Yap, Y. K. Zhang, D. Yapici, N. B, “High-Brightness Fluorophores,” US Patent Application US20180296705A1.
⁵Lee, C. H., et al, “Effective growth of boron nitride nanotubes by thermal chemical vapor deposition”. Nanotechnology, 19(45), 455605 2008.
⁶ (Review) Jiesheng Wang, Chee Huei Lee and Yoke Khin Yap, “Recent advancements in boron nitride nanotubes,” Nanoscale 2, 2028 (2010).

Pottery brings the dawn of manufacturing in human history. With it, one can readily design, build, and assemble hollow containers with tailored shapes for various applications. However, this important concept has yet to be emulated in nanoscience. We report a facile synthetic methodology: Nanopottery, where hollow fullerene compartments with tailored shapes and precise stoichiometry can be readily created and assembled via the manipulation of their liquid template, advancing from isolated hollow units to multi-compartment vessels.¹
Precisely controlled docking, merging, and welding of hollow nano-/micro-structures are essential in constructing sophisticated hollow systems, in ways similar to the building of plumbing and biosystems. To this end, regioselectivity during the processes is an important milestone demanding new tools.
We bring steric effect, a powerful regioselective method in organic reactions, to nanoscale for the precise assembly of fullerene nanobowls, reaching dimers of 93.6% purity in one-step. To the best of our knowledge, the dimerization sets a new record of the highest purity sample before purification. M-xylene liquid nanodroplets that template the growth of bowls can be readily docked and merged, producing the dimers and tetramers. The regioselectivity is controlled by steric hindrance, i.e., the relative size of the exposed liquid droplets vs. the hemispherical shell, so that the docking process can be readily modulated to govern the stoichiometry. The mechanism is studied in detail and further supported by geometrical models. We believe that the development of new regioselective tools and the understanding in docking and welding hollow structures would expand the horizon of nanoscience, opening new possibilities for designing sophisticated hollow nano-systems.²
Reference:
1. Fei Han and Hongyu Chen* et al. “On demand synthesis of hollow fullerene nanostructures.” Nat. Commun., 2019, 10, 1548.
2. Fei Han and Hongyu Chen* et al. “Precise dimerization of hollow fullerene compartments.” J. Am. Chem. Soc., 2020, Just accepted (DOI 10.1021/jacs.0c06190).

DNA-carbon nanotube (DNA-CNT) hybrids are useful constructs for CNT sorting and biosensing applications. Historically, shorter sequences (~ 10 to 12 mers) are found to give rise to better separation outcome. Even though it is known that sequences shorter than 10 mers leads to less stable dispersions, the length limit has never been explored systematically in terms of dispersion stability and separability. We have recently combined experimental and machine learning guided search to explore short ( N ≥5) DNA sequence space in a non-biased manner. In this talk, I will present our new CNT resolving sequences identified through this work, and their utility in chiral sensing of small molecules.

Having access to SWCNTs samples enriched in certain structures is a fundamental goal in order to exploit their properties within the scope of specific applications. One way to produce such samples is to achieve structurally selective growth of SWCNTs. Aside from the obvious scientific challenges related to this very active research field, being able to precisely and accurately assess the composition of a growth sample is a key point for understanding the phenomena underlying growth selectivity.
A widely used characterization methodology for assessing the selectivity of CVD grown SWCNT on flat substrates is based on resonant Raman spectroscopy mappings using a set of discrete laser lines. In this work we thoroughly investigate the reliability of this methodology through cross-characterizations with other techniques on specifically chirality- and /or diameter-sorted samples. By comparing, first, Raman results with atomic resolution transmission electron microscopy statistical analyses, we evidence significant discrepancies between the two techniques. Further comparison with photoluminescence and optical absorption measurements shows that the observed discrepancies clearly stem from the chirality-dependence of SWCNT Raman cross-sections and the patchy vision offered by the use of only a few discrete excitation wavelengths, allowing us to propose some insights for a more reliable methodology.

Narrowband emission in the near-infrared and electrical generation of excitons make long, polymer-sorted semiconducting single-walled carbon nanotubes (SWNTs) desirable materials for light-emitting devices. Their successful functionalization with sp³ defects acting as luminescent exciton traps (ACS Nano 2019, 13, 9259) has emerged as a powerful route to accomplish red-shifted emission with increased efficiency and even single-photon emission at room temperature. Since the emission properties of individual defects depend crucially on their binding configuration to the SWNT lattice and the nature of the attached functional group, they can be tuned over a certain energy range. Here, we present functionalization strategies enabling precise control of the defect binding configuration and thus emission wavelength and lifetime in polymer-wrapped (6,5) and (7,5) SWNTs. Electroluminescence from the introduced defects is readily achieved by incorporating such tailored SWNTs into a light-emitting field-effect transistor structure. To add further functionality, we have created sp³ defects bearing stable organic radicals. These paramagnetic and redox-active moieties respond to magnetic and electric fields and thereby allow for unprecedented control of the electronic structure at the defect site.

The thermodynamic properties of fluids confined within nanometer-sized pores greatly differ from the ones of their bulk form. In particular, as the pore size becomes comparable to the size of the fluid’s constituent molecules, the continuum assumption breaks down and peculiar size-dependent physicochemical behavior emerges. Here, we use Raman spectroscopy to probe the liquid-vapor phase transition of water inside individual, free-standing single-walled carbon nanotubes of different diameters. We report controlled and reversible vaporization of the nanoconfined water by varying the laser power of the Raman excitation laser. The Raman G band serves as built-in thermometer of the local nanotube temperature. We show that our measurements can be described by a diffusive heat transfer model, which allows extraction of the diameter-dependent phase transition temperature based on the characteristic redshift of the nanotube’s radial breathing mode upon vaporization. We further perform all-atom molecular dynamics simulations to computationally corroborate our experimental results and to elucidate the underlying molecular behavior of water in these single-digit nanopores. Our results shed new insights on the physicochemistry of nanoconfined fluids, and will inform ongoing efforts in the field towards establishing a unified force field for water.

Over the past decade, substantial progress has been made in the chemical control of single-wall carbon nanotubes (SWCNTs). Large, horizontally aligned films can now be created out of post-processed SWCNT solutions, which has lead to advances in SWCNT physics, including the observation of intersubband plasmons, hyperbolic thermal emission, ultrastrong exciton-polariton coupling, nanotube quantum wells, and directional nanotube optoelectronics. Here, we use machine-vision automation to simultaneously produce globally aligned SWCNT films using pressure-driven filtration. Feedback control enables filtration to occur with a constant flow rate that not only improves the nematic ordering of the SWCNT films, but also provides the ability to align a wide range of SWCNT types and on a variety of nanoporous membranes using the same filtration parameters. Using polarized optical spectroscopy, we show that under standard implementation meniscus combing produces a two-dimensional radial SWCNT alignment on one side of the film. After we flatten the meniscus through silanation, spatially resolved nematicity maps on both sides of the SWCNT film reveal global alignment across the entire structure. From experiments changing ionic strength and membrane charging, we provide evidence that the SWCNT alignment mechanism stems not from pre-existing membrane grooving, but from membrane charging.

Transparent conducting films are now in limelight of modern electronics driven by the expanding field of flexible devices that include displays, touch screens, solar cells, etc. Beside high transparency and good conductivity, such applications require rather good flexibility of materials to be preferably made under cost-effective fabrication protocols. As a result, the dominance of classical TCF material, indium tin oxide, is being impugned by alternatives like Ag nanowires mesh, PEDOT:PSS, graphene, reduced graphene oxide and single-walled carbon nanotubes (SWCNTs).

Here, we developed a novel easy strategy of simultaneous outer- and inner-surface SWCNT doping with HAuCl₄ ethanol solution for efficient optoelectrical performance enhancement. Application of the proposed strategy allowed us to obtain transparent conductive SWCNT films with a record equivalent sheet resistance value of 31 ± 4 Ω/sq at the annealing temperature of 400°C. We also showed that enhancement of optoelectrical properties of thermally treated SWCNT films should be attributed to the cap's removal during the annealing, thus providing feasible penetration of dopant solution into the inner SWCNT cavity under capillary forces. Electrochemical investigation of doping process confirmed more efficient p-doping of annealed SWCNTs in comparison to pristine. Besides, the origin of these differences was proposed to be switch of doping species from [AuCl₄]^- to stronger electron-accepting [AuCl₂]^-. DFT-calculations of SWCNT doping proved more significant Fermi-level downshift in case of simultaneous doping from outside and inside of nanotube confirming stronger doping. Based on UV-vis-nIR and Raman spectroscopies we have established that caps’ removal process starts from 300 °C annealing, while comparing the equivalent sheet resistances of doped films we found the optimal treatment temperature range to be 300 - 400 °C. The reliability of conclusions was confirmed by the results consistency of UV-vis-nIR and Raman spectroscopies, TEM imaging, electrochemical measurements and DFT-calculations.

The experimental part of the research was supported by the Russian Science Foundation (No. 17-19-01787).

Because of the rapid growth of integrated wireless sensor networks (WSNs), for diverse applications from health to environmental monitoring, recharge-free, safe, and flexible power sources are in urgent demand. Thermoelectric (TE) generators based on macroscopic, neat assemblies of carbon nanotubes are strong candidates due to their superb electrical, thermal, and mechanical properties, combining the advantages of inorganic and organic TE materials (1). Here we report an ultrahigh value of thermoelectric power factor at room temperature (14±5 mWm^-1K^-2) for carbon nanotube fibers with an ultrahigh electrical conductivity (>10⁷ Sm^-1). These fibers are also flexible, strong, and refractory at the same time (2). By combining these unique properties, we fabricated a wearable power generator. Through temperature and magnetic field dependent electrical conductivity measurements, we found that electrical transport in the fiber is highly metallic, showing small quantum corrections at the lowest temperatures (< ∼40K). Our theoretical simulations, combined with Fermi-energy-dependent experiments through doping and gating, show that the observed ultrahigh power factor is a consequence of simultaneously enhanced conductivity and Seebeck coefficient when the Fermi energy is near a van Hove singularity in the electronic density of states of carbon nanotubes.

Reference:
1. J. L. Blackburn, A. J. Ferguson, C. Cho, and J. C. Grunlan, Carbon-Nanotube-Based Thermoelectric Materials and Devices. Adv. Mater. 30, 1704386 (2018).
2. N. Behabtu, C. C. Young, D. E. Tsentalovich, O. Kleinerman, X. Wang, A. W. K. Ma, E. A. Bengio, R. F. ter Waarbeek, J. J. de Jong, R. E. Hoogerwerf, S. B. Fairchild, J. B. Ferguson, B. Maruyama, J. Kono, Y. Talmon, Y. Cohen, M. J. Otto, and M. Pasquali, Strong, Light, Multifunctional Fibers of Carbon Nanotubes with Ultrahigh Conductivity. Science. 339, 182 (2013).

In microelectronic packaging, an interposer is an intermediate substrate acting as a bridge connecting the nanometer-level I/Os at the die to the micrometer-level package at the substrate. A through-silicon-via (TSV) interposer is very common one with copper filled inside the via as interconnections. As electronic devices continue miniaturization, the significantly increased heat generation inside the miniature devices deteriorates their lifetime/reliability, generally caused by delamination or break at the interface due to the non-uniform strain distribution induced by the mismatch of the coefficient of thermal expansion (CTE) between Si and copper. Therefore, the demands for interposer materials with high electrical conductivity but low CTE are growing. Here we demonstrate a fabrication/application feasibility of carbon nanotube-copper (CNT-Cu) composite using as interposer utilizing its superior electrical and thermal properties. The CNT-Cu composite showed a Cu-level electrical conductivity (~2.5×10⁵ S/cm) and Si-comparable CTE (~7 ppm/K). The CTE mismatch between CNT-Cu and Si was greatly reduced, only 1/5 of that between Cu and Si. Finally, we demonstrated several applications of CNT-Cu TSV interposer. The CNT-Cu TSV interposer may be one of potential candidates in microelectronic packaging.

Composites consisting of a metal matrix with embedded carbon nanostructures, such as graphene and carbon nanotubes, can have properties that take advantage of the excellent charge carrier mobility, thermal conductivity and mechanical strength of the carbon nanostructures and the high density of electrons in the metal. The combination of the composites’ high mechanical strength with high electrical and/or thermal conductivities make them unique candidates in applications such as high power transmission lines, interconnects, heat exchangers, motors, photovoltaic cells and transparent electrodes, among others. Metal/nanocarbon composites made by chemical vapor deposition, friction stir, ball milling, and plasma spraying have yielded materials with enhanced hardness and tensile strength but unimproved electrical and thermal conductivities. We use an electrocharging assisted process to produce composites, which consists of the application of a high DC current to a mixture of liquid metal and particles of activated carbon. The high current density transforms the activated carbon particles from amorphous to crystalline graphitic nanoribbons in the liquid metal. Upon solidification of the metal the nanoribbons self-assemble with an epitaxial relation with the metal. We have used Al 1350 and activated carbon particles of <100 nm and obtained samples with global electrical conductivities more than 5% higher than the parent alloy as well as enhanced local stiffness, measured by nanoindentation. The conductivity enhancement is correlated with increasing crystallite size and concentration of the produced graphene nanoribbons. Molecular dynamic simulations of nanoindentation tests into the nanocarbon metal composite show how the graphene nanoribbons impede dislocation motion and increase hardness with little to no impact on elastic properties. Conductive AFM shows an increase in the local conductivity from these samples compared to the parent aluminum alloy.
Supported by DOE EERE Award EE0008313 and the Army Research Laboratory under Cooperative Agreement W911NF-19-2-0291.

Based on the IEA energy outlook [1], both solar and wind based energy supply will increase by more than one decade by the year 2040. This development lays foundation for the hydrogen economy concept where hydrogen serves as an energy carrier. Hydrogen utilization requires, however, introduction of efficient, durable and economically feasible electrochemical conversion technologies for converting electrical energy into hydrogen bond energy and vice versa. Electrochemical water splitting electrolyzers and fuel cells based on low-temperature membrane technologies can meet these expectations if their key components, such as electrocatalysts for hydrogen reactions, can be improved to meet the sustainability and cost requirements. Today scarce platinum group metals (PGMs) are utilized to electrocatalyze the hydrogen evolution and oxidation reactions met in electrolyzers and fuel cells, respectively. In addition to PGM availability and cost issues, these electrocatalysts suffer from inadequate durability.
Here, utilization of high aspect ratio electrocatalyst comprising of Pt nanowire (PtNW) and particles on single-walled carbon nanotubes (SWNTs) is suggested as low PGM electrocatalyst [2]. SWNTs have several beneficial properties needed for electrochemical applications: In addition to high conductivity and good chemical and electrochemical durability, they have appropriate properties for fabricating 3D electrodes needed for efficient mass transfer during the reactions.
The feasibility of composite Pt/SWNT electrocatalysts is verified in a single cell laboratory-scale polymer electrolyte electrolyzer. In terms of activity, even with one tenth of Pt mass loading at the cathode (0.02 mg_Pt cm^-2), this catalyst accomplishes close to the level of the state-of-the-art Pt/C. The high activity is attributed to favorable PtNW interaction with the SWNTs as well as exposed PtNW edge-sites which adsorb hydrogen optimally and help to alleviate repulsive interactions on the nanowire surface. In addition, the metallic nature of Pt, morphological effects and enhanced surface wetting contribute positively to the performance.
The stability and durability are confirmed with 8,000 h of chronopotentiometry measurements and 10,000 potential cycles in the electrolyzer. These are combined with in-situ electrochemical and post-mortem analysis to investigate the durability of the electrocatalyst and aging mechanisms. Overall, the Pt/SWNT compares favorably to the reference Pt/C.

[1] Annon., World Energy Outlook. Part B. Special focus on renewable energy. IEA 2016.
[2] T. Rajala, T. Kallio, Ultra-low Pt electocatalyst, Invention disclosure has been filed to Aalto University with nr. IPID2180 27.6.2018.
[3] T. Rajala, R. Kronberg, R. Backhouse, M. E. M. Buan, M. Tripathi, A. Zitolo, H. Jiang, K. Laasonen, T. Susi, F. Jaouen, T. Kallio, A platinum nanowire electrocatalyst on single-walled carbon nanotubes to drive hydrogen evolution, Applied Catalysis B: Environmental 265 (2020) 118582.

Scanning Transmission Electron Microscopy (STEM) is a key technique for probing the local defect microstructure of 2D materials and their parent crystals at the atomic scale. By combining STEM with electron energy loss spectroscopy and energy dispersive X-ray spectroscopy the local chemistry can also be investigated. Here we demonstrate the use of STEM imaging and analysis to investigate the microstructure of mechanically deformed and liquid phase exfoliated 2D van der Waals materials (graphite, boron nitride, MoSe₂).
We find that at the atomic scale the bending behaviour, and types of microstructural defect that result, can be predicted from just the bend angle and thickness of the materials.[1] In particular, we find that above a critical thickness the deformed materials exhibit numerous twin boundaries and for large bend angles these can contain nanoscale regions of local delamination. Such microstructural features are proposed to be important in determining how easily the material can be thinned by mechanical or liquid phase exfoliation.[1] Recent work has extended these studies to consider the microstructure of liquid exfoliated 2D van der Waals materials at the early stages of processing.[2] We demonstrate that during ultrasonic liquid phase exfoliation, the transition from graphite flakes to graphene takes place in three distinct stages. Firstly, sonication leads to the rupture of large flakes and the formation of kink band striations on the flake surfaces, primarily along zig-zag directions. Secondly, cracks form along these striations, and together with intercalation of solvent, lead to the unzipping and peeling off of thin graphite strips that in the final stage are exfoliated into graphene.[2] We anticipate that the findings will be of great value in the quest to optimize the lateral dimensions, thickness and yield of graphene and other 2D materials for various applications.
Furthermore, we demonstrate that in deformed graphite, zigzag kink bands (and associated twin boundaries) induce local stacking faults. Thus, the Raman signature of zigzag kink bands in graphite can be used to determine crystallographic directions. A sequence of ideal zigzag twin boundaries produces a region of crystal with a complex and highly unfavourable stacking sequence AABBCC.[1] We find that by peeling along specific crystallographic direction mechanical exfoliation can be used to induce large areas of thermodynamically unfavourable rhombohedral (ABC) stacking in graphite. then perform directional encapsulation of ABC-rich graphite crystallites with hexagonal boron nitride (hBN). Encapsulation with hexagonal boron nitride, which is introduced parallel to the graphite zigzag edges, preserves ABC stacking, while encapsulation along the armchair edges transforms the stacking to ABA. [3] The ability to create and preserve ABC stacking has recently been used to reveal an abundance of exotic interaction-induced physics including topological surface states in this material. [4]

References
[1] A. P. Rooney et al. Anomalous twin boundaries in two dimensional materials, Nature Communications (2018) 9, 3597
[2] Z. Li et al Mechanisms of Liquid Phase Exfoliation for the Production of Graphene, ACS Nano, Article ASAP, 2020, 10.1021/acsnano.0c03916
[3] Y. Yang et al. Stacking Order in Graphite Films Controlled by van der Waals Technology, Nano Lett. 2019, 19, 12, 8526–8532
[4] Y. Shi et al Electronic phase separation in topological surface states of rhombohedral graphite,
arXiv:1911.04565

Two-dimensional (2D) materials show a variety of promising properties, and characterizing their structural properties is fundamental for basic research and practical applications. 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 in-situ TEM technique, the physical and chemical properties of nanomaterials have been investigated. In this presentation, we will report our progress on studies of electrochemical properties and phase transition mechanism of carbon nanostructures and 2D layered transition metal dichalcogenides (TMDs) by alkali metal storage. And the epitaxial growth of large-scale single crystal hBN monolayer will be also included.

Van der Waals heterostructures give access to a wide variety of new phenomena that emerge due to the combination of layered materials with different properties. One of the key engineers the properties of 2D materials could be in the ability to alter their structure in a controllable way. Different methods are possible: functionalization, intercalation, inducing defects etc. Whatever the chosen method the consequences is a strong modification of their structure and thus on their electronic and vibrational properties. All these effects can be probed efficiently by optical phonons. Up to now various methods have been used as argon bombardment, electron beam irradiation, graphene oxidation, ..ect.

In this work we will try to unravel the structural modification induced by defects in the case of graphene and MoS2. In the case of few- and single-layer MoS2 hosting substantial defects densities, these defects are thought to influence the doping level, the crystal structure, and the binding of electron–hole pairs. We disentangle the concomitant spectroscopic expression of all three effects and identify to what extent they are intrinsic to the material or extrinsic to it, i.e., related to its local. We discover a defect-bound state having a low binding energy of 20 meV that does not appear sensitive to strain and doping, unlike charged excitons. Conversely, the defect does not significantly dope or strain MoS2 [1].

We also show here that due to an enhanced interaction cross section in such structure, made of molybdenum disulphide and boron nitride, electron-hole pairs can be generated by incident electrons and give rise to cathodoluminescence. Using Raman spectroscopy and photoluminescence, we show that low energy electron beam irradiation can nevertheless cause irreversible structural damages in molybdenum disulphide. A correlation between molybdenum disulphide/boron nitride coupling and the defect creation is established. Our work demonstrates that cathodoluminescence is powerful tool images the electronic properties in van der Waals heterostructures at the nanometer scale.
In the case of graphene, we report the observation of an intense anomalous peak in the Raman spectrum in specific growth conditions that cannot be attribute to structural defects. In fact, bombardment with an electron beam demonstrates that this new peak is clearly distinct from the well-studied D’ peak appearing as defects are created in graphene [3].
[1] S. Dubey, et al, ACS Nano, 2017, 11 (11), pp 11206–11216
[2] G. Nayak et al, Phys. Rev. Materials 3, 114001 (2019)
[3] D. Kalita et al, submitted to PRB.

Covalently bound impurity atoms in crystal lattices can be manipulated using the atomically focused electron probe of an aberration-corrected scanning transmission electron microscope. This has unveiled new perspectives for top-down atomic engineering, with the potential to surpass existing techniques in both versatility and capabilities. Such advances have been made possible by developments in electron optics and instrument stability, and the incorporation of impurity elements using techniques such as ion implantation [1].

The first system where this potential was realized was incidental silicon impurities in single-layer graphene. Elastic backscattering of an energetic probe electron from a moving C nucleus [2] causes the Si to directly exchange places with one neighboring C atom via an out-of-plane displacement [3], and such dynamics can be controlled by directing the focused electron beam at the desired atom [4,5]. Recent experiments have demonstrated greatly improved control [6], with a manipulation rate already nearly on par with any atomically precise atom manipulation technique. Such manipulation is also possible in large-diameter single-walled carbon nanotubes [7].

Besides Si impurities, P dopants in graphene can be manipulated with an electron beam [8], but at least for the out-of-plane displacement mechanism, it seems there are physical limits on what is feasible since significantly heavier Ge impurities cannot be thus manipulated [9]. The curious replacement of irradiated impurities by carbon atoms has also emerged as a practical hurdle for the further scaling of the technique. However, there are many possible lattice impurity atoms whose atomic dynamics under electron irradiation have been observed, including N and B [10], though their manipulation has not yet been demonstrated.

Even more excitingly, the electron-beam manipulation of Bi dopants in bulk silicon was recently reported [11], although the precise mechanism remained unclear. We have applied our established ab initio modeling methodology [12] to address this question, revealing a novel type of mechanism we call indirect exchange. Contrary to the process in graphene, the primary knock-on atom does not end up as a neighbor of the impurity, but as a next-nearest neighbor, displacing another silicon atom during the dynamics. It is thus clear that electron-beam manipulation of lattice impurities has opened an exciting new frontier for materials science and nanotechnology.

References:

[1] T. Susi et al., 2D Mater. 4, 021013 (2017)
[2] T. Susi, J.C. Meyer, J. Kotakoski, Nat. Rev. Phys. 1, 397 (2019)
[3] T. Susi et al., Phys. Rev. Lett. 113, 115501 (2014)
[4] T. Susi et al., Ultramicroscopy 180, 163 (2017)
[5] O. Dyck et al., Appl. Phys. Lett. 111, 113104 (2017)
[6] M. Tripathi et al., Nano Lett. 18, 5319 (2018)
[7] K. Mustonen et al., Adv. Func. Mat. 29, 1901327 (2019)
[8] C. Su et al., Sci. Adv. 5:eaav2252 (2019)
[9] M. Tripathi et al., ACS Nano 12, 4641 (2018)
[10] T. Susi et al., 2D Mater. 4, 042004 (2017)
[11] B. Hudak et al., ACS Nano 12, 5873 (2018)
[12] T. Susi et al., Nature Communications 7, 13040 (2016)

Engineering the metal-carbon hetero-interface has become an increasingly important route toward achieving cost effective and high performing electrocatalysts. In general, these interfaces can alter the valence states of metal electrocatalysts, changing the adsorbate energy of intermediates, and thus the reaction kinetics. The unique properties of graphene edge sites, such as the high available density of states and extended unpaired π-bonding, make it a promising candidate to tune the electronic properties of metal catalysts. Yet to date, understanding and leveraging graphene edge-metal catalysts for improved electrocatalytic performance remains largely elusive.

We demonstrate an efficient yet tuneable method to synthesize graphene edge planes at scale by combining plasma-enhanced chemical vapor deposition (PECVD) methods with a post-treatment Ar plasma. PECVD results in the growth of vertically aligned graphene (VG), with high surface area, an open and interconnected 3D structure, good mechanical stability, and high conductivity, on a range of substrates such as metal foams, foils, and carbon fibers. On the other hand, the Ar plasma post-treatment acts to induce branching of the graphene edges, rearranging carbon atoms under the plasma induced electric field, systematically increasing their exposed surface. By employing this method, it becomes possible to synthesize carbon-based electrocatalytic supports with desirable properties and edge-states, at large scale.

To demonstrate a specific application which exploits the exposed edge planes of VG, we employed this combined PECVD method with Ar plasma post-treatment to synthesize edge-rich VG (er-VG), and used it as a support for electrodeposited Ni-Fe hydroxides in the oxygen evolution reaction (OER). The hybrid Ni-Fe/er-VG catalyst exhibits excellent OER performance with a mass current of 4051 A g^-1 (at overpotential η = 300 mV) and turnover frequency (TOF) of 4.8 s^-1 (η = 400 mV), outperforming Ni-Fe deposited on pristine VG and other metal foam supports.

To understand how the edges were able to influence the valence state properties of the deposited metal, angle-dependent X-ray absorption spectroscopy was used to show that the edge-rich VG support can preferentially template Fe-O units with a specific valence orbital alignment interacting with the unoccupied density of states on the graphene edges. This graphene edge-metal interaction was shown to facilitate the formation of undersaturated and strained Fe-sites with high valence states, while promoting the formation of redox-activated Ni species, thus improving OER performance.

