Nb/A1-AlO_X/Nb隧道结的制备研究

通过改进RIE的刻蚀工艺和绝缘层的生长工艺,在SiO2/Si衬底上制备出了性能良好的超导Nb/A1-AlOX/Nb隧道结。采用CF4作为刻蚀气体,降低了RIE对结势垒层和衬底SiO2层的刻蚀。使用PECVD生长绝缘层SiO2,改善了绝缘性能,从而降低了隧道结的漏电流。     

Nb/Al-AlO_x/Nb超导隧道结的制备

在高阻硅衬底上采用光刻、直流磁控溅射、反应离子刻蚀(RIE)、等离子体增强化学气相沉积法(PECVD)等方法研究制备了高质量的Nb/Al-Al Ox/Nb超导隧道结。在4.2K下,测量了直径8μm的圆形结样品,得到临界电流密度约为1.6k A/cm2,漏电流约为50μA。制结工艺流程的重复性较好。     

Nb/Al-AlO_x/Nb隧道结的制备

本文报道了在射频磁控溅射装置上Nb/Al-AlO_x/Nb隧道结的制备工艺和所获得的结果。对SIS三层结构形成时基片的温度、势垒,以及电极形成方法等问题进行了讨论。     

Nb/Al-AlOx/Nb隧道结的制备

本文报道了在射频磁控溅射装置上Nb/Al-AlO_x/Nb隧道结的制备工艺和所获得的结果。对SIS三层结构形成时基片的温度、势垒,以及电极形成方法等问题进行了讨论。 关键词：     

脉冲激光沉积制备YBa2Cu3O7-δ/Nb-doped SrTiO3双层结

超导体/半导体结(Superconductor/semiconductor p-n junction)在制备场效应管,晶体管方面具有巨大的潜力.本文通过脉冲激光沉积的方法,使用Nb掺杂的(100)方向SrTiO3作为薄膜衬底,沉积了厚度约为350nm c轴取向的YBa2Cu3O7-δ薄膜,从而得到YBa2Cu3O7-δ/Nb:SrTiO3双层结.R～T曲线,以及XRD曲线显示YBa2Cu3O7-δ薄膜具有良好的超导电性和晶体结构,在零磁场不同温度下测量得电流-电压曲线显示YBa2Cu3O7-δ/Nb:SrTiO3构成的超导体/半导体双层结在小于YBa2Cu3O7-δ临界转变温度Tc时具有p-n结整流特性,当大于YBa2Cu3O7-δ超导转变温度时,呈现出非典型肖特基结的特性.     

Al/AlO_x/Al超导隧道结的制备工艺研究

研究了在高阻硅衬底上Al/AlO x/Al隧道结的制备技术,采用电子束蒸发制备Al/AlO x/Al三层材料,湿法刻蚀制备底电极和上电极以及电路连线,PECVD法生长绝缘层(SiO2)保护超导隧道结,RIE刻蚀上电极窗口。在400mK温度下测量了Al/AlO x/Al隧道结样品,得到了较好的隧道结I-V曲线,能隙电压Vg为0.325mV,超导临界电流I c为55nA,漏电流为5nA。     

用于电压基准的Nb/NbxSi1-x/Nb约瑟夫森单结的研制

现代可编程约瑟夫森电压基准的核心器件是约瑟夫森结阵.目前最具有优势的约瑟夫森结阵是 Nb/Nb_xSi_1-x/Nb材料的结阵. Nb/Nb_xSi_1-x/Nb材料的约瑟夫森结 具有三层薄膜的制作过程简便, Nb和Nb_xSi_1-x刻蚀工艺相同以及Nb_xSi_1-x 势垒层成分可调等优点.中国计量科学研究院设计制作了Nb/Nb_xSi_1-x/Nb约瑟夫森单结. 通过在4.2 K低温下对所做单结进行直流电流-电压特性测量,观测到了清晰的超导隧穿电流和 从零电压态向电压态的跳变,最后就测量结果进行了分析讨论.此项工作属于国内首个开展 Nb/Nb_xSi_1-x/Nb材料约瑟夫森单结研究的工作.     

