Conductors and Superconductors

Polyions, polymers, and polymeric membranes also provide suitable compartments for semiconductor particles and particulate films [668-682]. With improved chemical and physical methodologies, polymer chemists will soon be able to construct supramolecular, dimensionally controlled assemblies which will rival the sophistication of LB and SA films. 

Particularly promising is the development of nanoporous ceramic semiconductor membranes [692-695], They not only possess all of the advantages of ceramic materials, but they may also be efficient light harvesters having large surface areas which could provide sites for sensitizers [108, 711-714]. Indeed, FeS2 particles, deposited into (and onto) a porous Ti02 electrode, sensitized photoelectron conversion well (Fig. 118) [714]. 

Bulk crystalline radical ion salts and electron donor-electron acceptor charge transfer complexes have been shown to have room temperature d.c. conductivities up to 500 Scm-1 [457, 720, 721]. Tetrathiafiilvalene (TTF), tetraselenoful-valene (TST), and bis-ethyldithiotetrathiafulvalene (BEDT-TTF) have been the most commonly used electron donors, while tetracyano p-quinodimethane (TCNQ) and nickel 4,5-dimercapto-l,3-dithiol-2-thione Ni(dmit)2 have been the most commonly utilized electron acceptors (see Table 8). Metallic behavior in charge transfer complexes is believed to originate in the facile electron movements in the partially filled bands and in the interaction of the electrons with the vibrations of the atomic lattice (phonons). Lowering the temperature causes fewer lattice vibrations and increases the intermolecular orbital overlap and, hence, the conductivity. The good correlation obtained between the position of the maximum of the charge transfer absorption band (proportional to 

Conductivities can be measured across (i.e. perpendicular or normal to the plane of the aligned surfactants) or in the plane (i.e. parallel to the plane of the aligned surfactants) of LB and SA films. Surfactants possess large apolar regions, have high dielectric constants, and can, thus, be considered as insulators. Placing 

Construction of LB films having lateral d.c. conductivities is a burgeoning activity. Results of published work are summarized in Table 9 [726-772]. The first formation of a conducting LB film was reported by French workers in 1985 [726]. Non-conducting LB films were formed from N-docosylpyridinium TCNQ. Subsequent exposure to iodine vapor resulted, however, in the lateral conductivities in the order of 0.1 S cm-1 [726]. The initially formed LB film was shown to consist of (TCNQ. )2 dimers whose molecular planes were almost parallel to the substrate. Iodination resulted in the development of a brown-purple color, the partial oxidization erf the radical anions to TCNQ° and, most importantly, a dramatic rearrangement of the LB film. In iodine-doped films, the TCNQ molecules have been shown to assume a position almost perpendicular to the substrate [721, 773], 

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For these volumes in the Springer book review series Topics in Current Chemistry, it seemed natural to blend a mix of theory and experiment in chemistry, materials science, and physics. The content of this volume ranges from conducting polymers and charge-transfer conductors and superconductors, to single-molecule behavior and the more recent understanding in single-molecule electronic properties at the metal-molecule interface. 

Jerome D, Schulz FU (1982) Organic conductors and superconductors. AdvPhys 31 299 90... 

Much has been said about the application of this heterocyclic system in supramolecular chemistry and in materials chemistry, particularly in the preparation of organic conductors and superconductors. It should not be forgotten however that heterocyclic compounds in general are extremely important medicinal compounds. Although medicinal applications of this heterocyclic system have been rare in the years since CHEC-II(1996), some have been reported. Townsend and co-workers have described the preparation of imidazo[4,5-r/ isothiazole nucleosides 174-177 and have demonstrated their properties as antiproliferative and antiviral analogues of the antibiotic nebularine 172 and the highly cytotoxic 6-methylpurine nucleoside 173 <1997JME771>. 

Available results on the preparation, characterization, and utilization of metallic and catalytic particles (Sect. 3), semiconductor particles and particulate films (Sect. 4), conductors and superconductors (Sect. 5), magnetism and magnetic particles and particulate films (Sect. 6), and advanced ceramic materials (Sect. 7) will constitute the main body of the monograph. An attempt will be made to cover these materials exhaustively. 

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