Elastic properties of individual nanometer-size supported gold clusters

Abstract

An atomic force microscope has been used in the attractive (noncontact) force mode to image individual nanometer-size Au clusters preformed in the gas phase and deposited on a wide variety of atomically flat substrates. Using this noncontact technique, it is possible to reliably image preformed clusters in their as-deposited positions. This capability allows nanoindentation studies to measure the mechanical properties of individual nanometer-size Au clusters supported on atomically flat substrates and permits a measure of the deformation of a nanometer-size cluster as a function of the applied load. Applying a compression model to the deformed clusters, an elastic modulus roughly 2/3 that of bulk Au is obtained for annealed clusters with sizes between 3 and 18 nm. If the clusters are unannealed, a significantly smaller elastic modulus is observed (approximately 1/6 that of bulk Au). As the applied load increases beyond \ensuremath{\sim}20 nN, the data suggest that the yield point of an annealed Au cluster can be exceeded and the atomic force microscope tip can fracture the cluster.