Y-Ba-Cu-O/Nb Josephson tunnel junctions

The authors fabricated Y-Ba-Cu-O/Au/AlO_x/Nb and Y-Ba-Cu-O/AlO_x/Nb Josephson tunnel junctions using electron-beam evaporation of Al and Nb films and natural oxidation. Sintered Y-Ba-Cu-O was used as the base electrode. Superconducting Josephson current and hysteresis of the current-voltage characteristics, which are typical features of Josephson tunnel junctions, have been observed at 4.2 K. RF-induced voltage steps at a voltage greater than 0.4 mV have been clearly observed, and RF-induced subharmonic steps have also appeared. The superconducting Josephson current was modulated by the magnetic field     

FABRICATION OF HIGH-Tc SUPERCONDUCTORS

An overview is presented of techniques for fabricating high-T_c superconductors based on Y-Ba-Cu-O, Bi-Sr-Ba-Cu-0 and TI-Ca-Ba-Cu-O. Processing of both thin films and bulk forms such as wires and tapes is discussed. Thin films with high current densities can now be made reproducibly. In addition, several techniques for etching precise patterns into the films have been developed. Bulk forms have yet to be produced with current densities comparable to those in thin films. Improvement in superconducting current density remains the principal focus of much research on bulk forms of high-T_c superconductors.     

Evaporated YBa2Cu3O7 thin films and device technology

Epitaxial thin films of YBa₂Cu₃O₇ were grown by evaporation of the metals from electron-guns in the presence of atomic oxygen. The films were characterized structurally by X-ray diffraction and electrically by measurements of d.c. magnetization and flux creep. The progress in device technology is discussed. Results are presented on Josephson junctions, and a superconducting microwave filter with the ground plane grown on the back.     

Multifunctional modification of Fe3O4 nanoparticles for diagnosis and treatment of diseases: A review

With the rapid improvements in nanomaterials and imaging technology,great progresses have been made in diagnosis and treatment of diseases during the pastdecades.Fe₃O₄ magnetic nanoparticles(MNPs)with good biocompatibility and super-paramagnetic property are usually used as contrast agent for diagnosis of diseases inmagnetic resonance imaging(MRI).Currently,the combination of multiple imagingtechnologies has been considered as new tendency in diagnosis and treatment ofdiseases,which could enhance the accuracy and reliability of disease diagnosis andprovide new strategies for disease treatment.Therefore,novel contrast agents used formultifunctional imaging are urgently needed.Fe₃O₄ MNPs are believed to be a potentialcandidate for construction of multifunctional platform in diagnosis and treatment ofdiseases.In recent years,there are a plethora of studies concerning the construction ofmultifunctional platform presented based on Fe₃O₄ MNPs.In this review,we introducefabrication methods and modification strategies of Fe₃O₄ MNPs,expecting greatimprovements for diagnosis and treatment of diseases in the future.     

Speed-limiting factors in flash-type Josephson A/D converters

The authors discuss the causes of speed limitations in various A/D (analog/digital) converter designs. The upper limit on bandwidth is extracted with the help of Josephson SPICE simulations. In the Josephson A/D converter circuits discussed, the dynamic properties of the SQUIDs (superconducting quantum interference devices) determine the aperture time and dictate the bandwidth. Designs for 4-bit A/D converters that show potential for bandwidths on the order of 10 GHz are described. Particular attention is given to the bit-parallel A/D converter with self-gating AND comparator and bit-parallel A/D converters with CLAM (current latching analog microcomparator) and variable-pulse peak comparators     

1988 Applied Superconductivity Conference

The following topics are dealt with: superconducting electronics; superconducting quantum interference devices (SQUIDs); magnetometers; Josephson device memories; thin-film superconducting materials; tunnel junctions; Josephson device logic circuits; high-T_c (critical temperature) superconductors; YBaCuO superconductors: ceramic superconductor memories; millimeter-wave detectors; Josephson device mixers; superconducting transmission-line structure; superconducting microwave cavities; tunnel spectroscopy; laser-induced switching of superconductors; gradiometers; harmonic mixing; SIS (superconductor-insulator-superconductor) mixers; superconducting bolometers; superconductor device fabrication; SSC; (Superconductor Super Collider); magnets; superconducting magnets; chaos in Josephson junction systems; superconducting coils; superconducting material preparation; MHD; (magnetohydrodynamics) magnets; magnetic resonance imaging (MRI) magnets; and niobium materials devices     

