Synthesis and characterization of graphene grown by open flame deposition technique

Abstract

Ever since the discovery of graphene with its many unique properties, there has been demand for a production method that could cheaply produce high-quality and large-area graphene. So far, high-quality large-area graphene is grown through chemical vapor deposition either through thermal activation or plasma activation. Presently, there are many barriers to achieve mass production of such graphene. Current complexities in production method only allows batch production at extreme condition to achieve minimal defects in graphene. To achieve an economical method for high-quality large-area graphene production, simplification to the system is a must. Our group proposes to produce graphene through the flame deposition technique which unlike the conventional chemical vapor deposition (CVD) would drastically reduce energy consumption while still producing graphene of a reasonable quality. Amongst all deposition methods, CVD is one of the slowest compared to flame combustion which has the highest deposition rates without involving microwave plasma and direct current arc. We also aim to study the reaction kinetics involved in the production of graphene by this method. To achieve this, a normal horizontal CVD reactor was modified to allow flame deposition of graphene. Graphene deposits grown by flame deposition were characterized by Raman spectroscopy, sheet resistance and electrochemical impedance spectroscopy (EIS). Simultaneously, simulations on the chemical reactions were also performed to obtain information on the equilibrium concentrations of the gas species. It was shown that deposits obtained from the reactor that we designed were comparable to graphene grown flame deposition reported in literature. At its best, multilayer graphene with a monolayer ratio of 1.14 and defect ratio of 0.87 was successfully grown at 750°C through a 10 min reaction using a gas composition of 0.2 atm Ar, 0.3 atm CH4, 0.5 atm O2. Compared to literature using 0.07 atm H2, 0.68 atm CH4, 0.25 atm O2, monolayer ratio was 600% higher and defect ratio increased slightly by 9%. Additionally, using equilibrium concentrations of predicted products obtained from simulations of chemical kinetics provided the initial mechanism pathways and a gas phase species that have a close correlation to the deposition rates. Both Arrhenius and van't Hoff analysis shows a single growth mechanism the range of 400°C to 1000°C which further corroborates this. Our investigations revealed that when compared to conventional CVD grown graphene, this technique produces few-layer graphene growth through a different pathway and highlights flame deposition technique as a viable method for graphene production.