Phase growth analysis of sputtered TiO2 thin films at low oxygen partial pressures using XANES and XRR

Abstract

This paper reveals the impact of oxygen in the phase growth of titanium oxide thin films. Films were developed using dc magnetron sputtering with Ti metal target at very low oxygen partial pressures (0–0.04) for 30 min. X-ray reflectivity (XRR) of the films was done to ascertain the variations in the structural properties of the films. Film roughness continually increases even for slight variations in oxygen partial pressure while the film density stabilizes within 3.6–3.8 g cm−3 with increasing oxygen content. L2,3 and O K-edge x-ray absorption near-edge structure (XANES) spectroscopy was done to identify the phase structures and oxidation states of the films. As-deposited films are all amorphous in nature, with no major change in their properties apart from increased thickness (280–910 Å). After post heating the films at 400 °C for 5 h in vacuum (10−5 torr) various crystalline phases evolve. A slight increase in oxygen partial pressure leads to a gradual transformation in the evolved phase of TiO2 films. Ti2O3 phase with Ti [Varghese et al 2001 Sensors Actuators B Chem. 81 32–41] coordination environment and Ti3+ oxidation state was detected with O2 partial pressure of 0.015 whereas a metastable anatase and stable rutile phase with Ti [Mosquera et al 2014 J. Anal. At. Spectrom. 29 736] coordination environment and Ti4+ oxidation state was observed with 0.02 and 0.04 O2 partial pressures, respectively.