Niobium Layers Research Articles

Elucidation of the thickness inside the niobium anodic oxide film and its effect on adhesion to polyimide film

Niobium oxide films prepared via anodic oxidation are known to exhibit various colors. These colors are affected by the voltage during anodizing treatment to produce such thick film. The anodic oxidation reaction stops when the applied voltage reaches its saturation value. At this point the film stops growing, its thickness of the internal oxide layer being proportional to the applied voltage. Therefore, this study aims to clarify the relationship between the oxidation state inside the anodized film and its thickness.We also attempted to anodize a polyimide (PI) film, which is a flexible resin material. Because such a PI film is nonconductive, it was sputter-coated with an intermediate layer of niobium before anodization. To enable adhesion to the PI film, the Nb-sputtered film was subjected to surface modification via oxygen plasma treatment. Finally, the Nb-coated PI film was subjected to anodization. Detailed optical comparison was performed between the anodized Nb-coated PI substrate and anodized Nb plate substrate.

Fabrication Process for Deep Submicron SQUID Circuits with Three Independent Niobium Layers.

We present a fabrication technology for nanoscale superconducting quantum interference devices (SQUIDs) with overdamped superconductor-normal metal-superconductor (SNS) trilayer Nb/HfTi/Nb Josephson junctions. A combination of electron-beam lithography with chemical-mechanical polishing and magnetron sputtering on thermally oxidized Si wafers is used to produce direct current SQUIDs with 100-nm-lateral dimensions for Nb lines and junctions. We extended the process from originally two to three independent Nb layers. This extension offers the possibility to realize superconducting vias to all Nb layers without the HfTi barrier, and hence to increase the density and complexity of circuit structures. We present results on the yield of this process and measurements of SQUID characteristics.

Modeling and Design of Resistor Ladder Network for High Frequency Superconductor Flash ADC

We present in this paper the design and implementation of a multilayer 6-bit resistor ladder network capable of operating up to 50 GHz for use in superconductor flash analog to digital converters (ADCs). Implementation of such a resistor network requires the design and optimization of various resistors (25 Ohm, 37.5 Ohm, and 50 Ohm). It is important to minimize the parasitic elements (inductance and capacitance) associated with resistor layout in-order to maintain the performance of the resistor ladder network up to 50 GHz. The paper proposes the use of floating niobium layers around the resistor layer to minimize parasitic effects. The fabricated 6-bit resistor network has a size of 3.2 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ \times $</tex-math></inline-formula> 3.2 mm and is tested in a Lake Shore Cryogenic probe station. The measured results for the individual resistors and the overall integrated network are in agreement with the EM simulation results.

Повреждаемость ниобия импульсными потоками ионов гелия и гелиевой плазмы

The damageability of niobium by pulsed fluxes of helium ions (HI) and helium plasma (HP) in the Plasma Focus (PF) setup was studied at a flux power density qi ~ 108 W/cm2 and qp ~ 107 W/cm2, respectively, and pulse duration τi ≈ 30 – 50 ns and τp ≈ 100 ns. In the implemented irradiation conditions the erosion of the material is observed associated with the evaporation of the surface layer (SL), which occurs somewhat more intensively in the central part of the irradiation zone under the action of the most high-energy fluxes of HI and HP. The typical features of the damageability of the niobium SL under the considered irradiation conditions are revealed. These include: melting of SL with the formation of a wavy surface relief and a large number of blisters of two types — gas-filled and with destroyed shells, as well as the presence of microcracks. The appearance of blisters was associated with the formation of complexes based on the combination of implanted helium atoms with vacancies and interstitial impurity atoms (C, O, N, etc.) and their subsequent growth and coagulation in the liquid phase under pulsed action of energy fluxes on the irradiated Nb surface. Some of the microcracks formed in the SL under the action of thermal stresses coincide with the sliding lines of the material that arise under the action of high-speed plastic deformation. A network of such microcracks creates a block structure on the Nb surface. In the irradiated surface layer of niobium, zones of columnar crystals and a cellular microstructure of the surface are found, in which the average cell size is ~ 100 nm. It was shown by the method of numerical simulation that in the indicated zones the process of solidification of the SL proceeded through directional crystallization at a high speed, which reached ~ 35 m/s near the irradiated surface.

