Covalent Group IV Atomic clusters.

Atomic clusters containing from two atoms to several hundred atoms offer the possibility of studying the transition from molecules to crystalline solids. The covalent group IV elements, C, Si, and Ge are now being examined with this long-range objective. These are a particularly interesting series because of the very different character of their crystalline solids and because of their intermediate position between metals and insulators in the nature of their bonding. Small mass selected atom cluster ions are formed by pulsed laser techniques and identified by time-of-flight methods. Laser photoexcitation is used to study the relative stability of these clusters and their modes of fragmentation. These modes are found to be different for C+n clusters, which tend to fragment with a characteristic loss of a neutral C(3), than for Si+n and Ge+n clusters, which tend to fragment to "magic" clusters ions such as Si+4, Si+6 and Si+10.