AlNi纳米合金薄膜低温电阻率的特性研究

通过磁控溅射制备了AlNi纳米合金薄膜,并利用自制的直排四探针低温测量系统测量了薄膜电阻率随温度(8~300K)的变化规律。结果表明:由于电子-声子和电子-磁子相互作用,纯Al和Ni纳米晶薄膜的电阻率分别呈现出正的电阻率温度系数,且电子-磁子散射对电阻率的贡献主要体现在高温区(80~300K),在低温区(40K)电子-晶界/表面散射对电阻率的贡献占主导地位。Ni原子掺入量的增加,诱导了纳米晶薄膜无序程度的增强,从而使Al1-xNix纳米合金薄膜逐渐由晶体的金属特性过渡到半导体特性,导致其呈现出负的电阻率温度系数。由于增强的电子极化效应,Al1-xNix纳米合金薄膜电阻率与温度的关系并不完全遵循半导体的热激发导电模型。     

低温环境下霍尔探头标定

利用高精度低温霍尔探头可以测量永磁体在低温环境下的磁性能,如何对高精度霍尔探头在低温环境下进行精确标定对于永磁体低温磁性能研究有着重要意义。上海光源磁测实验室在霍尔探头常温标定的基础上,利用小型制冷机把霍尔探头置于液氮温区,通过在制冷机冷头上安装精确控制的电加热器可调节测试温度(6.5-300 K),并实现恒温。初步标定实验结果表明,低温霍尔探头灵敏度随着温度的下降逐渐上升,在50 K以下趋于平缓,相比常温灵敏度增大约4%。标定后的该探头可以测量低温环境下永磁体的磁性能,并可满足永磁体在低温环境下的性能研究需求。     

GaN基LED高能电子束流辐照效应研究

使用高能电子辐照对GaN基蓝光发光二极管(Light Emitting Diode,LED)光电学性能的影响进行研究。高能电子束流分别对不同组别的LED样品进行辐照实验,并通过自动测控系统对辐照过程中LED的电流、光强、光谱峰值波长进行全程测控。随后,在室温无辐照环境下对上述不同组别的LED样品进行跟踪对比测试研究。实验结果表明,高能辐照对LED的改性有明显效果,具体表现在工作电流和发光功率变化时受辐照影响的稳定性有所改善,光谱峰值波长出现蓝移。同时,GaN基LED在辐照过程中是否通电对LED的光电学性能有显著影响。     

基于功率MOSFET的高速高压脉冲产生器

通过研究功率MOSFET器件的开关特性和脉冲产生技术,设计了互补推挽和集成芯片两种MOSFET栅驱动脉冲电路,其较好的驱动能力,极大的提升了MOSFET的开关速度,分别实现了上升(下降)时间小于5 ns和2.5 ns、输出幅度300~500 V、脉冲宽度5 ns~0.2ms可调的高速、高压的脉冲产生与放大。据此研制成功的脉冲产生器具有稳定性好、带负载能力强、输出脉宽调节范围大、体积小等特点。该脉冲产生器已成功应用于像增强器高速摄影的电子快门装置,并在其他需要高速、高压脉冲领域有一定应用前景。     

GaN与Si器件作为辐伏电池换能单元性能比较

利用63Ni和3H源等分别辐照两种可作为辐伏电池换能单元的GaN基和Si基PiN结型器件,比较了他们的输出电性能结果,以及两种器件的温度、辐照性能等。结果表明,GaN器件开路电压Voc比Si基器件有非常明显的提高,而短路电流Isc有较大下降;GaN基结型器件在高温和高能辐照条件下的性能比Si基结型器件有较大优势。     

GaN核辐射探测器的性能研究

GaN作为第3代半导体材料,具有禁带宽度大、电子饱和漂移速度大、抗辐射能力强等特点。制备了GaN半导体探测器,并应用该探测器对²⁴¹Am α粒子能谱进行测量,得到α粒子能谱的能量分辨率约30%。同时,以Si半导体探测器为标准,对GaN探测器进行了能量及探测效率的测量,得到探测器的探测效率最高可达80.1%。最后,应用Keithley 2635静电计对GaN探测器的I-V曲线等进行测试,发现在-15 V偏压下,GaN探测器的本底电流密度小于70 nA/cm²。     

ICF用靶丸内燃料充填参数对温度的依赖

通过BWR(Bcncdict-Wcbb-Rubin)方程研究了内径分别为100、200、400、520μm的薄壁玻璃微球在500、400、300、77、35K的温度下,其内部的压力值和在工作温度(22K)下内部液层厚度之间的对应关系。结果发现,在低温下燃料的压力比常温下低很多。     

