DISSOCIATION OF LARGE SILICON CLUSTERS - THE APPROACH TO BULK BEHAVIOR

The dissociation of silicon cluster ions containing up to 70 atoms has been examined using a multicollision excitation method. Clusters with 19-35 atoms dissociate mainly by loss of Si10 species. Larger clusters fragment by Si6 loss. For clusters with n > 60, loss of an individual Si atom (as occurs for bulk silicon) begins to become an important dissociation channel. These changes in the observed products can be attributed to changes in the clusters' cohesive energies. When highly excited, the large clusters dissociate by sequential loss of Si6 units until they reach a size of approximately 30 atoms. They then disintegrate into fragments containing 6-11 atoms. Dissociation energies have been estimated from the experimental results. Substantial variations in the dissociation energies are observed for clusters with up to 25 atoms. For clusters with n > 25 the dissociation energies increase smoothly.