Dependence of formation energies of tin nanoclusters on their size and shape

In a novel molecular beam experiment we have calorimetrically investigated the dependence of the formation energies of isolated Sn(N) clusters on their size. The experimentally determined size dependence of the formation energy for Sn(N) clusters consisting of between 95 and 975 atoms can be explained by the existence of two different types of cluster isomers: One class of isomers is characterized by formation energies proportional to N(-1/3), indicating compact spherical-like shapes. The other class has constant formation energies for the investigated size range, which is consistent with quasi-one-dimensional geometries.