Anodic growth of $TiO_2$ nanopore arrays at various temperatures

Nanoporous anodic titanium oxide (ATO) layers with different cell sizes, pore diameters and the thicknesses are successfully grown by three-step self-organized anodization in ethylene glycol containing 0.38 wt% of NH4F and 1.79 wt% of H2O at applied potential differences ranging from 30 V to 70 V at various electrolyte temperatures. A relatively high growth speed (about 40 μm h−1) of nanopore arrays is achieved at 30 °C under the potential difference of 70 V. The morphology and the structure of ATO layers are directly affected by anodizing conditions, especially temperature and potential difference. It was found that the oxide thickness and the cell size are linearly dependent on anodizing potential difference. On the other hand, the anodizing temperature in the range of 10–30 °C does not affect the cell size in ATO films. Analyses of the pore diameter, pore circularity and regularity of the pore arrangement suggests that nanoporous anodic titania with the best pore arrangement can be formed in a controlled manner by anodization performed at 50 V and 20 °C. Surprisingly, below and above this critical potential difference and temperature, pore diameters are smaller and obtained ATO structures are less regular. At higher anodizing temperatures, the regularity of pore arrangement observed at the surface and the pore diameter are considerably affected by the precipitated hydrous titanium dioxide