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A novel approach based on conventional solution-coating and wire-drawing processes has been employed for the production of carbon nanotube (CNT) coated conductors. The solution process employs a mesoscopic building block, a CNT fibril dispersion formed in acid from forest-grown, long-length multiwall CNTs, to help bridge the transition from nanomaterials to thick, highly aligned technical coatings. The coatings are formed onto a roughened copper wire former through dip-coating. The roughened surface provides for mechanical attachment between the CNT coating and copper wire core that allows for the composite to be wire-drawn while wet to further shape, densify, and align the CNT coating. The wet chemistry approach offered a facile integration of different CNT and dopant types in the CNT coatings. For the specific process described here, it was observed that the CNT coatings were simultaneously doped with acid and copper nanoparticles. Coated wires were produced with conductivities on par with copper but in...

Low-energy ion-beam irradiation (

A novel strain mismatch induced tilted epitaxy method has been demonstrated for producing high quality (000l) hexagonal films on (001) cubic substrates. Highly oriented hexagonal (000l) ZnO films are grown on cubic (001) MgO substrates using Sm Zr O (SZO) as a template. The large lattice mismatch of >13% between the obvious crystallographic matching directions of the template and substrate means that cube-on-cube epitaxy is energetically unfavorable, leading to growth instead of two high index, low energy compact planes, close to the {111} orientation. These planes give three different in-plane orientations resulting from coincidence site lattice matching (12 in-plane orientations in total) and provide a pseudo-hexagonal symmetry surface for the ZnO to grow on. The texture of the ensuing (000l) ZnO layer is markedly improved over the template. The work opens up both a new avenue for growing technologically important hexagonal structures on a range of readily available, (001) cubic substrates, as well as showing that there are wide possibilities for heteroepitaxial growth of a range of dissimilar materials. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. 0.28 0.72 2-δ

Both the structure and the type of the nucleation surface play a key role in texture development of IBAD MgO films. We have examined these features in Al2O3 and Y2O3 thin films using two different types of deposition methods, atomic layer deposition (ALD) and electron beam evaporation (EBE). Examination of EBE Al2O3 with in situ reflected high-energy electron diffraction (RHEED) films reveals the presence of a nanocrystalline structure that remains unchanged after and is insensitive to ion irradiation with 750 eV argon ions. In contrast, ALD Al2O3 examined with the same method reveals a featureless image that appears amorphous. Use of the ALD Al2O3 film can result in well-textured films with reasonable in-plane mosaic spread values (~ 14°) without process optimization. Similar results were obtained on ALD and EBE Y2O3 films, although, the EBE Y2O3 appeared amorphous in the RHEED even before exposure to the ion beam. The ALD Y2O3 film resulted in an in-plane texture of ~ 10°. Finally, bare silicon substrates were examined. It was found that even with the native oxide remaining on its surface, the silicon underneath was amorphized by the ion beam and provided a suitable surface for the deposition of biaxial textured MgO with an in-plane texture of ~ 7° FWHM.

One of the crucial steps in the second generation high temperature superconducting wire program was development of the buffer-layer architecture. The architecture designed at the Superconductivity Technology Center at Los Alamos National Laboratory consists of several oxide layers wherein each layer plays a specific role, namely: nucleation layer, diffusion barrier, biaxially textured template, and intermediate layer providing a suitable lattice match to the superconducting Y1Ba2Cu3O7 (YBCO) compound. This report demonstrates how a wide range of ion beam analysis techniques (SIMS, RBS, channeling, PIXE, PIGE, NRA and ERD) was employed for analysis of each buffer layer and the YBCO film. These results assisted in understanding of a variety of physical processes occurring during the buffer layer fabrication and helped to optimize the buffer-layer architecture as a whole.

A composite layer has been successfully implemented in high temperature superconducting (HTS) coated conductors (CCs) based on ion beam assisted deposition (IBAD) MgO technology. This layer serves a dual function: a nucleation layer for the growth of high quality biaxially aligned MgO and a diffusion barrier to inhibit interdiffusion between the Ni-alloy substrate and the superconductor. The composition of the composite Y2O3-Al2O3 influences the texture and superconducting properties of YBCO films grown on STO buffered MgO/Y2O3-Al2O3/Ni-alloy. Our experimental results demonstrate that the superconducting properties of YBCO grown on STO buffered MgO/Y2O3-Al2O3/Ni-alloy are comparable with those of YBCO on standard architecture. The use of a single composite Y2O3-Al2O3 layer instead of individual layers of Y2O3 and Al2O3 for the fabrication of HTS CCs based on IBAD MgO provides advantages such as simplified architecture and potentially reduced cost due to the reduced number of fabrication steps.

The nucleation and growth of magnesium oxide (MgO) deposited using the ion beam-assisted deposition (IBAD) technique was investigated using a specially designed in-situ quartz crystal microbalance (QCM), which acted as the substrate during deposition. The mass accumulation of the growing film was collected while simultaneous reflected high-energy electron diffraction (RHEED) patterns were taken. IBAD MgO films deposited on the QCM with an amorphous silicon nitride layer showed an inflection point in the data. This inflection separated two distinct regions with the initial region having a slope greater than that of the final region. Experiments run at different ion-to-molecule ratios had similar inflection points that corresponded to a thickness of ~2 nm and could not be explained by an elementary growth and surface coverage model. Correlation of this inflection point with RHEED images showed that the point of inflection corresponds to the onset of in-plane texture. This result suggests that the IBAD MgO process is more complex than previously suggested and may depend upon a solid phase recrystallization process.

