Quantum-sized particles

The zeolite matrix allows the preparation of dispersions with distinctly different and narrow particle size distributions in a range where size dependent electronic properties can be studied (quantum size particles). Quantum-mechanical calculations suggest that the energy level of the first excited state of the exciton increases with decreasing particle size of the semiconductors in correspondence with the experimentally observed blue-shift of the optical absorption edge (refs. 8-10). 

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). 

Early in 1993, a special issue of The Israel Journal of Chemistry which was devoted to quantum-size particles, contained several reports that were concerned predominantly with the synthesis and characterization of Il-VI-semiconductor nanoparticles [55-61]. Later that year, two (now frequently cited) reports provided a summary of the achievements in the field [62, 63]. Notably, the characterization of wet-chemical-synthesized CdTe and HgTe, as well as of ternary HgCdTe compounds (including XRD, TEM and photoluminescence), formed the focus of a series of studies by Milllenborn et al. [64]. In this case, the nature of the stabilizer was shown to play an... 

The large uniform-shaped cavities of mesoporous molecular sieves can provide many interesting possibilities for the fabrication and hosting of quantum-sized particles. An example is the fabrication of stable carbon wires in the pore structure of mesoporous materials by polymerizing acrylonitrile within the channels. It is also possible to fill the mesopores with a semiconductor such as germaiuum. This type of molecular and quantum wires may have many... 

A very different nucleation scheme by Grieser and co-workers employs ultrasonic irradiation of salt solutions to create H- and OH- radicals in solution [73]. These radicals proceed to nucleate growth of quantum-sized (Q-state) particles of cadmium sqlfide. Similar initiation has been used for polymer latices [74]. 

Katsikas L, Eychmuller A, Giersig M, WeUer H (1990) Discrete excitonic transitions in quantum-sized CdS particles. Chem Phys Lett 172 201-204... 

Vogel R, Hoyer P, WeUer H (1994) Quantum-sized PbS, CdS, AgiS, SbiSs, and BiiSs particles as sensitizers for various nanoporous wide-bandgap semiconductors. J Phys Chem 98 ... 

The rapid development of nanotechnology has revolutionized scientific developments in recent decades [1]. The synthesis, characterization, and application of functionalized nanoparticles are currently a very active field of research [2], Due to the size limitation of metal nanoparticles, they show very unique properties, which are called nano-size effect or quantum-size effect , which is different from those of both bulk metals and metal atoms. Such specific properties are usually dominated by the atoms located on the surface. In nanoparticles systems, the number of atoms located on the surface of the particles increases tremendously with decreasing of the particle diameter [3]. 

Absorption spectra of CdS colloid indicate the formation of quantum sized CdS particles. The particle size increased upon sonication, indicated by the red shift in the onset of absorption. The particle size was highly dependent on the mercaptan used, because of the absorption of the mercaptan on the particle acting as a capping agent and the rate of H2S produced. Study of mercaptan systems revealed that there was also a thermal process responsible for CdS formation. 25% of the total CdS produced sonochemically was formed via a thermal mechanism presumably in the hot shell around the compressed bubble. CdS colloid could be dissolved quite readily by sonicating solutions under air saturated conditions [89] by the following reaction,... 

Chemseddine, A. and Weller, H. (1993) Highly monodisperse quantum sized CdS particles by size selective predpitation. Berichte der Bunsen-GeseUschafiJur Physikalische Chemie, 97 (4), 636-638. 

Composites containing nanometer-sized metal particles of a controllable and uniform size in an insulating ceramic matrix are very interesting materials for use as heterogeneous catalysts and for magnetic and electronic applications. They show quantum size effects, particularly the size-induced metal-insulator transition (SIMIT) [1],... 

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