空间用GaN功率器件单粒子烧毁效应激光定量模拟技术研究

利用飞秒脉冲激光对氮化镓(GaN)功率器件进行单粒子烧毁效应定量评估技术研究,针对器件结构建立脉冲激光有效能量传输模型,理论计算了激光有效能量与重离子线性能量传输(LET)的等效关系并开展了试验验证.考虑器件材料反射率与吸收系数对激光的影响,针对介质层界面间的激光多次反射进行参数修正,减小有源区有效能量计算误差.选择一款氮化镓高电子迁移率晶体管(GaN HEMT)与一款肖特基势垒二极管(SBD)功率器件作为典型案例,分别开展飞秒脉冲激光正面与背部辐照试验,计算诱发单粒子烧毁的有效能量,并得到不同入射激光波长的烧毁等效LET阈值,对比了模型理论计算值与实际测量值.同时,研究结果对材料参数未知的GaN功率器件,提供了正面与背部辐照模型的激光试验波长选择参考.该工作将为激光定量评估空间用GaN等宽禁带半导体器件的单粒子烧毁效应机理研究及加固设计与验证提供技术支撑.     

Hexagonal boron phosphide and boron arsenide van der Waals heterostructure as high-efficiency solar cell

The rapid development of two-dimensional (2D) materials offers new opportunities for 2D ultra-thin excitonic solar cells (XSCs). The construction of van der Waals heterostructure (vdWH) is a recognised and effective method of integrating the properties of single-layer 2D materials, creating particularly superior performance. Here, the prospects of h-BP/h-BAs vdW heterostructures in 2D excitonic solar cells are assessed. We systematically investigate the electronic properties and optical properties of heterogeneous structures by using the density functional theory (DFT) and first-principles calculations. The results indicate that the heterogeneous structure has good optoelectronic properties, such as a suitable direct bandgap and excellent optical absorption properties. The calculation of the phonon spectrum also confirms the well-defined kinetic stability of the heterstructure. We design the heterogeneous structure as a model for solar cells, and calculate its solar cell power conversion efficiency which reaches up to 16.51% and is higher than the highest efficiency reported in organic solar cells (11.7%). Our work illustrates the potential of h-BP/h-BAs heterostructure as a candidate for high-efficiency 2D excitonic solar cells.     

Quantum oscillations in a hexagonal boron nitride-supported single crystalline InSb nanosheet

A gated Hall-bar device is made from an epitaxially grown, free-standing InSb nanosheet on a hexagonal boron nitride (hBN) dielectric/graphite gate structure and the electron transport properties in the InSb nanosheet are studied by gate-transfer characteristic and magnetotransport measurements at low temperatures. The measurements show that the carriers in the InSb nanosheet are of electrons and the carrier density in the nanosheet can be highly efficiently tuned by the graphite gate. The mobility of the electrons in the InSb nanosheet is extracted from low-field magneotransport measurements and a value of the mobility exceeding $\sim 1.8\times10^4$ cm$^{2}\cdot$V$^{-1}\cdot$s$^{-1}$ is found. High-field magentotransport measurements show well-defined Shubnikov-de Haas (SdH) oscillations in the longitudinal resistance of the InSb nanosheet. Temperature-dependent measurements of the SdH oscillations are carried out and key transport parameters, including the electron effective mass $m^{\ast }\sim 0.028 m_{0}$ and the quantum lifetime $\tau \sim 0.046 $ ps, in the InSb nanosheet are extracted. It is for the first time that such experimental measurements have been reported for a free-standing InSb nanosheet and the results obtained indicate that InSb nanosheet/hBN/graphite gate structures can be used to develop advanced quantum devices for novel physics studies and for quantum technology applications.     

Effective sideband cooling in an ytterbium optical lattice clock

Sideband cooling is a key technique for improving the performance of optical atomic clocks by preparing cold atoms and single ions into the ground vibrational state. In this work, we demonstrate detailed experimental research on pulsed Raman sideband cooling in a $^{171}$Yb optical lattice clock. A sequence comprised of interleaved 578 nm cooling pulses resonant on the 1st-order red sideband and 1388 nm repumping pulses is carried out to transfer atoms into the motional ground state. We successfully decrease the axial temperature of atoms in the lattice from 6.5 μK to less than 0.8 μK in the trap depth of 24 μK, corresponding to an average axial motional quantum number $\langle n_z\rangle<0.03$. Rabi oscillation spectroscopy is measured to evaluate the effect of sideband cooling on inhomogeneous excitation. The maximum excitation fraction is increased from 0.8 to 0.86, indicating an enhancement in the quantum coherence of the ensemble. Our work will contribute to improving the instability and uncertainty of Yb lattice clocks.     