In thin films of rare-earth manganites, RE1−xMxMnO3 (RE=rare earth, M=Ca, Sr, Ba), with mixed-valence perovskite structure, the transport properties highly depend on the deposition technique, processing conditions, and the substrate used. Chemical solution deposition techniques provide many advantages, such as low cost, easy setup, and coating of large areas. However, the crystalline quality, uniformity, and reproducibility of the film depend on the reactivity of the chemical used for solution preparation. In this paper, we report a novel process to grow rare-earth manganite films using low-cost polymer-assisted deposition technique. In this process, polymer controls the viscosity and binds metal ions, resulting in a homogeneous distribution of metal precursors in the solution and a uniform film. These solutions were stable, and crack-free films were obtained using these solutions. In this paper, thin films of La1−xSrxMnO3, La1−xCaxMnO3, and Pr0.5Ca0.5MnO3 were grown on (001) LaAlO3 substrates. The La1−xSrxMnO3 and La1−xCaxMnO3 films were highly c-axis oriented and epitaxial, and showed high magnetoresistance near their Curie temperature. Charge ordering was observed in the Pr0.5Ca0.5MnO3 film at 220 K and high magnetoresistance of nearly −100% was obtained at low temperatures. The structural, transport, and magnetic properties of these films were similar to those obtained for films grown by physical vapor deposition.

From the stone ages to modern history, new materials have often been the enablers of revolutionary technologies. [1] For a wide variety of envisioned applications in space exploration, energy-efficient aircraft, and armor, materials must be significantly stronger, stiffer, and lighter than what is currently available. Carbon nanotubes (CNTs) have extremely high strength, [2–5] very high stiffness, [6,7] low density, good chemical stability, and high thermal and electrical conductivities. [8] These superior properties make CNTs very attractive for many structural applications and technologies. Here we report CNT fibers that are many times stronger and stiffer per weight than the best existing engineering fibers and over twenty times better than other reported CNT fibers. Additionally, our CNT fibers are nonbrittle and tough, making them far superior to existing materials for preventing catastrophic failure. These new CNT fibers will not only make tens of thousands of products stronger, lighter, safer, and more energy efficient, but they will also bring to fruition many envisioned technologies that have been to date unavailable because of material restrictions. Strong, stiff, and lightweight are critical property requirements for materials that are used in the construction of space shuttles, airplanes, and space structures. These properties are assessed by a material’s specific strength and specific stiffness, which are defined as the strength or stiffness (Young’s modulus) of a material divided by its density. [9] The combination of high strength, high stiffness, and low density affords CNTs with extremely high values for specific strength and specific stiffness. The most effective way to utilize these properties is to assemble CNTs into fibers. However, despite extensive worldwide efforts to date, the specific strength and specific stiffness of CNT fibers that have been reported by various research groups are much lower than currently available commercial fibers. [10–22] In early studies, researchers attempted to reinforce polymer fibers with short CNTs, but the reinforcement was limited by several issues, including poor dispersion, poor alignment, poor load transfer, and a low CNT volume fraction. [10–15] Recently, pure CNT fibers (also called yarns) were reported with and without twisting. [16–22] For example, Zhang et al. [20] demonstrated that spinning from aligned CNT

It is widely known that materials properties are very sensitive to the presence of impurity elements. In this study we performed Rutherford backscattering spectroscopy (RBS) and particle induced X-ray emission (PIXE) analysis of impurity elements in carbon nanotubes (CNTs) fabricated by chemical vapor deposition. Impurities such as O, Si, P, S, Cl, Ar, Ti, Cr and Fe were found. The O was uniformly distributed and the most abundant impurity in CNTs. Sources of contamination were investigated and it was suggested that the presence of Si, S, Cl, Ti and Cr can be eliminated.

Biaxially textured SmxZr1-xOy (SZO) thin films have been grown directly on an ion beam assisted deposited (IBAD) MgO template, without using an intermediate homoepitaxial MgO layer. SZO buffer layers were deposited using reactive magnetron sputtering of a Sm (50 at.%)-Zr (50 at.%) alloy target. The SZO texture is similar to that of the MgO template. Epitaxial YBCO films, ~1mum-thick, grown by pulsed laser deposition on SZO buffered coated conductors have high critical current densities. The in-field measurements indicate that superconducting samples with SZO as buffer are as good as STO/homoepitaxial MgO buffered samples. These results demonstrate that SZO is an appropriate buffer for the fabrication of low cost YBCO/IBAD MgO coated conductors with excellent transport properties.

Ion beam assisted deposition (IBAD) of magnesium oxide (MgO) has been shown to be a viable route for producing biaxially textured template films on flexible polycrystalline metal substrates for high-performance coated conductor development. We have refined the technique of IBAD by using a dual ion assist approach. Dual ion assist beam deposition (DIBAD) of MgO reduces the requirements for substrate surface finishing while maintaining comparable film quality (phi scan full-width at half-maximum values between 7 and 8deg). Furthermore, this adaptation of the IBAD process eliminates the degradation of MgO texture observed in IBAD MgO films deposited on silicon nitride. We have deposited films up to 50 nanometers thick without degradation of the in-plane texture. Increasing the MgO thickness increases the chemical stability of template layer and can eliminate the necessity for subsequent buffer layers or the application of the homoepitaxial MgO layer needed to stabilize the thin, conventional IBAD MgO layer. The initial performance of coated conductors made with DIBAD templates is quite promising.

