Catalyst-assisted thermal CVD syntheses of large area uniform mono- and few-layer graphene*

Catalysts with carbon solubilities varying from low to intermediate solubilities were utilized to synthesize large area uniform mono- and few-layer graphene employing catalyst-assisted thermal CVD at both ambient and low pressures. Our results demonstrate that both APCVD and LPCVD from a low carbon solubility catalyst resulted in uniform growth of monolayer graphene. Uniform growth of multi-layer graphene was observed while employing catalysts with intermediate carbon solubility in a LPCVD process that is in contrast to previous reports using APCVD process. In an APCVD process (for low solubility catalysts such as Copper), the graphene synthesis at high temperatures ($\sim $1000 $^{\circ}$C) proceeds in mass-transport limited regime, and in a LPCVD process, proceeds in a surface-reaction limited regime. The role of kinetic factors in graphene growth using APCVD and LPCVD processes would be discussed with reference to aforementioned results.