Adsorption of chlorine on the Si(0 0 1)-2×1 surface

It is shown that the room-temperature dissociative adsorption of Cl2 on the Si(0 0 1)-2×1 surface results in the bonding of Cl atoms to both the up- and down-dimers which then become symmetrical. At saturation coverage the Si 2p core-level spectra exhibit only a single Cl-induced component with emission twice as strong as that from the up-dimer of the clean surface and with a core-level shift of +930±8 meV. These results were obtained using an analysis in which the intensities of the core-level spectra from the individual Si layers are constrained by an escape depth. It facilitates the identification of components down to the second subsurface layer and yields an inelastic mean free path of 3.4±0.2 إ at a photon energy of 140 eV.