The titanium oxide, silicon oxide and aluminium oxide thin films were prepared by reactive magnetron sputtering in a high vacuum deposition chamber using an Ar/02 gas mixture. The mass flow ratio is set to 35:5 for titanium and silicon oxide and to 37:3 for aluminium oxide. The magnetrons are driven by bipolar-pulsed power for the Ti target (50 kHz at 200 W) and for the Al target (50 kHz at 150 W) and by medium frequency RF power (13.5 kHz at 100 W) for Si target. During the thin film deposition carried out at room temperature, the grounded substrates face the target at a distance between 5 and 8 centimeters. A working pressure of around 3 x 10-3 mbar is adjusted by throttling the pumping system. Ti02, Si02 and Al203 films are deposited on glass AF45 and monocrystalline silicon (with its native oxide) substrates 4×4 cm2 for the characterization optical techniques. For the in-situ photoelectron spectroscopy thin films are deposited on sputter cleaned copper substrates. The high vacuum deposition chamber is connected to an ultrahigh vacuum (UHV) electron spectrometer. Samples can be transferred from one system to the other without breaking the vacuum to get chemical information about the deposited films. The electron spectrometer is equipped with a hemispherical analyzer (Leybold EA 10/100) and a X-ray source for core level spectroscopy (X-ray photoelectron spectroscopy XPS: Mg Ka excitation, ho = 1253.6 eV). The typical resolution is 0.8 eV for the XPS measurements. A gold sample with the Au 4f7/2 core level signal at 83.9 eV binding energy is used as a reference for the electron energy calibration.

Ti 2p, Si 2p, Al 2p and 01s core levels were recorded in the case of Ti02, Si02and Al203 to determine the chemical composition for each layer. Atomic concentration ratios were calculated by integrating the peaks area after subtracting a Shirley background [12]. From the photoionization cross-sections given by [13], the atomic concentration at the films surface is calculated using UNIFIT program [14]. In our deposition conditions, the stoichiometry ofthe Ti02, Si02and Al203 films is reproducible.