Thickness and ion irradiation induced structural phase changes in the thin films of titanium dioxide

Abstract

Titanium dioxide (TiO2) thin films of thicknesses in the range of 20–60 nm were deposited by sol-gel dip coating method, and their structural and morphological properties before and after irradiation with 100 MeV Ni7+ ions were investigated. A systematic analysis of the hydrolysis reaction in the sol and films showed that complete hydrolysis of the precursor in the films can occur at room temperature in air ambient. However, aging of the sol for a minimum of 24 h prior to coating and drying / annealing the films at temperatures above 150 °C after deposition can favor the formation of regular –O–Ti–O– structural framework. The structural studies revealed a thickness dependent phase change in the films. Then it was found that this phase change can be precisely reversed by ion irradiation. The mixed rutile-anatase phase evolved towards pure anatase phase with increase in the thickness of the films, and that exactly traced back up on irradiation with increase in the ion fluence. The morphological studies showed a progress of the large island like structure with voids in the pristine film towards homogeneous nanosized particles and continuous morphology upon irradiation with increase in the ion fluence. The observed thickness and ion irradiation dependent structural and morphological changes of the TiO2 films can be used for tuning precisely their structural phase and morphology, which is relevant for photo-catalysis and sensing applications.