Nb5+掺杂对低氟MOD法制备的YBCO薄膜性能的影响

本研究通过低氟MOD法成功地制备了Nb⁵⁺掺杂的YBa₂Cu₃O_7-x(YBCO)薄膜, Nb⁵⁺在薄膜中生成了大小在20~30 nm之间的纳米颗粒; 纳米颗粒的生成不会对 YBCO薄膜的织构和临界温度(T_c)构成明显的影响。由于纳米颗粒的引入, 掺杂后薄膜的临界电流密度(J_c)在整个磁场范围内都要高于纯的YBCO, 自场下的Jc更是达到了3.4 MA/cm²。掺杂薄膜的钉扎力(F_p)也远远大于纯YBCO, 最大钉扎力达到了3.25 GN/m³, 有效地提高了YBCO在外加磁下的超导性能。     

正负错配纳米颗粒掺杂对YBCO薄膜性能影响的研究

利用低氟MOD工艺制备了Ba₂YTaO₆(BYTO)单一纳米颗粒掺杂及BYTO和LaAlO₃(LAO)双纳米颗粒共掺杂的YBCO复合薄膜。研究表明BYTO在YBCO薄膜中的最优掺杂量为6mol%, 此时薄膜的自场J_c为1.25 MA/cm ², 在1.2 T下获得的最大钉扎力为3.02 GN/m ³。共掺杂试验中引入与YBCO具有正错配度的BYTO粒子和负错配度的LAO粒子, 两者相互作用使有效掺杂总量提高至10mol%。调整两种纳米粒子的配比发现6mol% BYTO+4mol% LAO掺杂的YBCO复合薄膜样品在外加磁场为2 T时, J_c值高达0.27 MA/cm ², 获得最大钉扎力时的磁场由纯YBCO薄膜的0.42 T提高至共掺杂的1.6 T, 此时最大钉扎力为5.6 GN/m ³。正负错配纳米颗粒共掺杂有效地提高了YBCO复合薄膜在外加磁场下的超导性能。     

Ba源配比对MOCVD法制备YBCO薄膜性能的影响研究

采用单一液相混合源进液及闪蒸的MOCVD系统在LaAlO₃(001)单晶基片上制备YBa₂Cu₃O_7-x(YBCO)薄膜, 研究混合源中Ba含量对YBCO超导薄膜成分、结构及电流承载能力的影响。结果表明, 当Ba含量较小时, YBCO薄膜中易于形成尺寸较小的CuO颗粒; 随着Ba含量的增加, 薄膜中形成Ba₂CuO₃晶粒, 并且Ba₂CuO₃晶粒尺寸随Ba含量的增加而逐渐增大。杂质相的含量、尺寸以及与YBCO的晶格匹配程度对YBCO薄膜的双轴取向生长和电流承载能力具有重要影响。当原料摩尔配比Ba/Y=3.9时, 成功制备出了具有优异面内面外取向、结构致密的YBCO超导薄膜, 77 K下的300 nm厚度薄膜的临界电流密度达到4.0 MA/cm², 该研究结果对于第二代涂层导体的发展具有重要意义。     

铁磁(La0.7Ca0.3MnO3)/高温超导（YBa2Cu3O7）双层薄膜微结构的高分辨电镜研究

采用脉冲激光沉积法在LaAlO3(LAO)衬底上生长了YBa2Cu3O7/La0.7Ca0.3MnO3(YBCO/LC-MO)和La0.7Ca0.3MnO3/YBa2Cu3O7(LCMO/YBCO)两种外延薄膜,利用高分辨电子显微镜研究了其微观结构。在YBCO/LCMO/LAO薄膜中,LCMO以层-岛模式生长,并形成层状取向畴结构。YBCO层均由c轴取向晶粒组成,其中含有c/3平移畴界、额外CuO层及Y2O3第二相等缺陷结构。在LCMO/YBCO/LAO薄膜中,LAO衬底上初始生长的YBCO为c轴取向,至一定厚度(几个纳米)转为c与a轴混合生长。LCMO层在YBCO上外延生长并具有[100]m与[011]m混合取向畴结构。在LCMO/YBCO界面未观察到失配位错,因此二者界面属应变型界面。     

