Core-level photoemission study of additional in adsorption on the Si(111)√3x√3-in surface

Additional In adsorption onto the Si(111)√3x√3-In surface at room temperature has been known to induce spontaneous structural transformations into a 2 X 2 and a √7 X √3 phase, which accompany a drastic change of the surface electric property. These structural transformations have been studied by low-energy-electron diffraction and core-level photoemission spectroscopy using synchrotron radiation. The transformation from √3 X√3 to 2 x 2 is characterized by the appearance of an extra In 4d component shifted by -0.41 eV in binding energy. The 2 X 2 phase fully develops at the In coverage of ∼0.8 monolayer (ML), which has two different In sites as indicated by the In 4d spectra. This and the Si 2p core-level data deny the present structural models of the 2 X 2 phase. The In 4d line shape of the √7 X √3 phase formed above ∼ 1.2 ML exhibits a strong asymmetry, indicating a metallic character of this surface in clear contrast to √7 X √3 and 2 2 phases. A unique Si 2p surface component, which represents the topmost Si layer, is identified for the √7 X √3 phase with a surface core-level shift of - 0.20 eV. These results are generally consistent with the √7 X √3 structure model consisting of one planar In overlayer on top of a bulk-terminated Si(111). Accompanying the structural transformations, a drastic lowering of the surface Fermi-level position is observed until the In coverage increases up to ∼ 1.0 ML.