Ion Beam Assisted Deposition MgO Research Articles

Formation of qualified BaHfO3 doped Y0.5Gd0.5Ba2Cu3O7−δ film on CeO2 buffered IBAD-MgO tape by self-seeding pulsed laser deposition

Improvement in the in-filed transport properties of REBa2Cu3O7−δ (RE = rare earth elements, REBCO) coated conductor is needed to meet the performance requirements for various practical applications, which can be accomplished by introducing artificial pinning centers (APCs), such as second phase dopant. However, with increasing dopant level the critical current density Jc at 77 K in zero applied magnetic field decreases. In this paper, in order to improve Jc we propose a seed layer technique. 5 mol% BaHfO3 (BHO) doped Y0.5Gd0.5Ba2Cu3O7−δ (YGBCO) epilayer with an inserted seed layer was grown on CeO2 buffered ion beam assisted deposition MgO (IBAD-MgO) tape by pulsed laser deposition. The effect of the conditions employed to prepare the seed layer, including tape moving speed and chemical composition, on the quality of 5 mol% BHO doped YGBCO epilayer was systematically investigated by X-ray diffraction (XRD) measurements and scanning electron microscopy (SEM) observations. It was found that all the samples with seed layer have higher Jc (77 K, self-field) than the 5 mol% BHO doped YGBCO film without seed layer. The seed layer could inhibit deterioration of the Jc at 77 K and self-filed. Especially, the self-seed layer (5 mol% BHO doped YGBCO seed layer) was more effective in improving the crystal quality, surface morphology and superconducting performance. At 4.2 K, the 5 mol% BHO doped YGBCO film with 4 nm thick self-seed layer had a very high flux pinning force density Fp of 860 GN/m3 for B//c under a 9 T field, and more importantly, the peak of the Fp curve was not observed.

Ultrathin IBAD MgO films for epitaxial growth on amorphous substrates and sub-50 nm membranes

A fabrication process has been developed for high energy ion beam assisted deposition (IBAD) biaxial texturing of ultrathin (∼1 nm) MgO films, using a high ion-to-atom ratio and post-deposition annealing instead of a homoepitaxial MgO layer. These films serve as the seed layer for epitaxial growth of materials on amorphous substrates such as electron/X-ray transparent membranes or nanocalorimetry devices. Stress measurements and atomic force microscopy of the MgO films reveal decreased stress and surface roughness, while X-ray diffraction of epitaxial overlayers demonstrates the improved crystal quality of films grown epitaxially on IBAD MgO. The process simplifies the synthesis of IBAD MgO, fundamentally solves the “wrinkle” issue induced by the homoepitaxial layer on sub-50 nm membranes, and enables studies of epitaxial materials in electron/X-ray transmission and nanocalorimetry.

High-performance irreversibility field and flux pinning force density in BaHfO3-doped GdBa2Cu3Oy tape prepared by pulsed laser deposition

The high irreversibility field Bi and strong flux pinning force were obtained for BaHfO3-doped GdBa2Cu3Oy tapes on a metallic Hastelloy substrate with an ion beam-assisted deposition MgO buffer layer. At 77.3 K, Bi of 15.8 T and the maximum flux pinning force density of 23.5 GN/m3 for B ∥ c were achieved for the 1.5 vol % BaHfO3-doped GdBa2Cu3Oy tape, which are the world's highest recorded values for REBa2Cu3Oy-coated conductors on metallic substrates (RE = rare earth). From the flux pinning analysis, the c-axis correlated pinning by well-aligned BaHfO3 nanorods plays an important role in achieving the high irreversibility field and flux pinning force density performance.

