Surface OH groups governing surface chemical properties of SiO2 thin films deposited by RF magnetron sputtering

We investigated the effects of metal doping on the surface chemical properties of silicon oxide (SiO2) thin films. The SiO2 thin films, doped with aluminium (Al), titanium (Ti) or zirconium (Zr), were deposited onto glass by RF magnetron sputtering. The contact angle of water droplets was measured for the films as a function of elapsed time. The hydrophobicity, resulting from the adsorption of organic substances in the atmosphere was significantly altered by metal doping. The surface reactivity of the metal doped films with a polyfluoroalkyl isocyanate silane was also changed. It was found that these alterations were due to the difference in surface OH group density of the film. Furthermore, there was a tendency that the surface OH group density increased along with the amount of non-bridging oxygens in the films. The formation ability of non-bridging oxygens may be closely related with the bonding nature and co-ordination number of the doped element with oxygens in the SiO2 structure