These findings open new opportunities in rationally designing the graphene edge-metal interface in electrocatalysts for various energy conversion and chemical synthesis reactions.

Many simulations and experiments have investigated pressure-driven fluid flow in carbon nanotubes (CNTs) and demonstrated enormous transport rates through these channels. Comparatively little attention has been given so far to concentration-driven transport^1,2 in CNTs despite its importance in a large variety of fields. While several studies assumed bulk/hindered diffusion for small molecules through nm-wide CNTs, other simulations have predicted self-diffusion coefficients several times larger than in the bulk. These large uncertainties in the magnitude of the diffusion rates through CNTs have hampered their full exploitation in nanofluidic devices.³

To obtain a precise quantification of the diffusive flow in CNTs, we have fabricated membranes with a large but known number of single-walled carbon nanotubes (SWCNT) as fluid transport pathways. Contrary to previous membrane systems, this platform enables us to minimize uncertainties in the calculation of the per-pore flow rate. A series of stringent control experiments confirms that these membranes are defect free and that transport occurs only through SWCNTs. Once corrected for the boundary layer resistance at the membrane/fluid interface, our measurements reveal that the transport diffusivity of small ions in single-walled carbon nanotubes is more than one order of magnitude faster than in the bulk.⁴ This flow enhancement scales with the ion free energy of transfer from bulk solutions to a nanoconfined, lower-dielectric environment. Together with indicating that CNT membranes could enable dialysis processes with unprecedented efficiency, these results have important implications for a broad range of applications such as energy storage/harvesting and chemical separation/detection, where ion permeation through nanoporous carbon materials is key.

References
1. Y. Li, C. Chen, E. R. Meshot, S. F. Buchsbaum, M. Herbert, R. Zhu, O. Kulikov, B McDonald, N. Bui, M. L. Jue, S. J. Park, C. Valdez, S. Hok, C. J. Doona, K. J. Wu, T. M. Swager, F. Fornasiero, Adv. Funct. Mater (2020)
2. N. Bui, E. R. Meshot, S. Kim, J. Peña, P. W. Gibson, K. J. Wu, F. Fornasiero, Adv. Mater., 28 (2016) 5871.
3. S. Guo, E. R. Meshot, T. Kuykendall, S. Cabrini, F. Fornasiero, Adv. Mater. 28 (2015), 5871.
4. S. Buchsbaum, M. L. Jue, C. Chen, E. R. Meshot, S. J. Park, A. Sawvel, E. Lau, T. A. Pham, K. J. Wu, F. Fornasiero, under review (2020)

Spin filtering, which is an important prerequisite for spin logic, involves the selective transmission of spin-polarized carriers. A perfect spin filter allows all majority (or minority) spin carriers to pass through a channel while blocking the minority (or majority) carriers. Since the discovery of magnetism in polymerized C₆₀, the search for a novel low-dimensional metal-free material that would exhibit magnetism at a higher temperature with excellent spin filtering property has been intensively pursued. In this talk, I will give an example of a spin filter comprised of a metal-free fluorinated single-wall boron nitride nanotube (F-BNNT) coupled to non-magnetic electrodes to elucidate the physics of spin filtering. Upon functionalization with fluorine, BNNT is found to display long-range ferromagnetic ordering of spins that is stable at a temperature much above the room temperature.The quantum transport approach is adopted to model the spin filter. Spin filter efficiency as high as 99.8% is found in a model F-BNNT junction.

In recent years, many nanosystems, namely, carbon nanotube (CNT), graphene, BN sheet, metal dichalcogenides (MDC), borocarbonitride (BCN), black phosphorus (BP) etc. have been shown to exhibit many fold benefits for applications in a number of fields, namely, absorbates, chemical sensors, field effect transistors, solar cells, rechargeable battery, to name a few. In fact, recent experimental advancements on the control over the structural aspects of nanomaterials has enabled material scientists to tailor the material properties with improved reliability and functionality. We have been modeling these materials for their applications in electronic charge transport, as Li/Na/Mg Anode and various electronic and optical sensing behaviors. We have derived relaxation time formulation from complete Boltzmann transport equation and obtained all the parameters from ab-initio density functional theory. Using this formalism, we have calculated charge carrier mobilities of a few BN-modified graphene layers and bilayer systems. We have shown that leading carrier transport in BCN layers can be changed from electrons to holes with high mobility values through change in surface topology[1]. We have computed mobility values for trilayer phosphorene and bilayer MoS₂ polytypes. The microscopic reason behind the carrier anisotropy and variation in terms of polytypes have been obtained [2,3]. In the case of rechargeable battery, we have looked at the potential of using Boron-sheet, BCN layer and BP as anode materials for Li, Na and Mg ion rechargeable battery and super-capacitors [4-6]. If time permits, I shall discuss Born-Oppenheimer Molecular Dynamics (BOMD) and DFT studies on trapping of BPA (Bisphenol A) with solvent [7], gaseous pollutants [8], DDT [9] on MDC, doped graphene and doped CNT respectively. We also have shown that it is possible to tune the interlayer coupling dynamically by signing light on the superlattices of graphene and BN sheet [10].

1. S. Banerjee and S K Pati, “Criticality of Surface Topology for Charge-carrier Transport Characteristics in Two-Dimensional Borocarbonitrides: Design Principle of an Efficient Electronic Material”, Nanoscale 6, 13430 (2014).
2. S. Banerjee and S K Pati, “Charge Transport Anisotropy in Black Phosphorus: Critical dependence on the number of layers”, Phys. Chem. Chem. Phys. 18, 16345 (2016).
3. S. Banerjee, J. Park, C. S. Hwang, J -H Choi, S -C Lee and S K Pati, ”Polytypism regulates the transport property: A computational study on bilayer MoS₂”, Phys. Chem. Chem. Phys. 19, 21282 (2017).
4. S. Banerjee, G. Periyasamy and S K Pati, “Possible application of 2D-Boron sheets as Anode Material in Lithium Ion Battery: A DFT and AIMD study”, J. Mater. Chem. A 2, 3856 (2014).
5. S. Banerjee, S. Neihsial and S K Pati, “First-principles Design of a Borocarbonitride based Anode for Superior Performance in Sodium-ion Battery and Capacitor”, J. Mater. Chem. A 4, 5517 (2016).
6. S. Banerjee and S K Pati, “Anodic performance of Black Phosphorus in Magnesium-ion Battery: The Significance of Mg-P Bond synergy”, Chem. Commun. 52, 8381 (2016).
7. S. Banerjee and S K Pati, “Surface Mediated Extraction and Photo-response Modulation of Bisphenol A derivatives: A Computational Study”, ACS Appl. Mater. Interfaces 7, 23893 (2015).
8. D. Ghosh and S. K Pati, “Trapping of gaseous pollutants on defective N-doped graphene”, Phys. Chem. Chem. Phys. 19, 636 (2017).
9. A. Bandyopadhyay, D. Ghosh and S K Pati, “Sensing and Trapping Hazardous Insecticides by Single Walled Carbon Nanotubes”, Phys. Chem. Chem. Phys (revision, 2017).
10. P. Kumar et. al, “Laser Shock Tuning Dynamic Interlayer Coupling in Graphene−Boron Nitride Moire' Superlattices”, Nano Lett. 19, 283 (2019).

We have developed a new nanotube technonogy for producing a series of dyes with ultra-high fluorescent brightness for biomedical application [1]. The brightness of our dyes is widely tunable, up to 1000 times brighter than any known dyes. Based on this technology, we have synthesized three types of new dyes NovoLux^® 488 (488/515 nm), NovoLux^® 560^® (560/580 nm), and NovoLux 640^® (640/660 nm). The design, synthesis, antibody conjugation, and extinction coefficient data of these new dyes will be presented in the meeting.

Organic dyes, and fluorescent proteins are widely used for biomedical application such as fluorescent microscopy and flow cytometry. Conventional organic dyes are not as bright as protein dyes such as PE (extinction coefficient, ∈ = 2.5x10⁶ M^-1 cm^-1; quantum yield, QY= 0.8) and APC (∈=7.0x10⁵ M^-1 cm^-1, QY=0.68). Our new platform dye technology allows us to synthesize ultra-high brightness dyes with extinction coefficient as high as 10¹⁰ M^-1 cm^-1 [1]. Our dyes are constructed by three components: DSPE-PEG(5000)Amine, 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[amino(polyethylene glycol)-5000] as the polymeric linkers, carbon nanotubes (CNTs) and boron nitride nanotubes (BNNTs) as the nanocarriers, and organic dyes as the fluorescent elements. DSPE-PEG (5000) Amine are used as the linkers to conjugate organic dye molecules and antibody on CNTs or BNNTs. BNNTs are chosen because they are electrically insulating and optically transparent (band gap of 6eV) [2-4]. BNNTs also offer defect-free surfaces with fully coordinated hexagonal boron nitride (h-BN) network that allow simple pi-pi conjugation of polymer linkers. Because of these unique properties, hundreds of organic dyes can be self-assembled on the surfaces of BNNTs through the DSPE-PEG linkers without quenching. This contributes to the high extinction coefficient and high-brightness of our dyes. Details of the design, synthesis, antibody conjugation, and extinction coefficient data of these new dyes will be presented in the meeting.

[1] Y. K. Yap, D. Zhang, N. B. Yapici, “High-Brightness Fluorophores,” US Patent Application US20180296705A1.
[2] (Review) J. Wang, C. H. Lee, Y. K. Yap, “Recent Advancement in Boron Nitride Nanotubes,” Nanoscale 2, 2028 (2010)
[3] C. H. Lee, et al, Advanced Materials 25, 2544 (2013).
[4] J. K. Qin, et al, Nature Electronics, 3(3), 141 (2020).

NovoLux^® 488 and NovoLux^® 640 are developed under the support of National Science Foundation (IIP 1521057, IIP 1738466). NovoLux^® 560 is developed under the support of M-TRAC for Life Sciences Innovation Hub co-managed by the University of Michigan and the Michigan Economic Development Corporation (MEDC). We acknowledge supports from the Michigan Corporate Relations Network (MCRN) Small Company Innovation Program (SCIP), The Michigan Emerging Technologies Fund (ETF).

We have developed a platform technology which allow us to synthesize new dyes with ultra-high brightness for flow cytometry applications. Our unique technology allows us tuning brightness to desired levels (10X to 1000X brighter than commercial dyes) for detection of undetectable by achieving femtomole detection level.
Brightness of dyes are defined by multiplication of quantum yield (QY) and extinction coefficient of a dye. The known brightest commercial dyes are PE and APC with extinction coefficients 2.5x10⁶ M^-1 cm^-1 (QY=0.8) and 7.0x10⁵ M^-1 cm^-1 (QY=0.7), respectively. To date, we have developed ultra-high brightness fluorescent dyes in three colors: NovoLux® 488, NovoLux® 560 and NovoLux® 640. For one of our NovoLux 488 samples, the extinction coefficient is 7x10⁷ M^-1 cm^-1 (QY= 0.5). This is brighter than FITC dye by 897X (extinction coefficient of FITC is 7.8x10⁴ M^-1 cm^-1 QY=0.5). This make NovoLux 488 the brightest dye in the 488 channels. On the other hand, one of our NovoLux 560 samples offers an extinction coefficient of 3x10⁷ M^-1 cm^-1 (QY=0.3), which resulted in 400X enhancement of conventional rhodamine B (extinction coefficient of 7.5x10⁴ M^-1 cm^-1, QY=0.3). Furthermore, NovoLux 560 is more photostable than rhodamine B and 6X brighter than PE. Finally, we have developed NovoLux 640 as the photostable and brighter dye option in the 640 channel. One of our NovoLux 640 sample offers an extinction coefficient of 4x10⁷ M^-1 cm^-1 (QY=0.11). This NovoLux 640 sample is 110X brighter than Cy5.5 dye (extinction coefficient 2x10⁵, QY=0.2). Furthermore, NovoLux 640 is more photostable than Cy5.5 and 8X brighter than APC.
As mentioned, the fluorescent brightness of NovoLux dyes can be tuned for desired brightness to meet various sample needs. The extinction coefficient of NovoLux dyes can be as high as 1x10¹⁰ M^-1 cm^-1 [1].This unique property allow increase in signal to noise ratio, thus results in detection of rare antigens. The spectral properties, tunability, and application of NovoLux dyes in flow cytometry will be presented during the meeting.

[1] Y. K. Yap, D. Zhang, N. B. Yapici, “High-Brightness Fluorophores,” US Patent Application US20180296705A1.
NovoLux 488 and NovoLux 640 are developed under the support of National Science Foundation (IIP 1738466) STTR Phase I and II awards. NovoLux 560 is developed under the support of M-TRAC for Life Sciences Innovation Hub co-managed by the University of Michigan and the Michigan Economic Development Corporation (MEDC). We acknowledge supports from the Michigan Corporate Relations Network (MCRN) Small Company Innovation Program (SCIP), The Michigan Emerging Technologies Fund (ETF).

Carbon-based nanomaterials including low dimensional hollow carbon spheres (HCS) as well as graphene (GO) and carbon nanotubes (CNTs) have found increasing application in various fields of our research and everyday life, being even considered as carriers for therapeutics and as intracellular imaging units. However, when it comes to medicinal applications of nanomaterials, toxicity remains a key issue. Approval of new therapeutic tools requires a detailed understanding of material-cell interactions starting with interactions with the first line of defense in our body, the immune system. We therefore synthesized HCS and GO nanosheets and evaluated their cytotoxic potential in comparison to single-walled CNTs (SWCNTs) towards human-monocyte derived macrophages. Besides electron microscopic evaluation of nanomaterial uptake and intracellular distribution, the formation of reactive oxygen species (ROS) and secretion of pro-inflammatory cytokines and chemokines was investigated revealing significant differences between carbon-based materials. Moreover, receptor line specific assays as well as by computational data were performed to analyze the roll of toll-like receptors (TLRs) in immunological nanomaterial sensing.

Over the last few decades, catalytic chemical vapor deposition (CVD) has matured as a synthetic technique for producing carbon nanotubes (CNTs) and graphene. The general mechanism of graphene and CNT formation during CVD is now well established [1]; nucleation and growth begin with the precipitation/aggregation of carbon atoms on a catalyst surface to form extended carbon chains, which quickly combine and oligomerise to form “islands” of sp²-hybridized carbon. Larger nanostructures then form via the coalescence of these structures on the catalyst surface, which are stabilised through strong carbon-catalyst σ-bonding.

However, by and large this picture of nucleation has been developed by considering the chemistry of carbon by itself, when, in reality, there are many other chemical species present in a CVD reaction chamber. In this lecture I will discuss our recent work that shows the influence of such species on the nucleation and growth mechanisms of carbon nanomaterials during CVD (e.g. H₂ [2,3], H₂O [4], NH₃ [5], acetonitrile [6] etc.). I will also discuss how they influence catalyst formation and CNT nucleation during floating-catalyst CVD with ferrocene precursors [7]. Our simulations demonstrate how each of these parameters can potentially be exploited towards controlling growth. Importantly, we show that chemical etchants play key roles regarding growth control and kinetics, despite being overlooked in popular growth models to date.

[1] B. McLean et al., Phys. Chem. Chem. Phys. 19, 26466-26494 (2017).
[2] I. Mitchell et al., Carbon 128, 215 (2018).
[3] A. Saeed et al., Adv. Func. Mater., (2020) DOI: 10.1002/adfm.202005016
[4] Hussein, A. et al., Nanoscale. 12, 12263-12267 (2020).
[5] C. A. Eveleens et al., Nanoscale 9, 1727 (2017).
[6] C. A. Eveleens et al., Carbon 146, 535-541 (2019).
[7] B. McLean et al., J. Appl. Phys. (submitted)

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. 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. 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. 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.

We propose a few interesting novel methods for SWCNT doping: aerosol doping and dip-coating methods will be discussed.

The effect of the presence of catalyst particles on the optoelectronic properties of the SWCNT films is also investigated.

Also, we propose a novel approach to enhance optoelectronic performance of SWCNTs using ionic liquid. The method provides fine and reversible tuning of optoelectrical properties of SWCNT films over a wide range of parameters. Using imidazolium-based ionic liquid with a wide electrochemical window (BMIM-PF₆), we achieved the film sheet resistance as low as 53 Ω/sq at the 90% transmittance, thereby shifting the SWCNT Fermi level up to 1.4 eV. We believe the results to promote collateral research of adjustable tuning of the electronic structure of carbon nanomaterials as promising components for future electronics, electrochromic devices, and ionotronics.

Although carbon nanotubes have been already demonstrated to be a promising material for bolometric photodetectors, the sensitivity enhancement while maintaining the speed of operation remains a great challenge. Here, we present a holey carbon nanotube network, designed to improve the temperature coefficient of resistance for highly sensitive ultra-fast broadband bolometers. Treatment of carbon nanotube films with low frequency oxygen plasma allows fine tuning of electronic properties of the material. The temperature coefficient of resistance of our films is much greater than reported values for pristine carbon nanotubes, up to -2.8% K^-1 at liquid nitrogen temperature. The bolometer prototypes made of the treated films demonstrate high sensitivity in a wide IR range, short response time, smooth spectral characteristics and low noise level.

And finally, we develop a novel transparent p-type flexible electrode based on SWCNTs combined with poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), molybdenum oxide and SWCNT fibers. We achieved a record equivalent sheet resistance of 17 Ω/sq with a transmittance of 90% at 550 nm and a high degree of flexibility. We demonstrate that our solar cells based on the proposed electrode and hydrogenated amorphous silicon (a-Si:H) yield an outstanding short-circuit current density of J_sc = 15.03 mA/cm² and a record power conversion efficiency of PCE = 8.8% for SWCNTs/a-Si:H hybrid solar cells.

This work was supported by the Russian Science Foundation (Project identifier: 17-19-01787) and RFBR (project number: 20-03-00804).

Carbon nanotube (CNT) membranes are known to have enhanced transport of fluids, including water vapor, gases, and liquids. They are not known for having enhanced ion transport or being ion-selective, unless their pores are sub-nanometer in diameter or their tips/surfaces are functionalized. On the other hand, recent experiments with single ~30-80nm-diameter boron-nitride nanotubes (BNNTs) have reported large surface charge in aqueous solution, and ion selectivity for diameters beyond the well-known Donnan exclusion that is typical of separation membranes. When placed in a salt-concentration gradient, the single BNNT generated electrical power from the Gibbs free energy of mixing at power densities up to 4,000 W/m² when extrapolated to macroscopic membranes. However, no such macroscopic BNNT membranes have ever been fabricated, and their performance at large scales and pore densities has been unknown.

Here, we describe the scalable fabrication of the first macroscopic, vertically aligned- (VA-) BNNT membranes with pore densities of 10⁷ open-BNNTs/cm², and report their remarkable osmotic-power-generation performance. We make comparison to vertically aligned carbon-nanotube membranes fabricated by the same solution-based technique, which have similar atomically perfect, 1D (but uncharged) pores. We find that that the fast, selective ion transport in 3 and 12 nm-diameter BNNT pores arises from enhanced diffusio-osmotic transport of concentrated cations next to the negatively charged surface, coupled with the deformation or removal of hydration shells around the ions. Due to nanoscale confinement and surface charge in their pores, the BNNT membranes were highly cation-selective, generating an open circuit potential of 295mV and a short circuit current of 20µA, even for 1M solution for which the Debye length is smaller than the nanotube radius. In comparison, CNT membranes with the same 3 nm-diameter pores showed no selectivity and generated negligible osmotic power. The BNNT pores showed fast cation transport rates under a concentration gradient, exceeding the rate of bulk diffusion by at least 21× for Li⁺. This ultrafast, selective cation transport in BNNT pores generated osmotic power via reverse electrodialysis at extraordinary power densities of 14,000 W/m² of open pore area for 1M:1mM LiCl solutions at pH 11. With surface-dominated transport, novel ion-selective membranes with 1D BNNT pores overcome the traditional trade-off between selectivity and transport rates in polymeric membranes, and may enable harvesting of blue energy, as well as efficient desalination and other separations, via a fundamentally different mechanism than conventional systems.

Thin-film solar cells show promise for light-weight, low-cost, large area, flexible devices. Unlike competing materials, zinc oxide (ZnO) and molybdenum trioxide (MoO₃) are relatively abundant, environmentally stable, and have been proven effective for use in quantum dot-sensitized solar cells. The surfaces of nanostructures are often dominated with dangling bonds capable of trapping charges and limiting effective charge transport after electron-hole separation. Thus, it is anticipated that quantum dot-sensitized ZnO solar cells will be more efficient than devices constructed with traditional ZnO nanostructures. Molybdenum disulfide (MoS₂) has attractive features, including its semiconducting nature and indirect-to-direct band gap transition when cleaved from bulk to monolayer. MoS₂ quantum dots have been shown to have broad absorption bands, potentially making them invaluable for QD-sensitized photovoltaic devices. In this work, we use conventional thin film technology to fabricate MoS₂ QD-Sensitized ZnO thin film solar cells.

A top-down approach was employed to convert bulk MoS₂ powder into QDs via sonication and solvothermal methods. The MoS₂ QDs absorb a wide spectrum of white, ranging from 320 nm to 520 nm, and fluoresce wavelengths ranging from 385 nm to 569 nm. This broad absorption wavelength contains the peak of the solar radiation spectrum, which enables effective photoelectron production in our device. Additionally, the QDs were found to exhibit fluorescence dependent on the excitation wavelength, enabling the production of excitons from a wider range of solar wavelengths.

Morphological characterization of the produced MoS₂ QDs was carried out using transmission electron microscopy (TEM) and atomic force microscopy (AFM), and statistical analysis of the lateral dimension and thickness was conducted. The MoS₂ QDs range from 2 – 40 nm in dimension. The devices were fabricated by depositing ZnO, MoS₂ QDs, MoO₃, and Au respectively onto commercial indium tin oxide (ITO) glass using pulsed laser deposition (PLD).Fluorometry measurements were conducted following each deposition to obtain the fluorescence spectra. The current-voltage characteristics of the devices were measured under the illumination of a solar simulator, and the fill factor and power conversion efficiency (PCE) were calculated. A detailed discussion of the results of optimized devices will be had during the presentation.

Lithium-ion-batteries (LIBs) are one of many applications that is expected to benefit from mechanical strength, high surface area and electrical conductivity of graphene when incorporated into electrode materials. For the integration in commercial LIBs, it is important to develop simple, cost effective and scalable methods for the production of graphene-like structures.
Here we report on a green and simple wet chemical synthesis for the controlled formation of freestanding paper-like structures of regularly arranged graphene oxide (GO) flakes, using GO as starting material. As obtained structures were mechanically stable, scalable to mass production and could be used as flexible electrode materials in LIBs. Besides superior mechanical properties, rGO films led to increased volumetric energy densities due to the reduction in weight, making use of a current collector and the preparation of a battery slurry obsolete.
Moreover, morphology and structure of the material was significantly influenced by pre-reduction and vapor treatment of the films leading to enhanced electrical conductivities and lithium storage capacities. Especially in terms of defects and interlayer distances the results confirm the subtle interplay of chemical treatments and electronic properties of graphene oxide materials, which was additionally proven by DFT calculations.
In terms of cathode materials, freestanding 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.
Our results demonstrate the integration of freestanding and flexible rGO films into LIB half-cells highlighting their exceptional versatility and high application potential.

Hydrogen is a promising sustainable alternative to conventional fuels that can push forward the energy transition because of its prominent advantages such as high energy density (142 MJ kg^-1 ), great variety of potential sources, light weight, and low environmental impact, while the storage remains a formidable scientific challenge. Magnesium hydride, with its inherently high gravimetric and volumetric density (7.6 wt.% & 110 g L^-1 ), presents a compelling platform for hydrogen storage, however, two major impediments hindered its practical utilization: the sluggish hydrogen kinetics of uptake and release process and high temperature operation.
Herein, a novel porous heterostructure material with high specific surface area and narrow pore size distribution was synthesized by sol-gel reaction of Graphene Oxide and an organosilicon precursor, followed by MgH₂ particle (d <5nm) grown in the framework. The material was characterized with BET, SEM, XRD and TEM and shows remarkable crosslinked layered structure with narrow interlayer distance. Studies of hydrogen storage properties showed that hydrogen released at low temperature (110 °C) and centred at 350 °C with kinetics dependent to some extent on the particle size.

We have synthesized a new coaxial nanotube structure, in which mono- or few-layer hexagonal boron nitride nanotube (BNNT) seamlessly wrap around a single-walled carbon nanotube (SWCNT); SWCNT@BNNT [1]. We named these as one-dimensional van der Waals hetero-nanotubes, because we found no correlation between chiral angle of inner SWCNT and outer BNNT for ‘double-walled’ SWCNT@BNNT. We have further developed the 1D coating CVD of transition metal dichalcogenide nanotubes (TMD-NT), such as MoS₂ nanotubes [1]. These nanotubes can be labelled as SWCNT@BNNT@MoS₂. Because BNNT is thermally more stable than SWCNT, we can remove SWCNT from SWCNT@BNNT by the gentle oxidation process. Hence, we can produce BNNT with inner diameter determined by the original SWCNT. Then, the MoS₂ CVD can result BNNT@ MoS₂. These hetero-nanotubes are characterized by HR-TEM, STEM-EELS, absorption, Raman and photoluminescence (PL) spectroscopy. We found the bright PL from MoS2 nanotubes for BNNT@ MoS₂. From DFT calculations, we expect that the K point direct band gap for 2D MoS₂ should appear for MoS₂ nanotubes with larger diameter such as 3-4 nm. The PL from MoS₂ was quenched by inner SWCNT (metallic or small band-gap semiconductor) in the hetero-nanotube, SWCNT@BNNT@MoS₂. So far, the coating growth can be efficiently performed for vertically aligned array of SWCNT, suspended SWCNTs between pillars, zeolite based bulk sample and dry-deposited random network films. For field effect transistor (FET) devices, we need to start from suspended SWCNTs. We will demonstrate the growth of suspended hetero-nanotubes between pillars and the transfer to Si/SiO₂ substrate for device characterizations.

Reference:
[1] R. Xiang, T. Inoue, Y. Zheng, A. Kumamoto, Y. Qian, Y. Sato, M. Liu, D. Tang, D. Gokhale, J. Guo, K. Hisama, S. Yotsumoto, T. Ogamoto, H. Arai, Y. Kobayashi, H. Zhang, B. Hou, A. Anissimov, M. Maruyama, Y. Miyata, S. Okada, S. Chiashi, Y. Li, E. I. Kauppinen, Y. Ikuhara, K. Suenaga, S. Maruyama, Science 367, 537-542 (2020).

