Symposium NM08 : Graphene Oxide Liquid Crystals and 2D Soft Material Systems

The performance of graphene-based bulk materials is dependent not only on the structure and properties of individual sheets, but also on the intersheet interactions and their hierarchical texture or its supramolecular structure. Our group has been studying the supramolecular chemistry of chemically converted graphene and how non-covalent interactions can be utilized to create carbon-based functional soft materials that are difficult to obtain with other techniques. We have demonstrated that hydration of graphene not only enables its solution processability, but more importantly, offers simple and scalable ways to assemble graphene into well-controlled nano-architectures with extraordinary macroscopic properties. This talk will highlight how the architecture of graphene-based gels can be engineered to enable new functions that are difficult to achieve with traditional materials.

References
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[4]. Qiu, L., Liu, D., Wang, Y., Cheng, C., Zhou, K., Ding, J., Truong, V.& Li, D, Adv.Mater., 26, 3333-3337 (2014).
[5]. Yang, X., Cheng, C., Wang, Y. Qiu, L. & Li, D. Science, 341, 534-537 (2013).
[6]. Cheng. C. & Li, D. Adv. Mater. 25, 13-30 (2013).
[7]. Qiu, L., Liu, Z., Chang, S., Wu, Y. & Li, D. Nature Commu. 3, 1241 (2012).
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Metallic transition metal dichalcogenides (MTMDCs) have manifested a wealth of intriguing properties in their bulk states, such as magnetism, charge density waves, and superconductivity, attracting worldwide attention from condensed-matter physicists over several decades. Very recently, nano-thick MTMDCs have been reported to be essential building blocks for constructing next-generation electronic and energy-storage applications, as well as for exploring unique physical issues associated with the dimensionality effect. However, batch production of such envisioned few-layer MTMDCs remains challenging based on the existing physical or chemical exfoliation methods. Our group reported the direct synthesis of high-quality semiconducting and metallic TMDCs materials of MoS₂, WS₂, VS₂, and TaS₂, etc., on both on conducting Au foil substrates and insulating substrates towards different applications ^[1,2]. Particularly, we designed a facile chemical vapor deposition route (CVD) for the direct production of VS₂ nanosheets with sub-10 nm thicknesses on SiO₂/Si substrates. The obtained nanosheets represented spontaneous superlattice periodicities and excellent electrical conductivities (~3×10³ S cm^-1), enabling a variety of applications as contact electrodes for monolayer MoS₂, and as supercapacitor electrodes in aqueous electrolytes.^[3] Subsequently, we also developed a van der Waals epitaxial strategy for the direct synthesis of thickness tunable metallic 1T-VSe₂ monocrystalline nanosheets on mica substrate via a similar CVD method. In particular, our synthesized few-layer 1T-VSe₂ nanosheets possess extremely high electrical conductivity of up to 10⁶ S m^-1, which is 1-4 orders of magnitude higher than that of state-of-the-art conductive 2D materials. The charge-density wave (CDW) phase transition is also detected with the transition temperature presenting the same dependence on thickness as that of exfoliated VSe₂ nanosheets.^[4] More intriguingly, we also realized the first achievement of thickness-tunable 2H-TaS₂ flakes and centimeter-size ultrathin films on an electrode material of Au foil via a facile CVD route. We also detected the transition from nearly commensurate to commensurate CDW phases with our ultrathin 2H-TaS₂ flakes. Remarkably, we obtained extra high hydrogen evolution reaction efficiency on as-grown 2H-TaS₂ flakes directly synthesized on Au foils with the efficiency even comparable to traditional Pt catalyst. ^[5] All these work therefore provides brand new insights into the direct synthesis and property investigations of nano-thick metallic 2D TMDs crystals.
References
1. Yanfeng Zhang*, Zhongfan Liu*, et al., Chem. Soc. Rev. 2015, 44, 2587; Adv. Mater. 2016, 28, 6207.
2. Yanfeng Zhang*, et al., Adv. Energy. Mater. 2016, 6, 1600459; Adv. Mater. 2016, 28, 10664.
3. Lin Gu*, Zhongfan Liu*, Yanfeng Zhang*, et al., Nano Lett. 2017, 17, 4908.
4. Yanfeng Zhang*, et al. Adv. Mater. 2017, 1702359.
5. Yanfeng Zhang*, et al. Nature Commun. 2017, 8, 958 .

The shape anisotropy and enhanced solubility of graphene oxide (GO) in a wide variety of solvents provides the perfect environment to showcase isotropic-to-nematic colloidal phase transitions. As a result, the fluid phase of GO starts to demonstrate properties such as higher viscosity and elasticity compared to the isotropic phase. Thin films of graphene oxide have primarily been fabricated from isotropic phase of GO by processes such as vacuum filtration; which does not attend to manufacturing speeds required by industries. Our research program endeavours to address this issue given the large possibilities in applications ranging from permeable filtration membranes, strategically constructed battery separators, strain sensors, lab-on-chip devices, and supercapacitors.
We have over the years developed quantitative polarized light imaging techniques to quantify fine structure, alignment, texture of the liquid crystalline phases and thin films of GO; which have helped us develop processing-property correlations. We have also shown that large-area GO (13 x 14 cm²) filtration membranes can be produced in < 5 seconds using a high speed gravure printer which have demonstrated molecular sieving properties and suitability in membrane separation processes. Using vinyl-cut stencils and our thin film formation technique various patterns can be produced in flexible, porous, non-porous substrates which can be utilized in applications such as strain sensors & micro-/nano-fluidic components of lab-on-chip devices such as rectifiers and capacitors with enhanced properties. We have also demonstrated that the permeable films GO films can be directly formed over a sulphur cathode in a Li-S battery configuration leading to dramatic improvements in cycle life and capacity.
The scalability and adaptability of our thin film fabrication technique is leading to commercial adaptation and laboratory-to-market translation of products such as nanofiltration membranes.

Transition metal dichalcogenides (TMDCs) are important for both their intriging physics and potential applications. Revealing the electronic and spin structure is critical for understanding the physical properties as well as exploring their potential appications. Here I will present our experimental investigations on the electronic structures of a few TMDCs using advanced electron spectroscopies, including angle-resolved photoemission spectroscopy, Nano-ARPES and spin-resolved ARPES.

STANDARD GRAPHENE, headquartered in South Korea, is a company that specializes in high quality graphene and application products. Based on 21 years of intensive research on Carbon Nano Tech field, it is considered to be the only company in the world at this point who can mass produce high quality graphene. With more than 100 global partners across many different industries such as aerospace, automobile, water purification, military, STANDARD GRAPHENE has developed more and better graphene application products than anyone has developed. Now the world is at the point of graphene market explosion and STANDARD GRAPHENE is the absolute forerunner in this war.

Lee JoungHoon, the CEO of STANDARD GRAPHENE, will introduce the products of STANDARD GRAPHENE and some its graphene application products which are ready for the commercial market.

Graphene oxide (GO) nanosheets have emerged as important sheet-like, giant molecular precursors for assembling new carbon materials. Colloidal populations of GO nanosheets can be aligned, stacked, folded, crumpled, wrapped, gelled and/or deposited to create a variety of novel material structures. Some of these nanosheet-based materials are not accessible through traditional methods of carbon synthesis that use molecular or bulk solid-state precursors. This approach of “building with graphene” is informed by the science of soft matter, since the key colloidal interactions and conformational changes of GO nanosheets involve weak intermolecular forces and they result in mechanically soft and flexible final products.

This talk will describe our laboratory’s recent work on the systematic exploitation of soft matter behavior to make new GO-based material architectures. We will show how the phenomenon of surface anchoring in lyotropic liquid crystal phases, driven by entropic forces at interfaces, can be used to create vertically aligned GO nanosheets. This lyotropic behavior of GO will be contrasted to the thermotropic behavior shown by molecular systems (discotic liquid crystals), which exhibit multiple anchoring states (homeotropic, planar) depending on both enthalpic and entropic forces that can be tuned by substrate selection. The talk will also describe conformation changes in GO-based films on soft substrates driving by surface instabilities under in-place compression. A variety of wrinkled, crumpled, and hierarchically textured GO films will be demonstrated, and their example applications discussed as stretchable barriers, high-area membranes, and complex templates for ink-based fabrication of textured and tiled ceramic coatings.

Graphene and its oxidized form of graphene oxide (GO) have been of particular interest in material science due to their exceptional physical properties. However, relatively little attention has been paid to the GO dispersions although the state of dispersions directly affect to the material property. For example, GO can be well-dispersed in water due to their hydrophilic functionalities and form liquid crystals (LC); however, they easily form gels or glass around 1 wt%, which often act as an obstacle in GO based composite production. Thus, to understand the structure and dispersing mechanism of GO dispersions is an essential step before reaching the application stage.
In this talk, the detailed structural and rheological studies for GO dispersions are introduced with extensive scattering and rheology experiments. We first systematically investigate the phase behavior and structural evolution of GO LC suspensions under various experimental conditions and disclose how the glass transition of GO dispersions is affected particularly in the presence of strongly interacting polymers. An intriguing observation was that adding polymer can effectively retard glass transition of GO in water. Furthermore, by varying polymer type, functionality, and molecular weight, the GO structures and LC properties can be changed significantly, suggesting the possibility of controlling the process conditions in GO employed applications.

Since the Scotch Tape Method has been discovered in the early 21^st century, Graphene has attracted a gob of attention due to its novel electrical, mechanical and thermal properties. It can be produced by various methods such as chemical and thermal reduction of graphene oxide (GO), epitaxial growth by chemical vapor deposition, oxidation by microwave assisted heating and via micro-mechanical cleavage of graphite. Apart from the layered structure, GO nanosheets profusely contain hydroxyl, epoxide, carbonyl and carboxyl groups which make it hydrophilic in nature and leads to the formation of a stable colloidal suspension. In this study, Graphene oxide (GO) has been synthesized by Improved Hummers method or Tour’s method with some modifications and it is converted to reduced graphene oxide (rGO) via thermal treatment. The current work focuses on the characterization of the colloidal suspension of GO and rGO which includes measurement of thermal conductivity, surface tension and detailed study on the rheological properties. Here, authors have measured the thermo-physical properties of GO and rGO at different concentrations ranging from 50-200 ppm (30^oC). It has been observed that maximum thermal conductivity for both the nanofluids viz. GO and rGO are found to be at 50 ppm and 100 ppm, respectively. Higher thermal conductivity and lower surface tension of the nanofluid are considered beneficial for any heat transfer application as higher thermal conductivity results in more efficient heat transfer in shorter time and lower surface tension helps in improving the coolant spreadability over the hot surface. Authors have further inquired about the surfactant aided (Cetyl trimethylammonium bromide (CTAB), Sodium Dodecyl Sulfate (SDS) and Tween 20) thermo-physical properties of the nanofluids at the optimized concentration. Surfactant addition leads to reduction in surface tension for both GO and rGO which enhances the wettability of the nanofluid and also contributes in making the suspension stable.The maximum reduction in surface tension for both nanoparticle (rGO) and surfactant aided nanoparticle (SDS + rGO)suspension was found out to be 14.11% and 56.14%, respectively. Similarly, for GO it is 2.55% and (GO+SDS) it is 58.58 %. Maximum enhancement in thermal conductivity of rGO is observed at 100 ppm which is 28.87% higher than that of the base fluid while almost three times increment (88.70%) is reported with addition of SDS. However, the trend is quite different for GO as there is slight increment in thermal conductivity (3.3%) with respect to base fluid and is merely insignificant with addition of SDS(0.4%). In terms of the rheological property, both GO and rGO nanofluids follow shear thinning non-newtonian behavior and are viscoelastic in nature.

We demonstrate the orientation control of graphene flakes by a weak static magnetic field and subsequently achieve high order parameter alignment by rotating magnetic field. Several devices such as magnetic field sensor, display, polarizer and graphene pattern were exhibited as example of novel applications of macroscopically aligned graphene. The control is made by weak static magnetic field (hundreds of Gauss) for large diamagnetic susceptibility of exfoliated graphene. Viewed as a non-magnetic material, a liquid suspension of graphene flakes is firstly used for magnetic field sensing and display with sensitivity and spatial resolution higher than traditional iron filings or particles. The graphene suspension is then packaged as a writing and/or display board that can be controlled by magnets or magnetic field. Both applications require no external lighting or polarizing optics because they utilize macroscopic alignment and anisotropic optical properties of graphene.
Then graphene suspension was firstly aligned with high order parameter of 0.8 by rotating magnetic field. Macroscopic optical properties of aligned graphene flakes such as birefringence and diffraction were investigated as graphene flakes was controlled in specific orientation and aligned parallel to each other. After mixing with UV cured resin, graphene flakes suspension was aligned as high performance polarizer. By combination lithography process with rotating magnetic field alignment, graphene flakes were assembled into patterns of different orientations with lithography mask. The macroscopic control and alignment of graphene can not only transfer unique properties of graphene from microscopic to macroscopic scale, but also be used to align other nanomaterials. Thus, our demonstration opens door to enormous new device applications.

