Structural transition in nanosized silicon clusters

Abstract

The structural transition to bulk diamond structure in nanosized silicon clusters has been studied by tight-binding calculations. For intermediate-size clusters (<200 atoms), the energetically favorable structures obtained consist of small subunits like ${\mathrm{Si}}_{10}$ and ${\mathrm{Si}}_{12},$ qualitatively consistent with the experimental fragmentation behavior of these clusters. For spherical silicon nanocrystals, the surface atoms reconstruct to minimize the number of dangling bonds, forming a continuous surface. The large curvature of the continuous surface causes lattice contraction in the nanocrystals. Present calculations predict the lattice contraction versus the particle radius as $\Delta a\approx 0.4/R,$ with $\Delta a$ and R in Å. By comparing cohesive energies of the two sorts of structures, the structural transition is estimated to occur in the range of 300–500 atoms, or about 2.3–2.7 nm in diameter.