用可变电阻调压与可变电阻的选择

如图电路1和电路2可变电阻尺的接法不同。RL为负载电阻，E为电源电动势（设内阻为0），S为开关。     

次谐波聚束系统固态放大器相位特性

 为研究BEPCⅡ直线加速器次谐波聚束系统使用的两台固态放大器（20 kW/142.8 MHz,10 kW/571.2 MHz）的相位特性,利用基于现场可编程门阵列(FPGA)的数字测量方法对两台固态放大器的脉内相移和相位稳定度进行了测量。测量系统硬件包括频率综合器、FPGA数字信号处理板和PC;软件部分包括FPGA内部算法、通信及PC端界面程序。该测量系统能真实地反映两台固态放大器的相位特性,为次谐波聚束器的相位补偿提供了参考。     

Thermal stress reduction of GaAs epitaxial growth on V-groove patterned Si substrates

We investigate the thermal stresses for GaAs layers grown on V-groove patterned Si substrates by the finite-element method. The results show that the thermal stress distribution near the interface in a patterned substrate is nonuniform,which is far different from that in a planar substrate. Comparing with the planar substrate, the thermal stress is significantly reduced for the Ga As layer on the patterned substrate. The effects of the width of the V-groove, the thickness, and the width of the SiO₂ mask on the thermal stress are studied. It is found that the SiO₂ mask and V-groove play a crucial role in the stress of the Ga As layer on Si substrate. The results indicate that when the width of V-groove is 50 nm, the width and the thickness of the SiO₂ mask are both 100 nm, the Ga As layer is subjected to the minimum stress. Furthermore,Comparing with the planar substrate, the average stress of the Ga As epitaxial layer in the growth window region of the patterned substrate is reduced by 90%. These findings are useful in the optimal designing of growing high-quality Ga As films on patterned Si substrates.     

基于配位键和次级作用力协同效应构建的两个Co (Ⅱ)/Cd (Ⅱ)配位超分子网络的结构及荧光性质

以3-羧基-1-（4-羧基苄基）吡啶溴酸盐（（H₂L） Br）分别与Co （Ⅱ）和Cd （Ⅱ）金属盐反应,制备了2个配合物[Co （L）₂（H₂O）₄]·2H₂O （1）和[Cd （L）2（H₂O）]·3H₂O （2）。晶体结构分析揭示配合物1是一个中性的单核配合物,其拥有丰富的并可作为超分子合成子的氢键和π-π作用力组分。对于1,单核的[Co （L）₂（H₂O）₄]实体首先通过氢键形成具有孔道结构的二维层,该二维层进一步通过π-π堆积作用形成三维的多孔配位超分子。配合物2具有一维的“之”字形链状结构,该链通过悬挂的L配体之间的π-π作用力形成一维梯形结构。该一维梯形链进一步通过梯形边之间存在的2种π-π堆积作用形成波浪状的二维层。二维层进一步通过8种类型的O—H…O氢键连接形成三维的超分子结构。根据拓扑的观点,配合物2中的一维链采取胶合板排列。此外,配合物2显示了强的紫外荧光发射,平均寿命为2.54 ns。     

横向外延过生长磷化铟材料的生长速率模型

分别考虑气相扩散和掩膜表面扩散过程，建立了金属有机化学气相沉积条件下横向外延过生长的速率模型. 在砷化镓衬底上外延磷化铟条件下，模拟得到了生长速率随掩膜/窗口宽度(m/w)变化的关系. 通过讨论掩膜/窗口宽度的影响，说明了掩膜宽度、窗口宽度以及有效掩膜宽度是决定生长速率的关键因素. 以上结论与实验结果一致. 关键词： 横向外延 生长模型 扩散 生长速率     

First-Principles Calculations of Electronic Structures of New Ⅲ-Ⅴ Semiconductors： BxGa1-xAs and TlxGa1-xAs alloys

