Iskandar Kholmanov

Improved Electrical Conductivity of Graphene Films Integrated with Metal Nanowires

Polycrystalline graphene grown by chemical vapor deposition (CVD) on metals and transferred onto arbitrary substrates has line defects and disruptions such as wrinkles, ripples, and folding that adversely affect graphene transport properties through the scattering of the charge carriers. It is found that graphene assembled with metal nanowires (NWs) dramatically decreases the resistance of graphene films. Graphene/NW films with a sheet resistance comparable to that of the intrinsic resistance of graphene have been obtained and tested as a transparent electrode replacing indium tin oxide films in electrochromic (EC) devices. The successful integration of such graphene/NW films into EC devices demonstrates their potential for a wide range of optoelectronic device applications.

Reduced graphene oxide/copper nanowire hybrid films as high-performance transparent electrodes.

Hybrid films composed of reduced graphene oxide (RG-O) and Cu nanowires (NWs) were prepared. Compared to Cu NW films, the RG-O/Cu NW hybrid films have improved electrical conductivity, oxidation resistance, substrate adhesion, and stability in harsh environments. The RG-O/Cu NW films were used as transparent electrodes in Prussian blue (PB)-based electrochromic devices where they performed significantly better than pure Cu NW films.

Low-Temperature Chemical Vapor Deposition Growth of Graphene from Toluene on Electropolished Copper Foils

A two-step CVD route with toluene as the carbon precursor was used to grow continuous large-area monolayer graphene films on a very flat, electropolished Cu foil surface at 600 °C, lower than any temperature reported to date for growing continuous monolayer graphene. Graphene coverage is higher on the surface of electropolished Cu foil than that on the unelectropolished one under the same growth conditions. The measured hole and electron mobilities of the monolayer graphene grown at 600 °C were 811 and 190 cm(2)/(V·s), respectively, and the shift of the Dirac point was 18 V. The asymmetry in carrier mobilities can be attributed to extrinsic doping during the growth or transfer. The optical transmittance of graphene at 550 nm was 97.33%, confirming it was a monolayer, and the sheet resistance was ~8.02 × 10(3) Ω/□.

Inductive Tuning of Fano-Resonant Metasurfaces Using Plasmonic Response of Graphene in the Mid-Infrared

Graphene is widely known for its anomalously strong broadband optical absorptivity of 2.3% that enables seeing its single-atom layer with the naked eye. However, in the mid-infrared part of the spectrum graphene represents a quintessential lossless zero-volume plasmonic material. We experimentally demonstrate that, when integrated with Fano-resonant plasmonic metasurfaces, single-layer graphene (SLG) can be used to tune their mid-infrared optical response. SLGs plasmonic response is shown to induce large blue shifts of the metasurfaces resonance without reducing its spectral sharpness. This effect is explained by a generalized perturbation theory of SLG-metamaterial interaction that accounts for two unique properties of the SLG that set it apart from all other plasmonic materials: its anisotropic response and zero volume. These results pave the way to using gated SLG as a platform for dynamical spectral tuning of infrared metamaterials and metasurfaces.

Chlorination of Reduced Graphene Oxide Enhances the Dielectric Constant of Reduced Graphene Oxide/Polymer Composites

14–19 ] The conductor-insulator composites are attracting much attention for potential applications of charge-storage capacitors, thin-fi lm transistors, and antistatic materials owing to their unique properties, i.e., a dramatic increase in dielectric constant in the conductor-insulator composite fi lms near the percolation threshold.

