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Scanning transmission electron microscopy studies of the deposition of size-selected sub-nanometre platinum clusters

ABSTRACT: Size-selected cluster ions containing four atoms of platinum (Ptf) have been deposited onto graphite at different deposition energies and investigated by high angle annular dark field imaging in a scanning transmission electron microscope. PL clusters deposited at 50 eV were observed to diffuse and aggregate on the surface, while Pt4 clusters deposited at 1 keV were found to be implanted and immobilised. An intermediate regime of deposition energy, in which only a fraction of the incident clusters are implanted, was also identified. 1

1. INTRODUCTION

Clusters of atoms have physical properties that differ considerably from those of a single atom or the correspondent bulk solid. Moreover, these properties depend strongly on the size (number of atoms) of the clusters (see, for example, deHeer 1993) also motivating studies of the deposition of clusters to create nanostructured materials which employ the clusters as novel “building blocks” (Palmer 1997). Several groups (Perez et al (1997) and Haberland et al (1996)) have shown that thin films with new properties can be produced in this way.