双层谐衍射元件的衍射效率分析

单层谐衍射元件由于只在谐振波长处能精确闪耀,随着波长偏离谐振波长,衍射效率迅速下降,导致宽波段成像质量变差。为了将谐衍射元件的应用拓展到宽波段,本文重点对可等效为普通单层衍射元件的双层谐衍射元件的衍射效率进行了详细的分析。理论分析得出此种双层谐衍射元件的衍射效率在整个设计波段明显高于单层（谐）衍射元件的衍射效率,而且在整个设计波段的分布基本平衡。进一步以红外波段的常用材料Ge和ZnSe构成的双层谐衍射元件以及由它们分别构成的单层（谐）衍射元件为例,应用Matlab对其衍射效率进行了模拟。模拟结果得出双层谐     

新型半导体功率器件在现代雷达中的应用研究(Ⅰ)

目前第一代半导体功率器件的制造技术和应用技术已趋于成熟,S波段及以下波段功率器件的输出功率、工作效率和可靠性指标都已达到相当高的水平。近年来第二代半导体功率器件的制造技术和应用技术发展迅速,S波段、C波段和X波段的器件已经形成了一定的系列化商品。但是面对现代雷达等新一代电子装备的需求,半导体功率器件在高功率、高效率和高频率等方面与真空管器件相比仍逊色许多,Si和GaAs功率器件的输出功率工作频率短期内不大可能有大的提高,而第三代半导体功率器件——宽禁带半导体器件固有的宽禁带、高击穿场强和良好的热稳定性等特性,决定了其可以输出更高功率、工作在更高频率、具有更高效率,并可更好地满足现代雷达的要求。     

高频大带宽滤波器

高频大带宽滤波器采用常规设计方法具有损耗大、带内波动和群时延特性差的缺点。文章介绍了采用倾斜色散换能器结构在Ｙ１２７．８６°ＬＮ基片上实现中心频率为７４０ＭＨｚ、带宽为４００ＭＨｚ的滤波器的设计方法和实验结果。     

宽频带光纤耦合器的近似模型和实验验证

本文用理论分析证明了将单模光纤耦合器的腰部熔锥区域简化成等效平行波导的近似模型必须作弱导近似和弱耦合近似,并在实践上用弱熔锥工艺制成了宽频带单模光纤耦合器,对该器件有关参量和尺寸的测量及计算,表明具有哑铃形腰部横截面结构的宽频带熔锥型耦合器的组合波导满足弱导近似和近似条件,用等效平行波导的近似模型计算耦合器转换功率随波长变化的曲线,不仅宽频带特性的理论曲线与实验符合得好,而且耦合器的耦合特性对二光纤芯径比及熔锥长度变化十分灵敏,这也是与实验相符。     

Nuclear quadrupole resonance studies of209Bi in Bi4(GeO4)3 and Bi4(SiO4)3

Nuclear quadrupole resonance (NQR) of²⁰⁹Bi has been studied in Bi₄ (GeO₄)₃ and Bi₄ (SiO₄)₃ using a wide band coherence-controlled superregenerative oscillator-detector. All the four allowed (ΔM _I=±1) transitions are observed. In both cases the electric field gradient (EFG) tensor is axially symmetric (η=0.0). The quadrupole coupling constante ² qQ is measured to be 490.8±1 MHz and 470.4±1 MHz respectively. It is pointed out that the purely ionic model is inadequate to understand these results. With the available experimental accuracy and the strength of the applied electric field (∼ 6 KV/cm), no field-induced effects on the NQR spectrum could be observed in the case of Bi₄ (SiO₄)₃.     

8GHz～12GHz推-推压控振荡器设计

文章介绍了利用推-推的方法实现宽带低相噪压控振荡器,论述了其基本原理和分析方法,并利用计算机辅助设计(CAD)对该方法进行了分析。根据分析结果制作了8GHz～12GHz压控振荡器。测试结果表明,分析结果较好地反映了实际结果。推-推的方法能有效提高晶体管的工作频率,同时还可以改善压控振荡器的负载牵引能力。这种方法适用不同形式的器件,对高频率、宽频带压控振荡器的制作有一定指导意义。     

Al ohmic contacts to HCI-treated Mg<Subscript>x</Subscript>Zn<Subscript>1−x</Subscript>O

The Al nonalloyed ohmic contacts were fabricated on Mg_xZn_1−xO (0≤x≤0.2) thin films. HCl surface treatment significantly reduced the specific contact resistances to value around 10⁻⁴ Ω cm². X-ray photoelectron spectroscopy (XPS) analysis revealed that the HCl treatment increased the oxygen vacancy density and introduced chlorine to the semiconductor surface, resulting in a thin conductive layer and thus reduced specific contact resistance. A subsequent oxygen plasma treatment reduced the oxygen vacancy density, and correspondingly increased the specific contact resistance. Al-ZnO contacts were insensitive to the HCl treatment, due to the formation of a highly conductive Al-doped thin interface layer.     

Properties of phosphorus-doped (Zn,Mg)O thin films and device structures

The properties of phosphorus-doped (Zn,Mg)O polycrystalline and epitaxial thin films are described. The as-deposited (Zn,Mg)O:P films are n type with high electron carrier density. High resistivity is induced in the films with moderate temperature annealing, which is consistent with suppression of the donor state and activation of the deep acceptor. The resistivity of the as-deposited and annealed film is an order of magnitude higher than similar samples with no Mg, consistent with a shift in the conduction band edge relative to the defect-related donor state. The capacitance-voltage characteristics of annealed metal/insulator/P-doped (Zn,Mg)O structures in which the (Zn,Mg)O is polycrystalline exhibit p-type polarity. In addition, multiple polycrystalline devices comprising n-type ZnO/P-doped (Zn,Mg)O thin-film junctions display asymmetric I–V characteristics that are consistent with the formation of a p-n junction at the interface, although the ideality factor is anomalously high.     

GaN静态性质的LMTO第一原理计算

本文用ＬＭＴＯ能带从头计算方法和局域密度泛函理论，计算了闪锌矿和纤锌矿两种不同结构ＧａＮ晶体的静态性质：平衡晶格常数ａ，体模量Ｂ，体模量的压强微商Ｂ＇和结合能Ｅｃｏｈ。在闪锌矿结构和纤锌矿结构的研究中，分别考察了不同ｄ态处理方案和空原子球大小设置方式对计算结果的影响，确定了比较合理的计算方案，获得与实验值比较接近的计算结果。     

Structural aspects of suspension poly(vinyl chloride): Influence of temperature on the macro- and microstructure

The structural aspects of rigid suspension poly(vinyl chloride), PVC, have been investigated on the basis of two independent series of suspension PVC samples, polymerized at temperatures between 26 and 84°C. The reproducibility of the suspension polymerization process and the importance of the polymerization temperature with respect to the macro- and microstructure is demonstrated. Quantitative examination of the grain structure by small angle neutron scattering, Brunauer-Emmett-Teller absorption technique, and mercury porosimetry clarifies the gradual increase of the specific surface on lowering the polymerization temperature. A detailed WAXS study shows an increasing degree of crystallinity on lowering the polymerization temperature, which can be associated with the corresponding increase of the syndiotacticity. Furthermore, the presence of a polymerization history in the PVC powders with respect to the crystallinity is evidenced. This effect seems to be related to chain mobility restrictions during the polymerization process and is determined by the difference between the polymerization temperature and the glass-transition temperature (T_g) of rigid PVC. This so-called T_g effect is indicative of the fact that no appreciable swelling of PVC by its monomer occurs. © 1994 John Wiley & Sons, Inc.