10 V SINIS Josephson junction series arrays for programmablevoltage standards

A programmable dc voltage standard for output voltages of up to 10 V has been realized. The series arrays, consisting of about 69120 overdamped superconductor/insulator/normal metal/insulator/superconductor (SINIS) Josephson junctions, have been fabricated using the reliable Nb-Al/Al₂O₃ technology. The arrays can be operated in conventional Josephson voltage standards at microwave frequencies from 70 GHz to 75 GHz. Steps of constant voltage are observed at very low microwave power levels, since the major part of the microwave power is generated by the junctions themselves. The operation of the arrays and the formation of Shapiro steps are discussed     

DC Josephson current in S/F/S jucntions

The d. c. Josephson current in unconventional-superconductor / ferromagnet / unconventional-superconductor junctions is calculated for various cases to reveal the influence of the exchange interaction on the Josephson effect. When the two superconductors have d-wave symmetry, the Josephson current is drastically suppressed with the increase of the exchange interaction. On the other hand, when the two superconductors have different parities, e.g. s-wave and p-wave, an enhancement of the Josephson current is obtained with the increment of the exchange interaction in Ferromagnet. The direction of the Josephson current is reversed by the flip of the magnetization axis.     

Effective microwave surface impedance of superconducting films inthe mixed state

The effective microwave surface impedance of multilayer structures made of high-T_c superconducting films in the mixed state, lossy dielectrics, and normal metals are theoretically calculated. The linear response of the superconductor to a microwave field is analyzed within both transmission line theory and the framework of a self-consistent treatment of vortex dynamics reported by Coffey and Clem (1991). The microwave properties are investigated as a function of static field and film thickness for nonresonant structures. The effect of substrate thickness on the resonant phenomenon is carefully studied as well. Numerical results reveal that the substrate resonance in the Meissner state behaves like a parallel lumped-parameter resonator, while in the vortex state it behaves as a series lumped resonant circuit. The basic distinction suggests that care should be taken in microwave applications when using superconducting films in the vortex state     

A new 10-V array of Josephson junctions based on low-frequencydesigns scaled up to 94 GHz

A novel approach is described for the design of improved coupling of millimeter-waves in a 10-V array of Josephson junctions. In this approach, microwave structures were fabricated and tested in the range 2.8 GHz to 3.6 GHz, and a scaling calculation was then used to transform them to 94 GHz. By optimizing the trade-off between antenna size and efficiency, it was possible to make more space available on the device chip to increase the number of Josephson junctions. Simulation results showed that the optimal antenna is a short double-fin-line type. This antenna type allowed us to fabricate a Josephson junction array that had 25944 Nb/Al-AlO_x/Nb junctions. For this new array, zero-crossing steps were observed up to 18.5 V. The new array was then successfully used to calibrate a Zener voltage standard that had a 10-V output     

基于铁粉还原的LiFePO4/C合成路径及其电化学性能研究

使用还原铁粉作为铁源, 通过超细球磨与喷雾干燥、高温煅烧技术制备了球形微纳米LiFePO₄/C复合材料。使用DSC/TG以及XRD对LiFePO₄/C复合材料的形成过程进行了分析; 使用SEM、穆斯堡谱仪等手段对复合材料进行分析; 使用电化学工作站、容量测试仪对其充放电行为进行分析。研究发现, 使用该合成技术路线, 在500~700℃下能够合成LiFePO₄/C复合材料。获得的LiFePO₄/C复合材料具有规则的球形外貌, 平均尺寸4~5 μm。该微米颗粒由200 nm左右细小颗粒组成, 颗粒间具有纳米尺寸微孔。穆斯堡谱仪测试结果表明, 复合材料中Fe处于+2价的价态。复合材料在1C倍率下表现出稳定的充放电行为, 平均比容量在156 mAh/g, 300次循环后, 容量保持率为92.8%。该技术制备的LiFePO₄/C复合材料具有潜在的应用价值。     

