Structure and stability of germanium nanoparticles

In order to tailor the properties of nanodots, it is essential to separate the effects of quantum confinement from those due to the surface, and to determine the mechanisms by which preparation conditions can influence the properties of the dot. We address these issues for the case of small Ge clusters (1–2.5 nm), using a combination of empirical and first-principles molecular-dynamics techniques. Our results show that over a wide temperature range, the diamond structure is more stable than tetragonal-like structures for clusters containing more than 40 atoms; however, the magnitude of the energy difference is strongly dependent on the structure and termination of the surface. On the basis of our calculations, we propose a possible mechanism for the formation of metastable tetragonal clusters observed in vapor deposition experiments, by cold quenching of amorphous nanoparticles exhibiting unsaturated, reconstructed surfaces.