Structural transition in nanosized silicon clusters

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 Si₁₀ and Si₁₂, 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 Δa≈0.4/R, with Δa and R in {}. 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.