Abstract
Abstract It has been found previously that the initial stages of oxygen adsorption on Si(lll) occur via a metastable molecular precursor which decays to dissociated oxygen in a SiO.Si bridge configuration. In the present study using synchrotron radiation, surface techniques such as UPS, XAES, and NEXAFS were employed for a detailed characterization of this intermediate state which is stabilized at LN2 temperature and at low coverages. The UPS data showing a pronounced σ-shape resonance and the high resolution O KVV Auger data corroborate our earlier suggestion of a molecular species and exclude dissociative oxygen, e.g. in an on-top position, for the precursor. The polarization dependent NEXAFS data show π- and σ-resonances and unambiguously prove the presence of an oxygen molecule with its molecular axis parallel to the surface. From the energy position of the a-shape resonance we derive an increase of the O-O bond length as compared to isolated O2.
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