Nanocrystals as a Class of Macromolecule Paul Alivisatos, University of California, Berkeley

Nanocrystals are under active investigation because it is possible to control their physical properties by variation of the size and shape. Most of these variations can be understood as arising from changes in the density of states in finite size. An equally important theme in the study of nanocrystals arises when we consider the structure and chemical composition of nanocrystals. Nanocrystals behave as single structural domains with single nucleation events in pressure induced structural transformations. Elementary processes such as diffusion and ion exchange, which are difficult to study and control in extended solids, become highly regular in nanocrsytals, leading to new compositions and even topologies of nanocrsytals. Further nanocrystals, artificial atoms, can be placed in well defined spatial arrangements with respect to each other, similar to the ways in which atoms are placed within molecules. Thus the study of nanocrystals creates an opportunity to prepare artificial solid state materials with significantly improved precision, complexity, and design.