Tellurium can form nanowires of helical atomic chains. With their unique one-dimensional van der Waals structure, these nanowires are expected to show physical and electronic properties that are remarkably different from those of bulk tellurium. Here, we show that few-chain and single-chain van der Waals tellurium nanowires can be isolated using carbon nanotube and boron nitride nanotube encapsulation. With this approach, the number of atomic chains can be controlled by the inner diameter of the nanotube. The Raman response of the structures suggests that the interaction between a single-atomic tellurium chain and a carbon nanotube is weak, and that the inter-chain interaction becomes stronger as the number of chains increases. Compared with bare tellurium nanowires on SiO2, nanowires encapsulated in boron nitride nanotubes exhibit a dramatically enhanced current-carrying capacity, with a current density of 1.5 × 108 A cm−2 that exceeds that of most semiconducting nanowires. We also use our tellurium nanowires encapsulated in boron nitride nanotubes to create field-effect transistors with a diameter of only 2 nm. The work is in close collaborations with the research teams of Profs. Moon J. Kim, Wenzhuo Wu, Xianfan Xu, Hai-Yan Wang, Li Yang, Yoke Khin Yap.

In field-effect transistors made of atomically-thin nanomaterials such as carbon nanotubes or graphene, functionalization of the nanocarbon surface is necessary to control its interaction with surrounding media, especially for applications as chemical or biosensors. Aryldiazonium salts are a common approach to form covalent adducts on nanocarbon materials, but controlling the density and position of grafts is a challenge. In this presentation, I will describe the recent development of approaches based on nanolithography and electrochemistry to control the distribution of aryldiazonium-based adducts on nanocarbon materials. I will discuss differences between carbon nanotubes and graphene, as well as applications of such functionalized field-effect transistors for biosensing and single-molecule experiments.

In the past, the application of carbon nanotube-silicon solar cell technology to industry has been limited by the use of a metallic frame to define the active area in the middle of a silicon wafer. In our work, we use industry standard device geometries with a front- and back-junction design which allow for the entire wafer to be used as the active area. These are enabled by the use of an intermixed Nafion layer which simultaneously acts a passivation, antireflective and physical blocking layer as well as a nanotube dopant. This leads to the formation of a hybrid nanotube/Nafion passivated charge selective contact (PCSC) and solar cells with active areas of 1 – 16 cm² are fabricated. Record maximum power conversion efficiencies of 15.2% and 18.9% are reported for front- and back-junction devices for 1 cm² and 3 cm² active areas, respectively. By placing the nanotube film on the rear of the device in a back-junction architecture many of the design related challenges for carbon nanotube silicon solar cells are addressed and their future application to industrialized processes are discussed.

Additionally, traditional silicon solar cells extract holes and achieve interface passivation with the use of a boron dopant and dielectric thin films such as silicon oxide or hydrogenated amorphous silicon. Without these two key components, few technologies have realized power conversion efficiencies above 20%. We now develop a carbon nanotube/Nafion ink that can be spin coated directly onto a silicon wafer to serve simultaneously as a hole extraction layer, but also to passivate interfacial defects. This enables a low-cost fabrication process that is absent of vacuum equipment and high-temperatures. Power conversion efficiencies of 21.4% on an device area of 4.8 cm² and 20% on an industrial size (245.71 cm²) wafer are obtained.

[1] D. D. Tune, N. Mallik, H. Fornasier, B. S. Flavel, Adv. Energy Mater. 10, 2020, 1903261. DOI: 10.1002/aenm.201903261
[2] J. Chen, D. D. Tune, K. Ge, H. Li, B. S. Flavel, Adv. Funct. Mater. 2020, 2000484.
DOI: 10.1002/adfm.202000484
[3] J. Chen, L. Wan, H. Li, J. Yan, J. Ma, B. Sun, F. Li, B. S. Flavel, Adv. Funct. Mater. 2020, just accepted manuscript. DOI: 10.1002/adfm.202004476

Our group has recently demonstrated low frequency (1-200 MHz) and low power (<100 W) radio frequency (RF) heating of carbon nanomaterial-loaded structures such as thin films and polymer nanocomposites using an array of contact and non-contact applicators. These heating techniques have opened up routes for faster and efficient composite manufacturing, 3D printing, and fiber processing. It is known that electrical conductivity is required for RF heating of carbon-based nanomaterials. However, it is not well understood how RF heating rates vary with conductivity and if the pattern is generalizable for all types of RF susceptor-loaded structures. In this work, we use experiments and simulations to explore the universal patterns observed between RF heating rates and in-plane electrical conductivity for different nanomaterial-loaded thin films. We also show existence of similar patterns in chirality-sorted nanomaterial films, and finally we show a novel RF heating-based high-throughput quality screening technique for carbon nanotube circuits.
We synthesize multi-walled carbon nanotube (MWCNT) films, laser-induced graphene (LIG) films, and carbon nanofiber-polyamide (CNF-PA) composites of varying electrical conductivity by changing sprayed film thickness, laser parameters, and CNF content, respectively. We use a coplanar strip fringing-field applicator to assess RF heating behavior of nanomaterials in the frequency range of 1-200 MHz and at power of 2 W. This applicator allows for non-contact capacitive coupling of RF fields with the sample and heat it as high as 70°C/s at 2 W.
We find that for each of the nanomaterials tested, the highest heating rate observed across all frequencies is non-monotonically related with the in-plane electrical conductivity. This relationship has a distinguished maximum at approximately the same DC in-plane electrical conductivity (in the range of 0.1-0.2 mS) for all nanomaterials. We find that the point of maximum heating rate is closely associated with the percolation threshold. It is because at percolation a conductive network is formed and if the conductivity is increased further, reflections of RF fields lead to decrease in heat rates. This is also confirmed by our assessment of RF heating behavior of sorted and purified metallic (m-) and semi-conducting (s-) single-walled carbon nanotubes (SWCNTs). We find that 98% pure m-SWCNT film reflect RF fields and heat at a highest rate of 2 °C/s compared to 100% pure s-SWCNT film’s highest heating rate of 26 °C/s. We also find that the presence of impurities in the m-SWCNT film increases its heating rate to 10 °C/s due to disruption of the conductive network. These findings could make RF heating a promising metric for evaluating m-SWCNT film purity.
Finally, we apply the conductivity dependent RF heating behavior to demonstrate a reliable and high-throughput screening method for screen-printed MWCNT circuits. We show that large amounts of circuits can be simultaneously scanned over a fringing-field applicator which allows for rapid screening based on the uniformity of thermal response and the heating temperature observed using a thermal camera. This method is ideal for faster production of CNT circuits and replaces previous time-consuming quality metrics such as 2-point probe and 4-point probe measurements. It provides a tenfold increase in speed, allowing for real-time monitoring of circuits as they are produced. The scanning method is more reliable than the traditional metric in screening-out faulty circuits and can also be employed at various stages of the circuit manufacturing process.

Single-walled carbon nanotubes (SWNTs) are promising nanomaterials for incorporation into solution-processed organic electronic devices (OEDs). As-synthesized SWNTs are insoluble and comprised of a mixture of metallic and semiconducting SWNTs (sc-SWNTs), necessitating dispersal and purification before integration into OEDs. Refinement of conjugated polymer extraction techniques has allowed for the isolation of sc-SWNTs from metallic in a reproducible and scalable manner, affording highly-soluble dispersions of sc-SWNTs for potential integration into inexpensive solution-processing techniques. Furthermore, the availability of ultrapure sc-SWNT materials has facilitated the production of field-effect transistors (FETs) with very high charge carrier mobilities and good on-off ratios, outperforming most organic semiconducting small molecules and polymers.
Despite the plethora of high-quality polymer-sorted sc-SWNT dispersions reported in the literature, the realization of commercial OED applications has not yet been achieved. This is partially attributed to the prohibitive time and materials costs associated with purifying sc-SWNTs. Current protocols for dispersing sc-SWNTs with conjugated polymers typically involve three broad steps: (1) dispersion of bulk SWNT material with the conjugated polymer, (2) removal of non-dispersed carbonaceous materials, and (3) removal of excess polymer through filtration or centrifugation. While the first two steps are relatively facile and can be performed on large scales, the final step of removal of excess polymer is laborious and resource-intensive. However, removal of excess polymer is viewed as essential for preparing high-performing FETs, as the conjugated polymer has much lower performance compared to SWNTs.
In this study, we performed the first systematic investigation of the effect of excess polymer during device fabrication on SWNT FET performance. Large numbers of replicate FET devices were characterized using several metrics, including mobility, threshold voltage, on/off ratios and hysteresis. Two different conjugated polymers were investigated at three different SWNT concentrations, with varying ratios of excess polymer added. Extensive analysis of the polymer-sorted sc-SWNT films through Raman spectroscopy and atomic force microscopy (AFM) showed that below a threshold amount of excess polymer, a simple rinsing step was sufficient to remove all unbound polymer from the substrate surface. The volume of solvent required for this rinsing step was substantially lower than that required for filtration or centrifugation; additionally, many literature procedures for sc-SWNT FET device fabrication already incorporate similar solvent rinses. Most importantly, at higher SWNT concentrations, the presence of excess polymer during device fabrication resulted in moderately improved device performance in both mobility and on/off ratios, with preeminent devices achieved from the original dispersions (before removal of excess polymer) for both polymer systems. Analysis of AFM images of these polymer-sorted sc-SWNT films with a novel Machine Learning algorithm showed that improved device performance could be attributed to more even sc-SWNT films and reduced bundling. Our results have important implications in the development of SWNT inks for commercial printing applications, as the presence of excess polymer can both increase the stability of the inks, as well as improve viscosity.

Graphene nanoribbons (GNRs) exhibit unique electronic and magnetic properties that do not appear in two-dimensional graphene. These properties can emerge from the structural boundary conditions imposed by the atomically precise width and edge structure of GNRs. For instance, armchair-edged GNRs (AGNRs) show sizable gapped electronic states established by the quantum confinement and edge effects. In graphene-based electronics, AGNRs with finite bandgaps at room temperature have attracted much attention for their potential reliability as semiconducting channels for field-effect transistors (FETs).
For fabricating atomically precise GNRs, a bottom-up synthesis technique has recently been demonstrated via on-surface-assisted polymerization and subsequent cyclodehydrogenation of precursor monomers on metal substrates [1]. The bottom-up synthesis of N-AGNRs (where N is the number of carbon atom pairs across the ribbon) has been widely conducted because the bandgap of AGNRs can be tuned by changing their width. According to first-principles calculations using many-body perturbation theory (GW approximation) for freestanding N-AGNRs, the quasiparticle gap is predicted to be 3.80 eV for N = 7, 2.16 eV for N = 9, and 2.25 eV for N = 13 [2]. Previous studies on FETs using bottom-up AGNRs with widths of N = 7, 9, and 13 presented their electrical transport characteristics [3, 4]. However, in such GNR-based FETs, the intrinsic transport properties of AGNRs were obscured by a large Schottky barrier resistance between the AGNRs and metal contacts due to the large bandgaps in the above AGNRs, substantially exceeding 1 eV. These transport characteristics can be improved with wider AGNRs, as they are expected to have lower Schottky barriers arising from their small bandgap features.
In our presentation, we show the bottom-up synthesis of well-structured 17-AGNRs and 13-AGNRs on Au(111) by using 1,2-bis-(2-anthracenyl)-3,6-dibromobenzene and 1,2-bis-(2-naphthalenyl)-3,6-dibromobenzene, respectively [5]. To systematically control the width of these AGNR, in the precursor monomers, either two anthracene or naphthalene units were attached at the ortho-positions of p-dibromobenzene. Characterization of the atomic and electronic structures of the 17- and 13-AGNRs on Au(111) was carried out by combining scanning tunneling microscopy and spectroscopy (STM/STS) and non-contact atomic force microscopy (nc-AFM). In both AGNRs, STM and nc-AFM observations revealed their widths and armchair-edged structures at atomic precision. In the GW calculations, the quasiparticle gap for freestanding 17- and 13-AGNRs is predicted to be 0.63 and 2.25 eV, and their values are corrected as 0.20 and 1.29 eV considering the image-charge effects from the metal substrates [6]. By STS measurements, we revealed that the experimental gap is 0.19±0.03 and 1.34±0.03 eV for the 17- and 13-AGNRs on Au(111), which is consistent with the accordingly corrected quasiparticle gaps predicted from the GW calculations. For more detailed discussions on the electronic band dispersions of the 17- and 13-AGNRs, we carried out Fourier-transformed STS (FT-STS) measurements. We found that the FT-STS provides the electronic band dispersions, which reasonably match the simply rigid-shifted GW quasiparticle bands in both AGNRs. As far as we know, the bottom-up synthesis of 17-AGNRs is the first demonstration of GNRs having a bandgap smaller than 1 eV in a controlled manner, which will pave the way for the development of GNR-based electronic devices.
This work was supported by CREST JST (no. JPMJCR15F1) and MEXT/JSPS KAKENHI grant nos. 26105004, 16H02286, 18K14190, and 18H01807.

[1] J. Cai et al., Nature 466, 470 (2010).
[2] L. Yang et al., Phys. Rev. Lett. 99, 186801 (2007).
[3] P. B. Bennett et al., Appl. Phys. Lett. 103, 253114 (2013).
[4] J. P. Llinas et al., Nat. Commun. 8, 633 (2017).
[5] J. Yamaguchi et al., Commun Mater 1, 36 (2020).
[6] O. Deniz et al., Nano Lett. 17, 2197 (2017).

Transparent conductive electrodes (TCEs) are of enormous significance to the continued growth of optoelectronic devices and the emergence of flexible and wearable electronics in the foreseeable future. Versatile and tunable TCEs, featuring not only high optical transmittance but also intriguing features of electrochemical energy-storage capability, flexibility, and transferability, remain a significant challenge. Here we strategically develop a graphene-conjugated V2O5/poly(3,4-ethylene dioxythiophene (from hereon, V2O5/PEDOT) hybrid, serving as an easily transferable, transparent, capacitive active electrode films. The constructed electrodes exhibit a high areal capacitance of 50-60 mF cm−2 at optical transparency of > 60 percent with a record durability over thousands of cycles. As demonstrated by experimental results, both the kinetic blocking of the PEDOT layer and the anchoring capability of graphene upon soluble vanadium ions from V2O5 nanoribbons/nanotubes contribute synergistically to the unusual electrochemical stability and electroactivity shown using scanning electrochemical microscopy. Transparent symmetric and asymmetric solid-state supercapacitors made of the as-fabricated pseudocapacitive TCEs deliver a broad voltage window of 1.4 V or higher under two different electrolytes (aqueous LiCl and organic gel made from LiCl and polyvinyl alcohol) demonstrate highest power and energy density that outperforms all the previously reported transparent devices (< 0.1 microWatt h cm^-2).

Thermal diode is a two-terminal device which rectifies heat flow. For its non-linear nature, interest in thermal diode has been growing for more than 15 years. Thermal diodes have been numerically and experimentally realized with bulk as well as nanomaterial. Among them, phase transition material can realize high rectification with relatively narrower temperature bias. Current optimization studies of phase transition junction thermal diode consider phase transition as a step function of temperature, while in some cases phase transition could happen in a temperature range in the same magnitude with temperature bias. In this study we simulated and optimized the thermal diode based on our recently experimentally realized phase transition of polyethylene nanofiber with a finite temperature range of phase transition.

There is a phase transition within polyethylene nanofiber with high degree of crystallinity: crystalline structure shifts from orthorhombic to hexagonal cell with a sharp decrease of thermal conductivity within about 5K temperature range at around 430 ~ 450K[1]. E-beam irradiation can alter the phase transition behavior. Phase transition retains with a lower critical temperature if irradiation is weak, while phase transition disappears if irradiation is strong[2]. Thus, heavily-irradiated-pristine (HI-P) and lightly-irradiated-pristine (LI-P) junction diode can be fabricated by partially irradiating the PE nanofiber with different exposure time. HI-P junction can rectify heat flow in one certain direction, while LI-P junction can rectify heat flow in both directions under different working temperature.

Calculation based on finite temperature range of phase transition shows a smooth heat flow curve with a better match with experimental data. Calculation based on step-function phase transition gives a limit of rectification value but tends to overestimate the rectification performance under small temperature bias. Optimization formula derived from step-function model can still be used for estimating optimized length fraction of e-beam irradiation despite the range of temperature bias, as maximum rectification value always occurs when interface temperature difference is zero. Specifically, a proper value of thermal conductance value is required for LI-P junction such that rectification performances in both directions can be optimized with one single length fraction of irradiation.

[1] R. Shrestha, Y. Luan, S. Shin, T. Zhang, X. Luo, J.S. Lundh, W. Gong, M.R. Bockstaller, S. Choi, T. Luo, R. Chen, K. Hippalgaonkar, S. Shen, High-contrast and reversible polymer thermal regulator by structural phase transition, Sci. Adv. 5 (2019) eaax3777. https://doi.org/10.1126/sciadv.aax3777.
[2] Unpublished.

A bottleneck in the development of enzyme-based graphene field effect transistors is the protein immobilization method used. Non-specific adsorption of protein on graphene is undesirable as it hinder access to the enzyme’s active site whilst also changing the natural conformation of proteins by having surface residues bind to the graphene surface. Proteins require specific 3D conformation to be functional and so label-free immobilisation methods is preferred as it increases sensing capabilities of biosensors by maintaining proteins catalytic activity upon immobilization.

Here, a bi-functional self-assembling and graphene-binding peptide was fused to a QueF nitrile reductase protein to create a fusion protein for nitrile detection. The peptide was derived from silk protein fibroin and is capable of forming stable antiparallel β-sheet structure on graphene (1) and so is used to guide protein immobilization. Incorporating this tag into various proteins for enhancing biosensing applications offers a new and effective platform for enzyme-based graphene field effect transistors.

QueF nitrile reductase was chosen because it is the only known enzyme capable of NADPH-mediate nitrile to amine reduction (2). Surface topology of the fusion protein functionalized graphene was observed by atomic force microscopy and showed that both oligopeptide and the fusion protein incorporating it formed a monolayer with six-fold symmetry.

The QueF fusion protein sensing capabilities was first assessed on its natural nitrile substrate which upon immobilisation on graphene field effect transistor showed a 1.4-fold increase in binding affinity compared the wild-type protein which did not incorporate the peptide tag.
Fusion protein was also used to create an agricultural biosensor through the detection on benzyl cyanide. Benzyl cyanide is a chemical distress signal produced by plants and detection of this compound could therefore be used to provide means for crop monitoring and pesticide administration. The fusion protein showed a 3.3-fold increase in response to benzyl cyanide when compared to the wild-type protein. Work here provides a novel immobaliastion method for enzyme based graphene field effect transistor biosensing.

(1) Li, P.; Sakuma, K.; Tsuchiya, S.; Sun, L.; Hayamizu, Y. Fibroin-like Peptides Self-Assembling on Two-Dimensional Materials as a Molecular Scaffold for Potential Biosensing. ACS Appl. Mater. Interfaces 2019, 11 (23), 20670–20677. https://doi.org/10.1021/acsami.9b04079.
(2) Moeller, K.; Nguyen, G. S.; Hollmann, F.; Hanefeld, U. Expression and Characterization of the Nitrile Reductase QueF from E. Coli. Enzyme Microb. Technol. 2013, 52 (3), 129–133. https://doi.org/10.1016/j.enzmictec.2012.12.003.

Carbon materials have widely been used to enhance the performance of a plethora of supercapacitor electrode materials. In this regard, it is crucial to identify carbon materials that function over a wide pH range while enjoying a wide potential window. Herein, the DFT calculations were used to elucidate the electronic performance of C₇₆ and the C₇₆/electrolyte interface. The electronic investigation revealed the nature of the conductivity and charge storage mechanism of C₇₆ based on the bandgap and quantum capacitance calculations. Also, the electrochemical and electronic properties of fullerene C₇₆ have been extensively investigated over a wide pH range; acidic H₂SO₄, basic KOH, and neutral Na₂SO₄. The results showed a promising performance in the three electrolytes. Moreover, C₇₆ electrodes exhibited a potential window of 1.9 V in Na₂SO₄ electrolyte, resulting in capacitances of 171 F/g and 142 F/g at a scan rate of 1 mV/s in the positive and negative potential windows, respectively. The material showed a pseudocapacitance performance of 65% in Na₂SO₄ electrolyte in the positive potential window. We believe higher fullerenes provide a new class of materials for developing versatile supercapacitor devices for efficient energy storage

There is a growing need for new techniques to synthesize metallic copper nanoparticles due to their remarkable use in many advanced technologies. Herein, a novel method to synthesize stable and non-agglomerated zero-valent copper nanoparticles (ZVCNPs) via the in-situ formation of reduced graphene oxide (rGO) during the electrospinning process in the presence of polyvinylpyrrolidone (PVP) as a carbon source is presented. X-ray diffraction (XRD), Raman spectroscopy, electron paramagnetic resonance (EPR), transmission electron microscopy (TEM), and x-ray photoelectron spectroscopy (XPS) techniques were used to investigate the morphology, structure, and composition of the fabricated materials. The synthesized ZVCNPs were coupled with TiO2 nanofibers and rGO to form an efficient photoactive material to photocatalytically produce hydrogen via water splitting, resulting in 344% increase in the hydrogen yield compared to that of TiO2 nanofibers. The density functional theory (DFT) calculations showed that the ZVCNPs enhance the charge transfer and lower the energy needed for photocatalytic water splitting. This study suggests a novel method for metallic copper stabilization and illustrates the effect of metallic copper as a catalyst for the in-situ formation of rGO.

Aim of this article is to study the effects of hydroxyl functional group with different coverage percentages on the mechanical strength and fracture toughness of graphene. The hydroxyl functional group forms the backbone of intrinsic atomic structure of graphene oxide (GO).

Molecular dynamics based simulations were performed in conjunction with reactive force field (ReaxFF) parameters to capture the mechanical properties and Mode-I fracture toughness of functionalized graphene. Moreover, these simulations helped in concluding that spatial distribution and concentration of hydroxyl functional group significantly affects the fracture morphology of graphene nanosheet. Room temperature (300 K) was used for the simulations and virial stress components were evaluated for predicting the stress tensor.

In contrast to literature investigations, here the atomistic simulations have predicted a transition in the failure morphology of hydroxyl functionalised graphene from brittle to ductile as a function of its spatial distribution on graphene sheet. This transition in failure morphology from brittle to ductile was gradual in nature and was observed at lower percentage coverage of graphene in the range of 25-50%. Failure morphologies depict that hydroxyl groups tend to boost the ductility through atomic chains and elongated rings formation at lower percentage coverage.

As the graphene nanosheet is highly brittle in nature, so the authors have evaluated the fracture toughness of graphene with the help of Griffith’s criteria. We then functionalized the graphene sheet (with an pre-crack) with epoxide functional group and observed that a chemical epoxide-to-ether chemical transformation enhanced the fracture toughness value by 25%, as compared to the pristine graphene.

From this investigation, we concluded that spatial distribution and concentration of functional groups significantly affects the mechanical and fracture behavior of oxide functionalized graphene nanosheet.

Enduring an ultrahigh mechanical strength and thermal conductivity, pristine two-dimensional graphene is still a hypothetical concept in the scientific community. Fabrication techniques for this quantum confined two-dimensional nanomaterial in the experimental environment induce various defects in its polycrystalline domain such as the atomic level grain boundaries (GB). Various computational techniques such as the molecular dynamics and density functional theory have unravelled complex mechanisms operating in the presence of these boundary phases to tune graphene’s mechanical, fracture and thermal properties.

Molecular dynamics-based simulations were performed in conjunction with reactive force field (ReaxFF) parameters to capture the mechanical properties of functionalized GB in graphene. Room temperature (300 K) was used for the simulations and virial stress components were evaluated for predicting the stress tensor.

Herein this article, the authors have predicted certain spatial configurations of epoxide functionalized bicrystalline graphene, which could dilute its catastrophic brittle nature and transform it into stable ductile behavior. Altering of failure path and epoxide-to-ether chemical transformations were the chief mechanisms behind the enhanced plasticity for functionalized graphene. Due to brittle nature of graphene, it was expected that failure of graphene would tend to take place from the GB, but in contrast, we found that the failure started from the interior of crystal. This tailoring of failure path induced plasticity in the domain and acted as an energy dissipation mechanism.

The present work provided new insights into the mechanical behavior of bicrystalline GO and predicts plasticity in epoxide functionalized sandwich structure. This persisting ductility of epoxide rich configurations would enable GO to absorb more energy prior to failure and amplified toughness as well, leading to improved structural integrity.

Desalination corresponds to supplying of potable water from oceans and seas, which can dissolve the water scarcity problem for human consumption, agriculture use and energy needs. Conversion of earth’s 97% salty water into a fresh source is still an ambiguous challenge for the research community. Moreover, conducting costly and time consuming commercial experimental techniques such as reverse osmosis and thermal desalination have consistently proved to be a brain storming challenge for the scientists. So, in order to rectify this problem, herein the authors have performed molecular dynamics simulations to investigate the transport of water molecules through artificially created pores on the honeycomb lattice domain of two-dimensional hexagonal Boron Nitride (h-BN) nanosheet. Initially, a reactive force field (ReaxFF) was developed that had water parameters in conjunction with vacancy defects data for monolayer h-BN derived from the density functional theory incorporated in it. We then checked the structural stability of an h-BN monolayer (both pristine and defected) at different temperatures (300, 500 and 800 K) and ensembles (NVT and NPT); thus, predicting that the developed ReaxFF showed a minimal out-of-plane displacement. From the interaction point of view, we revealed that the water molecules tend to accumulate (droplet formation) and form sharp contact angles (hydrophobic nature) with h-BN. Furthermore, on compressing water molecules by applying external pressure on h-BN nanosheet the water molecules tend to arrange themselves in a layered structure. Finally, we investigated the water dissociation mechanism on a defected h-BN nanosheet, and noticed that the water molecule dissociates into hydroxyl group and hydrogen atom thereby getting attached to boron and nitrogen vacancy edge atoms, respectively (Relative energy barriers with respect to initial configurations were 0.395 and -2.18 eV). These outcomes on h-BN nanosheet may prove to be valuable for designing of 2D nanodevices/nanomembranes for water desalination purpose.

A one-step synthesis/functionalization of carbon nanospheres (CNS) is presented. The synthesis was carried out vía the APCVD method using toluene and ethanol (0wt%- 5wt% ethanol) as precursors. Different weight percentages of ethanol were implemented in order to evaluate their effect on the CNS’s solubility in water, size distribution, morphology, surface area and surface chemistry. Since this method is a one-step in situ functionalization (with oxygen-containing groups), there’s no need of a post-treatment to functionalize the sample or the use aggressive chemical reactants that could significantly modify the nanomaterial. Characterization techniques implemented for this study included FT-IR, SEM, EDX, XPS, Raman spectroscopy, BET and solubility tests. Results indicated that CNS possess higher water solubility when a 3 wt% ethanol solution is implemented for the synthesis. It was also demonstrated that higher ethanol concentrations decrease CNS’s diameter and induce polydispersion. Finally the increased solubility and stability of the functionalized CNS are highlighted, envisaging applications in the biomedical field were hydrophilicity and availability of functional groups are mandatory.

