From clusters to semiconductor nanostructures.

In the last two decades there has been tremendous interest in various aspects of nanoscience and nanotechnology. Now the subject has matured into an important field in the general area of science and technology that has been identified as one of the thrust areas. Nanoscience and nanotechnology is really an interdisciplinary and/or multidisciplinary subject. This review describes work on transition metal molecular level clusters. The clusters were fabricated by making very dilute solutions and also by doping them in lattices of alkali halides and alkali cyanides. Size dependence of the bandgap was shown for the first time by using site-selective dye laser spectroscopy, time resolved spectroscopy, optical absorption and molecular orbital calculations. A number of semiconductor nanostructures such as quantum wires, quantum wells, and coupled quantum wells, and many-body effects in nanostructures such as self-assembled quantum dots, exciton-phonon interactions, four wave mixing, polymer composites, metallic nanoparticles and metal oxides are discussed.