This study shows that biaxially textured SmxZr1−xOy(SZO) with a wide range of compositions (0.06

Carbon nanotubes (CNTs) are the strongest materials ever discovered by mankind. With measured tensile strengths as high as 150 GPa and a high modulus of 1 TPa, CNTs are very promising for many high-strength, lightweight applications. Several approaches have been reported to process micrometer-long CNTs into fibers, including dispersing CNTs into polymer or acid solutions and then spinning them into composite or pure CNT fibers. Unfortunately, difficulties in CNT dispersion and alignment have hindered the full utilization of CNT strength. Recently, CNT yarns have been directly spun from CNT arrays. This new approach has the advantage of good CNT alignment and high CNT volume fraction, and therefore is very promising for producing higher strength CNTyarns and fibers. So far, CNT fibers can only be spun from CNTarrays that are less than 300 lm long, and this has limited their tensile strengths to only a few hundred MPa. Therefore, it is critical to synthesize spinnable long CNT arrays so that higher strength can be obtained in the spun CNT fibers. Long active growth is the key to growing long CNT arrays. However, during CVD processes using thin Fe catalyst films, the catalysts usually become inactive within several minutes due to either interdiffusion with the substrate or the accumulation of amorphous carbon. In order to achieve sustained growth for long CNT arrays, catalysts like ferrocene have been added continuously or intermittently into the system to nucleate new catalyst particles during the growth. This makes individual CNTs much shorter than the array height. In addition, CNTs synthesized in this way are often thick and dirty with undesirable excessive catalytic particles and amorphous carbon. Alternatively, sustained growth was realized by introducing a thin buffer layer, either Al2O3 [18,19]

We have studied the influence of naturally grown SrTiO3 particles at the buffer layer surface on the in-field critical current density (Jc) dependence of coated conductors. The presence of the SrTiO3 particles induces the growth of extra-correlated pinning along the c-axis direction in the YBa2Cu3O7 films that thread samples as thick as 5 µm. These correlated pinning centres produce a bigger c-axis peak and effectively reduce the Jc magnetic field (H) decay characterized by a smaller exponent α of the power law decay. This method opens up a new approach for how to increase Jc under an applied magnetic field without the need for an extra process. This study brings new meaning to the so-called optimal deposition conditions, since it will depend on the field and temperature region of the application.

The correlation of radiation damage recovery with crystallographic orientation in magnesium oxide (MgO) single crystals during isochronal post-implantation annealing was investigated. Samples of (1 0 0), (1 1 0) and (1 1 1) MgO were implanted with 100 keV Ar+ ions at room temperature and annealed in vacuum at temperatures ranging from 600 to 1300 °C for 3 min. Rutherford backscattering spectrometry combined with ion channeling was used to analyze radiation damage and recovery. The results indicated that the radiation damage was stable up to the annealing temperature of ∼600 °C. At higher annealing temperatures orientation dependent lattice recovery was observed. No complete lattice recovery was achieved, but in (1 1 0) MgO the lattice recovery was more effective than in (1 0 0) and (1 1 1) oriented samples.

Single crystals of magnesia (MgO) and yttria-stabilized zirconia (YSZ) with (1 0 0), (1 1 0) and (1 1 1) orientations were implanted with 100 and 150 keV Ar + ions at room temperature. Rutherford backscattering spectrometry combined with ion channeling (RBS/C) was used to analyze radiation damage. Results showed that there is strong crystallographic orientation dependence for damage accumulation. In both materials, the greatest amount of damage was observed in samples with (1 1 1) orientation and the least in (1 1 0) samples. This variation in the amount of damage may be due to the dynamic annealing rate anisotropy. Such behavior of YSZ and MgO under ion bombardment confirms the damage anisotropy model describing the biaxial texture development in these materials during ion beam assisted deposition (IBAD).

This report describes recent developments of second-generation Y1Ba2Cu3O7−δ (YBCO) coated conductors deposited on biaxially textured MgO templates. The materials system architecture implemented to achieve high critical currents in YBCO films is described. The average full-width at half maximum (FWHM) in-plane texture obtained for MgO films processed on meter-length tapes is 7°, while that for the YBCO films is 3°. The best YBCO in-plane values approach 2° and the out-of-plane values approach 1°. Critical currents (1 cm wide tapes, 75 K, self field) have attained 423 A for 7 cm length and 233 A for 50 cm length tapes.

The diffusion behavior of elements constituting Hastelloy C-276 (C, Si, Mn, Co, W, Fe, Cr, Mo, and Ni) in alumina films was investigated using secondary ion mass spectroscopy. The films were deposited by ion-beam-assisted deposition and annealed in vacuum over a temperature range of 500–1000 °C. Characterization of film microstructure was performed using transmission electron microscopy and selected area diffraction analyses. The films were predominantly amorphous with alumina nanocrystallites nonuniformly dispersed throughout the volume both before and after annealing. A relatively wide interface region between the Hastelloy substrate and alumina film was formed in the as-deposited sample due to ion beam mixing. No diffusion of any of the substrate elements was observed after annealing, except for Mn, Cr, and Ni. The impurity depth distributions consisted of two components, which differed by several orders of magnitude with respect to diffusion coefficient and solubility. Activation energies and temperature dependencies of the diffusion coefficients were determined, and a diffusion mechanism was discussed.

