Sequential reactions of bare silicon clusters with SiD4: Constrained heterogeneous nucleation of deuterated silicon particles

Abstract

Bare silicon cluster ions are observed to undergo exothermic sequential clustering reactions with SiD4 at room temperature. Si+1–7 and Si−1–7 are created by laser evaporation and trapped in the ion cell of a Fourier transform mass spectrometer in the presence of SiD4. Clustering reactions are observed only for Si+1–3 and Si+5. Si+4,6,7 and the negatively charged silicon clusters do not react exothermically with SiD4. All of the reactive silicon clusters encounter chemical constraints to rapid growth of increasingly larger SixD+y species. Ab initio electronic structure calculations are used in concert with phase space theory calculations to deduce the structures of the products of the clustering reactions. These structures are found to be closely related to the lowest energy structures of the bare clusters if the degree of deuterium saturation is low. The inertness of unreactive clusters with 2–5 silicon atoms is correlated to unusually stable structures. Larger unreactive clusters with six or more silicon atoms appear to lack the divalent silicon center required to activate the Si–D bonds of SiD4. These findings are related to the phenomenon of hydrogenated silicon particle formation in silane plasmas.