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.

The growth mechanism of TiO(2) films and their morphology are reported using the reactive-layer-assisted deposition (RLAD) method under ultrahigh vacuum conditions. The oxide film formation involves Ti atom deposition on top of amorphous solid water (ASW) condensed on a SiO(2)/Si(100) support at 90 K. Subsequent annealing leads to the desorption of all nonreacted buffer molecules, resulting in the deposition of the titanium oxide film. Employing mass spectrometry and using D(2)O as a buffer, we detected the evolution of deuterium molecules during titanium atom deposition. A solid state sol-gel-like formation mechanism of titanium oxide is proposed on the basis these observations. The morphology of the oxide films is characterized by AFM as a rather uniform amorphous thin film at room temperature. Upon further annealing above 750 K, crystallization of the titanium oxide film has set in, coinciding with a dewetting process of the oxide layer, and information obtained from similar growth procedure on an amorphous carbon-covered TEM grid. It was shown that these films are rather insensitive to the underlying substrate at temperatures below 500 K.

Enhanced photodecomposition of ethyl chloride (EC) adsorbed on SiO2/Si (100) supported silver nanoparticles (Ag NPs) under ultrahigh vacuum (UHV) conditions has been studied in order to assess the potential contribution of plasmonic effects. The cross section for photodecomposition of EC and overall photoyield were found to increase with increasing photon energy regardless of the plasmon resonant wavelength and with Ag coverage without any noticeable particle size effect. The influence of EC-Ag NPs separation distance on the rate of EC decomposition was studied in order to examine potential local electric field influence on the photodissociation process. Long (∼5 nm) photoactivity decay distance has been observed which excludes local surface plasmon dominance in the photodecomposition event. These findings suggest that the alignment of excited electron energy and adsorbate affinity levels is central for efficient photochemical reactions, whereas short-range electric field enhancement by plasmon excitation on top and at the immediate vicinity of silver nanoparticles does not have any measurable effect.

Novel procedures to grow pure thin metal oxide films are always welcome in view of their wide range of applications including photocatalysis, solar cells, sensors, and more. In this paper we present a unique way to grow pure nanofilms of metal oxides in vacuo at the temperature range 110-170 K. The reactive layer assisted deposition (RLAD) procedure for thin oxide films growth is based on the evaporation of a reactive metal element on top of a condensed layer of amorphous solid water (DO-ASW). When applied to metals that do not react with the water layer, the process yields metal nanoclusters on the substrate. We observed that metal oxide films are formed if the redox potential is of -1.0 V or less, leading to deuterium molecules ejection to the gas phase (e.g., Ti and Al) while metals such as Zn, Fe, and Ag, with redox potentials more than -1.0 V, transform into nanoclusters, as revealed by SEM studies. We conclude that the redox potential ia a parameter that enables one to predict the nature and outcome of the ASW buffer layer assisted chemistry.