  In order to control and tailor the properties of nanodots, it is essential to
separate the effects of quantum confinement from those due to the surface, and
to gain insight into the influence of preparation conditions on the dot
physical properties. We address these issues for the case of small Ge clusters
(1-3 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, ST12-like structures for
clusters containing more than 50 atoms; however, the magnitude of the energy
difference between the two geometries is strongly dependent on the surface
properties. Based on our structural data, we propose a mechanism which may be
responsible for the formation of metastable ST12 clusters in vapor deposition
experiments, by cold quenching of amorphous nanoparticles with unsaturated,
reconstructed surfaces.
