Chemisorption of chlorine on Si(111) 7 × 7 and 1 × 1 surfaces

Using ultraviolet photoemission spectroscopy (UPS) in conjunction with theoretical calculations, we have studied the reaction of gaseous chlorine with Si(111) 7 × 7 and 1 × 1 surfaces. The UPS spectra of the two chlorine saturated surfaces are very similar and consist of four peaks, a sharp main peak at -10.7 eV and smaller ones at -7.5, -13.0, and -15.7 eV relative to vacuum level. Both the peak positions and their relative intensities are in quantitative agreement with a theoretical calculation for a structural model in which a single chlorine atom sits on top of each surface Si atom, indicating that ${\mathrm{Cl}}_2$ decomposes at the surface to make strong covalent bonds with Si.