We synthesized MoS₂ and GO composites through a facile solution process to fabricate transparent and flexible gas sensor devices. The composites were coated by spin coater on SiO₂/Si substrate, and after coating, the thin film was annealed at 600 ° C for reduction from GO to rGO. Finally, the completed MoS₂/rGO thin film was patterned by soft lithographic patterning process and transferred to a transparent and flexible PET substrate. To fabricate a gas sensor, Au/Cr electrodes were deposited at the edges of the patterned MoS₂/rGO channel, and the gas sensor characteristics were analyzed using scanning electron microscopy (XPS), atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectra, X-ray photoelectron spectroscopy (XPS), UV/Visible and gas sensing system. As a results, the patterned MoS₂/rGO gas sensor was very thin with a thickness of 10 nm or less, and the transmittance was confirmed to be 93%. In addition, the characteristics of NO₂ gas were confirmed by varying the concentration of NO₂ gas from 0.15 ppm to 5 ppm. The sensing sensitivity of the MoS₂/rGO composite channel was improved about four times as compared to that of the rGO single channel. In this presentation, we will discuss potential applications of MoS₂/rGO composites.

In recent past carbon allotropes like carbon nanotubes, graphene and graphene quantum dots have attracted the interest of both industry and the scientific fraternity for their incredible electrical, thermal, optical and mechanical properties. Graphene is monolayer of carbon atoms bound in honeycomb lattice structure. The current work states a comparatively easier and inexpensive chemical route for synthesis of graphene oxide (GO) from graphite and preparation of reduced graphene oxide (rGO) by thermal treatment. GO has been prepared by introducing some modifications over improved Hummers method or more widely known as Tour’s method. The method reports only 7.5% less yield than Tour’s method whereas, requirement of acid and oxidizer have been cut off by 40% and 33%, respectively.
Thermal reduction of GO has been observed by exfoliation and weight loss of the end product. GO has high amount of oxygen containing functional groups in its lattice, which are responsible for its difference in physical properties as compared to graphene. Elimination of the functional groups due to sudden thermal shock and evolution of gasses viz. water, CO and CO₂ create a huge pressure in GO lattice which leads to exfoliation. Exfoliation of graphene sheets has been analyzed both qualitatively and quantitatively by FESEM analysis and from measurement of specific surface area respectively. Enhancement of specific area has measured to be almost 9 times from GO to rGO. The current work reports in detail, the onset temperature of thermal exfoliation which is found to be 325 ^oC. Present work also determines the impact of reduction temperature on carbon-oxygen ratio of the end product. At higher temperature, carbonyl and epoxy groups are eliminated as CO, CO₂ by taking out carbon atoms from the graphene oxide plane, which causes defect in the lattice and this affects its carrier transport properties. At reduction temperature of 350 ^oC highest carbon-oxygen ratio has been obtained. From FTIR analysis removal of oxygen containing functional groups at different reduction temperatures has been studied. Thermal degradation kinetics of GO and rGO have also been performed from TGA data. Thermal degradation rate of GO is found to be concentration independent and is a sole function of temperature.
Presence of graphene quantum dots has been detected by TEM analysis of rGO specimens. Graphene quantum dots have potential applications in the field of bio-imaging, bio-sensing, photovoltaic devices and in light emitting devices. Fluorescence property of the quantum dots have also been investigated in present study.

Graphene has extraordinary electronic, mechanical and thermal properties due to an atomically thin two-dimensional lattice of sp₂-bonded carbon atoms. Owing to this extreme thinness of graphene, the interesting phenomena such as wetting-, electron transfer-, and chemical reactivity- transparencies as well its superior material properties have been studied by many researchers. Here, we investigated the lattice transparency of graphene to the atomic arrangement of a substrate surface, using first principles density functional theory (DFT) calculations. Firstly, we calculated binding energies of various model substrates for crystalline oxygen terminated ZnO layers (c-ot-ZnO). To more clearly understand the mechanism for the lattice transparency, we also calculated the charge density differences for the contacts between c-ot-ZnO and model substrates. As a result, we could know that graphene gains “ZnO-mimic” charge distribution by supported on ZnO substrate, and the interaction between nucleating ZnO and graphene would be vdW interaction reinforced with Coulomb interaction.

Liquid-phase exfoliation of graphene from graphite is an economical and increasingly popular method of graphene production. Shear exfoliation processes have achieved some of the highest production rates of few-layer graphene and show great promise for industrial scale up. In addition to manufacturing graphene for use by itself, the systems of graphene dispersed in liquid directly produced by exfoliation have great potential as (multi-)functional fluids, inks for circuit and/or 3D printing, and can be an attractive precursor to polymer nanocomposites. Successful realization of these applications depends on the colloidal stability of these systems over practical time scales and under mechanical stresses experienced during processing and use.

However, attempts at predicting and explaining the stability of graphene dispersions in a variety of liquids are still limited. Much early work on the exfoliation and dispersion of graphene focused on matching the surface energy of graphene/graphite to that of the exfoliating or dispersing liquid. Recent work suggests that while surface tension may be appropriate for exfoliation, liquids with similar surface tension have been found to have different dispersibilities of graphene. This has led new research to consider the use of Hansen solubility parameters for predicting the dispersibility of graphene in liquids, which allows for the separate consideration of different interactions. However, it is hard to predict these parameters for arbitrary solvents. The dispersion solubility parameter has been found to be the most important of the three Hansen parameters for the stability of graphene sols, and we propose an alternative approach based on this. In classical colloid theory, the dispersion interaction is predicted by the dielectric constants and refractive indices of the particle and dispersing medium. We propose to study the stability of graphene dispersions in various organic solvents as a function of these physical properties, which are more easily determined than Hansen parameters. We predict that liquids with dielectric constants and refractive indices closer to that of graphite should show improved dispersibility of graphene. Ultraviolet-visual spectroscopy will be used to measure dispersed graphene concentration and changes over time will provide an understanding of storage stability. Rheological measurements will probe the stability of the dispersions under stress and provide information on the strength of interparticle interactions.

The development of simple solution based techniques for the formation of graphene oxide (GO) films onto conductive substrates is of great interest for the rapid development of electrically active and chemically resistant coatings. This work demonstrates the controlled formation of metal-ion-containing GO films using a new deposition approach based on pulsed-potential and alternating current electrocoagulation (EC) and subsequent electrophoretic deposition (EPD) of GO particles on copper electrodes. Specifically, films were deposited from GO based aqueous dispersions using an electrochemical set up in which copper is used as the anode. Based on the choice of the key experimental variables namely frequency (5-50000Hz), amplitude (2-10V), and duty cycle (5-75%), films of controllable thickness (1-100 microns), microstructure and composition (i.e. GO and copper) were readily obtained. The deposited films consisted of two distinct regions: region I, with randomly oriented GO assemblies and region II consisting of oriented lamellar GO assemblies. Of particular interest was the fact that the spatial extent of region I was highly tunable for specific combinations of the experimental variables (low frequency, low duty cycles), while the relative amount of metal-ion incorporation was dependent on the amplitude. The findings of this work enable controllable pathways towards obtaining ordered lamellar assemblies of metal incorporated GO films and coatings, which are of great technological importance impacting diverse research areas that include filtration membranes, electrochemical energy storage, corrosion and electronic packaging.

Here, a straightforward fabrication method to produce graphene oxide (GO) fibers liquid crystal (LC) dispersion using trivalent cation salts as ionic binder is presented. The multivalent metal cations aid in coagulating GO liquid crystalline dispersions on the fiber structures. To utilize the full potential of GO fiber, it is critically important to control the microstructure of fiber. The microstructure of GO fibers, such as shape and d-spacing between sheets, is ultimately controlled by the metal cation coagulants. Compared to divalent cations, the fast diffusion of trivalent cations induces highly dense structures. The modulation of chemical interactions and induced cross-linking by trivalent metal cations is advantageous in improving the mechanical properties of GO fibers. The increased interlayer attraction due to trivalent cation binders results in mechanically stable fibers that exhibit tensile strength and Young's modulus as high as 486 MPa and 81 GPa, respectively.

Due to the unique two-dimensional honeycomb flat structure as well as the specific surface area, graphene is expected to become a new generation of absorption material. In this paper, the calculations are performed by first-principle approach based on the density functional theory (DFT). Using the Castep module of Materials Studio software to establish super cell models of graphene oxide, vacancy graphene oxide and doped graphene oxide, then add CO molecule to form adsorption models on graphene oxide, so it can be detected the best absorption position on graphene oxide. Furthermore, the best adsorption ability on CO molecule in doped graphene oxide can also be found by making change the doping content. By discussing the calculation absorption energy, band structure, density of states and density of electronic，the doped graphene oxide could effectively improve the adsorption ability to CO molecule.

In this work, we demonstrate a novel method for direct synthesis of patterned graphene on insulators by Cu vapor assisted chemical vapor deposition using a solid aromatic carbon source, 1,2,3,4-tetraphenylnapthalene (TPN), as a precursor. The UV/O₃ treatment of the TPN film induces the crosslinking of the TPN film and a strong interaction between substrate and TPN which prevents complete sublimation of carbon sources from the substrate. Substrate adhered-crosslinked TPNs can be successfully grown to graphene on the substrate without any organic contaminants. Graphene synthesized by using this method shows excellent chemical and mechanical stability. This method also allows simultaneous patterning of graphene by selective UV/O₃ exposure, therefore it can be used for transparent electrode for electronic devices. The proposed method of synthesizing patterned graphene directly on the insulators would be widely applied for organic and soft hybrid electronic applications.

High-power laser processing is rapid, continuous, area-selective material fabrication method which is useful for the display application such as crystallization of silicon or oxides. Two-dimensional materials, such as graphene, are under intensive development for manufacturing flexible devices owing to its outstanding physical properties. Here, we demonstrate an area-selective ultrafast nanofabrication method for directing self-assembly of block copolymer films into highly ordered manufacturing-relevant architectures at the scale below 12nm without surface prepatterned structures by using low-intensity infrared or visible laser irradiation. The fundamental principle of this light-induced nanofabrication mechanism are: 1) the self-assembly of block copolymers with desired orientations by passing the disorder-order transition under large thermal gradients, 2) the photothermal conversion of chemically modified graphene films which are used as a flexible and conformal light-absorbing layers for transparent, mechanically flexible surfaces and nonplanar 3D geometry substrates.

Process compatibility of block copolymers with a high Flory–Huggins interaction parameter (χ) is one of the principal challenges encountered in successful incorporation of directed self-assembly in sub- 10 nm scale practical nanolithography. In this study, sub-10 nm self-assembled nanopatterns have been assured in wafer-scale and reliable, fab-compatible, ultrafast directed self-assembly is achieved with high χ block copolymer by using intense flash light. Flash light irradiation raises instantaneous heating/quenching process over an extremely high temperature (over 600 °C). Millisecond-level rapid photo-thermal process with high temperature enables large grain growth without thermal degradation or dewetting. Photo-thermal effects to block copolymer self-assembly for highly ordered structures are identified based on the kinetics and thermodynamics with strong segregation. Furthermore, this flash light self-assembly process is combined with graphoepitaxy to prove directed self-assembly over large area. A chemically modified graphene film is used as a flexible and conformal light-absorbing layer. Subsequently, transparent and mechanically flexible nanopatterning with flash light can be intergrated with roll-to-roll process, and thereby can be widely used to next-generation nano-device applications; electronics, optoelectronics, sensors, catalysts, etc.

Common methods of growing large area graphene on copper by thermal chemical vapor deposition (CVD) are constructed by multiple steps and high temperature (~1,000°C). It usually derives strain and surface defects from different thermal expansion coefficient. Moreover, high processing temperatures might affect the thermal budget which limits us to apply it to back-end process of devices.
Here we show a low temperature (< 420°C) plasma-enhanced CVD to fabricate graphene [1] in a short time(~15 mins). After we adjusted each parameter, Optical Microscope, Scanning Electronic Microscope and Raman spectrum were used to examine the quality of graphene film, to ensure its high quality. Subsequently, we transferred it onto Silicon Dioxide substrate and ODTS substrate to fabricate Graphene Field Effect Transistor(GFET), in order to extract the carrier mobility of it. We also compared the result with the GFET made of commercial-graphene. For the result, we successfully get a piece of good quality single layer graphene with high uniformity, few defects, and room temperature carrier mobility up to 1.6×10⁴ cm² /V×s, better than the commercial-graphene made by thermal CVD.
Additionally, for the investigation on contact resistance, we used Transfer Length Method(TLM) and, subsequently, compared our graphene with the thermal CVD graphene. We also analyzed the interaction between graphene and metal electrodes by X-ray Photoelectron Spectroscopy and Ultraviolet Photoelectron Spectroscopy. From our previous work[2], we showed that the contact resistance of graphene will depend on the contacted metal. Nevertheless, we did show that when we use same metal, the contact resistance of our graphene is much lower than that of thermal CVD graphene.

[1] “Single-step deposition of high mobility graphene at reduced temperatures”, D.A. Boyd, W.H. Lin, C.-C. Hsu, M.L. Teague, C.C. Chen, Y.Y. Lo, W.Y. Chan, W.B. Su, T.C. Cheng, C.S. Chang, C.I. Wu & N.C. Yeh, Nat. Communication 6, 6620–6627 (2015)
[2] Kuo-You Huang, Chia-Shuo Li, Luo-HongWen, Ang-ShengChou, Mon-Shu Ho and Chih-I Wu. (2017). Investigating and optimizing charge transfer between graphene and metal by using double layer electrode and polymer-free transfer method. Mater. Res. Express 4.

