Characterization of titania thin films prepared by reactive pulsed-laser ablation D. Luca a, * , D. Macovei b , C.-M. Teodorescu b a Faculty of Physics, Alexandru Ioan Cuza University Iasi, 11 Carol 1 Blvd., 700506 Iasi, Romania b National Institute of Materials Physics, Atomistilor 105b, P.O. Box MG07, 077125 Bucharest-Magurele, Romania Available online 22 May 2006 Abstract Results are reported on the characterization of 200–250 nm thick TiO x transparent films grown at temperatures of 150 °C and 500 °C by reactive pulsed-laser ablation of a metallic Ti target under 0.13–13.3 Pa oxygen atmosphere. Film structure and composition were investigated by X-ray diffraction and X-ray photoelectron spectroscopy. The samples deposited at 150 °C reveal a mixture of amorphous TiO 2 and Ti 2 O 3 , irrespective of oxygen pressure. The O:Ti atomic ratio fluctuates in their surface around 1.83 for oxygen pressure rang- ing between 0.13 Pa and 2.66 Pa. The samples deposited at 500 °C feature different characteristics, as a function of oxygen pressure: (a) below 2.66 Pa of O 2 the films contain a mixture of significant amount of anatase and rutile TiO 2 phases, along with titanium suboxides; (b) above this threshold, the rutile phase vanishes, the anatase TiO 2 phase remaining dominant along with small amounts of nanocrys- talline suboxides. The size of the anatase nanocrystallites decreases with the increase of oxygen pressures. The samples deposited at 500 °C feature a slight improvement of surface stoichiometry, from roughly TiO 1.8 to TiO 1.9 . The films deposited at high substrate tem- perature and oxygen pressure are highly hydrophilic. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Reactive laser ablation; TiO x films; XPS; XRD; Anatase; Rutile; Suboxides; Hydrophilicity 1. Introduction Titanium oxides have been intensively studied over the last decades owing to their special physical and chemical properties. As thin films, they are involved in numerous applications in environment protection, photonics, electron- ics, and X-ray techniques [1–3]. Among other deposition techniques, the pulsed-laser ablation of an oxidic target be- came a well-established way of preparation, due to its ability to grow films with quasi-congruent film-target composition [4–6]. On the other hand, the formation of Ti–O bond is exo- thermic, the binding energy is 6.98 eV and the cross-section of the oxidation reaction is 22.6 A ˚ 2 in the gas phase [7]. Therefore, ablating a metallic Ti target in oxygen atmo- sphere can be a means to grow titania films, provided that adequate measures are taken to avoid target splashing and occurrence of particulates in the films. We report here on the characterization of the RPLA- deposited films, focusing on film structure and composition as effects of O 2 pressure substrate temperature. Our results demonstrate that growing titania films by reactive pulsed- laser ablation (RPLA) of a Ti target in O 2 atmosphere is a good candidate method to prepare titania films, as pointed out recently [8,9]. 2. Experimental Thin films were prepared in an UHV ablation chamber with a base pressure of 1.3 · 10 5 Pa. A 2.5 cm diameter Ti (99.5% purity) disk was used as ablation target under 15 000 laser shots (20 ns duration, 50 Hz repetition rate, 60 mJ/pulse) from a 308 nm XeCl excimer laser. The laser beam was focused on a 2.5 · 1.5 mm 2 area of the target. 0039-6028/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.susc.2006.01.162 * Corresponding author. Tel.: +40 232 201 179; fax: +40 232 201 150. E-mail addresses: dumitru.luca@uaic.ro, dluca@uaic.ro (D. Luca). www.elsevier.com/locate/susc Surface Science 600 (2006) 4342–4346