Embedded structure of silicon monoxide in SiO2 films

The structure of SiO_x (x = 1.94) films has been investigated using both X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). The SiO_x films were deposited by vacuum evaporation. XPS spectra show that SiO_1.94 films are composed of silicon suboxides and the SiO₂ matrix. Silicon clusters appeared only negligibly in the films in the XPS spectra. Si₃O⁺ ion species were found in the TOF-SIMS spectra with strong intensity. These results reveal the structure of the films to be silicon monoxide embedded in SiO₂, and this structure most likely exists as a predominant form of Si₃O₄. The existence of Si-Si structures in the SiO₂ matrix will give rise to dense parts in loose glass networks.