Two-dimensional (2D) metallic transition metal dichalcogenides (MTMDs) have recently emerged as a new class of materials for the engineering of novel electronic phases, 2D superconductors, magnets, as well as novel electronic applications. However, the mechanical exfoliation route is predominantly used to obtain such metallic 2D flakes, the batch production remains challenging. Herein, we report the van der Waals epitaxial growth of monocrystalline, 1T-phase, few-layer metallic VSe₂ nanosheets on an atomically flat mica substrate via a "one-step" chemical vapor deposition (CVD) method. The thickness of the VSe₂ nanosheets is precisely tuned from several nanometers to several tenths nanometers. More significantly, the 2D VSe₂ single crystals are found to present excellent metallic feature, as evidenced by an extra-high electrical conductivity of up to 10⁶ S m^-1, 1-4 orders of magnitude higher than that of various conductive 2D materials. The thickness-dependent CDW phase transitions are also examined through low-temperature transport measurements, which reveal that the synthesized 2D metallic 1T-VSe₂ nanosheets should serve as good research platforms for the detecting novel many-body states. The present results open a new path for the synthesis and property investigations of nanoscale-thickness 2D MTMDs crystals.
Reference
1. Zhepeng Zhang, Yanfeng Zhang*, et al., Adv. Mater. 2017, 29, 1702359.
2. Zhepeng Zhang, Yanfeng Zhang*, et al., ACS Nano, 2017, 11, 4328.
3. Jianping Shi, Yanfeng Zhang*, et al., Nature Commun. 2017, 8, 958.

Hexagonal boron nitride nanosheets (BNNSs) is the isoelectric analogue of graphene. Compared with graphene, BNNSs has many peculiar properties, including high temperature stability, broad bandgap, anti-oxidation ability,corrosion-resisitant and so on. These unique features lead to BNNSs having a promising application, such as semiconductor devices working at high temperature, composite material with high thermal conductivity, optical and electronic materials and so on. However, it is hard to exfoliate hexagonal boron nitrde (h-BN) by the traditonnal methods like graphite, as the bonding between neighboring boron nitrde layers is stronger than the weak Van der Waals force between grapheme layers. In this paper, the liquid phase stripping boron nitride nanotubes preparation were studied. Mainly through the comparative study, the best BN: NaF ratio was determined, and heat treatment and powder and ultrasonic assisted intercalation, can promote the stripping of h-BN. By these way, the best liquid stripping process of boron nitride was confirmed.

Single layer graphene and few layer graphene have numerous scientific and technological breakthroughs for various nano-device applications. Manipulation of pristine graphene, however, is challenging since van der Waals energy stored in π–π stacked graphenes within a graphite crystal is relatively huge, which make graphene insoluble in water and organic solvents. Subsequently, extensive studies have been done on functionalization on the numerous defect sites and various oxygenated groups on graphene oxide (GO) or reduced graphene oxide (rGO). Due to the highly uncontrollable degraded carbon, GO/rGO has been limited into high performance materials. Thus, a synthetic method for graphene with controllable functional groups is extremely attractive. Here, we show a new method for breaking a wide area network of van der Waals coupling between graphene galleries. A new Hyperstage-1 graphite intercalation compound (GIC) is electrochemically activated and undergoes spontaneous exfoliation when reacted with diazonium ions to produce soluble graphenes with high functionalization densities of one pendant aromatic ring for every 12 graphene carbons. Significantly, the atomic force microscopy (AFM) profile reveals two distinct thicknesses of 2.4 and 4.4 nm. These heights correspond to two-sided functionalized single and double layer graphene structures and suggests that our method specifically produces dominantly single/double layer exfoliations. Critical to achieving high functionalization density is the Hyperstage-1 GIC state, are a weakening of the van der Waals coupling between adjacent graphene layers, and the ability of reactants to diffuse into the disordered intercalate phase between the layers. Functionalized graphene can be formed graphene composite through Meisenheimer complex formation. The formation of a Meisenheimer graphene complex has utility for creating new forms of functional graphenes.

Similar with graphene, currently two dimensional (2D) boron nitride (BN) nanosheets, consisting of a few layers of hexagonal boron and nitride planes, are of particularly research interest. Since this nanomaterial possesses electrical-insulating property, good chemical inertness, high thermal conductivity and stability.¹ So far, BN nanosheets have been widely applied to environmental, electronic packaging and lubrication industry.^2,3,4 Nevertheless, as inorganic ceramic materials, pure BN nanosheets membrane is brittle and fragile, which limits their further applications. To satisfy the mechanical performance, BN nanosheets based composite membranes are therefore fabricated. For trapping the emulsified oils and organic molecules, novel porous BN nanosheets/ polyvinylidene fluoride (PVDF) ultrafiltration composite membranes are reported.⁵ The membranes are whitish and thin with porous BN network incorporating into the PVDF chains. Meanwhile, the PVDF serves as the binder and adheres the BN nanosheets firmly, thereby improving the mechanical performance. Owing to the hydrophobicity for both BN and PVDF, the membranes are efficient to separate organic moiety or oil from water. However, in most cases, the BN nanosheets could not be well dispersed in the polymer due to the poor affinity, which results in agglomeration and affects the final properties. In terms of that, amino group functionalized BN (FBN) nanosheets are rationally designed.⁶ The FBN is highly hydrophilic with impressive water concentration (30 mg ml^-1). Moreover, it could be mixed with some water-soluble polymers such as polyvinyl alcohol (PVA) and poly (diallyl dimethyl ammonium chloride) (PDDA) at arbitrary ratios without precipitation, implying the super compatibility. By facile vacuum-assisted filtration of the aqueous mixture, the freestanding FBN based composite membranes are successfully weaved with layer by layer laminate nanostructures. The films show good flexibility and toughness, which could be folded and rolled for more than 100 times. More importantly, extra-high thermal conductivity (212.8 W m^-1 K^-1) and pronounced fire-retardancy capacity are obtained, which are promising for light-weight, soft thermal management materials.
1 W. Lei, D. Portehault, D. Liu, S. Qin, Y. Chen, Nat. Commun. 2013, 4, 1777.
2 D. Liu, W. Lei, S. Qin, Y. Chen, Sci. rep. 2014, 4, 4453.
3 W. Lei, D. Liu and Y. Chen, Adv. Mater. Interfaces 2015, 2, 1400529.
4 D. Liu, W. Lei, S. Qin, K. D. Klika,Y. Chen, Phys. Chem. Chem. Phys. 2016, 18, 84-88
5 D. Liu, L. He, W. Lei, K. D. Klika, L. Kong, Y. Chen, Adv. Mater. Interfaces 2015, 2, 1500228.
6 W. Lei, V. Mochalin, D. Liu, S. Qin, Y. Gogotsi, Y.Chen, Nat. Commun. 2015, 6, 8849.

Integrating functionalized 2D materials into multilayer device architectures increasingly requires an understanding of the behavior of noncovalently adsorbed ligands during solution and thermal processing conditions. One common functionalization approach involves assembly of alkynoic acids with an internal diyne on HOPG or graphene, forming a lying down phase monolayer in epitaxy with the substrate, that can then be photopolymerized to enhance robustness. Using a combination of contact angle titrations and molecular dynamics simulations, we demonstrate that headgroup dynamics and tail-substrate interactions can be altered by changing the position of the internal diyne or the length of the fatty acid, thereby modulating wettability of the 2D material. Molecules with short chain segments proximal to the carboxylic acid head undergo significant dynamics after polymerization, allowing the headgroups to interact more readily with solvents and increasing hydrophilicity. For specific terminal alkyl segment lengths, we instead observed a decrease in hydrophilicity of the monolayer post-polymerization, suggesting chain-length specific differences in the polymerization. Together, these observations enable us to selectively control the surface chemistry of the 2D material to create desired interactions with the environment.

In this work we start with the Hummers technique in order to obtain Graphite Oxide, once that we obtained a black paste, then we perform a heat treatment using a conventional microwave, the result is a black dust called Graphene Oxide Reduced (GOR), we realize diferents probes of caracterization like as, SEM, AFM anf FTIR, our results are compatible with those reported in the literatura. GOR is perhaps the least known of the carbón family, however its has a wide variety of properties due it has hydroxyl and carboxyl functional groups, making it a stable material for example in water or etanol, so this solution allows the addition of other particles, for example TiO₂, at diferent concentrations, the results shows that small spheres of TiO₂ have been embedded in the graphene oxide reduced in a molecular level, in the same way we add micro spheres of SiO₂ over GOR, a SEM analysis shows that the micro spheres of SiO₂ have been embedded in GOR, the following is to study this mixture GOR/TiO₂ and GOR/SiO₂ with potencial aplications in field of healthcare, cosmetics, optics and electronics.

Structured surfaces are attractive in various applications including stretchable electronics, photonics, wettability control, micro-fluidic devices, cell-based biosensors. They also have been used to measure the mechanical properties of thin films and to manufacture optical components such as diffraction gratings and optical diffusers. Various techniques have been employed for the fabrication of micro- and nano-structures on solid substrates, such as colloidal lithography, surface relief grating, electro spinning, or nano-imprinting. Especially, complex patterns with gradients of amplitudes and tailor-made geometries have remained a challenge.
Here, we describe a simple approach to fabricate periodic structure based on liquid crystalline (LC) monomer having reactive mesogenic group through utilizing surface modifications of plasma treatment in micro-scale. Upon curing using the plasma, the liquid LC monomer develops a depth-wise gradient in degree of cross-linking or solidification. Also, we are proposing an alternative and simple method for the formation of an anisotropic pattern through utilizing anisotropic nature of molecularly aligned LC in two-dimensional space. The proposed methods enable the pattern formation of well-aligned one- or two-dimensionally periodic micro-structures over the large area, without the additional template or patterning steps.

The notion of Nature-inspired materials is known for hundreds of years, but the challenges for transition from the replication of some geometrical parameters to purpose-driven biomimetic materials design become fully appreciated only recently. The first challenge is the ’coherent’ engineering of materials at multiple of scales spanning ten orders of dimensional organization from Ångströms to meters. The second one is simultaneous optimization of 10-15 or more materials characteristics with many of them mutually contrarian. The third one is the need to produce and integrate the optimized material into devices. This talk will cover experiment, theory, and simulations of layered graphene/graphene oxide composites that addreess these challenges.

Formation of nanocomposites with ordered layered architectures from graphene and its oxides using layer-by-layer assembly (LBL) provided the first example of self-organization that led to well-known advancements in different fields of technology. Self-assembly of anisotropic platelet-like nanoparticles of graphene afford scalable manufacturing of high performance composites for different applications. Advances in the computational description of layered biomimetic composites afford now ab ovo design and their direct synthesis using LBL and similar approaches.
Optimization of multiple parameters also required the development of new methods to combine contrarian properties in one material. Such conflicting but much needed properties are exemplified by transparency and conductivity, high strain and stiffness or high temperature resilience and elasticity. Understanding the architechture of natural materials and the role of interfaces in nanocomposite design affords new biomimetic composites with previously unknown combination of properties. The concept of kirigami composites provides a new toolbox to resolve the fundamental challenges related to multiscale structural optimization, parameter optimization, and device integration. Kirigami composites from graphene enable thermally-resistant conductors with unprecedented strains that can be used in plasma devices. Futhermore, the conductance of such layered composites become indepeendent on strain which is essential for most flexible electronic and electrooptical devices. The simplicity of computatinal design of kirigami composites with desirable properties will be highlighted. The pathway to integration of biomimetic graphene nanocomposites into the devices will be demonstrated by incorporation of ultrastrong graphene oxide kirigami sheets in the beam steeres.

Chirality is one of the essential properties of materials in Nature. Nanocarbon nanocomposites incorporating chiral multiscale structures will be demonstrated; their mechanical and optical properties will be described from experimental and computational stand points. Their integration in reconfigurable devices will be exemplified by chiroptical devices for beam steering, polarization modulation and photonics.

Graphene, the unique ultrathin 2D carbon sheet, has exceptional mechanical and electrical properties that promote it to be a promising material in multiple applications. However, to translate these properties into macroscopic materials is a challenge.
In this speech, I will present developments of the assembling of graphene oxide liquid crystal into macroscopic materials and their applications. First of all, we discovered that graphene oxide (GO) can form liquid crystals in water and polar organic solvents, and the mesophases can be nematic, lamellar, and chiral. Second, utilizing this liquid crystal feature, we invented macroscopic graphene fibers, films, foams and non-woven fabrics (F4) by wet-spinning assembly methodology. They showed high tensile strength, Young’s modulus, high electronic conductivity and thermal conductivity, which are useful in many applications such as flexible supercapacitors and light weight cables. Lastly, we demonstrated that these flexible and robust graphene macroscopic materials can be used as cathode for fabrication of high performance Al-ion batteries.

