Novel interactions of supported clusters: contact epitaxy

The study of clusters of 'model' metal systems such as Cu and Ag provide a valuable route to explore critical issues in materials epitaxy. Our investi gations have led to observations of novel interactions between supported me tal clusters in both homo- and heteroepitaxial configurations. In the exper iments, clusters of both Cu and Ag were produced by inert gas condensation and deposited on the clean (001)Cu surface under ultrahigh vacuum. Followin g deposition, the Cu clusters were observed to be of initially random orien tation on the substrate surface, undergoing reorientation upon annealing by a mechanism involving sintering and grain growth. In the case of Ag cluste rs, the formation of a heteroepitaxial layer between the particle and subst rate was observed upon initial contact. The phenomenon, which we call 'cont act epitaxy', may be understood from molecular dynamics simulations of a 's oft impact' between the nanoparticle and substrate which indicate that the ordered layers form within picoseconds of impact. The experiments were perf ormed in an ultrahigh vacuum transmission electron microscope equipped with an in-situ nanoparticle sputtering system. (C) 1999 Published by Elsevier Science S.A. All rights reserved.