Characterization of GaSb substrate wafers for MOCVD III-V antimonides

The qualities of GaSb substrates commonly used for the preparation of III-V antimonide epilayers were studied before and after growing GaInAsSb multi-layers by MOCVD using PL, FTIR and DCXD together with the electrical properties and EPD value. The correlation between the substrate qualities and epilayer properties was briefly discussed. The good property epilayers of GaInAsSb and, then, the high preformance of 2.3 um photodetectors were achieved only using the good quality GaSb wafers as the substrates.

Electronic investigation of self-organized InAs quantum dots

Deep Level Transient Spectroscopy (DLTS) has been applied to investigate the electronic properties of self-organized InAs quantum dots. The energies of electronic ground states of 2.5ML and 1.7ML InAs quantum dots (QDs) with respect to the conduction band of bulk GaAs are about 0.21 eV and 0.09 eV, respectively. We have found that QDs capture electrons by lattice relaxation through a multi-phonon emission process. The samples are QDs embedded in superlattices with or without a 500 Angstrom GaAs spacing layer between every ten periods of a couple of GaAs and InAs layers. The result shows that the density of dislocations in the samples with spacer layers is much lower than in the samples without the spacer layers.

Material transport in self-assembled InAs/GaAs quantum dot ensemble

Introducing the growth interruption between the InAs deposition and subsequent GaAs growth in self-assembled quantum dot (QD) structures, the material transport process in the InAs layers has been investigated by photoluminescence and transmission electron microscopy measurement. InAs material in structures without misfit dislocations transfers from the wetting layer to QDs corresponding to the red-shift of PL peak energy due to interruption. On the other hand, the PL peak shifts to higher energy in the structures with dislocations. In this case, the misfit dislocations would capture the InAs material from the surrounding wetting layer and coherent islands leading to the reduction of the size of these QDs. The variations in the PL intensity and Linewidth are also discussed.

Influence of interdot electronic coupling on photoluminescence spectra of self-assembled InAs/GaAs quantum dots

The influence of interdot electronic coupling on photoluminescence (PL) spectra of self-assembled InAs/GaAs quantum dots (QDs) has been systematically investigated combining with the measurement of transmission electron microscopy. The experimentally observed fast red-shift of PL energy and an anomalous reduction of the linewidth with increasing temperature indicate that the QD ensemble can be regarded as a coupled system. The study of multilayer vertically coupled QD structures shows that a red-shift of PL peak energy and a reduction of PL linewidth are expected as the number of QD layers is increased. On the other hand, two layer QDs with different sizes have been grown according to the mechanism of a vertically correlated arrangement. However, only one PL peak related to the large QD ensemble has been observed due to the strong coupling in InAs pairs. A new possible mechanism to reduce the PL linewidth of QD ensemble is also discussed.

The enhancement of diffusion by strain of InAs quantum dots in a GaAs matrix

We investigate the annealing behavior of Photoluminescence (PL) from self-assembled InAs quantum dots (QDs) with different thicknesses GaAs cap layers. The diffusion introduced by annealing treatment results in a blue-shift of the QD PL peak, and a decrease in the integrated intensity. The strain present in QDs enhances the diffusion, and the QDs with the cap layers of different thicknesses will experience a strain of different strength. This can lend to a, better understanding of the larger blue-shift of the PL peak of the deeper buried QDs, and the different variance of the full width at half maximum of the luminescence from QDs with the cap layers of different thicknesses.

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.

Heteroepitaxy of cubic GaN: influence of interface structure

We report on the epitaxial growth and the microstructure of cubic GaN. The layers are deposited by plasma-assisted molecular beam epitaxy on GaAs and Si substrates. Despite the extreme lattice mismatch between these materials, GaN grows in the metastable cubic phase with a well-defined orientation-relationship to the GaAs substrate including a sharp heteroboundary. The preference of the metastable phase and its epitaxial orientation originates in the interface structure which is found to be governed by a coincidence site lattice.

CSR测量控制网的建立及元件的准直安装

针对cSR元件定位要求高精度，元件数量多，分布范围广的特点，本沦文详细介绍了主环测量控制网的建立过程，以及运用激光跟踪仪测量三维I程控制网的方法，并给出了控制网的测量结果。这种测网方法有别于传统测量学中平面网和高程网相分离的处理办法，在国内加速器准直同行中是没有过的。在元件准直部分，着重叙述了元件准直的思想和方法。通过FidLlcial过程建立元件坐标系以确定靶标点的坐标位置。用激光跟踪仪测量控制网，恢复局部坐标系，移动测量坐标系到元件的理论中心。运用跟踪仪实时监测靶标点的三维坐标值，就可以很方便地调整磁铁的位置。最后用自编软件Best-fit给出调节结果。该方法思想比较新颖，也是我们准直测量组的一个创举。第四章介绍了最佳拟合的理沦依据和计算方法并且给出了Mat 1 abs．3环境下的原代码，我们用最佳拟合的结果来描述磁铁最后的位置。第五章介绍的非接触测量是测量界比较热的研究课题之一，结合我们自己的条件，发展了控制网加全站仪的方法，当然这一方法还有待进一步研究；最后用很少的篇幅介绍了准直测量常用的Insigllt4．O等基本软件。

