采用快速升温烧结方法生长Tl-1223超导薄膜的研究

报道了在铝酸镧(00l)衬底上生长Tl-1223超导薄膜的快速升温烧结方法以及铊(Tl)源陪烧靶的配比对Tl-1223薄膜晶体结构的影响.扫描电子显微镜观测表明,采用快速升温烧结方法生长的Tl-1223超导薄膜具有致密的晶体结构.X-射线衍射等测试表明,采用合适配比的陪烧靶在氩气环境下可以制备出纯c轴取向的Tl-1223超导薄膜,充氧退火后的薄膜具有较好的电学性能,其临界转变温度T_(c onset)达到116K,临界电流密度达到1.5MA/cm~2(77 K,0 T).实验结果表明,采用这一新的烧结方法制备Tl系超导薄膜具有升降温时间和恒温时间短、生产成本低等特点.     

High-performance InGaN/GaN MQW LEDs with Al-doped ZnO transparent conductive layers grown by MOCVD using H_2O as an oxidizer

In this study,the high performance of InGaN/GaN multiple quantum well light-emitting diodes(LEDs) with Aldoped ZnO(AZO) transparent conductive layers(TCLs) has been demonstrated.The AZO-TCLs were fabricated on the n~+-InGaN contact layer by metal organic chemical vapor deposition(MOCVD) using H_2O as an oxidizer at temperatures as low as 400 ℃ without any post-deposition annealing.It shows a high transparency(98%),low resistivity(510 ~4 Ω·cm),and an epitaxial-like excellent interface on p-GaN with an n+-InGaN contact layer.A forward voltage of 2.82 V @ 20 mA was obtained.Most importantly,the power efficiencies can be markedly improved by 53.8%@20 mA current injection and 39.6%@350 mA current injection compared with conventional LEDs with indium tin oxide TCL(LED-Ⅲ),and by28.8%@20 mA current injection and 4.92%@350 mA current injection compared with LEDs with AZO-TCL prepared by MOCVD using O_2 as an oxidizer(LED-Ⅱ),respectively.The results indicate that the AZO-TCL grown by MOCVD using H_2O as an oxidizer is a promising TCL for a low-cost and high-efficiency GaN-based LED application.     

Influence of the Tl- and Hg-content on magnetic and transport properties of the Pb, Sr-doped Tl-1223 and Hg-1223 superconductors

The effects of the thallium and mercury content x on the as-sintered and post annealed samples of M_xPb_0.4Sr_1.6Ba_0.4Ca₂Cu₃O_8+δ {M: Tl (0.32≤x≤0.74) or Hg (0.18≤x≤0.68)} have been studied by magnetization and transport measurements. For Tl-1223 we have found the optimum Tl doping level to be x=0.53 regarding the grain properties, the content of superconducting phase, the first penetration field H_pl^wl, the transport (J_c^tr), magnetic intergrain (J_c^M) and intragrain (J_c^g) critical current densities. The critical temperature T_c of the as-sintered Tl-1223 sample decreased with increasing Tl content. Post-annealing in oxygen improved the T_c for Tl contents of x≥0.53 and had generally positive effects on the critical current densities. The intergrain properties of the Hg-1223 samples were much worse than those of the Tl-based superconductors.     

Performance at 10–50 K of Bi-2212/Ag multilayer tape fabricated by using pre-annealing and intermediate rolling process

High-transport critical current density (J_c-oxide)>500 kA/cm² at 4.2 K, 10 T can be obtained for Bi-2212/Ag tapes fabricated by using pre-annealing and intermediate rolling (PAIR) and melt-solidification process. In this paper, we report high-temperature properties of PAIR-processed Bi-2212/Ag multilayer tape in order to show their potential for practical applications operated at cryocooling temperatures. Magnetic field dependence and angular dependence of critical current (I_c) are investigated at temperatures ranging 10–50 K by using helium gas cooling and liquid neon. Field-temperature curves for I_c=0.2 and 2.0 A are also determined in order to show the approximation of the irreversible field. High-temperature performance of the tape is attractive to consider future applications. For example, the best sample carries I_c=267 A (engineering-J_c=303 A/mm², J_c-oxide=151 kA/cm²) and 92 A (104 A/mm², 52 kA/cm²) at 27.1 K (in liquid neon), in magnetic fields (parallel to the tape surface) of 2 and 10 T, respectively. Engineering-J_c of 100 A/mm² is obtained even in the perpendicular field of 0.5 T at 27.1 K.     