位移损伤效应对AlGaN/GaN HEMT器件的影响

对AlGaN/GaN高电子迁移率晶体管(HEMT)分别进行3 MeV质子辐照和14 MeV中子辐照实验。3 MeV质子辐照下累积注量达到1×10¹⁵ cm^-2或14 MeV中子辐照下累积注量达到2×10¹³ cm^-2时，AlGaN/GaN HEMTs饱和漏电流下降，阈值电压正向漂移，峰值跨导降低。分别对3 MeV质子辐照和14 MeV中子辐照后的AlGaN/GaN HEMTs进行深能级瞬态谱(DLTS)测试。3 MeV质子辐照后缺陷浓度下降降低了反向栅极漏电流，而14 MeV中子辐照会导致缺陷浓度增加，使得反向栅极漏电流增加。根据质子和中子辐照后的缺陷能级均为(0.850±0.020) eV,推断缺陷类型均为氮间隙缺陷，质子辐照和中子辐照后氮间隙缺陷的位移导致的位移损伤效应是AlGaN/GaN HEMT器件电学性能退化的主要原因。     

用离子束技术研究稀磁半导体和纳米磁性材料

综述用离子束技术研究稀磁半导体和纳米磁性材料的构建、调控和改性的进展和现状。离子束注入是优选的构建和调控方法,测试结果表明在GaN和ZnO等新半导体光电材料中注入Mn、Ni和Co等过渡金属离子可得到低温和室温下的铁磁性。离子束分析技术给出这些新材料薄膜的微结构信息,透射电镜下观察到过饱和剂量Mn+注入GaN形成的纳米磁性颗粒。     

应用于空间系统的Power MOSFET辐射响应特性

为给金属氧化物半导体场效应功率管（Power MOSFET）在航天系统中的应用提供辐照数据基础和依据。用60^Co源对将应用于空间系统的两种Power MOSFET进行了不同总剂量的辐照实验。从微观氧化物陷阱电荷和界面态的辐射感生角度，分析了Power MOSFET器件在60^Co γ，射线辐射下的总剂量和剂量率效应以及辐照后70℃退火特性。试验表明与N沟道Power MOSFET相比，P沟道Power MOSFET可能更适合空间应用。     

Design and test of elementary digital circuits based on monolithic SOI JFETs

Silicon on insulator (SOI) junction field effect transistor (JFETs) are used to develop digital gates for cryogenic applications. Only one type of JFET is necessary to design an NOR gate using a basic inverter circuit and a level shifter. The JFET's involved in these designs are available in a process radiation hard at room temperature and operate with improved characteristics at cryogenic temperatures (90 K, temperature of liquid argon calorimeters for high-energy physics). Test circuits have been designed to evaluate their performance. The measured characteristics prove to be satisfactory compared to the simulated ones, although some improvements are still necessary. A propagation delay of 4.4 ns per gate for a power dissipation of /spl ap/3 mW per gate is obtained. With the present development of cryogenic front end preamplifiers for the readout of calorimeter signals, this study opens some prospects for integrating more mixed digital analog electronics such as pipelines within the detectors.     

The Successful Operation of Hole-Type Gaseous Detectors at Cryogenic Temperatures

We have demonstrated that hole-type gaseous detectors, gas electron multipliers and capillary plates (CPs) can operate at temperatures down to 77 K. For example, a single CP can operate at gains above$10^3$in the entire temperature interval between 77 and 300 K. The same CP combined with CsI photocathodes operates perfectly well at gains of 100–1000, depending on the gas mixture. The obtained results open new fields of applications for CPs as detectors of ultraviolet light and charged particles at cryogenic temperatures: liquid noble gas time-projection chambers, detectors for weakly interacting massive particles or liquid Xe scintillating calorimeters, and cryogenic positron-emission tomography.     

金属氧化物半导体场效应晶体管中总剂量效应导致的阈值电压漂移研究现状

为了研发可用于核与辐射应急响应与准备的机器人,对比了多种具有不同结构和生产工艺的金属氧化物半导体场效应晶体管(MOSFET)由于总剂量效应(TID)导致的阈值电压漂移(ΔVth)。注意到了栅宽和栅长对器件耐辐射能力的影响在体CMOS器件和纳米线(NW) MOSFET器件之间、高的和低的工艺节点之间的不同,并从辐射诱导的窄通道效应(RINCE)和辐射诱导的短通道效应(RISCE)两方面解释了这种区别的原因。发现近年来前沿的一些研究在考虑辐射效应时,修正了负偏压不稳定性(NBTI)的影响。并讨论了几种新型器件包括锗沟道、氮化镓沟道管和具有特殊几何布局的晶体管。此外,介绍了计算机辅助设计技术(TCAD)在几种新型场效应管的机理研究和建模验证中的应用。     

Gas flow proportional counter for low temperature conversion electron Mössbauer spectroscopy

The construction of a simple gas flow proportional counter suitable for operation between 100 K and 400 K without the need for an evacuated cryogenic system is described. Different gas mixtures have been studied over the temperature range and it was found that He/5% CO is most suitable at 100 K. The system has been tested using standard foils to obtain the optimum operating conditions. Low concentration iron based samples have also been studied to show the importance of investigating surface phenomena at different temperatures.     

