共查询到20条相似文献,搜索用时 187 毫秒
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一、引言一些物质在温度低于某一值(T_c)时,其电阻率突然转变为零.这种状态称作超导状态,这类物质称为超导体。T_c 称作超导体的转变温度.不同的超导材料,其转变温度也不同.因而,超导体的转变温度(T_c)是超导材料最基本、最重要的物理参数之一,其它物理量无不与此相关.精确测量超导体的 T_c值已成为超导电性研究中必备的手段.为了培养高水平的接触近代科学前沿的硕士和博士人才,我们连续三年对固体物理、实验物理和低能核物理等专业的研究生开设了超导转变温度(T_c)测量的实验.结果表明,同学们不仅能完成实验要求,掌握实验技 相似文献
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采用粉末烧结方法在不同温度(650℃,700℃,750℃,800℃,850℃,900℃)制备了MgB2超导块材.采用X射线衍射(XRD)和扫描电镜(SEM)研究了热处理温度对MgB2超导材料的成相及微结构的影响.采用磁化法测定不同温度制备MgB2超导材料的超导电性.结果显示热处理温度对MgB2超导材料的晶粒尺寸、形状和超导电性有明显影响,700℃制备的MgB2超导体具有最高的临界电流密度和最好的磁通钉扎特性,细小的晶粒尺寸是样品磁通钉扎特性改善的原因. 相似文献
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用SEM(扫描电子显微镜)研究YBaCuO超导体及YBaCuO/YSZ 超导薄膜经质子辐照所引起的微结构变化,发现质子辐照可使超导晶粒变细、变密、分布较均匀,并在YSZ 衬底上发生趋向排列.这些都有利于超导电性的改善. 相似文献
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超导电性既是物理学中一个光彩夺目的领域,也是电力工程和电子学中许多独特的新应用的源泉.工作于液氦或液氮温区的超导电子器件,固然有赖于“低温”的极端手段,却能在灵敏度、频带宽度、响应速率等方面达到极端的目标.文章以液氦温区超导体为主,简述了有关的电子器件的基本原理和应用类型,并展示了其发展前景,以纪念超导现象发现一百周年. 相似文献
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本文用扫描隧道电子显微镜和原子力显微镜观察了不同实验条件一利用激光沉积技术制备的YBqa2Cu3O7-x超导薄膜的微观结构,并分析了薄膜细胞与超导电性的关系。螺旋生长结构能减少薄膜中的弱连结和在薄膜中形成磁通钉扎中心,因此使超导薄膜的临界电流密度比同类超导体材大得多。 相似文献
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Transport measurements were made on a system consisting of a zinc nanowire array sandwiched between two bulk superconducting electrodes (Sn or In). It was found that the superconductivity of Zn nanowires of 40 nm diameter is suppressed either completely or partially by the superconducting electrodes. When the electrodes are driven into their normal state by a magnetic field, the nanowires switch back to their superconducting state. This phenomenon is significantly weakened when one of the two superconducting electrodes is replaced by a normal metal. The phenomenon is not seen in wires with diameters equal to or thicker than 70 nm. 相似文献
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We present heat capacity measurements on crystalline Zn nanowires with diameters of 230 and 23 nm, bracketing the superconducting coherence length of 155 nm. Transport measurements on superconducting nanowires have found a crossover from three-dimensional to one-dimensional behavior as the wire diameter was reduced below the coherence length. In contrast, the normalized heat capacity peak of the 23 nm Zn nanowires is found to be nearly identical to that of 230 nm wires and bulk Zn, indicating their thermodynamic properties remain three dimensional. 相似文献
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S. Bhunia T. Kawamura S. Fujikawa K. Tokushima Y. Watanabe 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):583
Metalorganic vapor phase epitaxial technique has been used to grow surface mounted vertical and uniform cross-sectional InP nanowires on a wafer scale basis. The growth was carried out under the vapor–liquid–solid mechanism using Au colloidal nanoparticles of nominal diameters of 10 and 20 nm, and their properties were compared. The effect of the pre-growth anneals and growth temperatures on the stability of the nanowires were studied in detail. Scanning electron microscopy and transmission electron microscopic studies showed average diameter of the nanowires in the range of 20–35 nm, and of length 700 nm with growth direction of 1 1 1. Room temperature photoluminescence measurements of the nanowires grown on 10 and 20 nm Au particles showed strong peaks, which were blue shifted by 25 and 32 meV, respectively, compared to bulk InP. 相似文献
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Using first principles density functional theory calculations, we investigated the X and X–N–X (X = Al and Ga) doped 3C–SiC
nanowires grown along the [111] crystal direction with diameter of 1.00 and 1.33 nm. We found that the ionization energy of
acceptor state is much larger in nanowires than that in the bulk SiC as a result of quantum confinement effect. Simulation
results show that the reduced dimensionality in p-type SiC nanowires strongly reduces the capability of the materials to generate free carriers. It is also found that X–N–X
(X = Al and Ga) complexes are energetically favored to form in the materials and have lower ionization energy than single
doping. It is confirm that codoping is more suitable method for achieving low-resistivity semiconductors either in nano materials
or bulk material. 相似文献
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With intense femtosecond laser excitation, multiphoton absorption-induced stimulated emission and laser emission in ZnO bulk crystal and nanowires have been demonstrated at room temperature. UV-stimulated emission peaks appeared in both bulk crystal and nanowires when the excitation exceeded certain thresholds, and a sharp lasing peak with a linewidth of ~0.5 nm was observed from ZnO nanowires. The emission properties were attributed to the band-edge emission of the recombination of carriers excited by two- and three-photon absorption processes in the wide-bandgap semiconductor. 相似文献