A single LaMnO3 buffer layer was developed for the growth of superconducting thick YBa2Cu3O7−δ (YBCO) films on polycrystalline Ni-alloy substrates where a biaxially textured MgO layer, produced by ion-beam assisted deposition (IBAD), was used as a template. Using pulsed laser deposition, a 1.65-μm-thick YBCO film with a critical current density of 1.4 × 106 A/cm2 in self field at 75 K was achieved on sputtered LaMnO3-buffered IBAD MgO substrates. This corresponds to a critical current (Ic) of 231 A/cm-width. This result demonstrates the possibility of using both LaMnO3 buffer and IBAD MgO template for producing high current density YBCO-coated conductors.

We present our results to improve ion beam assisted deposition (IBAD) of magnesia (MgO) templates for subsequent YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) deposition. The substrate surface roughness has a significant effect on the initial nucleation texture of IBAD MgO films. We have found that reduction in our substrate surface roughness to /spl sim/ 3.5 nm has resulted in better in-plane texture for IBAD MgO films than those deposited on rougher metal substrates. We have further improved the IBAD MgO deposition parameters by using an in situ reflected high-energy electron diffraction (RHEED) analysis tool that allows for monitoring of IBAD MgO growth. We have found a direct correlation between the RHEED generated intensity versus time curve and in-plane texture. Utilizing X-ray diffraction analysis, we have been able to determine the optimum deposition parameters to routinely grow films in batch mode that have a phi scan /spl Delta//spl phi/ from 6 - 7/spl deg/. Coupling the improvements in substrate preparation with optimization of IBAD MgO deposition has allowed for both batch and continuous deposition (termed c-IBAD MgO) on metallic substrates that result in superior superconducting properties. We have demonstrated that deposited meter lengths have had phi scan FWHM values from 8 - 9/spl deg/ with /spl plusmn/ 10% uniformity. Additionally, we have been able to widen the processing zone in our system and coat two, one-meter lengths simultaneously while preserving good texture quality (/spl Delta//spl phi//sub ave/ /spl sim/ 8/spl deg/) and uniformity (60 - 80% of tape length within /spl plusmn/ 5% of /spl Delta//spl phi//sub ave/) for both tapes.

We discuss our recent progress using IBAD MgO as a template for subsequent deposition of YBa 2 Cu 3 O 7− δ (YBCO) high-temperature superconductors on metallic substrate tapes. We have refined the process by improving substrate preparation and by using reflected high-energy electron diffraction to monitor and improve IBAD MgO films. High quality, continuously processed IBAD MgO (c-IBAD) has been deposited on moving meter-length metal tape. By incorporating these optimized processing parameters, we have been able to deposit biaxially textured MgO on metallic substrates continuously with the best in-plane mosaic spreads near 9°. The subsequent pulsed laser deposition of 1–2 μm thick YBCO films on c-IBAD has resulted in superconducting transport critical current densities>1 MA/cm 2 (75 K, SF) on small area samples. Longer 4.5 cm samples of c-IBAD tape have also been coated with a 1 cm wide sample carrying 93 A (75 K, SF) for a 1.5 μm thick YBCO.

Abstract This work summarizes our progress on the development of carbon nanotube (CNT) composite cables for ultra-deepwater oil and gas fields. Near- and long-term intended applications include, for example, more efficient hangar penetrations, sub-sea floor power distribution, and ultra-deepwater dynamic power umbilicals. The project goals are to produce by scalable production methods high-conductivity CNT composite wires that can be wound together to make under sea (and / or in-wellbore) cables. In order to the make practical use of the nanotubes, technologies need to be developed that can deal with or manipulate CNTs in great quantities. For power transmission applications one will need to make dense structures of the CNTs that are aligned simultaneously along the direction of current flow. Also, methodologies that can electrically connect the tubes together in their transverse direction are needed to enable high percolation conductivity though the entire CNT/Metal matrix ensemble. In this work we will summarize our progress towards CNT wire development with descriptions of the wire processing, wire performance, and correlation of performance with structural properties. To date, we have successfully produced wires that display high conductivity values for CNT coatings. Addtionally, these conductors are much lighter compared to pure Cu wires and offer additional advantages for applications needing lightweight materials. Prospects for near and long-term application testing will be discussed.

Nickel-based superalloys have been coated with magnesium oxide (MgO) using ion-beam-assisted deposition (IBAD). This technique produced a well-oriented bi-axially textured MgO template layer with a Ф scan full width half maximum of 6.4°. The layer architecture for these samples was as follows: polished hastelloy C276/amorphous Si3N4/IBAD MgO/ pulsed laser deposited (PLD) Y2O3–ZrO2/PLD CeO2/PLD YBa2Cu3O7?δ. The subsequent heteroepitaxial PLD of 1.5-mm-thick YBCO showed a nominal critical current density of over 1 MA/cm2 (75 K, self-field) along a microbridge and had an in-plane mosaic spread of 4.8° and an out-of-plane spread of 1.3°. These results compare well with our earlier work using IBAD yttria-stabilized zirconia (YSZ) as a template layer and indicate that IBAD MgO is a suitable substitute. Furthermore, these results suggest that IBAD MgO could be adapted to and increase the feasibility of a continuous process to fabricate longer lengths of coated conductors at speeds 100 times faster than that previously realized with IBAD YSZ.

