Fabrication of Graphene/Cu Composite by Chemical Vapor Deposition and Effects of Graphene Layers on Resultant Electrical Conductivity

Graphene(Gr)has unique properties including high electrical conductivity;Thus,graphene/copper(Gr/Cu)composites have attracted increasing attention to replace traditional Cu for electrical applications. However,the problem of how to control graphene to form desired Gr/Cu composite is not well solved. This paper aims at exploring the best parameters for preparing graphene with different layers on Cu foil by chemical vapor deposition(CVD)method and studying the effects of different layers graphene on Gr/Cu composite’s electrical conductivity. Graphene grown on single-sided and double-sided copper was prepared for Gr/Cu and Gr/Cu/Gr composites. The resultant electrical conductivity of Gr/Cu composites increased with decreasing graphene layers and increasing graphene volume fraction. The Gr/Cu/Gr composite with monolayer graphene owns volume fraction of less than 0.002%,producing the best electrical conductivity up to59.8 ×10^(6)S/m,equivalent to 104.5% IACS and 105.3% pure Cu foil.

Direct growth of graphene on gallium nitride by using chemical vapor deposition without extra catalyst

Graphene on gallium nitride （GaN） will be quite useful when the graphene is used as transparent electrodes to improve the performance of gallium nitride devices. In this work, we report the direct synthesis of graphene on GaN without an extra catalyst by chemical vapor deposition. Raman spectra indicate that the graphene films are uniform and about 5-6 layers in thickness. Meanwhile, the effects of growth temperatures on the growth of graphene films are systematically studied, of which 950 ℃ is found to be the optimum growth temperature. The sheet resistance of the grown graphene is 41.1 Ω/square, which is close to the lowest sheet resistance of transferred graphene reported. The mechanism of graphene growth on GaN is proposed and discussed in detail. XRD spectra and photoluminescence spectra indicate that the quality of GaN epi-layers will not be affected after the growth of graphene.

Chemical vapor deposition growth behavior of graphene

The optimized growth parameters of graphene with different morphologies,such as dendrites,rectangle,and hexagon,have been obtained by low-pressure chemical vapor deposition on polycrystalline copper substrates.The evolution of fractal graphene,which grew on the polycrystalline copper substrate,has also been observed.When the equilibrium growth state of graphene is disrupted,its intrinsic hexagonal symmetry structure will change into a non-hexagonal symmetry structure.Then,we present a systematic and comprehensive study of the evolution of graphene with different morphologies grown on solid copper as a function of the volume ratio of methane to hydrogen in a controllable manner.Moreover,the phenomena of stitching snow-like graphene together and stacking graphene with different angles was also observed.

Influence of reaction parameters on synthesis of high-quality single-layer graphene on Cu using chemical vapor deposition

Large-area monolayer graphene samples grown on polycrystalline copper foil by thermal chemical vapor deposition with differing CH4 flux and growth time are investigated by Raman spectra, scanning electron microscopy, atomic force microscopy, and scanning tunneling microscopy. The defects, number of layers, and quality of graphene are shown to be controllable through tuning the reaction conditions： ideally to 2-3 sccm CH4 for 30 minutes.

Invisible vapor catalysis in graphene growth by chemical vapor deposition

Vapor catalysis was recently found to play a crucial role in superclean graphene growth via chemical vapor decomposition(CVD).However,knowledge of vapor-phase catalysis is scarce,and several fundamental issues,including vapor compositions and their impact on graphene growth,are ambiguous.Here,by combining density functional theory(DFT)calculations,an ideal gas model,and a designed experiment,we found that the vapor was mainly composed of Cui clusters with tens of atoms.The vapor pressure was estimated to be~10^(-12)-10^(-1)1 bar under normal low-pressure CVD system(LPCVD)conditions for graphene growth,and the exposed surface area of Cui clusters in the vapor was 22-269 times that of the Cu substrate surface,highlighting the importance of vapor catalysis.DFT calculations show Cu clusters,represented by Cu17,have strong capabilities for adsorption,dehydrogenation,and decomposition of hydrocarbons.They exhibit an adsorption lifetime and reaction flux six orders of magnitude higher than those on the Cu surface,thus providing a sufficient supply of active C atoms for rapid graphene growth and improving the surface cleanliness of the synthesized graphene.Further experimental validation showed that increasing the amount of Cu vapor improved the as-synthesized graphene growth rate and surface cleanliness.This study provides a comprehensive understanding of vapor catalysis and the fundamental basis of vapor control for superclean graphene rapid growth.

