Silicon clusters: chemistry and structure

Abstract

The chemical reactions of size selected silicon cluster ions (containing up to 70 atoms) have been studied with a number of different reagents using injected ion drift tube techniques. Both kinetic and equilibrium measurements have been performed as a function of temperature, and the influence of cluster annealing on chemical reactivity explored. Unlike metal clusters, where bulk behavior appears to be approached with around 30 atoms, large silicon clusters (n up to 70) are much less reactive than bulk silicon surfaces. These results suggest that the clusters in the size range examined here are not small crystals of bulk silicon, but have compact, high coordination number structures with few dangling bonds. PACS: 36.40. + d, 82.20.Pm, 82.30.Fi

Nanosurface Chemistry on Size-Selected Silicon Clusters

“…Smalley and co-workers have shown that laser annealing of silicon clusters can influence their reactivity (10). In our experiments coltisional annealing is used (9,11). The clusters are injected at high kinetic energy (50 to 200 eV) into the drift tube where they are heated by collisions with the buffer gas.…”

“…With oxygen the umeactive clusters are those with 13 and 14 atoms. Clusters with 11,13,14,19, and 23 atoms are particularly unreactive toward water. Clusters with 13, 14, and 23 atoms are also particularly unreactive toward ethylene (7,9).…”

Temperature Measurement from the Translational Kinetic Energy Release Distribution in Cluster Dissociation: A Theoretical Investigation

“…At lower excitations, the distribution of kinetic energy released after dissociation carries a lot of information about the energetics and kinetics of the reactions . In general, the binding energies or temperatures are deduced in experiments − through a comparison with some established statistical rate theories such as those pioneered by Weisskopf or by Rice, Ramsperger, and Kassel (RRK) . Significant progress was made by Klots − who developed the quasi-equilibrium theory (QET) of unimolecular decomposition and later introduced the concept of the “evaporative ensemble”.…”

Cluster Coagulation and Growth Limited by Surface Interactions with Polymers

“…In this case, the model has to promote the growth of particles formed from smaller fragments, because this growth will minimize their free energy by reducing the number of coordinatively unsaturated surface atoms. 43,44 Therefore, the expression that we propose for the coefficients of coagulation of the cobalt fragments in our model (with or without polymer interactions) is for j,k ) 1, 2, ..., where 0 e R, β e 1, 0 < µ e 1 is a weighting parameter that denotes the fraction of cobalt clusters that are permitted to enter into the coagulation reaction (µ ) 1 if no polymer is present), and σ > 0 denotes the critical size of the cobalt clusters beyond which the coagulation rates will drop as a function of size increase. The first part of this equation describes the mechanism of cluster formation due a combination of chemical bonding (for small clusters) and surface interactions (for larger clusters), without specifying the critical crossover cluster size.…”