Enhancement of band gap and evolution of in-gap states in hydrogen-adsorbed monolayer graphene on SiC(0001)

Abstract

We have performed high-resolution angle-resolved photoemission spectroscopy (ARPES) on hydrogen-exposed monolayer graphene grown on SiC(0001). In the valence-band region, we observed the π and σ bands of graphene together with the buffer-layer bands, which hybridize with each other at specific momentum points. Upon hydrogen exposure, the ARPES-spectral intensity of buffer layer is reduced and the band hybridization is weakened, suggesting the intercalation of hydrogen atoms between graphene and buffer layer. On further hydrogen exposure, we observed the enhancement of the band gap accompanied with the evolution of in-gap states. These results are interpreted in terms of the partial transformation of C 2pz orbitals into the sp3 hybridized orbitals with covalent bonding between carbon and hydrogen atoms. The present results pave an important path toward feasible application of graphene-based hydrogen-storage devices.