Titanium nanotubes grown by titanium anodization

Abstract

In this work we investigated the structural and electrical properties of titanium dioxide (TiO2) nanotubes (NTs) grown by electrochemical anodization of Ti metal sheets in NH4F+H2O+glycerol electrolyte at different anodization voltages (Va) and electrolyte composition. Our results revealed that TiO2 NTs can be grown in a wide range of anodization voltages from 10 to 240 V. The maximum NH4F acid concentration, at which NTs can be formed, decreases with the anodization voltage, which is 0.7% for Va<60 V, and decreases to 0.1% at Va=240 V. Addition of water to the electrolyte results in an increase in NT growth rate and modification of NT film morphology. Glancing angle x-ray diffraction experiments show that as-grown amorphous TiO2 transforms to anatase phase after annealing at 400 °C and further transforms to rutile phase at annealing temperatures above 500 °C. Samples grown in 30–120 V voltage range have higher crystal quality as seen from anatase (101) peak intensity and reduced linewidth. The electrical resistivity of the NTs varies with Va concentration and increases by eight orders of magnitude when Va increases from 10 to 240 V. The resistivity is also greatly dependent on H2O concentration increasing with its concentration up to nine orders of magnitude. Temperature dependent I-V and photoinduced current transient spectroscopy were employed to analyze electrical properties and defect structure on NT samples.