温度控制织构金属基带上YBCO外延薄膜生长及缺陷研究

采用直流溅射法在Y₂O₃/YSZ/CeO₂(YYC)缓冲层的织构NiW基带上, 通过基片温度调制YBa₂Cu₃O_7-δ(YBCO)外延薄膜生长。X射线衍射仪(XRD)表征显示, 基片温度强烈地影响YBCO薄膜的外延生长: 在较低的基片温度下薄膜趋于a轴取向生长, 随基片温度升高薄膜逐渐变为纯c轴取向生长。由于a轴晶粒引起的大角度晶界会阻碍超导电流在a-b面内的传输, 因此YBCO薄膜的微观结构和超导电性能随温度升高而得到改善, 但是随着基片温度继续升高, 基带的氧化程度加剧, YBCO与缓冲层间发生界面反应, 从而导致薄膜质量衰退。本     

TFA-MOD方法制备YBCO超导薄膜生长研究

TFA-MOD方法是制备YBCO涂层导体的最有应用前景的方法之一.本文采用TFA-MOD方法在LaAlO3单晶基片上生长YBCO薄膜并系统地研究了高温退火不同的停留时间对其影响.XRD分析表明退火时间较短时仍有明显的YBCO(00l)取向,但也有其它杂相峰存在,而延长退火时间可以使杂相峰消失而得到纯的且强度更高的YBCO(00l)取向.SEM分析表明未完全结晶的YBCO薄膜表面晶粒大小不一致,而且气孔较多.而结晶良好的YBCO薄膜表面平整致密,空洞较少.随着退火时间的增加YBCO颗粒尺寸在增大.但是,退火时间太长,会有大的空洞,甚至出现裂纹.超导电性能测试表明,随着退火时间的增加超导临界电流(Ic)在增加,但是退火时间达到60min后,Ic即达到最大值,表明60min就能使前驱膜在该实验条件下完全的结晶形成取向良好的YBCO薄膜,YBCO薄膜的生长速度达到0.16nm/s.     

YBa2Cu3O7-δ薄膜的BaCl2/BaF2-MOD法制备及超导特性研究

传统三氟乙酸金属有机化学溶液沉积法(TFA-MOD)制备YBa₂Cu₃O_7-δ (YBCO)超导层,Ba倾向于与F结合,从而避免BaCO₃的形成。本工作开展了新型基于BaCl₂/BaF₂途径的化学溶液法生长YBCO超导薄膜的研究。重点研究了添加Cl对YBCO薄膜晶粒取向、微观结构和超导性能的影响,并通过生长反应的热化学计算,分析了BaCl₂途径YBCO薄膜的物相转变机制。结果表明:添加Cl有利于抑制a轴晶粒取向,促进c轴晶粒成核。添加Cl的YBCO双层膜起始转变温度(Tc-onset)没有明显变化,约为89.6 K,其临界电流密度(Jc)显著提升, Jc达到2.07 MA/cm²(77K,自场)。此外,生长反应过程的物相转变分析表明Cl优先与Ba结合形成BaCl₂,有效避免BaCO₃的形成。本研究结果表明:添加Cl对制备YBCO超导厚膜有促进作用,这为MOD法制备YBC...     

氩离子刻蚀对TFA-MOD法YBa2Cu3O7-x薄膜性能的影响研究

TFA-MOD工艺制备的YBa₂Cu₃O_7-x(YBCO)薄膜有独特的生长机制, 高温晶化后的YBCO薄膜表面存在一层由Ba-Cu-O异质相及a轴生长的YBCO晶粒组成的杂质层。为了满足零电阻超导焊接和超导带材钎焊搭接的研究需要, 在不破坏超导特性和晶体结构的前提下, 采用Ar离子对TFA-MOD工艺制备的YBCO薄膜进行刻蚀, 对薄膜进行纳米级的减薄, 实现对薄膜表面杂质的去除。利用拉曼光谱、扫描电子显微镜和X射线衍射等方法对不同刻蚀时间下的薄膜状态进行表征。结果表明, 1.3 μm厚的YBCO薄膜表面杂质层厚度约为220 nm, 并且在过度刻蚀的情况下, YBCO薄膜仍然是c轴取向, 晶体结构没有被破坏。刻蚀后,薄膜内部氧空位缺陷的产生会造成超导转变及载流性能的降低, 但通过吸氧处理后薄膜性能可恢复。     

