Monodisperse tungsten oxide cluster deposition from solution:66th Annual Meeting of the Austrian Physical Society

Müllner, Matthias and Balajka, Jan and Schmid, Michael and Diebold, Ulrike and Mertens, Stijn F. L. and Hemmi, Adrian (2016) Monodisperse tungsten oxide cluster deposition from solution:66th Annual Meeting of the Austrian Physical Society. In: 66th Annual Meeting of the Austrian Physical Society, 2016-09-272016-09-29.

Abstract

Perfectly monodisperse clusters of oxides are critically important model systems for catalysis studies because they allow the rigorous analysis of reaction mechanisms, and variations at the single-atom level can already be reflected in their reactivity. The generation and intact immobilisation on a suitable substrate of such clusters is quite challenging, and usually requires mass spectrometric size selection and sophisticated soft landing protocols to make such studies successful. Tungsten (VI) oxide in particular holds promise as a visible-light photocatalyst, but is quite reactive and can be challenging to immobilise in a well-defined manner in vacuum [1]. Here, we present a solution-based protocol for the preparation of monodisperse cyclic tris (tungsten (VI) trioxide) clusters, (WO3) 3. The clusters can be harvested efficiently on the boron nitride nanomesh [2], an atomically thin layer of hexagonal boron nitride on Rh (111) with strong corrugation, and a promising platform for self-assembly [3] and electrochemical functionality [4]. The triangular (WO3) 3 clusters adsorb in the ‚pores‘ of the nanomesh, where they were imaged with submolecular resolution using electrochemical scanning tunnelling microscopy. The decorated surface was transferred to vacuum where the chemical identity of the clusters was confirmed with XPS. To our knowledge, this is the first successful example of self-assembly on the nanomesh from solution. We expect that proper control over deposition conditions will allow tuning of the number of clusters per pore, making this a promising model system for on-surface catalysis studies. We contrast this finding with deposition of the same source material on rutile TiO2 (110) in liquid, on which the clusters appear to react and form chains, akin to some observations of sublimated WO3 in vacuum [5]. Even though the clusters are likely hydroxylated in aqueous solution, this behaviour indicates surprising parallels with UHV and suggests that, in many cases, solution-based procedures complement vacuum methods.