Chemical functionalisation is critical to a wide range of nanocarbon technologies, but needs to be versatile and applicable at scale. Existing approaches tend to rely on liquid phase reactions, often requiring damaging sonication or lengthy work up through filtration or centrifugation. The formation of individualized functionalised single wall nanotubes (SWNTs) and graphenes is a particular challenge.
One approach is to shift the modification reaction into the gas phase. We have developed a generic, scalable furnace treatment, based on the thermochemical activation followed by reaction with functional organic monomers. This approach allows the introduction of a wide variety of functional groups whilst maintaining the excellent properties of the untreated materials. The reaction is extremely versatile and can be carried out with a variety of monomers and carbon-based materials. Water dispersible materials with cationic, anionic, and non-ionic surface functionalities provide simple processing routes to a range of applications, and are particularly well suited to studying biological interactions, including with lung epithelial cells and macrophages, as well as microglial cells.
A different approach to nanotube processing, relies on reductive charging. Pure nanotubides (nanotube anions) and graphenides can be redissolved, purified, or optionally functionalised, whist avoiding the damage typically associated with sonication and oxidation based processing. The resulting nanocarbon ions can be readily chemically grafted for a variety of applications, depending on the reagent, charge density, and ionic concentration in the reaction medium. The nature of the reactivity of charged nanotubides/graphenides is unusual, due to the continuum density of states of these otherwise molecularly discrete species. Interestingly, the chemical charging agent can be avoided by a pure electrochemical process that yields both nanotube anions and cations, suitable for purification, functionalization, or electrodeposition. In all these charged systems, the optimal absolute charge concentration has been found to correlate consistently and systematically with the efficiency of individualisation, subsequent functionalization, and the properties of constructs. Dispersed nanocarbon related materials can be assembled, by electrophoresis, cryogel formation, or direct cross-linking to form reinforced fibres, Joule heatable networks, protein nucleants, supercapacitor electrodes, and catalyst supports, particularly suited to combination with other 2d materials, such as layered double hydroxides. Comparative studies allow the response of nanocarbons with different dimensionalities to be assessed to identify fundamental trends and the most appropriate form for specific situations.

The family of 2D transition metal carbides and nitrides (MXenes) has been expanding rapidly with about 30 different MXenes synthesized to date, such as Ti₂C, Ti₃C₂, Nb₂C, V₂C, Mo₂C, Mo₂TiC₂, and Nb₄C₃, and several more theoretically predicted.¹ Because of the wet etching synthesis methods, all of the MXenes reported so far have surface functionalities, such as hydroxyl, fluorine, and oxygen, which add hydrophilicity to their surfaces. In addition to water, MXenes can be dispersed in a variety of organic solvents, expanding the possible MXene processing techniques, for example printing, spray and spin coating as well as fabricating hydrogels, and ionogels.^2,3 Due to the solution-based processing of MXenes, they are ready to be mixed with other nanomaterials and polymers to form nanocomposites.⁴ Additionally, MXene surfaces are shown to induce oxidant-free in-situ polymerization when mixed with different polymers such as pyrrole and EDOT.⁵ In this talk, we will present the processing of MXene solutions and discuss their nanocomposites with different polymers and nanomaterials.

References
1. Anasori, B.; Lukatskaya, M. R.; Gogotsi, Y. Nat. Rev. Mater. 2017, 2, 16098.
2. Maleski, K.; Mochalin, V. N.; Gogotsi, Y. Chem. Mater. 2017, 29, 1632-1640.
3. Lukatskaya, M. R.; Kota, S.; Lin, Z.; Zhao, M.-Q.; Shpigel, N.; Levi, M. D.; Halim, J.; Taberna, P.-L.; Barsoum, M. W.; Simon, P., et al. Nature Energy 2017, 6, 17105.
4. Shahzad, F.; Alhabeb, M.; Hatter, C. B.; Anasori, B.; Hong, S. M.; Koo, C. M.; Gogotsi, Y. Science 2016, 353, 1137-1140.
5. Boota, M.; Anasori, B.; Voigt, C.; Zhao, M.-Q.; Barsoum, M. W.; Gogotsi, Y. Adv. Mater. 2016, 28, 1517-1522.

Graphene fiber (GF) is a well-aligned assembly of graphene sheets. Research on GF based micro-supercapacitors have tremendously advanced in recent years by incorporating functional materials such as CNT, activated carbon, pseudo capacitive inorganic moieties, and conducting polymers which were demonstrated to improve the capacitive energy storage performance. Yet, there is room for improvement as desirable performance for real world electronic application is still very high. We report graphene@polymer core−shell fibers (G@PFs) composed of N and Cu codoped porous graphene fiber cores uniformly coated with semiconducting polymer shell layers with superb electrochemical characteristics. Aqueous/organic interface-confined polymerization method produced robust highly crystalline uniform semiconducting polymer shells with high electrical conductivity and redox activity. When the resultant core−shell fibers are utilized for fiber supercapacitor application, high areal/volume capacitance and energy densities are attained along with long-term cycle stability. Desirable combination of mechanical flexibility, electrochemical properties, and facile process scalability makes our G@PFs particularly promising for portable and wearable electronics .

Upon their introduction, certain classes of nanomaterials such as carbon nanotubes (CNTs) and graphene appeared completely disjointed from the area of soft matter—in part because forming stable fluid phases with such materials appeared nearly impossible. In this talk, I will discuss the importance of classical soft matter physics in the development of high-performance CNT materials. I will describe how classical concepts from colloids and polymer science, such as intrinsic viscosity, persistence length, liquid crystalline phase transitions, are key to understanding and controlling CNT fluid phases, and how this degree of control is now yielding a new class of soft materials that combines the most attractive traits of polymers (mechanical softness, easy flow processing) with the properties of conductors and semiconductors, that had remained so far elusive. I will discuss how these advances on controlling CNT phases have allowed rapid progress on the understanding and processing of graphene and graphene oxide. Finally, I will offer my perspective on the advantages and disadvantages of two-dimensional vs. one-dimensional building blocks for multifunctional nanomaterials.

Macroscopic graphene structures such as graphene papers and fibers can be manufactured from individual 2D graphene oxide sheets by fluidics-enabled assembly followed by high temperature carbonization and graphitization. However, challenges exist to achieve high thermal-mechanical and electrical properties due to non-optimized microstructures and morphology. Here, we report the fabrication of highly thermally/electrically conductive and mechanically strong graphene fibers with a unique inner fiber structure, consisting of large-sized graphene sheets forming a highly ordered fiber arrangement intercalated with small-sized graphene sheets filling the space/micro-voids. The graphene fibers exhibited a sub-micron crystallite domain size through high temperature treatment, achieving an enhanced thermal conductivity up to 1290 Wm^-1K^-1, outperforming the best carbon fibers.
In addition, multiscale graphene structures with tunable graphene sheet alignment and orientation order are achieved by microfluidics design with strong size and geometry confinements and varied flow patterns. The microfluidics-enabled control of orientation order and microstructure accompanied with superior thermal-mechanical properties may enable their immense potentials in diverse technological applications, including thermal managements for effective heat transfer and reinforced fillers in structural composites.

The lyotropic liquid crystal formation of GO was first reported by Kim et al [1], but the concentration of the liquid crystal was relatively lower (<1 wt. %) and also the reported fiber spinning rate from the solution was lower (2m/min).
The ultimate goal of this study is to prepare highly ordered GO-mesophase carbon fiber through melt spinning process at higher spinning rate and also to achieve homogeneous dispersion of high concentration of GO in aromatic hydrocarbon through introduction of π-π’ interactions among aromatic hydrocarbons and GO.
In this study we have successfully prepared highly ordered GO- mesophase carbon fiber with GO 10wt% at a high spinning rate of 350 m/min. GO was first physically mixed in meso-phase pitch by using mortar and later the fiber was produced using melt spinning process. The spinning rate of the GO- mesophase pitch based carbon fiber is sensitive of the oxygen content present in GO. In order to achieve superior spinnability, the GO used in our experiment was tuned by microwave treatment at certain time and power.
The structure of the melt spun fiber etched by quinoline and THF solution were investigated by SEM analysis. Etching was done in order to confirm the dispersion of GO inside the fiber.

Reference
[1] Sang Ouk Kim et al, Graphene Oxide Liquid Crystals, Angew. Chem. Int. Ed. 2011, 50, 3043 –3047.

Liquid photonic crystal can be manipulated by applying external stimuli, which provides promising pathway for its applications in electro-optical devices, sensors, and displays. To date, most of photonic crystal colloid has been obtained by dispersing spherical nanoparticles in solvents. In the spherical colloids, the mean distance among spherical particles is the only parameter to achieve the controllable photonic crystallinity, and for the purpose, swelling/deswelling or concentration change is commonly used. Recently, another type of photonic crystal colloids using two-dimensional (2D) particles have been introduced. In these materials, not only the mean distance between particles but also the rotational ordering of particles can be controlled independently, that is, both the positional order and orientational order of particles are controlled to manipulate the photonic crystallinity in 2D colloids. In this presentation, we will introduce several new 2D colloids exhibiting abundant novel phenomena including controllable photonic crystallinity. In particular, we will demonstrate that the structural color reflection in 2D photonic crystal colloids can be electrically manipulated via three different physical mechanisms: the dielectrophoretic density modulation, the rotational manipulation of particles using the anisotropy in Maxwell-Wagner polarization, and electric field-induced anomalous orientation of 2D particles. The distinctive behaviors and features in each mechanism will be discussed. Differently from spherical colloids, not only the reflection peak wavelength but also the reflectance is electrically tuned, which is required to accomplish the full color and full gray scale display applications. We also demonstrate that the field-induced particle ordering structure is sustained even after turning off the signal, resulting in multi-stable photonic crystalline reflectance. Using the property, one can make a low-power reflective display with non-volatile images without power.

Batteries and supercapacitors, are required not only to be lighter and faster, which nanotechnology have done very well, but also to be smaller, that is, storing more energy in a limited space, which the present nanotechnology rarely do well. Graphene goes the same way as other nanomaterials and has been widely investigated as the electrode for supercapacitors to make the devices “lighter” and “faster”, which is, unfortunately, hardly converted into a real commercial application considering its cost-effectiveness vs. traditional activated carbon-based supercapacitors. In recent years, our group restarted our study on graphene supercapacitors highlighting its role as an ideal remedy for low volumetric performance of the traditional carbon-based capacitors (due to the low density of carbons). That is, we have been devoting to making carbon-based supercapacitors “smaller” through dense assembly of graphene units. We have proposed a general strategy, namely nano-densification of networked graphene by interfacial capillary shrinkage, for producing dense carbon- or carbon caged-electrodes towards high volumetric performance energy storage. In this talk, we will present strategies, methods, materials, electrodes and devices for producing high volumetric performance energy storage devices and give typical examples including electrode and device constructions in supercapacitors, lithium ion batteries and post-lithium ion batteries.

High dielectric permittivity and electromechanical coupling are critical to store and convert electrical and mechanical energy in various applications of electrostrictive polymers. We report a giant electrostriction effect in liquid crystalline graphene doped elastomers. The materials are formulated by an original phase transfer method which allows the stabilization of graphene oxide monolayers in non-polar solvents. It is shown that liquid crystal transition leads to an increased percolation threshold associated to an enhancement of permittivity. Dielectric spectroscopy is combined with tensile deformations to measure the true electrostriction coefficients with differentiating the Maxwell stress effect. Because of their unique liquid crystal structure, the resultant composites show a giant electrostriction coefficient (M~10^-14 m²/V² at 0.1 Hz) coupled with good reproducibility during cycles at high deformation rates. This work offers a promising pathway to design novel high performance electrostrictive polymer composites as well as to provide insights into mechanisms of true electrostriction in electrically heterogeneous systems.

Ref. Yuan, J et al. (2015) Graphene liquid crystal retarded percolation for new high-k materials. Nature Communications.

2D materials have exciting prospects for chemical sensing devices due to their exceptional electrical, mechanical, and surface properties. Large surface-to-volume ratio of the 2D materials leads to dense number of adsorption sites, and the customized sensing channel with appropriate band gap can be easily realized by tuning the number of the layers in the 2D materials. Also, these materials have various active sties for selective molecular adsorption including vacancy, edge, basal planes, and defects. In addition, 2D materials can be operated in room temperature, which is impossible in metal oxide based semiconductors. Various 2D materials, which include graphene, transition metal dichalcogenides (TMDs), boron/carbon nitride and MXene, have been suggested as potential chemical sensing materials. Each material has its own advantages onto target molecules depending on their band gap opening status, molecular adsorption energy, and physical properties. For examples, graphene and reduced graphene oxide (rGO) possess low signal-to-noise level and stable response to target analytes, which arise from high electrical conductivity of semi-metallic channel characteristics. Also, graphene has high charge carrier mobility at room temperature and strong mechanical stability, which is critical to practical chemical sensing applications. On the other hand, TMDs such as MoS₂ or WS₂ are layer dependent semiconducting materials, which can be fabricated into highly sensitive and user-defined sensing circuits with mono to few layers. Further surface functionalization and defect engineering such as exposure of edge sites of TMDs, ligand conjugation, chemical doping, and molecular physisorption can improve chemical sensing performance and lead to easy modulation of response onto target. Recently, it is demonstrated that black phosphorus (BP), a new emerging class of 2D materials can show both high sensitivity and selectivity onto paramagnetic molecules. In this talk, we present precise comparison study of sensing performance of each 2D materials including rGO, MoS₂, and BP. In addition, based on discovered basic characteristics of each materials, we show how we can efficiently enhance their sensitivity and selectivity: via alignment control and chemical doping status. These studies are expected to elucidate the key morphological, materials, and chemical factors that govern the sensing performance of 2D materials. The chemical sensing ability of MXene is also discussed.

