Quantum Size Effects in the Electronic Properties of Small Semiconductor Crystallites

Abstract

Metals and semiconductors have strong interatomic chemical bonds. The valence electrons determine the bonding energies, crystal structure, and excited electronic states of the infinite crystal; these electrons are extensively delocalized. Delocalization implies that the electronic properties of these materials develop gradually as a small cluster or crystallite grows in size. In the small size regime where bulk electronic properties have not yet been achieved, such clusters are partially molecular in nature in that their properties depend upon the size and shape of the crystallite. Small metal clusters in this range (perhaps 5–100 atoms) are effective heterogeneous catalysts, and intense interest has recently developed in understanding their transition from molecules to bulk metals as a function of size.