We describe a method using grazing incidence diffractometry (GID) with a rotating anode X-ray source to measure the in-plane alignment of ∼10-nm thick MgO films deposited by ion beam assisted deposition (IBAD). In conjunction with these measurements, we have calibrated the IBAD film growth process by monitoring the film in situ with reflected high-energy electron diffraction and comparing the intensity versus time curve with results obtained from the ex situ GID measurements. GID has also been used to identify differences in the observed in-plane texture for samples with and without the addition of a homoepitaxial layer. Improvements in texture after the addition of the homoepitaxial layer are attributed to the healing of ion induced damage during growth of the IBAD layer. Further analysis has revealed that standard X-ray diffraction measurements of these overcoated films do not sufficiently quantify the in-plane alignment of the initial IBAD layers.

We have examined the effect of film thickness on in-plane texture for ion-beam assisted deposition (IBAD) of MgO films. Plan-view dark-field transmission electron microscopy (TEM) has revealed that texture develops rapidly, reaching its best value at a critical thickness of/spl sim/10 nm. These results have been confirmed by quantifying the in-plane texture of these samples at each thickness with X-ray diffraction /spl phi/-scans. We have also examined the effects of variable deposition rate on texture formation. X-ray diffraction shows that the optimum in-plane texture is achieved at the critical thickness with a rate of 0.2 nm/s. However, TEM imaging has shown that the distribution of well-aligned grains decreases with an increase in rate. As such, deposition at 0.1 nm/s was found to be sufficient for achieving good in-plane distribution values and good surface coverage for subsequent depositions. By combining the results of both of these experiments, we were then able to optimize our deposition process and apply them to the growth of IBAD MgO on metal substrates.

The microstructures of continuously processed YBa/sub 2/Cu/sub 3/O/sub y/ (YBCO) coated conductors processed with three different architectures are presented. YBCO films were deposited directly on ion-beam-assisted deposition (IBAD) yttria-stabilized zirconia (YSZ) or on intervening layers of Y/sub 2/O/sub 3/ or CeO/sub 2/. Different interfacial reactions were observed in each case. The volume changes that occur with the interfacial reactions were calculated based on the identified reaction products. The calculated volume changes correlate with the observed microstructures and appear to be an important factor in determining an optimal buffer layer system. The interfacial reactions do not preclude the attainment of high I/sub c/ and J/sub c/ values in these coated conductors.

Monolithic integration of high quality YBCO films on polycrystalline yttrium-iron-garnet (YIG) substrates represents an advance of great technical significance for magnetically tunable microwave components. We have solved the problems of crystallographic incompatibility between the two materials and the lack of an epitaxial template for the growth of well-oriented YBCO films. Using a buffer layer of biaxially oriented yttria-stabilized zirconia (YSZ), deposited by an ion-beam-assisted-deposition (IBAD) technique, we routinely produced device quality YBCO films on polycrystalline YIG substrates. The YBCO films were c-axis oriented with an in-plane mosaic spread of less than 7/spl deg/ FWHM. The films had transition temperatures above 88 K, transition widths less than 0.3 K, and critical current densities above 10/sup 6/ A/cm/sup 2/ in self-field at 75 K. The surface resistance of the films was /spl sim/0.86 m/spl Omega/ at 10 GHz and 76 K.

A “second-generation” of high Tc conductors, consisting of YBCO coatings on flexible metal substrates, has recently reached a milestone with meter-long tapes capable of carrying over 100 A in a 1 cm width at liquid nitrogen temperature. Having reached this level of performance, however, we have encountered difficulties in the self-field characterization of such high current material. In particular, measurement of critical current uniformity along the tape length has in some cases resulted in damage to weaker tape segments during measurement of higher-current ones. To address this problem we have developed a novel measurement technique that uses permanent magnets to locally suppress the critical current of the tape section being measured to a level that is “safe” for the rest of the tape.

Processes for producing both the yttrium-stabilized zirconia (YSZ) template film by ion beam-assisted deposition (IBAD) and the YBa 2 Cu 3 O x (YBCO) superconducting film by pulsed laser deposition (PLD) at 1-m lengths have achieved I c values of 122 A and J c values of 1 MA/cm 2 . Improvements have been made in all stages of the process. Variations of I c along the length of the 1-m samples stimulated development of a new in-field I c measurement capability. The use of MgO as an IBAD template film has made great progress and can potentially decrease the time to produce the template film by more than an order of magnitude. A combination of electrical and microstructural investigations is being made to understand and improve the properties of the YBCO-coated conductors.

A metal organic chemical vapor deposition (MOCVD) method has been developed to achieve high currents in Y–Ba–Cu–O (YBCO) superconducting films deposited on biaxially textured buffer layers on polycrystalline (untextured) flexible metal substrates. Optimization of the MOCVD process parameters has yielded critical currents ( I c ) greater than 50 A and critical current densities ( J c ) higher than 1 MA/cm 2 at 77 K in self-field conditions. High values of critical currents were found to be maintained also in the presence of a magnetic field. At 75 K, with the magnetic field perpendicular to the c -axis ( B ⊥ c ), J c values of 570,000 A/cm 2 ( I c =20 A) and 240,000 A/cm 2 ( I c =8.5 A) were achieved in fields of 1 and 5 T respectively. With the magnetic field parallel to the c -axis ( B ∥ c ), J c values of 215,000 A/cm 2 ( I c =7.6 A) and 100,000 A/cm 2 ( I c =3.6 A) were achieved in fields of 1 and 2.5 T respectively. At 64 K, the J c values were 1.2 MA/cm 2 ( I c =43 A) and 770,000 A/cm 2 ( I c =27 A) at 2 and 5 T respectively in the B ⊥ c orientation. In the B ∥ c orientation, the J c values were 680,000 A/cm 2 ( I c =23.7 A), 520,000 A/cm 2 ( I c =18.2 A) and 300,000 A/cm 2 ( I c =10.6 A) at 1, 2, and 5 T respectively.

