Reactive direct current magnetron sputtered TiO 2 thin films with amorphous to crystalline structures S. Boukrouh a,b , R. Bensaha a , S. Bourgeois b , E. Finot b , M.C. Marco de Lucas b, ⁎ a Ceramics Laboratory, University Mentouri of Constantine, Road Ain El-Bey (25000) Constantine, Algeria b Institut Carnot de Bourgogne, UMR 5209 CNRS-Université de Bourgogne, 9 Av. A. Savary, BP 47 870, F-21078 DIJON Cedex, France Received 4 April 2007; received in revised form 10 November 2007; accepted 14 December 2007 Available online 31 December 2007 Abstract TiO 2 thin films were deposited on soda–lime glass substrates by reactive direct current magnetron sputtering in a mixture of pure argon and oxygen. The influence of both the deposition time, t d , and the post-annealing treatments on the films morphology, composition and structure was analyzed by scanning electron microscopy, ellipsometry, X-ray photoelectrons spectroscopy, X-ray diffraction (XRD) and Raman spectroscopy. Amorphous TiO 2 was obtained for the shortest deposition time, t d = 15 min. Increasing t d up to 30 min, poorly crystallized anatase and rutile phases were formed together with amorphous TiO 2 , as was revealed by complementary XRD patterns and Raman spectra. For longer t d , the growth of the anatase phase dominates that of the rutile phase. The post-annealing treatment of the films in air at 450 °C. induced the complete crystallization of the films leading to mainly anatase films for all the deposition times. All these results show the feasibility to fabricate stoichiometric TiO 2 thin films with amorphous to crystalline structures by means of soft fabrication conditions: low substrate temperature and moderate annealing treatment. © 2008 Elsevier B.V. All rights reserved. Keywords: Titanium dioxide; DC magnetron sputtering; Microstructure; X-ray diffraction, Raman spectroscopy 1. Introduction Titanium dioxide powders and thin films are of industrial interest because of their outstanding chemical, electrical, and optical properties. Titanium dioxide (TiO 2 )-based thin films have been processed using a wide range of deposition techniques including sol–gel [1], chemical vapor deposition [2], chemical spray pyrolysis [3], sputtering methods [4,5], …. Among these techniques, reactive direct current (DC) magne- tron sputtering has gained significant importance because it enables control of the structure, composition and properties of TiO 2 films by adjusting the deposition conditions [6,7]. This results in high quality thin films with thickness uniformity over large areas and well controlled stoichiometry. Moreover, sputtering methods are widely used in industrial processes because such high quality films can be obtained at low substrate temperatures. Indeed low temperature deposition is of particular interest in the thin film industry since special substrates capable of withstanding high temperatures are not needed, thereby reducing production costs. Among all the properties of titanium dioxide, a special emphasis is given to the photocatalytic activity, as attested by the increasing number of publications and patents [8,9]. When TiO 2 is illuminated by photons having an energy higher than TiO 2 band gap, charge carriers are photogenerated promoting oxidation and reduction reactions. This photocatalytic activity is applied, for example, in water purification [10,11] and air cleaning [12]. To improve the photocatalytic efficiency of titanium dioxide thin films, controlling the chemical and structural properties of the films is of fundamental importance. Indeed the photo- catalytic activity of the films can vary with the composition (stoichiometry, hydroxyl and impurity concentrations), the porosity, the surface roughness, the film thickness, the micro or nanostructure, …, although the influence of all these Available online at www.sciencedirect.com Thin Solid Films 516 (2008) 6353 – 6358 www.elsevier.com/locate/tsf ⁎ Corresponding author. E-mail address: delucas@u-bourgogne.fr (M.C.Marco de Lucas). 0040-6090/$ - see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2007.12.150