Chemistry of semiconductor clusters: Large silicon clusters are much less reactive towards oxygen than the bulk

Abstract

The chemical reactions of Si+n (n=10–65) with O2 have been investigated using selected ion drift tube techniques. The smaller clusters are etched by O2 to give Si+n−2 (and two SiO molecules) and the larger clusters chemisorb oxygen forming an SinO+2 adduct. The transition occurs between n=29 and 36 under the conditions employed. There are large variations in the reactivity of the smaller clusters: Si+13, Si+14, and Si+23 are particularly inert. The variations in reactivity are rapidly damped with increasing cluster size and for clusters with 40–65 atoms the reactivity is nearly independent of size. However, these large clusters are ∼102 times less reactive towards O2 than most bulk silicon surfaces. Studies of the temperature dependence of the reactions reveal that they proceed through a metastable precursor state which is probably molecular O2 physisorbed to the cluster surface. Variations in the size of the activation barrier for dissociative chemisorption account for the changes in reactivity with cluster size. However, the difference between the cluster and surface reactivities is not due to the size of the activation barrier, but could be accounted for by the presence of only a few reactive sites on the clusters.

Nanostructured silicon films obtained by neutral cluster depositions

“…Finally, covalentlike and metalliclike bonds may coexist in clusters as in liquid silicon. 19 In medium size range (NϾ20-25 atoms͒, theoretical arguments 20-28 and experiments [29][30][31][32][33] tend to indicate the existence of cagelike clusters. In such structures the silicon atoms retain the main features of the sp 3 basis with the T d point group symmetry.…”

Interaction of silicon cluster ions with ammonia: Annealing, equilibria, high temperature kinetics, and saturation studies

“…[7][8][9] The cluster ions are generated by pulsed laser vaporization of a silicon rod in a continuous flow of helium buffer gas. The cluster ions are derived from the laser vaporization plasma and undergo> 105 collisions with the buffer gas, so they are expected to be at room temperature when they leave the source.…”

Polarizabilities of Isolated Silicon Clusters

“…The chemical reactivity of several silicon cluster ions [14] exhibits deep minima in silicon clusters contain ing 33, 39 and 45 atoms. Special features, which are consistent with the existence of two structural isomers, are also found in the behaviour of the drift mobility of size-selected silicon cluster cations in rare gases in the size range with 24-34 atoms per clusters [15].…”