碳纤维增强镁基复合材料制备技术与新进展

碳纤维增强镁基(Cf/Mg)复合材料以其高比强度、高比刚度、接近于零的热膨胀系数及良好尺寸稳定性等独特优势,在航空、航天、车辆等领域具有广阔的应用前景.本文综述了可用于制备Cf/Mg复合材料的粉末冶金、扩散黏结、挤压铸造等方法的工艺原理和特点、国内外发展现状及面临的关键技术问题.在此基础上,梳理了近年来Cf/Mg复合材...     

Direct comparison of two independent Josephson voltage standards at1 V and precision measurements up to 10 V

Two Josephson voltage standards have been compared using a room-temperature electronic nanovoltmeter with a peak-to-peak noise of about 2 nV at the 1-V level corresponding to a RMS uncertainty of 4×10^-10. The excellent stability in maintaining the desired voltage steps makes it possible to obtain recorder traces comparing Nb/Al₂O₃/Nb Josephson standards with Weston cells and Zener reference standards at 1 V and 10 V. At 10 V the best result shows a peak-to-peak noise of 250 nV corresponding to a RMS uncertainty of 5×10^-9 for a Zener reference and 50 nV corresponding to 1×10^-9 for a series connection of nine Weston cells. As an example for the application of the Josephson standard as a potentiometer the deviation in the linearity of a digital voltmeter is confirmed to be on the order of 0.1 p.p.m. in the range from -10 V to +10 V     

平纹编织SiCf/SiC复合材料的中温蠕变断裂时间及损伤机制

碳化硅纤维增强碳化硅复合材料(SiC_f/SiC)是制造下一代航空发动机热结构件的关键材料,中等温度(～800℃)下,SiC_f/SiC的蠕变断裂时间t_u显著下降。为此,研究了平纹编织SiC_f/SiC (2D-SiC_f/SiC)在空气中500～1 000℃的蠕变性能及损伤机制,应力水平为100～160 MPa。利用SEM、TEM和EDS分析了断口形貌、微观组织和化学成分。结果表明：2D-SiC_f/SiC的t_u与温度和应力水平有关。相同温度下,2D-SiC_f/SiC的t_u随着应力增加而变短。当温度为800℃、蠕变应力大于基体开裂应力(PLS)时,2D-SiC_f/SiC发生中温脆化现象,其t_u下降。2D-SiC_f/SiC的中温脆化机制为基体开裂、BN界面氧化和SiO₂替代BN界面导致的强界面/基体结合。2D-Si...     

TiO2/C复合材料用于钠离子电池负极的性能研究

近年来,TiO₂作为钠离子电池(NIB)负极材料,因其低成本和高稳定性等优势受到广泛关注。但受TiO₂本征电子导电性的固有限制,使得TiO₂作为NIB负极材料导电性较差,导致其容量和倍率等性能不理想。利用海藻酸钠与金属离子自主交联反应的特性,将反应产物在最佳温度下进行简单碳化,制备了具有分级多孔结构的TiO₂/C复合材料,其中TiO₂纳米颗粒均匀地分布在多孔互连的碳基体中,该结构提升了复合材料导电性的同时扩展了钠离子反应的附着位点。将TiO₂/C复合材料用于NIB负极材料,在100 mA·g^-1的电流密度下循环300圈后,电池可逆比容量维持在180.4 mAh·g^-1;进一步,在更高的1000 mA·g^-1电流密度下经过1000次循环后,电池可逆比容量维持在102.3 mAh·g^-1,充分显示出TiO₂/C复合材料作为NIB负极材料的应用潜能。     

