Growth dynamics and kinetics of monolayer and multilayer graphene on a 6H-SiC(0001) substrate

Using Scanning Tunnelling Microscopy (STM), the transformation from the commonly known carbon-rich (6 root 3 x 6 root 3)R30 degrees reconstructed surface to graphene on the 6H-SiC(0001) substrate is systematically investigated with the aid of adsorbing cobalt (Co) which acts as a tracer to map the evolution of these surfaces. The formation of graphene is observed to begin from the step-edges as Si desorption occurs and the growth process continues akin to that of a step flow growth mode. Analysis of the surface step-height evolution at various stages of graphitization shows that as the initial (6 root 3 x 6 root 3)R30 degrees surface converts to form graphene, three Si-C bilayers beneath collapse to regenerate a C-rich structure which also has a (6 root 3 x 6 root 3)R30 degrees periodicity at the interface between graphene and the SiC bulk. Based on these observations, a structural mechanism for the growth of mono-and multilayer graphene is proposed. In addition, we also examine the rate at which the initial (6 root 3 x 6 root 3)R30 degrees surface coverts to graphene as a function of time and temperature. Kinetic analysis of the growth process reveals that the transformation occurs with an activation energy of 3.0 +/- 0.4 eV, a value close to the breaking of a Si-C bond.