Electronic shell structures in bare and protected metal nanoclusters

This short review discusses the concept of the electronic shell structure in the context of metal nanoclusters. Electronic shell structure is a natural consequence of quantization of fermionic states in a quantum confinement, where the symmetry of the confining potential creates energetically close-lying sets of states that reflect the symmetry of the potential. It was introduced in cluster physics in early 1980s and initially influenced greatly by the related model of nuclear shell structure from 1950’s. Three application areas are discussed consisting of free gas phase clusters, clusters supported by insulating oxides or oxide thin films, and clusters that are synthesized by wet chemistry and stabilized by an organic ligand layer. In all these systems, the concept of electronic shell structure has turned out to be useful to organize a vast amount of observations on abundance, stability, chemical reactivity and optical properties. Although this review focuses on theoretical concepts and computational results, relevant experiments are discussed as well.