Surface properties of doped and undoped TiO 2 thin films deposited by magnetron sputtering J.O. Carneiro a, * , V. Teixeira a , A.J. Martins a , M. Mendes a , M. Ribeiro b , A. Vieira b a Physics Department, University of Minho, Campus Gualtar, 4710-057 Braga, Portugal b CeNTI, Centre for Nanotechnology and Smart Materials, 4760-034 Vila Nova de Famalica ˜o, Portugal Keywords: Titanium dioxide Photocatalytic activity Fe-doping effect Contact angle Sputtering pressure abstract In this work, transparent titanium dioxide (TiO 2 ) thin films were deposited onto microscope glass slides by means of the d.c. reactive magnetron sputtering method. The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV–visible spectroscopy (UV) and contact angle analysis using the Owens–Wendt method for the surface energy calculation. The photocatalytic activity of the films was tested by measuring the photodegradation of Rhodamine-B (RhB) dye under radiation of UV light. Iron-doped TiO 2 films were also prepared in order to study the Fe-doping effect on TiO 2 photocatalytic activity. The influences of different iron concentrations on the contact angle of the series of Fe-doped TiO 2 thin films, were investigated. The influences of total sputtering pressures on TiO 2 photocatalytic activity were also investigated. It was observed that the photocatalytic activity of the TiO 2 thin films was slightly improved by increasing the total sputtering pressure. Moreover, it was also observed that in general, iron-doping was detrimental for photocatalytic activity, nevertheless the films with low iron concentrations showed better photocatalytic activity than those with high iron concentrations. It was found that iron-doping has changed the wettability appe- tency of TiO 2 coated surfaces. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Titanium dioxide is a non-toxic metal oxide semiconductor with many industrial uses. In recent years exhaustive investigation has been performed on the TiO 2 as an efficient photocatalyst [1,2] and its use has been applied to environment problems such as water decontamination processes in association with the treatment of industrial effluents, air purification and destruction of microor- ganisms [3,4]. The mechanism of the photocatalysis using TiO 2 has been explained by chemical redox reactions induced by the gener- ation of electron–hole pairs (e  /h þ ) in the TiO 2 particles after the absorption of UV light [5,6]. The photo-generated holes in the semiconductor particles, the hole-trapping radical species and the activated oxygen species (by electron trapping) are all strong oxidation agents for organic compounds [7]. On the other hand, the enhanced photocatalytic effects of doped titanium dioxide have been recently reported [8]. Doping of TiO 2 with transition metal ions such as iron, may offer a way to trap charge carriers and extend the lifetime of one or both of the charge carriers. TiO 2 thin films can be prepared by a variety of methods. Among these, magnetron sputtering is an interesting method for preparing TiO 2 thin films because it is a friendly environment industrial process applicable to large-area deposition (or even when large-scale production is needed), and high quality TiO 2 films can be achieved even at low substrate temperatures [9]. The TiO 2 photocatalysis is very useful not only in environment purification but also in some outdoor situations. For example, most of external building walls become spoiled from automobile exhaust gases, which contain oil compo- nents. By coating the original building materials with a hydrophilic photocatalyst, the dirt of the walls can be washed away by rain, keeping the building external material wall clean for long times. In this work we investigate the effect of some of the deposition parameters such as total sputtering pressure and iron-doping on the structure and photocatalytic activity of TiO 2 films deposited on glass substrates. The results were analysed and discussed. 2. Experimental 2.1. Preparation of iron-doped TiO 2 film Fe-doped TiO 2 films with an average thickness of about 700 nm (evaluated by SEM), were deposited on glass substrates of the * Corresponding author. Tel.: þ351 253510477/00; fax: þ351 253510401. E-mail address: carneiro@fisica.uminho.pt (J.O. Carneiro). Contents lists available at ScienceDirect Vacuum journal homepage: www.elsevier.com/locate/vacuum 0042-207X/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.vacuum.2009.03.028 Vacuum 83 (2009) 1303–1306