Anomalous bonding in SiO₂ at the SiO₂–Si interface

Ultraviolet photoelectron spectroscopy valence-band spectra measured at 51 eV for a series of thin oxide layers thermally grown on Si(111) and Si(100) surfaces show that anomalous bonding configurations exist in SiO2 near the interface. A comparison with theoretical density-of-states calculations indicate that these configurations cannot be related to the existence of a strained SiO2 layer with a distribution of Si–O–Si bond angles different to what is found in bulk SiO2. The results support the existence of threefold-coordinated oxygen centres as described in the valence-alternation-pair model.