1 Overview Daniel L. Feldheim North Carolina State University, Raleigh, North Carolina
Colby A. Foss, Jr. Georgetown University, Washington, D.C.
I. INTRODUCTION Over the last decade there has been increased interest in â€œnanochemistry.â€? A variety of supermolecular ensembles (1), multifunctional supermolecules (2), carbon nanotubes (3), and metal and semiconductor nanoparticles (4) have been synthesized and proposed as potential building blocks of optical and electronic devices (5). This has arisen for a variety of reasons, not the least of which is technological advance, and the promise of control over material and device structure at length scales far below conventional lithographic patterning technology. Metal particles are particularly interesting nanoscale systems because of the ease with which they can be synthesized and modified chemically. From the standpoint of understanding their optical and electronic effects, metal nanoparticles also offer an advantage over other systems because their optical (or dielectric) constants resemble those of the bulk metal to exceedingly small dimensions (i.e., 5 nm). Perhaps the most intriguing observation is that metal particles often exhibit strong plasmon resonance extinction bands in the visible spectrum, and therefore deep colors reminiscent of molecular dyes. Yet, while the spectra of molecules (and semiconductor particles) can be understood only in terms of quantum mechanics, the plasmon resonance bands of nanoscopic metal particles can often be rationalized in terms of classical free-electron theory and simple electrostatic limit models for particle polarizability (6). Furthermore, while the composition of a metal particle may be held constant, its plasmon resonance extinction maximum 1
Chemistry of metal nanoparticles