永磁伺服电动机的矢量调速控制系统研究

永磁同步伺服电动机（PMSM）以其优越的性能广泛应用于各个机械传动领域。对PMSM的研究具有非常大的实际意义和价值，尤其对于我们单位目前在建大科学工程CSR。本文采用美国TI公司专用于电动机控制的数字信号处理器（DSP）芯片TMs320LF2406A作为核心，设计和开发全数字化的PMSM矢量调速控制系统。深入研究永磁同步电动机的矢量控制理论，建立起相应数学模型，然后提出矢量控制调速方案，并通过Mat lab仿真论证其可行性。介绍了硬件，软件结构及其实现。硬件方面主要介绍了控制电路各部分的设计和调试。在硬件基础上，用T工公司DSP汇编语言编程，实现电流环和速度环的双环控制，给出了系统程序和PWM信号产生的思路，并给出了主要模块的源程序。为了提高程序的运行效率，节省存储空间和提高系统的可靠性，程序中尽可能多的采用了数据表结构。

不同N素形态对落叶松苗木根/土界面pH值及养分有效性的影响

The effect of different nitrogen and phosphorus sources on pH and the availability of mineral nutrients in the root/soil interface of Larix gmelinii seedlings were studied by means of root-mat method. The results showed that the addition of NH~+_4-N decreased the pH in the root/soil interface, while the addition of NO~-_3-N increased the pH in contrast with the control treatment. The sort of the P sources and the distance from the root plane remarkably influenced the changes of pH in the root/soil interface induced by the addition of the nitrogen sources. Compared with the addition of only NH~+_4-N, the extent to which the pH in the root/soil interface decreased was obviously smaller when treated by NH~+_4-N and rock P. When treated with different P sources, the contents of available P in the root/soil interface were affected by the sort of the N sources. When treated with soluble P, the contents of the available P in the root/soil interface obviously increased for the addition of both NH~+_4-N and NO~-_3-N. When treated with rock P, the contents of the available P increased only in the area 0～3 mm from the root plane for NH~+_4-N, whereas the contents of available P in the root/soil interface changed little for NO~-_3-N. The results above showed that the protons excreted by the roots were the main driving force for the solution of the rock P in the root/soil interface. The availability of Fe in the root/soil interface increased as a result of acidity induced by the NH~+_4-N, whereas the availability of Fe in the root/soil interface decreased because of the pH increase induced by the NO_3~-_N. The effect of different N sources on the availability of Fe in the root/soil interface was also affected by the sort of P sources. The concentrations of P、Fe in the leaves remarkably differed when treated by different N、P sources and concentrations of the P、Fe in the root/soil interface were correlated to those in the leaves of the seedlings.

土壤持水曲线vanGenuchten模型求参的Matlab实现

土壤持水曲线是研究土壤水力学性质必不可少的 ,在已经建立的众多数学模型中 ,vanGenuchten模型是目前运用最广泛的模型 ,而运用该模型的关键是其 4个参数的求解。为此 ,本文对同一组东北褐土的土壤水吸力和对应的土壤含水量数据较详细地介绍了Matlab软件的非线性拟合和非线性回归函数的运用 ,得出了该土壤vanGenuchten模型的 4个参数值 ,分别建立了该土壤的vanGenuchten模型 ,并利用Mat lab强大的绘图功能对它们进行了直观比较。最后运用方差分析和残差分析对该模型的计算值与实测数据进行了分析 ,结果表明 :非线性拟合和非线性回归函数求参结果的显著水平均达到p<0 0 0 0 1,残差平方和均小于 0 0 0 0 5 ,其中非线性回归函数的求参结果较非线性拟合好。因此 ,运用Matlab软件的非线性拟合和非线性回归函数对土壤持水曲线的vanGenuchten模型进行求参是切实可行的 ,从而为土壤学工作者寻求出了一条运用数值计算方法的新途径。

Modification of electrode surface through electrospinning followed by self-assembly multilayer film of polyoxometalate and its photochromic

Electrospun poly (vinyl alcohol) (PVA) nanofibers mat was collected on indium tin oxide (ITO) substrate. Heat crosslinked nanofibers mat became water-insoluble and firmly fixed on ITO substrate even in water. Oppositely charged poly (allylamine hydrochloride) (PAH) and Dawson-type polyoxometalate (POM), Na6P2Mo18O62 (P2Mo18), were alternately assembled on PVA nanofibers-coated ITO substrate to construct multilayer film through an electrostatic layer-by-layer (LBL) technique. The scanning electron microscope (SEM) images showed that P2Mo18 multilayer film was selectively deposited on PVA nanofibers while the unoccupied space by nanofibers on bare ITO was acted as substrate at the same time because the electrospun nanofibers have larger surface area and surface energy than the flat substrate. The cyclic voltammograms current responses of the P2Mo18 multilayer film on PVA/ITO electrode showed three well-defined redox couples of P2Mo18, but very small because P2Mo18 multilayer film was selectively deposited on PVA nanofibers with poor conductivity. In addition, the photochromic behavior of P2Mo18 multilayer film on PVA/ITO was investigated through UV-vis spectra and electron spin resonance (ESR). Fourier-transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) proved that the charge-transfer complex was formed between PAH and P2Mo18 after UV irradiation.