Theoretical investigations on the growth of graphene by oxygenassisted chemical vapor deposition

Recently,graphene has drawn considerable attention in the field of electronics,owing to its favorable conductivity and high carrier mobility.Crucial to the industrialization of graphene is its high-quality microfabrication via chemical vapor deposition.However,many problems remain in its preparation,such as the not fully understood cracking mechanism of the carbon source,the mechanism of its substrate oxidation,and insufficient defect repair theory.To help close this capability gap,this study leverages density functional theory to explore the role of O in graphene growth.The effects of Cu substrate oxidation on carbon source cracking,nucleation barriers,crystal nucleus growth,and defect repairs are discussed.OCu was found to reduce energy change during dehydrogenation,rendering the process easier.Moreover,the adsorbed O in graphene or its Cu substrate can promote defect repair and edge growth.

Transfer-free chemical vapor deposition graphene for nitride epitaxy: challenges, current status and future outlook

Graphene, a two-dimensional material with outstanding electrical and mechanical properties, has attracted considerable attention in the field of semiconductor technologies due to its potential use as a buffer layer for the epitaxial Ⅲ-nitride growth. In recent years, significant progress has been made in the chemical vapor deposition growth of graphene on various insulating substrates for the nitride epitaxy, which offers a facile, inexpensive, and easily scalable methodology. However, certain challenges are still present in the form of producing high-quality graphene and achieving optimal interface compatibility with Ⅲ-nitride materials.In this review, we provide an overview of the bottlenecks associated with the transferred graphene fabrication techniques and the state-of-the-art techniques for the transfer-free graphene growth. The present contribution highlights the current progress in the transfer-free graphene growth on different insulating substrates, including sapphire, quartz, SiO_(2)/Si, and discusses the potential applications of transfer-free graphene in the Ⅲ-nitride epitaxy. Finally, it includes the prospects of the transfer-free graphene growth for the Ⅲ-nitride epitaxy and the challenges that should be overcome to realize its full potential in this field.

Porous Carbon Grown by Chemical Vapor Deposition on Copper Substrates

Amorphous porous carbon was synthesized by chemical vapor deposition on copper substrates. The average size of the pores is around 1.2 microns with some small pores decorating the big ones. Lamellar samples of this carbonaceous material can be separated from the copper support and may be useful as electrode due to its low electrical resistivity of the order of 0.4 Ωcm.

Direct deposition of graphene nanowalls on ceramic powders for the fabrication of a ceramic matrix composite

Uniform mixing of ceramic powder and graphene is of great importance for producing ceramic matrix composite. In this study, graphene nanowalls(GNWs) are directly deposited on the surface of Al2 O3 and Si3 N4 powders using chemical vapor deposition system to realize the uniform mixing. The morphology and the initial stage of the growth process are investigated. It is found that the graphitic base layer is initially formed parallel to the powder surface and is followed by the growth of graphene nanowalls perpendicular to the surface. Moreover, the lateral length of the graphene sheet could be well controlled by tuning the growth temperature. GNWs/Al2 O3 powder is consolidated by using sparking plasma sintering method and several physical properties are measured. Owing to the addition of GNWs, the electrical conductivity of the bulk alumina is significantly increased.

Ultrahigh thermal conductive graphite film via the in-situ construction of aligned nanographene skeleton using chemical vapor deposition

Both high thermal conductivity(K)and large cross-sectional area are essential for thermal dissipation materials to maximize their heat transfer capability.However,the drastic decrease of K values with the increased thickness makes the existing graphite/graphene films less favored for practical applications.In this work,graphite film with both large thickness and high K value is produced based on an in-situ com-position strategy between nanographene(G)and pyrocarbon(PyC)via chemical vapor deposition(CVD)using CH_(3) OH/C_(2)H_(5)OH mixed precursors.It’s found that an optimized O/C ratio of precursors facilitates the construction of ordered G skeletons within the deposited G/PyC composites.Such G/PyC compos-ites can be completely graphitized at a lower temperature than the existing products.After 2400℃ an-nealing,dense,thick,and highly aligned graphite films were prepared.Their K values reach 1350 and 1010 W m^(-1) K^(-1) at the thickness of 40 and 120μm,respectively,surpassing the existing records with similar thicknesses.More importantly,the proposed method is insensitive to the deposition substrates,and the G/PyC can be infiltrated into large-size fiber preforms as a matrix for preparing centimeter-thick high K materials.Besides,the G/PyC also exhibits better mechanical and electromagnetic shielding per-formances than the existing products,indicating a promising multifunctional application prospect.