Graphene oxide (GO) is intermediate in the process making graphene, GO can be synthesized by slight modification to Hummers method. The reduction product (rGO) is falsely similar to the graphene. GO is single discrete sheets, and can be considered as oxidized form of graphene containing various carbonaceous functional groups. The polar oxygen atoms show strong affinity for incoming a variety of cations even proton. The negative GO nanosheets show strong electrostatic attraction toward positively charged metal ions to form GO-metal complexes. These complexes undergo reduction accompanied by shifting of some oxygen atom from GO precursor to metal ions and rGO-metal oxide hybrid is formed finally. Furthermore, GO has many epoxy group (C-O-C), the groups can make a bond with amine groups. Therefore, a various of GO hybrids, not only GO-metal hybrids but also GO-organic, metal complex and so on hybrids, can be produced. After reduction of GO hybrids, rGO-hybrids also can be produced. We have aimed at developing multi-functional materials synchronizing both GO / rGO and metal complex properties.

Recent advances in the ability to to synthesize metal-ion coagulated graphene oxide (GO) colloidal dispersions has provided new avenues for fabrication of GO and reduced graphene oxide (rGO) based thin films and membranes for applications as mechanically robust coatings as well as anti-corrosive protective layers. To this end, a fundamental study on the interplay between composition, thermal stability and mechanical properties of metal-GO as well as metal- rGO thin films was carried out employing multiscale models that couple molecular dynamics simulations in conjunction with mesoscale techniques such as finite element methods (FEM) and peridynamics (PD). Transition metals such as iron, vanadium and nickel were considered in this study. The investigations reveal that for a given concentration of metal ions, iron containing GO and rGO films demonstrate higher elastic modulus as well as a marked increase in tensile and shear strength, whereas incorporation of nickel and vanadium ions lead to a decrease in mechanical strength of the resulting GO/rGO films. Furthermore, the degree of orientation mismatch between neighboring GO/rGO grains was shown to have a significant effect on the tensile strength, implying a crucial role of the interfacial structure on the mechanical response of the thin films. Valuable lessons learned from this work provide important insights into the design and development of GO and rGO films for targeted mechanical and chemical applications.

Since the isolation of monolayer of graphene,(1) two-dimensional (2D) materials have attracted significant interest due to their exceptional properties and widespread range of applications. Among several existing 2D materials, a family of 2D transitional metal-based carbides and nitrides, known as MXenes (2). The MXene family has been growing and there are already more than 20 synthesized members (3). The interest in the MXenes originates from their metallic conductivity and hydrophilicity of functionalized surface.
Here, we report on a scalable synthesis and processing of titanium-based carbide and carbonitrides MXenes (Ti₂C, Ti₃C₂, and Ti₃CN) made using minimally intensive layer delamination (MILD) approach. Up to 100 g of MXenes can be synthesized per single batch and can be processable into a liter-size and surfactant-free aqueous colloidal solution containing large flakes from 1-10 µm in lateral size. Moreover, these colloidal solutions can be processed into flexible MXene papers with high electrical conductivity (~ 10,000 S/cm for Ti₃C₂). The MILD synthesis approach improves the quality of MXenes, efficiency of the current synthesis methods, and scalability in production.




References:
1. K. S. Novoselov et al., Electric field effect in atomically thin carbon films. Science 306, 666-669 (2004).
2. B. Anasori, M. R. Lukatskaya, Y. Gogotsi, 2D metal carbides and nitrides (MXenes) for energy storage. Nat. Rev. Mate. 2, 16098 (2017).
3. M. Alhabeb et al., Guidelines for Synthesis and Processing of Two-Dimensional Titanium Carbide (Ti3C2Tx MXene). Chem. of Mate. 29, 7633-7644 (2017).

Graphene oxide has become one of the most widely used 2D materials, not only for use as a solution-processable precursor to graphene but also due to its own unique properties, such as its liquid crystalline behavior. Graphene oxide exhibits high colloidal stability in aqueous environments, and under specific temperature and concentration conditions, can spontaneously align via liquid crystallinity. However, graphene oxide continuously undergoes chemical transformation in water due to water’s nucleophilic nature, thus losing its unique properties over time, as demonstrated recently by Dimiev et al. The step usually taken to remediate this in experiments is to synthesize a fresh batch, which is time-consuming and futile because the fresh batch also goes through the same chemical transformation as soon as water is introduced during the washing process. In this work, we study the physical and chemical stability of graphene oxide in simple alcohol-based solvents. We demonstrate several unique phenomena that make a subset of these solvents ideal for processing. X-ray diffraction carried out on concentrated slurries of graphene oxide in the alcohol dispersions indicate that they form crystalline domains of alternating graphene oxide and oriented 1-alcohol layers. This and their colloidal stability suggest that alcohol acts as a strong steric stabilizer preventing restacking. In addition, chemical degradation is slowed or inhibited for longer-chain water-immiscible alcohols. We demonstrate that these attributes allow us to process graphene oxide dispersions in water-immiscible solvents for the high yield transfer of graphene oxide monolayers as Langmuir-Blodgett films. Furthermore, the ability to retain a high oxidation degree enables higher flux membranes for water desalination. These membranes from the graphene oxide alcohol dispersions demonstrate fluxes of 14.3 L/m²h at 35 °C while maintaining NaCl salt rejection at >99.8%.

Discotic liquid crystalline property of Graphene Oxide (GO) in colloidal foam has gained considerable interest. Small flake size of GO can limit the mechanical and electrical properties of GO-based materials. Also broad size and shape distribution of sonochemically exfoliated GO from graphite is also an unfortunate case.
Here, we have exploited liquid crystallinity and investigated the size-dependent N-doping and oxygen reduction catalysis, after introduction of facile size selection of large-size GO. Spontaneous concentration of large-size GO flakes (>20 μm) are observed within the liquid crystalline phase in biphasic GO dispersion. Dependency of N-dopant type on GO flake size is also observed with quaternary N-doping dominating in large-size GO. The lowest onset potential (-0.08 V) for oxygen reduction is also demonstrated by large-size GO as quaternary N-dopants serve as principal catalytic sites

A key part of efforts to tune the chemical, electrical, and optical properties of graphene oxide (GO) is the need to accurately characterize GO’s complex structure. Raman spectroscopy and confocal Raman mapping are widely used for insight into the size of GO’s nanoscale graphene-like domains, the degree of lattice order, and sheet stacking structure. It has also been shown, however, that GO can be intentionally modified by laser sources similar to those used for Raman spectroscopy. The extent to which GO is modified under typical Raman measurement conditions has not previously been studied, making it unclear how reliable published Raman data is.
In this presentation, we will discuss the effects of Raman laser exposure on GO structure and recommend protocols for accurate Raman characterization of GO. We exposed GO to laser doses spanning over four orders of magnitude. Subsequent Raman spectroscopy (performed using minimally invasive conditions), X-ray photoelectron spectroscopy, and atomic force microscopy revealed that GO reduction occurs at all laser intensities that are practical for Raman characterization, with the degree of reduction increasing with laser dose. At higher laser doses, GO was ablated, resulting in significant material loss. These sample modifications can lead to erroneous Raman data. For example, Raman metrics, such as the 2D- to G-band intensity ratio, can drop by as much as 50% during acquisition at a high laser dose. To minimize the physical damage that takes place in GO during Raman spectroscopy, and obtain data that is representative of unmodified GO, we encourage the use of a minimal laser dose (8 x 10⁷ J/m² or below), despite the loss in signal. In other words, reliable measurements can be obtained when sample integrity is prioritized over signal intensity.

Graphene oxide paper (GOP) and its composite materials are considered as the key components for the fabrication of supercapacitors, fuel cells, Li ion batteries, chemical and biochemical sensors, UV-visible photosensors, flexible surface-enhanced Raman scattering substrates, magnetic and thermal conductive materials, nanofiltration membranes, and bactericidal agents for water disinfection, among others. Most of the applications rely upon GOP functionalized, doped or mixed with a variety of organic and inorganic compounds, including other nanomaterials. The target composite paper can be either assembled from individual chemical components, or obtained by means of functionalization of prefabricated GOP sheets. Both strategies contemplate the use of large amounts of solvents, and are time and labor-consuming.
Here we demonstrate the possibility of fast, efficient and environmentally friendly solvent-free functionalization of prefabricated free-standing graphene oxide films by using four representative amines of different structure, as well as a detailed comparative characterization of the spectral, morphological, thermal and conductivity properties of the functionalized GOP samples. We employed one monofunctional aliphatic amine (1-octadecylamine; ODA), one monofunctional aromatic amine (1-aminopyrene; AP), one bifunctional aliphatic amine (1,12-diaminododecane; DAD), and one aromatic diamine (1,5-diaminonaphthalene; DAN). Similarly to the functionalization protocol described for graphene oxide powder,¹ GOP mats were treated with amine vapors under reduced pressure at about 150 °C in the case of aliphatic amines, and about 170 °C in the case of aromatic amines. The covalently modified GOP samples were characterized by means of a variety of analytical techniques including Fourier-transform infrared and Raman spectroscopy, thermogravimetric and differential thermal analysis, scanning and transmission electron microscopy, as well as atomic force microscopy. In addition, we performed current–voltage (I-V) conductivity measurements on GOP samples before and after functionalization, and found that functionalization increases conductivity roughly by one (DAD), two (ODA), four (DAN) and six (AP) orders of magnitude.
This work was supported by the projects CONACYT-250655 and UNAM DGAPA-IN100815.
(1) N. Alzate-Carvajal, et al., RSC Adv., 6, 113596 (2016).

Graphene sheets have been recently attracted considerable attention, perhaps by the predicted excellent mechanical, structural, thermal, and electrical properties of graphite. Exfoliation of graphite oxide represents an attractive route to functionalized graphene as versatile 2D carbon nanomaterials and components of a variety of polymer nanocomposites. We obtain Reduced Graphene Oxide by chemical exfoliation and high temperature reducction, so we study the preparation method’s of nanocomposites RGO/polymer and its molecular–level dispersion of individual, chemically modified graphene oxide within polymer matrix. This particles adding interesting properties at the polymer matrix, generating nanocomposites with a wide versatility aplications in diferents fields of Engineering.

The in-situ detection of air bubbles in fluid transport lines is a significant problem in both industry and medicine. To address this challenge, we designed a microfluidic device embedded with a piezoresistive film made by evaporating metallic nanoislands on graphene. The piezoresistive film senses bubbles by measuring the change in the elastohydrodynamic deformation of the channel wall. By embedding the piezoresistive film a few microns away from the channel, we create a device that is non-contact, resistant to extreme environments (acidic, basic, turgid, etc.), and doesn’t interfere mechanically or electrically with the sample fluid. In addition to the advantages in other non-contact detectors, our sensor allows us to create a low power device with a high signal to noise ratio. We are able to detect bubbles in a fluid and report these events to a smartphone wirelessly through our battery-powered device.

2D graphene and its derivatives have been receiving increasing attention, due to its extraordinary properties, opening the window of opportunity to develop materials and devices with novel functionalities. Graphene derivatives, graphite fluoride and fluorinated graphene (GF), which exhibits excellent properties, such as extremely low surface energy, high chemical inertness and thermal stability, and it is an ideal filler material for polymer composites. But GF usually has large contact angles with most of the liquids due to its extremely low surface energy, which leads to its poor dispersion and stability in solvents and polymers. Hence, it is pivotal to study on the fabrication of high-quality GF and its dispersion in various systems.

In our research, the laminates of Carbon Fiber-Reinforced Polymer (CFRP) composites were synthesized through optimized Vacuum-Assisted Resin Transfer Molding (VARTM). In order to reduce the surface defects and the existence of pinhole phenomena, we extended our research mainly by epoxy resin modification, especially by the introduction of GF. We have explored a core dispersion technique to obtain a stable GF dispersed system. With the well dispersion of GF in epoxy resin, the liquidity of the resin was affected, which increased the wettability to fiber and lead to much less surface defects and porosity. The final CFRP composite appeared improved mechanical, hydrophobicity, sorption and corrosion property.

It is believed that this manufacturing process will be potential to mass-produce hydrophobic CFRPs with high strength and modulus. Thus, such-prepared GF can be more widely applied in biomedical, aerospace, automobile and wherever potentially graphene and 2D materials can be applied to.

Carbon composite materials have attracted wide industrial interest due to high strength, light weight, chemical resistance, long durability, and so forth. In recent decades, a lot of efforts have been made to study graphene-based composites in both academy and industry. However, the reinforcing efficiency of graphene largely depends on the effective dispersion and distribution of individual graphene sheets.
Herein, we report the synergistic enhancement in mechanical and electrical properties of graphene-based ternary composite materials in the form of films and fibers. We found that the remarkable synergistic toughening of polyimide (PI) nanocomposite films by hydrogen-bond assisted 3D network of both pyridine-functionalized reduced graphene oxide (Py-RGO) and carbon nanotubes (Py-MWCNTs). As fiber form, newly designed PI/RGO/CNT composite fibers in combination of polymer infiltration followed by photonic flash irradiation were developed. The mechanical strength, modulus, and electrical conductivity can be enhanced simultaneously by molecular-level coupling of PI/graphene with CNT fibers via photonic flash sintering. These high-performance multifunctional composites have potential applications as structural composites, multifunctional fibers, catalyst supports, energy storage materials, artificial tissue, and so on

Cost effective scalable method for uniform film formation is highly demanded for the emerging applications of 2D transition metal dichalcogenides (TMDs). We demonstrate a reliable and fast interfacial self-assembly of TMD thin films and their heterostructures. Large-area 2D TMD monolayer films are assembled at air-water interface in a few minutes by simple addition of ethyl acetate (EA) onto dilute aqueous dispersions of TMDs. Assembled TMD films can be directly transferred onto arbitrary nonplanar and flexible substrates. Precise thickness controllability of TMD thin films, which is essential for thickness-dependent applications, can be readily obtained by the number of film stacking. Most importantly, complex structures such as laterally assembled 2D heterostructures of TMDs can be assembled from mixture solution dispersions of two or more different TMDs. This unusually fast interfacial self-assembly could open up a novel applications of 2D TMD materials with precise tunability of layer number and film structures.

