Self-organized TiO2 nanotubes grown on Ti substrates with different crystallographic preferential orientations: Local structure of TiO2 nanotubes vs. photo-electrochemical response

Abstract Here we report on structural properties and the photo-electrochemical response of annealed TiO 2 nanotube layers, grown on four different Ti substrates by an identical anodization process. TiO 2 nanotube layers were grown on Ti substrates by anodization in glycerol containing NH 4 F and water. The layers were then annealed at 400 °C for 1 h in air. Photocurrent densities of annealed nanotubes were recorded upon irradiation with ultraviolet (UV) light at a constant potential of 0.4 V, in a 0.1 M Na 2 SO 4 aqueous solution. Approximately, a 280% difference in the photocurrent densities was recorded from TiO 2 nanotubes fabricated from different Ti substrates. To elucidate the origin of this difference, the nanotube layers were scrutinized by Mott-Schottky measurements, X-ray diffraction (XRD) and Electron Energy Loss Spectroscopy (EELS). Inspection of the XRD patterns revealed preferential crystallographic orientations in various Ti substrates from which TiO 2 nanotube layers were produced. Subsequent EELS analyses of the annealed nanotube layers disclosed significant differences in the Ti:O stoichiometry, in accordance with XRD evaluation of preferential orientation differences among used Ti substrates.