Controllable current oscillation and pore morphology evolution in the anodic growth ofTiO2 nanotubes

Abstract

The spatial heterogeneities and temporal instabilities in the anodic growth ofTiO2 tubes are very important for nanostructure fabrication, but few orderedcases have been reported. In this work, we represent a new currentoscillation with pore morphology evolution in the formation of anodicTiO2 tubes. Small (less than 8.0% of the minimum value) and fast (period ∼ 100 s) current oscillation was formed under static conditions in a wide range,while significant morphological change such as periodical narrowing, abruptionand small pits appeared in the pore with characteristic length scale of101–102 nm. Surprisingly, the roughness in the pore would be totally eliminated instead of beingenhanced by high speed stirring or periodically modulated voltage with the currentoscillation still being enhanced, which indicates an important involvement of the iontransport process. It has also been found that the growth rate could be significantlyaccelerated by tuning the stirring rate or the periodical modulation of the voltage.The mechanism has been described with consideration of the local reactions andthe ion transport with a key involvement of the convection process, which canbe strongly influenced by the mechanical stirring and the modulated voltage.