Titanium dioxide (TiO2) thin films were deposited on unheated quartz (SiO2) substrates in “pure oxygen” plasma by reactive radio-frequency (rf) magnetron sputtering. The structural and optical properties of deposited films were systematically studied by changing the deposition parameters, and it was very recently found that crystalline TiO2 films grew effectively in pure O2 atmosphere. For TiO2 films deposited at a rf power Prf of 200 W, x-ray diffraction patterns show the following features: (a) no diffraction peak was observed at a total sputtering pressure ptot of 1.3 Pa; (b) rutile (110) diffraction was observed at 4.0 Pa, (c) the dominant diffraction was from anatase (101) planes, with additional diffraction from (200), under ptot between 6.7 and 13 Pa. For the deposition at 140 W, however, crystalline films with mixed phases were observed only between 4.0 and 6.7 Pa. The peaks of both the deposition rate and the anatase weight ratio for the films produced at 140 W were found at ptot of approximately 6.7 Pa. This suggests that the nucleation and growth of TiO2 films were affected by the composition, density, and kinetic energy of the particles impinging on the substrate surface. The optical absorption edge analysis showed that the optical band gap Eg and the constant B could sensitively detect the film growth behavior, and determine the film structure and optical absorption. The change in the shape of the fundamental absorption edge is considered to reflect th- e variation of density and the short-range structural modifications. © 2004 American Institute of Physics.