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Radiation Chemistry Vol.II Gases, Solids, Organic Liquids by Gould R.F. (ed.)

By Gould R.F. (ed.)

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Au NPs also exhibit quite different optical properties from the bulk. The plasmon resonance that dominates their absorption spectrum is very sensitive to both size and shape (32) and is useful for applications such as plasmonic waveguides, surface enhanced spectroscopies, and biological markers. As in the previous section, before considering Au NPs we briefly review the properties of the bulk material. Gold adopts the fcc crystal structure with lattice ˚ and remains solid up to temperatures of about 10008C.

These reconstructions involve surface atoms adjusting into more closely packed arrangements and the corresponding unit cells can be quite large. 1 Morphology Au NPs can be fabricated using a wide range of techniques that can result in an equally wide range of morphologies. Ionized mass selected clusters can be produced by plasma sputtering in an inert gas and may subsequently be deposited onto various substrates (33). Alternatively, gold can be evaporated directly onto a substrate allowing NPs to nucleate and grow at defects or steps, for example.

9. If we assume the binding energy per atom in the problem above is linearly proportional to its coordination number, what is the ratio of (111) and (100) surface energies? 10. Low coordinated atoms on metallic NPs have been proposed to be catalytically active sites. How many atoms with a coordination of six or lower are there on icosahedral, octahedral, and truncated octahedral Au NPs. ANSWERS 1. First we need to estimate the number of atoms in the NP. This can be done by assuming it is approximately spherical in shape and has a similar density to bulk Li.

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