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.
A new Doppler-free optical-optical triple-resonance (DF~UI'R) spectmscopy is reported for the fist time. This high resolution technique is simply wried out using one single mode laser like Doppler-free two-photon speclroscopy, and can reach arbitrary levels in the high-lying p-parity states like fhe optical-optical double-resonance technique in atomic or molecular systems. It is an effective but simple meethod for the systematic study of atomic or molecular SVUC~UIW and their intra or internal dynamics.
The basal-plane anisotropy of the antiferromagnetic phase of the hexagonal heavy-fermion superconductor UPd 2 Al 3 has been studied via the magnetic torque. Torque measurements were performed as functions of magnetic field and angle, with the field rotated in the a-b-plane, at temperatures between 4.2 and 30 K and in fields of up to 20 T. We interpret our results within a mean-field model and derive expressions for the basal-plane anisotropy energy. Further, we studied the anisotropy and temperature dependence of the metamagnetic transition of UPd 2 Al 3 at 18 T and we discuss its nature.
The electrical and optical properties of amorphous indium gallium zinc oxide (a-IGZO) thin films and thin film transistors (TFTs) were investigated for their applications in flat panel displays (FPD). The device characteristics were found to be sensitive to gate dielectric and interlayer film material. TFTs using SiO 2 as a gate dielectric and passivation showed very good characteristics when measured in the dark, with mobility above 10 cm 2 V À1 s À1 , on/off ratio of %10 8 , sub-threshold swing less than 0.2 V/decade and the threshold voltage (V th ) 0.9 V. However when exposed to light of wavelength below 420 nm V th shifted markedly. The shift in V th increased with increasing power density, irradiation time, and decreasing wavelength. The shift is attributed to trapping of photogenerated holes in the light induced traps in SiO 2 close to the IGZO interface. It is postulated that these traps are created due to the unstable IGZO surface. Shielding TFTs from light stabilizes the characteristics, however, stabilization of the IGZO surface is required to realize stability for practical applications.
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