Clusters quasi-metallic

Nan-metallic Clusters, Quasi-metallic Clusters, and Nanosized Metallic Particles... 

Figure 7. Schematic model based on the TEM image analysis and on in situ 7Li-NMR during galvanostatic reduction/oxidation of the carbon composite. During insertion, ionic lithium penetrates at first in the smallest interlayer spacings, then it diffuses in the slit-shaped pores where quasi-metallic clusters are formed.

The detection of sharp plasmon absorption signifies the onset of metallic character. This phenomenon occurs in the presence of a conduction band intersected by the Fermi level, which enables electron-hole pairs of all energies, no matter how small, to be excited. A metal, of course, conducts current electrically and its resistivity has a positive temperature coefficient. On the basis of these definitions, aqueous 5-10 nm colloidal silver particles, in the millimolar concentration range, can be considered to be metallic. Smaller particles in the 100-A > D > 20-A size domain, which exhibit absorption spectra blue-shifted from the plasmon band (Fig. 80), have been suggested to be quasi-metallic [513] these particles are size-quantized [8-11]. Still smaller particles, having distinct absorption bands in the ultraviolet region, are non-metallic silver clusters. 

Controlled reduction of cadmium (or lead) ions on surfaces of nanosized silver (or gold) metallic particles results in the formation of double-layer colloids [532-534]. Depending on the coverage, the second layer can vary from being non-metallic clusters to quasi-metallic and metallic colloids. Growth of the second-layer particles can be monitored by absorption spectrophotometry. For... 

Regarding the reversible capacity of disordered carbons, we found that lithium is mainly in a quasi-metallic state, another minor part being in a state comparable to intercalation. If we consider that the lithium density in the intercalated domains is comparable to that of graphite, we can conclude that the enhanced reversible capacity of the disordered carbons is related with the quasi-metallic state of lithium. In this paper, we postulate that the electron density of the quasi-metallic lithium clusters is related with the size of the neighbour carbon layers. In future work, we plan to investigate different materials in order to determine if there is any relationship between the reversible capacity and the fringe length. 

Although the Ira and Ir clusters catalyze the same reactions as metallic iridium particles, their catalytic character is different, even for structure-insensitive hydrogenation reactions. It is inferred [15] that the clusters are metal-like but not metallic consistent with the structural inferences stated above, we refer to them as quasi molecular. Thus these data show the limit of the concept of structure insensitivity it pertains to catalysis by surfaces of structures that might be described as metallic, i.e., present in three-dimensional particles about 1 nm in diameter or larger. This conclusion suggests that supported metal clusters may be found to have catalytic properties superior to those of conventional supported metals for some reactions. The suggestion finds some support in the results observed for platinum clusters in zeolite LTL, as summarized below. 

It is noteworthy that the NH4 radical has the /g (4.65 eV) [12] close to those of alkali metals (see Table 1.2) and thus can be regarded as a quasi-metal. For homo-atomic clusters of metal atoms, M , the ionization potentials (U) decreases with the increase of n and ultimately approaches the work function bulk metal, according to Eq. 1.7 [13],... 

Mostly, positive-ion FAB yields protonated quasi-molecular ions [M -i- H]+, and the negative-ion mode yields [M - H]. In the presence of metal salts (e.g., KCl) that are sometimes added to improve efficiency in the LC column, ions of the type [M -i- X]+are common, where X is the metal. Another type of ion that is observed is the so-called cluster, a complex of several molecules with one proton, [M -i- H]+ with n = 1, 2, 3,. .., etc. Few fragment ions are produced. 

The chalcogen-capped clusters M M2Co(/(3-S)(CO)s()/ -CsH5) (M M2 = MoEc, MoRu, WFe) and MoFeCo(/r ,-Se)(CO)H()) -CsH3) underw ent a one-electron, quasi-reversible reduction. Addition of an electron proceeded more readily for the clusters w ith the lighter metals and for the selenium capped cluster relative to its sulfur analogue. 

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