Defect engineering of graphene is attractive for a wide range of applications. Here, we present a mask-less, resist-free, and fully reversible process to engineer defects in graphene using electron-beam (e-beam) chemistry with radiolyzed water. This process was performed inside a variable pressure scanning electron microscope by generating radiolysis products using reactions between the e-beam and water vapor, which in turn reacted with the graphene at the location of the probe. These reactions enabled controlled chemistry on the graphene surface at a resolution of ~ 60 nm and hence created defects in precise locations defined by the e-beam. Detailed characterization and theoretical analyses suggested the presence of sp³-type defects, the density of which was tuned by varying the e-beam dose. In addition, these sp³-type defects were cycled in and out of graphene by alternating e-beam chemistry and thermal annealing. We present initial results showing the ability to manipulate the plasmonic response in graphene though the creation of quickly patterned nanoribbons.

Misfit layered compounds (MLCs) are consist of two alternating sub-lattices with different lattice constants at least in one of the directions. One can selectively alter one of the sub-lattices without affecting the other that can tune both the physical and electronic properties. Among them, calcium cobaltite (Ca₃Co₄O₉, CCO)¹ and strontium cobaltite (Sr₃Co₄O₉, SCO)² are gained interest as potential thermoelectric materials. Bringing them to low-dimensions could further enhance their thermoelectric properties. However, synthesizing them in a one-dimensional structure is extremely difficult. Recently, we have synthesized calcium deficient cobalt oxide-based misfit nanotube^3,4 from the bulk starting material. However, the yield of these nanotubes is rather low. Besides, the physical and electrical properties of these nanotubes have not been explored yet. Here, we present the synthesis of 1D nanotubes (NT) from oxide misfit compounds with a very high yield (80%) by a combination of solid-state and solution-based synthesis. We have also studied their electrical properties on individual nanotube level by patterning with electron beam lithography.
All the synthesized nanotubes are thoroughly characterized by a combination of X-ray diffraction pattern (XRD), scanning electron microscope (SEM,) high-resolution scanning transmission electron microscopy (HRSTEM), electron diffraction (ED) and X-ray photoelectron spectroscopy (XPS). It is found that the crystal structure varies in the case of nanotubes from the bulk starting material. Absorption studies show the bandgap of 2.7 eV and 1.7 eV in case of CCO and SCO NTs, respectively. We have fabricated source-drain channels on individual nanotubes by electron beam lithography to find out their electronic properties. In the case of CCO nanotubes, it is found that the nanotubes are of p-type semiconductor with a high charge carrier concentration of 7.05*10¹⁹ per cm³, which suggest that these NTs are promising conducting materials. The current-carrying capacity of these nanotubes is around 6.5*10⁵ A/cm² (for an individual nanotube). But surprisingly, in the case of SCO nanotube, it shows a very high current carrying capacity of 0.88*10⁸ A/cm² for a single NT. These values are close to the reported WS₂ NTs having the highest current carrying capacity (ampacity) of 2.4*10⁸ A/cm² among the inorganic nanotubes.⁵ Temperature dependent resistivity measurements show that both the nanotubes are semiconducting in nature. However, we have observed a voltage-induced semiconductor to metal transition in the case of SCO NTs. We have observed the four-probe resistance for the SCO nanotube to be 10 kΩ which is lowest among the existing oxide-based inorganic nanotubes. We believe electronic properties can be further tuned by changing the chemical composition between Ca/Co and Sr/Co. These results demonstrate that the high conductivity of these nanotubes could be a potential building block for future thermoelectric devices and interconnects.

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Chemically synthesized graphene or reduced graphene oxide (rGO) is very promising for many applications from coatings and fillers to electronics, as it is economic, easy to prepare and scale up, and has unique properties. Despite the huge expansion of GO/rGO market, there is a clear lack of experimental and computational studies on getting high quality GO and rGO nanosheets/thin films. This caused a huge variation in the reported properties of GO/rGO, with a majority of low quality and low competency in electronic applications. In this work, a detailed experimental study of the factors affecting GO/rGO properties, supported by Density Functional Theory (DFT) calculations, is introduced to help prepare pristine graphene-like rGO. In addition, the impact of lateral sheet size on GO/rGO properties, as one of the factors addressed in this work, was studied using DFT calculations and experimental measurements for the first time, to the best of our knowledge. Field-effect transistor (FET) was used to study and optimize rGO. The optimized rGO-FET device showed the lowest resistance (200±20 Ω) and the highest charge carrier mobilities (53279 and 39891 cm²/V.s for holes and electrons, respectively) reported. Furthermore, FET characteristic curve of rGO-FET showed the ambipolar behavior of high-quality graphene, with Dirac point around zero. In addition, the optical band gap of rGO nanosheets (0.4 eV) prepared in this work is the smallest reported, so far. These results highlight the importance of this study for both researchers and companies aiming at using rGO as an alternative for graphene obtained by liquid phase exfoliation or chemical vapor deposition.

Laser-induced graphene (LIG) has been utilized as a non-metallic conductor for the development of various electronics due to its facile, direct, and scalable synthesis process. Here, the graphitization degree of LIG is simply controlled by adjusting the lasing conditions to encode different electronic functionalities such as resistance and capacitance on commercially available papers. The effect of lasing conditions including the number of lasing scans and the lasing power on the graphitization degree of paper-derived LIG is systematically investigated by evaluating the optical, chemical, and electrical properties. The paper-derived LIG with various lasing conditions exhibits a relatively wide sheet resistance range of 61.5 to 9140 Ω sq^-1. The corresponding LIG is used to fabricate resistors and capacitors, and the different electronic functionality encoding is successfully demonstrated by monolithically fabricating non-volatile read-only memory and resistor-capacitor circuits and verifying the electrical performance of the fabricated devices. This work presents a practical approach to develop paper electronics for cost-effective and environmentally-friendly manufacturing.

Structural superlubricity, which results from the incommensurability of directly contacted crystalline surfaces, achieves ultralow friction and inspires disruptive innovations in applications across length scales. It is a common belief that this phenomenon requires the contact interface being ultra-clean, ensured by either a clean environment or self-cleaning of the contact. However, in this paper, the observation of robust superlubricity with a contaminant-rich interface is reported. After intentionally introducing airborne contaminants into microscale superlubric graphite contacts, we surprisingly find that two important features of structural superlubricity are well preserved: the nearly-zero friction coefficient and the drastic commensurate/incommensurate anisotropy of frictional force. Moreover, contaminants are found to reduce the friction of a commensurate contact, but increase the friction of an incommensurate contact, which leads to the decrease of anisotropy ratio in friction as the contaminant concentration increases. Molecular dynamics simulations reveal the different roles of the third bodies in commensurate and incommensurate contacts. Our results encourage explorations of structural superlubricity in contaminant-rich environments that practical devices could be facing.

The oxidation of hydrazine (N₂H₄) is an important challenge in electrocatalysis, with applications in direct hydrazine fuel cells and in medical and environmental sensing. Interest in alternative, nitrogen-based fuels for fuel cells was rekindled by recent advances in alkaline membranes, and by the surfacing of challenges in the transportation of hydrogen. Direct hydrazine fuel cells promise high theoretical voltage (1.56 V with O₂), clean emissions, and improved fuel transportability.
We now report a multi-doped carbide–carbon composite with excellent hydrazine electro-oxidation (HzOR) activity in alkaline pH. While iron carbide containing materials are well known catalysts for several applications (e.g. oxygen reduction), our N-doped, Fe₃C-embedded carbons provide the first examples of a carbide-based HzOR catalyst. Multi-doping was thought to enhance reactivity (possibly through cooperation of M=Cu/ Zn, Fe, and edge N atoms), possibly by pore-etching, layers exfoliation or graphitization promotion, thus modulating surface area, mass transfer and conductivity.
To prepare the composites, we designed tunable multi-doped precursors: an organometallic structure combining iron with either copper, zinc, or iron, to investigate the effect of molybdenum-doping reported earlier. Pyrolysis and washing of the fore mentioned precursors yielded HzOR-active composites of Fe₃C nanoparticles and a hierarchically porous, partially graphitic N-doped carbon (NC). Thorough characterization by voltammetry and by a broad range of spectroscopic and microscopic methods revealed that the activity is ordered as: Cu-derived NC > Zn-derived NC > Fe-derived NC. While the catalysts had similar compositions, their nanostructure varied: both Zn- and Cu-doping induced the formation of micropores and small mesopores (5–13 nm diameter). The dopant-induced active site exposure (affecting micropore volume) and improved material flow (linked to mesopore volume) contributed to enhanced HzOR electroactivity. Furthermore, the intimate mixing of the metals in the precursor is hypothesized to homogenize and enhance the doping effect, as the structure enhancing metal ions (Zn²⁺ or Cu²⁺) exposed the nearby catalytic Fe₃C sites. Acid washing of the pyrolyzed carbon was crucial for producing microporosity in the Cu-based carbon, but had little effect on the Zn-derived one. This revealed the importance of micropores and small mesopores for HzOR electrocatalysis, and the different nanostructuring mechanisms of the two dopants: while Zn_(g) boils during pyrolysis and thus etches micropores into the carbon, Cu_(s) diffuses and spreads throughout, making exfoliation by acid reaction more efficient. Further work in our group is dedicated to the catalytic activity of pure phase Fe₃C, and its modification by other dopants.
[Burshtein et al., J. Mater. Chem. A, 2019, doi: 10.1039/C9TA03357B]

Flexible nanoscale electrode can be used in many applications such as electrochemical energy storage, electrocatalysts and solid memory devices by providing higher density faradaic reaction sites. Although many processing techniques have been used to produce nano-structured electrodes on flexible substrates, prior ones lack the mechanical stability. Here, the mechanical properties and flexibility of the TiN nanotube array on the Pt substrate were improved using a Ti interlayer as an adhesion promoter. Highly aligned TiN nanotube array was fabricated on a Pt substrate using an anodized aluminum oxide (AAO) template and atomic layer deposition (ALD) system. We show that with the use of a Ti interlayer as adhesion promoter between the TiN nanotube arrays and Pt substrate, the TiN nanotube arrays could perfectly attach to the Pt substrate without delamination and faceted phenomena. Peeling was not observed even when the bending test was performed at a high curvature (radius of curvature, -2 mm). In addition, reliable and uniform contact the nanotube and the substrate evidenced by conducting atomic force microscopy (C-AFM) analysis proved the excellent local transport properties of our electrodes. Furthermore, the mechanical bending test results attest to the excellent flexibility for use in flexible electronic devices. We envision that our 3D electrodes will be implemented as embedded electrodes in semiconductors as well as flexible plastic substrates.

Cancer is the second leading cause of death worldwide. Current treatments frequently rely on surgical resection, radiotherapy, and high-dose chemotherapy, with unsatisfactory outcomes and side effects. Thus, there is a great need for novel and more effective strategies. Photothermal therapy (PTT), a non-invasive alternative based on near-infrared (NIR) light energy conversion into heat, results in hyperthermia (39-47 °C) and induces higher nanoparticle/drug uptake due to increased membrane permeability and tumor cell apoptosis. Nanomaterials, like graphene-based materials (GBM), hold potential as photothermal absorbers to enhance PTT selectivity within the target tumor tissue toward achieving therapeutic temperatures using less total light energy, minimizing damage to the healthy surrounding tissue [1]. This study explored GBM and GBM loaded with 5-fluorouracil (5-FU), an anti-cancer drug, as platforms for combined chemo-photothermal therapy.
Nanographene oxide (GOn) was produced through the modified Hummer’s method [2] followed by ultrasonication in a custom-built industrial grade system. Following a one-step procedure, GOn was thermally reduced and non-covalent functionalized with poly(ethylene) glycol (PEG) to obtain stable aqueous dispersions (rGOn-PEG) [3]. GOn and rGOn-PEG (0.25 mg/mL) were mixed with 5-FU at a drug concentration varying between 0.25-5 mg/mL. GBM aqueous dispersions were irradiated with a LED source of 812.8±29.9nm (150 mW/cm2) and temperature recorded using a thermocouple. The effect of GBM and NIR irradiation was evaluated by resazurin cell viability assay using a human skin carcinoma cell line (A431 cells, ATCC).
Reduction and PEGlyation of GOn were confirmed by chemical characterization through FTIR, XPS and UV-vis spectroscopy, as well as thermal analysis by TGA. GOn and rGOn-PEG were obtained with mean lateral dimensions of 287 nm and 521 nm, respectively as determined by TEM. GOn and rGOn-PEG dispersions showed colloidal stability with zeta potential values around -25.6±0.8 mV and -10.2±0.3 mV (pH=7), respectively. Loading capacity of 5-FU on GBM reached 5.8±0.8 mg 5-FU/mg GOn and 3.6±1.2 mg 5-FU/mg rGOn-PEG by simple molecular physisorption. NIR irradiation increased rGOn-PEG temperature to 47 °C after 30 min, which is within temperature ranges of hyperthermia. rGOn-PEG in combination with NIR reduced A431 cells viability, in opposition to rGOn-PEG alone.
This study demonstrated the successful non-covalent functionalization and reduction of nanographene oxide, rendering a material with potential to be further explored for combined chemotherapy and PTT for cancer treatment.

Acknowledgements: This work was financed by FEDER - Fundo Europeu de Desenvolvimento Regional funds through the COMPETE 2020 - Operacional Programme for Competitiveness and Internationalisation (POCI), Portugal 2020, and by Portuguese funds through FCT/MCTES in the framework of the projects POCI-01-0145-FEDER-031143; POCI-01-0145-FEDER-006939; POCI-01-0145-FEDER-007274; PTDC/BTM-MAT/31143/2017, and Unidade de Investigação UID/EQU/00511/2019 - Laboratório de Engenharia de Processos, Ambiente, Biotecnologia e Energia – LEPABE.

REFERENCES:
[1] Doughty ACV et al., Materials, 2019, 12.
[2] Pinto AM et al., Carbon, 2015, 99:318.
[3] Chen J et al., Biomaterials, 2014, 35: 4986.

Carbon-based supports have been widely used to support Pt catalysts in polymer electrolyte fuel cells (PEMFCs) [1]. In our group, we developed polybenzimidazole (PBI)-wrapping onto carbon support that successfully achieved higher cell performance [2].
In this study, we present a dispersion investigation of the catalyst ink using PBI-wrapped catalyst (CB/PBI/Pt) and non-wrapped (CB/Pt) catalyst with a wide range of ionomer: carbon ratio (I/C). The effects of ink parameters, which include carbon black structure, and ionomer concentration, on the ink microstructure of catalyst ink were studied using visual study in combination with dynamic light scattering (DLS). Heterogeneous porous structure of the catalyst layer in PEMFCs is a significantly important parameter because it strongly determines the gas diffusion properties of the catalyst layer. And the connectivity of the network structure is largely depended on the structure of the catalyst agglomerations as well as the homogeneity of the ionomer on the carbon supporting materials. Therefore, we used scanning electron microscopy combined with focused ion beam (FIB-SEM) to visualize the nano-scale pore structure of the catalyst layer. Post-processing of a series of two-dimensional images reconstructed the three-dimensional pore-space of the catalyst layer.
We found that the catalyst ink of CB/PBI/Pt remained as a very stable dispersion in the range of I/C = 0.2~1.4, whereas for CB/Pt, the catalyst ink easily forms aggregation at high I/C (>0.6). The FIB-SEM images of CB/Pt catalyst layer with optimum I/C = 0.6 and CB/PBI/Pt catalyst layer with optimum I/C = 0.2 was analyzed. It is found that the CB/Pt catalyst layer has isolated large pores with the porosity of 0.55, while CB/PBI/Pt catalyst layer shows a uniform porous structure with the porosity of 0.7. It is reported that the presence of isolated pores increases the O₂ transport resistance in the catalyst layer, resulting in lower fuel cell performance [3,4]. Therefore, we concluded that the dispersion stability of catalyst ink is enhanced by PBI wrapping onto the CB surface, thus ensuring a better porous structure of the catalyst layer in PEMFCs. Furthermore, the particle-particle interactions in catalyst ink will be discussed in the presentation.


References

[1] Xin, L.; Yang, F., Polybenzimidazole (PBI) Functionalized Nanographene as Highly Stable Catalyst Support for Polymer Electrolyte Membrane Fuel Cells (PEMFCs). J. J. Electrochem. Soc. 2016, 163, 10.
[2] T. Fujigaya, et al., Improved Durability of Electrocatalyst Based on Coating of Carbon Black with Polybenzimidazole and their Application in Polymer Electrolyte Fuel Cells. J. ACS Appl. Mater. Interfaces 2016, 8, 23, 14494–14502.
[3] Inoue, G.; Kawase, M., Effect of porous structure of catalyst layer on effective oxygen diffusion coefficient in polymer electrolyte fuel cell. J. Power Sources 2016, 327, 1-10.
[4] Inoue, G.; Yokoyama, K.; Ooyama, J.; Terao, T.; Tokunaga, T.; Kubo, N.; Kawase, M., Theoretical examination of effective oxygen diffusion coefficient and electrical conductivity of polymer electrolyte fuel cell porous components. J. Power Sources 2016, 327, 610-621.

Single-walled carbon nanotube (SWNT) are attracting increasing attentions in biological applications because of their unique thermal, physical and optical properties. To use SWNT for in vivo applications, SWNT need to be biocompatible. Up to date, coating of SWNT with biocompatible materials especially polyethylene glycol (PEG) has been investigated due to its stealth property. However, it was pointed that the PEG-modified materials are rapidly excreted from the blood due to an immune reaction when they are repeatedly administered, which is known as accelerated blood clearance (ABC) phenomenon. To avoid such a problem, serum albumin (SA) attracts recent attention as an alternative material of PEG since SA is a blood protein derived from a living body. However, since the adsorption coefficient of SA onto SWNT surface is lower than that of the other proteins, the increase of the adsorption to avoid the risk of the replacement might be necessary. Therefore, in this study, we introduced fatty acid onto the surface of SWNT to improve the binding of SA by utilizing the strong binding between SA and fatty acid , where the introduction of the fatty acid was carried out by the radical grafting of the fatty acid derivative onto the SWNT sidewall. Here, the adsorption behavior was monitored by monitoring of the unique red-shifted and brighter photoemission (PL) generated from the grafting site compared to that of the non-functionalized SWNT.

Micro- and meso-porous structures of alumina have attracted attention for their potential use in different applications. In this research, a novel and facile route was introduced for dual growth of alumina nanoparticles and carbon nanotubes together to fabricate nanocomposites at low temperature 250°C through explosive processes of solid fuel. In this trend, series of alumina species with and without carbon nanotubes were prepared and characterized by X-ray diffraction, Raman spectra and transmission electron microscopy. The surface properties of the alumina-CNT nanocomposites were characterized and compared with the prepared nanoparticles of alumina by adsorption–desorption system. The specific surface area of the prepared alumina-CNT nanocomposites was increased from257.9 to 307.7 m2/g and 314.8 m2/g with growing CNTs inside the porous structure of alumina. These increments were observed because of the dual growth of nanoparticles and nanotubes by which new micropores inside their nanocomposites were created. When the source of CNTs was changed from ethanol to methanol, pure mesoporous structure with narrow pore size distribution was observed for the alumina-CNT nanocomposite. In addition, the surface area and the total pore volume increased to be 324.9 m2/g and 0.673 cm3/g; respectively. The detonation technique of an explosive solid has been used for the first time to improve and control the porous structure of alumina through dual growth of CNTs and alumina at low temperature to meet the special requirements of the markets of catalysis and water purification.

Nanowires have become an increasingly prevalent nanomaterials in composites and devices. In both surface coatings and mechanically coupled sensing applications, arrays and other complex geometries provide numerous design advantages, such as pixel like features. However, little investigation has been done regarding the mechanical behavior of these micron sized structures. With contact and load bearing applications, both the failure behavior and the underlying failure mechanisms are critical for robust device design. Though in-situ microcompression experiments on highly aligned dense bundles of single crystalline zinc oxide (ZnO) nanowires we investigate these types of structures to build a model for better understanding structural failure.

The ZnO nanowires are formed through hydrothermal growth from an aqueous zinc nitrate solution with hexamethylenetetramine (HMTA) and electrolysis conditions to promote fast growing high aspect ratio nanowires. 2μm and 4μm diameter bundles with individual nanowires of approximately 300nm in diameter and 4μm tall were investigated. These structures provides a range of 10-130 nanowires per bundle and thus probes an order of magnitude in scale. Experiments show two regimes of failure in the nanowire bundles: localized non-catastrophic events and global structural failure. No size dependence is observed in either regime and failure stress ranges from 0.3-1.3GPa and 0.83-2.20GPa respectively. Localized failure corresponds to interfacial splitting between nanowires and can be modeled using a mode I double cantilever beam tests. Analysis of this mechanism provides insight to the flaw size and failure initiation in the structures. Ultimate global failure can be modeled by coupling the accumulation of local failure from interfacial splitting to specific failure parameters of the nanowire material. Utilizing Weibull statistics and experimental results, we demonstrate the validity of this technique for analyzing flaw distribution and predicting the expected failure stress range of the bundle structures. The technique shows the sensitivity of failure behavior to degree of alignment, flaw size, interfacial interactions of constituents, and structural surface effects. Through analysis of behavior in this specific system, we develop insight to broader fundamental mechanisms for local failure and statistical techniques for assessing and predicting failure behavior of highly aligned structures.

Polymer materials with superior properties have been more and more widely used in our daily life. As compared to metals, light weight and good-processability are particularly beneficial properties of polymer materials. However, there are also several properties of polymers which are required to be improved, e.g. mechanical, electrical and thermal properties, and thus a plenty of research to improve these properties have been conducted so far. Improving these properties can realize the extension of applicable fields of polymer materials.
In order to improve objective properties of polymers, incorporation of appropriate kinds of fillers into polymer matrix is frequently adopted. For instance, carbon nanotubes (CNTs) are one of the most prominent fillers with superior properties such as high mechanical strength and electrical conductivities. Nanocomposite materials with CNTs have been widely explored and various kinds of nanocomposites possessing improved properties have been fabricated so far. However, addition of substantial amount of nanofillers, not limited to CNTs, is required in most cases, and thus the inherent properties of polymer matrix, such as good-processability, tend to be degraded. These kinds of nanofillers are basically aggregated in a pristine form, and are required to be dispersed properly in their nanocomposites, in order to extract their potential as a filler.
In this presentation, we will describe the relationship between the dispersibility of CNTs and the resultant properties of their nanocomposites. As an example, the thermal stability of CNT nanocomposite will be focused on. We successfully fabricated the CNT/silicone rubber nanocomposites with high thermal stability achieved by well-dispersed single-walled CNTs. The temperature at 5 % weight loss (T_{d,5 %}) of silicone rubber, obtained from thermogravimetric analysis, was increased by incorporation of low amount of CNTs. Remarkably, we found that the degree of increase in the T_{d,5 %} depends on the dispersion process of CNTs, and appropriate dispersion process can realize higher increase in the temperature than that of the CNT dispersion process only by stirring. This phenomenon is considered to be originated from the homogeneity in the distributions of CNTs in nanocomposites, which has been ascertained by analytical techniques. We also confirmed that the CNT/silicone rubber nanocomposites fabricated by appropriate dispersion process can retain rubbery elasticity after a thermal aging test, while pristine silicone rubber was embrittled soon after the onset of the test. These results indicate that appropriately dispersed CNTs can impart thermal stability in both short- and long-term to silicone matrix only by small amount of loading. Our findings indicate that appropriate dispersion of CNTs can enhance the effectiveness of incorporation of CNT to matrix, and we believe that these kinds of approach can be applicable to a broad range of matrix, not limited to polymers.

In polymer electrolyte fuel cells (PEFC), a composite of carbon black (CB) with platinum particles (Pt) is widely used as an electrode catalyst after mixing with acidic electrolyte. However, low platinum utilization efficiency because of the uneven distribution of acid electrolyte on the CB surface that caused the insufficient protons transport was the issue [1]. We reported that improvement of platinum utilization efficiency and power density by coating of polybenzimidazole (PBI) onto CB surface prior to the platinum loading [2], in which the distribution of the electrolyte become uniform by the coating of PBI. However, it coating homogeneity of PBI onto CB has not been clarified yet.
In this study, the adsorption state of PBI on CB was studied by estimating the adsorption isotherm and the interaction acting between the carbon materials and PBI was investigated.
From the adsorption isotherm of PBI on CB, it was revealed that PBI adsorption reached adsorption equilibrium from a low concentration, suggesting that PBI was adsorbed in a monolayer on the carbon materials efficiently. In addition, the PBI coverage at the coating concentration of 0.50 mg /mL, used for coating, calculated from the Langmuir equation showed as high as 99.9%. Therefore, we concluded PBI uniformly coats CB. Also, based on the calculation of thermodynamic parameters, it was found that ΔH and ΔS were 14 kJ/mol, and 0.11 kJ/mol, respectively. The temperature dependence of the isotherm revealed that this adsorption process was entropy driven since the PBI adsorption amount increased with increasing the temperature. The adsorption behavior and interaction of PBI with other carbon materials will be discussed in the presentation.

References
[1] S. Jayawickrama et. al., Electrochim. Acta. 2019, 312, 349.
[2] T. Fujigaya, et al., ACS Appl. Mater. Interfaces 2011, 8, 14494.

Low-dimensional all-carbon nanostructures are promising candidates for future flexible and transparent transistors, as well as light-emitters [Pyatkov et al, Nature Photonics 10 , 420–427 (2016)]. Carbon nanotube field-effect transistors with graphene electrodes offer high thermal stability and allow for ultra-flat devices able to carry high current densities. Understanding quantum transport in such systems is essential for device manufacturing. However, conventional simulation methods are limited to local contacts with an overlap width of only a few angstroms, and first-principle quantum transport calculations in systems with realistic contact geometries remained unfeasible. Simulation methods for extended CNT/metal contacts were presented in prior theoretical studies [Fediai et al, Nanoscale, 8, 10240 (2016)]. Here, we report quantum transport calculations based on the non-equilibrium Green function formalism and density functional theory, which are capable of treating ~100nm long CNT/graphene overlap regions and electrostatic gating at a pure ab-initio level. These calculations are compared with experiments where graphene electrodes were fabricated and dielectrophoretically bridged with single semiconducting CNTs followed by an electrical characterization over a wide temperature range. The simulation results are in agreement with the experimental data and the fabricated devices exhibit ambipolar behavior, consistent with the theory. Due to large CNT/graphene spacing and small CNT/graphene overlap, only a fraction of the quantum conductance can be achieved for the on-state conductivity. A remarkable feature of the all-carbon transistor with graphene electrodes is electrostatically induced doping of the carbon-system in the contact regions caused by the gate electrode. This is made possible by the low density of states in graphene near the K-point. We hope that this newly developed and verified simulation approach will accelerate progress in fabrication as well as the understanding of advanced all-carbon devices.

