DC Magnetron Sputtering Deposition of Titanium Oxide Nanoparticles: Influence of Temperature, Pressure and Deposition Time on the Deposited Layer Morphology, the Wetting and Optical Surface Properties Laurent Dreesen,* Francesca Cecchet, Ste ´phane Lucas Introduction In 1972, Fujishima and Honda discovered the remarkable photocatalytic properties of titanium dioxide (TiO 2 ). [1] Since then, the material has been intensively studied due to its interesting properties. Indeed, TiO 2 is, for instance, promising for the development of powerful anti-bacterial and self-cleaning coatings, or for building efficient solar cells. [2–4] Its high refractive index also allows its use in the development of optical waveguides, antireflection and multilayer optical coatings. [5–7] The photocatalytic applications are based on the ability of the semiconductor to generate an electron-hole pair across the band gap. This process requires UV light because the band gap is close to 3 eV, while it is the visible radiation which is mainly delivered by the sun. Moreover, the efficiency of the photocatalytic process is limited by the electron-hole pair lifetime which is directly correlated to the optical band gap and to the crystalline quality of the deposited layer. [8] Many research groups are therefore working on the TiO 2 doping as well as on ways to improve its crystallinity. TiO 2 nanoparticles (NPs) may be an alternative approach to solve the aforementioned problems. They offer interesting advantages over thin films such as increased active surface area and reduced electron-hole pair recombination. TiO 2 NPs can be synthesized by many techniques, including sol-gel process, hydrothermal meth- ods, sparking process, laser ablation, laser pyrolysis, spray Full Paper L. Dreesen Biophotonics, Department of Physics, Institute of Physics, Uni- versity of Lie `ge, B5, B-4000 Lie `ge, Belgium E-mail: Laurent.Dreesen@ulg.ac.be F. Cecchet Laboratoire Spectroscopies et Lasers (LLS), Centre de Recherche en Physique de la Matie `re et du Rayonnement (PMR), University of Namur (FUNDP), rue de Bruxelles, 61, B-5000 Namur, Belgium S. Lucas Laboratoire d’Analyses par Re ´actions Nucle ´aires (LARN), Centre de Recherche en Physique de la Matie `re et du Rayonnement (PMR), University of Namur (FUNDP), rue de Bruxelles, 61, B-5000 Namur, Belgium Titanium dioxide nanoparticles were prepared on glass substrates by reactive DC magnetron sputtering. As highlighted by the atomic force microscopy characterization, we were able to control the nanoparticles’ surface coverage and diameter by varying the deposition time and the total pressure, respectively. The titanium dioxide energy band gap, determined by using ultraviolet-visible spectroscopy, depends on the total pressure but is quite independent on the deposition temperature. On the contrary, it is blue shifted when the pressure increases. Finally, the contact angles slightly decrease after ultraviolet illumination irrespective of the different deposition parameters, indicating an improvement of the hydrophilic properties of the adsorbed layer. After 21 h in dark, the contact angles are nearly identical to the ones before exposure to UV light: the samples do not keep their hydrophilic behaviour. Plasma Process. Polym. 2009, 6, S849–S854 ß 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/ppap.200932201 S849