Mechanistic Insight into Transfer-Free CVD Growth of Graphene on SiO2

The mechanism of direct growth of graphene on SiO2/Si remains elusive due to the complex interplay between substrate chemistry and gas molecule interactions. Here, by bridging experimental results with theoretical calculations, the complex growth kinetics of graphene on SiO2 is uncovered. Our results emphasize that oxygen vacancy sites on the surface of SiO2, formed at high temperatures, act as activation sites for the nucleation of graphene, where the dissociative adsorption of CH4 is energetically favored. Furthermore, a comparative study using density functional theory (DFT) on the energy barrier for CH4 decomposition on SiO2 and Al2O3 suggests a more kinetically favorable decomposition of CH4 on SiO2 than Al2O3 with an energy of 1.62 and 1.94 eV, respectively. By leveraging the temporal evolution of oxygen vacancy defects, few-layer graphene (FLG) formation is realized on SiO2/Si under atmospheric pressure chemical vapor deposition (APCVD). However, nanoscopic imaging of the grown sample showed the discontinuous graphene film made up of partially coalesced domains with submicron grain sizes (<300 nm). Our study not only adds to existing evidence that oxygen vacancies are key in graphene nucleation on oxide substrates but also emphasizes the need of nanoscopic characterization to understand the complex defect structures and growth homogeneity on a wafer scale.