The microstructural development of YBa2Cu3Oy (Y-123) coated conductors based on the ion-beam-assisted deposition (IBAD) of yttria-stabilized zirconia (YSZ) to produce a biaxially textured template is presented. The architecture of the conductors was Y-123/CeO2/IBAD YSZ/Inconel 625. A continuous and passivating Cr2O3 layer forms between the YSZ layer and the Inconel substrate. CeO2 and Y-123 are closely lattice-matched, and misfit strain is accommodated at the YSZ/CeO2 interface. Localized reactions between the Y-123 film and the CeO2 buffer layer result in the formation of BaCeO3, YCuO2, and CuO. The positive volume change that occurs from the interfacial reaction may act as a kinetic barrier that limits the extent of the reaction. Excess copper and yttrium generated by the interfacial reaction appear to diffuse along grain boundaries and intercalate into Y-123 grains as single layers of the Y-247, Y-248, or Y-224 phases. The interfacial reactions do not preclude the attainment of high critical currents (Ic) and current densities (Jc) in these films nor do they affect to any appreciable extent the nucleation and alignment of the Y-123 film.

One meter long tapes based on 50-100 /spl mu/m thick by 1 cm wide nickel alloy substrates have been coated in a continuous process with a textured yttria-stabilized zirconia layer by ion beam-assisted deposition, followed by a 1-2 /spl mu/m thick layer of YBCO by pulsed laser deposition. The best result to date is a tape with a critical current (I/sub c/) at 75 K of 96 A over an 87 cm measurement length. The overall critical current density and engineering current density are 1 MA/cm/sup 2/ and 10 kA/cm/sup 2/, respectively. Using a special probe, individual I-V curves were generated for each centimeter of tape length in order to investigate longitudinal uniformity of the transport properties: the highest and lowest I/sub c/ values fall within a range of /spl plusmn/25%.

In this paper, the role of substrate temperature in the crystalline texture of MgO films grown by ion beam assisted deposition (IBAD) is investigated. This study reveals that the best in-plane alignment for MgO films grown on Y2O3/Si is obtained at ~25??C. At this temperature, MgO films with an in-plane orientation distribution as low as 3.7? full width at half maximum (FWHM) have been attained. MgO films deposited at temperatures higher than 100??C have broad in-plane alignment. Although the deposition at the lowest temperature (?150??C) did not improve the in-plane texture, the acceptable deviation from the optimum ion to molecule ratio for achieving biaxially textured films was the largest. As a trend, the acceptable ion to molecule deviation decreases with increasing substrate temperature. This study is especially important for continuous IBAD MgO depositions where less restrictive conditions are desired.

We measured the thickness dependence of the superconducting properties in epitaxial δ-MoN thin films grown on α-Al2O3(001) substrates by polymer-assisted deposition. Our results indicate that the superconducting properties such as the upper critical field (μ0Hc2 ≈ 10 T) and the superconducting critical temperature (Tc = 12.5 K) are thickness independent for films thicker than ~36 nm. By measuring the critical current density (Jc) in the vortex-free state, which coincides with the depairing current density (J0), we estimate that films thicker than ~36 nm have a coherence length ξ(0) = 5.8 ± 0.2 nm and penetration depth λ(0) = 420 ± 50 nm. We found that it is possible to enhance the Hc2(0) values to close to 10 T without any appreciable reduction in Tc. Fil: Haberkorn, Nestor Fabian. Comision Nacional de Energia Atomica. Gerencia del Area de Investigaciones y Aplicaciones no Nucleares. Gerencia de Fisica (CAB); Argentina Fil: Zhang, Y. Y.. Tsinghua University; China Fil: Kim, Jeehoon. Institute for Basic Science and Department of Physics; Corea del Norte Fil: Mccleskey, Thomas M.. Los Alamos National High Magnetic Field Laboratory; Estados Unidos Fil: Burrell, Anthony K.. Argonne National Laboratory; Estados Unidos Fil: Depaula, R. F.. Los Alamos National High Magnetic Field Laboratory; Estados Unidos Fil: Tajima, T.. Los Alamos National High Magnetic Field Laboratory; Estados Unidos Fil: Jia, Q. X.. Los Alamos National High Magnetic Field Laboratory; Estados Unidos Fil: Civale, Leonardo. Los Alamos National High Magnetic Field Laboratory; Estados Unidos

A coating system for the deposition of in-plane oriented yttria-stabilized zirconia (YSZ) template films on 1 cm wide flexible metal substrates is presented. In static mode, the system is capable of producing high quality template films on 20 cm substrate lengths. In a continuous coating mode, the system is capable of producing good quality template films on 1.1 m substrate lengths. Superconducting YBa 2 Cu 3 O 7− δ (YBCO) films subsequently deposited onto these template films have demonstrated critical currents ( I c ) of 200 A (1.5 cm length), 70 A (12 cm length) and 4 A (1 m length).

