Anisotropic spillover from elongated nanoparticles

Reaction processes have only recently been imaged at the nanoscale and advances in this direction are being made by the use of ultramicroscopies such as scanning probe methods. In this paper we describe the application of high temperature STM to the imaging of nanoparticles of Pd fabricated on TiO2. We have imaged 'spillover' of a reactant from the Pd particles (which are active for adsorption) onto the surrounding TiO2 (which is inactive for adsorption). A surprising observation is made with nanoparticles with a high aspect ratio of length to width. In that case spillover occurs preferentially from the ends of the nanoparticle, and it is speculated that this is due to higher reactivity there for O-2 dissociation, which is due in turn to the lower average coordination of surface Pd atoms at the ends of the particle. (C) 2001 Elsevier Science B.V. All rights reserved.