Theoretical Studies On The Oxidation Pattern Of Silicon Clusters

Due to the importance of silicon oxide materials in science and technology and the important role of silicon oxide in the recent chemical vapor deposition growth of silicon nanowires and nanostructures, silicon oxide clusters have attracted more and more attention both from experimental and theoretical studies in recent years.Using photoelectron spectroscopy, small anionic silicon oxide clusters such as Si₃O_n (n = 1 - 6) has been investigated by Wang and co-workers. Their results provide very useful information on the electronic properties and structure assignment of these small Si₃O_n clusters. Experimental studies of reaction of silicon clusters with oxygen have been performed by Creasy et al. and by Jarrold et al. Creasy and co-workers studied the reactions of cationic silicon clusters containing up to six atoms with oxygen. Their study shows that the small cationic silicon clusters were etched away by the oxidation reaction, two silicon atoms at a time, all the way down to Si²⁺ or Si⁺. Jarrold et al. studied the chemical reactions of medium-sized ionic silicon clusters, Si_n⁺ (n = 10 - 65) with oxygen. Their experimental results suggested that for clusters containing fewer than 29 atoms, the main products were found to be Si_n-2⁺ and two SiO molecules. Each reaction of an oxygen molecule with the silicon cluster results in the loss of two Si atoms in two SiO radicals. Bergeron and Castleman, Jr. has also studied the stability of silicon cluster ions by O₂ etching, suggesting that Si_n⁺ (n = 4, 6, 9, 13, 14, and 23) and Si_n^- (n = 18, 21, 24, 25, and 28) have very large stability. Recently, the experimental study on the oxidation of the Si nanostructures has also been performed, suggesting that the reactivity of oxygen with Si nanostructures is relatively low, and imposes some restriction on the oxidation of Si films.On the theory side, ab initio calculations of small Si_nO_m with n≤5 clusters have been carried out to study the structures and potential energy surfaces of small silicon oxide clusters in great detail. Chelikowsky and co-workers have investigated the geometric structures and electronic properties of neutral and charged Si_nO_n (n = 3, 4 and 5) clusters. Their computational results suggested that buckled rings are more stable than planar ones for Si₄O₄ and Si₅O₅. Lu et al. have studied systematically the structures and fragmentation stabilities of Si_mO_n (m = 1 - 5, n = 1...