Processing of thallium-based superconducting tapes for high current density

Optimum thermomechanical processing conditions have been developed to achieve a high current density in powder-in-tube (PIT) thallium-based (Tl,Pb)-1223 and (Tl,Bi)-1223 tapes. Critical currents in excess of 25 A corresponding to a current density of 20 000 A/cm² have been achieved in these tapes at 77 K. Heat treatment and intermediate deformation sequences, heating rates, and starting precursor phase assemblages have been examined to optimize the current density. A combination of processing conditions that result in incremental densification, less microcracking and liquid formation in the early and final stages of thermomechanical treatment is found to result in the highest current densities.     

氧离子注入微晶金刚石薄膜的微结构与光电性能研究

本文系统研究了氧离子注入剂量和退火温度对含有Si-V发光中 心的微晶金刚石薄膜的微结构和光电性能的影响. 结果表明, 氧离子注入并在较高温度退火有利于提高薄膜中Si-V中心的发光强度. 当氧离子注入剂量从10¹⁴ cm^-2增加到10¹⁵ cm^-2时, 薄膜中Si-V发光强度增强. Hall效应测试结果表明退火后薄膜的面电阻率降低. 不同温度退火时, 氧离子注入薄膜的Si-V发光强度较强时, 薄膜的面电阻率增加, 说明Si-V发光中心不利于提高薄膜的导电性能. Raman光谱测试结果表明, 薄膜中缺陷数量的增多会增强Si-V的发光强度, 而降低薄膜的导电性能. 关键词： 金刚石薄膜 氧离子注入 电学性能 Si-V缺陷     

退火温度对溶胶-凝胶法制备锌锡氧化物薄膜晶体管的影响

采用溶胶-凝胶法制备了非晶锌锡氧化物(ZTO)薄膜晶体管(TFT),通过热重-差热分析(TG-DTA)对ZTO胶体中的化学反应进行了分析,研究了不同退火温度对ZTO TFTs性能的影响。结果表明:当退火温度在300~500℃范围内时,薄膜为非晶态结构,薄膜表面致密、平整。当退火温度达到400℃时,薄膜在可见光范围内具有高透过率(>85%)。随着退火温度的升高,器件阈值电压明显降低,由15.85 V降至3.76 V,载流子迁移率由0.004 cm²·V^-1·s^-1提高到5.16 cm²·V^-1·s^-1,开关电流比达到10⁵。退火温度的升高明显改善了ZTO TFT的电学性能。     

As+注入硅的紫外-可见椭圆偏振光谱

本文采用椭圆偏振光谱法研究了剂量为1×10¹⁶—3×10¹²cm^-2的As⁺注入硅,及其在700℃退火后的光学性质。得出:当As⁺注入剂量增大到某一程度后,便呈非晶特性。低于临界剂量的样品,其n-λ,ε₂-λ关系曲线随剂量的增大而往下方移动,呈有规律变化;退火后,在大于4000?波段,n-λ与ε₂-λ曲线基本恢复到单晶硅状态。但在小于4000?的紫外区却未完全恢复,注入剂量越大,偏离单晶硅就越大。并指出,紫外光区是离子注入硅的信息敏感区;用有效质量模型计算出注入剂量与损伤度的关系。计算结果与实验符合得较好。 关键词：     

