Chemical Properties of Small Silicon Clusters.

The microscopic surfaces of small silicon clusters offer a model for studying chemistry at highly reactive silicon centers. Positively and negatively charged silicon clusters are prepared and reacted with a variety of reagents in the trapped ion cell of a Fourier transform mass spectrometer. Prototypical etching and deposition reactions are observed which are analogous to chemistry of activated silicon surfaces. These reactivities correlate with chemistry of two distinct types of dangling bonds in the clusters. Sequential reactions of bare silicon cluster and subsilane cations with silane also occur. All of these clustering sequences, however, encounter early bottlenecks which prevent infinite growth to form large particles. Studies of the individual steps of these clustering reactions yield extensive information about nucleation under subsaturated conditions. These findings indicate that reactions of silicon cluster and subsilane cations with silanes do not lead to the formation of hydrogenated silicon dust in silane plasmas.