Photoluminescence linewidth broadening due to alloy/thickness fluctuation of CdxZn1 − xSe/ZnSe triple quantum wells

Photoluminescence (PL) linewidth broadening of Cd_xZn_{1 − x}Se/ZnSe triple quantum wells, grown on GaAs substrates by molecular beam epitaxy (MBE), has been investigated. Various quantum well (QW) samples have been prepared with different QW thickness and composition (Cd-composition). Measured and calculated PL linewidth are compared. Both composition and thickness fluctuations are considered for the calculation with the parameters such as the volume of exciton, nominal thickness and composition of QWs. Surface roughness measured by atomic force microscopy (AFM) is used to estimate the interface roughness. Results show that when Cd-composition increases additional linewidth broadening due to Zn/Cd interdiffusion is enhanced.     

电子束驱动的回旋激射不稳定性

对弱相对论性电子束驱动的回旋激射(maser)不稳定性的一般理论作了详细讨论.对在获得增长率实用表达式过程中若干解析表达式的推导与细节做了仔细的补充讨论和说明，还增加了增长率的近似表达式，并由此得到了回旋激射不稳定性主要特征的解析分析以及与精确计算的比较，使整个理论有一个完整的描述.侧重解析讨论，也提供了部分一般性的数值计算结果. 关键词： 回旋激射不稳定性 弱相对论性电子束 增长率     

Crystallization and morphology of poly(vinylidene fluoride)/poly(3‐hydroxybutyrate) blends. I. Spherulitic morphology and growth by polarized microscopy

The development of the poly(3‐hydroxybutyrate) (PHB) morphology in the presence of already existent poly(vinylidene fluoride) (PVDF) spherulites was studied by two‐stage solidification with two separate crystallization temperatures. PVDF formed irregular dendrites at lower temperatures and regular, banded spherulites at elevated temperatures. The transition temperature of the spherulitic morphology from dendrites to regular, banded spherulites increased with increasing PVDF content. A remarkable amount of PHB was included in the PVDF dendrites, whereas PHB was rejected into the remaining melt from the banded spherulites. When PVDF crystallized as banded spherulites, PHB could consequently crystallize only around them, if at all. In contrast, PHB crystallized with a common growth front, starting from a defined site in the interfibrillar regions of volume‐filling PVDF dendrites. It formed by itself dendritic spherulites that included a large number of PVDF spherulites. For blends with a PHB content of more than 80 wt %, for which the PVDF dendrites were not volume‐filling, PHB first formed regular spherulites. Their growth started from outside the PVDF dendrites but could later interpenetrate them, and this made their own morphology dendritic. These PHB spherulites melted stepwise because the lamellae inside the PVDF dendrites melted at a lower temperature than those from outside. This reflected the regularity of the two fractions of the lamellae because that of those inside the dendrites of PVDF was controlled by the intraspherulitic order of PVDF, whereas that from outside was only controlled by the temperature and the melt composition. The described morphologies developed without mutual nucleating efficiency of the components. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 873–882, 2003     

Cu~+、Ag~+、Au~+与乙硫醇的气相化学反应

利用激光溅射 分子束的技术 ,结合反射飞行时间质谱计 ,研究了Cu+、Ag+、Au+与乙硫醇的气相化学反应。结果显示这三种金属离子与 (CH3 CH2 SH) n 反应形成一系列团簇离子M+(CH3 CH2 SH) n,且团簇离子尺寸不一样。Ag+、Au+与乙硫醇的反应还生成了 (CH3 CH2 SH) +n ,由此推测Cu+、Ag+、Au+与乙硫醇团簇的反应存在两种通道 ,一种通道是生成M+(CH3 CH2 SH) n,另一种是生成 (CH3 CH2 SH) +n 。Cu+、Au+与乙硫醇的反应还生成了M+(H2 S) (M =Cu、Au) ,但是实验中没有观察到Ag+(H2 S) ,理论计算表明Ag+(H2 S)很不稳定。另外 ,分析产物离子M+(CH3 CH2 SH) n 的强度发现 ,n =1～ 2之间存在明显的强度突变现象     

基于光敏自组装多层膜的液晶光控取向膜

采用layer-by-layer(LBL)的方法，将基板依次在具有光敏双键的季铵盐水溶液和聚乙烯基苯磺酸钠水溶液中浸泡，石英基板表面形成了自组装多层沉积膜。经线性偏振紫外光辐照后，LBL多层膜表现出明显的紫外吸收各向异性。将两片带有各向异性薄膜的基板做成平行液晶器件。在正交的偏光显微镜下观察，发现取得均一、稳定的取向效果。该种光控取向膜有望用作LCoS微显示的取向层。     

320×240 Pixels CMOS Digital Image Sensor with Wide Dynamic Range

A 320×240 CMOS image sensor is demonstrated,which is implemented by a standard 0.6 μm 2P2M CMOS process.For reducing the chip area,each 2×2-pixel block shares a sample/hold circuit,analog-to-digital converter and 1-b memory.The 2×2 pixel pitch has an area of 40 μm×40 μm and the fill factor is about 16%.While operating at a low frame rate,the sensor dissipates a very low power by power-management circuit making pixel-level comparators in an idle state.A digital correlated double sampling,which eliminates fixed pattern noise,improves SNR of the sensor, and multiple sampling operations make the sensor have a wide dynamic range.     

Spectral shifts and spectral switches in diffraction of ultrashort pulsed beams passing through a circular aperture

Based on the Fourier transform method, a simple closed-form expression for the on-axis power spectrum of ultrashort Gaussian pulsed beams in diffraction at a circular aperture is derived, which permits us to study spectral changes both analytically and numerically. It is shown that for diffracted pulsed beams there exist spectral red and blue shifts, spectral narrowing, and spectral switches in the near field. The aperture diffraction plays an important role in spectral switching, but both the truncation parameter and bandwidth (or equally, Fourier transform limited pulse duration) affect the behavior of spectral switches.     

4-Benzoylbenzoate intercalated in layered double hydroxides: a new catalyst for photo-oxidation of sulfides in solution and in the gas phase

A new mixed organic-inorganic photosensitizer, based on 4-benzoylbenzoate intercalated into a layered double hydroxide has been prepared, characterized and successfully tested for the photo-oxidation of dialkylsulfides, both in acetonitrile and in the gas phase.     

Small and high-density GeSiC dots stacked on buried Ge hut-clusters in Si

Self-assembled GeSiC dots stacked on a Ge hut-cluster layer buried in Si have been investigated. The critical thickness for formation of GeSiC dots is reduced owing to the strain fields from the buried hut-clusters. By utilizing the stacked structure, the dot size is decreased and the uniformity is improved. The highest density of the GeSiC dots with stacked structures is 7.4×10¹⁰ cm⁻², which is six times larger than that of single GeSiC dots. The formation of the self-assembled GeSiC dots is strongly influenced by being stacked with buried Ge dots as well as C incorporation.