Large Semiconductor Molecules

Two crucial factors required for the successful development of these applications are the need to synthesize the appropriate nanoduster molecules in such a manner as to have zero size distribution and to be able to structurally characterize the products obtained. The numerous practical applications of binary late-metal chalco-genide semiconductors [1] have spurred the development of chemical methods to access nanometer-sized pieces of these solid materials, where single crystal diffraction can be used to eluddate the three-dimensional structure of the clusters obtained. 

The Chemistry of Nanomaterials Synthesis, Properties and Applications, Volume 2. Edited by C. N. R. Rao, A. Muller, A. K. Cheetham 

Copyright 2004 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 3-527-30686-2 

The success of this synthetic approach for the delivery of Te(0) to the metal centers requires the presence of additional PEts in the reaction solutions, in order to circumvent the deposition of tellurium metal from the facile reduction of RsP Te to R3P (RsP Te RsP + Te) [17]. In contrast, metal-sulfide clusters are generally not accessible from trialklyphosphine sulfides, due to the inherent strength of P=S bonds, unless more forcing conditions are used [22, 23]. 

The utility of silylated chalcogen reagents as a soluble delivery source oP E has developed into a powerful method for the generation of nanocluster materials. 

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Semiconductor materials are rather unique and exceptional substances (see Semiconductors). The entire semiconductor crystal is one giant covalent molecule. In benzene molecules, the electron wave functions that describe probabiUty density ate spread over the six ting-carbon atoms in a large dye molecule, an electron might be delocalized over a series of rings, but in semiconductors, the electron wave-functions are delocalized, in principle, over an entire macroscopic crystal. Because of the size of these wave functions, no single atom can have much effect on the electron energies, ie, the electronic excitations in semiconductors are delocalized. 

There are many other experiments in which surface atoms have been purposely moved, removed or chemically modified with a scanning probe tip. For example, atoms on a surface have been induced to move via interaction with the large electric field associated with an STM tip [78]. A scaiming force microscope has been used to create three-dimensional nanostructures by pushing adsorbed particles with the tip [79]. In addition, the electrons that are tunnelling from an STM tip to the sample can be used as sources of electrons for stimulated desorption [80]. The tuimelling electrons have also been used to promote dissociation of adsorbed O2 molecules on metal or semiconductor surfaces [81, 82]. 

To dissociate molecules in an adsorbed layer of oxide, a spillover (photospillover) phenomenon can be used with prior activation of the surface of zinc oxide by particles (clusters) of Pt, Pd, Ni, etc. In the course of adsorption of molecular gases (especially H2, O2) or more complex molecules these particles emit (generate) active particles on the surface of substrate [12], which are capable, as we have already noted, to affect considerably the impurity conductivity even at minor concentrations. Thus, the semiconductor oxide activated by cluster particles of transition metals plays a double role of both activator and analyzer (sensor). The latter conclusion is proved by a large number of papers discussed in detail in review [13]. The papers cited maintain that the particles formed during the process of activation are fairly active as to their influence on the electrical properties of sensors made of semiconductor oxides in the form of thin sintered films. 

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