Germanium films with strong in-plane and out-of-plane texture on flexible, randomly textured metal substrates

High efficiencies have been achieved in photovoltaic cells based on III–V compounds grown on single crystal germanium substrates. Since the size of these substrates is limited and their cost is very high, such III–V photovoltaics have not found widespread terrestrial use. The objective of this work is to develop highly textured, epitaxial germanium thin films on inexpensive substrates suitable for roll-to-roll continuous processing to serve as templates for III–V compounds. Germanium films with a high degree of in-plane and out-of plane texture have been demonstrated on randomly textured, flexible nickel alloy substrates by epitaxial growth on template films made by ion beam-assisted deposition (IBAD). In order to achieve epitaxial growth, an intermediate layer of CeO 2 was found to be required between the IBAD MgO template and the Ge film. Our study shows that structural match between Ge and the underlying oxide layer is the key to epitaxial growth. Room temperature optical bandgap of the Ge films was identified at 0.67 eV suggesting minimal residual strain in the film. Refraction index and extinction coefficient values of the epitaxial Ge film were found to match well with that measured from a reference Ge single crystal.

Composite ${\rm Y}_{2}{\rm O}_{3}-{\rm Al}_{2}{\rm O}_{3}$ as Diffusion Barrier/Nucleation Layer for HTS Coated Conductors Based on IBAD MgO

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.

High Yield and High Throughput Reactive IBAD MgO Process for Long-length, HTS Wire Production at SuperPower

AbstractSuperPower's IBAD (ion beam assisted deposition) MgO process has been changed to reactive ion beam sputtering of Mg metal target instead of MgO ceramic target, which gives ∼ 60 % increase in deposition rate. The process speed was increased from 195 m/h to 360 m/h. Texture of IBAD MgO tapes by this reactive process was found to degrade faster during long length run. This uniform issue was resolved with feedback control during long run and from run to run. The bottleneck of alumina layer process due to slow ion beam sputtering deposition was removed by new high rate reactive magnetron sputtering at transition mode. The new alumina process speed can be as high as 3,000 m/h in our Pilot Buffer system. The yttria layer process was also changed to high rate reactive magnetron sputtering at transition mode with achievable speed as high as 10,000 m/h in our Pilot Buffer system. The routine production speed of alumina and yttria is 750 m/h due to limitation of tape driving system. The high rate magnetron-sputtered alumina/yttria yields the same texture of IBAD MgO as ion beam sputtered alumina/yttria. Now we are routinely producing IBAD MgO template tapes of ∼ 1.4 km with a uniform in-plane texture ∼ 6-7 degrees. Record high critical current of 813 A/cm over a one meter length and a world record critical current times length value of > 233,8100A-m was obtained with our routinely-produced high throughput IBAD MgO buffers. The requirements for a better IBAD texturing layer than IBAD MgO are also suggested.

High Throughput Processing of Long-Length IBAD MgO and Epi-Buffer Templates at SuperPower

SuperPower has successfully transferred from low throughput IBAD (Ion beam assisted deposition) YSZ technology to high throughput IBAD MgO technology. Pilot-scale IBAD system and pilot-scale epi-buffer deposition system, each with capabilities of producing single-piece lengths over 1000 m have been established. Helix tape handling approach instead of wide tape approach is chosen due to its immense advantages over wide tape approach. High-performance IBAD MgO buffer stack and their processes have been developed together with high throughput where each layer in the buffer stack is processed at 40 m/h tape speed or higher during our Phase I scale up. Both pilot systems are in routine production mode since March 2006. More than 14 km IBAD MgO buffer tapes of 12 mm width were produced for Albany cable project. 700-800 m IBAD MgO tape per run is routinely produced in pilot IBAD system with single piece tape length ~570 m. 400-550 m epi-buffer tape per run is routinely produced in pilot buffer system. High throughput IBAD MgO buffer gives better texture of YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> (YBCO) film compared with IBAD YSZ, and superior superconducting properties. A high critical current of 557 A/cm in short tapes and a world record critical current times length value of > 70, 000 A - m were obtained with the high throughput IBAD MgO buffers.