Recently, various studies on novel materials for transparent conductive electrodes (TCEs) such as metal meshes, metal nanowires, conductive polymers, graphene, and carbon nanotubes have been progressing actively. Among these materials, metal nanowires may have potential for flexible device applications because they can be fabricated easily by using low-cost solution-based processes. Metal nanowires, however, still have several problems to be resolved before commercialization, including a relatively high sheet resistance due to poor contacts at wire-wire junctions. Also, they have an instability problem that may lead to an increase in their electrical resistance when exposed to air for a long time due to the oxidation of metals. Therefore, decreasing the junction resistance between the metal nanowires as well as enhancing the oxidation stability may be essential for improving their performances, especially in terms of the electrical figure of merits.
In this study, we present solution processes for fabricating hybrid-type flexible copper nanowires (CuNWs) which can significantly improve their electrical properties and oxidation stability. This has been achieved by depositing CuNWs on flexible substrates via spray coating and coating the CuNWs with nickel (Ni) via electroplating. For all of the fabricated CuNWs, their surface morphologies, electric sheet resistances, visible-light transmittances and reflectances, and color properties were characterized. Furthermore, the effects of Ni coating on the wire-to-wire junction resistances of the CuNWs as well as their oxidation and corrosion stabilities were investigated.

2D soft materials, namely graphene, offer an attractive platform for hybridization with various organic materials. In particular, combination of graphene and semiconducting photosensitizers present a new area of photoactive materials for photovoltaics. Here, highly dispersible graphene was hybridized with a phthalocyanine derivative via covalent linkage to create a new type of donor-acceptor hybrid exhibiting photoinduced charge separation. Graphene is beneficial for the hybridization due to its easy functionalization and the unique electron accepting ability. A phthalocyanine (PC) derivative, pyrazine-based silicon phthalocyanine dichloride, possessing rich π-conjugated macrocycle was used for the electron donating purpose. The hybrid molecule showed a significant decrease in fluorescence of π-conjugated PC, implying an efficient photoinduced charge transfer occurring within the covalently-linked molecular structure consisting of “donor-acceptor”. The graphene-PC hybrid molecule has also been demonstrated as an active layer material in organic photovoltaic device as well. Thus our results indeed underline the efficacy of the molecular level heterojunction of the covalently linked graphene-PC molecule in a single cell and will open new opportunities ahead for active layers research to go beyond conventional bulk-heterojunction.

Here, we report an ultrafast synthesizing method for large area transparent film of assembled pristine graphene platelets at liquid surface in two-minutes. Some 2−.3 layer pristine graphene platelets temporally solvated with N-methyl-2-pyrrolidone (NMP) are assembled at the surface of a dilute aqueous suspension using an evaporation-driven Rayleigh-Taylor instability and then are driven together by Marangoni forces. At their edges, physical binding works and the platelets are fixed. Typically, 8-cm-diameter circular graphene films are grown in two minutes. After graphene films formed, the films can be transferred onto various substrates with flat or textured topologies. This interfacial assembly protocol is generally applicable to other nanomaterials, including 0D fullerene and 1D carbon nanotubes, which commonly suffer from limited solution compatibility.

Nanomaterial devices have been proposed for high performance electronics. Some interesting nanomaterials are nanocarbons such as graphene and CNT due to high mobility and unique band structure. Especially, Dirac cone band structure is of great interest to elicit new functions. This study proposes new band engineering device and fabrication process to realize low contact field-effect transistor (FET) using a unique band structure of graphene contacted to semiconducting carbon nanotube network film on Si/SiO₂ substrate. Effect of CNT/graphene junction was evaluated by comparing mobility and ON/OFF current ratio with and without graphene junctions for source and drain. Although the effect of this junction is unique and interesting phenomena, there are few researches on the junction analysis. It is found that CNT network FETs with graphene contacts show higher performance than ones without graphene.
To evaluate band engineered CNT/graphene junction, two types of devices with/without graphene junction were prepared. The mechanism to enhance the performance is due to valence band contact for p-type CNT-FET using the graphene dirac cone depending on the gate bias. Without graphene, work function of metal mainly determines the contact resistance of FET regardless state. On the other hand, having the Dirac cone band structure, by applying negative bias, Fermi level of graphene is closer to valence band of CNT, resulting in that contact resistance decreases. To realize this structure, we developed a unique fabrication process. CNT/graphene distributions were confirmed by Raman spectroscopy. By monitoring RBM peak (~160 cm^-1) for CNT network and 2D peak for graphene, it is found that the unique structure is successfully fabricated. Electrical switching characteristics with and without graphene were measured to compare the effect of graphene contacts to CNT channel. The results clearly show that FETs with graphene junction have higher on-current while off-current is almost the same level. ON/OFF current ratio extracted is ~2×10⁵ and ~10⁵ for with and without graphene junction, respectively. This difference is due to on-current difference. The mobility for CNT/graphene structure is ~1.56±0.43 cm²/Vs while the one for CNT/metal structure is ~1.09±0.22 cm²/Vs. Based on the results, by having graphene contact, the mobility was enhanced up to ~50 %, which improvement is significant for the FET applications although the base mobility of CNT-FET regardless graphene junction is still low. This result may be explained by low contact resistance between CNT and graphene compared with the one between CNT and Cr/Au as explained above. Furthermore, another possibility is the injection difference between them, which is the future topic to confirm the phenomena.
In conclusion, by proposing new structure and fabrication process, we confirmed that FET performance can be boosted up for future low power and high speed electronics.

Carbon based nanomaterials like carbon nanotubes and graphene are often regarded as one of the most promising candidates for future nanoelectronic devices. To maximize their potential capabilities, chemical modulation and property control such as doping, functionalization and unzipping of graphitic planes are essential. Among them, unzipping of carbon nanotubes is in high demand to enable customizing structures and properties for different applications. However, previous unzipping processes have been based on chemical oxidation under harsh acidic condition leading to form many defects on the graphene basal plane and degrade electrical, magnetic, and mechanical properties. Herein, we present heteroatom dopant specific unzipping reaction of carbon nanotubes without any defects via electrochemical method. The resultant nanostructures consisting of unzipped graphene nanoribbons wrapping around the carbon nanotube cores maintain the atomically crystalline graphitic structures with well-defined atomic configuration at the unzipped edges. The synergistic effects of enhanced surface area and high electrical conductivity demonstrate ultrahigh-power supercapacitor performance.

Graphene oxide liquid crystal (GOLC) made from the discotic shape anisotropy of GO is a perspective building block for highly aligned graphene based materials such as aerogel, film, and fiber. Among them, graphene fiber (GF) is suitable for the wearable architectures and devices due to their properties such as high flexibility, high electrical/thermal conductivity, freestanding, low density and good mechanical properties.
In this work, we utilized RGO fiber as efficiently electron supplier for hydrogen evolution reaction (HER). GF was spun from aqueous solution followed by chemical reduction for 1D fiber structure with high roughness. Amorphous molybdenum sulfide (MoS_x) was selected as HER catalyst, which had many unsaturated defects that could provide sufficient active sites of catalytic reaction for HER. Nevertheless, low electrical conductivity of amorphous MoS_x was a main demerit for applications. In this regard, we conducted electroplating of MoS_x at the surface of GF. Amount of electroplated MoS_x could be simply controlled by number of electrodeposition cycles at room temperature. Synergetic effect from combining high electrical conductivity and surface area of GF and high electrochemical activity of amorphous MoS_x improved properties of fabricated MoS_x/GF. The resulting MoS_x/GF exhibited lower overpotential of 229 mV at 10 mA cm^-2 and higher stability than MoS_x/ITO.

Two-dimensional layered trichalcogenides are of current research interest because of their robust opto-electronics, and thermal properties. Mechanical and phonon vibrational properties of these materials are of significant importance in the field of stress and thermal management. Here we report the pressure dependence of structural and phonon behaviors of high quality few-layers vanadium diselenide nano-sheets, grown by hydrothermal method, employing synchrotron x-rays and micro-Raman scattering techniques. The high crystalline nature of the nanosheets was examined using transmission electron microscopy. Synchrotron x-ray studies at high pressure (up to 22 GPa) using a diamond-anvil cell identify a displacive type phase transition to a low symmetry monoclinic phase (C2/m) around 7 GPa corroborated with the P-dependent Raman scattering results. Raman spectroscopic studies at high pressure (up to 34 GPa) identify two prominent Raman bands with symmetry E_g and A_1g. Upon increasing pressure E_g band at 207 cm^-1 shows normal hardening and A_1g band at 236 cm^-1softens. The first order pressure derivatives of these phonons at ambient phase (P-3m1) are found to be -3.547(2) and 0.388(6) cm^-1/ GPa, respectively. Using the experimental mode Grüneisen parameter of E_g Raman mode, the in-plane thermal expansion coefficient of the titular compound at the ambient phase is estimated. The observed results are expected to be useful in calibration and performance of next generation nano-electronics and optical devices under extreme stress conditions. These experimental results corroborated with our ab-initio calculations will be presented later.

Developing catalytic materials with high activity for oxygen reduction reaction (ORR) is of great significance for commercial fuel cell applications. Although Pt-based materials are known as the most efficient ORR catalysts, they still suffer from several serious problems, including high cost, low abundance, weak durability, crossover effect and CO poisoning; these obstacles hinder the large-scale application of fuel cells. To solve these issues, numerous efforts have been devoted to exploring metal-free or non-precious transition metal catalysts to replace Pt-based catalysts.
Here, a novel hybrid material consisting of N-doped graphene and carbon nanofibers, synthesized by electrospinning and nitrogen doping through annealing in NH₃ gas, is reported as an ORR catalyst. The film-typed material is used as the catalyst directly. The addition of graphene to the composite has significantly improved the catalytic property, which is further enhanced by nitrogen doping. The hybrid exhibits similar catalytic activity but superior stability to Pt in alkaline solution.

We introduce experimental and theoretical investigation of a new structure using graphene based schottky diode (graphene-metal-semiconductor junction) in non-enzymatic glucose sensing applications by oxidation and reduction of glucose molecules on the surface of Pt-thin film and enhancement of current in presence of graphene layers on the surface of Pt. It was noticed by increasing Pt-thickness, the higher graphene growth, the higher the output current values (15µA for 50nmPt at 10mM glucose). In addition, sensitivity of the structure was tested by varying glucose concentrations between 2-15mM. Furthermore, Electrochemical measurements demonstrated glucose molecules adsorption and desorption on the surface of the structure when prepared in phosphate buffer saline (pH=7.4). Besides, selectivity test has shown the selectivity of the structure toward glucose molecules in presence of other solutions i.e. NaCl, KCl, sucrose, Na₂SO₄, urea and H₂O₂. Theoretical modeling by using tight binding and first principles confirmed glucose molecules adsorption and diffusion through the surface of graphene and charge density due to glucose oxidation and formation of gluco-lactone molecules as noticed from density functional theory, the binding energy is -0.27 eV. Moreover, charge distribution is noticed at the interface between glucose and Pt-Graphene layers. The physisorption interaction between graphene and Pt results in shifting fermi-level position and p-doping graphene so, oxidation of glucose molecules on the surface of the structure will change the local electric field distribution and the variation in schottky barrier height (SBH) in Pt/n-Si will result in detectable current changes due to molecules adsorption. This structure can be useful in future sensing applications i.e. gas sensors and electro-chemical sensors.

The piezoelectric response of ionic solids, which is measured by the piezoelectric modulus tensor d, is driven by the redistribution of a charge on the application of stress. The soft materials possess higher piezoelectric response compared to a stiffer material with same polarization sensitivity. Motivated by the soft nature of the Van der Waals bonded quasi-2D solids, we focus our search domain into this particular family of materials for discovering new piezoelectric compounds. The quasi-2D structures are identified using an automated algorithm from a pool of 11500 structures reported in the Inorganic Crystal Structure Database (ICSD). We have identified 572 materials with d > 0.1 pC/N, out of which 192 materials have d greater than AlN, which is a common material used in high-frequency resonators. We have also found 32 new piezoelectric compounds with modulus even higher than PbTiO3, another very common piezoelectric material. Based on the predicted value of d, several candidate materials have emerged, including TaSe2, In2Se3, GeTe, Li2Mn2O4, and CuVO3, AsCuLi2, that have not been previously considered for piezoelectric applications. Our results provide guidance for future experimental efforts in regard to selecting quasi-2D materials for applications where very high piezoelectric modulus (d) is necessary.