退火温度对硼掺杂纳米金刚石薄膜微结构和p型导电性能的影响

采用热丝化学气相沉积法制备硼掺杂纳米金刚石 (BDND) 薄膜, 并对薄膜进行真空退火处理, 系统研究退火温度对BDND薄膜微结构和电学性能的影响. Hall效应测试结果表明掺B浓度为5000 ppm (NHB) 的样品的电阻率较掺B浓度为500 ppm (NLB) 的样品的低, 载流子浓度高, Hall迁移率下降. 1000 ℃退火后, NLB和NHB 样品的迁移率分别为53.3和39.3 cm²·V^-1·s^-1, 薄膜的迁移率较未退火样品提高, 电阻率降低. 高分辨透射电镜、紫外和可见光拉曼光谱测试结果表明, NLB样品的金刚石相含量较NHB样品高, 高的硼掺杂浓度使薄膜中的金刚石晶粒产生较大的晶格畸变. 经1000 ℃退火后, NLB和NHB薄膜中纳米金刚石相含量较未退火时增大, 说明薄膜中部分非晶碳转变为金刚石相, 为晶界上B扩散到纳米金刚石晶粒中提供了机会, 使得纳米金刚石晶粒中B浓度提高, 增强纳米金刚石晶粒的导电能力, 提高薄膜电学性能. 1000 ℃退火能够恢复纳米金刚石晶粒的晶格完整性, 减小由掺杂引起的内应力, 从而提高薄膜的电学性能. 可见光Raman光谱测试结果表明, 1000℃退火后, Raman谱图中反式聚乙炔 (TPA) 的1140 cm^-1峰消失, 此时薄膜电学性能较好, 说明TPA减少有利于提高薄膜的电学性能. 退火后金刚石相含量的增大、金刚石晶粒的完整性提高及TPA含量的大量减少有利于提高薄膜的电学性能. 关键词： 硼掺杂纳米金刚石薄膜 退火 微结构 电学性能     

过量B的Ta/CoFeB/MgO薄膜垂直各向异性和温度稳定性的增强

以CoFeB/MgO为核心单元的垂直各向异性薄膜体系和相关的垂直磁隧道结已获得广泛研究,其中CoFeB的B含量基本都保持为原子比20%.本文采用磁控溅射制备了Ta/(Co0.5Fe0.5)1-xBx/MgO三明治结构及生长顺序相反的系列薄膜,并在573—623K进行真空退火,研究了样品垂直各向异性随B成分的变化.结果显示,当B含量减小到10%时,Ta/CoFeB/MgO体系的垂直各向异性明显降低;相反,当B含量增加至30%时,该体系的垂直各向异性明显增强;发现在高B含量的情形下,样品的垂直各向异性大小与温度稳定性均与三明治结构的生长顺序密切相关;获得了具有优异温度稳定性的垂直磁化MgO/CoFeB/Ta样品.结果表明适当增加B含量是增强CoFeB/MgO体系垂直各向异性和温度稳定性的有效途径之一.     

Microwave resonant-cavity-produced air discharges

Air discharges produced in an Asmussen microwave cavity (0-300 W, 2.45 GHz, CW) between 0.5 and 100 torr were investigated. Gas temperatures (1000-2500 K) were estimated from rotational temperatures obtained from optical emission spectroscopy (OES). These agreed with a simple model of the heat transfer of the gas where joule heating was included as the source term. Vibrational temperatures (3700-7300 K) were also determined from OES and followed the electron energy trends. Electron density (10¹¹-10¹³ cm^-3), collisional frequency (10¹¹-10¹² s^-1), and plasma conductivity (0.09-0.3 (Ω-m)^-1) were calculated from a self-consistent electromagnetic model of the cavity where the plasma was assumed to be a lossy dielectric. Absorbed power, electric, and optical probe measurements were used as the input parameters to the model     

闪烁晶体的发光研究进展

概述了近年来闪烁体发光研究的进展,主要介绍用于未来高能物理实验的新型闪烁体发光机理研究,选取我们在研BaF₂,BaF₂:RE,CeF₃以及PbWO₄中的一些新进展。重点谈及三点:(1)在BaF₂的“价带^→芯带”跃迁发光研究基础上进行稀土(Gd³⁺-Eu³⁺)掺杂时观察到的量子剪裁以及对多光子发光的新思考;(2)CeF₃晶体发光的级联能量传递中,Ce³⁺(290nm发射带)与缺陷发光中心(340nm发射带)间能量传递及其传递效率的温度依赖;(3)PbWO₄晶体的发光中心研究中,提出以“WO₄^-2+O_i”绿光中心替代“WO³+F”中心观点的依据。同时也简介了医用闪烁体的最新进展。     

