Nanoscale metal particles

Figure 12.10. Micrographs of devices fabricated using gravure printing technology. Left—shows the interdigitated transistor gate fabricated by an ink composed of nanoscale metallic particles. Right—Channel fabricated when using a silver-filled adhesive to print the transistor source and drain.

Highly reactive nanoscale metal particles (3 to 15 nm in diameter) are formed by reducing metal salts to metals by solvated elecrons or alkali metal anions that may also find use in organometallic synthesis [35]. 

The study of nanosized particles has its origin in colloid chemistry, which dates back to 1857 when Michael Faraday (1791-1867) set out to systematically investigate the optical properties of thin hhns of gold. Faraday prepared a suspension of ultra-small metaUic gold particles in water by chemically reducing an aqueous solution of gold chloride with phosphorus (Faraday, 1857). To this day, nanoscale metal particles are stiU produced by chemical reduction in aqueous solutions. 

This review is concerned with the advances in our understanding of chemical problems that have occurred as a result of developments in computational electrodynamics, with an emphasis on problems involving the optical properties of nanoscale metal particles. In addition, in part of the review we describe theoretical methods that mix classical electrodynamics with molecular quantum mechanics, and which thereby enable one to describe the optical properties of molecules that interact with nanoparticles. Our focus will be on linear optical properties, and on the interaction of electromagnetic fields with materials that are large enough in size that the size of the wavelength matters. We will not consider intense laser fields, or the interaction of fields with atoms or small molecules. 

Metal clusters have been considered as models for monodispersed nanoscale metal particles in a dielectric matrix or as precursors for nanoscale particles (see Chapter 12.03 for organometallic-derived metals, colloids, and nanoparticles). The number of metal atoms in well-defined molecular compounds can be varied from 2 to 3 up to hundreds, and the physical properties change from localized molecular to nearly bulk metal. They offer the advantage that clusters can be studied by a wide variety of experimental techniques. 

Zhang W, Wang C. (1997). Nanoscale metal particles for dechlorination of PCE and PCBs. Environmental Science and Technology 31 2154-2156. 

It is important to point out that the invariance observed here is in quite a different context to that of originally proposed in the Friedel-Heine invariance theorem, which refers to the invariance of electronic properties in bulk environments of dilute alloys. The situation is quite different for nanoscale metal particles from those of bulk Pt, due to the presence of the surface and the significant reductions in the particle volume. However, the Ef-l DOSs still show a remarkable invariance towards changes in surface chemical environment, even though they vary from those of bulk Pt. These results may also be expected to lead to useful general correlations between electronic properties and more conventional chemical descriptions such as ligand electronegativity. 

Although these represent giants in molecular clusters, they are small compared to what has been prepared in the nanoscale metal particle area, which will now be discussed. 

Since catalyst performance for the HOR is strongly dependent on the total active surface area, supported catalysts have been developed to maximize the catalyst surface area. Compared to bulk Pt catalysts, supported catalysts show higher activity and stability due to fine dispersion, high utilization, and stable nanoscale metallic particles. 

The nanoscale metal particles obtained via RESOLV were sensitive to oxidation both in stabilized suspensions and in the solid state. In particular, the Fe nanoparticles required storage under rigorously air-free conditions. Exposing a solid sample of the Fe nanoparticles to air in a sudden fashion resulted in fireworks-like flames. Under more controlled conditions, oxidation of the Fe nanoparticles produced iron oxide (Fc203) nanoparticles, which remained amorphous. The powder x-ray diffraction pattern of the thermally annealed Fc203 nanoparticles is also shown in Figure 33. 

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