Metals on the Nanoscale

Metals also have unusual properties on the 1—100-nm-length scale. Fundamentally, this is because the mean free path (Section 10.8) of an electron in a metal at room temperature is typically about 1—100 nm. So when the particle size of a metal is 100 nm or less, one might expect unusual effects. 

Other physical and chemical properties of metallic nanoparticles are also different from the properties of the bulk materials. Gold particles less than 20 nm in diameter melt at a far lower temperature than bulk gold, for instance, and when the particles are between 2 and 3 nm in diameter, gold is no longer a noble, umeactive metal in this size range it becomes chemically reactive. 

How many bonds does each carbon atom in Cso make Based on this observation would you expect the bonding in Ceo to be more like that in diamond or that in graphite  

The molecule has a highly symmetric structure in which the 50 carbon atoms sit at the vertices of a truncated icosahedron. The bottom view shows only the bonds between carbon atoms. 

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Prashant KJ, Huang X, El-Sayed IH, El-Sayed MA. Noble metals on the nanoscale Optical and photothermal properties and some applications in imaging, sensing, biology and medicine. Acc Chem Res 2008 in press. 

To summarize, we have shown here that enhanced electric-field distribution in metal nanoparticle assemblies can be visualized on the nanoscale by a near-field two-photon excitation imaging method. By combining this method and near-field Raman imaging, we have clearly demonstrated that hot spots in noble metal nanoparticle assemblies make a major contribution to surface enhanced Raman scattering. 

Further modification of the above nanostructures is useful for obtaining new functional materials. Thirdly, we apply the dopant-induced laser ablation technique to site-selectively doped thin diblock copolymer films with spheres (sea-island), cylinders (hole-network), and wormlike structures on the nanoscale [19, 20]. When the dye-doped component parts are ablated away by laser light, the films are modified selectively. Concerning the laser ablation of diblock copolymer films, Lengl et al. carried out the excimer laser ablation of diblock copolymer monolayer films, forming spherical micelles loaded with an Au salt to obtain metallic Au nanodots [21]. They used the laser ablation to remove the polymer matrix. In our experiment, however, the laser ablation is used to remove one component of block copolymers. Thereby, we can expect to obtain new functional materials with novel nanostmctures. 

As already briefly mentioned in the introduction, some metals exhibit so-called plasmon resonances in the UV-visible spectra, attributed to the interaction of electromagnetic waves (visible light) and the confined electron gas, if a critical size on the nanoscale is reached. The process is sketched in a simplified manner in Figure 8. 

Although, for obvious reasons, classical thermod5mamics caimot provide a quantitative account of the vast variety of phenomena occurring on the nanoscale, it does make some useful semiquantitative predictions in the scalable size interval. For example, based on the Gibbs-Thompson relation, Pheth predicted that for a metal composed of small particles, the redox potential E d) of the transition... 

Brock SL, Perera SC, Stamm KL. Chemical routes for production of transition-metal phosphides on the nanoscale implications for advanced magnetic and catalytic materials. Chem Eur J 2004 10 3364-3371. 

HREM methods are powerful in the study of nanometre-sized metal particles dispersed on ceramic oxides or any other suitable substrate. In many catalytic processes employing supported metallic catalysts, it has been established that the catalytic properties of some structure-sensitive catalysts are enhanced with a decrease in particle size. For example, the rate of CO decomposition on Pd/mica is shown to increase five-fold when the Pd particle sizes are reduced from 5 to 2 nm. A similar size dependence has been observed for Ni/mica. It is, therefore, necessary to observe the particles at very high resolution, coupled with a small-probe high-precision micro- or nanocomposition analysis and micro- or nanodiffraction where possible. Advanced FE-(S)TEM instruments are particularly effective for composition analysis and diffraction on the nanoscale. ED patterns from particles of diameter of 1 nm or less are now possible. 

In this chapter we present a few selected results on the nanoscale electrodeposition of some important metals and semiconductors, namely, Al, Ta and Si, in air- and water-stable ionic liquids. Here we focus on the investigation of the electrode/electrolyte interface during electrodeposition with the in situ scanning tunneling microscope and we would like to draw attention to the fascinating... 