Подбор режимов интенсивной пластической деформации кручением под высоким давлением для изготовления композита гибридной системы Al – Nb

A hybrid composite material fabricated from the Al – Nb system using severe plastic deformation by high-pressure torsion (HPT) up to 30 turns has been studied in the present work. To fabricate the composite, deformation of a three-layer Al – Nb – Al package was carried out at room temperature on Bridgman anvils with grooves under a pressure of 5 GPa at N = 10, 25 and 30 revolutions, at a strain rate of ω = 1 and 2 rpm. Initial disc diameters from pure metals and HPT conditions were experimentally optimized to obtain monolithic and defect-free composite samples. The most intensive fragmentation and stirring of niobium in the aluminium matrix was observed if diameter of aluminium discs was 10 mm and deformation conditions N = 25 and 30 revolutions and ω = 2 rpm were applied. Three microstructural zones were observed after HPT under optimal conditions: the central zone with wide curved layers of niobium in aluminium, the mid-radius zone with finely dispersed layered structure, and periphery with a uniform distribution of niobium in the aluminium matrix. It was shown that HPT led to formation of the intermetallic Al3Nb phase. The microhardness measured along the diameter of the obtained composite materials changed nonmonotonically depending on the produced structure (microstructural zone).

Study on bonding properties between arc surfacing layers and 1045 steel substrate using pull-lift test method

Three kinds of surfacing layers of the austenitic steel, niobium alloyed steel and hypereutectic high chromium alloyed cast iron were prepared on 1045 steel substrate by arc surfacing process with self-shielding flux-cored wires. The bonding strength between surfacing layers and the substrate was tested by pull-lift test method. The experimental results show that the bonding strength between austenitic steel surfacing layer and the substrate is the highest up to 549.1 MPa, and the fracture location is near the fusion line with quasi-cleavage fracture characteristic. The bonding strength between the surfacing layer of niobium alloyed steel and the substrate is 314.4 MPa and the fracture mainly occurred at the bottom of the surfacing layer, which also presents quasi-cleavage characteristic. While the bonding strength between hypereutectic high chromium alloyed cast iron surfacing layer and the substrate is as low as 170.7 MPa and the specimen ruptures along the fusion line with brittle fracture characteristic. The bonding properties between surfacing layers and the substrate are directly related to the compositions and microstructures near the fusion line.

Modeling the processes of atom structure formation of a superconducting spin valve

The paper considers the modeling of a multilayer nanocomposite, the combination of elements of which gives rise to a spin valve effect. The relevance and importance of effects in the field of spintronics and related materials and devices are described. We study the composition and atomic structure of individual layers of a multilayer nanocomposite, as well as the composition and morphology of the interface of nanocomposite layers. We analyzed a sample with a periodic superconductor-ferromagnet structure consisting of more than 20 alternating layers of niobium and cobalt. The deposition process took place in a deep vacuum. The simulation was carried out by the molecular dynamics method using the potential of the modified immersed atom method. The formation of layers was carried out in a stationary mode. The temperature was adjusted using the Nose-Hoover thermostat. The deposition of each nanofilm ended with a relaxation stage for the necessary stabilization and restructuring of the formed nanocomposite. Three deposition temperature regimes were considered: 300 K, 500 K, and 800 K. For these modes, we analysed the atomic structure of nanofilms and transition regions (interface) formed between the layers. A study of the atomic structure of nanofilms showed that niobium is formed by crystalline regions of different orientations. A cobalt nanofilm is characterized by a structure close to amorphous. The structural features of the interface between the superconductor-ferromagnet layers largely depend on a relief of the surface onto which the deposition is made. The smallest variation in atomic composition is observed in the first niobium-cobalt contact zone, since the formation of the first nanofilm occurs on an even plane of the substrate. An analysis of the influence of the temperature regime during the formation of the nanosystem shows the dependence of the processes of formation of multilayer nanofilm formation, the interface of nanolayers, as well as the composition and morphology of heterostructures on the temperature at which a nanocomposite is manufactured. An increased temperature leads to the formation of a more rarefied structure of nanolayers and an increase in the zones of the interface of nanolayers due to the diffusion of atoms of the sprayed materials.

Optimization of high pressure torsion processing for fabrication of the Al-Nb hybrid system

A hybrid composite material fabricated from the Al-Nb system using high-pressure torsion (HPT) up to 30 turns has been studied in the present work. To fabricate the composite, deformation of a three-layer Al-Nb-Al package was carried out at room temperature on Bridgman anvils with grooves under a pressure of 5 GPa at N=10, 25 and 30 revolutions, at a strain rate of ω=1 and 2 rpm. Initial disc diameters from pure metals and HPT conditions were experimentally optimized to obtain monolithic and defect-free composite samples. The most intensive fragmentation and stirring of niobium in the aluminium matrix was observed if diameter of aluminium discs was 10 mm and deformation conditions N=25 and 30 revolutions and ω=2 rpm were applied. Three microstructural zones were observed after HPT under optimal conditions: the central zone with wide curved layers of niobium in aluminium, the mid-radius zone with finely dispersed layered structure, and periphery with a uniform distribution of niobium in the aluminium matrix. It was shown that HPT led to occurrence of strain-induced ageing resulting in formation of the intermetallic Al3Nb phase. The microhardness measured along the diameter of the obtained composite materials changed nonmonotonically depending on the produced structure (microstructural zone).

