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Total energy minimization is applied to semiempirical tight-binding CdSe nanocrystal models with diameter up to 31 Å. The crystallites have wurtzite lattice structure and ligand-terminated surfaces. It is found that the qualitative features of the surface relaxation in nanocrystals and at bulk surfaces are similar. When surface relaxation is incorporated, the onsets of absorption are determined by interior-to-interior transitions with little contribution from surface-localized states. The fine structure and exchange splittings derived from these clusters are in good agreement with experimental measurements. The effects of ligand parametrization, surface atom composition, and the contribution of surface states to the exciton fine structure are analyzed.

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Atomic force microscopy studies have been performed on GaAs (001) homoepitaxy Rlrns grown by molecular beam epitaxy. Multilayered features are seen to evolve when the growth conditions favor island nucleation. As the epilayer thickness is increased these features grow in all dimensions but the angle of inclination remains approximately constant at 1". The mounding does not occur on surfaces grown in step flow. We propose that the multilayered features are an unstable growth mode which relies on island nucleation and the presence of a step edge barrier.