ELASTIC PROPERTIES OF INDIVIDUAL NANOMETER-SIZE SUPPORTED GOLD CLUSTERS

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 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. © 1995 The American Physical Society.