Paramagnetic intrinsic point defects in nm-sized silica particles: Interaction with SiO at elevated temperatures

Point defects in ∼ 7 nm-sized fumed silica nanoparticles have been studied by Q-band electron spin resonance (ESR) following 10-eV irradiation to photodissociate H from passivated defects. In studying the influence of vacuum annealing special attention has been paid to the behaviour of the structure of the nanoparticles when brought into contact with ‘bulk’ Si/SiO2 entities at elevated temperatures in vacuum (Tan = 1005 °C), i.e., the presence of an Si/SiO2 interface. Alterations in the ESR characteristics of the observed intrinsic point defects are monitored. As indicated by the observed increase in E′ defect density and alterations in ESR properties it appears that the copresence of the Si/SiO2 structure affects the fumed SiO2(x) network structure distinctly, which is ascribed to the reaction of SiO released at the Si/SiO2 interface. In addition to the vulnerability for SiO attack, it is also found that the surface and near surface layers of the nanoparticles respond differently to the presence of SiO during the anneal than the core region. Results are ascribed to the reaction with SiO released at the Si/SiO2 interface.