Structural models and core-level shifts of the oxidation of the Si(001) surface

A first-principles investigation of the oxygen adsorption processes on the Si(001) surface is presented. Our optimized full core potential calculations give nine energetically stable structural models for the suboxide Si1+, Si2+, and Si3+ components. Our computed initial state Si 2p core-level shifts for the most stable configuration, of each Sin+ species, gives -0.96, -1.89, and -2.28 eV for n=1, 2, and 3, respectively. These results are in good agreement with high-resolution photoemission spectra, which allow us to determine the structural model of each Sin+ species. Also we verified a connection between the adsorption energies of the structural models and the measured intensity ratios of each suboxide component. The calculated adsorption energies of the most stable structural model for each species, in decreasing order, are Si2+, Si1+, and Si3+, in agreement with experimental intensities for low O-2 dose results.