Oscillating magnetoresistance in diluted magnetic semiconductor barrier structures

Ballistic spin polarized transport through diluted magnetic semiconductor single and double barrier structures is investigated theoretically using a two-component model. The tunneling magnetoresistance (TMR) of the system exhibits oscillating behavior when the magnetic field is varied. An interesting beat pattern in the TMR and spin polarization is found for different nonmagnetic semiconductor/diluted magnetic semiconductor double barrier structures which arises from an interplay between the spin-up and spin-down electron channels which are split by the s-d exchange interaction.

Photoluminescence behavior of quantum dots in spherical glass microcavity

Micrometer-sized spherical glass microspheres were fabricated. CdSeS semiconductor nanometer clusters were incorporated into spherical microcavities. When a single microsphere was excited by a laser beam, the whispering gallery mode resonance of the photoluminescence of CdSeS quantum dots in the spherical microcavities was realized by the multiple total internal reflections at the spherical interface. The coupling of restricted electronic and photonic states was realized.

Detection of efficient carrier capture in ultrathin InAs/GaAs layers using a degenerate pump-probe technique

By analysing the carrier dynamics based on the rate equations and the change of the refractive index due to the efficient carrier capture, we have calculated the carrier capture process in the InAs/GaAs system detected by a simple degenerate pump-probe technique. The calculated results are found to be in good agreement with the experimental findings. Our results indicate that this simple technique, with the clear advantage of being easy to carry out, can be very useful in studying the carrier dynamics for some specific structures such as InAs ultrathin layers embedded in a GaAs matrix described here.

Optical anisotropy of InAs submonolayer quantum wells in a (311) GaAs matrix

The steplike density of states obtained from reflectance-difference spectroscopy demonstrates that ultrathin InAs layers should be regarded as two-dimensional quantum wells rather than isolated clusters, even for the sample with only 1/3 monolayer InAs in (311)-oriented GaAs. The degree of anisotropy is within the intrinsic anisotropy of (311)-oriented ultrathin quantum wells, indicating that there is little structural or strain anisotropy in the InAs islands. (C) 1998 Elsevier Science B.V.

Optical anisotropy of InAs monolayer in (311)-oriented GaAs matrix

In-plane optical anisotropy which comes from the heavy hole and the light hole transitions in an InAs monolayer inserted in (311)-oriented GaAs matrix is observed by reflectance difference spectroscopy. The observed steplike density of states demonstrates that the InAs layer behaves like a two-dimensional quantum well rather than isolated quantum dots. The magnitude of the anisotropy is in good agreement with the intrinsic anisotropy of (311) orientation quantum wells, indicating that there is little structural or strain anisotropy of the InAs layer grown on (311)-oriented GaAs surface.

Optimization of VI/II pressure ratio in ZnTe growth on GaAs(001) by molecular beam epitaxy

ZnTe epilayers were grown on GaAs(0 0 1) substrates by molecular beam epitaxy (MBE) at different VI/II beam equivalent pressure (BEP) ratios (R-VI/II) in a wide range of 0.96-11 with constant Zn flux. Based on in situ reflection high-energy electron diffraction (RHEED) observation, two-dimensional (2D) growth mode can be formed by increasing the R-VI/II to 2.8. The Te/Zn pressure ratios lower than 4.0 correspond to Zn-rich growth state, while the ratios over 6.4 correspond to Te-rich one. The Zn sticking coefficient at various VI/II ratios are derived by the growth rate measurement. The ZnTe epilayer grown at a R-VI/II of 6.4 displays the narrowest full-width at half-maximum (FWHM) of double-crystal X-ray rocking curve (DCXRC) for (0 0 4) reflection. Atomic force microscopy (AFM) characterization shows that the grain size enlarges drastically with the R-VI/II. The surface root-mean-square (RMS) roughness decreases firstly, attains a minimum of 1.14 nm at a R-VI/II of 4.0 and then increases at higher ratios. It is suggested that the most suitable R-VI/II be controlled between 4.0 and 6.4 in order to grow high-quality ZnTe epitaxial thin films.

