上转换激光晶体研究进展

本文综述近年来晶体材料的上转换过程研究进展，介绍了上转换发光晶体材料研究中的一些新动向以及在室温环境下，掺杂稀土离子的晶体上转换激光运转的成功经验，列举了几种室温上转换激光器的泵浦条件、发射波长、以及转换效率等参数，说明晶体材料的上转换激光技术已趋于实用化。     

Modulating dopant segregation in floating-zone silicon growth in magnetic fields using rotation

The feasibility of modulating dopant segregation using rotation for floating-zone silicon growth in axisymmetric magnetic fields is investigated through computer simulation. In the model, heat and mass transfer, fluid flow, magnetic fields, melt/solid interfaces, and the free surface are solved globally by a robust finte-volume/Newton's method. Different rotation modes, single- and counter-rotations, are applied to the growth under both axial and cusp magnetic fields. Under the magnetic fields, it is observed that dopant mixing is poor in the quiescent core region of the molten zone, and the weak convection there is responsible for the segregation. Under an axial magnetic field, moderate counter-rotation or crystal rotation improves dopant uniformity. However, excess counter-rotation or feed rotation alone results in more complicated flow structures, and thus induces larger radial segregation. For the cusp fields, rotation can enhance more easily the dopant mixing in the core melt and thus improve dopant uniformity.     

Oriented polycrystalline α-HgI2 thick films grown by physical vapor deposition

This work investigates the growth of polycrystalline α-HgI₂ thick films from physical vapor deposition. By varying the growth conditions, the as-deposited thick films are characterized by scanning electron microscopy, X-ray diffraction, current–voltage and photoconductivity measurements. The growth mechanism and its effects to the properties of these polycrystalline α-HgI₂ thick films are then discussed. Finally, the best deposition conditions for polycrystalline α-HgI₂ thick films compactly formed by separated columnar monocrystallines with uniform orientation along c-direction and with good crystallinity are reported.     

Synthesis, thermal and magnetic properties of new metal iodate: (LiFe1/3)(IO3)2

This paper reports the detail synthesis of a new kind of metal iodate, anhydrous (LiFe_1/3)(IO₃)₂, from aqueous solutions. The synthesized compound shows spinal morphology and is chemical stable up to 400°C. The iodate shows paramagnetic behavior from room temperature down to 4.2 K. At room temperature, the new compound has a hexagonal structure with the lattice parameters a=5.4632(2) Å, c=5.0895(6) Å, Z=1, space group of P6₃.     

光纤光栅温度传感器稳定影响因素研究

提出一种可用于航天系统温度监测的光纤布拉格 光栅(FBG)温度传感器及其封装方式。通过对FBG温度传感器结构进行力学仿真,分析了FB G的预拉伸幅度、低熔点玻璃厚度对传 感器稳定性的影响;提出了优化传感器封装性能的方法,并通过实验进行了验证;对封装的 FBG传感器进 行四次稳定性实验,每次实验相隔二十天。实验结果表明:FBG传感器在各个温度点(－70℃,……, 30℃)波长的标准差小于0.57pm;FBG传感 器温度灵敏度为8.4pm/℃,温度测量标准差小于0.067℃; 在液氮环境中,FBG传感器波长的标准差为0.43pm,具有良好的低温 稳定性。     

Electrical and Thermal Conductivity and Conduction Mechanism of Ge<Subscript>2</Subscript>Sb<Subscript>2</Subscript>Te<Subscript>5</Subscript> Alloy

Ge₂Sb₂Te₅ alloy has drawn much attention due to its application in phase-change random-access memory and potential as a thermoelectric material. Electrical and thermal conductivity are important material properties in both applications. The aim of this work is to investigate the temperature dependence of the electrical and thermal conductivity of Ge₂Sb₂Te₅ alloy and discuss the thermal conduction mechanism. The electrical resistivity and thermal conductivity of Ge₂Sb₂Te₅ alloy were measured from room temperature to 823 K by four-terminal and hot-strip method, respectively. With increasing temperature, the electrical resistivity increased while the thermal conductivity first decreased up to about 600 K then increased. The electronic component of the thermal conductivity was calculated from the Wiedemann–Franz law using the resistivity results. At room temperature, Ge₂Sb₂Te₅ alloy has large electronic thermal conductivity and low lattice thermal conductivity. Bipolar diffusion contributes more to the thermal conductivity with increasing temperature. The special crystallographic structure of Ge₂Sb₂Te₅ alloy accounts for the thermal conduction mechanism.     

