Size-dependent melting temperature of individual nanometer-sized metallic clusters

Gold and silver clusters with diameters in the nanometer-size range were grown in an inert-gas beam and deposited on the end of a tungsten field emitter. The field-emission current from an individual cluster is used to study a size-dependent change in shape of the cluster as a function of temperature. Three experimental signatures indicate an abrupt change in cluster shape at a temperature below the bulk melting point. This temperature is found to depend on cluster size and is in agreement with a thermodynamic model for cluster melting, provided the cluster diameter is greater than 2 nm.