Nanoparticles exhibit unique materials functions not realizable in the bulk solid, leading useful practical applications. Recent progresses in synthesis show possibility of producing them down to 1 nm comparable to molecular sizes in different geometrical structures. In such nano-structures, the number of constituent atoms becomes less than a hundred and their stabilities and properties depend sensitively on their number. Those with certain numbers are found particularly stable and can be produced selectively in the synthesis. Such nanoparticles were recently synthesized in (CdSe)n and other group II-VI semiconductors.
This selective stability is the key factor to produce well-defined atomic arrangement which is extremely important in making any nano-structure precisely controlled, characterized, and mass-synthesized under atomic resolution for basic studies and applications.