No abstract

Structures of Si n O n clusters are of great interest because of the observed growth of oxide-coated Si nanowires from gas-phase SiO. We studied the geometries of Si n O n clusters with n ranging from 12 to 18 using first-principles density functional calculations. We found a new structural motif which produces structures that are energetically more favorable than those proposed in recent literature. These structures consist of polygonal bipyramidal Si clusters of sizes between 5 and 7 attached to low-energy Si8O12 or Si12O18 wheel structures previously discovered. The segregation of silicon to the side of the cluster is intriguing and contradicts previous models that assumed silicon segregation nucleates in the center of the monoxide clusters. Electronic structure analysis shows that the HOMO and LUMO states of the monoxide clusters are localized on the segregated silicon cluster, indicating that the segregated Si may act as a nucleation site for further nanostructure growth.