The constant and growing need in new catalysts for hydrogen evolution reaction is triggered by increasing energy demands and promises of its eco-friendliness combined with large gravimetrical storage capacity. Carbon nanotubes are also known to be quite promising for hydrogen (and oxygen) evolution reaction and are characterized by large specific surface area, excellent conductivity, and rather good durability.

We report a cathode material based on plasma-treated single-walled carbon nanotubes decorated by RuO_x nanoparticles using atomic layer deposition (ALD). We have examined cathode performance towards hydrogen evolution reaction by tailoring material wettability, conductivity yielded by plasma-treatment, and the catalyst loading [1]. We discuss that nucleation of particles is facilitated by the appearance of carboxylic and hydroxyl groups triggered by oxygen plasma action. The best performance is associated with samples containing RuO_x particles of 4-5 nm, which show hydrogen evolution onset potential to be about -5 mV (vs. RHE) in 0.5 M H₂SO₄ measured at a current density of -1 mA cm^-2 and Tafel slope of 47.5 mV/dec. The material possesses stable performance at -10 mA cm^-2 with a potential of about - 160 mV.

The reported study was funded by RFBR, project number 20-03-00804

[1] Fedor Fedorov, Daniel Settipani, Marthe Emelie Melandsø Buan, Jani Sainio, Farhan S.M. Ali, Daniil Ilatovskii, Tanja Kallio, Albert G. Nasibulin (2020) ChemElectroChem https://doi.org/10.1002/celc.202000528.

Using solar energy to convert CO₂ into hydrocarbon fuel is a promising technique for harvesting solar energy storage and reducing carbon dioxide. Recently, Graphene-based semiconductor composites have been a topic of great interest, especially in the field of photocatalysis. Graphene has the advantages of high surface area, excellent conductivity, and anticorrosion capacity, which can overcome the limitations of traditional photocatalysts. Thus, graphene-based material can be a feasible photocatalyst for photocatalytic CO₂ reduction. Besides, as an environment-friendly and earth abundant material, Cu_xS has considered as a good candidate for photocatalytic reactions, due to its unique optical, electronic, physical and chemical properties. Herein, we report the photocatalytic reduction of CO₂ using Cu_xS/graphene aerogel as the photocatalyst, which was prepared by hydrothermal method. The as prepared Cu_xS/graphene aerogel exhibited pretty good activity for photocatalytic reduction of CO₂. C₂ products (ethanol, acetate) are main products. In this composite photocatalyst, graphene aerogel not only serves as a 3 dimensional support for Cu_xS, but also transfers the photo generated charges. Moreover, density functional theory calculations were performed to reveal the chemical reactions and the charge transfer between Cu_xS and graphene. Also, the study of Cu_xS/graphene aerogels photocatalyst presents useful information for efficient photocatalytic CO₂ reduction without noble-metals.

There is a growing need for devices that operate at THz frequencies, and with the end Moore’s device scaling law approaching, alternatives to solid-state transistors need to be explored. The inherent limitation of solid-state transistors such as the metal-oxide semiconductor field-effect transistor (MOSFET) is the semiconductor channel, which not only causes carrier scattering, velocity saturation of carriers due to optical phonon scattering, but is also susceptible to high temperature and radiation effects. Current research attempts to mitigate these negative effects focus on using wide bandgap semiconductor channels. In contrast, the use of ‘empty-space’, which can be regarded as the ultimate wide bandgap material, as the device channel could overcome these limitations. This is because in vacuum, there is no carrier scattering (ballistic transport), avalanche breakdown or thermal generation. The absence of any atoms further enhances the tolerance to high temperature as the channel retains its properties. Nanotechnology and nanofabrication has enabled the realization of nanoscale vacuum channel transistors (NVCTs) that could potentially surpass solid state devices of equivalent channel length owing to ballistic transport of electrons, shorter transit time and higher intrinsic breakdown field. Hence, transistors with a vacuum channels could have very high Johnson figure of merit (J_FoM = E_BDv_sat/2π) of ~10¹⁴ V/s, even exceeding ultra-wide bandgap materials such as AlGaN and diamond.

We report the demonstration of NVCTs based on gated vertical silicon field emission arrays with two self-aligned gates. The two gates are separated by an oxide with thickness of 350 nm. A first gate with aperture diameter of 360 nm is used to extract electrons from a sharp emitter tip (radius < 7 nm) and the second gate, with aperture diameter of 570 nm, is used to focus the electron in to a vacuum channel. The emitter tips density is 10⁸ emitters/cm². NVCTs with such electron sources are highly sensitive to barrier variations caused by surface adsorption of molecules on the tip in poor vacuum environment. Here we demonstrate the nano-encapsulation of the electron source for operation in poor vacuum, using several layers of graphene, which are transparent to electrons but impermeable to the larger gas atoms in a poor vacuum.This device architecture with two self-aligned gates also enables the application of a different voltage bias on the graphene and hence controlling the energy of the electrons in the channel, while reducing the encapsulation volume significantly. We demonstrate turn-on voltages below 10 V and operation in poor vacuum and at atmospheric pressure. This device architecture is highly promising to realize empty space electronics capable of functioning at higher power and harsher conditions (high radiation and high temperature, such as in space and in nuclear reactors) transcending the performance of solid state electronics.

Given the increase in technology development the need for more energy efficient devices is required. In mechanical systems a large amount of energy is lost due to friction between sliding surfaces. For this reason, the creation of effective lubricants is needed. Transition metal disulfides such as WS₂ and MoS₂ fulleroids have been used as oil additives. However, disulfides are prone to oxidation and release of sulphide compounds under heat and may corrode metal surfaces creating metal sulphides. Carbon materials can exhibit higher chemical inertness and therefore exhibit longer lubrication lifetime under heat than transition metal disulfides. Among carbon materials; graphene, carbon nanotubes and fullerenes have been added into oil to decrease friction between two metal surfaces. Unfortunately, the molecular interaction between carbon nanomaterials and lubricants has not been fully understood. We studied the molecular interactions between fullerenes and mineral oil, known as “nano oil”, by ultraviolet Raman spectroscopy and molecular dynamics simulations. The results indicate that aromatic molecules help to disperse individual C_60/70 molecules from aggregates whereas the alkane molecules help to stabilize fullerenes by forming a dynamic shell structure around them. Our findings demonstrate that fullerenes can be used as high-performance additives for effective lubrication.

Hybrid carbon nanotube (CNT) composites consisting of multiple types of fillers have been developed to provide enhanced characteristics as compared to CNT single-filler composites. The incorporation of secondary fillers, such as silica, CaCo₃, and BaSO₄, yields remarkably improved mechanical strength and stiffness of the CNT composite and electrical conductivity of the hybrid composite network under the control based on geometry and content of the constituent particulate fillers. In particular, higher electrical conductivity can be attained with the addition of micro-scale secondary fillers to the CNT composite network, while the addition of nano-scale particulate fillers incurs lowering the electrical conductivity of the nanocomposite network. Such electrical conductivity transition is attributed to distinct variations in the network topology caused by the excluded volume originating from the loading of secondary fillers with different scales. Micro-silica composites result in dense clusters of CNTs, thereby forming CNT conducting paths, while densely-dispersed nano-size fillers cause severely twisted CNTs, reducing forming a conducting network.
In this work, Monte-Carlo simulation is first conducted for the estimation of the electrical conductivity of the CNT network of hybrid composites. To obtain a realistic model, flexible CNTs are modeled as long thin cylindrical objects with many joints interconnected in a row. In addition, to take the resistance of the conducting CNTs into account, individual joints are considered to be tiny lumped resistor elements. A computational characterization approach based on numerical linear algebra technique is applied under various size and concentration configurations of composite components, and the corresponding electrical conductivity of the network is derived. The computational results exhibit that the ratio of the average diameter of the particulate filler to the nanotube length governs the tendency of the electrical conductivity variation, as compared to the change of filler contents only affecting the degree of the conductivity change. As the ratio of the silica diameter to the CNT length increases, the ratio of the conductivity without (σ₀) and with (σ) the secondary particulate fillers, i.e. σ/σ₀, increases from the value less than one to the value more than one. This indicates that the impact of the second fillers on the electrical conductivity of the composites shows a transition. By contrast, if the geometric configuration of the fillers is almost fixed, the degree of the conductivity variation increases as the silica content increases, while decreasing for the increasing CNT content.
The electrical behaviors of hybrid composites can be simply characterized by the combination of computational geometry centric notions such as Voronoi tessellations and Swiss cheese model along with their associated percolation theory. In the developed model, the CNT dispersed around particulate fillers indicating effective conducting paths can be classified with tessellations from Voronoi cells. The conductance of each effective path is designated by local conductance determined from the density of CNTs in the local region. The reliability of the model is validated based on comparison with the numerical results obtained from the MC simulation. The developed approach achieves, as compared to the MC simulation, remarkable computing cost reduction. Therefore, the combined computational framework enables to provides a novel strategy to estimate for the electrical conductivity of the hybrid composites under the external deformation such as bending, stretching, and patterning, and it is a viable model for the design of the hybrid composites at hand.

Aerosol jet printing has gained a considerable amount of attention as a method to additively fabricate electronic device. In part, this is due to the compatibility with a wide range of ink viscosities (1-1000 cps) and the ability to print on non-planar surfaces. One elusive material for aerosol jet printed active electronics is a high-performance semiconducting ink with low-variability. One potential promising ink would be a combination of high-mobility carbon nanotubes (CNTs) with highly uniform semiconducting polymers. However, CNTs fully encapsulated by semiconducting polymers have not shown noteworthy improvement. One method to capture both positive attributes of CNTs and semiconducting polymers is through a hierarchical nanostructured composite. The conjugated polymer regioregular poly(3-hexylthiophene) (P3HT) has the ability to self-assemble and form periodic crystals on CNTs due to π-π interactions. These structures, coined nano-hybrid shish kababs (NHSKs), may directly improves charge carrier transport in printed thin-film electronic devices.
The objective of this project is to fabricate a novel semiconducting ink that consists of P3HT/CNT NHSKs. In developing this ink, we investigated the P3HT shish kabab crystallization and kinetic growth on (6,5) chirality SWNTs. This was done by manipulating the P3HT-SWNT concentrations, the solvent concentration, and crystallization temperature. The P3HT fibril shape, size, and period were found to be correlated to the above parameters. The morphology and purity/concentration were measured using atomic force microscopy (AFM) and ultra-violet/visible spectroscopy.
NHSKs were fabricated via a 6:1 P3HT to SWNT mass concentration solution mixed in 70°C anisole solution. The P3HT supramolecular structures were found to be 32±3.7 nm wide and 269±11.4 nm long. At higher mass ratios (40:1 P3HT to SWNT), full encapsulation was observed with little periodicity. In conclusion, this work investigates the growth mechanisms of P3HT polymer crystals on single chirality CNTs for semiconducting ink applications. Next steps include the manipulation of the solution to increase printability and the fabrication of NHSK-based thin-film transistors.

The unique thermal conductivity of graphene makes it one of the most promising materials for next generation heat transfer applications that, given the increasing demand for energy supply from sustainable energy sources such as concentrated solar power, has emerged as key technology. The incorporation of graphene and graphene-like nanomaterials into conventional heat transfer fluids has been shown to significantly improve their thermal transport properties. Due to their cost-efficient carbon-based starting material, its high surface area and sheet-like structure, graphene nanoplatelets (GNPs) are suitable for colloidal thermal conductive fluids demonstrating enhanced heat transfer efficiencies.
In this work, hydrophobic graphene nanoplatelets were used as starting material and surface functionalized by acid treatments to synthesize highly stable, exfoliated, surfactant-free and highly concentrated (4 wt.%) graphene nanofluids maintaining high thermal conductivity. Characterization by SEM, XPS, XRD, Raman and FT-IR spectroscopy revealed a significant influence of shape, reaction period, acid volume and temperature on the resulting thermal conductivity values of the nanofluids relative to the carrier fluid. After 14h of measurement in a dormant system, thermal conductivities up to 0.586 W/m*K (base fluid: 0.391 W/m*K) were measured. In combination with a low viscosity of 6.39 cP the overall efficiency of the functionalized particles could be increased to 77 % in comparison to the base fluid. The combination of both low viscosity and high thermal conductivity, even after 14h in a standing system, demonstrate the extraordinary properties of surface functionalized graphene nanoplatelets prepared in this work in comparison to other nanofluidic systems.

Robust materials with high conductivity are essential to electronic devices and systems. Nanocarbon-metal composites have the potential to improve upon the electrical conductivity of established metals and alloys such as Al and Cu by incorporating carbon nanostructures known for their superior electrical properties. During the fabrication of novel nanocarbon-metal composites called covetics, direct electric current applied to a metal melt containing a dispersion of carbon source material is believed to ionize carbon atoms and lead to the formation of nanoscale graphitic ribbons and chains that ultimately incorporate within the metal lattice upon solidification. The electrical conductivity of the resulting composites is consistently greater than the original alloy, but the magnitude of conductivity enhancement varies significantly from sample to sample, and the theoretical upper limit of conductivity enhancement in these systems remains unclear.

This work combines fundamental assumptions about the nature of covetics, specifically a tightly bound metal-carbon interface, with a simple effective-medium model to estimate the bulk conductivity of ideal Al and Cu covetics with randomly distributed graphene nanoribbons (GNRs). Density-functional theory estimates of charge transfer at the graphene-metal interface, local electrical conductivity measurements, and transmission electron microscopy investigation of the interface region provide inputs to the model. The implications of quantum confinement in narrow GNRs are also explored. We use the model to project a range of performance-enhancement goals for the covetics fabrication community and find the potential for conductivity improvements on the order of 10% under ideal conditions, however fabrication challenges remain before these gains may be realized on an industrial scale.

This work is supported by the U.S. Department of Energy under Award No. DE-EE0008313.

Water desalination has been a critical issue for reserving the freshwater for human survival, further civilization, industry development. Pressure retarded osmosis (PRO) is desalination technology emerging from the osmosis phenomenon; water flux through the membrane, excluding undesired macromolecules or ions with applying pressure. Thus, a high water permittable membrane with stronger mechanical strength to bear in high water pressure should be developed for a high-performance PRO desalination process. High mechanical strength and water permittivity could be a trade-off relationship based on thickness and porosity. Thus, vertical oriented polyvinylidene fluoride (PVDF) membrane with 3D connected carbon nanotube (CNT) is presented. Vertical pores made of hydrophobic polyvinyl fluoride (PVDF) and hydrophilic metal-organic framework (MOF) decorated on the surface improve their water permeability and salt rejection. The CNT embedded structure in the vertically aligned membrane improves mechanical strength along the in-plane direction. This work presents CNT additives can significantly improve the mechanical properties of water desalination membranes by smartly designing the morphology of the substrate and properly inserting functional materials in the active layer.

Single-walled carbon nanotubes (SWNTs) have attractive optical properties based on their unique one-dimensional nano structures. Especially, semiconducting SWNTs emits photoluminescence (PL) originating from the E₁₁ emission of photogenerated exciton in the near infrared regions (900-1600 nm), which can be applied for bioimaging and telecom devices. Compared to such E₁₁ PL, redshifted and brighter E₁₁^* PL have been recently reported by the sp³ carbon defect doping to the crystalline sp² carbon lattice of SWNTs. The resultant SWNTs are locally functionalized SWNTs (lf-SWNTs) [1] that have the doped sites with narrower bandgaps and exciton trapping features. We have reported proximal modification using bis-aryldaizonium salts (bADs). The lf-SWNTs modified with bADs (lf-SWNT-bA) showed largely redshifted PL (E₁₁^2*) than E₁₁^* PL [2] and were found to show sensitive E₁₁^2* PL property changed depending on the chemical structures of bAD, in which the E₁₁^2* PL wavelengths were shifted with strong dependence of methylene spacer lengths and connected positions in the bADs [3]. Therefore, proximal modification is useful approach for remarkable PL property modulation of the lf-SWNTs compared to typical mono-aryl functionalized lf-SWNTs.
In this study, we newly synthesize modifiers having multiple reactive groups for structural changes of the proximal modification sites of lf-SWNTs.
The SWNTs (CoMoCAT, (6,5) chirality-rich) were solubilized in D₂O containing sodium dodecyl sulfate by sonication and separated by ultracentrifugation. A tris-aryldiazonium salt (tAD) having three aryldiazonium groups was mixed with the solubilized SWNTs for local chemical functionalization. After the chemical modification, multiple PL peaks appeared over typical E₁₁^* regions (>1200 nm). The NIR absorption and Raman scattering measurements supported the local chemical functionalization of the modifiers on the SWNTs, in which small absorbance changes at 980 nm and the increase of D-band intensity due to the defect introduction were observed, respectively. In addition, the reaction conditions such as solution concentrations were found to show significant influence on such new longer wavelength PL generation. The detail results including chemical structure effects of the modifiers and the reaction condition dependency will be discussed at 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] T. Shiraki, B. Yu, T. Shiraishi, T. Shiga, T. Fujigaya, Chem. Lett. 2019, 48, 791.

Atomically thin graphene membrane has been considered as an ideal candidate for next-generation membrane-based technologies. While catalytic chemical vapor deposition (CVD) has been demonstrated to be an economical and versatile way of enabling the commercial production of high-quality graphene, CVD graphene has to be transferred from the growth substrate onto a porous support substrate to provide mechanical stability for membrane applications. However, commonly used polymer scaffold methods typically leave polymer residues detrimental to membrane performance, while transfers without sacrificial polymers suffer from low transfer yield leading to high membrane leakage. Hence, high-yield transfer of clean large-area graphene onto appropriately porous supports using scalable processes for membrane applications remains elusive. In this work, we systematically investigate the factors influencing the transfer of CVD graphene from a Cu foil onto a model polycarbonate track etch (PCTE) support for fabricating large-area atomically thin membranes via manual compression, mechanical press and scalable lamination approaches. Particularly, we report on a novel roll-to-roll manufacturing compatible isopropanol-assisted hot lamination that allows for facile, clean and scalable transfer of centimeter-scale graphene onto model PCTE supports with coverage ≥ 99.2% without compromising support porosity, which is one of the best values reported to this date for centimeter-scale atomically thin membranes. The remaining 0.8% of leakage is attributed to defects (>50 nm) primarily along wrinkles formed during CVD growth. Furthermore, water-assisted oxidation effectively detaches CVD graphene from the Cu foil and helps graphene transfer, but significantly damages (~10%) graphene along wrinkles. Finally, fully functional centimeter-scale atomically thin membranes are demonstrated. Our work provides a facile and effective method for the fabrication of atomically thin graphene membranes and can help on the progress towards the practical application of graphene membrane technologies relevant to gas separation, nanofiltration, desalination, ionic/molecular transport, energy and biomedical fields and beyond.

Graphene has several fascinating characteristics such as high thermal and electrical conductivity. Graphene polymer composites is usually made using molding. To enhance the application of graphene in nanocomposites controlling its alignment is important as graphene has different conductivity along and perpendicular to its surface. The orientation of graphene in polymeric materials is a challenging task. Recently 3D printing has been used for aligning graphene in composites. In this research varying amounts of graphene (grade H5 – XG Sciences) was mixed with PBAT-PLA mixture and molded. Also 3D printed PBAT-PLA-graphene composites were made. The dielectric measurements were made by placing the composites between two brass electrodes of diameter 1cm. The dielectric measurements were made using Wayne-kerr- 6500p LCR meter. The frequency was varied from 100 to 10⁶ Hz. The measurements were made at room temperature (22 °C). The samples had cuboid shapes. The measurements were made along height and depth of the samples. The height corresponded to the direction of application of pressure during molding and the depth corresponded to the direction perpendicular to the direction of application of pressure and parallel the surface of the samples. The following observations were made. (A) The dielectric constant for 3D printed samples (along height) was less than dielectric constant for 3D printed samples (along depth) which was less than dielectric constant for molded samples (along height). (B) The dielectric constant for molded samples (along depth) was less than dielectric constant for molded samples (along height). (C) Along depth, for molded samples the dielectric constant becomes negative for 20% graphene containing samples indicating percolation. (D) The electrical conductivity for 3D printed samples (along height) was less than conductivity for molded samples (along height) and (E) Electrical conductivity for 3D printed samples (along depth) was less than electrical conductivity for molded samples (along depth). The observed variations in dielectric and electrical characteristics are attributed to the orientation of graphene in the composites.

Graphene, which is an atomic layer carbon with the honeycomb structure, has several interesting properties, such as high optical transparency, high electrical and thermal conductivities. Graphene possesses also unusual properties in plasmon, such as the confinement, long lifetime, and long propagation distances of plasmons. Due to the tunability of plasmon, graphene is promising for the plasmon-based application, such as THz technologies and gas sensors. For the device application, the investigation of interaction between graphene and metal is also essential, because the graphene-metal contacts are unavoidable of every graphene-based device, and the electronic properties of graphene strongly depends on the substrate.
It is known that the plasmon in free standing graphene show the different properties from those supported by substrate. It is also known that the properties of plasmon in graphene depend on the materials used for substrate, which is important for graphene plasmonics. On the other hand, the interaction between the substrate and graphene is not fully understood. Especially in nanoscale structures, it is not well known how plasmons in graphene are affected by the metal substrate. In this study, p-plasmon in single-walled carbon nanotube (SWCNT) with and without the deposition of gold nanoparticles (Au NPs) was investigated using TEM-EELS (Transmission Electron Microscopy – Electron Energy Loss Spectroscopy) method as the first step to elucidate the effect of the gold substrate on p-plasmon in honeycomb structured carbon. The plasmons show the linear dispersion in monolayer graphene-metal interface similar to that in SWCNT-metal interfaces, and the controllability of Au NPs in shape and size is much higher on SWCNTs than on graphene. So, the investigation using SWCNT-Au NPs system would be the simplified model system for the honeycomb structured nanocarbon on metal substrates.
The solution of SWCNTs dispersed in an organic solvent, was dropped on the a microgrid for TEM. Then gold nanoparticles were vapor-deposited thereon. In order to avoid the contamination during TEM-EELS measurement, the microgrid thus prepared was pre-heated for 10 min in 1x 10^-5 Pa. TEM observation and EELS measurement performed using JEM-F200 (JEOL) and GIF Quantum (Gatan), respectively. The accelerating voltage for the TEM observation and EELS measurement was 80 kV for preventing sample damage. The energy resolution of zero loss peak was below 0.5 eV.
On the microgrid, various types of SWCNTs with and without Au NPs were recognized such as isolated, bundled, and cross-linked ones. The peak shift in the energy loss spectra of p-plasmon was biggest for the bundled SWCNTs without Au NP. The peak shift increased for an isolated SWCNT with an Au NP, and was highest for SWCNTs sandwiching a Au NPs. These results showed the plasmon energy can be controlled by the configuration of SWCNTs and Au NPs.

Carbon Nanotubes (CNT) and graphene are considered highly promising nanomaterials for composite reinforcement. The nanoscale dimensions of the carbon structures provide ultra-high surface-to-volume ratio, nearly defect-free structure, and their exceptional properties: mechanical (1TPa – five times the value for steel), thermal conductivity (2000-6000 Wm-1K-1 – four to ten times the value for silver) and electrical conductivity (roughly equivalent to copper) makes them highly useful in very many applications. However, these same scale and properties complicate the processing and fabrication of polymer based nanocomposites: high surface-to-volume means that even in small filler concentrations composite process-affecting properties as melt viscosity, heat transfer and other characteristics will drastically change. Morphology control, and thus post-processing behavior prediction, are also challenging – as dispersion and orientation are applied indirectly in the process, and different mechanisms are dominant at different length-scales. Therefore, transferring the exquisite properties of the CNT and graphene to the composite level have been proven less than ideal, as the measured mechanical, electrical and thermal properties of the nanocomposites are usually lower than predicted by rule-of-mixture calculations.
In this talk, various approaches for carbon nanocomposite fabrications, both “top-down” and “bottom-up”, will be presented in case-studies. A few of the major issues inhibiting nanocarbon based composites from achieving their true potential will be highlighted. Effects of different fabrication techniques, including 3D printing, on the morphology of nanocomposites and the resultant behavior will be discussed, and possible solutions to the aforementioned issues will be presented. The new methods can provide better control for improved planning and designing of nano carbon based composites.

New opportunities have been created along with the advances of the wearable device technology. For pressure sensing and transduction in soft objects like human skin, direct contact between sensor and target area is necessary; therefore, sensor flexibility is a very important parameter for the viability of the sensing device.
In this work, we report on the development of a sensing system that translates the electric signals of low cost composites based on polyurethane (PU) and reduced graphene oxide (r-GO) fabricated in-house. The graphene oxide (GO) is deposited by dispersion in PU foam. The GO reduction is carried out by immersion in ascorbic acid. Different commercial foams were tested and sample heights could be reduced to 1mm with electrical resistance range of 1-100 kΩ for a 90% compression.
Electrical resistances were measured in function of the applied force and an exponential character was identified. With the force range which the foams endure and the calibration curve obtained for the samples, a rigid device was developed by integrating an Arduino system to the sensors so that responses could be obtained via a graphical interface, adapted to visual feedback.
The foam shows great conformity with surfaces; flexible contacts, printed in Kapton film using conductive paint, are used to obtain the flexible device. We thus expect to have a flexible sensor integrated to a functioning system fully prepared to neurological rehabilitation applications.

Electrochemical capacitors (ECs) or supercapacitors (SCs) are considered to be most promising energy storage devices and have received great attention because of their excellent electrochemical performance with high output power, short discharging time and long-term cycle stability. Transition metal chalcogenides (especially selenides and tellurides) have recently attracted considerable attention for electrochemical applications mainly due to better electronic conductivity, facile charge transfer, redox tunability, and chemical stability. In the current project, transition metal telluride-based nanostructure composites were studied for supercapacitor applications. The nickel telluride nanostructures were grown directly on Nickel foam by hydrothermal method as well as electrodeposition process without addition of any binder to the catalyst. The capacitor performance was measured in a three-electrode system with the nickel-telluride electrode as the anode. A specific capacitance of 1826 F/g was achieved at a current density of 1 A/g. The composite electrode maintained cyclic stability of more than 90 % at a higher current density of 10 A/g after 1000 cycles. Also, more than 80 % current density retention achieved at higher current density of 20 A/g. Moreover, doping effect on the transition metal site on the supercapacitor performance was also illustrated in this work. Doping in the transition metal site had a positive influence on the supercapacitor activity since, it led to lattice distortion, electronic structure modification as well as helped to tune the surface redox behavior. Also, combining different carbon-based materials (carbon nanotubes, activated carbons and graphene) with the active nickel telluride nanostructures enhanced specific capacitance and overall cyclic stability by increasing the active surface area and porosity of the composite. In this presentation we will discuss the supercapacitor performance of these telluride nanostructures as well as the effect of transition metal doping and carbon nanostructure additives, and explain how the chemistry of transition metal chalcogenides influences their electrochemical functionality and potential as future energy storage devices.