Controlled Growth of MoS2 Nanosheets on 2D N‐Doped Graphdiyne Nanolayers for Highly Associated Effects on Water Reduction

The first utilization of nitrogen‐doped graphdiyne (NGDY) as an efficient catalytic promoter for hydrogen evolution reaction (HER) is reported. X‐ray powder diffraction and X‐ray photoelectron spectroscopy studies indicate the presence of strong interactions between NGDY and MoS₂, which should effectively facilitate the charge transport behavior and improvement of the HER kinetics. The creative hybridization of MoS₂ and NGDY endows such heterostructure with structural and compositional advantages for boosting the catalytic activity (low overpotential of 186 mV at 10 mA cm^?2 and Tafel slope of 63 mV dec^?1) and extraordinary stability (higher than all reported MoS₂‐based materials and even better than that of commercial Pt and almost all benchmarked electrocatalysts). All of the results not only demonstrate that NGDY can be used as an effective catalytic promoter for hydrogen production, but also provide new strategy for fabricating efficient water‐splitting electrodes.     

Design and implementation of a 94 GHz CMOS down-conversion mixer with integrated miniature planar baluns for image radar sensors

A 94 GHz down-conversion mixer for image radar sensors using standard 90 nm CMOS technology is reported. The down-conversion mixer comprises a double-balanced Gilbert cell with peaking inductors between RF transconductance stage and LO switching transistors for conversion gain (CG) enhancement and noise figure suppression, a miniature planar balun for converting the single RF input signals to differential signals, another miniature planar balun for converting the single LO input signals to differential signals, and an IF amplifier. The mixer consumes 22.5 mW and achieves excellent RF-port input reflection coefficient of ?10 to ?35.9 dB for frequencies of 87.6–104.4 GHz, and LO-port input reflection coefficient of ?10 to ?31.9 dB for frequencies of 88.2–110 GHz. In addition, the mixer achieves CG of 4.9–7.9 dB for frequencies of 81.8–105.8 GHz (the corresponding 3-dB CG bandwidth is 24 GHz) and LO–RF isolation of 37.7–47.5 dB for frequencies of 80–110 GHz, one of the best CG and LO–RF isolation results ever reported for a down-conversion mixer with operation frequency around 94 GHz. Furthermore, the mixer achieves an excellent input third-order intercept point of ?3 dBm at 94 GHz. These results demonstrate the proposed down-conversion mixer architecture is promising for 94 GHz image radar sensors.     

A 90–96 GHz CMOS down-conversion mixer with high conversion gain and excellent LO–RF isolation

A 90–96 GHz down-conversion mixer for 94 GHz image radar sensors using standard 90 nm CMOS technology is reported. RF negative resistance compensation technique, i.e. NMOS LC-oscillator-based RF transconductance (GM) stage load, is used to increase the output impedance and suppress the feedback capacitance C_gd of RF GM stage. Hence, conversion gain (CG), noise figure (NF) and LO–RF isolation of the mixer can be enhanced. The mixer consumes 15 mW and achieves excellent RF-port input reflection coefficient of ?10 to ?36.4 dB for frequencies of 85–105 GHz. The corresponding -10 dB input matching bandwidth is 20 GHz. In addition, for frequencies of 90–96 GHz, the mixer achieves CG of 6.3–9 dB (the corresponding 3-dB CG bandwidth is greater than 6 GHz) and LO–RF isolation of 40–45.1 dB, one of the best CG and LO–RF isolation results ever reported for a down-conversion mixer with operation frequency around 94 GHz. Furthermore, the mixer achieves an excellent input third-order intercept point of 1 dBm at 94 GHz. These results demonstrate the proposed down-conversion mixer architecture is very promising for 94 GHz image radar sensors.     

梁式封装二极管的微组装技术

该文介绍了梁式封装二极管(BED)的微组装技术(MPT)的现状及其问题,重点对超声热压倒装焊与粘胶互联进行了实验与仿真,分析了不同电极与基板镀层等因素对装配方案的影响,并通过受力实验进行验证。提出了有效规范的装配方案和可靠、易行的工程结论,解决了梁式封装二极管装配方案混乱,批量一致性差,调试难度大,成本高等问题。