Nanoscale Barrier Layers to Enable the Use of Gallium-Based Thermal Interface Materials with Aluminum

Performance of thermal interface materials (TIMs), such as thermal pastes and mats, hinders the advance of integrated circuit (IC) devices. Current state-of-the-art TIMs suffer from low thermal conductivity, thick cross sections, and poor long-term performance. Gallium (Ga) and gallium-based alloys and amalgamations, in liquid and solid form, have demonstrated up to three times greater thermal conductivity than conventional TIMs, but rapidly alloy with and destroy aluminum (Al) components, which are commonly found in IC devices. In this work, we investigate the use of thin-film barrier layers on Al to prevent Ga alloying and characterize their performance through accelerated Ga exposure experiments and scanning electron microscopy. It is found that 100-nm-thick layers of the common passivation materials niobium and 304 stainless steel do not sufficiently prohibit Ga migration, but a 100 nm layer of titanium (Ti) does. No alloying is evident in Ti-coated Al samples after exposure to a liquid Ga alloy droplet at 300 °C for 168 h, 250 thermal cycles from room temperature to 150 °C with 30-min dwell, or 50 thermal cycles from room temperature to 300 °C with 2-min dwell. The results present a clear and direct path to the use of Ga and Ga alloys as TIMs through the addition of a thin inexpensive barrier layer on Al components and may enable future IC device technologies.

High-resolution x-ray scattering from epitaxial thin films of Y/Nb on Al2O3

During the 1990s, Roger Cowley had a strong interest in the crystal and magnetic structures of rare-earth superlattices as a means to understand the rich and exotic magnetic properties of the rare-earth metals. High-quality samples can be grown by molecular beam epitaxy on sapphire substrates by first depositing a thin epitaxial layer of niobium, then a layer of yttrium or lutetium as a seed. High-resolution x-ray scattering is an excellent probe to characterise the crystal quality and was used to study the structure of the niobium layer. However, relatively little attention was paid to the seed layer. This article summarises some of the x-ray experiments performed by the Cowley group to study the structure of epitaxial niobium on sapphire, and extends the work to report some results on the structure of thin yttrium seed layers. The structure of the yttrium films is shown to have a strong dependence on the thickness of the niobium buffer, with the buffer needing to be thicker than a critical value of ∼80 for the formation of misfit dislocations at the Nb/Al2O3 interface before highly coherent Y films can be grown. Yttrium films grown on Nb buffers thinner than ∼500 show a similar two-peak line shape in scans through their specular Bragg peaks to that seen in the specular Nb Bragg peaks, with a resolution-limited feature on a broader diffuse peak. The resolution-limited feature depends on the thickness of the yttrium film, becoming weaker and having a stronger decay with increasing as the film thickness increases, while the width of the yttrium broad peak evolves as the square root of the width of the niobium Bragg peak. The data are discussed within the context of theories describing the scattering from films with misfit dislocations.

Structure and Mechanical Properties of the Molybdenum–Steel Bimetal Fabricated by Hot Isostatic Pressing

Abstract—The structure and the ultimate tensile strength of the bimetallic joints of a TsM2A (Mo–Ti–Zr system) molybdenum alloy and a corrosion-resistant 12Kh18N10T steel are studied. These joints are formed by diffusion welding under hot isostatic pressing conditions using the following combined intermediate layers: vanadium–electrical sheet steel, vanadium–copper, and titanium–niobium–copper. The highest strength of the joint (419 MPa) is reached when a combination intermediate layer of titanium, niobium, and copper is used.

Very Large Scale Integration of Josephson-Junction-Based Superconductor Random Access Memories

Arrays of vortex transitional (VT) memory cells with functional density up to 1 Mbit/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> have been designed, fabricated, and successfully demonstrated. This progress is due to recent advances in design optimization and in superconductor electronics fabrication achieved at MIT Lincoln Laboratory. As a starting point, we developed a demo array of VT cells for the 100-μA/μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> MIT LL fabrication process SFQ5ee with eight niobium layers. The studied two-junction memory cell with a two-junction nondestructive readout occupied 168 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , resulting in an over 0.5 Mbit/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> functional density. Then, we reduced the cell area down to 99 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (corresponding to over 0.9 Mbit/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> functional density) by utilizing self-shunted Josephson junctions (JJs) with critical current density JC of 600 μA/μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and eliminating shunt resistors. The fabricated high-JC memory cells were fully operational and possessed wide read/write current margins, quite close to the theoretically predicted values. We discuss approaches to further increasing the integration scale of superconductor memory and logic circuits: 1) miniaturization of superconducting transformers by using soft magnetic materials; and 2) reduction of JJ area by using planar high-JC junctions similar to variable thickness bridges.

