title: Direct observation of ordered configurations of hydrogen adatoms on graphene.
abstract: Ordered configurations of hydrogen adatoms on graphene have long been proposed, calculated, and searched for. Here, we report direct observation of several ordered configurations of H adatoms on graphene by scanning tunneling microscopy. On the top side of the graphene plane, H atoms in the configurations appear to stick to carbon atoms in the same sublattice. Scanning tunneling spectroscopy measurements revealed a substantial gap in the local density of states in H-contained regions as well as in-gap states below the conduction band due to the incompleteness of H ordering. These findings can be well explained by density functional theory calculations based on double-sided H configurations. In addition, factors that may influence H ordering are discussed.
authors.affiliation: State Key Lab for Mesoscopic Physics, School of Physics, Peking University , Beijing 100871, China.
authors.forename: Chenfang
authors.initials: C
authors.lastname: Lin
authors.forename: Yexin
authors.initials: Y
authors.lastname: Feng
authors.forename: Yingdong
authors.initials: Y
authors.lastname: Xiao
authors.forename: Michael
authors.initials: M
authors.lastname: Dürr
authors.forename: Xiangqian
authors.initials: X
authors.lastname: Huang
authors.forename: Xiaozhi
authors.initials: X
authors.lastname: Xu
authors.forename: Ruguang
authors.initials: R
authors.lastname: Zhao
authors.forename: Enge
authors.initials: E
authors.lastname: Wang
authors.forename: Xin-Zheng
authors.initials: XZ
authors.lastname: Li
authors.forename: Zonghai
authors.initials: Z
authors.lastname: Hu
keywords: Graphene; STM; double-sided; gap; hydrogen; ordered