Open-atmosphere flame synthesis of monolayer graphene

Abstract

An open-atmosphere, unconfined setup comprising a novel multiple inverse-diffusion flame (m-IDF) burner modified with extended precursor tubes is employed to synthesize graphene on substrates. Growth conditions of mono-, bi-, and few-layer graphene (MLG, BLG, and FLG, respectively) are investigated, with systematic variation of parameters such as substrate temperature, methane-to-hydrogen volume flow rate ratio (JCH4:JH2), growth duration, post-flame flow profiles, substrate material, precursor species (e.g., CH4, C2H2, C2H4), and in-situ post-growth hydrogen annealing. Graphene growth on copper is observed for a wide range of temperatures from 850 °C to 1000 °C, with high-quality BLG created at a substrate temperature of 1000 °C with JCH4:JH2 of 1:100 for 5 min growth duration. A sequential in-situ post-growth hydrogen annealing treatment, where the hydrocarbon precursor flow is terminated but the hydrogen m-IDFs are maintained, is found to be effective for etching adlayers of graphene. As such, BLG is reduced to MLG by increasing the post-growth hydrogen annealing duration at 1000 °C to 10 min. In-situ gas-phase Raman measurements characterize the evolution of the gas-phase precursor species in the synthesis flow field. CH2 is determined to be the main gas-phase carbon species needed near the substrate to form graphene in our flame synthesis system.