激光熔覆原位合成Nb(C,N)陶瓷颗粒增强铁基金属涂层

采用预涂粉末激光熔覆技术,在42CrMo基体上制备出原位合成Nb(C, N)颗粒增强的铁基复合涂层。X射线及扫描电镜分析结果表明:激光熔覆获得的涂层基体为耐氧化、耐蚀性良好的Fe-Cr细晶组织及少量的-Fe相,原位合成的Nb（C, N）呈块状弥散分布在基体上。进一步的磨损试验表明:这些颗粒增强相极大增强了抗磨损性能,与未熔覆的母材相比,其磨损失重仅为母材的1/9左右; 涂层在750 ℃恒温氧化条件下具有较好的抗氧化性能,氧化层主要由NbO1.1,Cr2O3相组成; 母材的氧化产物为Fe2O3,容易脱落,保护性能较差; 激光熔覆涂层的氧化膜厚度仅为未涂层的1/5。     

Nb/AlOx-Al/Nb超导隧道结制备氧化工艺与特性研究

提出一种氧的等离子氧化的方法改善结区边缘绝缘性能,降低超导隧道结的漏电流。对Al膜进行等离子氧化能够有效的改善氧化膜的绝缘性能,AES分析表明:氧化绝缘层均匀,界面清晰;应用此方法成功制备出较好性能的Nb隧道结。     

用电子束蒸发制作Nb超导薄膜和Nb隧道结

本文报道了在10~(-5)—10~(-6)托的高真空下用电子束蒸发制作高质量的Nb超导薄膜的实验结果,Nb膜的临界温度T_c可以达到9.2K,接近大块纯Nb的T_c值(～9.3K)。研究了薄膜厚度、蒸发速率、衬底温度和真空度等淀积条件对Nb膜T_c的影响。用X射线衍射、电子显微和表面分析等方法分析了Nb膜的成分和结构。 用热氧化、直流辉光放电氧化和射频氧化等方法制成了Nb-NbO_x-Pb隧道结,通过表面分析研究了氧化位垒层的成分。对Nb隧道结的稳定性作了初步考察,40个串联结经过61次室温-4.2K之间的热循环和在室温下保存200天以上,结的I-V特性没有显著变化。     

铌合金电子结构及其高温氧化行为

为了从电子层面揭示Nb合金高温氧化的物理本质,采用递归法计算了Nb合金的电子态密度、原子镶嵌能、亲和能等电子结构参数,探索Nb合金高温氧化机理.研究表明:氧在Nb中具备较高的扩散速率和溶解度,且氧与Nb较易发生反应,生成氧化物,这使Nb的抗高温氧化性较差.原子镶嵌能的计算结果表明,合金元素Ti,Si,Cr在基体中稳定性较低,易向Nb合金表面扩散,形成富Ti,Si,Cr的表层.合金表层中氧与Nb,Ti,Si,Cr间具有较大亲和性,可以生成相应的氧化物,形成对合金具有保护作用的氧化膜. 关键词： 递归法 高温氧化 Nb合金     

Nb/Al-AlOx/Nb junctions with controllable critical current density for qubit application

Nb/Al-AlOx/Nb tunnel junctions with controllable critical current density Jc are fabricated using the standard selective Nb etching process.Tunnel barriers are formed in different oxygen exposure conditions (oxygen pressure P and oxidation time t),giving rise to Jc ranging from 100 A/cm2 to above 2000 A/cm2.Jc shows a familiar linear dependence on P × t in logarithmic scales.We calculate the energy levels of the phaseand flux-type qubits using the achievable junction parameters and show that the fabricated Nb/Al-AlOx/Nb tunnel junctions can be used conveniently for quantum computation applications in the future.     