蛋白类药物缓释微球制备方法的研究:纳米吸附-水包油包固体乳化法

本论文研究了一种制备蛋白类药物缓释微球的纳米吸附-水包油包固体乳化法。模型药物为牛血清白蛋白BSA。首先用纳米二氧化硅吸附溶液中的BSA制备出纳米级的药物颗粒，然后再用水包油包固体(S/O/W)乳化法将该含药粒子用可生物降解的高分子材料包载起来制成蛋白药物控制释放制剂。 纳米材料吸附蛋白药物后的吸附产物仍为纳米粒子。在纳米二氧化硅表面引入不同的功能基团可以改变其Zeta电位从而改变其对BSA的吸附能力，在其表面引入氨基可以使BSA的吸附量由20%提高到35%，引入羧基则使BSA的吸附量降低到11%。在二氧化硅表面接枝低分子量的聚合物均降低其吸附BSA的能力，并且BSA的吸附量随着聚合物接枝量的增加而减少。 将具有不同表面改性的纳米二氧化硅吸附BSA后的吸附产物用水包油包固体乳化法制备成聚合物微球，均具有很高的包裹率，大于90%；并且该释放体系服从Fick扩散机理，载药微球的药物累积释放量与时间的平方根成良好线性关系。在二氧化硅表面接枝低分子量PLLA，可以提高BSA在聚合物微球中分布的均匀性，解决药物释放时的突释现象，使BSA的第一天释放量由25%降低到15%。 另外，初步研究了三种不同的介孔材料对于BSA的吸附能力以及表面具有氨基的介孔二氧化硅吸附BSA后的释放行为。

功能高分子微球的制备及其在某些方面的应用研究

功能高分子微球由于具有粒径小、比表面积大以及含有多种功能基团，在诸如生物化学及生物医学、微电子工业等领域具有广泛的应用前景。由于其广泛的应用前景，已受到越来越多的重视和研究。本论文是基于对功能高分子微球的制备，及其在固定酶，传感器及自组装等方面的应用研究，主要研究内容和结论如下：1、采用间歇无皂乳液聚合法制备了P（SAA）PAA核一壳纳米高分子微球，对在其上固定胰岛素进行了研究。发现固定胰岛素量随着微球粒径的增大而减小，固定胰岛素活性随固定胰岛素量的增大而降低。2、利用自组装的方法，将表面琉基化功能高分子微球、金纳米粒子、辣根过氧化物酶依次组装在金电极上，构建了一种新型的第三代过氧化氢生物传感器。结果表明，该生物传感器在没有电荷传递介质存在的情况下，对过氧化氢显示了诗良高的灵敏度。另外，该生物传感器还具有良好的童复性和长期稳定性。3、采用后加功能单体的无皂乳液聚合法制备出了St/ANPA共聚发光纳米微球。然后利用自组装的方法，得到了不同于无机及金属粒子的高分子发光纳米微球的二维网络结构，以及直径一民度可控的一维发光纳米线。4、采用后加功能单体的无皂乳液聚合法制备了水分散性的St/PANDMEA共聚荧光纳米微球，此微球可用作化学与生物传感器，能很好的检测溶液中的有机亲电子试剂及抗生物素蛋白。5、采用分散聚合法制备了P（St／DVB）高分子微球。然后利用化学沉积法在P(St/DVB）高分子微球表面沉积Ni和Au。得到了核为P（St／DVB）高分子微球，壳为Ni和Au粒子的复合微球。6、利用种子乳液聚合、萃取和表面修饰的方法制备了一种新型的不同于普通的多孔高分子微球的表面含有琉基的AAOVB共聚中空多孔高分子微球。然后利用自组装的方法，制得过氧化氢生物传感器。该生物传感器检测极限达到0.5μM，检测的线性范围从1.0μM到8mM。

BAND-STRUCTURE OF MG1-XZNXSYSE1-Y

The empirical pseudopotential method within the virtual crystal approximation is used to calculate the band structure of Mg1-xZnySySe1-y, which has recently been proved to be a potential semiconductor material for optoelectronic device applications in the blue spectral region. It is shown that MgZnSSe can be a direct or an indirect semiconductor depending on the alloy composition. Electron and hole effective masses are calculated for different compositions. Polynomial approximations are obtained for both the energy gap and the effective mass as functions of alloy composition at the GAMMA valley. This information will be useful for the future design of blue wavelength optoelectronic devices as well as for assessment of their properties.

GROWTH OF WIDE-BAND GAP IMMISCIBLE II-VI ALLOYS BY METALORGANIC VAPOR-PHASE EPITAXY

Although metalorganic vapor phase epitaxy (MOVPE) is generally regarded as a non-equillibrium process, it can be assumed that a chemical equilibrium is established at the vapor-solid interface in the diffusion limited region of growth rate. In this paper, an equilibrium model was proposed to calculate the relation between vapor and solid compositions for II-VI ternary alloys. Metastable alloys in the miscibility gap may not be obtained when the growth temperature is lower than the critical temperature of the system. The influence of growth temperature, reactor pressure, input VI/II ratio, and input composition of group VI reactants has been calculated for ZnSSe, ZnSeTe and ZnSTe. The results are compared with experimental data for the ZnSSe and ZnSTe systems.

