Upper Critical Fields of Nb/Pd Multilayers

We measured critical temperature and critical magnetic fields of Nb/Pd multilayers where the Nb thickness is held constant (d _Nb =250 Å) while the Pd thickness, d _Pd , is systematically varied from 10 to 200 Å. The critical temperature shows a monotonic decrease as a function of the Pd thickness, which can be tentatively described using the classical de Gennes-Werthamer theory for proximity coupled systems. The critical magnetic field measurements reveal unusual behavior, like a positive curvature of H_c2(T) close to T _c and a dimensional 3D-2D crossover, already present in multilayers with very thin Pd layers. In particular the angular behavior of the upper critical field, in the case of small d _Pd values, confirm the 2D nature of all the samples at T=4.2 K, giving also indication of the columnar nature of the Nb layers. These unusual behaviors might be related to the strong paramagnetic nature of the Pd layers. On the other hand also the proximity theory for S/N systems describes the perpendicular critical field data, but some inconsistencies are found quantitatively.     

Repulsive Flux Pinning Force in NbTi/Nb Superconductor/Superconductor Multilayers

Flux pinning characteristics have been investigated for the Nb _x Ti_100-x /Nb(x = 65, 50 and 28) and Nb ₂₈ Ti ₇₂/Nb ₆₅ Ti ₃₅ superconductor(S)/superconductor(S^′) multilayers. The maximum of the pinning force F _{p⊥ max} perpendicular to the layer plane as a function of the structure modulation length λ has a peak in the quasi-two-dimensional region (λ～20 nm). The maximum. values of the F _{p⊥ max} versus λ curve are proportional to the difference of the GL coherence length (ξ _GL ) between the superconductive sublayers S and S^′. The results suggest that the large F _{p⊥ max} in the S/S^′ multilayer is caused by the repulsive pinning force due to Nb layers with larger ξ _GL .     

Cu对NiFe/Cu/NiFe层状薄膜的巨磁阻抗效应影响的研究

用直流磁控溅射方法制备了NiFe/Cu/NiFe层状薄膜 ,研究了Cu膜宽度对NiFe/Cu/NiFe层状薄膜的巨磁阻抗效应的影响 ,结果表明 ,层状薄膜的巨磁阻抗效应随Cu膜宽度发生振荡现象 ;并提出了一个等效电路模型直观地解释了层状薄膜增强巨磁阻抗效应的机理     

ZrC/ZrB2纳米多层膜的微观结构与机械性能的研究

选择ZrC和ZrB2为个体层材料,利用射频磁控溅射系统在室温下制备具有纳米尺寸的ZrC/ZrB2多层膜.通过X射线衍射仪、扫描电子显微镜、俄歇电子能谱、表面轮廓仪及纳米力学测试系统研究了调制周期与ZrC,ZrB2单层厚度比例(tZrCtZrB2)对多层膜生长结构和力学性能的影响.结果表明,多层膜的界面清晰,调制周期性好,大部分多层膜的纳米硬度和弹性模量值都高于两种个体材混合相的值,在调制比例tZrCtZrB2=11.7、调制周期为32 nm时,薄膜显示出很强的ZrC(111)择优趋向和较弱的ZrB2(001)及ZrB2(002)结构,同时产生硬度异常升高的超硬效应,其硬度达到42 GPa.多层膜的机械性能改善明显与其调制结构和多晶结构有着直接的联系.     

