Chemical Vapor Deposition Synthesis And Structural Characterization Of Graphene Films On Different Substrates

Graphene, an ideal two-dimensional film material backboned with sp2-hybridized carbon atoms, has drawn significant interest due to its outstanding electrical properties. Since its first isolation by mechanical exfoliation, large-scale production of graphene has been one of the urgent issues. Among various preparation methods, the chemical vapor deposition (CVD) process takes special attention as it guarantees high-quality graphene in large scale with high yield.The CVD process, using metal substrates to catalyze the growth of graphene films, has already made some achievements. Recently, researches on CVD graphene films applied as an electrode material have mainly focused on the effective transfer methods. Meanwhile, the internal relations between structure and properties of graphene are also of great importance for the application in photoelectric devices. In this paper, graphene films were prepared by CVD method using copper foils as substrates and the influence of growth temperature on their structure was studied. The rules of transmittance and sheet-resistance of graphene films associated with the change of structure have also been discussed.The results show that high-quality and few-layer graphene can be synthesized around1000centigrade, and graphene grown in1000centigrade shows fewer layers and better transmittance. The sheet-resistance of graphene indicates a linear downtrend with the increase of growth temperature. This is mainly because that the lower temperature goes against the synthesis of graphene, and with an increasing growth temperature the defect density is reduced and the electrical conductivity is improved.Since transition metals such Cu and Ni were usually used as substrates in traditional CVD method, some mechanical defects and organic contaminants can be caused during the transfer process. Recently, CVD growth of graphene films directly using insulator or semiconductor materials as substrates has been proved to be feasible. In this study, nanographene films were directly synthesized by CVD method using silicon dioxide as a substrate. Primary research on the effect of some assisted methods used in CVD growth process of graphene films with silicon dioxide as a substrate was conducted, and probable growth mechanism was also investigated.The results indicate that flat and uniform nanographene films are synthesized directly on silicon dioxide substrate and their grain size are estimated to be6-10nm. Both Raman and XPS spectra analysis indicate that a thin carbide buffer layer is formed on flat silicon dioxide substrates in early phases of growth. The presence of silicon carbide also implies the strong interaction between of graphene and substrate, thus, the strong strain effect in graphene layers has been induced, which causes the remarkable wave-shift of Raman G peak with the nanocrystalline nature of graphene film. It is also found that oxygen-aided and copper-vapor-assisted CVD processes facilitate the synthesis of graphene with low defect density on silicon dioxide surface. The former may form oxygen-base nucleation sites in high-temperature activation process, which enhances the adsorption of hydrocarbon molecules. The copper-vapor-assisted CVD process may be attributed to the catalytic pyrolysis of methane with the copper vapor which is produced by the sublimation of copper foil on the top of silicon dioxide substrate.