Initial stages of oxygen adsorption on Si(111): The stable state.

Abstract

We present new experimental results from a comprehensive study of the chemisorption of oxygen on differently prepared Si(111) surfaces, using low-energy electron diffraction and high-resolution electron spectroscopies such as x-ray photoemission spectroscopy, x-ray-initiated Auger-electron spectroscopy, and polarization-dependent ultraviolet photoemission spectroscopy. In the monolayer regime two different states of oxygen have been observed: a molecular precursor and a stable dissociated configuration. The latter is the subject of this paper. Its electronic structure and local symmetry are compatible only with a bridge-bonded atom between Si atoms in the first and second layer, respectively, with relatively little influence on the dangling bonds. The presence of a second dissociated oxygen adsorbate, e.g., a diatomiclike monoxide, is excluded by our data. The coverage dependent O 1s and Si 2p data indicate that the observed satellite structures in the submonolayer regime are due to excitations rather than to chemically shifted peaks from atoms in different bonding situations.