Nucleation and growth of graphene/Mo2C heterostructures on Cu through CVD

Abstract

We investigated the chemical vapor deposition synthesis of Mo2C/graphene heterostructures on a partially wetted liquid copper surface, studied the morphology of resulting phases using electron and optical microscopy, and determined the rate-limiting step for the growth of Mo2C on graphene. The morphology of the Mo2C crystals varied from the center to the edge of the copper substrate because of the change in the Mo diffusion pathways owing to the variation in the thickness of the Cu substrate. Thin, hexagonal-shaped crystals of Mo2C were found in the central region, where Cu is the thickest. In addition, the growth pressure substantially affects the nucleation and growth kinetics of both Mo2C and graphene. At high pressures (750 Torr), the graphene layer fully covered the Cu surface and Mo2C crystals formed with a regular shape, while at low pressures (5 Torr), the nucleation of both domains was suppressed, leading to the evolution of Mo2C crystals with irregular shapes. The activation energy for the growth of Mo2C on graphene was calculated to be 3.76 +/- 0.3 eV, and the diffusion of Mo to the Cu surface through uncovered Cu or graphene vacancies/defects was determined to be the rate-limiting step.