Microstructure and In-plane Resistivity of Cu/Ni Multilayers

1.IDtroductiGnInrecellty6ars,interesthasgrowninmodulatedcompositestructurescomposedofperiodicallychang-inglayersoftwodifferentmaterials.Itwasshownthatthematerialsmayacquireimprovedqualitiestothoseofcorrespondingpuremetalswhenthemodu-lationwavelengthisverythinatafewnanometersinthickness.ItiswellknownthattheCu/Nimultilayershavebeenstudiedalotbecauseofitsabnormalphysicalproperties,includingelectricalresistivity[1,2],elasticmoduli[3],magneticproperties['l.Asthethicknessofanindividuallayerinmulti…     

Electrical transport in Nb/Cu multilayers

The longitudinal resistance,R _xx , the Hall resistance,R _xy , and the critical current density,j _c , were measured for two Nb/Cu multilayers with different thickness of the Cu layers. The magnetic field was applied perpendicular to the layers. A peak-like anomaly ofR _xy , accompanied by a sign reversal, is interpreted using a phenomenological model. The temperature dependence ofj _c (T)=j _c0 (1−T/T _c0 )²/T ^5/2 coincides with the theory of Aslamazov, D'yachkov, and Lempitskii.     

Silicide formation and phase separation from Cu/Nb and Nb/Cu bilayers on silicon

Electron beam evaporation was used to produce Nb/Cu and Cu/Nb bilayers on silicon. The phase sequence and morphology were investigated as a function of annealing temperature in the temperature range between 200 °C and 800 °C, using Auger electron spectroscopy, Rutherford backscattering spectrometry, X-ray diffraction, and transmission electron microscopy. Independently of the sequence of deposition, the phases Nb₃Si and Nb₅Si₃ are the two first niobium phases to be formed as a very thin layer at the Nb---Si interface. However, there is evidence that the reaction between niobium and silicon depends strongly on the presence of copper at the Nb---Si interface. The unusual coexistence of Nb₅Si₃, NbSi₂ and niobium phases was also observed. The formation of the ternary phase Nb₅Cu₄Si₄ was detected after annealing Cu/Nb at 700 °C and Nb/Cu at 800 °C. In the latter case the NbSi₂ and Cu₃Si+Cu₄Si phases were formed through a layered growth process.     

Magnetic Correlations in Some FeNi/Cu(100) Multilayers

We present a first-principles electronic structure based study of magnetic correlations in the paramagnetic phase of some Fe and Ni multilayers on Cu(100) substrates. We have used the screened Korringa–Kohn–Rostoker method to calculate the electronic structure within the spin-density functional theory and used the disordered local moments model to describe the paramagnetic phase above the Curie temperature. We find that in the Ni/Cu(100) films, there are no local moments formation for any thickness. For the multilayers of Fe and Ni, we find that there is some, although very small, local moment formation in the interior of the Ni film if the Ni layer is more than 6 monolayers thick. However, the Ni layers facilitate the magnetic correlation between the Fe layers. The Curie temperatures of the multilayers also depend upon the Ni layer thickness.     

ZrN/TiAlN纳米多层膜的制备及其结构与性能的研究

利用高真空离子束辅助沉积系统在室温下制备了ZrN,TiAlN和一系列ZrN/TiAlN纳米多层膜,利用X射线衍射仪、纳米力学测试系统和多功能材料表面性能实验仪表征了薄膜的微结构和机械性能,分析了调制周期对薄膜结构与机械性能的影响.结果表明大部分多层膜的纳米硬度与弹性模量值都高于两种个体材料硬度的平均值,当调制周期为6.5 nm时,多层膜硬度达到最高(30.1 GPa),弹性模量、粗糙度、摩擦以及划痕测试均达到最佳效果.     

坡莫合金/铜磁性多层膜微观力学性能的研究

本文用直流磁控溅射方法在玻璃基片上制备了具有不同坡莫合金层厚度的坡莫合金/铜磁性多层膜,并采用纳米力学系统分别以压痕法、划痕法测定了坡莫合金层厚度对多层膜显微硬度、弹性模量以及划痕的临界载荷、宽度和深度等的影响.研究结果表明:在既定的接触深度,多层膜的显微硬度及弹性模量随坡莫合金层厚度变化不大,它们分别约为4.5 GPa和80 GPa,比坡莫合金单层膜的值低而比铜单层膜的值高;坡莫合金层厚度对多层膜微观摩擦学性能有较大的影响:随坡莫合金层厚度减小,特别是当其小于等于1.6 nm时,划痕有较高的临界载荷、较小的宽度和较浅的残余深度;多层膜的划痕临界载荷高于坡莫合金单层膜的值.     