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Semiconducting nanowires in proximity to superconductors are promising experimental systems for Majorana fermions which may ultimately be used as building blocks for topological quantum computers. A serious challenge in the experimental realization of the Majorana fermion in these semiconductor-superconductor-nanowire structures is tuning the semiconductor chemical potential in close proximity to the metallic superconductor. We show that presently realizable structures in experiments with tunable chemical potential lead to Majorana resonances, which are interesting in their own right, but do not manifest non-Abelian statistics. To resolve this crucial barrier to the solid state realization of Majorana fermions, we propose a new topological superconducting array structure where introducing the superconducting proximity effect from adjacent nanowires generates Majorana fermions with non-Abelian statistics. 相似文献
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本文采用顶部籽晶熔融织构方法(TSMTG)制备出了具有不同纳米Gd2Ba4CuWOx(GdW2411)掺杂量的系列单畴GdBCO超导块材,并研究了GdW2411的掺杂量对其微观形貌以及磁悬浮力大小的影响.研究结果表明,通过添加GdW2411粒子,可以成功的在单畴GdBCO超导块材中引入纳米GdW2411磁通钉扎中心,其粒径约在50~200nm之间;随着GdW2411掺杂比例的增加,纳米粒子的密度逐渐变大,粒度也有所变大;GdBCO超导块材磁悬浮力的大小与GdW2411掺杂量密切相关,只有当GdW2411的掺杂比例达到最佳值时,样品的磁悬浮力才达到最大.这些结果对进一步提高GdBCO超导块材性能具有重要的指导意义. 相似文献
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Thermodynamic Parameters of Single‐ or Multi‐Band Superconductors Derived from Self‐Field Critical Currents 下载免费PDF全文
Key questions for any superconductor include: what is its maximum dissipation‐free electrical current (its ‘critical current') and can this be used to extract fundamental thermodynamic parameters? Present models focus on depinning of magnetic vortices and implicate materials engineering to maximise pinning performance. But recently we showed that the self‐field critical current for thin films is a universal property, independent of microstructure, controlled only by the penetration depth. Here, using an extended BCS‐like model, we calculate the penetration depth from the temperature dependence of the superconducting energy gap thus allowing us to fit self‐field critical current data. In this way we extract from the T ‐dependent gap a set of key thermodynamic parameters, the ground‐state penetration depth, energy gap and jump in electronic specific heat. Our fits to 79 available data sets, from zinc nanowires to compressed sulphur hydride with critical temperatures of 0.65 to 203 K, respectively, are excellent and the extracted parameters agree well with reported bulk values. Samples include thin films, wires or nanowires of single‐ or multi‐band s ‐wave and d ‐wave superconductors of either type I or type II. For multiband or multiphase samples we accurately recover individual band contributions and phase fractions. 相似文献
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Large-scale synthesis of ZnO nanowires using a low-temperature chemical route and their photoluminescence properties 总被引:3,自引:0,他引:3
B.Y. Geng T. Xie X.S. Peng Y. Lin X.Y. Yuan G.W. Meng L.D. Zhang 《Applied Physics A: Materials Science & Processing》2003,77(3-4):363-366
Single-crystalline zinc oxide (ZnO) nanowires were synthesized from zinc powder and H2O through a simple chemical route at 730 °C in Ar atmosphere. The potential exists for bulk synthesis of ZnO nanowires at temperatures significantly less than the 200–300 °C of thermal evaporation methods reported formerly. Scanning electron microscopy and transmission electron microscopy observations reveal that the ZnO nanowires are structurally uniform, have lengths up to several hundreds of micrometers and diameters of about 40–60 nm and crystallize in a hexagonal structure. The growth of ZnO nanowires is controlled by the vapor–solid crystal-growth mechanism. Photoluminescence measurements show that the ZnO nanowires have a strong near-band ultraviolet emission at 380 nm and a green light emission at 520 nm caused by oxygen vacancies. PACS 81.05.Ys; 78.55.Et 相似文献
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Semiconductor nanowires are unique as functional building blocks in nanoscale electrical and electromechanical devices. Here, we report on the mechanical properties of ZnO nanowires that range in diameter from 18 to 304 nm. We demonstrate that in contrast to recent reports, Young's modulus is essentially independent of diameter and close to the bulk value, whereas the ultimate strength increases for small diameter wires, and exhibits values up to 40 times that of bulk. The mechanical behavior of ZnO nanowires is well described by a mechanical model of bending and tensile stretching. 相似文献