Metal-catalyst-free and controllable growth of high-quality monolayer and AB-stacked bilayer graphene on silicon dioxide

A systematic study shows that continuous graphene with controllable number of layers and stacking structure can be directly grown on SiO₂/Si without any metal catalysts by chemical vapor deposition. Raman spectroscopy and mapping confirm the monolayer, bilayer and few-layer nature of the graphene with a high coverage over ∼95%. Ultraviolet photoemission spectroscopy verifies that the monolayer graphene and AB-stacked bilayer graphene have a work function of 4.46 eV and 4.50 eV, respectively, which are close to that of the intrinsic graphene. This is in contrast to the much lower work function of 4.26 eV observed on Cu-catalyzed graphene probably due to contaminants produced during the transfer process. Field-effect transistors were directly fabricated on graphene/SiO₂/Si for evaluating their electric properties. Importantly, we reveal a crucial role of SiO₂ layer thickness in controlling the graphene structure: (1) monolayer graphene preferably grown on thick SiO₂ layer (∼300 nm or higher) by a surface-catalyzed process, and (2) AB-stacked bilayer or few-layer graphene favorably formed on thin SiO₂ layer by a surface-adsorption/precipitation process. This study sheds light on the graphene growth mechanism on SiO₂/Si and this insightful understanding is important to large-scale, controllable CVD growth of graphene in absence of metal catalysts.