We investigate the electronic structures of new semiconductor alloys BxGa1-xAs and TlxGa1-xAs, employing first-principles calculations within the density-functional theory and the generalized gradient approximation. The calculation results indicate that alloying a small TI content with GaAs will produce larger modifications of the band structures compared to B. A careful investigation of the internal lattice structure relaxation shows that significant bond-length relaxations takes place in both the alloys, and it turns out that difference between the band-gap bowing behaviours for B and TI stems from the different impact of atomic relaxation on the electronic structure. The relaxed structure yields electronic-structure results, which are in good agreement with the experimental data. Finally, a comparison of formation enthalpies indicates that the production Tlx Ga1-xAs with TI concentration of at least 8% is possible.     

GaAs纳米线及GaAs/In_xGa_(1-x)As/GaAs纳米线径向异质结构的无催化选区生长的实验研究

利用无催化选区金属有机化学气相沉积(SA-MOCVD)法在GaAs(111)B衬底上分别制备了GaAs纳米线和GaAs/InxGa1-xAs/GaAs纳米线径向异质结构.系统地研究了生长条件对GaAs纳米线生长的影响.实验结果显示,GaAs纳米线的形貌和长度依赖于生长温度、AsH3的分压以及SiO2掩膜表面的圆孔直径.因此可以通过调节以上因素来得到高质量的GaAs纳米线.并且发现扩散是影响无催化选区生长GaAs纳米线的主要机理.微区光致发光谱(μ-PL)表明,GaAs/InxGa1-xAs/GaAs纳米线径向异质结构被成功合成,室温(300 K)下它的发光波长为913 nm.这些结果对于GaAs纳米线及其异质结构制备的进一步研究及其在光电子器件中的应用具有很好的参考价值.     

A Fully Vectorial Effective Index Method for Accurate Dispersion Calculation of Photonic Crystal Fibres

A fully vectorial effective index method is developed for accurate dispersion calculation of photonic crystal fibres （PCFs）. In order to improve the accuracy of the model, different values for the effective core radius are used when PCFs have different fibre parameters. The accuracy of our approach is demonstrated by comparing our results with other numerical and experimental results reported in literature. It is found that the accuracy of the fully vectorial effective index method is improved and our results agree well with accurate numerical results obtained by other methods as well as the previously reported experimental data.     

高速高饱和单行载流子光探测器的设计与分析

设计了一种In P基的背入射台面结构的单行载流子光探测器.通过在吸收层中采取高斯型掺杂界面及引入合适厚度和掺杂浓度的崖层,使得光探测器同时具备了高速和高饱和电流特性.理论分析表明,在光敏面为14μm2、反向偏压为2 V条件下,该器件的3 d B带宽可达58 GHz,直流饱和电流高达158 m A.在大功率光注入条件下,详细分析了光探测器带宽降低和电流饱和现象,得出能带偏移和电场坍塌是其根本原因的结论.     

新型含2-噁唑啉基三角架配体-银(I)一维配位聚合物的合成与结构

通过含2-噁唑啉基三角架配体1,3,5-三(2-噁唑啉基)苯(L)与三氟醋酸银反应合成了配合物[Ag₄(L)₂(CH₃CN)₂(CF₃CO₂)₄]_n (1), 并利用元素分析、电喷雾质谱、X射线单晶衍射等方法对其进行了表征. 晶体结构解析结果显示配合物1属三斜晶系, 空间群P-1, a＝0.83731(6) nm, b＝1.22828(9) nm, c＝1.33997(10) nm, α＝102.9760(10)°, β＝107.3050(10)°, γ＝93.8600(10)°, Z＝1, R＝0.0365, wR₂＝0.0929. 该配合物是由[Ag₄(L)₂(CF₃CO₂)₂]^2＋笼状结构单元通过另外两个三氟醋酸根双桥连形成的一维链状结构. 相邻的链间通过C—H…O氢键进一步扩展为二维网状结构. 电喷雾质谱研究结果显示在实验条件下, 溶液中配合物1是以聚合状态存在的.