ABSTRACT
Atomic (or molecular) clusters are aggregates of atoms (or molecules). eir sizes vary from two or three up to tens or hundreds of thousands constituents. Medium-and large-sized clusters have diameters on the scale of nanometers, and are o en called nanoparticles (NPs) or nanocrystals (depending on their structure). Clusters show properties intermediate between those of individual atoms (or molecules), with discrete energy states, and bulk matter characterized by continua or bands of states. One can say that clusters represent a distinct form of matter: a “bridge” between atoms and molecules on the one hand and solids on the other. Clusters can be formed by most of the elements in the periodic table. ey can be of di erent types, compositions, and structures. A wide variety of clusters has been produced and investigated from precursors including metals, semiconductors, ionic solids, noble gases, and molecules. More detailed information about the classi cation of clusters, their bonding types, structures, and properties in the gas phase goes beyond the scope of this chapter and can be found elsewhere (Haberland 1994, Martin 1996, Johnston 2002, Alonso 2005, Baletto and Ferrado 2005).