Planarized Fabrication Process With Two Layers of SIS Josephson Junctions and Integration of SIS and SFS &lt;italic&gt;π&lt;/italic&gt;-Junctions

We present our new fabrication process for superconductor electronics that integrates two layers of Josephson junctions (JJs) in a fully planarized multilayer process on 200-mm wafers. The two junction layers can be, e.g., conventional superconductor-insulator-superconductor (SIS) Nb/Al/AlOx/Nb junctions with the same or different Josephson critical current densities, Jc. The process also allows integration of high-Jc superconductor-ferromagnet-superconductor (SFS) or SFS'S JJs on the first junction layer with Nb/Al/AlOx/Nb trilayer junctions on the second JJ layer, or vice versa. In the present node, the SFS trilayer, Nb/Ni/Nb is placed below the standard SIS trilayer and separated by one niobium wiring layer. The main purpose of integrating the SFS and SIS junction layers is to provide compact π-phase shifters in logic cells of superconductor digital circuits and random access memories, and thereby increase the integration scale and functional density of superconductor electronics. The current node of the two-junction-layer process has six planarized niobium layers, two layers of resistors, and 350-nm minimum feature size. The target critical current densities for the SIS JJs are 100 μA/μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and 200 μA/μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . We present the salient features of the new process, fabrication details, and characterization results on two layers of JJs integrated into one process, both for the conventional and π-junctions.

Fabrication of Magnetic Calorimeter Arrays With Buried Wiring

Future astrophysics missions such as the Lynx X-ray Microcalorimeter will comprise a very large array of X-ray microcalorimeters with greater than 100 000 pixels. One of the major challenges associated with the realization of large format arrays is the fabrication of high-density, high-yield, superconducting wiring between the pixels of the array. An attractive way to overcome this challenge is to use buried layers of multilayer wiring. Here we report on the fabrication of prototype arrays of magnetically coupled microcalorimeters (MMCs) using multiple niobium layers of buried wiring. In order to successfully scale MMCs to large arrays, so that the stray inductance of the wiring is sufficiently low and the sensor meander coil inductance is sufficiently high, the meander coil pitch is decreased. We have investigated linewidths as narrow as 400 nm. Fabricated devices have demonstrated high critical currents of 30 mA for the narrowest pitch.

Electrochemical properties of niobium and niobium compounds modified AISI430 stainless steel as bipolar plates for DFAFC

ABSTRACTThe highly conductive and corrosion resistant diffusion layers of niobium, niobium nitrides and niobium carbides have been successfully fabricated on AISI430 stainless steel (430 SS) via a plasma surface diffusion alloying (PSDA) method as bipolar plates for direct formic acid fuel cells (DFAFCs). The surface of niobium carbides modified 430 SS (NbC 430 SS) is relative densification and uniformity without other surface flaw and micropore. Potentiodynamic and potentiostatic polarisation measurements indicate that NbC 430 SS enhances the corrosion resistance more effectively than other modified samples and its corrosion current density is maintained approximately 2.5 μA cm–2 in the simulated anodic environment of DFAFC. Moreover, NbC 430 SS presents a superior hydrophobicity with a contact angle of 105.5° and a lower interfacial contact resistance (ICR) before and after potentiostatic polarisation tests than other specimens. Therefore, NbC 430 SS developed in this work has a great potential to be bipolar plates for DFAFCs.

Elevated and cryogenic temperature micropillar compression of magnesium–niobium multilayer films

The mechanical properties of multilayer films consisting of alternating layers of magnesium and niobium are investigated through micropillar compression experiments across a broad range of temperatures. The data collected from the variable temperature micropillar compression tests and strain rate jump tests are used to gain insight into the operative deformation mechanisms within the material. At higher temperatures, diffusion-based deformation mechanisms are shown to determine the plastic behavior of the multilayers. Diffusion occurs more readily along the magnesium–niobium interface than within the bulk, acting as pathway for magnesium diffusion. When individual layer thicknesses are sufficiently small, diffusion can remain the dominant deformation mechanism down to room temperature. Multilayer strengthening models historically rely solely on dislocation-based arguments; therefore, consideration of diffusion-based deformation in nanolaminates with low melting temperature components offers improved understanding of multilayer behavior.

