Effective dielectric constant of nanostructured Si layers

We calculate the dielectric response of single layers of cubic and spherical Si nanocrystals using a self-consistent tight binding approach. We show that the effective dielectric constant is strongly influenced by the nanostructuring, leading to a strong reduction with respect to the bulk dielectric constant and to the value for the perfectly crystalline layer. These results are explained by the effect of the local fields and by the reduction of the dielectric response near the surface of the nanocrystals. We provide analytical expressions for the effective dielectric constant versus size.