We have epitaxially deposited Ba0.6Sr0.4TiO3 (BST) thin films on SiO2∕Si substrates using pulsed laser deposition by introducing biaxially oriented ion-beam-assisted-deposited MgO as templates. The structural properties of the BST films were strongly affected by the crystallinity of the templates. The dielectric loss of the BST film was found to decrease as its in-plane texture alignment was improved. As a result, a relatively larger figure of merit K value, defined as tunability∕loss, was obtained for the films with better in-plane crystallinity. The K factor ranged between 7.5 and 3.5 when the in-plane alignment of the MgO templates was varied from 5.0° to 10.5°. This work demonstrates that the crystalline quality of the template layers plays a critical role in monolithic integration of BST with SiO2∕Si for frequency agile devices.

One of the most intensely researched subjects in the development of YBa2Cu3O7−δ (YBCO)-based coated conductors is the methodology for achieving ever-sharper film texture on flexible metal substrates. This is a critical issue due to the intrinsic weak-link behavior that results in depressed critical current density (Jc) in polycrystalline YBCO. Using ion-beam-assisted deposition of magnesium oxide, we have achieved YBCO texture on superalloy substrates approaching that on single-crystal oxide substrates. This advance has allowed us to fabricate coated conductor samples with Jcs that are as high as for films on oxide crystals; for example, >2 MA/cm2 (75 K, self-field) at a YBCO thickness of ∼1.5 μm.

High J/sub c/YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) films have been fabricated on LaMnO/sub 3/ buffered ion-beam assisted deposition (IBAD) MgO template layers. A LaMnO/sub 3/ buffer layer is compatible with MgO surfaces and also provides a good template for growing high current density YBCO films. LaMnO/sub 3/ buffer layers were deposited using rf magnetron sputtering. On LaMnO/sub 3/-buffered-MgO [100] single crystal substrates, YBCO films with a J/sub c/ of over 4 M/cm/sup 2/ were grown using both pulsed laser deposition (PLD) and ex-situ BaF/sub 2/ process. Using PLD, J/sub c/ of 1.8 MA/cm/sup 2/ at 77 K was obtained on 200-nm-thick YBCO films grown on LaMnO/sub 3/-buffered MgO IBAD/Ni-alloy substrates. In addition, an I/sub c/ of 230 A/cm-width was obtained for 1.65-/spl mu/m-thick YBCO films grown on LaMnO/sub 3/-buffered MgO IBAD/Ni-alloy substrates using PLD at Los Alamos National Laboratory. This performance is comparable to the best single-layer results achieved on IBAD-MgO substrates.

Driven by capillary force, wet carbon nanotube (CNT) arrays have been found to reorganize into cellular structures upon drying. During the reorganization process, individual CNTs are firmly attached to the substrate and have to lie down on the substrate at cell bottoms, forming closed cells. Here we demonstrate that by modifying catalyst structures, the adhesion of CNTs to the substrate can be weakened. Upon drying such CNT arrays, CNTs may slide away from their original sites on the surface and self-assemble into cellular patterns with bottoms open. It is also found that the sliding distance of CNTs increases with array height, and drying millimetre tall arrays leads to the sliding of CNTs over a few hundred micrometres and the eventual self-assembly into discrete islands. By introducing regular vacancies in CNT arrays, CNTs may be manipulated into different patterns.

A compact, high brightness accelerator was designed and fabricated by Los Alamos National Laboratory for use in the Advanced Free Electron Laser (AFEL) Facility. A brazed copper, 1300-MHz, 20-MeV structure is suspended within a thermally insulating vacuum vessel. Integral cooling passages allow introduction of cooling water for normal operation, or liquid nitrogen for cryogenic operation. Its exceptional beam quality is expected to enhance the performance of the FEL experiments planned for the AFEL Facility.

A 2.5 MeV, 428 MHz radio frequency quadrupole (RFQ) linac has been designed and fabricated by the Los Alamos National Laboratory and GAR Electroforming for the Superconducting Super Collider Laboratory. This device is a two segment accelerator fabricated from tellurium-copper (CDA14500) vane/cavity quadrants which are joined by electroforming. The structure incorporates an integral vacuum jacket and has no longitudinal rf or mechanical joints. The SSC RFQ linac is an extension of the design of the 1.0 MeV RFQ which was successfully flown on the BEAR Project.

A 6 MeV, 1300 MHz photocathode linear accelerator (linac) has been designed and fabricated by Los Alamos National Laboratory for The Netherlands Center for Laser Research at the University of Twente in Enschede, The Netherlands. The six-cell photoinjector linac is a brazed copper on-axis coupled structure inside a vacuum jacket with an integral vacuum bakeout system. It is a near duplicate of an accelerator which has been in service at the Los Alamos High Brightness Accelerator Facility since 1989.

YBa/sub 2/Cu/sub 3/O/sub x/ (YBCO) films have been deposited on buffered metal substrates by metal organic chemical-vapor deposition (MOCVD). Nickel alloy substrates with biaxially-textured yttria-stabilized zirconia (YSZ) buffer layers deposited by ion-beam-assisted deposition (IBAD) were used. A liquid-static precursor delivery system was designed, constructed, and used in the MOCVD facility at Intermagnetics for the reported work. At 77 K, under self-field conditions, we achieved a critical current (I/sub c/) of 97.5 A in YBCO film grown by MOCVD on an IBAD substrate. This I/sub c/ corresponds to a critical current density of 1.3 MA/cm/sup 2/ and 130 A/cm width of tape.