High current limits in chemical vapor deposited graphene spintronic devices

Understanding the stability and current-carrying capacity of graphene spintronic devices is key to their applications in graphene channel-based spin current sensors,spin-torque oscillators,and potential spin-integrated circuits.However,despite the demonstrated high current densities in exfoliated graphene,the current-carrying capacity of large-scale chemical vapor deposited(CVD)graphene is not established.Particularly,the grainy nature of chemical vapor deposited graphene and the presence of a tunnel barrier in CVD graphene spin devices pose questions about the stability of high current electrical spin injection.In this work,we observe that despite structural imperfections,CVD graphene sustains remarkably highest currents of 5.2×10^(8)A/cm^(2),up to two orders higher than previously reported values in multilayer CVD graphene,with the capacity primarily dependent upon the sheet resistance of graphene.Furthermore,we notice a reversible regime,up to which CVD graphene can be operated without degradation with operating currents as high as 108 A/cm^(2),significantly high and durable over long time of operation with spin valve signals observed up to such high current densities.At the same time,the tunnel barrier resistance can be modified by the application of high currents.Our results demonstrate the robustness of large-scale CVD graphene and bring fresh insights for engineering and harnessing pure spin currents for innovative device applications.

Progress of graphene growth on copper by chemical vapor deposition:Growth behavior and controlled synthesis

Recently,chemical vapor deposition (CVD) on copper has been becoming a main method for preparing large-area and highquality monolayer graphene.In this paper,we first briefly introduce the preliminary understanding of the microstructure and growth behavior of graphene on copper,and then focus on the recent progress on the quality improvement,number of layers control and transfer-free growth of graphene.In the end,we attempt to analyze the possible development of CVD growth of graphene in future,including the controlled growth of large-size single-crystal graphene and bilayer graphene with different stacking orders.

Direct low-temperature synthesis of graphene on various glasses by plasma-enhanced chemical vapor deposition for versatile, cost-effective electrodes

Catalyst-free and scalable synthesis of graphene on various glass substrates at low temperatures is of paramount significance to numerous applications such as low-cost transparent electronics and state-of-the-art displays. However, systematic study within this promising research field has remained scarce thus far. Herein, we report the direct growth of graphene on various glasses using a low-temperature plasma-enhanced chemical vapor deposition method. Such a facile and scalable approach guarantees the growth of uniform, transfer-free graphene films on various glass substrates at a growth temperature range of 400-600 ℃. The morphological, surface wetting, optical, and electrical properties of the obtained graphene can be tailored by controlling the growth parameters. Our uniform and high-quality graphene films directly integrated with low-cost, commonly used glasses show great potential in the fabrication of multi-functional electrodes for versatile applications in solar cells, transparent electronics, and smart windows.

Large-area chemical vapor deposition-grown monolayer graphene-wrapped silver nanowires for broad-spectrum and robust antimicrobial coating

New types of antimicrobial systems are urgently needed owing to the emergence of pathogenic microbial strains that gain resistance to antibiotics commonly used in daily life and medical care. In this study we developed for the first time a broad-spectrum and robust antimicrobial thin film coating based on large-area chemical vapor deposition （CVD）-grown graphene-wrapped silver nanowires （AgNWs）. The antimicrobial graphene/AgNW hybrid coating can be applied on commerdal flexible transparent ethylene vinyl acetate/polyethylene terephthalate （EVA/PET） plastic films by a full roll-to-roll process. The graphene/AgNW hybrid coating showed broad-spectrum antimicrobial activity against Gram-negative （Escherichia coli） and Gram-positive bacteria （Staphylococcus aureus）, and fungi （Candida albicans）. This effect was attributed to a weaker microbial attachment to the ultra-smooth graphene film and the sterilization capacity of Ag＋, which is sustainably released from the AgNWs and presumably enhanced by the electrochemical corrosion of AgNWs. Moreover, the robust antimicrobial activity of the graphene/AgNW coating was reinforced by AgNW encapsulation by graphene. Furthermore, the antimicrobial efficiency could be enhanced to -100% by water electrolysis by using the conductive graphene/AgNW coating as a cathode. We developed a transparent and flexible antimicrobial cover made of graphene/AgNW/EVA/PET and an antimicrobial denture coated by graphene/ AgNW, to show the potential applications of the antimicrobial materials.

Synthesis of Large-Area, Few-Layer Graphene on Iron Foil by Chemical Vapor Deposition

We demonstrate a simple and controllable way to synthesize large-area, few-layer graphene on iron substrates by an optimized chemical vapor deposition （CVD） method using a mixture of methane and hydrogen. Based on an analysis of the Fe-C phase diagram, a suitable procedure for the successful synthesis of graphene on Fe surfaces was designed. An appropriate temperature and cooling process were found to be very important in the synthesis of highly crystalline few-layer graphene. Graphene-based field-effect transistor （FET） devices were fabricated using the resulting few-layer graphene, and showed good quality with extracted mobilities of 300-1150 cm2/（V.s）.

