Micron Size Graphene Sheets Synthesis by Methane Pyrolysis in an RF-ICP Thermal Plasma Reactor.

Abstract

Bottom-up synthesis of free-standing graphene using thermal plasma technology often results in flakes with smaller lateral dimensions (hundreds of nanometers) compared to top-down and substrate-based approaches (reaching centimeters in size) [1]. This limitation in size restricts the applicability of graphene in various applications. This study investigates a method to overcome this limitation by studying the reactor's quenching effect on the plasma plume exiting an RF-ICP thermal plasma torch. Local gas phase chemistry and graphene morphology were investigated during methane (CH4) pyrolysis in argon plasma. Natural quenching suppression led to a production of few-layer (2-5 layers), near-micrometer-sized un-supported graphene sheets (~2.8µm perimeter) with less crumpling and a projected area of (2-5)×105 nm². Raman, TEM, TGA, and XPS analysis confirmed the high quality of the synthesized graphene. Sp2 carbon composition in the sample was calculated using the D parameter obtained from the differentiated C KLL Auger peak in the XPS spectrum. A correlation between the gas phase chemistry and the graphene morphology demonstrated the significant effect of plasma reactor natural quenching and recirculation on the graphene synthesis and offers a potential for controlling the structure of unsupported graphene. The current study provides valuable insights that can pave the way for the development of reactors with a definite control over the morphology of synthesized graphene. .