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Surface structures of S/Ni(111) in (√3 × √3 )R30° and (5√3 × 2) phases studied by surface extended X-ray absorption fine structure spectroscopy |
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| Authors: | Y Kitajimaa S Yagi T Yokoyama A Imanishi S Takenaka and T Ohta |
| Institution: | a Photon Factory, National Laboratory for High Energy Physics, Oho, Tsukuba, Ibaraki 305, Japan b Department of Materials Science, Faculty of Science, Hiroshima University, Higashi-Hiroshima, Hiroshima 724, Japan c Department of Chemistry, School of Science, The University of Tokyo, Bunkyo-ku, Tokyo 113, Japan |
| Abstract: | The local surface structures of S/Ni(111) in the ( √3 × √3) R30° and (5√3 × 2) phases have been investigated by means of polarization-dependent sulfur K-edge surface EXAFS. In the (√3 × √3 ) R30° phase, sulfur adatoms are found to occupy threefold hollow sites with a S---Ni distance of 2.13 Å and an inclination angle ω of the Sz.sbnd;Ni bonds at 44° from the surface plane. In contrast, in the (5√3 × 2) phase, it is determined that the Sz.sbnd;Ni bond is longer, 2.18 Å, more inclined, ω = 31°, and that the coordination number is not 3 but 4. These results strongly support a picture involving reconstruction of the top nickel layer to form a rectangular structure. Consideration of several models proposed for the (5√3 × 2) phase leads to one which is compatible with both the present results and results recently reported using STM. |
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