Structural Investigation of the So-Called Ca/Si(111)-(5×1) Surface

We have investigated the geometric structure of the so-called Ca/Si(111)-(5×1) surface using low-energy electron diffraction (LEED) and high-resolution core-level photoelectron spectroscopy. In LEED, dim extra spots besides the ×5 spots were observed after cooling the sample to 100 K. The positions of these dim spots reveal that this phase has a ×2 periodicity along its one-dimensional (1D) chains. In Si 2p core-level spectra, we observed five surface components. By considering the energy shift and intensity of each surface component and the 0.3 ML Ca coverage, we propose a structural model of this surface.