Ag基底织构和表面状况对YBCO薄膜性能的影响

采用MOD方法在三种不同织构和表面状态的Ag基底上制备了YBCO薄膜,研究了Ag基底的织构和表面状态对YBCO超导薄膜的影响.在真空中退火的Ag基底上沉积的YBCO薄膜仅有c轴取向,且薄膜表面有很多平行条纹,薄膜的连接性不好,J_c不高;在氩气气氛中退火的Ag基底上沉积的YBCO薄膜,具有很强的c轴取向和良好的面内织构,J_c相对较高为1.2×10⁴A/cm²;冷轧Ag基底沉积的YBCO薄膜织构没有氩气退火的Ag基底上的强,但薄膜的表面平整,连接性好,临界电流密度最高为1.5×10⁴A/cm².     

High resolution electron microscopy study of ferromagnet （La0.7 Ca0.3 MnO3 ）/superconductor （YBa2 Cu3 07 ） bi-layer

采用脉冲激光沉积法在LaAlO3（LAO）衬底上生长了YBa2Cu3O7/La0.7Ca0.3MnO3（YBCO/LC-MO）和La0.7Ca0.3MnO3/YBa2Cu3O7（LCMO/YBCO）两种外延薄膜,利用高分辨电子显微镜研究了其微观结构。在YBCO/LCMO/LAO薄膜中,LCMO以层-岛模式生长,并形成层状取向畴结构。YBCO层均由c轴取向晶粒组成,其中含有c/3平移畴界、额外CuO层及Y2O3第二相等缺陷结构。在LCMO/YBCO/LAO薄膜中,LAO衬底上初始生长的YBCO为c轴取向,至一定厚度（几个纳米）转为c与a轴混合生长。LCMO层在YBCO上外延生长并具有[100]m与[011]m混合取向畴结构。在LCMO/YBCO界面未观察到失配位错,因此二者界面属应变型界面。     

Influence of Interfacial LSMO Nanoparticles/Layer on the Vortex Pinning Properties of YBCO Thin Film

YBa₂Cu₃O_7?δ (YBCO) thin films have been deposited on bare and La_0.67Sr_0.33MnO₃ (LSMO) modified single crystal SrTiO₃ (STO) substrates. The effect of randomly distributed ferromagnetic LSMO nanoparticles and a complete LSMO layer, present at STO/YBCO interface, on the superconducting properties of YBCO thin films has been investigated by temperature dependent magnetization studies. The YBCO thin film on LSMO nanoparticles decorated STO substrate shows significant improvement in the critical current density and pinning force density as compared to the YBCO thin film deposited on bare STO substrate and this improvement is more significant at higher applied magnetic field. However, the LSMO/YBCO bilayer showed the improved flux pinning properties only up to a magnetic field of 1.5 T above which it deteriorates. In the case of LSMO/YBCO bilayer, the underlying LSMO layer gives rise to magnetic inhomogeneities due to domain structure, which leads to improved flux pinning properties limited to lower field. However, in the case of LSMO nanoparticles decorated substrate, the presence of LSMO nanoparticles at YBCO/STO interface seems to introduce magnetic inhomogeneities as well as structural defects, which might be acting as correlated pinning sites leading to improved flux pinning properties of the YBCO thin film over a wide range of applied magnetic field.     

Optimization of YBCO surfaces of tunnel junctions

It is established that in YBa₂Cu₃O₇ films prepared by annealing amorphous oxide deposits, Ba segregation in the amorphous phase and YBCO decomposition after recrystallization are the major causes of surface degradation. The authors have grown films by entirely in-situ processing in which these effects are minimized. The films were epitaxially grown on (100) SrTiO ₃ substrates with the a-axis normal to the film plane. Both structural and chemical analyses indicated that they are homogeneous and have proper stoichiometry up to their surfaces. At 4.2 K, contact resistivities below 4×10^-10 ohm-cm² were obtained with gold overlayers. Junctions have been formed by depositing thin Au proximity layers over the YBCO films followed by MgO barriers and Nb counterelectrodes. In some of the junctions weak-link shorts were observed, providing unambiguous evidence that the growth procedures used can produce films that are superconducting up to their surfaces     

High density recording with perpendicular Co-Cr-Nb media and ring heads

Effective double layer structure was investigated by adding Nb to the sputtering source of Co-Cr thin film perpendicular magnetic recording tapes. The output from the tapes was measured with a ring head through to the short wavelength, λ50=0.19 μm (D50=267KFRPI).     

