Quantum size behavior

As already mentioned, these two electronic investigations of hot electron relaxation and the optical extinction of various clusters, are only part of many attempts to visualize quantum size behavior and, as a consequence, the transition from metal to molecule. Other chapters will provide more information about the results obtained. Catalysis using metal clusters, whether homogenous or heterogeneous, must be influenced by this fundamental difference between molecular clusters and clusters with a metallic inner life . It is surprising that these aspects have not been discussed previously in relation to catalytic effects. The purpose of this contribution is, there-... 

S. Hotchandani I. Bedja R. W. Fessenden P. V. Kamat, Electrochromic and photoelectrochromic behavior of thin WO3 films prepared from quantum size colloidal particles. Langmuir 1994, 10, 17—22. 

When the dimensions of the particles are shrinked from the bulk to a scale of the order of the Fermi wavelength of the electron, that is to a nanometer size, their behavior dominantly obeys the principles of quantum mechanics [6], One may therefore expect the emergence of new properties which may be entirely different from those of the bulk and sometimes are completely unexpected. It is believed that they are due to the so-called quantum size effect that modifies the electronic structure and increases the ratio... 

Louis E. Brus (NAS) is a professor of chemistry at Columbia University. He has been a pioneer in the synthesis, size control, and spectroscopy of nanometer-scale semiconductor crystallites. His elucidation of quantum-size effects in these materials is central to our understanding of the transition between molecular and bulk behavior. He received a B.S. in chemical physics from Rice University and his Ph.D. in chemical physics from Columbia University. 

Phase-separated metal-containing block co-polymers formed by ROMP offer interesting possibilities for the controlled formation of semiconductor and metal nanoclusters, which are of intense interest as a result of their size-dependent electronic and optical properties, as well as their catalytic behavior. Zinc-containing block co-polymers generated by ROMP have been shown to form ZnS nanoclusters within the phase-separated organozinc domains upon treatment with gaseous The cluster sizes generated were up to 30 A and their small size led to quantum size effects. For example,... 

These expected changes in magnetic behavior are just one example of so-called quantum-size effects arising from situations in which the Kubo gap , d, is comparable with, or greater than, the thermal energy, kT, at any particular temperature. 

The interpretation of the cesr signals in terms of particle size has not been attempted. All the authors notice Cuxie-Weiss behavior, which is indicative of quantum-sized particles [87,89]. One is tempted to locate these particles in the supercages. The maximum diameter is then aroimd 1.2 nm, which corresponds to 630 li, 252 Na, 88 K, 71 Rb or 48 Cs atoms in a closed packed spherical arrangement. The Hne width, increasing with the size of the atom, is qualitatively explained by this decrease of the number of atoms per cluster. The g values are equal to or somewhat lower than the free electron values. The deviation is explained by spin-orbit coupHng effects and thus is more pronounced for the heavier elements (Table 6). 

Zeolite-stabihzed oxides are of interest for catalytical application, due to their redox behavior as potential sensor materials and owing to the revealed quantum size effects for highly dispersed semiconductors. 

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