Buffer Layer Assisted Growth of Ag Nanoparticles in Titania Thin Films

Developing materials with improved photocatalytic activity is important for light energy conversion and storage within chemical bonds. Here we present a new type of hybrid film of silver nanoparticles (AgNPs) embedded within TiO_x (x ≤ 2) to approach this goal, introducing visible light absorption via surface-plasmon excitation of the AgNPs. Silver nanoparticles were prepared by an ultrahigh vacuum (UHV) based buffer layer assisted growth method. The titania films as a substrate and protective layers were grown by the reactive layer assisted deposition (RLAD) technique; in both cases amorphous solid water (ASW) was the buffer material. The thin titania films and the AgNPs were ex situ characterized by UV-vis, micro-Raman, XRD, XPS, SEM, and TEM techniques. The titania protective layers on top of the silver particles were found to introduce a dielectric environment for the AgNPs, leading to a significant red-shift of their plasmon resonance from 460 to 530 nm, in addition to avoiding oxidation of the small nanoparticles. Photoinduced activity of these hybrid films has been tested following the degradation of methylene blue (MB) in aqueous solution under both UV and visible pulsed laser irradiation. Preliminary results have shown photocatalytic activity of the RLAD titania film with only marginal influence due to the presence of the AgNPs. Possible reasons for this observation are discussed.