6.1 Introduction

Nanoparticles (NPs) refer to materials with size dimension on the length scale of a few to a few hundred nanometers. Both equilibrium and dynamic properties of nanomaterials can be very different from those of their corresponding bulk materials or isolated atoms and molecules (Henglein, 1989; Gratzel, 1989; Bawendi, et al., 1990a; 1990b; Wang, 1991; Schmid, 1994; Tolbert and Alivisatos, 1995; Miller, et al., 1995; Fendler and Meldrum, 1995; Alivisatos, 1996a; 1996b; Liu, et al., 1977; Kamat, 1997; Zhang. 1997; Collier, et al., 1998; Heath and Shiang, 1998). Their properties are often strongly dependent on the particle size, shape, and surface properties. It is fundamentally interesting to understand how properties of nanoparticles vary with these parameters. For example, spatial confinement is expected to lead to changes in the density of states (DOS) for both electrons and phonons and the rate of electron-hole recombination. The possibility to control the materials properties by varying these parameters is significant to many technological applications ranging from microelectronics to non-linear optics, opto-electronics, catalysis and photoelectrochemistry. For instance, the color and redox potential of semiconductor nanoparticles can be tuned by changing particle size. This can be very useful for applications in optics, non-linear optics and photocatalysis (Henglein, 1989; Kamat, 1993). The possibility to form surperlattices from NPs presents a whole new class of nanomaterials for photonics and other applications.

One complication involved with the study of nanoparticles is that the various parameters are not all independent. It is thus often difficult to...