Evidence of atomically resolved 6 × 6 buffer layer with long-range order and short-range disorder during formation of graphene on 6H-SiC by thermal decomposition

Scanning tunneling microscopy (STM) is performed to study the formation mechanism of graphene on 6H-SiC by thermal decomposition in situ and the evolution of an atomically resolved 6 × 6 structure in the buffer layer is revealed. The long-range order of the 6 × 6 structure is maintained during growth, but the short-range arrangement changes with temperature. Based on STM images acquired at different voltages, a structure consisting of triangular silicon clusters with the 6 × 6 structure and filled by amorphous carbon atoms is proposed. The 6 × 6 silicon clusters serve as the template and amorphous carbon atoms provide the carbon source for graphene growth.