含硫宽禁带Ga2Te3基热电半导体的声电输运特性

目前对宽禁带半导体热电材料的研究开始升温, 原因是本征情况下宽禁带半导体往往具有低的热导率和高的Seebeck系数. Ga₂Te₃ 是一类带有缺陷的宽禁带半导体, 其在临界温度680± 10 K和757± 10 K处会参与共析转变和包晶反应, 因此会产生反应热. 本次工作采用少量的S元素等电子替换Ga₂Te₃中的Te元素, 观察到在临界温度附近热焓的变化, 但没有相变发生. 受热焓变化的影响这类材料在临界温度附近出现了较活跃的声电输运行为, 具体表现为热容和Seebeck系数(α)明显增大及热扩散系数(热导率)和电导率下降. 例, 对于x=0.05的材料, 其α值从596 K 时的376.3(μV·K^-1)迅速增大到695 K时的608.2(μV·K^-1), 然后又随温度升高到764 K时迅速降低到213.8(μV·K^-1). 在596 K到812 K范围, Seebeck系数和电导率几乎随温度均呈Z字形变化. 这些输运行为的变化揭示了在Ga₂Te₃基半导体中声子和载流子的临界散射特点, 这种临界散射特征对以后的继续研究具有重要的参考价值.     

Creating homogeneous depth profiles in YBaCuO films by ion beam implantation for uniform supression of Tc

Critical temperature depth profiles were calculated for single and multiple energy oxygen ion implantation of YBaCuO thin films. Using the code and the diffusion equation the changes of the profiles during an annealing between 150 and 300°C were obtained. The results are in reasonable agreement with the experimental data. Experimentally we investigated further implantation of O⁺, Ne⁺ and Al⁺ with a homogeneous implantation profile. The critical temperature is depressed by the created defects and in the case of Al also by substitution of Cu. For O⁺ and Ne⁺ implantation the depression of the critical temperature is diminished by an annealing process. Depending on the quality of the films, T_c reaches in some cases the values of the unimplanted samples. For Al⁺ the critical temperature changes less by the annealing process compared to the O⁺ or Ne⁺ implantations and does not reach the starting values. Some results of an annealing made by laser treatment are presented, too.     

单晶CeB_6发射性能及磁电阻各向异性研究

采用X射线劳厄定向法对单晶CeB_6的(110),(111),(210)和(310)晶面进行了定向.系统研究了不同晶面热发射性能及磁场对电阻率的影响规律.结果表明,当阴极温度为1873 K时(110),(111),(210)和(310)晶面最大发射电流密度分别为38.4,11.54,50.4和20.8 A/cm~2,表现出了发射性能的"各向异性".RichardsonDushman公式计算逸出功结果表明,上述晶面中(210)晶面具有最低的逸出功,为2.4 eV.从实际应用来看,该晶面有望替代商业化的钨灯丝成为新一代的场发射阴极材料.磁电阻率测量结果显示,当晶体从[001]方向旋转至[011]方向时电阻率从73μ?·cm变化至69μ?·cm,表明电阻率在磁场中沿不同方向同样具有"各向异性"的特点.     

Laser ablated bismuth cuprate thin films preparation and effect of oxygen nonstoichiometry upon superconductivity

Thin films of Bi₂Sr₂CaCu₂O₈ and (Bi, Pb)₂Sr₂Ca₂Cu₃O₁₀ have been prepared on monocrystalline (100) MgO substrates, using a laser ablation method with post annealing treatment. The influence of substrate temperature and oxygen pressure during deposition were investigated. SEM observations, EDS analysis, electric and magnetic measurements have been used to characterize the films. Superconducting “2212” films, with T_c(R = 0) at 80–83 K and J_c (50 K) up to 5 × 10⁵ A/cm², have been currently achieved, while Pb-doped “2223” films exhibit T_c as high as 110 K with J_c = 5 × 10⁴ A/cm² at 77 K. The effect of annealing at low temperature (350°C) in an argon flow has been studied for the 2212 phase, it shows the influence of the oxygen non-stoichiometry, i.e. of the hole carrier density upon T_c's which can be measured up to 89 K (zero resistance).     

