Scanning-tunneling-microscopy images of oxygen adsorption on the Si(001) surface

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Abstract
We investigate the atomic structures and scanning-tunneling-microscopy (STM) images of oxygen adsorption on the Si(001) surface. Here, three (meta)stable sites for atomic adsorption are discussed: a backbond of down dimer atom, a dimer-bridge, and an on-dimer site. For this study, the first-principles molecular-dynamics method incorporating the ultrasoft pseudopotential scheme is applied. The oxygen gives a surface structure characteristic of the adsorption site. In particular, the Si-O-Si complex at the dimer-bridge site buckles so as to mimic the original dimer. In the filled states, the STM images for the backbond and the dimer-bridge site appear very similar. In contrast, the empty-states images show characteristic features of the oxygen site.