Controlling the size and shape of nanopores in two-dimensional materials is a key challenge in applications such as DNA sequencing, sieving, and quantum emission in artificial atoms. In single-layer hexagonal boron nitride (h-BN), under a high-energy electron beam with certain properties, triangular pores are formed whose edges are entirely made up of nitrogen atoms. This allows fabrication of triangular pores at will with matching orientation throughout the two-dimensional material. However, in multilayer h-BN, which is usually in the AA′ stacking, neighboring sheets are rotated by 60° with respect to each other, which causes triangular pores in consecutive layers to be misaligned. Here, we investigate experimentally and theoretically triangular vacancies in (unconventional) Bernal-stacked h-BN (AB-h-BN) formed using a high-energy electron beam. Due to the geometric configuration of AB-h-BN, triangular pores in different layers are aligned, and their sizes are controlled by the duration of the electron irradiation. Interlayer covalent bonding at the edge of the pore is not favored, as opposed to what occurs in the more common AA′-stacked BN. A variety of monolayer, concentric and bilayer pores in bilayer AB-h-BN are observed in high-resolution transmission electron microscopy and characterized using ab initio simulations. Bilayer pores in AB-h-BN are commonly formed, and grow without breaking the bilayer character. Nanopores in AB-h-BN exhibit a wide range of electronic properties, ranging from half-metallic to non-magnetic and magnetic semiconducting. Therefore, because of the controllability of the pore size, the electronic structure is also highly controllable in these systems, and can potentially be tuned for particular applications.

Graphene can be synthesized in the gas phase using atmospheric plasmas. Gas-phase-synthesized graphene (GSG) is pure and highly ordered. Additionally, GSG contains graphitic nanocrystals that provide the two-dimensional material with significant mechanical stability and enable GSG sheets to resist deformation. GSG is also more environmentally friendly to produce than graphene that is obtained from graphite. These unique features make GSG a promising filler material for fabricating high-strength multifunctional nanocomposites that have a wide range of applications, such as automobiles, aircraft, and wind turbines.

Here we present the results of an investigation into epoxy-matrix nanocomposites reinforced with GSG. We show that as-synthesized GSG effectively disperses in epoxy resins and resists aggregation indefinitely. We report that incorporating a relatively low loading of GSG into epoxy (0.1 wt%) results in nanocomposites that exhibit significant increases in both strength and strain at break. In contrast, epoxy-matrix nanocomposites that were filled with 0.1 wt% graphene nanoplatelets had enhanced strength but diminished strain at break. Scanning electron microscopy images of nanocomposite fracture surfaces will be presented, which indicate much higher matrix reinforcement by GSG relative to graphene nanoplatelets. These results indicate that (1) GSG could overcome the challenges of contemporary graphene-based nanocomposites and (2) unique strengthening mechanisms exist in polymers reinforced with GSG.

A simple and facile method to produce highly concentrated (> 5 mg/ml) and high-quality multi-walled carbon nanotube (MWCNT) dispersions by ordinary benchtop magnetic stirrer is reported here. Exfoliation and debundling of the MWCNTs were possible by stirring in the presence of a protein, driving the adsorption of the protein onto the nanotube surfaces. High concentrations of the debundled nanotubes were obtained (6 mg/ml) after stirring for 5 days, and these are much higher than other reports in the literature. The bioCNT aqueous dispersions are stable up to 6 months, which is important for storage and practical applications. We also fabricated the facile, inexpensive, highly conductive and flexible CNT paper (Bucky paper) by vacuum filtration of the dispersion through an ordinary filter, which composed of self-assembled, randomly oriented, and highly packed CNTs. These metal-free CNT films were flexible and showed a high electrical conductivity of > 1000 S/cm than expected. These biological CNT dispersions used as conductive ink on cellulose paper, which can be used in printed and flexible electronics, bio-electrochemical sensors, bio-supercapacitor electrode applications. Therefore, inexpensive, highly concentrated biological CNT dispersions prepared by a simple method of stirring provides new opportunities for a wider range of CNT applications.

Fluid transport through the inner cores of carbon nanotubes (CNTs) is known to occur at extraordinary rates, exceeding classical predictions by several orders of magnitude, especially for very-small-diameter nanotubes. However, macroscopic, vertically aligned- (VA-) CNT membranes with sub-nanometer pores have not been previously fabricated due to the difficulty in growing aligned forests of such small CNTs. Here, we report the scalable, solution-based fabrication of the first macroscopic membranes with VA-CNTs of sub-nanometer diameter, and the first water-vapor transport measurements for such membranes. Membranes were fabricated from CNT powder using electric-field alignment and electrophoretic concentration of suspended nanotubes, followed by solvent replacement with a liquid prepolymer and UV curing. The single-wall nanotubes are grown in bulk by chemical-vapor deposition with a specialized catalyst, tuned to produce long, 0.8 nm diameter CNTs. After etching to open CNT pores, the membranes filter out dye solution and demonstrate sublinear conductance scaling with salt concentration at low concentrations. These observations indicate that our fabrication process produces defect-free membranes with CNT pores as the primary trans-membrane pathway. Based on KCl-conductance estimates for the total open pore area in the membranes, the concentration-driven water-vapor permeability is enhanced by many orders of magnitude, well above values reported in literature for larger-diameter VA-CNT membranes. Interestingly, the enhancement in concentration-driven water-vapor transport appears to considerably exceed the enhancement present in the pressure-driven flux of dry nitrogen gas in the pores. Additionally, due to the size of the CNT pores, and the charge present on carboxyl groups at the CNT tips, the membranes demonstrate cation selectivity in KCl solution. Coupled with the enhanced flux of liquid water, such membranes could increase the energy efficiency of membrane-based desalination techniques. These findings present new opportunities to scalably fabricate VA-CNT membranes with sub-nanometer pores and study their fundamental transport properties, with possible applications in breathable and protective garments as well as desalination technologies.

Graphene direct growth on sapphire by metal-catalyst-free chemical vapor deposition (CVD) has attracted much attention as the method to avoid the transfer process [1]. The transfer process not only damages but also deteriorates the graphene. Recently, we reported a graphene direct growth on r-plane sapphire using metal-catalyst-free low-pressure CVD where the graphene grows very fast and quite uniformly comparing to that on c-plane sapphire [2]. However, there are many unknown parts in the growth mechanism. In this report, we focused on a-plane sapphire as a substrate, which is often used in horizontally-aligned growth of carbon nanotubes [3]. The growth pressure was systematically changed in metal-catalyst-free low-pressure CVD to reveal the growth mechanism.
Graphene was directly grown on a-plane sapphire using low-pressure CVD without using a metal catalyst. A mixture gas of N₂, H₂, and 3-Hexyne was flown in a reaction chamber at a constant flow rate of 1000 sccm. The growth temperature, H₂, and 3-Hexyne partial pressures were fixed at 1250 ^oC, 500 Pa, and 0.3 Pa while the growth pressure was systematically changed from 5 kPa to 50 kPa.
Raman measurements show that graphene was only grown below 17 kPa and all the grown graphene was smooth and uniform with mono-layer-thick. At the same time, the D/G ratio decreased with decreasing the growth pressure. To investigate the reason, the early stages of growth were studied between 5 kPa and 15 kPa. Consequently, AFM study showed that the density of graphene islands on the sample grown at 5 kPa was approximately 3 times lower than that of the sample grown at 15 kPa. On the contrary, the growth rate of graphene at 5 kPa was much faster than that at 15 kPa. A high growth rate usually means a high supersaturation, and, therefore, a high nucleation rate. In our case, however, the nucleation rate was slow at low growth pressure. This inconsistency suggests the existence of a special mechanism, which controls the nucleation. From the AFM study, the most graphene islands were found at the step edges of the sapphire substrate. At a low growth pressure, the thermal decomposition of the sapphire surface is enhanced and nucleation sites, in other words, surface steps are destroyed at the same time. This brings the difficulty to the graphene nucleation at the step edges even with a higher supersaturation at a low pressure. Consequently, excellent smooth monolayer graphene with a small D/G ratio of less than 0.2 was successfully obtained on a-plane sapphire at 5 kPa with forming larger grains.

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

Reference
[1] M. A. Fanton et al., ACS Nano 5, 8062 (2011).
[2] Y. Ueda et al., Appl. Phys. Lett. 115, 013103 (2019).
[3] N. Ishigami et sl., J. Am. Chem. Soc. 130, 9918 (2008).

Partially reduced graphene oxide (pRGO) has been found to enhance the enzymatic activity of microbial transglutaminase on the cross-linking of gelatin. To determine if this is a more general phenomenon in modification of enzymatic activity, we tested whether it has an effect on thrombin’s ability to clot fibrinogen, an easily quantifiable effect to measure.

Three ml of 10 mg/ml fibrinogen solution in PBS were tested with 8 μ thrombin/ml as a control. Upon adding thrombin, rheometry was used to measure the clotting time as well as the clot modulus. Sharp increases in modulus, shorter clotting times, and stronger clots would indicate enhancement of thrombin, whereas slow increases in modulus, longer clotting time, and weaker clots would indicate inhibition of the enzyme. Test samples included 0.5 ml of 1 mg GO/ml PBS in the fibrinogen mixture, and 0.5 ml of 1 mg pRGO/ml PBS added to the fibrinogen. The pRGO solution produced a clot with an elastic modulus four times greater than the control, and 1.5 times greater than the clot with GO. Different concentrations of pRGO in PBS were then added to fibrinogen solutions and tested. Increasing pRGO concentrations increased the maximum elastic modulus and decreased the clotting time. The elastic moduli were found to be logarithmic, as the logarithmic trendlines had relatively high R² values. Higher concentrations of pRGO had higher coefficients, indicating shorter clotting times. Results suggest further future study of partially reduced graphene oxide as a modifier of enzymatic activity.

Graphene Oxide, an oxidized form of graphene, a carbon allotrope, has many applications including the formation of conductive films for use in flexible electronics and chemical sensors, nanofiltration membranes, and even as a replacement for tin-oxide in batteries. One of the pressing issues with carbon allotropes in general and graphene oxide in particular, however, is that they cannot form freestanding films on their own, instead they rely on a secondary reactant to help aid in the synthesis of such films. To synthesize such nanocomposite substrates, cyclic voltammetry is a very commonly used technique, where an electrolyte containing a monomer to be electro – polymerized is used along with the nanoparticles. Electro-polymerized substrates consisting of GO and Polypyrrole (Ppy), an organic polymer created by polymerizing pyrrole, have drawn much attention owing to their applications in solid state supercapacitors, biosensing, tissue engineering, and artificial muscle studies. It has been proven theoretically and experimentally that Ppy and GO do interact and exhibit improvement in conductivity and thermal stability compared to pure Ppy and GO, but there is still very little information on the interactions at the molecular level between GO and pyrrole monomers especially during the synthesis of such nanocomposites. This work deals with the study of interactions at the interface of GO and pyrrole in order to better understand the evolution of polypyrrole over the surface of graphene oxide during the formation of these films. The system is modeled using Visual Molecular Dynamics (VMD) and all – atom simulations are carried out using Nanoscale Molecular Dynamics (NAMD) at ten different temperatures based on the peak currents and scan – rate through the Randles – Sevcik equation. Each simulation is carried out for 100ns, thereby looking into a total of one microsecond long window of interactions between GO and 50 pyrrole monomers as the polypyrrole film is evolved over the surface of GO. Stability of the GO/ Ppy nanocomposite is quantified through RMSD (Root Mean Square Deviation), conformational energies and center of mass deviations. Interaction energies are calculated to understand the role of non – bonding interactions such as Van der Waals and electrostatics between the monomers and between monomers and GO. It is anticipated that pyrrole monomers form dimers in the bulk of the solution, trimers when near the surface of GO, and tetramers when adsorbed on the surface of the GO. Based on these results, a potential mechanism is proposed on the way monomers interact with the nanoparticles during electro – polymerization and the role of such interactions in synthesizing carbon – based free – standing films.

Single-walled carbon nanotube (SWNT) is ideal materials for thermoelectric conversion because of their high Seebeck coefficient and electrical conductivity. Development of the wearable thermoelectric device using SWNTs is now investigated by taking advantage of their film toughness and flexibility. Up to date, π-shape structure has been proposed for the SWNT thermoelectric sheet. However, this structure needs to attach on a skin vertically and not preferable for the wearable application. Therefore, we proposed a new planar-type structure, in which the sheet can attach on the skin surface and preferable as a wearable device. Since sequential repeating of p-type and n-type properties are necessary for the devices, in this study, we investigated the patterned doping of p-type SWNT sheet into n-type. We found that the deposition of benzimidazole derivatives successfully turned un-masked area into n-type, giving a repeating of p and n-type structure. Detail characterization of the n-doping were carried out by Raman spectroscopy, X-ray photoelectron spectroscopy and Seebeck Coefficient measurements. Devise performance of the thermoelectric sheet will be introduced in the presentation.

Future society will enjoy augmented reality, haptic displays, intelligent cars, and robots in everyday life. Those devices require tactile enhancement which would be improved by high piezoelectric coefficient and strain limit. PbTiO₃ is one of the piezoelectric materials which has high piezoelectric coefficient, low price and wide application but at the expense of low elastic strain limit. In this work, we applied nanoscale truss structure to enhance the elastic stress limit while maintaining the high piezoelectric coefficient of PbTiO₃. Fabricating PbTiO₃ in multi-layered truss structure around 20~30 nm, we expect to improve both piezoelectric coefficient and strain limit up to 300% respectively. We deposited 8 nm PbTiO₃ layer 3 times on the Nickel template and after deposition of multilayers, Nickel template was removed. Each layer of PbTiO₃ was formed by depositing TiO₂ using atomic layered deposition (ALD) and PbO gas reaction in the tube furnace. The crystallinity of each PbTiO₃ layer was confirmed by XRD. We expect multi-layered PbTiO₃ to show 100% higher piezoelectric coefficient than single-layered PbTiO₃ showing better crystallinity. ^[1] After measuring the crystallinity, thickness was measured by TEM. By measuring the deposition thickness according to the distance, we will set thickness of single-layered PbTiO₃ to 8 nm. This will be a significant experiment in that it stacks nano layers of targeted thickness. Also, our approach will provide insight into making piezoelectric materials that have both high piezoelectric coefficient and strain limit, and realize various tactile applications.


^[1] M.Park et al., Appl. Phys, Lett.94, 092901(2009)

With the development of AI, 5G, and autonomous vehicles, higher performance electronic devices are required for more data collection and data processing. In addition, as electronic devices are gradually downsized and thinned, the amount of heat generated per unit area also increases exponentially, so conventional heat dissipation devices (e.g. Heat sink, Heat pipe and Vapor chamber) cannot satisfy these heat generation and electronic device manufacturing conditions. In order to improve the performance of these heat dissipating devices, many studies have improved heat transfer performance through various coating methods such as CVD, PVD, ALD and Spray coating. However, these coating methods are not suitable for heat sinks with complex shapes or heat pipes with a thin tube structure because they require special process conditions such as high temperature or vacuum, and the process cost is large or greatly affected by the shape and size of substrate.

The Layer-by-Layer (LbL) coating method is a solution-based technique which is a self-assembled coating using electrostatic force through the difference in zeta potential between positive and negative solution. Since the LbL coating method is based on a solution-based processing, it can be coated to the complex structures regardless of the size or shape of the substrate. This characteristic enables the direct applications to a heat sink within fin structures or a tubular heat pipe within an inner micro porous structure.

Herein, we present multi-functional LbL PEI/MWCNT-COOH nano-porous coatings based on a solution processing to improve the heat transfer characteristics of heat sinks and heat pipes. To investigate the direct correlation of the nano-porous coatings and the heat transfer characteristics, the LbL PEI/MWCNT coatings were prepared as bare, 10-bi, 20-bi, and 30-bi layers. The change in thickness and surface morphologies of LbL coatings was precisely analyzed through FIB and SEM image analysis, while the surface area and pore size distribution according to the number of LbL coatings was examined using BET surface area analysis. Furthermore, the wettability of the PEI/MWCNT coating was measured to confirm the capillary rise, which is one of the important factors to determine the heat transfer performances of the devices.

Through the natural convection test of the LbL coated heat sinks, it was confirmed that the enhanced thermal performances could be obtained due to increasing the porosity and surface area of the LbL coating. As the porosity and surface area was optimized in the number of coatings, the overall thermal performances including heat transfer coefficients were significantly improved up to 11% for 30 bi-layers coated heat sink due to the increase in the surface area, in comparison with that of the bare heat sink. Furthermore, the LbL functional coating layers could highly improve the heat transfer characteristics of the heat pipes, as well. Because a nano-micro sized bi-porous structure appeared in the microporous-sintered heat pipe with the LbL coating layers, such bi-porous structure could strengthen capillary wicking, fluid transportation, and superhydrophilicity as well as increasing surface area, thereby improving heat transfer efficiency and thermal resistance up to 14.3% in a 10 bi-layers coated heat pipe.

The PEI/MWCNT LbL nano-porous coating, which was used for the heat dissipation devices (i.e. heat sink and heat pipe) could show the enhanced heat transfer characteristics, while the fabricate process was based on the only simple and low-cost LbL coating technology. This multi-functional and thin PEI/MWCNT LbL nano-porous coating not only improved the performance of the conventional heat dissipation device, but also is expected the design trend of miniaturization, thinning, and lightweight electronic equipment.

We report the deposition and alignment of semiconducting carbon nanotubes with the alternating electric field-directed dielectrophoresis (DEP) method and the fabrication of carbon nanotube-based electronic devices with the DEP-aligned semiconducting carbon nanotubes (CNTs). Semiconducting carbon nanotubes, which were dispersed ultrasonically in the n-methyl pyrrolidone (NMP) solution, were deposited and aligned onto a pair of gold electrodes using the dielectrophoresis method. The excellent alignment of carbon nanotubes was achieved by optimizing the AC voltage, frequency, and deposition time of the applied AC signal. The DEP-aligned tubes were further fabricated into carbon nanotube field-transistors (CNTFETs) and CNTFET-based electronic devices such as CNT-based inverters using the microfabrication techniques. Plasma-enhanced atomic layer deposition (PE-ALD) was used to grow hafnium dioxide (HfO₂₎ as the high-k gate oxide in the fabrication of CNTFETs. 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. About 70% yield was obtained from the semiconducting carbon nanotube-based CNTFETs, and the fabricated CNTFETs and CNT-based inverters demonstrated excellent current (I) – voltage (V) curves and transfer characteristics.

Inertial sensors are devices that can monitor inertial movements like linear acceleration and angular motions, in various applications such as industrial and human monitoring. For wearable and portable applications, inertial sensors are better to be self-powered and miniaturized. Here, we developed a self-powered inertial sensor with various applications having high accuracy based on carbon nanotube (CNT) yarn. Our inertial sensor can sense and monitor inertial movements without any external power by harvesting the mechanical energy to electric energy by the coiled CNT yarn. For applications, the sensor can monitor practical kinds of inertial movements, such as impact energy, vibrations, tilting, and body motions such as walking, running, jump and squatting motions. These results suggest that the self-powered inertial sensor shows the advantages of portable and wearable application in industrial and human motion monitoring system.
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Vanadium oxide materials are renowned for their catalytic properties, super-capacitance, chemical sensing, and high energy density cathodic properties. A two-step synthesis method was applied to obtain 2D structures of vanadium oxide (V₂O₅) or vanadate (V_2-xO_5-x) nanosheets from bulk V₂O₅ where the first step involved the formation of vanadate nanoscrolls, 1D structures, that resulted from the dissociation of layered vanadium oxide. In the second step, the nanoscrolls were unfurled to obtain nanosheets, 2D materials. This latter step can be performed using a wet chemical process or annealing treatment. During the wet chemical process, vanadate nanoscrolls turn into thin-layered vanadate nanosheets, and with the annealing process, thin-layered vanadium oxide nanosheets are produced. The formation of these different types of nanosheets was confirmed by X-ray diffraction. Nanosheets obtained from the wet process showed the presence of organic groups that were detected using FTIR and Raman spectroscopy. Both the vanadate and vanadium oxide nanosheets were single or multilayered but only the latter one possesses irregular hexagonal shape which was confirmed through TEM.

As the novel “bottom-up” strategy for fabricating nanomaterials, molecular self-assembly has attracted considerable attention worldwide. On one hand, two-dimensional (2D) materials such as graphite and molybdenum disulfide (MoS₂) have been demonstrated as the platform for this self-assembly due to their unique electrical, optical properties, and atomically flat surfaces, etc. [1,2]. On the other hand, amphiphilic peptides with both of the hydrophobic and hydrophilic nature also have already been used as ideal building blocks for forming various sophisticated self-assembling materials with certain applications. Therefore, in order to functionalize the 2D material surface by peptides self-assembly, it is necessary for a deliberate understanding of the interaction between biomolecules and 2D substrate materials [3].
Molecular dynamics (MD) simulation provides insight into the molecular-scale structure detail of interface. Several works have been done on solid surface to understand the role of peptides, like on Au (111) for self-assembly [4] or on calcite for biomineralization [5]. More recently, peptides on graphene [6] or MoS₂ [7] have been studied because of the atomically flat surface and some progress in experiments exhibiting the molecular resolution morphology. From these, aromatic amino and charged amino acids are considered to have a meaningful interaction with those surfaces. Although the peptide-peptide interaction is also important for surface self-assembly of peptides, the understanding for both interpeptides and peptide-surface interactions are still limited.
In this work, we aim to utilize computational approaches to understand the molecular mechanism. For this purpose, we started with a tetrapeptide consisting of aromatic and charged amino acids, where these amino acids may play a role for the self-assembly. We performed the molecular dynamics simulation (MD) starting with single tetrapeptide on graphene surface. From this calculation, we obtained the most stable tetrapeptide structure on graphene surface. Analyses of center-of-mass distance between peptide and graphene surface, angle change of aromatic rings, and free energy distribution revealed that the balance between interpeptide and peptide-surface is a key to have a well assembled peptides on surface. Furthermore, information about binding process for tetrapeptide on 2D surface was also obtained. This work can be a foundation for building a conformation-property relation of amphiphilic tetrapeptide self-assembly on 2D material surfaces.
Reference:
[1] Li P, Sakuma K, Tsuchiya S, et al. ACS applied materials & interfaces, 2019.
[2] Chen J, Zhu E, Liu J, et al. Science, 2018, 362(6419): 1135-1139.
[3] Qiu F, Chen Y, Tang C, et al. International journal of nanomedicine, 2018, 13: 5003.
[4] Braun, R, Sarikaya, M, Schulten, K, Journal of Biomaterials Science, Polymer Edition, 2002, 12, 747-757.
[5] Mingjun Yand, P. Mark Rodger, John H. Harding & S.L.S, Molecular Simulation, 2009, 35:7, 547-553.
[6] Hughes, Z E; Walsh, T R, Journal of Materials Chemistry B, 2015, 3, 3211−3221.
[7] Huang C, Libo L, Tao Z, et al, J. Phys. Chem. C 2018, 122, 4, 2070–2080.

Single-walled carbon nanotubes (SWNTs) have unique near-infrared (NIR) absorption and NIR photoemission that are attractive for in vivo biological applications such as photothermal cancer treatment and imaging. Therefore, a smart functionalization strategy for SWNTs to create biocompatible surfaces and introduce various ligands to target cancer cells without losing their unique optical properties of the SWNTs is strongly required. We developed novel coating technique of SWNTs inspired by emulsion polymerization method, in which the micelle dispersion of SWNT was used for free radical polymerization. In the dispersion, polymerization takes place in the surfactant micelle having SWNT in the core. Thus the SWNTs were coated by polymer layer. When the cross-linker was added, the SWNTs were coated by gel layer, offering the highly stable coating of SWNT
We have revealed the requirement for the formation of the thin cross-linked polymer-wrapped SWNTs, in which the use of monomers that can undergo polymerization inside the micelles was important. In our study, such hybrids were formed when using various monomers in aqueous SDS dispersions of the SWNTs in the presence of APS and BIS as the initiator and cross-linker, respectively in high yeild (>75%) except acryl amide and hydroxymethyl methacrylate. The present study provides useful insight into preparing many polymer-SWNT hybrids with designed functions due to the wide availability of the monomers.

Nanocarbon-metal composites are sought after for their excellent mechanical, electrical and thermal properties. Electrocharging-assisted processing of a novel class of materials, called “covetics,” presents a practical option for macroscale production of nanocarbon-metal composites. This process incorporates carbon on the order of several weight percent in metals such as Al and Cu where carbon solubility is in the low ppm range. Increased tensile strength and electrical conductivity have been measured in Al covetics; however, there is limited understanding of the electrocharging-assisted process and subsequently high variability in measured properties among trials. It has been found that under the influence of a high direct current applied to the molten metal, the activated carbon precursor is converted to sp² graphitic carbon with increased crystallite size, as measured by the Tuinstra-Koenig relation for Raman spectra. Electrical conductivity is also enhanced in areas that show increased graphitic carbon crystallite size. A series of experiments varying applied current have been carried out to understand the effect of current density on carbon crystallization rate and size of reaction volume within the Al-1350 melt where carbon crystallization occurs. Local electromechanical behavior is measured by nanoindentation and AFM to gain insight into the structure-property relationship at the nanoscale, which can be used to further inform optimization of the electrocharging-assisted process.

Funded by DOE-EERE grant DE-EE0008313. Sponsored by the Army Research Laboratory under Cooperative Agreement W911NF-19-2-0291.

There is growing interest in using 2D graphene-related reinforcements to toughen brittle ceramics in nanocomposites. However, there is a lack of fundamental understanding of the toughening mechanisms and microstructural effects in such nanocomposites. To address this paucity, fully-dense nanocomposites of aluminum oxide (Al₂O₃) matrix and reduced graphene-oxide (rGO) reinforcements (~5 vol%) of different average-thicknesses and orientations are fabricated and characterized. The interactions between stably propagating cracks and rGO in the Al₂O₃/rGO nanocomposites are observed in situ inside a scanning electron microscope (SEM). Toughening by pullout of thick rGO in the crack-tip wake in the cross-section orientation is found to be the most effective, which is consistent with the highest fracture toughness (K_IC ~6.7 MPa.m^0.5) measured in those Al₂O₃/rGO nanocomposites. Interestingly, while achieving stable crack growth for flat punch compression of notched samples, we found that upon unloading and reloading, the intact rGO crack-bridges appear to crinkle and uncrinkle without a remnant crease, respectively, which is a unique deformation property of multi-layer graphene-like materials. Information extracted accompanied by the Raman spectroscopy studies has permitted to have a deeper understanding of the fatigue resistance mechanisms in this novel material. This is unlike conventional ceramic composites toughened by fibers or whiskers which have poor cyclic fatigue resistance due to the degradation of the crack-wake bridging and pointing to a possible new cyclic-fatigue resistance mechanism in the nanocomposites. The results from this study have implications for the creation of high-toughness, fatigue-resistant, and wear-resistant graphene-reinforced ceramic nanocomposites of the future.