Flux creep and flux flow for thallium ceramics in a pulsed magnetic field

The resistive properties of Tl-ceramics with T_c|=0=114 K were investigated in a pulsed magnetic field (B) up to 30 T and in the temperature range of 4.2 K<T<140 K. It was shown that the character of the field dependence of the resistance differs qualitatively in high-and low-temperature regions. At low (T80K) temperatures the dynamic magnetoresistance arising in the sample is analogous to that observed earlier in LaSrCuO [1] and YBaCuO [2] ceramics. This magnetoresistance is defined by the magnetic field variation rate and leads to the appearance of a minimum at the maximum of the magnetic field pulse, i.e. at . In the region of high temperatures (80 K T<T_c) or magnetic fields (at T60K) the sample resistance rises monotonically with B increase, and dynamic resistance is not observed. In this temperature range the existence of a scaling relation is shown (here B^* and T^* meet the condition k=(B^*, T^*)/ _n(T^*)=const) for the ceramics resistance (B,T), which can be represented as . An estimate for the upper critical field B_c2(0)B_o=1030±40 T is obtained.     

Crossover from thermally activated flux creep to quantum tunneling of vortices in a YBa2Cu3O7−x film

We present the results of a study of flux creep in a ring-shaped epitaxial superconducting YBa₂Cu₃O_7−x film at low temperatures. Measurements between 2 and 20 K have been made and it is confirmed that the flux creep is a thermally activated process at temperatures exceeding 10 K. The low-temperature data are analyzed by assuming a crossover to quantum tunneling of the vortex lines. Using the fact that the critical current in our sample is almost independent of temperature below 20 K, we establish the temperature dependence of the Euclidian action S directly from the experimental data without any a priori assumptions. Our results imply that at temperatures below 8.5 K S(T)=S(0)(1−T²/T_qc²), with approximately the same value of T_qc≈15 K for the case of the remnant magnetization as well as in an external magnetic field of 1 kOe.     

带有质量分析系统的强流质子束低能传输线研究

强流质子源与低能传输线（LEBT）是作为CIADS注入器的超导强流质子直线加速器的关键前端系统。目前LEBT采用双螺线管匹配结构设计,并安装有限制锥,但仍然不能避免少量H₂+和H₃+进入后端加速装置,这对直线加速器长期运行稳定性与可靠性会产生一定影响。为此,在LEBT加入分析磁铁对混合束（H+,H+2,H₃+）进行分离再注入后端加速器腔体,将是一个有效的方案。本研究对经过带有30度分析磁铁的LEBT的强流质子束的束流品质进行了模拟与实验测量。结果表明,分析磁铁高阶磁场的影响使经过分析磁铁的强流质子束束流品质变差,并且该影响随着束流包络的增大而增大。这些结果为CIADS注入器的低能传输线设计提供了参考依据。High current proton source and the low energy beam transport(LEBT) are the key front-end systems for CIADS injector:high current proton linac accelerator. CIADS injector's LEBT adopts double solenoid matching structure, using a limit cone which can partially avoid H₂+ and H₃+ which injecting into the back-end linac accelerator may impact the long-term stability and reliability of the whole system. It will be an effective method to separate the hybrid ions (H+, H₂+, H₃+) by adding a dipole magnet at LEBT. In this article, we simulated and mesasured the high current proton beam quality behind the LEBT with a 30 degree dipole. The results show that the the proton beam quality is significantly effected by high-order magnetic fields of the dipole magnet, and the effect increases with the increase of the beam envelope. The achieved result is useful for the LEBT design of CIADS injector.     

CsI(Tl)晶体的$lt;i$gt;α$lt;/i$gt;/γ 波形数字化实时甄别

基于CsI（Tl）探测器对α/γ 粒子的波形甄别能力,采用电荷比较法设计了一种波形实时甄别系统. 介绍了实时甄别系统的设计原理,利用⁶⁰Co-γ源、²⁴¹Am-α源对实时系统进行了甄别实验,探究了不同参数对甄别效果的影响,并给出了最优甄别效果下的参数设置. 研究表明,设计的数字化实时波形甄别系统体积小,能准确、实时地甄别开α/γ粒子,最佳品质因子大于1.4,事件计数率可达3× 10⁵/s. 关键词： 数字化波形甄别 实时 电荷比较法 CsI(Tl)晶体