The role of barrier layer temperature in the formation of long and small-diameter TiO2 nanotube arrays

Small-diameter TiO2 nanotubes (TNTs) are fabricated at a fast growth rate by developing an effective anodization method in an organic electrolyte. Two different temperatures are applied to both sides of sample in order to increase the current density during the anodization process. Here, we use a high temperature for the backside of the sample (direct heating of the barrier oxide layer) in order to increase the current density while keeping the electrolyte at a low temperature to decrease the chemical etching at top of the TNT arrays. Increasing the backside temperature up to 55 °C leads to the formation of longest TNTs with an average diameter of about 17 nm at high-speed TNT growth of about 2000 nm/h under 20 V. Based on the high-field theory and accurate estimation of the barrier layer (BL) temperature, the incremental effect of increasing the BL temperature on the anodization current is also investigated.