Surface photovoltage phase spectroscopy study of the photo-induced charge carrier properties of TiO nanotube arrays.

By using the surface photovoltage (SPV) technique based on a lock-in amplifier, surface states located 3.1 eV below the conduction band of TiO have been detected in TiO nanotube arrays prepared by anodization of titanium foil in fluoride-based ethylene glycol solution. The photo-induced charge transportation behavior of TiO nanotube arrays was also studied by qualitatively analyzing their SPV phase spectra measured under different external bias. When a negative bias was applied, carriers excited from surface states have the same transportation properties as those excited from the valence band; in contrast, when a positive bias was applied, these two kinds of photo-excited carriers exhibit different transportation behavior. [ABSTRACT FROM AUTHOR]