The development of methods for the reproducible and continuous production of metal and semiconductor particles with a typical size on the nanoscale is still an active field of research [61-65], The existing synthetic methods for isolated nanoparticles can be categorised into two major groups (i) Gas or plasma phase-based preparation from gaseous or liquid precursors, (ii) preparation of nanoparticles in... 

As will be shown, model systems for cells employing lipids or composed of polymers have been in existence for some time. Model systems for coccolith-type structures are well known on the nanoscale in inorganic and materials chemistry. Indeed, many complex metal oxides crystallize into approximations of spherical networks. Often, though, the spherical motif interpenetrates other spheres making the formation of discrete spheres rare. Inorganic clusters such as quantum dots may appear as microscopic spheres, particularly when visualized by scanning electron microscopy, but they are not hollow, nor do they contain voids that would be of value as sites for molecular recognition. All these examples have the outward appearance of cells but not all function as capsules for host molecules. 

As particle sizes decrease, the sensitivity of the thermite mixture to impact and friction increases. The micron scale thermites are usually quite insensitive to impact and shock, but thermites on the nanoscale can be quite sensitive to both or one of the two depending on the metal oxide. This is exemplified in the work of Spitzer, where a tungsten(VI) oxide and aluminum thermite was prepared by mixing nano and micron aluminum with nano and micron W03. The results of this are presented in Table 13.2. 

In real-world applications, the importance of interfaces is hard to overestimate and three chapters are devoted to the effects of radiation at aqueous-solid boundaries. Jonsson focuses on applications within the nuclear industry where basic studies on radiation effects at water-metal interfaces have enabled a proposal for safe storage of spent nuclear fuel. Also with implications for the nuclear industry, Musat et al. document alterations in the radiation chemistry of liquid water confined on the nanoscale. Such nanoconfmed solutions are prevalent in the media proposed and indeed in use for waste storage. In another application, radiation chemistry has successfully been used to produce nanoscale objects such as metallic clusters and nanoparticles, an area summarized by Remita and Remita. 

In Chapter 11, Molecular Electron Transfer, the broad and deep field of electron-transfer reactions of metal complexes is surveyed and analyzed. In Chapter 12, Electron Transfer From the Molecular to the Nanoscale, the new issues arising for electron-transfer processes on the nanoscale are addressed this chapter is less a review than a toolbox for approaching and analyzing new situations. In Chapter 13, Magnetism From the Molecular to the Nanoscale, the mechanisms and consequences of magnetic coupling in zero- and one-dimensional systems comprised of transition-metal complexes is surveyed. Related to the topics covered in this volume are a number addressed in other volumes. The techniques used to make the measurements are covered in Section I of Volume 2. Theoretical models, computational methods, and software are found in Volume 2, Sections II and III, while a number of the case studies presented in Section IV are pertinent to the articles in this chapter. Photochemical applications of metal complexes are considered in Volume 9, Chapters 11-16, 21 and 22. 

Abstract Nanophotonic stractures exhibit a large variety of effects on the nanoscale that can be used for biosensing in a biochip format. The resonance nature of these structures then allows high sensitivity to analytes, gases, or other external index perturbations down to the order of 10 refractive index unit. In this chapter, several configurations of nanophotonic structures and their use for sensing are reviewed with special emphasis on grating-based resonant strucmres, metallic nanoparticle, and nano apertures. 

Possible Mechanisms and Key Characteristics of Nanomaterials. A nanoparticle/nanomaterial is generally defined as a particle/ material having a physicochemical structure greater than typical atomic/molecular dimensions but at least one dimension smaller than lOOnm. It includes particles/ materials engineered or manufactured by humans on the nanoscale with specific physicochemical composition and structure to exploit properties and functions associated with its dimensions. Some of the common nanoparticle types are (1) carbon-based materials (e.g., nanotubes, fullerenes), (2) metal-based materials (e.g., nanogold, nanosilver, quantum dots, metal oxides), and (3) dendrimers (e.g., dendritic forms of ceramics). 

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