Interface feature characterization and Schottky interfacial layer confirmation of TiO2 nanotube array film

•Interfacial fusion of TiO2 nanotube film increases with annealing temperature.•Interface bonding force of the film increases with annealing temperature.•We report the forth stage of nanofibers formation in the growing mechanism.•TiO2 nanotubes grow from Schottky interface layer rather than from Ti substrate.•Schottky interface layer's thickness of 35–45nm is half the diameter of nanotube. We report here characterization of the interfacial microstructure and properties of titanium dioxide (TiO2) nanotube array films fabricated by anodization. Field effect scanning electron microscopy (FESEM), X-ray diffraction (XRD), nanoindentation, atomic force microscopy (AFM), selected area electron diffraction (SAED), and high-resolution transmission electron microscopy (HRTEM) were used to characterize the interface of the film. With increasing annealing temperature from 200°C to 800°C, the interfacial fusion between the film and the Ti substrate increased. The phase transformation of the TiO2 nanotube film from amorphous to anatase to rutile took place gradually; as the phase transformation progressed, the force needed to break the film increased. The growth of TiO2 nanotube arrays occurs in four stages: barrier layer formation, penetrating micropore formation, regular nanotube formation, and nanofiber formation. The TiO2 nanotubes grow from the Schottky interface layer rather than from the Ti substrate. The Schottky interface layer's thickness of 35–45nm was identified as half the diameter of the corresponding nanotube, which shows good agreement to the Schottky interface layer growth model. The TiO2 nanotube film was amorphous and the Ti substrate was highly crystallized with many dislocation walls.