Gd替代对La0.6-xGdxSr1.4MnO4磁性和输运性质的影响

随着x的增加，多晶La0.6-xGdxSr1.4MnO4（x=0, 0.1, 0.2, 0.4, 0.6）的零场冷却 曲线从类自旋玻璃型转变成顺磁型，并且每条零场冷却 曲线都有一在20K的拐点。这一行为可以从Gd和Mn各自对材料总磁性的不同贡献来理解。另外，在所有的样品中，从100K到室温，都观察到了热激活导电行为。由于Mn-Mn间强的反铁磁耦和，直到外场达到50 kOe，都没有观察到明显的磁电阻效应。     

光谱法研究2-(4-二甲氨基苯基)-5-氟-6-吗啉-1-氢-苯并咪唑与小牛胸腺DNA的相互作用

研究了2-(4-二甲氨基苯基)-5-氟-6-吗啉-1-氢-苯并咪唑(1)在不同pH条件下的紫外-可见吸收光谱,采用非线性最小二乘法得出分子1的三级加质子常数lgβ₁, lgβ₂, lgβ₃分别为4.96±0.03, 5.72±0.07和7.95±0.10。当pH 3.40时,分子1主要以一价离子状态存在,紫外-可见吸收光谱及荧光光谱表明该条件下分子与小牛胸腺DNA存在明显的相互作用,并得出分子1与DNA的结合常数K_b为(2.30±0.10)×104 mol-1·L。当分子浓度为10-8～1.2×10-6 mol·L-1时,荧光强度随DNA含量的增加而线性增强,分子1是一种潜在的测定DNA的定量试剂。     

一种高压光学样品池系统的设计与实验研究

设计和研制了一种用于溶液样品光学特性原位检测的高压光学样品池成套系统,组件包括手动泵、增压器和高压样品池。其中样品池开有3处光学窗口,以水为传压介质,设计的最高使用压力为600MPa。当用JGS1石英作窗口时,密封和保压效果良好;由于受到石英材质强度的限制,使用压力应控制在300MPa以下。为检验该系统在高压原位检测方面应用的可行性,进行了色氨酸高压荧光光谱的采集。     

N掺杂对α-石墨炔表面吸附H_2O,H,O和OH的电子性质和磁性的影响

石墨炔是一种新型的二维(2D)碳的同素异形体,炔键单元的高活性使其在小分子吸附方面相比石墨烯更具优势.本文基于密度泛函理论(DFT),研究了H_2O和H、O及OH分别在原始的和掺杂了N原子的α-石墨炔上的相互作用.研究结果表明,N掺杂和小分子吸附能够改变α-石墨炔的电子结构和磁性. N原子掺杂后α-石墨炔对小分子的吸附能力明显增强. H、O原子和OH吸附在N原子掺杂体系前后表现出明显的磁性差异:H原子和OH吸附在纯净的α-石墨炔上体系显示磁性,N原子掺杂后,磁性消失;而O原子则是吸附在纯净的α-石墨炔上未表现出磁性,N原子掺杂后,体系出现磁性.此外,α-石墨炔对水分子的吸附作用较弱,受范德瓦耳斯作用影响较大,属于物理吸附.本研究将为α-石墨炔中N杂质检测以及α-石墨炔基气体传感器的设计研究提供新的思路.     

Low-loss terahertz waveguide with InAs-graphene-SiC structure

We demonstrate a low-loss terahertz waveguide based on the InAs-graphene-SiC structure. By analyzing the terahertz waveguide proposed in this paper, we can obtain that it is the characteristic of a low transmission loss coefficient(αloss≈0.55 dB/m) for fundamental mode(LP01) when the incident frequency is larger than 3.0 THz. The critical radii of the inside and outside cylinders have been found for the high-quality transmission. The large inside radius and the high transmission frequency result in a flat transmission loss coefficient curve. As a strictly two-dimensional material, the double graphene surface rings perform better to improve the quality of transmission mode. These results provide a new idea for the research of the long-distance THz waveguide.     

High performance oscillator with 2-mW output power at 300 GHz

Material structures and device structures of a 100-GHz InP based transferred-electron device are designed in this paper. In order to successfully fabricate the Gunn devices operating at 100 GHz, the InP substrate was entirely removed by mechanical thinning and wet etching. The Gunn device was connected to a tripler link and a high RF(radio frequency)output with power of 2 mW working at 300 GHz was obtained, which is high enough for applications in current military electronic systems.