The fabrication of three-dimensional nanostructured foams from interconnected 2D materials such as graphene, h-BN, and transition metal dichalcogenides has shown to be a promising technique to explore their properties for several applications including energy storage, gas absorption, and catalysis applications [1-3]. Making bond-like interconnections between individual nanosheets can remarkably enhance their mechanical properties. Despite all advances, the controlled design of such interconnections remains a fundamental problem for many applications of h-BN foams. In this work, we report a technique to fabricate lightweight 3D macroscopic porous structures formed from h-BN nanosheets using a scalable in-situ freeze-drying synthesis. This method allows for the creation of intermolecular bonding between h-BN layers where PVA acts as a bridge to link the individual layers, thus forming a network-like structure at the nanoscale. Unlike pristine h-BN foams, which normally disintegrate immediately once removed from a freeze-drier, our h-BN/PVA foams show a robust freestanding structure with favorable mechanical stability. A detailed molecular dynamics (MD) study further verified and provided insights on the origins of such interconnections in improving the mechanical integrity. The foam also exhibits excellent CO₂ absorption and storage under varying pressure values. The foam mechanism of CO₂ absorption was also investigated through MD simulations.

On the nanoscale, boron nitride nanotubes (BNNTs) exhibit high thermal conductivity, high electrical resistance, high tensile strength, radiation absorption, and high chemical stability to elevated temperatures. With the recent development of high-throughput synthesis techniques and significant strides being made on purification, high-throughput processing routes are needed to translate the nanoscale BNNT properties to the macroscale. This report shows that the superacid, chlorosulfonic acid (CSA), is a good solvent for BNNTs. Cryogenic transmission electron microscopy (cryo-TEM) shows that CSA overcomes the inter-BNNT attractions to separate and dissolve BNNTs, permitting detailed analysis of the as-produced material. As a solvent, CSA can be used in the purification of BNNTs and can be used to produce aerogels and all-BNNT films with controlled dimensions. For these macroscopic articles, CSA is removed by water or an organic solvent after processing. Because these macroscopic articles are not composites with a second phase, they exhibit excellent material properties including the same oxidation resistance and electrical resistance observed on the nanoscale.

To fabricate reliable and repeatable 2-dimensional material electronic devices, the 2D film needs to be passivated in a dielectric to isolate it from the surrounding atmosphere and preserve its chemical and electronic properties. Just as in the case of un-passivated 2D materials on dielectrics, the visibility of encapsulated 2D films is dependent on the dielectric properties and thicknesses and can vary drastically. The visibility of the films is important for various metrological purposes such as determining layer identification, film uniformity and quality. In this work, we discuss our method of applying a passivation layer on graphene films through a combination of e-beam evaporation Al and atomic layer deposition (ALD) of HfO₂. The visibility of the buried graphene film is then modeled under different dielectrics and thicknesses and it is shown that the visibility of the films can be controlled by careful determination of the top or bottom dielectrics. The model is shown to be in good agreement with experimental results of SiO₂/Graphene/SiO₂ stacks of varying thicknesses. For electronic device applications, this allows for the maximization of the encapsulated graphene channel’s visibility, without having to compromise the device’s gate dielectric design parameters, which are typically designed for device performance and not visibility. Thus, this allows for easier characterization or failure analysis of graphene based devices.
Sandia National Laboratories is a multi mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525

Graphene oxide (GO) is a chemically versatile atomically thin material that is interesting for a variety of applications – especially electrochemical devices such as supercapacitors and electrolyzers for catalysis. The ability to tune the chemical, electronic and atomic structures of GO via controlled reduction to obtain reduced GO (rGO) provides pathways for accessing its novel properties. Interesting chemistry can be performed on as synthesized GO using its numerous functional sites arising from the presence of epoxy, hydroxyl, carboxyl and other oxygen groups. In this presentation, I will highlight some new results on the efficient reduction of GO using microwaves. In particular, we have demonstrated that it is possible to obtain high quality graphene fibers and thin films by irradiating GO with short pulses of microwaves. I will describe the electronic, energy storage and catalytic properties of microwaved rGO.

Lightweight electromagnetic interference (EMI) shielding materials have been attracted much attention for a wide range of applications in the modern high-power electronics, portable devices, and self-driving cars, as the highly integrated and high-speed wireless communication devices suffer from undesirable electromagnetic interference effect that not only deteriorates the performance of the devices but also brings serious concern on harmful health problem to human. In this presentation, I would like to briefly demonstrate that 2D nanomaterials including sulfur-doped graphenes and transition metal carbides (MXenes) can be considered as the best candidates for lightweight EMI shielding materials, as the 2D nanomaterials are lightweight, low-cost, and easily processable shielding materials. Sulfur-doping on graphene induces strong n-doping effect that gives rise to the strong improvement in electrical conductivity. Ti3C2 MXenes are also highly metallic. The large electrical conductivity of sulfur-doped graphenes and transition metal carbides (MXenes) is responsible for the exceptional EMI SE performance.

Carbon nanomembranes (CNMs) are two-dimensional materials that are made by cross-linking self-assembled monolayers (SAMs) of aromatic molecules via low energy electron irradiation. Previous studies of the charge transport in molecular junction incorporating SAMs and CNMs of oligophenyl thiols has been carried out by using conical eutectic Gallium-Indium (EGaIn) top-electrodes¹ and conductive probe atomic force microscopy (CP-AFM)². Additional investigations of the dielectric properties of pristine SAMs and CNMs were performed by impedance spectroscopy on EGaIn tunneling junction. Here we demonstrate the fabrication and characterization of all-carbon capacitors (ACCs) composed of multilayer stacks of CNMs that are sandwiched between two graphene sheets that act as conducting electrodes. Three-layer and six-layer CNMs were used as dielectric layers between the top and bottom graphene electrodes. The junction area of the nanocapacitors ranges from 1 to 2500 µm². Whereas the use of CVD graphene grown on copper only led to small-area capacitors with low yield, the utilization of nanocrystalline (NC) graphene from annealed CNMs and the involved avoidance of copper residuals between the electrodes caused high yield of large-area capacitors with a dielectric thickness of down to 4.5 nm. The results suggest that the combination of NC graphene and CNMs as well as other 2D materials in nanoscale functional devices may provide a promising approach toward further development of molecular electronics devices.

¹ P. Penner, X. Zhang, E. Marschewski, F. Behler, P. Angelova, A. Beyer, J. Christoffers, A. Gölzhäuser, J Phys Chem C, 2014, 118, 21687.
² X. Zhang, E. Marschewski, P. Penner, A. Beyer and A. Gölzhäuser, JOURNAL OF APPLIED PHYSICS, 2017, 122, 055103.

The ability to manipulate two-dimensional electrons with external electric fields provides a route to band engineering. By imposing artificially designed and spatially periodic superlattice potentials, two-dimensional electronic properties can be further engineered beyond the constraints of naturally occurring atomic crystals [1, 2]. Recently, we reported a new approach to fabricate high mobility superlattice devices by integrating surface dielectric patterning with atomically thin van der Waals materials [3]. By separating the device assembly and superlattice fabrication processes, we addressed the intractable tradeoff between device processing and mobility degradation that constrains superlattice engineering in conventional systems.
In this talk, we will theoretically investigate the electronic band structures of graphene on patterned dielectric superlattices [3]. We will show the effects of different superlattice symmetries (square or triangular) and interaction strengths on the band structures, such as the width of bands and the size of gaps. The fundamental difference between the different superlattice symmetries becomes more evident when external magnetic fields are applied to the superlattices. We developed a general effective theoretical model of graphene superlattices under magnetic fields. The calculated fractal evolution of electron energy gap structures, aka Hofstadter’s butterfly [4], reveals the intrinsic electron-hole asymmetry in the triangular superlattices. And the non-monotonic sequence of the quantized Hall conductivity is consistent with experimental data. The research findings open a route to engineer electronic structures beyond the constraints of the intrinsic symmetry of atomic layers.
[1] L. Esaki and R. Tsu, IBM J. Res. Dev. 14, 61 (1970).
[2] D. Weiss, K. von Klitzing, K. Ploog, and G. Weimann, EPL 8, 179 (1989).
[3] C. Forsythe et al., arXiv:1710.01365 (2017).
[4] D. R. Hofstadter, Phys. Rev. B 14, 2239 (1976).

Microsupercapacitors, are a key component in on-chip technologies driving miniaturization and providing stable power supplies to electronic devices. State-of-the-art microsupercapacitors are produced in 2D electrode configurations, resulting in relatively low energy densities which have become the key limitation for these devices. Adding hierarchical 3D structure through a micron-sized electrode would provide a dramatic improvement in the power and energy stored within a single device. 3D printing provides a platform to achieve 3D architectures, and it has seen a limited development on the micron size scale. Beyond graphene, 2D materials, including the transition metal dichalcogenide (TMD) family, are exceptionally promising materials for electrochemical devices due to their intercalation capacitance, high mechanical durability, chemical stability, and edge-site density. In order to utilize these attractive properties, spatial structuring is crucial. Here we report the first 3D printed architectures via robocasting of two-dimensional atomically thin transition metal dichalcogenides (TMDs) [1] demonstrating their use as miniaturized supercapacitors. The architectures are fabricated via direct printing of a liquid ink of chemically exfoliated 2D nanosheets.
The 3D printed architectures serve as electrodes for microsupercapacitors with mm² footprints, 100μm feature size with mechanical robustness and chemical stability. They exhibit areal capacitance of 1450 mF/cm² and an exceptionally high energy density of 0.5 mWh/cm² which rivals and surpasses comparable devices. These devices and platform technologies have the potential to allow for an innovation in the emerging field of micronsized supercapacitors, enabling more efficient power sources for on-chip electronics.


References
[1] C. Grotta, et. al. "3D Printing of 2D Atomically Thin Materials", Submitted: October 2017

MXenes, comprising few atoms thick layers of transition metal carbides, nitrides, or carbonitrides are an important class of two-dimensional inorganic compounds that combine metallic conductivity of transition metal carbides and hydrophilic character owing to their hydroxyl or oxygen terminated surfaces. Typically, the accordion-like morphology in Ti₃C₂T_x MXenes obtained via hydrofluoric acid etched Ti₃AlC₂ MAX phase comprises a stack of multi-layer MXene that is terminated with various functional groups (T_x) like oxygen (O), fluorine (F), and hydroxyls (OH). To be dispersed in suspension, we carried out delamination of Ti₃C₂T_x MXene in various solvents like dimethyl sulfoxide (DMSO), tetramethylammonium hydroxide (TMAOH), N-Methyl-2-pyrrolidone (NMP) and Isopropanol (IPA). Our strategies pertaining to the structural and functional manipulation of Ti₃C₂T_x MXene based on various scalable and controllable delamination methods in correlation to their band structure vis-à-vis electrical properties at various stages of delamination will be discussed. We will also highlight our approaches on energy storage systems based on the directed hybrid of delaminated Ti₃C₂T_x MXene and various layered double hydroxides (LDHs). Our work highlights how delamination could be effectively utilized for making stable dispersions of MXenes to form various composites with LDHs and modulation of their energy storage capabilities.

A simple and effective process combining pressure and gyration has been developed to produce graphene-nanoplatelets-fibres composites using thermoplastic polyurethane (TPU) and phenolic resin (PR) polymers. Processing parameters such as rotation speed, pressure and polymer concentration had a marked influence onthe fibre diameter. Morphological, rheological, physico-chemical and thermal properties of the composite fibres were evaluated to uncover possible application areas of these products. The aim ofthe work is to develop a novel processing route to generate well dispersed polymer-graphene composite fibres which could be used in fuel cells and in electronic packaging. The pressurised gyration processing conditions, such as vessel rotating speed, working pressure and the polymer concentration used, had a significant effect on fibre diameter. FTIR and Raman spectroscopy analysis confirmed the various bonding characteristics of the hybrid composite fibre structures. Focussed ion beam milling and etching verified the effective incorporation of graphene nano platelets into the fibre composites. The well dispersed and strongly adhered graphene in the polymer matrices will contribute to a unique reinforced polymer composite for many applications. Importantly, the approach is a promising large-scale manufacturing route for producing graphene reinforced composite fibres at low cost that has been developed here.

While dried 2D materials and their use in various types of electronics devices have been intensively studied during the latest decade, the research of colloidal materials using 2D materials has relatively less studied. However, the self-assembly properties of 2D colloid has attracted increasing attention, recently. In this presentation, we will introduce new types of 2D colloid contacting titanium phosphate with various functionalization. The 2D particles are prepared in various forms such as thick disk-like 3D particles, exfoliated thin particles, monomer tethered particles, and polymer tethered particles with varying length of polymer. In addition, various solvents are used in the preparation of colloid using the nanoparticles. Since the rheological, mechanical, and self-assembly properties of 2D particles are significantly influenced by the organic materials tethered on the 2D particles, and so, the abundant different phenomena are found depending on the functionalization and solvent effect, although the core material is the same.
One of interesting subject is to use 2D colloid for liquid crystal display. Our group reported that the Kerr coefficient of graphene oxide (GO) colloid is extremely large, but due to the low concentration of GO liquid crystal, the maximum birefringence is quite low compared to conventional liquid crystals. Using thicker 2D particles, we obtain high concentration 2D colloid more than 10 wt%, which is electrically switchable. Compared to GO material, the maximum concentration is increased more than ten times.
Monomer-tethered 2D particles can enhance the colloidal stability dramatically, and no sedimentation is observed for a couple of weeks storage. Using the method, the stability of the device using 2D colloid can be significantly improved.
The photonic crystal property of polymer-tethered 2D colloid is excellent; the reflection peak is beyond 50 %, which is almost 20 times larger than that in GO photonic crystal materials. Moreover, the controllable range of spectral peak wavelength is much enlarged by controlling the length of polymer. The solvent and polymer length also influence the rheological property of 2D colloid, that is, the interparticle friction, which is an important factor for electrical switching of photonic crystal properties. The interparticle repulsion force must be optimized to achieve both the high photonic crystal reflection and the low interparticle friction.
Summarizing, the abundant material properties and the wide controllability of photonic crystal colloid using 2D titanium-based lyotropic liquid crystal material can open new possibility and pathway of these materials for electro-optical devices and display applications.

