Core-level photoemission study of additional In adsorption on the Si(111)(formula presented)×(formula presented)-In surface

Additional In adsorption onto the (formula presented) surface at room temperature has been known to induce spontaneous structural transformations into a (formula presented) and a (formula presented) 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 (formula presented) to (formula presented) is characterized by the appearance of an extra In (formula presented) component shifted by -0.41 eV in binding energy. The (formula presented) phase fully develops at the In coverage of ∼0.8 monolayer (ML), which has two different In sites as indicated by the In (formula presented) spectra. This and the Si (formula presented) core-level data deny the present structural models of the (formula presented) phase. The In (formula presented) line shape of the (formula presented) phase formed above ∼1.2 ML exhibits a strong asymmetry, indicating a metallic character of this surface in clear contrast to (formula presented) and 2 2 phases. A unique Si (formula presented) surface component, which represents the topmost Si layer, is identified for the (formula presented) phase with a surface core-level shift of -0.20 eV. These results are generally consistent with the (formula presented) 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.