The electronic properties of oxygen vacancies in titania nanotubes were examined using electron spin resonance spectroscopy. The single-electron-trapped oxygen vacancy showed a Curie behaviour at 140 to 300K, which was indicative of localized electrons at the single-electron-trapped oxygen vacancy sites. On the other hand, the Ti3+ sites showed a thermally activated behaviour with an activation energy of about 120meV. Microwave saturation measurements revealed the single-electron-trapped oxygen vacancy signal to show apparent saturation with increasing microwave power. In contrast, the Ti3+ signal showed almost unsaturated behaviour, suggesting Ti3+ had faster spin-relaxation times than the single-electron-trapped oxygen vacancy. The difference between Ti3+ and single-electron-trapped oxygen vacancy appeared to be related to the difference between the bulk and surface spins.

Electronic Properties of Oxygen Vacancies in Titania Nanotubes. Cho, J.M., Seo, J.M., Lee, J.K., Zhang, H., Lamb, R.: Physica B, 2009, 404[1], 127-30