▎ 摘　　要

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 pi and sigma 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 2p(z) orbitals into the sp(3) 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. (C) 2017 Elsevier Ltd. All rights reserved.