We describe our efforts to control the grain boundary alignment in polycrystalline thin films of silicon by using a biaxially textured template layer of CaF2 for photovoltaic device applications. We have chosen CaF2 as a candidate material due to its close lattice match with silicon and its suitability as an ion beam assisted deposition (IBAD) material. We show that the CaF2 aligns biaxially at a thickness of ~10 nm and, with the addition of an epitaxial CaF2 layer, has an in-plane texture of ~15°. Deposition of a subsequent layer of Si aligns on the template layer with an in-plane texture of 10.8°. The additional improvement of in-plane texture is similar to the behavior observed in more fully characterized IBAD materials systems. A germanium buffer layer is used to assist in the epitaxial deposition of Si on CaF2 template layers and single crystal substrates. These experiments confirm that an IBAD template can be used to biaxially orient polycrystalline Si.

Recent efforts in investigating the mechanism of ion beam assisted deposition (IBAD) of biaxially textured thin films of magnesium oxide (MgO) template layers have shown that the texture develops suddenly during the initial 2 nm of deposition. To help understand and tune the behavior during this initial stage, we pre-deposited thin layers of MgO with no ion assist prior to IBAD growth of MgO. We found that biaxial texture develops for pre-deposited thicknesses < 2 nm, and that the thinnest layer tested, at 1 nm, resulted in the best qualitative RHEED image, indicative of good biaxial texture development. The texture developed during IBAD growth on the 1.5 nm pre-deposited layer is slightly worse and IBAD growth on the 2 nm pre-deposited layer produces a fiber texture. Application of these layers on an Al2O3 starting surface, which has been shown to impede texture development, improves the overall quality of the IBAD MgO and has some of the characteristics of a biaxially texture RHEED pattern. It is suggested that the use of thin (2O3 that are currently thought to be required for proper biaxial texture development in IBAD MgO.

Second generation, high-temperature superconducting wires are based on buffered, metallic tape substrates of near single crystal texture. Strong alignment of adjacent grains was found to be necessary from previous work that suggested large angle, YBa2Cu3O7−δ [001]-tilt boundaries reduce Jc exponentially with increasing misorientation angle (θ). We pursue the low-θ regime by evaluating single grain boundaries (GB) and biaxially aligned polycrystalline films utilizing both the rolling-assisted biaxially textured substrates and ion-beam assisted deposition coated conductor architectures. Analysis concludes that an exponential dependence on Jc is applicable for θ≳4°, where the spacing between the periodic disordered regions along the GB become smaller than a coherence length.

The use of an ion beam assist during the concurrent deposition of cubic materials can result in the growth of crystallographically oriented thin films. A model system, magnesium oxide (MgO), has been successfully used as a biaxially textured template film and develops texture in a different manner from that of other well-studied materials, like yttria-stablized zirconia. Here, we present data on the initial nucleation of biaxial texture in this model system using a novel in-situ quartz crystal microbalance (QCM) substrate combined with in-situ reflected high-energy electron diffraction (RHEED). Temporal correlation of mass uptake with the RHEED images of the growing surface can be used to elucidate the mechanism of texture development in these films. Experimental data shows that the initially polycrystalline MgO film develops biaxial crystallographic texture at a thickness of ˜2 nm, regardless of the ion-to-molecule ratio. RHEED images show the onset of texture occurs quickly and is somewhat analogous to a solid phase re-crystallization process with crystallite sizes of ˜3 to 4 nm. Imaging with transmission electron microscopy has corroborated these observations. Changes in the ion-to-molecule ratio can influence the crystallite size and affect the nucleation density of these films. Growth of these films on various substrates changes the sticking coefficient of the MgO and influences the nucleation density and film growth mode as well. This opens the possibility of using MgO and other materials to develop biaxially textured crystallites with a narrow, specified size distribution for nanoscale applications.

High critical current (>100 A) YBCO thick films, or coated conductors, are being developed for superconductor applications. The critical current I/sub c/ of these materials exhibits a magnetic field dependence that depends on the angle of the applied field. Measurement of this anisotropy is critical to the development of high temperature superconductor applications. We have developed the capability to characterize the magnetic field anisotropy of large, high critical current YBCO superconductors as a function of angle. We have measured the magnetic field anisotropy of the critical current in the H/spl perp/I orientation of three samples in fields from 0 to 7 T and at temperatures from 75 K to 64 K. The results of these measurements characterize the field dependence of these materials and reveal performance issues of importance to applications. In contrast to previous measurements on thin films, which show that I/sub c/ for the H/spl par/c orientation has the strongest field dependence, we demonstrate that the intermediate angle of /spl sim/45/spl deg/ to the normal to the tape plane shows the greatest field dependence for these coated conductors on technical substrates. The field performance, anisotropy, and temperature dependence are discussed in relation to sample quality.

We report the results of experiments with ion-beam-assisted deposition (IBAD) of MgO using in-situ monitoring with Reflected High-Energy Electron Diffraction (RHEED). Strips of polished Haynes 242 and Inconel 625 nickel-based super-alloys have been used as substrates for these experiments. The in-plane texture of the MgO, as measured by X-ray /spl phi/ scan, resulted in FWHM values between 11 and 15/spl deg/. Using pulsed-laser deposition, the IBAD MgO template films were then overcoated with buffer layer films and a final superconducting film of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//. The best superconducting transport properties measured on these YBCO films were: an Ic (75 K, self-field, 1 cm wide) of 41.6 A, and a narrow-bridge J/sub c/ (1.35 /spl mu/m thick film) of 0.46 MA/cm/sup 2/.