Effect of sol–gel composition ratio and laser power on phase transformation of crystalline titanium dioxide under CO2 laser annealing

Abstract

The crystalline structure of titanium dioxide (TiO2) is very much related to its properties. The sol–gel process and CO2 laser annealing instead of conventional furnace annealing have been performed to investigate the crystalline TiO2 formation. The sol–gel solution was mixed by tetraisopropyl orthotitanate (TTIP), acetonylacetone, distilled water and alcohol at various molar ratios and spin-coated on the p-Si(100) substrate. Then the CO2 laser annealing in air at powers of 0.5, 1.5 and 3.0 W in the defocus mode was performed on the coatings for studying the crystallisation of titanium oxide. The microstructure and phase transformation of titanium dioxide were examined by X-ray diffraction pattern. Increasing TTIP concentration and decreasing laser power were favourable for anatase phase formation. The grain size of titanium dioxide calculated using Scherrer's formula was between 10 and 32 nm, which increased with increasing laser power. The ANSYS simulation was employed to calculate the temperature distribution of films to correlate with the phase transformation of titanium dioxide. This sol–gel processing combined with CO2 laser annealing had advantages of low cost, controllable titanium dioxide phase, selective area annealing and easy operating at room temperature.