Onsager and Samara have shown that electrical image charge forces acting on ions dissolved in water can explain the observed increase of the surface tension due to the presence of dissolved ions. Electrical image charge forces at the interface of a salt solution and air are repulsive, but at the interface between the salt solution and a dielectric of higher dielectric constant than that of the solution or a metal, in contrast, the force is attractive. It has also recently been shown that electrical image forces may play a role in the attraction of ions to the electrodes in capacitive desalination, and to play an important role in the freezing of a confined room temperature ionic liquid. Here, the effect of electrical image forces on the distribution of salt ions in a solution that is in contact with a metallic or dielectric surface is considered. It is shown that in the case of either a metallic or dielectric surface, the salt ion concentration near the surface can be very large, raising the possibility that this could result in precipitation of the salt. In fact, solidification of ionic liquids near a metallic surface with which they are in contact has been observed. Concentration of ions near a metallic surface could be used to desalinate salt water by pushing the salt water between an array of parallel plates of a conducting material. Graphene would be an excellent coating for these plates because the friction between flowing water and graphene is known to be extremely small. In order to support our prediction of a high ionic concentration near metallic and dielectric surfaces, we have performed a variational calculation of the grand canonical partition function to lowest order in the ion density, which is the Debye-Huckel approximation. This calculation supports our conclusion. Our calculation also confirms the concentration dependence of the surface tension found by Onsager and Samarasa in the small salt concentration limit.

Graphene, a representative two-dimensional material, has excellent electronic properties due to its high mobility and specific surface area. Biosensors based on graphene field-effect transistor (GFET) are expected to be applied in various fields such as medical diagnosis, environmental monitoring, and security management. A number of studies on biosensors using GFET have been carried out so far. The surface functionalization with probe molecules is crucial, which gives a high affinity to the target molecule. In this process, covalent bonding and π-π interaction have been used to immobilize probe molecules to the surface. However, there are two disadvantages with these detection methods. Firstly, chemical modifications may degrade inherent electronic properties of graphene. Secondly, random adsorption of probe molecules on the surface may result in loss of the probe activity. These lead to a decrease in sensitivity as a sensor.
So far, there have been various demonstration of GFET biosensors reported. The target of the biosensors have been living cells, virus, DNA, and proteins. There is a still challenge here to detect relatively small molecules. These small molecules have low molecular weight and generally do not have a polarization. GFET-based biosensors have a drawback for these small molecules, because the detection mechanism depends on the Coulombic interaction between trapped molecules and graphene. In addition, most of the small molecules are volatile and insoluble. Therefore, in aqueous solutions, it is very difficult to detect volatile molecules dissolved in small amounts. This is also one of the challenges for biosensors.
To solve these problems, we suggest an alternative surface modification method using peptide self-assembly. Peptides are known to recognize crystalline structures of inorganic material surfaces and form uniform structures through interactions among molecules [1]. These peptides are physically adsorbed to the surface. Thus, the surface can be modified without losing their intrinsic electronic properties. These self-assembly of peptides has been demonstrated on gold, boron nitride (BN), transition metal chalcogenides, and graphene in previous studies. The self-assembly of peptides have potential as a scaffold domain for biosensors [2]. In this study, we aimed to develop a new technique to detect an odor molecule, which is relatively small and volatile. For this sake, we utilized rationally designed peptides as a molecular scaffold [3] and probe peptides on graphene surface. Then, we performed odor sensing with limonene, a representative molecule for the smell of lemons. We successfully detected limonene with high sensitivity. We also found that the sensitivity to limonene was altered by the amino acid sequence of the probe domain.
This work was supported by the Cabinet Office (CAO), Cross-ministerial Strategic Innovation Promotion Program (SIP), “An intelligent knowledge processing infrastructure, integrating physical and virtual domains” (funding agency: NEDO).

[1] Y. Hayamizu, C. So, S. Dag et al.; Scientific Reports, 2016, 6, 1-9
[2] D. Khatayevich, T. Page, C. Gresswell et al.; Small, 2014, 10, 8, 1505-1513
[3] P. Li, K. Sakuma, S. Tsuchiya et al. ACS Appl. Mater. Interfaces, 2019, 11, 20670−20677

We have clarified the tensile properties and electron transport capacity properties of macro-sized continuous crystal few-walled CNT forests, which have a height of 14 cm. The present CNT is the highest forest ever reported. The CNT was grown by a CVD method using a Fe-Gd catalyst on Al oxide support [1]. The crystal structures of CNT were evaluated by SEM, TEM, and Raman measurements. Then, the bundle taken out from the CNT forest was converted to a cylindrical structure to define a cross-sectional area and weight density. The cylindrical specimens were tailored by passing through a pinhole with a diameter of 30-100 μm. The reshaped CNT bundle enables to measure tensile tests and electrical measurements by the conventional methods for macroscale specimen. From tensile measurements, it was found that the nominal tensile strength and Young's modulus of the individual CNT were 0.59 GPa and 48 GPa, respectively. This nominal tensile property was obtained by using the entire cross-sectional area, including the inner hole space of the tubular structure for calculation. These results are comparable with reported values, which were measured on various types of CNT by the microscopic methods, and it is lower than theoretical values. The difference between the theoretical and the experimental results is because the present extremely long bundle includes a large number of crystal defects. Also, bundling of millions of CNTs induces further weakening of tensile properties compared to those of micro-sized single CNTs. As for the electrical properties, conductivity and the current-carrying capacity, ampacity, were 140 S/cm and 6700 A/cm², respectively. These properties were improved significantly by heat treatment at 2800°C in Ar, up to 340 S/cm and 8800 A/cm², respectively. These results correspond to the specific conductivity of 1560 S*cm²/g and ampacity per CNT of 5.2×10⁴ A/cm². The ampacity of our CNT was as high as that of commercially available Cu wire (5.8×10⁴ A/cm²).
[1] Hisashi Sugime, Toshihiro Sato, Rei Nakagawa, Cinzia Cepek, and Suguru Noda, ACS Nano 13, 13208-13216, 2019.

Aviation turbine fuel, Jet A-1 contains trace metals that catalyze carbonaceous nanostructures formation and their transformation to carbon spheres in the liquid phase at low temperature (190 ⁰C) by flask tests. Thermal stressing of Jet A-1 produced nanospheres, solid and hollow carbon spheres in this work, which is consistent and continuation of a previous study [1]. Focus of the current study is to identify the trace metallic compounds that catalyze the growth of spherical nanoparticles and carbon spheres in thermally stressed Jet A-1. In the previous study [1], however, the formation of carbon spheres by self-assembly was observed, and their characterization was conducted. Heteroatoms and trace metals are precursors to the deposit formation in the thermally stressed jet fuel [2, 3]. The presence of trace metals and heteroatoms in the Jet A-1 deposits is validated by transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDS), scanning transmission electron microscopy (STEM) and high-angle annular dark-field (HAADF), and high-resolution transmission electron microscopic (HRTEM) micrographs. Heteroatomic species were also recorded by Fourier transform infrared (FTIR) spectroscopy. Trace metal copper oxide nanocrystals (CuO and Cu₂O) were identified by HRTEM and selected area electron diffraction (SAED) analysis. TEM EDS spectra provided the ratio of Cu and O; Cu to O ratio approximately 1:1 and 2:1. Indexing of the polycrystalline SAED pattern generated the d-values corresponding with copper oxides nanoparticles. Copper oxides nanocrystals as constituents of spherical particles were confirmed by comparing the measured d-values and calculated Miller indices (h k l) for copper oxides with i) ICSD database and, ii) simulated diffraction pattern of the Cu₂O, CuO by Crystal Maker software. Furthermore, structure elucidation of Fe and S nanocrystals is in progress and can suggest the effect of trace metal catalysts on the spherical nanoparticles, and carbon spheres formation in the thermally stressed kerosene type fuel.

Keywords: Jet A-1, copper oxide, trace metals, carbon spheres, nanostructures

References

1. P. Sharma et al, Formation of hollow and solid carbon spheres in thermally stressed jet fuel in the low temperature autoxidation regime, Chem. Engg. Sci, 206(2009), 335-347.

2. Robert N. Hazlett, Thermal Oxidative Stability of Aviation Turbine Fuels, ASTM, 1991.

3. P. Sharma, Spectroscopic analysis of Jet A-1 heteroatomic components, Chem. Engg. Sci, 207(2009), 588-599.

The carbon nanotube field-effect transistor (CNT FET) has been intensively studied due to the high mobility and large current carrying capacity, thus considered as a promising material for nano-scale electronics. For the commercialization of the CNT FETs, the accurate and reliable model is an essential requirement. Especially, transport characteristics of the CNT FETs at high temperature (>300K) is crucially important since the CNT FETs typically operate at elevated temperature. We now report on an improved compact model of the CNT FET. The model is based on the unified charge control model (UCCM) suitable for implementation in standard computer-aided design (CAD) environment such as SPICE. The model accurately describes the current-voltage characteristics for all operation regimes over a wide range of temperatures from 295 to 523K. The model accounts for the temperature and bias effects on the threshold voltage and mobility as the key metrics impacting the CNT FET's performance. It reproduces the mobility, subthreshold swing, on- and off-state current, and threshold voltage behavior as functions of the operating temperature. The model is validated by comparison with the experimental data for the CNT FET reported earlier. The model applications include the device design, characterization, large scale simulation, and parameter extraction of the CNT-based devices and integrated circuits.

Laser shock peening is performed on chromium based electrochemical coatings consisting of 3 mol% yttria stabilized zirconia nanoparticles (YSZ) and carbon nanotubes (CNT) as reinforcements, deposited on steel substrate as a suitable strategy to further enhance mechanical and tribological properties of protective coatings. Coated Cr has shown an increased hardness after laser peening from ∼8 GPa to ∼9.4 GPa, whereas, upto 26 GPa hardness is obtained for Cr-YSZ-CNT coating. Increased hardness might be accredited to high compressive stresses, ranging up to ∼1757 MPa, induced as a result of laser peening. Synergistically reinforced with YSZ and CNT after laser peening treatment, minimum wear rate of ∼1.8×10⁻⁵ mm³/Nm by fretting wear test is recorded in the Cr matrix, which is concomitant with maximum dislocation density of ∼3.0×10¹⁶ m⁻². An overall improvement in mechanical and tribological properties i.e. low wear constant of the order of 10⁻⁶ is achieved, out of which Cr-YSZ-CNT outperformed the other coating systems. Addition of YSZ strengthens the Cr matrix, whereas, multi-functionality of CNT provides with lubrication along with matrix strengthening as well as bridging effect to crack propagation. Therefore, synergistic effect of two reinforcements (YSZ, CNT) in Cr matrix combined with the laser peening treatment lead to superior properties of the coating (Cr-YSZ-CNT) capable enough of limiting the problems of wear and erosion.

Graphene is suitable for an active layer for biosensors with high-sensitivity because of their fascinating electrical properties with atomically-flat surface and high specific surface area. Biomolecular immobilization on the active layer of biosensing devices is of vital importance for the functionality, such as sensing with biomolecular probes and protecting from unnecessary unspecific adsorption of biomolecules. However, the immobilization by chemical bonding will introduce atomic defects for graphene, which influences its intrinsic properties to some extent. Self-assembled peptide can be a good candidate. Specific peptides spontaneously form ordered structures through non-covalent intermolecular interactions on the surface of graphene without losing the intrinsic electrical properties of the materials.[1][2][3] On the other hand, non-specific adsorption of biomolecule causes a background noise and decrease the sensing ability of a bio-probe. Therefore, the suppression of nonspecific adsorption is an important issue for the realization of high-performance biosensors. To solve these problems, in this research, we designed new self-assembled peptides and evaluated their performance, aiming at construction of surfaces with the anti-fouling property. The designed peptides consisted of three main domains. (1) antifouling domain: hydrophilic and zwitterionic, which is effective in reducing protein non-specific adsorption. The hydrophilic groups are known to form a hydration layer and create a physical energy barrier that prevents adsorption. (2) Peptide-to-peptide interaction domain: inspired by fibroin, a protein of silk thread. The repetitive sequences of glycine (G) and alanine (A) are introduced. Here we expect the formation of a strong and stable peptide monolayer derived from the β-sheet structure.[2] (3) Anchoring domain: electrons in tyrosine are expected to help to have a stacking of the aromatic ring with the surface of two-dimensional materials. The aqueous solution was placed on the surface of graphite to form a self-assembled film of peptides. The surface structure of these samples was characterized using atomic force microscopy (AFM). We found that peptides had a tendency coverage with increasing concentration. The peptide structure had a six-fold symmetry, which is same as one of underlying graphene lattice. The hydrophilic properties of the peptide film were characterized using contact angle measurements. Furthermore, the antifouling performance was evaluated by AFM and graphene field effect transistors (GFETs). It showed that the adsorption of proteins was greatly inhibited. The peptide offer to be a new molecular scaffold for sensitive graphene biosensors.


Reference
[1] Hayamizu, Yuhei, et al. "Bioelectronic interfaces by spontaneously organized peptides on 2D atomic single layer materials." Scientific reports 6 (2016): 33778.
[2] Li, Peiying, et al. "Fibroin-like peptides self-assembling on two-dimensional materials as a molecular scaffold for potential biosensing." ACS applied materials & interfaces 11.23 (2019): 20670-20677.
[3] Sun, Linhao, et al. "Water stability of self-assembled peptide nanostructures for sequential formation of two-dimensional interstitial patterns on layered materials." RSC advances 6.99 (2016): 96889-96897.

Proton Exchange Membrane Fuel Cells (PEMFC) are considered to be one of the most promising clean energy sources to mitigate the global crisis of climate change and air pollution. However, its dependence on expensive catalyst materials with low durability, such as platinum, prevent this technology from being widely commercialized. In this study, we present the application of a metal-free starch-derived graphene quantum dot (GQD) supported on highly porous carbon aerogel (GQD/CA) in PEMFC to overcome these technical barriers. Structural, morphological, and crystalline features of GQDs and GQD/CA are analyzed using HRTEM, TEM, AFM, and XRD. Further electrochemical characteristics are investigated using cyclic voltammetry (CV), CO-stripping, ORR polarization, and fuel cell testing. Additionally, the durability of the catalyst is measured using the DOE2020 accelerated stress test (AST). The TEM imaging shows the small size and uniformity of GQDs, which allows for an even distribution of GQDs onto the support and a higher electrochemical surface area (ECSA). The presence of functional groups on GQD is shown to improve ORR performance by up to 10 times compared to platinum. In addition, the structural integrity of both GQD and CA create a synergistic effect to prevent the agglomeration of particles during AST. As a result, compared to a commercial standard catalyst, platinum supported on carbon black (Pt/CB), GQD/CA shows significantly higher electrocatalytic activity, with up to 220% increase in ECSA and 1432% increase in peak power density. After 30,000 cycles of AST testing, GQD/CA is shown to retain 92.9% of its ECSA, 97.1 % of its specific activity, and 98.4% of its mass activity. Thus, GQD/CA is demonstrated to be a highly efficient, durable, and economical catalyst for PEMFCs to mitigate the ever-present effects of climate change and air pollution.

A wealth of studies utilizing graphene to sense biomolecules (such as glucose, DNA, Concanavalin A) across different sensing modalities (such as surface plasmon resonance, redox, field effect transistor) have been published due to graphene’s unique properties including high surface area and conductivity. However, in any sensor device where graphene interacts with a biofluid, the graphene must be supported by some underlying substrate. Moreover, previous studies indicate that the substrate can influence graphene's properties, where substrate hydrophilicity can affect graphene's water contact angle and substrate polarity can affect the success of epitaxial growth through a graphene layer. Despite this, little to no work has been completed describing how the substrate support effects the graphene-biological solution interaction.

In this study, ex situ protein adsorption is measured via ellipsometry and X-ray photoelectron spectroscopy (XPS) of model small (Lysozyme), medium (Bovine Serum Albumin, BSA), and large (Fibrinogen) proteins on substrates with a variety of hydrophobicity and surface polarity with and without a transferred graphene monolayer. Additionally, we investigate the in situ adhesion of lysozyme on Si and Au substrates with and without transferred graphene via quartz crystal microbalance with dissipation (QCM-D) to monitor kinetic differences in attachment. Fully coalesced graphene was synthesized via Chemical Vapor Deposition and transferred onto various substrates using a wet transfer process and PMMA scaffold.

Ex-situ ellipsometry and XPS results reveal that the impact of the substrate on protein attachment to graphene depends on the protein studied. The largest model protein, Fibrinogen, shows a similar level of attachment across all 4 substrates regardless of the presence of graphene. Lysozyme, the smallest model protein, shows a difference in adsorption only when a graphene monolayer is added to non-polar substrates. The adsorption of BSA, the intermediate size protein, is influenced strongly by substrate hydrophilicity, where less adsorption is observed on more hydrophilic substrates with or without the presence of graphene. Overall, a more hydrophobic substrate leads to a larger amount of adsorption to graphene.

In-situ QCM-D results show that not only the equilibrium attachment, but also the kinetics of interaction, can be affected by the substrate. Modeling the attachment of lysozyme to graphene on Au and Si substrates indicates that the appropriate kinetic model may be determined by the substrate even in cases where differences in absolute adsorption are observed, further indicating that support substrates have a significant effect on protein adsorption behavior to graphene.

This work indicates that the substrate of a graphene-based biosensor is an important but currently overlooked parameter when understanding and optimizing the performance of the device. The ex-situ ellipsometry and XPS analysis of protein attachment indicates that the substrate can have a profound impact on protein-graphene interactions, to the extent that twice the BSA attachment to graphene is observed when graphene is supported by TaN rather than Si. The level of non-selective protein adsorption on graphene can be independently engineered through modifying the support substrate without directly modifying the graphene itself.

Carbon nanotubes have been an important subject of many recent studies owing to their possible potential applications in nano-scale technologies. Carbon nanotubes can be described as fiber like structures consisting of concentric graphite sheets nested along their long axis and extending to several micrometers. Single-walled carbon nanotubes (SWNTs) can be either metallic or semiconductors depending on the diameter and chirality . All the synthetic methods can be roughly categorized into three groups: the carbon arc-discharge method, laser vaporization of a graphite electrode and chemical methods . In this work, carbon nanotubes were obtained by chemical vapor deposition using high-density plasma processes. Structural studies of carbon nanotubes have relied heavily on Raman spectroscopy. Raman spectroscopy is an analytical technique largely used for characterization of different carbon based materials, either graphite-like or diamond-like. The great versatility of carbon materials rises from the strong dependence of their physical properties on the ratio of sp² (graphite-like) to sp³ (diamond-like bonds). Raman spectroscopy of carbon nanotubes has attracted a lot of attention in recent years, both theoretically and experimentally. Theoretically, it is possible to predict morphological characteristics such as the diameter of the tubes or their conductance properties, especially of single wall carbon nanotubes. Experimentally, it is a powerful method for determining the degree of structural ordering or presence of contaminants [3]. In the Raman spectra of graphite and SWCNTs, there are many features that can be identified with specific phonon modes and with specific Raman scattering processes that contribute to each feature. The Raman spectra of SWCNTs can be provide us much information about the exceptional 1D properties of carbon materials, such as their phonon structure and their electronic structure, as well as information about sample imperfections (defects). Raman spectra provide much general information about the structure and properties of SWNTs. The Radial Breathing Mode (RBM) is a unique phonon mode, appearing only in carbon nanotubes and its observation in the Raman spectrum provides direct evidence that a sample contains SWNTs. The RBM is a bond-stretching out-of-plane phonon mode for which all the carbon atoms move coherently in the radial direction, and whose frequency w_RBM is about 100-500 cm^-1 .
The results obtained with the Raman spectroscopy have been compared with the results obtained by Fourier Transformed Infrared (FTIR) spectroscopy, and by Scanning Electronic Microscopy (SEM) . The results obtained by these technical analyzes confirm the deposition of single-walled carbon nantotubes with metallic features by high-density plasma chemical vapor deposition.
The results obtained in this work, show the possibility to obtain higher aligned single-walled carbon nanotubes deposited at room temperature by HDPCVD. In this way, it was necessary the increase of the surface energy, that promotes the nano-structuration of the carbon materials, using diamond powder as a seed. It was observed the presence of carbon nanotubes and other kinds of nano-structures of carbon. The results obtained by SEM, Raman spectroscopy and Fourier Transformed Infrared spectroscopy FTIR, comproved the carbon nanotubes bundles and “islands” of amorphous carbon materials and, due the different of surface energy promoted by the precursor.

Electrically-doped graphene supports highly-confined and actively-tunable plasmons that exhibit lower losses than their conventional noble metal counterparts, positioning the atomically-thin carbon layer as an ideal active ingredient in nanophotonic devices. These appealing properties are maintained in nanostructured graphene, which is emerging as a promising candidate for the excitation and guiding of propagating plasmons in future optoelectronic circuitry. Here we employ realistic quantum-mechanical simulations to describe the nonlocal optical response associated with highly-confined propagating plasmons in graphene nanoribbons, accounting for quantum finite-size and edge-termination effects in their electronic band structure. In addition to strong nonlocal effects manifesting in the linear dynamics of plasmons moving in the direction of transverse symmetry, we observe a stronger dependence on quantum finite-size effects in the nonlinear optical response, which involves additional transitions among the quantized electronic Bloch states. We further explore the breaking of inversion symmetry that occurs for optical excitation with large in-plane optical momenta along the transverse direction of the ribbon and reveal that even-ordered nonlinear optical processes such as a second-harmonic generation can occur with remarkably-high efficiency when enhanced by plasmonic resonances. These findings suggest possibilities to exploit the active tunability of graphene to engineer interactions among individual quantized propagating plasmons supported by 1-D nanoribbons.

Climate change is a major threat to the future of our planet and its inhabitants, and there is no doubt that human activities have been the dominant contributor. Scientists can play an important role in mitigating these contributing factors by utilising green approaches in manufacturing and developing eco-friendly materials in different fields. This work presents how our interdisciplinary collaborative research team, consisting of contemporary artists, a materials scientist, and a climate scientist, promote environmental sustainability through the development of ‘green‘ materials and techniques. The aim of the project is to develop a graphene-based ink through a green chemistry/engineering approach and use the ink to create conductive screen-printed e-texitle artworks that communicate climate science. Graphene is a unique two-dimensional carbon structure with excellent electrical, thermal and mechanical properties that make it ideal candidate for a variety of applications1,2. However, converting graphene to a processable material involves hazardous chemical reactions using toxic materials3. We developed a graphene-based ink without using any hazardous or toxic chemicals through a facile mechanical exfoliation method. The viscosity of the ink is easily tunable owing to its thermos-sensitive nature, which makes it a suitable material for screen-printing. The ink is used to screen-print electrically conductive patterns for the e-textile art works. The results of the phase 1 of the project were exhibited at the Museum of Applied Arts and Science in Sydney and attracted over 26,000 visitors. Preliminary experiments demonstrated that this material is a suitable candidate for developing sustainable sewable smart electronics.

In this work, we have obtained nano-structured carbon films using ceramic powder (alumina) as seed and pure methane plasmas. The nano-structured carbon films were obtained using a high density plasma chemical vapour deposition system. The present study demonstrates the creation of hydrophobic surface using the nano-scale roughness inherent in high-aligned carbon nanotubes forest, when we used alumina as precursor material. The hydrophobic properties of the nano-structured carbon films were analyzed by Atomic Force Microscope (AFM), Scanning Electron Microscope (SEM) and Contact Angle Measurements (drop shape method), and the structural properties of the nano-films were analyzed by Far-FTIR.
The high-density plasma chemical vapour deposition (HDPCVD) system uses a new conception on plasma generation: a planar coil coupled in a RF system and an electrostatic shield for plasma densification. In this mode, are obtained high-density plasmas and for the ion acceleration we have used another RF system on planar configuration. The substrates used to deposit the films were 75 mm diameter silicon wafers, 380 µm thick and orientation (100). They were submitted to a Piranha clean, followed by a diluted HF dip, before the modification of the surface. The alumina ceramic powder presence promotes the increase of the surface energy of the silicon wafers. In this case, nano-structures are formed. Before the films deposition, alumina ceramic powder was deposited on the silicon wafers by spinner (1000 rpm, 30 sec.). The alumina powder dispersion was made in acid solution. We have used different final deposition times (30 min, 1h, 2h, 3h, 4h and 5h). After preparation of the sample, the DLC films were deposited. The parameters of the DLC films depositions were: 15 mTorr, 250 W (coil power, RF, 13.56 MHz, remote plasma), 40 sccm (methane).
The hydrophobic properties of the nano-structured carbon films were analyzed by Atomic Force Microscope (AFM), Scanning Electron Microscope (SEM) and Contact Angle Measurements (drop shape method), and the structural properties of the nano-films were analyzed by Far-FTIR. High-density plasma is quite for the growth of good quality nano-structured carbon films. But the properties of these films are largely dependent on the deposition conditions. The roughness of the nano-structured carbon films is important, in this situation, because it is affected by surface topography and the hydrophobic properties of these nano-materials.
The surface morphologies of the nano-structured carbon films obtained with alumina powder varied with the final time of deposition process. When the final time is increased, the atoms fill the holes and are accumulated around the islands (formed by the filled holes) and the roughness decreases. This effect promotes the reduction of the surface energy and the hydrophobicity of these films increases too. For longer deposition time, the atoms cover every nano-islands and the spaces between one island and another, forming a continuous film (for deposition time of 4 hours, the roughness was 40 nm). In this way, we noticed that the contact angle measurements showed that nano-structured carbon films obtained using alumina as precursor materials obtained for longer deposition time, showed more super hydrophobicity effect

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 SWCNTs 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 0.8 and 1.1 nm. 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.

Electrochemical exfoliation has emerged as a green, effective and scalable route to mass production of graphene.[1] The use of reductive cathodic exfoliation of graphite, offers a direct production of high quality and low defect graphene.[2] However, cathodic exfoliation protocols reported to date use organic solvents in which often requires extended intercalation time, and post-treatment to further exfoliate the intercalated graphene layers.[3] In contrast, the employment of environmentally friendly aqueous-based electrolytes, coupling with a shorter exfoliation period would be attractive features of any new protocol. Here, we demonstrate for the first time, efficient cathodic electrochemical exfoliation of graphite to graphene in aqueous electrolytes using common and inexpensive alkali-metal salts such as KCl. The key to exfoliate graphite successfully in aqueous electrolyte is applying a sufficiently high voltage, and a high salt concentration which facilitates hydrated cationic intercalation, and promotes hydrogen evolution to exfoliate the graphene. The cathodic exfoliated graphene produced using KCl electrolyte exhibits a low defect density (I_D/I_G of 0.06, a C/O ratio of 57.8), high graphite exfoliation yield (>80%) in short time (< 10 mins for 1 cm² electrodes) and the highly conductive 6 to 7 layers graphene sheets served as an excellent support materials for electrocatalytic reactions. This environment-benign aqueous-based cathodic electrochemical graphite exfoliation approach opens a new opportunity in large-scale and low cost production of high quality graphene.