Powder metallurgical production of 316L stainless steel/niobium composites for Proton Exchange membrane electrolysis cells

ABSTRACTIn this study, a composite made of a porous stainless steel (SS) 316L substrate coated with Nb was investigated as a novel porous transport layer (PTL) for proton exchange membrane electrolysis cells (PEMECs). The fabrication of such SS316L/Nb composites using scalable and automatable powder metallurgical techniques as tape casting, screen-printing and field assisted sintering technology/spark plasma sintering (FAST/SPS) was described. Sintering behaviour and the interdiffusion at the SS316L/Nb interface were investigated. Powder metallurgical techniques such as screen-printing are the preferred method to achieve a porous Nb coating, while FAST/SPS is the preferred method for a better control of the SS316L/Nb interface by lowered interdiffusion. First electrochemical performance tests with SS316L/Nb composites demonstrate they have potential to replace the state-of-the-art titanium-based PTLs. The use of SS316L is expected to decrease manufacturing costs of PTLs, while the addition of niobium layer, due to its excellent corrosion resistance in acid environment, aims to improve PEMECs lifetime and performance.

Microstructure and corrosion behavior of high carbon content FeTiNbC alloys in 3.5 wt% NaCl

The aim of the present work is to study the relationship between the microstructure and the corrosion behavior, in a 3.5 wt% NaCl solution, of high carbon content FeNbTiC alloys. Eutectic and mainly primary carbides are formed during the solidification and the carbon content contributes largely to the formation of both of them. The eutectic ones are homogeneous and present a chinese script morphology, which can be avoided with higher carbon amount. The primary particles show essentially a core–shell structure described as a Ti-rich carbide core, surrounded by several layers of niobium (Nb, Ti)C1-x mixed carbides, where the titanium amount decreases from the core to the shell. The electrochemical tests show is that the higher carbon content better is the corrosion behavior, while a high niobium amount has an adverse effect. A compromise between Ti, Nb and C has been defined to enhance the corrosion resistance of this type of alloys. This type of microstructure, involving ceramic particles, the increasing of (Nb, Ti)C1-x hardness compared to NbC1-x and the corrosion resistance of high carbon FeTiNbC could promote them for replacing some iron based alloys such as, cutting tools, tool steels and high speed steel.

Targeted influence on the weld strength of high-strength fine-grain structural steels in the GMA welding process through functionalized weld material surfaces

The development of high-strength and ultrahigh-strength fine-grain steels is especially enhanced due to requirements in the range of mobile crane construction, bridge construction, and general steel construction purposing a consistent utilization of lightweight construction and an increase of payloads. However, currently available filler metals limit the use of novel fine-grained structural steels in modern welded constructions, since the strength of the steels in the weld metal can neither be achieved nor exceeded Heuser and Jochum (Mater Werkst 38(7):515–520, 2007). The coating of GMA welding wire electrodes by means of PVD coating processes enables the application of thin, functional layers influencing the welding process and the weld metal. The mechanical and technological properties of the weld metal can thus be influenced to an extent that cannot be achieved even with state-of-the-art welding consumables. The influence of niobium, zirconium, and nickel layers is shown in the described investigations. In particular, the fine-grain and carbide-forming effect of niobium and zirconium and the associated influence on the mechanical and technological characteristics are illustrated. In addition, the effect of a nickel-coated welding wire electrode on the weld metal is explained. The toughness properties are at the focus of the investigations. The aim is to increase the strength while retaining the toughness properties as far as possible.

Corrosion Resistance of Niobium-Coated Carbon Steel

In this work, the effectiveness of niobium coatings for the corrosion protection of carbon steel was studied. Three niobium resins, containing different molar proportions of citric acid:ethylene glycol, were coated separately onto samples of carbon steel (SAE 1020). The niobium layers were obtained by the polymeric precursor method (Pechini). Potentiodynamic polarization curves (anodic and cathodic) and electrochemical impedance spectroscopy were used to evaluate the corrosion resistance of the niobium-coated carbon steel samples in a 0.5 mol L−1 NaCl electrolyte solution. X-ray diffraction analysis of the niobium layers showed that they are composed of the niobates: NbO, NbO2 and Fe0.998Nb0.002. Surface observation by scanning electron microscopy revealed a uniformly deposited niobium coating on the surface. The electrochemical results showed that niobium was effective in the corrosion protection of the carbon steel substrate. The results also suggested that niobium can be coated onto the substrate to form a layer with advantageous corrosion properties.