Mesoscopic simulation of the impregnating process of unidirectional fibrous preform in resin transfer molding

The resin transfer molding has gained popularity in the preparation of fiber-reinforced polymer-matrix composites because of its high efficiency and low pollution. The non-uniform inter-tow and intra-tow flows are regarded as the reason of void formation in RTM. According to the process characteristics, the axisymmetric model was developed to study the interaction between the flow in the inter-tow space and that in the intra-tow space. The flow behavior inside the fiber tows was formulated using Brinkman's equation, while that in the open space around the fiber tows was formulated by Stokes' equation. The volume of fluid (VOF) method was applied to track the flow front, and the effects of filling velocity, resin viscosity, inter-tow dimension and intra-tow permeability on fluid pressure and flow front were analyzed. The results show that the flow front difference between the inter-tow and intra-tow becomes larger with the decrease of intra-tow permeability, as well as the increase of filling velocity and inter-tow dimension.

甲状腺素脱碘抗体酶制备半抗原和全抗原的合成与单克隆抗体的制备

甲状腺素脱碘酶是能够催化甲状腺激素不同降解反应的一簇含硒酶 [1,2 ] ,由于其含量低 ,分离纯化困难等[3] ,严重阻碍了其生物化学性质和应用研究 .自 Lerner[4 ] 和 Schultz等 [5] 分别制备出了具有催化作用的抗体酶以来 ,抗体酶在天然酶的模拟研究中已展示了巨大潜力 ,有些抗体酶已达到或超过了天然酶的活力 [6 ] .我们曾用抗体酶技术制得具有脱碘酶活性的抗体酶 [7] .为进一步提高脱碘抗体酶活力 ,本文以疏水腔修饰法 [8] 为指导 ,用铜离子络合保护法设计合成了 3种甲状腺素衍生物半抗原和全抗原 ,并制备出了一种半抗原的单克隆抗体 .试剂和仪器 :五水甲状腺素钠 ( T4 )为 SIGMA产品 ;牛血清白蛋白 ( BSA )和卵清白蛋白( Ovalbumin) ,SIGMA分装 ;戊二醛 ,硫酸二甲酯 ,溴化苄 ,对硝基溴苄和其它试剂均为国产分析纯 .Finni- gan mat LCQ电喷雾多极串联质谱仪 ;KONTRON公司 92 2型紫外可见分光光度仪 ;德国Elementar Anallysensysteme Gmb H Vario EL元素分析仪 ;美国 Varian...

低纬度西太平洋硅藻席沉积时空分布及群落组成研究

大洋硅藻席沉积是硅藻大规模“勃发”的产物，且其样品采集具有很大的偶然性，本文利用在低纬度西太平洋136°~140°E，15°~21°N区域内首次发现的硅藻席沉积岩芯为研究对象，确定了成席硅藻的种类，探讨了硅藻席的时空分布，并对WPD03和WPD12两个岩芯的硅藻进行分析鉴定，通过对深海沉积硅藻组合的变化探讨低纬度西太平洋硅藻席形成时期的环境变化状况，进一步分析了该区域硅藻席沉积的形成机制。 通过研究，得出如下主要结论：1）出现于这一低纬西太平洋的硅藻席的成席藻类为“树荫种”硅藻Ethmodiscus rex（Wallich）Hendey；2）硅藻席发现站位成带状分布，大致呈北西-南东向展布，且大部分散布在17° N～20° N之间水深在CCD以下4837-6150m较平坦海底的深水区；3）经AMS14C测年结果显示，富含硅藻席的沉积物发生于16.0 ~ 28.6 ka B.P. 14C年期间，即“勃发”发生于末次冰期最盛期；4）在WPD 03和WPD 12两个岩芯共155个样品中共鉴定硅藻40属101种（含变种），且Thalassionema frauenfeldii的相对百分含量最高，Thalassionema nitzschioides、Azpeitia nodulifera、Nitzschia marina、Hemidiscus cuneiformis等次之，这五种硅藻占整个硅藻物种相对百分含量的85%左右，说明在该海域表层水体硅藻席沉积过程中，这五种硅藻最容易与成席硅藻在同时期的环境中生存，形成勃发；5）MIS3期的晚期，该区域表层海水盐度降低，这有助于该区水体的成层化，从而使“树荫种”硅藻开始勃发，导致“秋季倾泻”；6）末次冰期由于南极中层水（AAIW）北扩，南大洋中层水将富含硅酸盐的海水带入了研究区，即南大洋的“硅溢漏”作用，使该区域硅藻得以勃发，同时，铁输入的增多，可能也是造成硅藻勃发的主要原因之一。