Identification of defect sites on SiO2 thin films grown on Mo(112)

SiO2 thin films on Mo(112) have been characterized using metastable impact electron and ultraviolet photoeloctron spectroscopies (MIES and UPS). The electronic properties Of SiO2 thin films with a thickness of 0.7-0.8 nm are identical to those of bulk SiO2. For defective SiO2 surfaces prepared by three different ways (synthesis without an anneal, e-beam bombardment, and Si-deposition), additional Features are observed in the band gap using MIES that are consistent with theoretical predictions of additional occupied states in the band gap of SiO2 due to vacancies or excess oxygen. In contrast, UPS did not show any changes within the band gap in the presence of these defects. Extended defect sites on SiO2 arc, identified using MIES/UPS by a narrowing of the O(2P) features with a reduction in the density of extended defect sites. MIES spectra for adsorbed Xe (MAX) are also used to estimate the density of extended defect sites.