Structural transition layer at SiO2/Si interfaces

The valence-band and the O 2s core-level spectra of ultrathin (about 1 nm) SiO2 layers [which are formed at the initial stages of oxidation of hydrogen-terminated Si(100) substrates] were measured by high-resolution x-ray photoelectron spectroscopy. The energy difference between the valence band and the core level was found to be greater than that for the bulk SiO2. A first-principle molecular-orbital calculation was performed on Si2O7H6 clusters in order to obtain the energy difference (which depends on the structure of SiO2 layers). A comparison of the experimental data and the molecular-orbital calculations indicates chat the intertetrahedral bond angle, theta(Si-O-Si), is 135 degrees to 140 degrees in the SiO2 structural transition layers at the SiO2/Si interfaces. [S0163-1829(99)03708-X].