Titanium nanotubes grown by titanium anodization

In this work we investigated the structural and electrical properties of titanium dioxide (TiO(2)) nanotubes (NTs) grown by electrochemical anodization of Ti metal sheets in NH(4)F+H(2)O+glycerol electrolyte at different anodization voltages (V(a)) and electrolyte composition. Our results revealed that TiO(2) NTs can be grown in a wide range of anodization voltages from 10 to 240 V. The maximum NH(4)F acid concentration, at which NTs can be formed, decreases with the anodization voltage, which is 0.7% for V(a)< 60 V, and decreases to 0.1% at V(a)=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 TiO(2) transforms to anatase phase after annealing at 400 degrees C and further transforms to rutile phase at annealing temperatures above 500 degrees 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 V(a) concentration and increases by eight orders of magnitude when V(a) increases from 10 to 240 V. The resistivity is also greatly dependent on H(2)O 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.