Recent demands and advances in biomedical applications drive a large amount of research to synthesize easily scalable low-density high strength and wear resistant biomaterials [1]. The chemical inertness and low density combined with high strength makes hexagonal boron nitride (h-BN) one of the promising materials for such application [2]. In this work [3], 3D h-BN interconnected with boron trioxide (B₂O₃) was prepared by easily scalable and energy efficient spark plasma sintering (SPS) process. The composite structure shows significant densification and high surface area at an extremely low SPS temperature. A high compressive strength with a reasonably good wear resistance was obtained for the composite structure. In order to understand the effect of SPS processing on the mechanical property enhancement in the h-BN/B2O3 composites, a structural model mimicking SPS process was proposed and carried out through full atomistic molecular dynamics simulations [4,5]. The efficiency of the mechanical response of the composite can be attributed to the formation of strong covalent bonds between h-BN and B₂O_3.

References
[1] D. Chakravarty, C. S. Tiwary, C. F. Woellner, S. Radhakrishnan, S. Vinod, S. Ozden, P. A. S. Autreto, S. Bhowmick, S. Asif, S. A. Mani, D. S. Galvao and P. M. Ajayan, Adv. Mater. 28, 8959 (2016).
[2] J. Yin, X. Li, J. Zhou, W. Guo, Nano Lett. 13, 3232 (2013).
[3] C. Gautam, D. Chakravarty, C. F. Woellner, V. K. Mishra, N. Ahamad, A. Gautam, S. Ozden, S. Jose, S. Biradar, R. Vajtai, R. Trivedi, C. S. Tiwary, D.S. Galvão, and P.M. Ajayan (submitted).
[4] S. Plimpton, J. Comput. Phys. 117, 1 (1995).
[5] A. C. T. van Duin, S. Dasgupta, F. Lorant, and W. A. Goddard III, J. Phys. Chem. A 105, 9396 (2001).

Graphene oxide (GO) has attracted enormous interests owing to its ease of manipulation to multi-dimensional and multi-functional materials. In particular, 1-dimensionally assembled graphene oxide fibers (GOFs) have been of great importance as a precursor for graphene or graphene-based hybrid fibers as well as multi-functional 1-D devices. During the assembly of GOFs, liquid crystalline (LC) GO colloids undergo following phase transition; LC solution-gel-solid during fiber forming process. Although the outstanding mechanical and electrical properties of graphene fibers were explored, the fundamental mechanism of the GOF assembly is still uncovered. Here, we report sequential changes in alignments of GO sheets after each phase transition, and direct control of GO sheets in GOFs. Finally, the effects of the 1-D architectures on the mechanical, electrical, and thermal properties are presented.

Graphene oxide has been an interesting topic in material field for decades, it has several similar properties to graphene, and was recently founded to have photonic crystal properties. Utilizing graphene oxide produced by modified Hummers’ method, and centrifuging methods, coloration on colloid solution of graphene oxide was observed. With the manipulation of graphene oxide concentration, the reflective photons were contained inside the visible light region. We studied the effect of concentration, method of preparation, and solvent effects on the reflective coloration of the colloid solution.

Anisotropic grain growth and anisotropic etching behavior of has been an active subject in the 2D materials research due to its importance in tuning property through controlling microstructure. Anisotropic growth is already a multi factor complicated process, while anisotropic etching would be more difficulty since the continuous 2D film formed through anisotropic or isotropic process would have different structure. It was reported before that hydrogen plays a dual role in the graphene and hBN growth process – it is required as a co-catalyst for dehydrogenization of hydrocarbon but also etches the growing crystal edges. A competition between the two defines not only the overall rate but the shapes of the individual domains. Analysis of hydrogen induced anisotropic etching can provide the necessary details and help to delineate the etching part from overall growth process.
Here we focusing on continuous anisotropic growth and etching process of hBN, and correlate the etching behavior with previous growth process.

Vertical alignment (VA) mode of liquid crystal (LC) device has many advantages of high contrast ratio and wide viewing angle, but a uniform initial arrangement of the LC molecules is necessarily required for high picture quality. In general, a polyimide alignment layer containing long alkyl chains is used for orientation of LCs because of its excellent stability and uniformity. In addition, the use of color filters containing red, green, and blue is essential for LCD devices to implement full-color images. Color filters included in LC device typically use pigments, however these have a fatal weakness that results in low transmittance due to their thickness.
In this study, we suggested a novel self-assembled alignment method that can give vertical alignment and photoluminescent properties of LC device. Pyrene-based 2D materials such as 1-pyrenesulfonic acid sodium salt, 1-pyrene carboxylic acid, 1-prene butylic acid, and 1-amino pyrene were employed as photoluminescent alignment agents to form vertical orientation of LCs. The fabricated LC device using photoluminescent alignment agent appeared to have a stable orientation property based on polarized optical microscopy. The electro-optical characteristics of the LC device using self-assembled layer of 2D materials showed better performance than those of the LC device containing a conventional polyimide layer. Our proposed self-assembled alignment method is sufficient to replace the conventional polyimide layers, which require complex layer forming process and high production costs. In addition, our proposed technique allows for simple doping using low concentrations of 2D materials (0.05 wt%). Furthermore, as LCs were mixed with 2D materials, photoluminescence under ultraviolet (UV) light was exhibited. Our proposed method has excellent LC alignment and PL property, both of which can be utilized in advanced display technologies for next-generation LC devices, such as polyimide-free alignment or color-filter-free color expression.

In recent years, applications of graphene-based materials for smart fiber have been intensively studied exploiting their outstanding mechanical and electrical properties. In particular, the self-assembly of graphene oxide liquid crystals (GO-LC) enabled the fabrication of super-strong fibers that exceed the mechanical strength of carbon fibers. However, compared to CVD graphene fibers, the electrical conductivity of GO-LC or rGO-LC fibers is still limited because of the inevitably formed defects during severe chemical oxidation and reduction processes. On the other hand, the highly conducting CVD graphene fiber is not mechanically strong enough to be used as stand-alone fibers. Here we report a simple method to fabricate multifunctional graphene-based smart fiber with mechanically strong rGO-LC cores and highly conductive CVD graphene shells (rGO@Gr fiber), taking advantages of the outstanding mechanical strength of rGO fibers as well as the high electrical conductivity of CVD fibers. The resulting fiber exhibits the electrical conductivity as high as ~137 S/cm and the maximum strain as high as 21%, which is believed to be the best values among polymer-free graphene-based fibers reported so far. The optical, mechanical, electrical, and electrochemical properties of rGO@Gr fibers have been carefully characterized by Raman spectroscopy, scanning electron microscopy, I-V measurement, cyclic voltammetry, etc. Finally, the application to high-performance fiber supercapacitors with enhanced mechanical stability and durability is successfully demonstrated, showing the highest power density among the graphene-based energy storage fiber electrodes. Thus, we expect that the rGO@Gr fiber supercapacitor with excellent conductivity along with remarkable stretchability would be an important component for various smart wearable devices in the future.

There is a worldwide need to design new and intelligent vehicles for drug delivery in order to improve the effectiveness of therapy. Graphene oxide presents structural and chemical properties, as well as biocompatibility that can be considered for biomedical applications including the design of drug delivery systems for therapy. The aim of this work was to target graphene oxide functionalized with lactose to the tumoral cell HepG2 that presents the asialoglicoprotein receptor. In order to accomplish this Graphene Oxide (GO) was synthesized by modified Hummer s method. The Hummers method consists in the oxidation of graphite. The GO was modified with lactose by a chemical procedure resulting in a product lactocylated. Afterward, blades of GO lactocylated were synthesized. The GO characterization was done by the following techniques Raman Spectroscopy, Fourier Transform Infrared Spectroscopy (FT-IR), Atomic Force Microscopy (AFM), and X-ray Photoelectron Spectroscopy (XPS). The results show that GO lactocylated is specifically recognized by HepG2 cell indicating that this product could be useful as vehicle tissue-specific for antitumor drug delivery or probe for cell and biological imaging.

We will present our research on the development of a sensitive hybrid photodetector that utilizes a graphene-based charge sensor capacitively coupled to a thick semiconductor absorber in depletion. Due to its high-mobility and broadband optical conductivity, graphene is emerging as an interesting material for photosensing applications capable of spanning the electromagnetic spectrum (ultraviolet to terahertz). Achieving high sensitivities in practical applications remains elusive, however, due to the difficulty associated with coupling light into an atomically thin layer that is at least an order of magnitude thinner than the wavelength which it is sensing. To circumvent issues with direct absorption into an atomically thin layer, we have developed a photodetector concept based on a deeply depleted graphene/oxide/semiconductor (D²GOS) junction. This photodetecting junction consists of a graphene field effect transistor (GFET) that is capacitively coupled, using a thin oxide layer, to a thick semiconducting absorber. Unlike other graphene-based detecting concepts, absorption of photons takes place in the semiconducting substrate and not the ultra-thin graphene layer. In this concept, the GFET acts as a high-sensitivity local charge detector that is capable of sensing photo-induced charge collecting in the potential well that forms near the absorber/oxide interface when the junction is biased into deep depletion. As photo-induced charge collects within the potential well, the GFET’s conductivity is altered due to the presence of capacitively-coupled charge that forms within the graphene channel. The behavior of this hybrid device is analogous to a self-sensing metal/oxide/semiconductor (MOS) capacitor, which is the fundamental building block of modern CCD imaging technology.

Under this paradigm, we have successfully fabricated D²GOS device arrays using commercial CVD graphene that has been transferred atop a thin layer of HfO₂ resting on a low-doped n-type silicon. We have measured responsivities in excess of 2500 A/W (25,000 S/W), for visible wavelengths, using moderate integration times. Consistent behavior for multiple devices fabricated on different chips was also observed, with signal-to-noise ratios comparable to commercial CCD technology. In addition to devices using Si absorbers, we have implemented the D²GOS detection concept in InGaAs which is an infrared absorber. Although similar devices have been fabricated in the past, we have developed an improved understanding of the working principles for this hybrid device and constructed a model to adequately describe its behavior.

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

The realization of a robust interfacial attachment mechanism between nanofillers and host polymer matrix holds great promise to enhance overall macroscale properties of nanocomposites. With this regard, the formation of periodically functionalized and crystalline texture shish-kebab architectures on matrix-embedded nanostrands through utilizing intrinsic characteristics of semicrystalline polymer systems represents a facile interfacial coupling scheme. In particular, successful protocols for the development of periodically assembled shish-kebab structures have been demonstrated on CNTs employing numerous semicrystalline polymer systems. Yet, the functionalized nano-hybrid shish-kebab configurations are essentially established via intrinsically semicrystalline thermoplastics which genuinely constitute inferior physical properties for high-performance demanding applications. Aromatic thermosetting copolyester (ATSP), introduced in the late 1990s, utilizes low cost, easily processable and highly crosslinkable oligomers to develop a high-performance polymer system. The crosslinked morphology of ATSP formed by an aromatic polyester backbone interconnected via covalent oxygen bonds enables strong physical properties and outstanding chemical inertness. Here, we report on in situ epitaxial step-growth polymerization driven interfacial functionalization of ATSP with multi-layered graphene wrapped alumina nanofiber (ANFC) surface. Unidirectionally oriented ANFC bundles are dip-coated with both dilute and concentrated ATSP oligomer solutions. During a thermal condensation polymerization, ATSP dip-coated fiber strands develop a nano-hybrid shish-kebab structure with periodically assembled and off-surface grown micron-scale lamella ATSP domains. The nano-hybrid ATSP-ANFC system is composed of the ANFC strand as “shish” and the ATSP lamellae as “kebab” in the nanocomposite structure, which also clearly highlights the epitaxial growth induced localized lamellae formation. The condensation polymerized thermoset nature of the lamellae also presents a unique synthetic route as compared to previously reported shish-kebab structures. We propose a mechanism combining the Plateau-Rayleigh instability, the Marangoni effect and the epitaxial growth phenomena to elucidate controlling parameters in the process. X-ray Diffraction measurements clearly demonstrate the formation of mesomorphic lamella phase not present within either the neat ATSP or pristine fiber samples. Results of solid-state Nuclear Magnetic Resonance and Thermogravimetric Analysis reveal the development of an interfacial coupling between the graphene-coated ceramic nanofibers and the ATSP matrix. This study lays the groundwork to initiate further analyses of the ATSP with various other nanofiller reinforcements on the in situ surface functionalization.