Experimental determination of deposition induced cluster deformation

Abstract

We describe an experimental method to measure the cluster deformation of metal clusters deposited on a substrate. It is based upon the sensitivity of the cluster plasmon resonance on the geometric shape of the clusters; it uses optical spectroscopy with polarized light in oblique incidence. The proposed method was applied to silver clusters (mean diameter 2R = 2nm) produced in a supersonic beam and deposited on a quartz glass substrate. Cluster deposition and optical measurements were performed in situ in vacuum. At an estimated particle velocity of 1.5 · 10³ ms ^-1, we evaluated an axial ratio of c/a = 0.86 for the deposition induced deformation. This result is compared to data from molecular dynamical simulations. By varying the substrate coverage, the critical cluster coverage for the onset of electromagnetic cluster-cluster coupling and coalescence was determined to amount to 0.1 cluster-monolayers.