An analysis is presented of optical absorption and emission in semiconducting, metallic, and mixed coreshell nanowires are considered theoretically. Due to image forces caused by the difference in dielectric constants between nanowires and their environment, absorption and emission coefficients are different for light polarized parallel or perpendicular to the nanowire axis. As a result, the intensity and spectra of absorption, luminescence, luminescence excitation, and photoconductivity in nanowires or arrays of parallel nanowires are strongly polarization-sensitive. In random nanowire arrays, the effect may result in a "polarization memory" where the polarization of the luminescence is determined by the polarization of the exciting light. In lightemitting core-shell nanowire structures, the described redistribution of ac electric field may result in an enhancement of the luminescence from the nanowire cores in the frequency region corresponding to the plasmon resonances of their metallic shells.

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The Vapor - Liquid - Solid (VLS ) technique allows the growth of high aspect ratio Si wires. The Si nanowires formed by this technique can be thinned down by oxidation. This approach allows the formation of very thin Si cores which may be used to research the properties of Si nanostructures. In this work the growth and oxidation of these wires is characterized.In the growth a very thin layer of Au is deposited on a Si (111) surface, silane gas is introduced into the chamber as the Si source gas and the temperature is raised to 300 – 600°C. Initially a catalytically active Au surface phase leads to the growth of a defective epitaxial Si layer. As Au / Si molten alloy balls nucleate and grow in size to approach the threshold size for VLS wire growth, which is determined by the Gibbs - Thomson effect, the epitaxial layer growth rate decreases and a transition to Si nanowire growth occurs. The morphology and width of the wires is strongly dependent on the growth temperature and pressure. At low pressure and high temperature relatively thick well-formed wires grow straight up from the substrate surface along the [111] direction. As the temperature is decreased and the pressure is increased thinner wires (as thin as 10 nm ) grow which tend to exhibit growth defects. A light oxidation yields Si cores which are of the order of 5 nm in diameter.

For semiconducting nanowires with the dielectric constant ε differing from that of their environment, the distribution of ac electric fields, created in a nanowire by an external lightwave and emitted outside by an effective dipole in a nanowire, is found. The results are used for calculating the spectra and polarization properties of optical absorption, luminescence, and photoconductivity in such nanowires. For relatively thick nanowires, with diameter a comparable to the light wavelength, all polarization characteristics exhibit strong oscillations with the light frequency ω and even change the sign over some intervals of ωa∕c. Some of these phenomena have already been observed experimentally. In a system of randomly oriented nanowires, they result in a polarization memory where polarization of photoluminescence is determined by the polarization of the exciting light, by a factor strongly dependent on the frequencies of both the exciting and emitted light.

The dehydrocoupling of the fluorinated secondary phosphine-borane adduct R2PH.BH3 (R = p-CF3C6H4) at 60 degrees C is catalyzed by the rhodium complex [{Rh(mu-Cl)(1,5-cod)}2] to give the four-membered chain R2PH-BH2-R2P-BH3. A mixture of the cyclic trimer [R2P-BH2]3 and tetramer [R2P-BH2]4 was obtained from the same reaction at a more elevated temperature of 100 degrees C. The analogous rhodium-catalyzed dehydrocoupling of the primary phosphine-borane adduct RPH2.BH3 at 60 degrees C gave the high molecular weight polyphosphinoborane polymer [RPH-BH2]n (Mw = 56,170, PDI = 1.67). The molecular weight was investigated by gel permeation chromatography and the compound characterized by multinuclear NMR spectroscopy. Interestingly, the electron-withdrawing fluorinated aryl substituents have an important influence on the reactivity as the dehydrocoupling process occurred efficiently at the mildest temperatures observed for phosphine-borane adducts to date. Thin films of polymeric [RPH-BH2]n (R = p-CF3C6H4) have also been shown to function as effective negative-tone resists towards electron beam (e-beam) lithography (EBL). The resultant patterned bars were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and time-of-flight secondary ion mass spectrometry (TOF-SIMS).