常压CVD法合成铌掺杂少层MoS2

利用粉体NbCl₅作为Nb掺杂源,采用常压CVD方法合成了大尺寸Nb掺杂的少层MoS₂薄膜。通过扫描电子显微镜和原子力显微镜观察获得了该薄膜样品的形貌和厚度信息。拉曼光谱和X射线光电子谱测试证实了Nb被掺入到了MoS₂薄膜中,Nb掺杂的MoS₂合金薄膜已经形成。最后,对Nb掺杂的少层MoS₂薄膜的电学性质进行了测试。     

通孔阳极氧化铝膜的制备及其性能的研究

在15% H₂SO₄阳极氧化液中添加硝酸镨制备阳极氧化铝(AAO)膜以提高AAO膜的性能,采用化学腐蚀和微波处理相结合的方法,去除AAO膜的阻挡层,制备通孔的AAO膜。分别研究镨的添加量、氧化电压对AAO膜的厚度和硬度的影响及腐蚀时间、微波处理时间分别对AAO膜的阻挡层的影响,分别用能谱和扫描电镜等对AAO膜进行了表征。在15% H₂SO₄阳极氧化液中添加硝酸镨,制备出的AAO膜具有更大的厚度和硬度,当氧化电压为23 V时,在15% H₂SO₄+0.14 Pr g·L-1混合液中制备的AAO膜的厚度和硬度分别为162 μm和275.1 HV,与在阳极氧化液为15% H₂SO₄溶液中制备的AAO膜的厚度和硬度(150 μm和224.8 HV)相比,分别提高8.0%和22.4%。当氧化电压在19～23 V范围时,AAO膜的厚度随着氧化电压的增大而增加;AAO膜的硬度随着氧化电压的增大而减小。将AAO膜在35 ℃和5% H₃PO₄溶液中腐蚀13 min,再用超声波处理10 min,可得到通孔的AAO膜。腐蚀后AAO膜表面絮状物为Al₂O₃。     

超导材料Nb3Ge表面氧化

运用密度泛函理论计算了氧（O）在Nb3Ge表面的吸附,结果表明O倾向于吸附在Nb原子周围,并与Nb的电子轨道发生了明显的交叠,O与Nb形成兼具共价键和离子键特性的化学键。利用X射线光电子能谱对自然氧化的Nb3Ge表面进行成分分析发现:氧化层中只存在Nb的氧化物,理论计算结果与实验结果一致。由于O容易与Nb结合,最外层的Nb因逐渐氧化而耗尽,在接触势的驱使下,内部的Nb原子与最外层的Ge原子交换,最终使得Nb与O的形成氧化物在Nb3Ge表面聚集,在该氧化层下面是由于Nb的耗尽而形成的Ge聚集层。     

An examination of the initial oxidation of a uranium-base alloy (U–14.1 at.% Nb) by O2 and D2O using surface-sensitive techniques

The corrosion resistance of uranium is greatly enhanced by alloying with niobium. In this study the initial stages of corrosion of a specific uranium-base alloy (U–14.1 at.% Nb) by O₂ or D₂O have been examined using the surface specific techniques of X-ray photoelectron spectroscopy (XPS), thermal programmed desorption (TPD), static secondary-ion mass spectroscopy (SSIMS), and sputtered neutrals mass spectroscopy (SNMS). XPS studies of the U–14.1 at.% Nb surface following oxidation using O₂ at 300 K indicate production of a thin oxide overlayer of stoichiometric UO_2.0 intermixed with Nb₂O₅. The same stoichiometry is exhibited for uranium when the oxide is prepared at 500 K with O₂; although, niobium is much less oxidized exhibiting a mixture of NbO and Nb. Contrary to previous XPS literature, SNMS depth profiling studies reveal that oxidation by O₂ is much greater (as judged by oxide layer thickness) than that exhibited by D₂O. An oxide layer thickness of less than 20 Å was created using D₂O as an oxidant at 300 K with exposures >3500 L (oxide layers created from O₂ are significantly greater at much smaller exposures). Formation of a critical density of Nb₂O₅ is suggested to be responsible for the enhanced corrosion resistance by preventing diffusion of O⁻ (O²⁻) or OD⁻/OH⁻ into the oxide/metal interface region. The domains of stability of hydroxyl formation have also been followed using TPD, SSIMS and XPS. Maximal surface hydroxyl concentrations (Θ_rel=0.30) are obtained at a surface temperature of 175 K for these experimental conditions.     

