Electronic and magnetic properties of alloys, compounds and other materials with nanometer-scale structure at solid surfaces are studied using scanning tunneling microscopy/spectroscopy (STM/STS), photoelectron spectroscopy and magneto-optical Kerr-rotation(MOKE)/second harmonic generation(SHG) measurements in an ultra high vacuum. Band structures of the filled surface states and the chemical bonds are studied by photoelectron spectroscopy using VUV light and soft-X-ray. Local atomic and electronic structures, formation processes of surface nano-structured materials and dynamical processes induced by electron tunneling or photo-excited carriers are examined by STM/STS. Local atomic structure can be manipulated through electron-lattice interaction by electronic excitation of tunneling electrons and photons.
Topographic image (a) and the Fermi-surface band mapping (b) of Au-adsorbed Ge(001) surface. Atomic-size protrusions align one-dimensionally on the surface. The one-dimensional structure consists of zigzag (A) and chevron (B) segments. The band at the Fermi surface very weakly disperses in the direction parallel to the line of the surface protrusions whereas the band disperses two-dimensionally in the occupied states below 80 meV from Fermi energy.
(a) STM image of single layer graphene grown on 8°-off SiC(0001) substrate by thermal decomposition. Graphene covers both the step edges and terraces continuously. (b-e) Constant-energy angle-resolved photoemission spectroscopy intensity maps at EF for the graphene samples formed on the 4°- (b,c) and 8°-off (d,e) substrates around K0° (b,d), K-60° (c), and K+60° (e). Here 0 degree indicates the tilting direction of the substrate. Dotted curves represent the constant-energy ideal π* band shape including the trigonal warping for flat graphene. The observed shape of the Dirac band for the 4°-off substrate is consistent with the ideal graphene while that for the 8°-off substrate is elongated in the tilting direction.
*Epitaxial Rh-doped SrTiO3 thin film photocathode for water splitting under visible light irradiation: S. Kawasaki, K. Nakatsuji, J. Yoshinobu, F. Komori, R. Takahashi, M. Lippmaa, K. Mase and A. Kudo, Appl. Phys. Lett.101 (2012) 033910 (1-4).
*Elucidation of Rh-Induced In-Gap States of Rh:SrTiO3 Visible-Light-Driven Photocatalyst by Soft X-ray Spectroscopy and First-Principles Calculations: S. Kawasaki, K. Akagi, K. Nakatsuji, S. Yamamoto, I. Matsuda, Y. Harada, J. Yoshinobu, F. Komori, R. Takahashi, M. Lippmaa, C. Sakai, H. Niwa, M. Oshima, K. Iwashina and A. Kudo, J. Phys. Chem. C116 (2012) 24445-24448.
† Joint research with outside partners. * Joint research between groups within ISSP.