金属纳米多层膜力学性能研究进展

新型功能材料及器件向小型化,集成化和复合化发展的趋势,使得尺寸在纳米尺度的层状材料和柔性多层器件在使用过程中的服役行为成为其发展的关键科学问题。本文结合作者近几年对Ag/M系列和Cu/M系列多层膜力学性能的研究工作,对金属纳米多层膜的微结构特征及其对力学性能的影响进行了回顾和总结,主要包括多层膜的晶粒形貌对其强化机制和塑性变形行为的影响,组元强度错配对多层膜硬化行为的影响,界面结构与其强度极值的关系、不对称界面结构引起的异常弹性模量增强和多层膜的室温蠕变机制及界面结构对蠕变性能的影响等几个方面,并对多层膜的力学性能研究进行了展望。     

Ceramic joining III bonding of alumina via Cu/Nb/Cu interlayers

A method of ceramic-ceramic joining that exploits a multilayer interlayer designed to form a thin, potentially transient layer of liquid phase has been used to join alumina to alumina. Microdesigned multilayer Cu/Nb interlayers were used to achieve bonding at 1150 °C. Flexure strengths of as-bonded samples ranged from 119 to 255 MPa, with an average of 181 MPa. The ability to form strong ceramic/metal interfaces is also indicated by instances of ceramic failure. Microstructural and chemical characteristics of fracture surfaces were evaluated using SEM, EDS and microprobe. The impact of post-bonding anneals of 10 h duration at 1000 °C in gettered argon on room-temperature joint strength was assessed. High strengths (198 to 238 MPa) were obtained. The retention of strength following annealing in low oxygen partial pressure argon differs from the behaviour previously observed in Cu/Pt bonded alumina. Effects of the anneal on interfacial microstructure were determined, and an explanation for this difference in behaviour is proposed.     

Ar/N2气体比例对TaN/NbN纳米多层膜机械性能的影响

采用射频磁控溅射系统,以TaN和NbN作为体材料,制备了一系列TaN/NbN纳米多层膜.通过XRD,纳米力学测试系统分析了该体系合成中Ar/N2气体比例对多层膜结构与机械性能的影响.结果表明,纳米多层膜的硬度值普遍高于两种个体材料混合相的值;当FArFN2=10时TaN的(110)峰加强,TaN的晶体结构以六方结构为主,NbN的晶体结构以面心立方结构为主,此时,多层膜体系的硬度、弹性模量以及膜基结合性能均达到最佳效果(最大硬度为30 GPa),摩擦磨损实验表明,Ar/N2比为101的TaN/NbN多层膜较其他Ar/N2比的多层膜耐磨性更好,不易发生破损,适合实际应用.     

Characterizations of NiCu/Cu Multilayers: Dependence of Nonmagnetic Layer Thickness

A series of NiCu/Cu multilayers were grown on (110) textured polycrystalline Cu substrates from a single electrolyte under potentiostatic deposition conditions. Microstructure, magnetoresistance and magnetic properties of the multilayers were investigated as a function of the nonmagnetic layer thicknesses. The structural studies by X-ray diffraction revealed that the multilayers have face-centered-cubic structure with preferred (110) crystal orientation as their substrates. The composition of the deposits determined by energy dispersive X-ray spectroscopy showed that the Cu content of the films increased as the Cu layer thickness increased. The scanning electron microscope studies showed that samples have homogeneous and smooth surfaces. Multilayers exhibited either anisotropic magnetoresistance (AMR) or giant magnetoresistance (GMR) depending on the non-magnetic Cu layer thickness. The multilayers with Cu layer thickness thicker than 0.7 nm exhibited GMR, but the AMR effect was observed to be dominant for the Cu layer thickness less than 0.7 nm. The GMR curves are broad in shape and the nonsaturated curves indicated the predominance of a superparamagnetic contribution. The GMR magnitudes of NiCu/Cu multilayers are found to be about 1–1.5 %. The vibrating sample magnetometer measurements revealed that the saturation magnetization decrease with increasing nonmagnetic layer thickness. The changes in the magnetic and magnetotransport properties might arise from the change in the Ni and Cu content of the samples caused by the variation of Cu layer thicknesses.     