Interfacial microstructures and impact properties for Nb/MOSi2 laminate composites

The purpose of present work is to investigate effects of fabricating temperature and ZrO₂, SiC and NbSi₂ addition on interfacial reaction layer and impact properties for Nb/MoSi₂ laminate composites. Four types of laminate composites alternating four layers of Nb foil with each MoSi₂, mixture layer containing ZrO₂. SiC and NbSi₂ particles were fabricated by hot pressing. The volume fraction of Nb foil involved in these system was nominally 10 vol%. It has been found that the impact value of Nb/MoSi₂ laminate composites decreased at a fabricating temperature higher than 1523 K, since the thickness of reaction layer between Nb and MoSi₂ increased along with fabricating temperature. However, the addition ofZrO₂ particles to Nb/MoSi₂ laminate composites fabricated at 1623 K resulted in a change of the interfacial microstructure as well as a reduction of the reaction layer. Nb/MoSi₂-ZrO₂ laminate composites maintained the same density as that of Nb/MoSi₂ laminate composites fabricated at 1773 K and showed a higher impact value than that of Nb/MoSi₂ laminate composites at 1523 K.     

Fabrication,characterization and biocompatibility of TiO2 nanotubes via anodization of Ti6Al7Nb

Ti6Al7Nb has been used as an implant material because of its good corrosion resistance and high mechanical properties. However, the presence of aluminium (Al), which may lead to ostemalacia, anaemia and nervous system disorders, limited its wide clinical use. In this study, a titanium oxide (TiO₂) nanoporous layer was fabricated on a Ti6Al7Nb alloy using an electrochemical anodic oxidation method. The structure of the TiO₂ nanoporous layer was examined by scanning electron microscopy. The chemical compositions of the samples were analysed by X-ray photoelectron spectroscopy (XPS). Biocompatibility was evaluated by culturing rat osteoblast cells. The result showed that TiO₂ nanoporous layers comprise a mixed oxide containing TiO₂ and a small amount of nobium oxides (Nb₂O₅) and almost no elemental aluminium. The outer layer of the TiO₂ nanoporous layer comprises highly ordered nanotubes and the inner layer forms disordered nanopores. The TiO₂ nanoporous layer could support the adhesion, proliferation, differentiation and gene expression of osteoblast cells. Therefore, a TiO₂ nanoporous layer could enhance the biocompatibility of Ti6Al7Nb alloy and is as a promising candidate for Ti6Al7Nb alloy implants.     

Fabrication of high-quality submicron Nb/Al--AlOx/Nb tunnel junctions

Nb/Al-AlOx/Nb tunnel junctions are often used in the studies of macroscopic quantum phenomena and superconducting qubit applications of the Josephson devices. In this work, we describe a convenient and reliable process using electron beam lithography for the fabrication of high-quality, submicron-sized Nb/Al-AlOx/Nb Josephson junctions. The technique follows the well-known selective Nb etching process and produces high-quality junctions with Vm=100 mV at 2.3 K for the typical critical current density of 2.2 kA/cm^2, which can be adjusted by controlling the oxygen pressure and oxidation time during the formation of the tunnelling barrier. We present the results of the temperature dependence of the sub-gap current and in-plane magnetic-field dependence of the critical current, and compare them with the theoretical predictions.