Advanced Materials Research Vols. 750-752

Abstract: Selected area laser-annealed polycrystalline silicon (p-Si) thin films were prepared by a 248 nm excimer laser. 1 μm thick p-Si films with grain size less than 100 nm were deposited on SiO₂ substrate by chemical vapor deposition using atmospheric pressure (APCVD). Grain sizes before and after annealing was examined by scanning electron microscopy (SEM) and the mechanism of grain growth was discussed in detail. The maximum grain size of a selected area laser-annealed p-Si film can be increased from 100 nm up to 2.9 μm on SiO₂ substrate by using appropriate laser energy densities. It indicated that silicon grains in laser-annealed regions had grown up competitively with three stages.

Abstract: Mott and Gurney point out¹, for defect-free semiconductors, I-V curve deviates from linear Ohmic type to nonlinear space-charge limited behavior at high electric field. A surprising large magnetoresistance (MR) has been reported in space-charge limited region by Delmo^2-4 recently. In present work, I-V and MR curves of silicon samples with different doping concentration are measured. It is observed that I-V curve enters into space charge region at lower voltage in heavily doped samples, however, space-charge limited current is absent in lightly doped samples. Two samples show different types of MR curve. In heavily doped samples, 8% MR is acquired at 3kG and the value of MR increases linearly up to 17%, while MR increases slowly up to 11% in lightly doped samples. It is believed that the dopant and trap in N-type silicon has a strong influence on the space-charge limited current and MR.

Abstract: The phosphors SrAl₂Si₂O₈ doped with different Eu²⁺ concentration were prepared by solid-state reaction technique, and their photoluminescent properties at different temperature were investigated. With the increase of Eu²⁺ content, two emission bands can be observed and this can be interpreted as Eu²⁺ ions occupying two types of sites in the crystal lattice. And their lifetime is decreasing, this result can be due to energy transfer among Eu²⁺ ions nonradiately at higher concentration of Eu²⁺ ions in the host lattices. The phosphor SrAl₂Si₂O₈:0.40Eu shares intense blue emitting with broad excitation in the near-UV range. This phosphor may be an excellent blue phosphor for near ultraviolet InGaN-based white diodes.

Abstract: This document explains and demonstrates how to design efficient amorphous silicon solar cells. Some of the fundamental physical concepts required to interpret the scientific literature about amorphous silicon are introduced. The principal methods such as plasma deposition that are used to make amorphous siliconbased solar cells are investigated. On the basis, high-efficiency solar cells based on amorphous silicon technology are designed. Multi-junction amorphous silicon solar cells are discussed, how these are made and how their performance can be understood and optimized. To conclude this document, some of the directions that are important for future progress in the field are presented.

Abstract: The [Fe-Co-Si (d)/native oxid₅₀ multilayer films were deposited on Kapton substrate and glass substrate by DC magnetron sputtering. The effect of substrate on magnetic and electric properties of the multilayer films was investigated. Compared to the films on glass substrates, higher coercivity, larger uniaxial-anisotropy field were achieved for the flexible films. The values of the resistivities for the flexible films are of the order of 10 mΩcm, which is two orders higher than the value of 0.1 mΩcm for the multilayer films on glass substrates. Furthermore, higher f_r was found in the flexible films. It is believed that the [Fe-Co-Si (d)/native oxide]₅₀ multilayer films on flexible substrates can find its wide applications at high frequency for various purposes.

Abstract: High-efficiency solar cells based on amorphous silicon technology are designed. Multi-junction amorphous silicon solar cells are discussed, how these are made and how their performance can be understood and optimized. Although significant amount of work has been carried out in the last twenty-five years, the Staebler-Wronski effect has limited the development of a-Si:H solar cells. As an alternative material, nc-Si:H has attracted remarkable attention. Taking advantage of a lower degradation in nc-Si:H than a-Si:H and a-SiGe:H alloys, the light induced degradation in triple junction structures has been minimized by designing a bottom-cell-limited current mismatching, and obtained a stable active-area cell efficiency. All this has been investigated in this paper.

Abstract: Effect of Y₂O₃ on the viscosity and Crystallization of of borosilicate glass at high temperature was investigated at high temperature. Melt viscosity as a function of temperature was determined by using a rotating spindle viscometer. Liquidus temperature was determined by the Gradient Furnace Method. The results show that the viscosity decreased as a function of Y₂O₃ content. The activation energy of glass without Y₂O₃ is about 110.3 kJ·mol^-1 and the activation energy increases with the Y₂O₃ addition up to the 2 wt%. At 2 wt% Y₂O₃, the specimen shows the maximum activation energy value of 112.6 kJ·mol^-1. As Y₂O₃ content increase, the activation energy decreases. The fiber-forming temperature of glass without Y₂O₃ is about 1342 oC and the fiber-forming temperature increases with the Y₂O₃ addition up to the 2 wt%. At 2 wt% Y₂O₃, the sample shows the maximum activation energy value of 1370 °C. When Y₂O₃ content increase, the fiber-forming temperature decreases. The liquidus temperature of glass decreases from 1313 °C to 1023 °C when Y₂O₃ content increases from 0 wt% to 6 wt%. The difference between the fiber-forming and the liquidus temperatures of glass increases from 30 oC to 336 °C when Y₂O₃ content increases from 0 wt% to 6 wt%.

Abstract: We derive the general expression of the anisotropic magnetoresistance (AMR) ratio of ferromagnets for a relative angle between the magnetization direction and the current direction. We here use the two-current model for a system consisting of a spin-polarized conduction state (s) and localized d states (d) with spin-orbit interaction. Using the expression, we analyze the AMR ratios of Ni and a half-metallic ferromagnet. These results correspond well to the respective experimental results. In addition, we give an intuitive explanation about a relation between the sign of the AMR ratio and the s-d scattering process.

Abstract: The present work describes a solution-liquid-solid (SLS) synthesis route for the preparation of CdSe nanocrystal quantum dots using the low-melting-point Bi nanoparticles as catalysts. UV-vis absorption spectra were used to determine the growth of CdSe cluster. The shape and size distribution of the CdSe QDs were determined by analysis of Transmission electron microcopy (TEM) images. A peak wavelength of 399nm in the absorption spectra on day 5 indicated that the CdSe cluster formed. TEM micrographs showed that CdSe QDs had a relatively narrow distribution of QD size, and the diameter of CdSe QDs was about 4 nm. Our preliminary results illustrated that smaller size of CdSe QDs could be prepared by SLS method and it was small enough for bioimaging applications.

Abstract: It has been investigated that the interaction force in hybrid magnetic levitation systems with a GdBCO bulk superconductor and a permanent magnet system and two permanent magnets (PM2) and two cubic permanent magnets (PM3) system in their coaxial configuration at liquid nitrogen temperature. A single-domain GdBCO sample is of 20mm and 10mm in thickness, the permanent magnet PM1 is of rectangular parallelepiped shape, the permanent magnets PM2 and PM3 are of cubic shape; the system placed on the middle of system and their coaxial configuration; It is found that the maximum levitation force decreases from 46.3N to 16.3N while the horizontal distance (Dpp) between the rectangle permanent magnet and two cubic permanent magnets (PM2) is increased from 0mm to 24mm and the horizontal distance (Dsp) between a GdBCO bulk superconductor and two cubic permanent magnets (PM3) is 0mm, The results indicate that the higher levitation force can be obtained by introducing PM-PM levitation system based on scientific and reasonable design of the hybrid magnetic levitation system, which is helpful for designing and constructing superconducting magnetic levitation systems.