Insight into the rapid growth of graphene single crystals on liquid metal via chemical vapor deposition

Previous reports about the growth of large graphene single crystals on polycrystalline metal substrates usually adopted the strategy of suppressing the nucleation by lowering the concentration of the feedstock, which greatly limited the rate of the nucleation and the sequent growth. The emerging liquid metal catalyst possesses the characteristic of quasi-atomically smooth surface with high diffusion rate. In principle, it should be a naturally ideal platform for the lowdensity nucleation and the fast growth of graphene. However,the rapid growth of large graphene single crystals on liquid metals has not received the due attention. In this paper, we firstly purposed the insight into the rapid growth of large graphene single crystals on liquid metals. We obtained the millimeter-size graphene single crystals on liquid Cu. The rich free-electrons in liquid Cu accelerate the nucleation, and the isotropic smooth surface greatly suppresses the nucleation.Moreover, the fast mass-transfer of carbon atoms due to the excellent fluidity of liquid Cu promotes the fast growth with a rate up to 79 μm s^-1. We hope the research on the growth speed of graphene on liquid Cu can enrich the recognition of the growth behavior of two-dimensional(2 D) materials on the liquid metal. We also believe that the liquid metal strategy for the rapid growth of graphene can be extended to various 2 D materials and thus promote their future applications in the photonics and electronics.

Synthesis of Isotopically-Labeled Graphite Films by Cold-Wall Chemical Vapor Deposition and Electronic Properties of Graphene Obtained from Such Films

We report the synthesis of isotopically-labeled graphite films on nickel substrates by using cold-wall chemical vapor deposition(CVD).During the synthesis,carbon from^(12)C-and^(13)C-methane was deposited on,and dissolved in,a nickel foil at high temperature,and a uniform graphite film was segregated from the nickel surface by cooling the sample to room temperature.Scanning and transmission electron microscopy,micro-Raman spectroscopy,and X-ray diffraction prove the presence of a graphite film.Monolayer graphene films obtained from such isotopically-labeled graphite films by mechanical methods have electron mobility values greater than 5000 cm^(2)·V^(-1)·s^(-1)at low temperatures.Furthermore,such films exhibit the half-integer quantum Hall effect over a wide temperature range from 2 K to 200 K,implying that the graphite grown by this cold-wall CVD approach has a quality as high as highly oriented pyrolytic graphite(HOPG).The results from transport measurements indicate that^(13)C-labeling does not significantly affect the electrical transport properties of graphene.

One-step synthesis of novel snowflake-like Si-O/Si-C nanostructures on 3D graphene/Cu foam by chemical vapor deposition

The recent development of synthesis processes for three-dimensional （3D） graphene-based structures has tended to focus on continuous improvement of porous nanostructures, doping modification during thin-film fabrication, and mechanisms for building 3D architectures. Here, we synthesized novel snowflake- like Si-O/Si-C nanostructures on 3D graphene/Cu foam by one-step low-pressure chemical vapor deposition （CVD）. Through systematic micromorphological characterization, it was determined that the formation mechanism of the nanostructures involved the melting of the Cu foam surface and the subsequent condensation of the resulting vapor, 3D growth of graphene through catalysis in the presence of Cu, and finally , nudeation of the Si-O/Si-C nanostructure in the carbon-rich atmosphere. Thus, by tuning the growth temperature and duration, it should be possible to control the nucleation and evolution of such snowflake-like nanostructures with precision. Electrochemical measurements indicated that the snowflake-like nanostructures showed excellent performance as a material for energy storage. The highest specific capacitance of the Si-O/Si-C nanostructures was - 963.2 mF/cm2 at a scan rate of 1 mV/s. Further, even after 20,000 sequential cycles, the electrode retained 94.4% of its capacitance.

Direct growth of graphene on vertically standing glass by a metal-free chemical vapor deposition method

A new method to directly grow graphene on quartz glass substrate by atmospheric-pressure chemical vapor deposition （CVD） without using any catalyst was developed. The prime feature of this method is to build a vertical-glass model in the quartz tube to significantly increase the collision probability of the carbon precursors and reactive fragments between each other with the glass surface. The growth rate of high-quality graphene on glass remarkably increases compared with the conventional gas flow CVD technique. The optical transmittance and sheet resistance of the graphene glass can be readily adjusted by regulating growth time. When growth time is 35 rain, the graphene glass presents an intriguing sheet resistance of about 1.48 kΩ sq^-1 at a transmittance of 93.08%and exhibits an excellent hydrophobic performance. The method is simple and scalable, and might stimulate various potential applications of transparent and conductive graphene glass in practical fields.