SiO2/聚苯乙烯疏水复合微球的一步法合成和性能

提出了以苯乙烯、二乙烯基苯和γ-甲基丙烯酰氧基丙基三甲氧基硅烷(KH570)为单体,通过伴随着溶胶-凝胶反应的悬浮聚合法一步制备表面构筑有SiO₂粗糙结构的交联聚苯乙烯微球(SiO₂/聚苯乙烯疏水复合微球)。研究了油相组成、KH570用量和溶胶-凝胶反应条件对SiO₂/聚苯乙烯疏水复合微球强度和疏水性能的影响。结果表明,当弃除油相中的溶剂甲苯,在50℃的恒温反应阶段采用氨水调控体系pH值为10~11时可以获得兼具持久疏水性能、高强度和超低密度的SiO₂/聚苯乙烯疏水复合微球。SiO₂/聚苯乙烯疏水复合微球的表观密度约0.9917 g?cm?3,69 MPa的闭合压力下破碎率低至2.53%,表面静态水接触角高达140.7°,耐热性能优异(玻璃化转变和分解温度分别高达160℃和390℃)。尤其是,在涠州X油田A5井的螯合酸HD和FA中持续回流30天的过程中,SiO₂/聚苯乙烯疏水复合微球表面的接触角变化仍分别保持在±10%和±7%以内。SiO₂/聚苯乙烯疏水复合微球具备作为深部储层开采用支撑剂的极大潜力,也可用作封隔体控水工艺中的充填材料。      

Josephson address control unit IC for a 4-bit microcomputerprototype

The authors describe the design and operation of a Josephson address control unit IC (integrated circuit), which will be used for controlling the instruction sequence of an experimental 4-bit Josephson microcomputer prototype system. The IC is composed of three sets of 7- to 10-bit-wide registers and combinational logic circuits driven by a two-phase monopolar power supply. 593 four-function logic gates have been used in the circuit and fabricated using 2.5-μm NbN/oxide/NbN junction technology with Mo resistors and SiO₂ insulation. The operation of the circuit has been successfully tested for all the instructions which control the program sequence of the computer system     

(K0.44,Na0.52,Li0.04) (Nb0.84,Ta0.10,Sb0.06)O3 Ferroelectric Ceramics

Recent progress in (K_0.44,Na_0.52,Li_0.043-based ceramics (KNN) with special emphasis on (K_0.44,Na_0.52,Li_0.040.84,Ta_0.10,Sb_0.06))O₃ (KNN-LT-LS) is reviewed concisely. The base KNN and its compositional derivatives are analyzed in terms of dopant-property relationships, which are then extended to the ternary derivatives. The effects of processing conditions such as humidity, precursor purity, and oxygen partial pressure during sintering are elaborated on from a phenomenological perspective. It is also shown that the spontaneous polarization is sensitive to the processing route chosen for synthesis (mixed oxide versus perovskite routes). Special attention is devoted to the discussion of the morphotropic phase boundary (MPB) dilemma in the KNN-LT-LS system, where it is shown that the origin of high piezoelectric activity is actually due to a polymorphic transition at room temperature. It is shown that prototype transducers based on pure and 1 mol% Ba²⁺ doped KNN-LT-LS exhibit performance metrics comparable to those fabricated using PZT-5H. Overall, KNNLT- LS ceramics show great promise for lead-free applications, although issues such as temperature dependence of properties and strong sensitivity to processing conditions remain as the 2 major challenges.     

SnO2/NiO复合半导体纳米纤维的制备及气敏性能研究

采用静电纺丝技术结合化学沉淀法和高温煅烧处理,制备了具有不同Sn含量的SnO2/NiO复合半导体纳米纤维.采用扫描电子显微镜(SEM),X射线衍射仪(XRD)和能量色散X射线光谱仪(EDS)对样品的形貌,结构以及各元素含量进行表征.以乙醇为目标气体,探究SnO2/NiO纳米纤维的气体传感性质,以及Sn含量对复合纳米纤维...     

Annular Long Josephson Junctions in a Magnetic Field: Engineering and Probing the Fluxon Interaction Potential

The interaction of a Josephson fluxon with an externalmagnetic field-induced potential in a long Josephson junctionis investigated experimentally. The thermal activation of thefluxon from a potential well is observed and experimentsprobing its predicted quantum properties are discussed. Amethod for engineering a magnetic double-well potential for afluxon is proposed and the use of the coupled fluxon statesfor quantum computation is suggested.