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An atomic force microscope tip is used as a vector positioner to manipulate nanometer-size preformed Au clusters deposited on atomically smooth substrates. Using this technique, two-dimensional cluster nanostructures can be assembled at room temperature.

We report results of experiments in which gold clusters with controlled diameters ranging from lnm to 20nm are grown in a gas aggregation reactor and are subsequently melted and slowly cooled in the gas phase. These clusters are soft landed on thin carbon films and their structure determined by means of HRTEM. All of the clusters down to the smallest whose lattice fringes could be resolved (N ~ 405) are single fcc crystals. MD calculations using an EAM potential for gold predict that the fcc motif seen in these experiments may indeed be the minimum-energy structure for gold clusters containing more than a few hundred atoms.