References

[1] S. Yang, M. R. Lohe, K. Müllen and X. Feng, Adv. Mater., 29 (2016) 6213-6221.
[2] A. M. Abdelkader, A. J. Cooper, R. A. W. Dryfe and I. A. Kinloch, Nanoscale, 16 (2015) 6944-6956.
[3] A. J. Cooper, N. R. Wilson, I. A. Kinloch and R. A. W. Dryfe, Carbon, 66 (2014) 340-350.

Recently, interfaces between graphene and diamond (carbon sp²-sp³ interfaces) has attracted much attention because the carbon sp²-sp³ interfaces become sources of various interesting physical phenomena and novel functions. Although there are many interesting theoretical predictions on the interfaces, experimental results regarding the electronic properties of such interfaces have rarely been reported. More recently, we found that vertically aligned graphene (carbon nanowalls: CNW)/diamond heterojunctions, that is, C sp²-sp³ interfaces became photo-controllable memristors [1], which are optically controllable memory-resistors with nonvolatile memory and switching functions. One of the most important application of the photo-controllable memristors is thought to be optoelectronic memory, which possess both photo-sensing and data storage function.
In this study, we show the CNW/diamond heterojunctions can be used as multibit optoelectronic memories, where light information stores as multilevel resistance in nonvolatile manner [2].
CNW were formed on B-doped diamond semiconductors in-situ by using microwave plasma CVD apparatus [1, 3]. Junctions using the CNW/diamond heterostructures were fabricated (area: 40-160 μm φ) and their current-voltage (I-V) characteristics were measured at room temperature in air, with or without photo-irradiation by using visible LED.
In the Raman spectrum of the CNW on diamond, four major peaks, which are characteristic of vertically aligned graphene, were observed: G, 2D, D' and D peaks, in addition to the diamond related peak (Dia.) at 1332 cm^-1. A SEM image of the CNW/diamond surface showed numerous wall-like structures, which also suggested formation of CNW on diamond. The transmission electron microscope (TEM) image of the interface of the CNW/diamond bilayers indicates that CNW with good crystallinity and clear interfaces were formed on the diamond semiconductors. These Raman, SEM and TEM results suggest CNW/diamond heterostructures with sharp interfaces were successfully formed. The CNW/diamond junctions exhibited hysteretic I-V behaviors. The resistance of the junctions was changed to low or high resistance states by the light irradiation with bias voltage application and the resistance states was maintained in nonvolatile manner. The mechanism for the photoconductive change is considered to be originated from oxidation-reduction of the CNW and/or CNW-diamond interfaces through the movement of oxygen ions by bias with photo-irradiation. The CNW/diamond junctions also show apparent response to optical pulses. The output current, that is, conductivity was increased (or decreased) step-by-step in proportion to the number of optical pulses under positive (or negative) bias. The numer of levels and heights of the current steps can be controlled by changing optical pulse intensity, pulse width, bias voltage, etc. To determine the relationship between output current and applied pulse numbers precisely, multiple (~10) optical pulses (38 µW/cm², 30 ms, 1 Hz) were applied to the junctions. The output current, that is, conductance increased linearly from 2 nA to 142 nA in response to the total optical pulse numbers from 1 to 10. The linear relationship between the number of optical pulses (n) and the output current [I(n) (nA)] can be expressed as “I(n)= 14.26*n + 2.27”. Application of one optical pulse induces current increase of ~14 nA. This means that the junctions are also used as optical computing-memory devices with arithmetic functions such as counting, addition, and subtraction. These results indicate the CNW/diamond heterojunctions are capable of multibit optoelectronic devices, where light information is stored as multilevel resistance in nonvolatile manner and the stored information is processed immediately.

Ref.:
[1] K. Ueda et al., J. Mater. Res. 34 (2019) 626.
[2] K. Ueda et al., Appl. Phys. Lett. 117 (2020) 092103.
[3] K. Ueda et al., Dia. Rel. Mater., 38 (2013) 41.

Nanoporous free-standing SWCNT films are essential for understanding porosity of these films which should be promising for catalyst supports and supercapacitors. The SWCNTs form networks of randomly distributed SWCNTs, giving materials such as transparent thin films and free-standing films. The transparent thin films of SWCNTs form two dimensional porous networks of randomly oriented SWCNTs whose pore sizes vary from micropores to mesopores, according to the SEM and TEM observation. On the other hand, porosity of the free-standing SWCNT films is not straightforward because the micropores and mesopores are hidden in the three-dimensional structures of these films. We use nitrogen adsorption at 77 K to characterize porosity of the free-standing SWCNT films. The nitrogen adsorption isotherm shows a prominent hysteresis loop over the wide relative pressure range of ~10^-3 to ~1, which we assigned to the presence of ultramicropores of < 0.7 nm. These ultramicropores were open during ultrasonication treatment of the SWCNTs prior to the free-standing film fabrication. The ultramicropores are evidenced as defects on SWCNTs using Raman spectroscopy. The D- and G-band ratio increases from pristine SWCNTs of 0.04 to SWCNTs of free-standing films of 0.11. The surface area increases from pristine SWCNTs of 320 and 280 m²/g (BET and αs) to free-standing SWCNT film of 605 and 590 m²/g (BET and αs). Micropore volume increases from pristine SWCNTs to free-standing SWCNT film from 0.06 to 0.18 cm³/g, respectively. High surface area of the free-standing SWCNT films is assigned to the ultramicropores. Also, the free-standing SWCNT film is composed of mesopores created by entangling of SWCNTs in the network as observed with SEM and TEM. Understanding porosity of the free-standing SWCNT films is important for developing the SWCNT electrodes of desired porosity and surface area for the electrochemical applications.

Interfacing two-dimensional graphene oxide (2D GO) platelets with one-dimensional zinc oxide nanowires (1D ZnO) would create mixed-dimensional heterostructures suitable for modern optoelectronic devices. However, there remains a lack in understanding of interfacial chemistry and wettability in GO-on-ZnO heterostructures. Here, we propose a hydroxyl-based dissociation-exchange mechanism to understand interfacial interactions responsible for GO adsorption onto ZnO hydrophobic substrates. The proposed mechanism would allow us to overcome the poor wettability of the super-hydrophobic ZnO surface (with contact angle 140.5°) to GO, from the dispersion of GO suspension with various organic media prior to drop-casting of GO on the ZnO. The addition of different classes of organics into the relatively high pH GO suspension with a volumetric ratio of 1:3 (organic-to-GO) is believed to introduce free radicals (OH and COOH), which consequently result in enhancing adhesion (chemisorption) between ZnO nanowires and GO platelets. The wettability study shows as high as 75% reduction in contact angle (θ = 35.5°) when the GO suspension is mixed with alcohols (e.g. ethanol) prior to interfacing ZnO nanowires. The proposed method brings forth a scalable tool for developing graphene-coated-ZnO heterojunctions for photovoltaics, photocatalysis, biosensors, and UV detectors.

In the recent time, the biomass-derived carbon materials have attracted attention for application to energy storage and battery devices based on the abundant resources, low cost, and sustainability of precursors. Among them, cellulose nanocrystal (CNC), which can be obtained from the removation of amorphous region of cellulose materials by acid hydrolysis, is regarded as promising carbon precursor. Its high crystallinity (54-88%) compared to other conventional cellulose causes high mechanical integrity, high thermal stability, and the formation of more developed carbon crystallites after carbonization.
Although it is prerequisite to thoroughly define the carbonization mechanism of CNC for use in a variety of applications, however, there is still an insufficient research. In particular, only speculations have been reported about the interesting phenomenon that the CNC often shows a graphitic phase at a low carbonization temperature of 1000 °C, unlike carbonized cellulose. Therefore, in the current study, we dried the CNCs by spray-freeze-drying method and carbonized them in the range of 1000-2500 °C. They showed interconnected fibrillar morphology and large surface area of 265.2 m²/g after carbonization at 2500 °C, which is favorable to use as a carbon nanofiller, purification, or catalyst support. In addition, the different behavior between amorphous and crystalline region of cellulose materials was thoroughly analyzed based on HRTEM, Raman, WAXD, and MD simulation results. The current study will not only open the new application of CNC-based nanocarbons but provide in-depth mechanism of carbonization of cellulosic materials.

Semiconducting single-walled carbon nanotubes (swCNTs) are a promising class of materials for emerging applications. In particular, they are demonstrated to possess excellent biosensing capabilities, and are poised to address existing challenges in sensor reliability, sensitivity, and selectivity.^[1,2] Functionalized and pristine individual CNTs have shown high sensitivity and selectivity down to the single molecule level.^[3,4] However, single CNT devices are challenging to make and characterize compared to CNT networks which add further complexity due to inter-CNT contacts. Such systems may not be as sensitive or selective compared to single CNT devices, but may be a cost-effective alternative for particular environments.
Here, we report on the characteristics of single-walled carbon nanotube (swCNT) networks exposed directly to aqueous solutions containing different solutes.^[1] This was made possible by employing a solid-state dielectric poly(vinylidene fluoride-co-hexafluoropropylene) (ePVDF-HFP), which has been demonstrated to be compatible with swCNTs and also enables low-voltage field-effect transistor (FET) operation.^[5,6]
These devices exhibit small device-to-device variation as well as high current output at low voltages (<0.5 V), making them compatible with most physiological liquids. Using this platform, the swCNT devices are directly exposed to aqueous solutions containing different solutes to characterize their effects on FET current–voltage (FET I–V) characteristics. Clear deviation from ideal characteristics is observed when swCNTs are directly contacted by water.
Such changes are attributed to strong interactions between water molecules and sp² -hybridized carbon structures. Selective response to Hg²⁺ is discussed along with reversible pH effect using two distinct device geometries. Additionally, the influence of aqueous ammonium/ammonia in direct contact with the swCNTs is investigated. Understanding the FET I–V characteristics of low-voltage swCNT FETs may provide insights for future development of stable, reliable, and selective biosensor systems.

[1] A. M. Foudeh, R. Pfattner, S. Lu, N. S. Kubzdela, T. Z. Gao, T. Lei, Z. Bao, Small 2020, 16, 2002875.
[2] V. Schroeder, S. Savagatrup, M. He, S. Lin, T. M. Swager, Chem. Rev., 2019, 119, 599.
[3] S. Sorgenfrei, C.-Y. Chiu, R. L. Gonzalez, Y.-J. Yu, P. Kim, C. Nuckolls, K. L. Shepard, Nat. Nanotechnol., 2011, 6, 126.
[4] J. Chaste, A. Eichler, J. Moser, G. Ceballos, R. Rurali, A. Bachtold, Nat. Nanotechnol., 2012, 7, 301.
[5] C. Wang, W.-Y. Lee, D. Kong, R. Pfattner, G. Schweicher, R. Nakajima, C. Lu, J. Mei, T. H. Lee, H.-C. Wu, J. Lopez, Y. Diao, X. Gu, S. Himmelberger, W. Niu, J. R. Matthews, M. He, A. Salleo, Y. Nishi, Z. Bao, Sci. Rep., 2015, 5, 17849.
[6] R. Pfattner, A. M. Foudeh, C. Liong, L. Bettinson, A. C. Hinckley, D. Kong, Z. Bao, Adv. Electron. Mater., 2018, 4, 1700326.

In-situ polymerization of polyacrylonitrile (PAN) polymer in the presence of cellulose nanocrystal (CNC) is conducted to produce CNC reinforced PAN nanocomposite fibers for high-performance carbon fiber. Cellulose is the most abundant organic material available on earth, therefore it can be an environmentally sustainable resource for producing carbon materials and carbon fiber. Also, CNC is useful for the reinforcing agent in nanocomposite materials due to its excellent properties such as high crystallinity and mechanical properties.
In the current study, there are two main effects 1) CNC into the nanocomposite fiber and 2) the impact of in-situ polymerization. We have conducted the thorough characterizations of CNC dispersion and radical polymerization of PAN polymer in the presence of about 1.5 wt% CNC. In-situ PAN/CNC nanocomposite fiber was produced by the dry-jet wet spinning method right after the polymerization was terminated.
From the mechanical and crystal orientation measurement, CNC is able to affect improving polymer chain orientation through interaction between PAN and hydroxyl groups of CNC. Furthermore, as the in-situ PAN/CNC nanocomposite solution is used directly without any removing PAN polymer with low molecular weight, it is supposed that they can act as plasticizers during the fiber spinning and affect the polymer chain structure transition during the heat-treatment process. Besides, using thermal analyses, the heat treatment conditions of precursor fiber have been set for manufacturing CNC reinforced high-performance carbon fiber. And the evolution of the structure from polymer chain to the graphite form during the stabilization and carbonization in the presence of CNC has been investigated.

We present a method for graphene transfer we refer to as “bifacial transfer” that allows transfer of multilayer chemical vapor deposition (CVD) graphene from both sides of a native metal substrate, such as an as-received nickel catalyst. In traditional transfer methods, the graphene on the “non-preferred” side, i.e. the bottom of the substrate, is removed with oxygen plasma before removal of the metal catalyst in etchant solution. Although this treatment prevents undesired aggregation of the graphene films, it fails to utilize both sides of CVD-grown graphene. Our bifacial transfer method reduces the cost of multilayer graphene by allowing the transfer of graphene from both sides of the substrate. After hot-press lamination to a polymer film and a temporary metal etching step, the graphitic films separate cleanly at the air-liquid interface due to an oxide interlayer. We characterize this separation layer and compare the quality of graphene transferred from both sides onto target glass and polymer substrates. The results of optical microscopy, confocal Raman spectroscopy, atomic force microscopy (AFM), and electronic transport measurements suggest that the quality of the multilayer graphene on the “non-preferred” side does not differ significantly from that of the “preferred” side. This method will allow more efficient and cost-effective use of graphene by doubling the usable graphene per area of growth substrate, and by eliminating the need for intermediate sacrificial transfer substrates such as poly(methyl methacrylate), PMMA.

Sensors that are thin and flexible and are yet highly sensitive to small deformations have become considerably crucial to a number of high-value-added applications such as wearable electronics, human machine interface, and condition monitoring of high-stake engineering structures. In recent years, these sensors have been undergoing rapid advancement owing to the development of low-dimensional nanomaterials. In particular, by optimizing the synthesis process, it is even possible to fabricate nanocomposite strain sensors that can be used to probe high-frequency, microscopic vibrations generated by ultrasonic waves. In fact, ultrasonic wave is one of the most widely used diagnostic means for in situ assessments of structural integrity.
The tunnelling effect and the piezoresistive effect are the main physics principles that allow nanocomposite strain sensors to acquire ultrasonic waves. When a sensor is impinged by ultrasonic waves, the conductive nanofillers inside the sensor will undergo high-frequency micro-vibrations. Such vibrations will cause the inherent electrical resistances of the nanofillers to fluctuate and the distances between adjacent nanofillers to vary, eventually resulting in changes in the overall electrical resistance of the sensor. However, the sensitivity of the existing nanocomposite strain sensors to ultrasonic waves is still far from satisfactory.
There are two main reasons behind the limited sensitivity. One is that the agglomeration of nanofillers or the poor capacitive compatibility between nanofillers and polymer matrices results in poor dispersion of nanofillers inside nanocomposite structures. The other is the lack of effective tunnelling nodes who is not conducive to the tunneling effect.
In this work, we fabricated a highly sensitive nanocomposite sensor for acquiring high-frequency micro-vibrations generated by ultrasonic waves, from polydopamine(PDA)-coated hybrid carbon nanofillers. First, multi-walled carbon nanotubes (MWCNTs) were coated by 10s nm thick viscous PDA to improve their compatibility with polyvinylidene fluoride (PVDF) substrates. The PDA nanolayers on MWCNTs do not only act as a dispersed phase that reduces the entanglement of MWCNTs, but also serves as the buffer layers between MWCNTs and PVDF matrices, helping to improve the responsiveness of the sensors to ultrasonic waves. Compared to uncoated MWCNTs, the use of 15 wt.% PDA-coated MWCNTs led to a 40% increase in sensitivity. Then, one-dimensional PDA@MWCNTs were mixed with two-dimensional single-layer graphene to enhance the geometric contact between nanofillers. Compared with the use of nanofillers of a single dimensionality, the mixing of nanofillers of different dimensionalities can effectively increase the number of tunneling nodes within a unit volume in a nanostructure. As the mass fraction of graphene within the hybrid nanofillers expanded from 33% to 66%, the sensitivity of the proposed sensor improved by approximately 120%, surpassing that of pure graphene sensors, which had been reported to possess the highest sensitivity to ultrasonic waves. The superior sensitivity of the proposed sensor, which actually utilizes a lower graphene content, was shown to be derived from the synergy between the two types of nanofillers which are of different dimensionalities.
Overall, we put forward new strategy for optimizing the sensitivity of nanocomposite strain sensors to high-frequency micro-vibrations. The feasibility of the idea has been validated by a series of experiments that encompass both material characterizations and measurements of ultrasonic signals.

Due to the current global water crisis, wastewater treatment requires considerable attention and development. Dissolved heavy metals in water trigger serious alerts and can have lethal effects on various components of the environment including water resources, soil, plants, animals, and can also be threatening the health of human beings. In this study, we addressed the issue by introducing novel Buckypaper membranes that were fabricated using a combination of biopolymers (i.e., chitosan and carrageenan) and multi-walled carbon nanotubes (MWCNTs). Three dispersions of MWCNTs with chitosan, carrageenan, and chitosan-carrageenan with 0.1% v/w were prepared using vacuum filtration. The removal of six heavy metals (i.e., cobalt, nickel, copper, cadmium, barium, and lead) was investigated in this study. The water permeability and the removal of heavy metals were evaluated using a dead-end (DE) filtration system. Heavy metals removal was studied at pH 7 and under a range of varying applied pressures (1 to 6 bar). At an applied pressure of 1 bar, the removal of lead and copper by the MWCNTs/carrageenan membrane reached 99% and 88%, respectively. However, MWCNTs/carrageenan membrane was found to be fragile. Nevertheless, adding chitosan to carrageenan had significantly improved the mechanical strength of the membrane while sustain the excellent removal properties of the heavy metals. That is, MWCNT/chitosan-carrageenan membrane significantly exceeds MWCNTs/carrageenan membrane in tensile strength, tensile strain and young’s modules by 400%, 17%, and 6%, respectively. On the other hand, the MWCNTs/chitosan membrane showed a high water permeate flux that reached up to 200 L/h.m². Also, the electrical conductivity of all membranes varied from 37 S/CM to 57 S/CM. Additional characterization techniques on the three membranes were conducted in this study as well.

A variety of innovative designs of wearable electronics require to be powered by energy storage devices such as supercapacitors based on flexible electrodes. One of the current challenges that would delay the implementations of supercapacitors is the high cost of the electrode materials. In this research, Abundant oil fly ash is obtained from a power plant in Jeddah, Saudi Arabia, as a source for the synthesis of carbon nanostructures by sonication (JSON) and carbon nanotubes (CNTs) by chemical vapor deposition [1,2]. These CNTs have diameters around 30-40 nm, few micrometers lengths, and clear zigzagged structures, which are mostly different than the commercial CNTs, as characterized by high resolution transmission electron microscope. To utilize the promising properties of CNTs in a practical application, flexible supercapacitor electrodes of CNTs have been fabricated on carbon cloth as a current collector in addition to H₂SO₄ electrolyte, then tested and compared with JSON electrode in terms of cyclic voltammetry, galvanostatic charging-discharging and electrochemical impedance spectroscopy. Interestingly, CNTs electrode exhibits maximum areal and gravimetric capacitances of 77 mF/cm² and 55 F/g, respectively, which are one order of magnitude higher than those of JSON electrode. This improvement can be attributed to the smaller size and hence the larger surface area of CNTs than JSON. Moreover, CNTs electrode shows exceedingly small equivalent series resistance and charge transfer resistance ascribing to the good contact of the electrode active materials within the carbon cloth substrate and the electrolyte. In addition, the vertical impedance line in the low frequency range of Nyquist plots indicates an excellent electrolyte ion diffusion into the electrode due to the porosity of CNTs. The successful fabrication of such flexible supercapacitors based on affordable and scalable CNTs would facilitate their cost-effective manufacturing.
ACKNOWLEDGMENT
This joint project was co-funded by King Abdulaziz University (KAU), Jeddah, and King Abdullah University of Science and Technology (KAUST), Thuwal, under grant number "JP-19-002". The authors, therefore, acknowledge with thanks KAU & KAUST for their technical and financial support.
REFERENCES
[1] N. A. Salah, Method of forming carbon nanotubes from carbon-rich fly ash. US patent Number: 8,609,189 B2 (2013).
[2] N. Salah, A. A. Al-ghamdi, A. Memic, S. S. Habib, Z. H. Khan, Formation of carbon nanotubes from carbon rich fly ash: growth parameters and mechanism. Mater. Manuf. Process 31, 146–156 (2016).

Pollution of drinking water sources by a variety of inorganic compounds has created a need to develop more efficacious removal technologies to ensure contaminant-free and clean water. Conventional methods for water decontamination involve physicochemical separation and chemical oxidation. Yet, physicochemical separation lacks pollutant selectivity and produces toxic waste streams,¹ while chemical oxidation requires intensive energy and chemical inputs and may form transformation byproducts.²
Nanotechnology-based approaches are increasingly explored as an alternative for decontamination methods. Many new technologies leverage the reactive and tunable properties of nanomaterials for increased cost-efficiency, selectivity toward priority pollutants and energy/chemical sustainability.³ Through manipulation of material size, morphology, and chemical structure, nanomaterials can have exceptional adsorptive and catalytic properties for water decontamination.
Molybdenum disulfide (MoS₂) nanosheets stand out as a promising advanced-material for water decontamination. MoS₂ act as an efficient and selective adsorbent for the removal of heavy metal ions (e.g., Hg²⁺ and Ag⁺) through strong Lewis acid and base soft−soft interactions with sulfur atoms in MoS₂. Affixing MoS₂ nanosheets onto a platform is essential minimize risk of nanomaterial release into the environment. In the context of nano-assisted water treatment technologies, affixing nanomaterials onto active platforms such as granular activated carbon media may enable multifunctional decontamination. Activated carbon is the predominant adsorbent used widely in water treatment today, due to its high affinity for organic pollutant adsorption, but lack affinity to inorganics. MoS₂ affixed onto activated carbon, enhances overall decontamination performance by enabling simultaneous adsorption of organic and inorganic pollutants.
In this research, we examined the tunable water decontamination capabilities of MoS₂ nanosheets grown on activated carbon (MoS₂@AC) in a hydrothermal method for the adsorption of organic (methylene blue) and inorganic (mercury) contamination from water. In a batch experiments, we demonstrated the high mercuric adsorption potential of MoS₂@AC (~2000 mg Hg/g MoS₂) in the absence and presence methylene blue. Furthermore, methylene blue was removed in similar rates by MoS₂@AC and pristine AC. These results suggest that while MoS₂ is active and enable the removal of mercury, its presence does not interrupt the activated carbon activity. Moreover, we will investigate the practical application of this nanocomposite by evaluating the effect of background ions on the mercuric adsorption capacity. We also assess the nanomaterial leaching during operation in various conditions to demonstrate the reuse capabilities and to assure safe and durable use. Overall, results from this study provide a proof-of-concept for water treatment enhancement by 2D nanomaterials.
Bibliography
1. Drewes, J. E., Reinhard, M. & Fox, P. Comparing microfiltration-reverse osmosis and soil-aquifer treatment for indirect potable reuse of water. Water Res. 37, 3612–21 (2003).
2. Hübner, U., von Gunten, U. & Jekel, M. Evaluation of the persistence of transformation products from ozonation of trace organic compounds – A critical review. Water Res. 68, 150–170 (2015).
3. Bhaduri, B. et al. Dual functionality of an Ag-Fe3O4-carbon nanotube composite material: Catalytic reduction and antibacterial activity. J. Environ. Chem. Eng. 6, 4103–4113 (2018).

Hexagonal boron nitride (h-BN) is a new material with potential for applications in electronic devices, tribology, and separation membranes. Limited theoretical and experimental researches have been conducted to explore their efficiency as a desalination membrane. With the recent advancement of their controlled synthesis, researchers have become more interested in exploiting their interaction with organic materials. The purpose of this work is to explore the efficiency and potential of porous h-BN as a separation membrane for ethylene glycol (EG) removal from water. Very few experiments have been previously conducted to assess the capability of porous h-BN for EG or other organic pollutants removal. However, no prior theoretical or computational work that studies the molecular interactions between EG and h-BN has been reported. In this work, a methodological approach to simulate the atomic interactions of h-BN and EG in different pore configurations is proposed and investigated using classical molecular dynamics. Our results exhibit that nanometer-scale pores in single layer h-BN can effectively reject approximately 90% of EG from EG contaminated water. We also report the removal performance of the freestanding porous h-BN sheet as a function of pore diameter and applied pressure.

Graphene oxide membrane(GO-M) has recently attracted a great interest because of its potential applications for desalination and for removal of organic matter. The carbon-based GO-M is excellent in chemical resistance, anti-fouling effect, low cost, and so forth as compared to polymer or ceramics membranes. It is known that GO has polar oxygen functional groups and is negatively charged in water, which makes it possible to remove ionic species in water. It has been reported that GO-M shows selective separability toward some neutral solvent molecules. However, its ionicity-based separation property has not yet been sufficiently understood. In this research, we focused on surface charging property of GO-M and examined its separation behaviors toward inorganic ions and organic dyes of different charging properties. It was found that the separation or permeation of inorganic cations by GO-M is dependent on the ionic type and charge number. The rejection ratio can be accounted for by the strength of their electrostatic interaction with the GO surface. GO-M shows good rejection toward anionic dyes but great adsorption toward neutral and cationic dyes, resulting in the blockade of membrane path.

For materials with high oxygen affinity, oxide layers will significantly change the material properties. At aluminum surfaces, an oxide layer may form in seconds, even under vacuum conditions. Recent studies show that thin amorphous oxide shell layers on aluminum surfaces significantly change the responses of the material. However, the relations between the thickness of the oxidized layer, the temperature and the mechanical response of nanowires have not been investigated intensively. In this study, we use a ReaxFF potential to analyze the influences of oxide shell layers on the material responses of the nanowires under uniaxial loading at different strain rates. We conduct simulations within a wide range of strain rates and temperatures varying between 10K and 500K. The Al-O interface leads to an increased defect nucleation rate at the oxide interface preventing localized deformation.