Continuous Carbon Nanotube–Ultrathin Graphite Hybrid Foams for Increased Thermal Conductivity and Suppressed Subcooling in Composite Phase Change Materials

Continuous ultrathin graphite foams (UGFs) have been actively researched recently to obtain composite materials with increased thermal conductivities. However, the large pore size of these graphitic foams has resulted in large thermal resistance values for heat conduction from inside the pore to the high thermal conductivity graphitic struts. Here, we demonstrate that the effective thermal conductivity of these UGF composites can be increased further by growing long CNT networks directly from the graphite struts of UGFs into the pore space. When erythritol, a phase change material for thermal energy storage, is used to fill the pores of UGF-CNT hybrids, the thermal conductivity of the UGF-CNT/erythritol composite was found to increase by as much as a factor of 1.8 compared to that of a UGF/erythritol composite, whereas breaking the UGF-CNT bonding in the hybrid composite resulted in a drop in the effective room-temperature thermal conductivity from about 4.1 ± 0.3 W m(-1) K(-1) to about 2.9 ± 0.2 W m(-1) K(-1) for the same UGF and CNT loadings of about 1.8 and 0.8 wt %, respectively. Moreover, we discovered that the hybrid structure strongly suppresses subcooling of erythritol due to the heterogeneous nucleation of erythritol at interfaces with the graphitic structures.

Enhanced dielectric performance in polymer composite films with carbon nanotube-reduced graphene oxide hybrid filler

The electrical conductivity and the specific surface area of conductive fillers in conductor-insulator composite films can drastically improve the dielectric performance of those films through changing their polarization density by interfacial polarization. We have made a polymer composite film with a hybrid conductive filler material made of carbon nanotubes grown onto reduced graphene oxide platelets (rG-O/CNT). We report the effect of the rG-O/CNT hybrid filler on the dielectric performance of the composite film. The composite film had a dielectric constant of 32 with a dielectric loss of 0.051 at 0.062 wt% rG-O/CNT filler and 100 Hz, while the neat polymer film gave a dielectric constant of 15 with a dielectric loss of 0.036. This is attributed to the increased electrical conductivity and specific surface area of the rG-O/CNT hybrid filler, which results in an increase in interfacial polarization density between the hybrid filler and the polymer.

Optical, Electrical, and Electromechanical Properties of Hybrid Graphene/Carbon Nanotube Films

By combining a graphene layer and aligned multiwalled carbon nanotube (MWNT) sheets in two different configurations, i) graphene on the top of MWNTs and ii) MWNTs on the top of the graphene, it is demonstrated that optical, electrical, and electromechanical properties of the resulting hybrid films depend on configurations.

Healing of structural defects in the topmost layer of graphite by chemical vapor deposition.

Very recently, Lahiri et al. reported the controlled production of extended line defects in graphene and suggested that such structures might function as metallic wires. [ 16 ] Studies such as these have demonstrated that defect engineering in graphitic systems is a promising approach towards controlling a variety of material properties. Despite this, defects are well-known for their ability to scatter charge carriers and phonons, thereby decreasing the ballistic transport path length and adversely affecting carrier mobility and thermal conductivity. The detrimental effects of defects are particularly pronounced in graphene fi lms. For example, defects were held responsible for a dramatic reduction in charge carrier mobility in graphene fi lms obtained by micromechanical cleavage. [ 17 ] The transport properties of graphene fi lms produced by chemical methods, such as the exfoliation and chemical reduction of graphene oxide platelets, have also been ascribed to defects (introduced by the chemical treatments used). [ 18 ] In this respect, defects are undesirable, and the ability to “heal” them is important for generating carbon nanostructures with high electrical and thermal conductivities and, potentially, enhanced mechanical strength. Improvements in these characteristics are of central importance because the successful realization of graphene-based electronic devices

Graphene Synthesis via Magnetic Inductive Heating of Copper Substrates

Scaling graphene growth using an oven to heat large substrates becomes less energy efficient as system size is increased. We report a route to graphene synthesis in which radio frequency (RF) magnetic fields inductively heat metal foils, yielding graphene of quality comparable to or higher than that of current chemical vapor deposition techniques. RF induction heating allows for rapid temperature ramp up/down, with great potential for large scale and rapid manufacturing of graphene with much better energy efficiency. Back-gated field effect transistors on a SiO2/Si substrate showed carrier mobility up to ∼14 000 cm(2) V(-1) s(-1) measured under ambient conditions. Many advantages of RF heating are outlined, and some fundamental aspects of this approach are discussed.