Metal nanoparticles such as gold and silver deposited on metal-oxide semiconducting materials such as TiO₂ and WO₃ are of increasing interest for catalytic applications, for instance photocatalytic oxidation reactions [1,2] and hydrogen evolution [3]. Traditional preparation methods for nanoparticles synthesis are commonly using wet-chemical reactions such as citrate reduction method [4]. However, reproducibility of deposition density and size distribution is limited. Magnetron sputtering in combination with thermal annealing is being applied as a simple reproducible synthesis method that is easily scalable and suitable for large scale energy applications introduced. In the new physical vapour deposition (PVD) process, first of all, a thin nano-sized metal layer is deposited onto the semiconductor. A subsequent thermal annealing step transforms the metal layer into isolated nanoparticles due to solid state dewetting [5]. By tuning the nominal thickness of the sputtered metal layer and by repetition of sputtering/annealing cycles, the particle diameter can be controlled. Because of their enhancing effect on catalytic activity of semiconductors, gold and silver are in the focus of this study. Furthermore, a combination of both materials was carried out, aiming at formation of Au/Ag core-shell structures. As semiconductor layers, TiO₂ and WO₃ were used as nontoxic and cost-effective materials and also synthesized by magnetron sputtering. The optical properties of both mono- and bimetallic particles are investigated using UV/Vis measurements. The microstructure and crystallinity of the nanoparticles are studied using a combination of SEM, HRTEM and GIXRD. The photocatalytic properties of the nanoparticle/semiconductor systems are also observed applying the materials as working electrodes in a photoelectrochemical cell.

[1] Remediakis, I. N.; Lopez, N., Norskov, J. K. CO Oxidation on Gold Nanoparticles: Theoretical Studies. Applied Catalysis A: General. 2005, 291, 13-20.

[2] Liu, X.; Wang, A., Li, L., Zhang T., Mou C.-Y., Lee, J.-F. Synthesis of Au–Ag Alloy Nanoparticles Supported on Silica Gel via Galvanic Replacement Reaction. Progress in Natural Science: Materials International. 2013, 23(3), 317-325.

[3] Linic, S.; Christopher, P.; Ingram, D. B. Plasmonic-Metal Nanostructures for Efficient Conversion of Solar to Chemical Energy. Nature Materials. 2011, 10, 911-921.

[4] Turkevich, J.; Stevemnson, P.C.; Hillier, J. A study of The Nucleation and Growth Processes in The Synthesis of Colloidal Gold. Discuss Faraday Soc., 1951, 11, 55-75.

[5] Mueller, C. M.; Spolenak, R. Microstructure Evolution During Dewetting in Thin Au Films. Acta Materialia, 2010, 58, 6035-6045.