Effect of hydrogen termination on carbon -edge X-ray absorption spectra of nanographene

Hou, Z.*; Wang, X.*; Ikeda, Takashi; Huang, S.-F.*; Terakura, Kiyoyuki*; Boero, M.*; Oshima, Masaharu*; Kakimoto, Masaaki*; Miyata, Seizo*

Carbon -edge X-ray absorption spectra of nanographene have been simulated by density functional theory calculations in order to obtain the information on the edge termination by hydrogen. Our results show that different edge terminations significantly affect the binding energy of 1s core-level of C atoms in the vicinity of edges because of the change in chemical bonding and the localized edge states. We find that a shoulder or a peak appears below the peak at relatively different positions with respect to the peak position in the theoretical spectra of zigzag graphene nano-ribbons, depending on the ratio of mono-hydrogen- to di-hydrogen-terminations. We also point out that the two additional features observed between the and peaks of an ideal graphene originate from the states of C-H bonding and C-H bonding at the edges.