Atomic and electronic structures of oxygen-adsorbed Si(001) surfaces

Abstract

We investigate the stable structures of oxygen-adsorbed Si(001) surfaces and their electronic states. For this study, the first-principles molecular-dynamics method with the ultrasoft pseudopotential scheme is applied. The oxygen and silicon atoms are fully relaxed according to the calculated atomic forces for the optimized geometries. We find three (meta)stable sites for atomic oxygen adsorption: a dimer-bridge site and two different backbond sites of the dimer atoms. The original dimer bond is decomposed, or preserved and twisted, respectively. Most energetically favorable is the backbond site of the down dimer atom. Here, the electronegativity of oxygen enhances the ionicity of the dimer bond. Further, we simulate scanning tunneling microscopy images of the oxygen-adsorbed surfaces. The features of the most stable geometry are in good agreement with the observed ones. © 1996 The American Physical Society.