Progress in scale-up of second-generation HTS conductor

Tremendous progress has been recently made in the achievement of high-performance, high-speed, long-length second-generation (2G) HTS conductors. Using ion beam assisted deposition (IBAD) MgO and metal organic chemical vapor deposition (MOCVD), SuperPower has scaled up tape lengths to 427m with a minimum critical current value of 191A/cm corresponding to a critical current×length performance of 81,550m. Tape speeds up to 120m/h have been reached with IBAD MgO, up to 80m/h with buffer deposition and up to 45m/h with MOCVD, all in single pass processing of 12mm wide tape. Critical current value of 227A/cm has been achieved in a 203m long tape produced in an all-high-speed fabrication process. Critical current values have been raised to 721A/cm, 592A/cm and 486A/cm in short, reel-to-reel processed tape, over 1m length and over 11.1m, respectively, using thicker MOCVD HTS films. Finally, over 10,000m of copper-stabilized, 4mm wide conductor has been produced and tested for delivery to the Albany Cable project. The average critical current of the 10,000m lot was 81A.

Engineered reactive cosputtered SmxZr1–xOythin films as buffer layers for YBa2Cu3O7−δcoated conductors

This study shows that biaxially textured SmxZr1−xOy(SZO) with a wide range of compositions (0.06 &lt;x&lt; 0.75) can be grown directly on ion-beam-assisted deposition (IBAD) MgO template using reactive cosputtering. The SZO crystal structure can be changed, and the lattice parameter can be tailored (from 5.23 to 5.49 Å) by changing the composition. We have developed a simplified high-temperature superconducting coated conductor using SZO as the buffer layer. YBa2Cu3O7−δ(YBCO) films grown by pulsed laser deposition on the SZO buffered IBAD MgO have self-field critical current densities (Jc) in the 2–4 MA/cm2range. The in-field measurements demonstrate that high-quality YBCO films can be grown on SZO buffered IBAD MgO. The present results are especially important because they were obtained on coated conductors with the simpler architecture by eliminating the additional homoepitaxial layer of MgO. This translates in faster production and lower manufacturing cost.

Effect of substrate temperature on the texture of MgO films grown by ion beam assisteddeposition

In this paper, the role of substrate temperature in the crystalline textureof MgO films grown by ion beam assisted deposition (IBAD) is investigated.This study reveals that the best in-plane alignment for MgO films grown onY2O3/Si isobtained at ∼25 °C. At this temperature, MgO films with an in-plane orientation distribution as low as3.7° fullwidth at half maximum (FWHM) have been attained. MgO films deposited at temperatures higherthan 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 tomolecule ratio for achieving biaxially textured films was the largest. As a trend, theacceptable ion to molecule deviation decreases with increasing substrate temperature. Thisstudy is especially important for continuous IBAD MgO depositions where less restrictiveconditions are desired.

Influence of tilted geometries on critical current in superconducting thin films

We present measurements of the angular dependent critical current (J/sub c/) of DyBa/sub 2/Cu/sub 3/O/sub 7/ on single crystal SrTiO/sub 3/ and YBa/sub 2/Cu/sub 3/O/sub 7/ on tilted Ion Beam Assisted Deposition MgO substrate. These experiments demonstrate that J/sub c/ angular dependences of tilted defects are a useful tool to detect misalignments between the internal and applied magnetic fields. The results show that, in order to understand vortex pinning in thin anisotropic samples below certain value of magnetic field, this misalignment must be taken into account.

Influence of the Substrate Temperature on the Texture of MgO Films Grown by Ion Beam Assisted Deposition

AbstractThe variation in the substrate temperature during ion beam assisted deposition (IBAD), which employs the use of energetic ions to bombard a growing film, has been shown to influence the quality of crystalline texture in MgO films. Determining the acceptable deviation from the optimum ion to molecule ratio for different substrate temperatures establishes the optimum MgO deposition conditions. For each fixed deposition temperature, a set of samples was produced by varying the ion assist beam current from sample to sample while keeping the deposition rate constant. In this way, the ion to molecule ratio was modified and the range of achieving well textured films was determined. The investigation of the MgO texture dependence on the substrate temperature reveals that the best in-plane alignment is obtained at ˜ 25°C. At this temperature, MgO films with 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 is especially important for continuous IBAD MgO depositions where less restrictive conditions are desired.