Enhanced Flux Pinning Properties of BaZrO3-doped YBCO Films Grown by Pulsed Laser Deposition on LaAlO3(100) Substrates Decorated with Y2O3 Nanoislands

In this work, we intend to investigate the interaction between two types of nanoscaled artificial pinning centers and their pinning properties in YBCO thin films grown by pulsed laser deposition technique. The two types of artificial pinning centers were prepared in different processes, (1) Y₂O₃ nanoislands decorated on substrates prior to the deposition of YBCO thin film, and (2) BaZrO₃ nanoparticles self-assembled within YBCO matrix during the deposition of YBCO thin film. We compared the transport characteristics of the YBCO thin films containing these two types of artificial pinning centers with those of pure YBCO thin films grown on decorated substrates and BZO-doped YBCO thin films grown on undecorated substrates. It was found that these two types of artificial pinning centers, which are simultaneously present, acted constructively to enhance the pinning properties of YBCO thin films.     

Reactions in Au/Nb bilayer thin films

The interdiffusion and intermetallic compound formation of Au/Nb bilayer thin films annealed at 200–400 °C have been investigated. The bilayer thin films were prepared by electron beam deposition. The Nb film was 50 nm thick and the Au film was 50–200 nm thick. The interdiffusion of annealed specimens was examined by measuring the electrical resistance and depth-composition profile and by transmission electron microscopy. Interdiffusion between the thin films was detected at temperatures above 325 °C in a vacuum of 10^-4 Pa. The intermetallic compound Au₂Nb₃ and other unknown phases form during annealing at over 400 °C. The apparent diffusion constants, determined from the penetration depth for annealing at 350 °C, are 3.5 × 10⁻¹⁵ m² s⁻¹ for Nb in Au and 8.6 × 110^7minus;15 m² s⁻¹ for Au in Nb. The Au surface of the bilayer films becomes uneven after annealing at over 400 °C due to the reaction.     

Ferroelectric/superconductor heterostructures

This review covers the fabrication and characterization of ferroelectric/superconductor heterostructures such as Pb(Zr_xTi_1−x)O₃/YBa₂Cu₃O_7−δ (YBCO), BaTiO₃/YBCO and Ba_xSr_1−xTiO₃/YBCO etc. on various single crystal substrates. Pulsed laser deposition, laser molecular beam epitaxy, and magnetron-sputtering methods are compared. This report shows that pulsed laser deposition equipped with in situ reflection high-energy electron diffraction is a good method to control the growth mode of YBCO thin films. Furthermore, laser molecular beam epitaxy is a superb method for research of complex oxide films and their superlattices. Atomic force microscopy and transmission electron microscopy showed the ferroelectric films grown on the rough surface of the YBCO films produced high-density planar defects in the film and is detrimental to the ferroelectric/dielectric properties of the heterostructures. Therefore, for device usage, it is more advantageous to use SrRuO₃ than YBCO as the bottom electrode material. For growing atomically smooth surface films step-flow mode is highly recommended. Prospects of microwave device application of the ferroelectric/superconductor heterostructures are discussed, and proposed the BSTO films as the best candidate for passive microwave components.     

YBCO Thin Film Preparation on Unbuffered Ag Substrate by Resistive Evaporation

It is widely accepted that thin film formation of YBCO on conducting and flexible substrate is one of the keys for further development of advanced devices in the microelectronics. Various fabrication methods such as spray pyrolysis, powder-in-tube processing, dip-coating rolling-assisted biaxially textured substrate, etc., widely used for YBCO thick films (few tens of m) production. However in this work we report for the first time on the preparation of YBCO thin film on unbuffered silver substrate using a simple conventional vacuum system equipped with only one single resistively heated evaporation source. The subsequent heat treatment was carried out under a low oxygen partial pressure and temperature that never exceeded 740° C. A thin film of Ag was first deposited on MgO substrate. A pulverized stoichiometric mixture of Y, Cu, and BaF ₂ was then deposited on this film. The amorphous YBCO film of a 500-nm thickness was obtained after the heat treatment. The results of the film evaluation are presented and discussed.