Crystal orientation effects of sapphire substrate on graphene direct growth by metal catalyst-free low-pressure CVD

Graphene was directly grown on r-plane (1-102), c-plane (0001), and a-plane (11-20) sapphires by low pressure chemical vapor deposition without the use of a metal catalyst. The growth temperature was systematically changed between 1090 and 1210 °C to investigate the effects of the crystal orientation of sapphire on the graphene growth. It was found that the growth rate of graphene on r-plane sapphire was very fast compared to that of the samples grown on other orientations. The surface catalytic effect of r-plane sapphire promotes the smooth and flat growth of single-layer graphene. The surface of the r-plane sapphire was kept smooth even at a high temperature of 1210 °C because a quick coverage of graphene protects the surface of the sapphire from thermal decomposition and roughening.