First-principles study of preferential sites of hydrogen incorporated in epitaxial graphene on 6H-SiC(0001)

The hydrogen (H) incorporation in the epitaxial graphene buffer layer on 6H-SiC(0001) with various H coverages is investigated using the density-functional method. The most stable site for a single H atom is on top of a threefold C atom in the graphene buffer layer, whereas the incorporation into the interfacial layer is less favored. However, when the H concentration is above 7.15 x 10(14) cm(-2), the H atoms are more stable in the interfacial layer. This is because the H passivation of the SiC surface expands the spatial gap between the buffer layer and the substrate. This eventually results in the complete delamination of the graphene buffer layer from the SiC substrate at high H densities. The band structure indicates that the detached buffer layer is electronically close to the free-standing graphene layer. The present results suggest that the exfoliation of the buffer layer could be realized by injecting atomic hydrogen.