Fabrication of nanostructured TiO2 by anodization: A comparison between electrolytes and substrates

Nanostructured TiO2 thin films with large surface to volume ratio are fabricated from titanium thin films deposited on various substrates employing an anodization technique. The effect of the electrolytes (e.g. HF-containing electrolyte or neutral electrolyte) and substrates (e.g. silicon substrate or silicon carbide substrate) on the microstructure of the anodized thin films are investigated. Nanoporous films on silicon substrates with an average pore diameter of 25 nm and interpore distance of 40 nm are obtained by anodizing in an aqueous HF electrolyte solution after a comprehensive investigation of the anodization conditions. When the anodization is performed in a neutral electrolyte without HF solution, discrete nanotubular thin films are formed. The anodic film on silicon carbide substrate shows a quite different morphology, which exhibits a layered structure after anodization. The nanostructured TiO2 films are characterized using SEM and XRD techniques and their formation conditions are discussed. In addition, a growth mechanism model is presented to explain the formation of different nanostructures.