Affiliation: | a NTT Basic Research Laboratories, Nippon Telegraph and Telephone Corporation, Surface Science Research Group, Morinosato Wakamiya, Atsugi, Kanagawa 243-0198, Japan b Department of Physics, Meiji University, Kawasaki, Atsugi, Kanagawa 214-8571, Japan c Sincrotrone Trieste, Bassovizza, 34012 Trieste, Italy |