Quantum confinement effect in thin quantum wires

The electronic states and optical transition properties of three semiconductor wires Si? GaAs, and ZnSe are studied by the empirical pseudopotential homojunction model. The energy levels, wave functions, optical transition matrix elements, and lifetimes are obtained for wires of square cross section with width from 2 to 5 (root 2a/2), where a is the lattice constant. It is found that these three kinds of wires have different quantum confinement properties. For Si wires, the energy gap is pseudodirect, and the wave function of the electronic ground state consists mainly of four bulk Delta states. The optical transition matrix elements are much smaller than that of a direct transition, and increase with decreasing wire width. Where the width of wire is 7.7 Angstrom, the Si wire changes from an indirect energy gap to a direct energy gap due to mixing of the bulk Gamma(15) state. For GaAs wires. the energy gap is also pseudodirect in the width range considered, but the optical transition matrix elements are larger than those of Si wires by two orders of magnitude for the same width. However, there is no transfer to a direct energy gap as the wire width decreases. For ZnSe wires, the energy gap is always direct, and the optical transition matrix elements are comparable to those of the direct energy gap bulk semiconductors. They decrease with decreasing wire width due to mixing of the bulk Gamma(1) state with other states. All quantum confinement properties are discussed and explained by our theoretical model and the semiconductor energy band structures derived. The calculated lifetimes of the Si wire, and the positions of photoluminescence peaks, are in good agreement with experimental results.

Shubnikov de Haas oscillations of a two-dimensional electron gas in a modulation-doped Zn0.80Cd0.20Se/ZnS0.06Se0.94 single quantum well

The magnetotransport properties of the two-dimensional (2D) electron gas confined in a modulation-doped Zn0.80Cd0.20Se/ZnS0.06Se0.94 single quantum well structure were studied at temperatures down to 0.35 K in magnetic fields up to 7.5 T. Well resolved 2D Shubnikovde Haas (SdH) oscillations were observed, although the conductivity of the sample in the as grown state was dominated by a bulk parallel conduction layer. After removing most of the parallel conduction layer by wet chemical etching the amplitude and number of SdH oscillations increased. From the temperature dependence of the amplitude the effective mass of the electrons was estimated as 0.17 m(0). Copyright (C) 1996 Published by Elsevier Science Ltd

色散效应对GaAs太阳电池双层减反射膜的影响

考虑双层减反射膜材料的折射率色散效应，采用光学干涉矩阵法计算了SiO2／ZnSe和SiO2／ZnS两种GaAs太阳电池双层减反射膜的反射率与波长的函数曲线，以及加权平均反射率随着顶层减反射膜SiO2厚度变化的函数曲线，并与未考虑色散效应的情况进行了对比．计算结果表明，色散效应对双层减反射膜的反射率有较大的影响，特别是对300-500nm波长范围的影响更大，且对不同材料的减反射膜的影响也是不同的．与未考虑色散效应的情况相比，考虑色散效应后，SiO2／ZnSe双层减反射膜的最小加权平均反射率从1．14％增加到1．55％，而SiO2／ZnS双层减反射膜的最小加权平均反射率却从1．49％减小到1.46％．

Upconversion emission of a Er3+-doped glass microsphere under 633 nm excitation

In this work, The TBS glass microspheres doped with Er3+ for morphology-dependent resonances of upconversion emission were designed. The glass sample components are 25TiO(2)-27BaCO(3)-8Ba(NO3)(2)-6ZnO(2)-9CaCO(3)-5H(3)BO(3)-10SiO(2)-7water glass-3Er(2)O(3) (wt%), and the emission spectra of TBS glass and a TBS glass microsphere (about 48 mum in diameter) were measured under 633 nm excitation and discussed. The strong morphology-dependent resonances of upconversion luminescences in the microsphere were observed. The observed resonances could be assigned by using the well-known Lorenz-Mie Formalism. (C) 2003 Elsevier Ltd. All rights reserved.

Optical anisotropy of InAs submonolayer quantum wells in a (311) GaAs matrix

The steplike density of states obtained from reflectance-difference spectroscopy demonstrates that ultrathin InAs layers should be regarded as two-dimensional quantum wells rather than isolated clusters, even for the sample with only 1/3 monolayer InAs in (311)-oriented GaAs. The degree of anisotropy is within the intrinsic anisotropy of (311)-oriented ultrathin quantum wells, indicating that there is little structural or strain anisotropy in the InAs islands. (C) 1998 Elsevier Science B.V.