Influence of plasma functionalization treatment and gold nanoparticles on surface chemistry and wettability of reactive-sputtered TiO ₂ thin films

Amorphous titanium oxide (TiO ₂ ) thin films were deposited on silicon substrates by DC-magnetron sputtering at room temperature. The surface of thin films were treated in argon plasma admixed with ammonia or nitrogen or oxygen or hydrogen. It was found that plasma treatments did not influence micron and nanometer-scale surface morphology of the treated films, as examined by atomic force microscope. However, the X-Ray photoelectron spectroscopy (XPS) showed that oxygen groups have been incorporated in various amounts. In contrast with untreated TiO ₂ which is hydrophobic, the plasma treatments improved the TiO ₂ hydrophilicity persistently up to 77%. The wettability of the thin films, as determined from water contact angle measurements, is discussed with reference to changes in surface chemistry after plasma treatment. In addition, deposition of gold (Au) nanoparticles (NP) onto TiO ₂ samples and their interaction with TiO ₂ has been discussed through XPS results. It was demonstrated that in its reduced state, TiO ₂ promotes electron donation to Au, whereas oxygen content does not seem to affect the interaction between Au NP and the TiO ₂ support.