Modeling the effects of size and surface broken bond on surface energy of nanocrystals

Based on an analytical formulation for the size-dependent melting temperature, a simple thermodynamic model has been developed to describe the surface energy of nanocrystals γ(D). The results show that, for face-centered cubic, body-centered cubic and hexagonal close packing metals, γ(D) of nanocrystals/nanocavities decreases/increases as D drops. The effect of surface broken-bond number on γ(D) has also been discussed. It is found that reducing the number of surface broken-bonds will slow down the decrease of γ(D). For facets of nanocrystals with different broken-bond number, the difference in size-dependent surface bond contraction determines the variation intensity of surface energy. The model has also been used to describe γ(D) of semiconductor Si nanocavities and bimetallic alloys nanocrystals. The predictions are in good agreement with the reported data and other theory model predictions.