▎ 摘　　要

We use in situ low temperature scanning tunneling microscopy (STM) to investigate the growth mechanism of epitaxial graphene (EG) thermally grown on Si-terminated 6H-SiC(0001). Our detailed study of the transition from monolayer EG to trilayer EG reveals that EG adopts a bottom-up growth mechanism. The thermal decomposition of one single SiC bilayer underneath the EG layers causes the accumulation of carbon atoms to form a new graphene buffer layer at the EG/SiC interface. Atomically resolved STM images show that the top EG layer is physically continuous across the boundaries between the monolayer and bilayer EG regions and between the bilayer and trilayer EG regions.