Giant Clusters and Nanoparticles

Small metal particles, called colloids or nanoparticles, have found uses for many years—medieval red stained glass contains colloidal gold, fM example. Very striking advances have been made in recent years in tlteir controlled synthesis, better characterization, and in the identification of new commercial applications. This has contributed to nanotechnology—the applications of material objects in the 100 A to 1000 A range. 

Traditional aqueous metal colloids were formed by reducing a metal salt in the presence of protective polymer such as polyvinyl alcohol (PVA), which absorbs on the surface. More recently large ligand-stabilized particles have been prepared that are intermediate between clusters and nanoparticles. 

None of the nanoclusters described in this section should be considered as having a precisely defined stoichiometry. The number of metals cited usually comes from the idealized formulations shown in Fig 13.11, which show hexagonal close-packed structures with one to five shells of atoms.  

FIGURE 13.9 (a) The crystallization of 7 A nanoparticulate iron cubes in a cubic lattice. (I ) The morphology of the resulting crystallite. lllustration.s kindly provided by B. Chaudrei.l 

FIGURE 13.10 Electron micrograph of Moiseev s giant palladium clusters on a carbon support. (Reproduced from Ref. 40a with permission of the Royal Society of Chemistry 1985.) 

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