Journal
ACS NANO
Volume 6, Issue 12, Pages 10590-10597Publisher
AMER CHEMICAL SOC
DOI: 10.1021/nn303485c
Keywords
scanning tunneling microscopy; scanning tunneling spectroscopy; graphene; hydrogenation; photoemission spectroscopy
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Funding
- DFG through the Research Unit [FOR 1154, HA6037/1, GR 3708/1-1]
- Graduate School [GRK 1621]
- APART fellowship from the Austrian Academy of Sciences
- European Community's Seventh Framework Program [226716]
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We report high-resolution scanning tunneling microscopy and spectroscopy of hydrogenated, quasi-free-standing graphene. For this material, theory has predicted the appearance of a midgap state at the Fermi level, and first angle-resolved photo-emission spectroscopy (ARPES) studies have provided evidence for the existence of this state in the long-range electronic structure. However, the spatial extension of H defects, their preferential adsorption patterns on graphene, or local electronic structure are experimentally still largely unexplored. Here, we investigate the shapes and local electronic structure of H impurities that go with the aforementioned midgap state observed in ARPES. Our measurements of the local density of states at hydrogenated patches of graphene reveal a hydrogen impurity state near the Fermi level whose shape depends on the tip position with respect to the center of a patch. In the low H concentration regime, we further observe predominantly single hydrogenation sites as well as extended multiple C-H sites in parallel orientation to the lattice vectors, indicating an adsorption at the same graphene sublattice. This is corroborated by ARPES measurements showing the formation of a dispersionless hydrogen impurity state which is extended over the whole Brillouin zone.
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