Improving the Thermal Conductivity of Niobium in Nb3Sn/Nb/Cu Structures by Solid-State Refining

Experimental data are presented which demonstrate that the thermal conductivity of Nb in Nb₃Sn/Nb/Cu structures can be raised by solid-state refining in the range 1200–1500 K, using titanium and zirconium electrolytic coatings, plates, or powders as impurity sinks. The removal of oxygen from the Nb layer increases its thermal conductivity by a factor of 3–4, without impairing the performance parameters of the superconducting Nb₃Sn layer.     

Magnetism and Its Dependence on Annealing Temperature for Sputtered Co/Cu Multilayers

Magnetism and its dependence on annealing temperature for r.f. sputtered Co/Cu multilayers have been investigated. It was found that the easy magnetization axes of the films are paralIel to the substrate and the magnetic properties of both as-sputtered and annealed multilayers are isotropic in the film plane. The coercive field Hc is 4.8 kA/m and the ratio of remanence-tosaturation magnetization Mi/M is about 0.73 for as-sputtered samples. Both Hc and Mr/Ms increase with increasing annealing temperatures, especially when annealing temperatures are higher than 400℃. These experimental results can be interpreted using the ferromagnetic exchange coupling and the pinning theory of the coercivity     

Growth and structural characterization of epitaxial Cu/Nb multilayers

Electron beam evaporation with optimized deposition parameters has been used to grow good quality epitaxial Cu/Nb nanoscale multilayered films on sapphire substrates. The quality of the epitaxial films, as measured by the intensities and widths of the X-ray diffraction peaks, increases with increasing deposition temperature. However, high deposition temperatures also enhance the tendency for layer pinch-off which eventually leads to spheroidization and growth of multilayer films with polycrystalline islands. Deposition temperatures and rates were optimized to produce the highest quality epitaxial films with continuous nanolayers, suitable for in situ deformation experiments in a synchrotron-based Laue micro-diffraction set up.     

Microstructure and ultrahigh strength of nanoscale Cu/Nb multilayers

The microstructure and mechanical properties of Cu/Nb multilayers were investigated by X-ray diffraction, transmission electron microscopy, scanning electron microscopy and nanoindentation. Ultrahigh strength of 3.27 GPa is achieved at the smallest layer thickness of 2.5 nm, which agrees well with the theoretical prediction based on the deformation mechanism of crossing of dislocations across interfaces. After that, the strength decreases with the increasing layer thickness and the transition of the deformation mechanism to confined layer slip occurs at the layer thickness of 6.5 nm. Additionally, strength of the Cu/Nb multilayers increases with increasing loading strain rate because of enhanced strain hardening.     

Transition temperatures and critical fields of Nb/Cu superlattices

We present experimental results on the superconducting properties of Nb/Cu superlattices. The transition temperature of the superlattice implies a decrease in the transition temperature of single Nb films as a function of layer thickness. This is interpreted as due to the mean free path-induced decrease in the density of states at the Fermi surface, in agreement with experimentally measured magnetic susceptibilities. The temperature dependence of anisotropic critical fields is in qualitative agreement with predictions based on effective mass theories. However, the behavior of the angular dependence is considerably more complicated. In addition to the anisotropy due to the layering, there is an anisotropy due to surface superconductivity. These results are discussed in light of theories of anisotropic critical fields.     

Giant Shapiro Steps in a Superconducting Network of Nanoscale Nb Islands

Recently, a dynamic vortex Mott transition has been observed in an array of superconducting nanodots. Here, we report the effect of the interaction of microwave radiation on this system and we show the occurrence of giant Shapiro steps.