冷冻靶降温过程温度场分布及冰层生存时间研究

为在冷冻靶上成功实现惯性约束核聚变点火,需在打靶前将冷冻靶丸内冰层温度降低1.5 K。针对冷冻靶快速降温过程温度场发生突变导致冰层质量恶化的问题,数值研究了快速降温过程中冷冻靶温度场的瞬态特性,并提出了优化降温方案。数值模拟基于Boussinesq假设,通过UDF编程,获得了降温速率的影响规律,并分析比较了不同延迟时间下延迟降温的数值结果。结果表明：降温开始时,最大温差急剧增大但最终趋于稳定;减小降温速率,可有效改善靶丸表面温度的均匀性,延长冰层的生存时间,使降温结束时冰层质量满足要求;具有特定延迟时间的延迟降温能改善靶丸外表面温度的均匀性从而增加冰层的生存时间,且存在最佳延迟时间使冰层的生存时间最长。     

Performance of the optically-coupled current-mirror with its input stage cooled to cryogenic temperature

The Optically-Coupled Current-Mirror (OCCM) is a novel feedback circuit architecture that allows linear transmission of analog signals via optical fibers. Its most distinctive feature is that the input stage is galvanically isolated and passive, as it consists just on the back-to-back connection of a LED and a photodiode. Only those components are required to be in close contact with the detector, and no power supply is required to be brought to the input stage. All active components are located at a safe distance, therefore saving them from being exposed to radiation, as it is common in most experiments at particle accelerators. We have investigated the properties of the OCCM when its passive input stage is cooled to cryogenic temperatures. Results have been extremely interesting as, for instance, the sharp increase in open-loop gain observed when cooling to 77 K, due to an enhanced LED efficiency. This translates into a higher dynamic range and still better linearity, opening new opportunities for the transmission of current signals generated in cryogenic detectors.     

Process Modeling and Dynamic Simulation for EAST Helium Refrigerator

In this paper,the process modeling and dynamic simulation for the EAST helium refrigerator has been completed.The cryogenic process model is described and the main components are customized in detail.The process model is controlled by the PLC simulator,and the realtime communication between the process model and the controllers is achieved by a customized interface.Validation of the process model has been confirmed based on EAST experimental data during the cool down process of 300-80 K.Simulation results indicate that this process simulator is able to reproduce dynamic behaviors of the EAST helium refrigerator very well for the operation of long pulsed plasma discharge.The cryogenic process simulator based on control architecture is available for operation optimization and control design of EAST cryogenic systems to cope with the long pulsed heat loads in the future.     

Channel electron multiplier detector for conversion electron Mössbauer spectroscopy at temperatures between 4 and 300 K

A technique is presented for measuring conversion electron Mössbauer spectra at temperatures between 4 K and 300 K, using a cryogenic channel electron multiplier detector in combination with a continuous-flow helium cryostat. The described setup is characterized by a very high signal-to-noise ratio. In particular, for ¹¹⁹Sn, a resonant effect of up to 2000% was measured, likely the largest ever observed in Mössbauer spectroscopy. Other advantages are top-loading capability, easy sample access, high cooling rate, capability of simultaneous Mössbauer transmission measurements, and adaptability to on-line experiments. Some observations of the performance of channel electron multipliers at low temperatures are also described. The setup presented in this work can be used both for CEMS measurements as a function of temperature and as a highly efficient resonant detector for measurements with weak Mössbauer sources or for detecting weak resonant signals.     

温度梯度对冷冻靶微管充气过程的影响

采用基于燃料室和靶室独立控温的温度梯度法开展了冷冻靶微管可控充气技术研究。理论计算结合实验研究了不同尺寸靶球充气过程中温度梯度对燃料注入过程的影响。结果表明,充气结束时燃料室最终温度变化对燃料初始注入量的差值影响随靶球尺寸变化不明显,即通过温度梯度法实现燃料可控注入的途径对任何尺寸靶球均适用。随着靶球尺寸的增大,燃料在充气管处液化时所需温度梯度越小,燃料注入过程温度梯度控制范围越大,燃料注入量控制精度越高。对于内径2 mm的靶球、1.6 mL燃料室,当燃料室温度升至75 K时,燃料注入量控制精度达±3 μm/K。这些结果为冷冻靶燃料高精度加载技术研究提供了重要基础。     

Search for cold fusion at D/Pd > 1 using ion implantation

Deuterium was introduced into palladium at atomic ratios greater than one by means of ion implantation at cryogenic temperatures, and a search was made for energetic charged particles from D-D nuclear reactions. Concentrations as high as 1.6 D/Pd were produced by 10 keV implantation at temperatures of 41 and 81 K, and the occurrence of lattice supersaturation in the Pd deuteride was indicated by a new, low-temperature stage of D redistribution. Fifteen hours of observation at low temperatures yielded no indication of energetic charged particles due to the reaction D(d,p)T or other nuclear processes. This result implies an approximate upper bound of 10^–21 events/s per D atom on the reaction rate in the supersaturated deuteride. Negative results were also obtained for D-implanted zirconium and titanium.