Influence of crystalline texture on vortex pinning near the ab-plane in YBa 2Cu 3O 7 thin films and coated conductors

We present a study of the sharp peak that develops near the ab-plane orientation in the angular dependent critical current of YBa 2Cu 3O 7 (YBCO) films. This peak arises from correlated pinning associated to intrinsic pinning by the layered structure of the YBCO, and from extended planar defects. We measure films produced by pulsed laser deposition (PLD) and metal organic deposition (MOD) on ion beam assisted deposition––MgO, and by PLD on single crystalline substrates. We show that the width and height of the peak increases with the out-of-plane mosaic spread of the films. We discuss the implications of the different structures (columnar and laminar respectively) of the PLD and MOD films.

Growth of thick Yba2Cu3O7−δ films carrying a critical current of over 230 A/cm on single LaMnO3-buffered ion-beam assisted deposition MgO substrates

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.

Reflection high-energy electron diffraction experimental analysis of polycrystalline MgO films with grain size and orientation distributions

Analysis of biaxial texture of MgO films grown by ion-beam-assisted deposition (IBAD) has been performed using a quantitative reflection high-energy electron diffraction (RHEED) based method. MgO biaxial texture is determined by analysis of diffraction spot shapes from single RHEED images, and by measuring the width of RHEED in-plane rocking curves for MgO films grown on amorphous Si3N4 by IBAD using 750 eV Ar+ ions, at 45° incidence angle, and MgO e-beam evaporation. RHEED-based biaxial texture measurement accuracy is verified by comparison with in-plane and out-of-plane orientation distribution measurements made using transmission electron microscopy and x-ray rocking curves. In situ RHEED measurements also enable the analysis of the evolution of the biaxial texture which narrows with increasing film thickness. RHEED-based measurements of IBAD MgO biaxial texture show that the minimum in-plane orientation distribution depends on the out-of-plane orientation distribution, and indicates that the minimum obtainable in-plane orientation on distribution is 2°.

Role of SrRuO3 buffer layers on the superconducting properties of YBa2Cu3O7 films grown on polycrystalline metal alloy using a biaxially oriented MgO template

A SrRuO3 (SRO) buffer layer has been developed for growth of superconducting YBa2Cu3O7 (YBCO) thick films on polycrystalline metal substrates where a biaxially oriented MgO layer—produced by ion-beam-assisted deposition (IBAD)—was used as a template. By using such an architecture, we have routinely deposited YBCO films with an in-plane mosaic spread in the range of 3°–6° in full width at half maximum. A critical current density of 3.0×106 A/cm2 in self-field at 75 K for a film thickness of over 1.3 μm has been achieved. We believe that the SRO buffer layer plays a significant role in the much improved performance of YBCO conductors built on IBAD MgO. The features of SRO, such as good lattice match with both MgO and YBCO, excellent thermal stability in an oxidizing environment, and planarization of growing surface, make it the ideal choice as the buffer layer for high-performance superconductor coatings.

Ultra-thin bi-axially textured IBAD MgO template layers resolved by grazing incidence X-ray diffraction

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.

Texture development in IBAD MgO films as a function of deposition thickness and rate

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.

Ion-beam Assisted Deposition of MgO with in situ RHEED Monitoring to Control Bi-axial Texture

ABSTRACTWe have studied the growth of magnesium oxide using ion-beam assisted deposition (IBAD) to achieve (100) oriented, bi-axially textured films with low mosaic spread, for film thicknesses of 10 nm on silicon substrates. We have refined the process by using reflected high-energy electron diffraction (RHEED) to monitor the growth of IBAD MgO films and found that the diffracted intensity can be used to determine (and ultimately control) final in-plane texture of the film. Here we present results on our work to develop the use of real-time RHEED monitoring to deposit well-oriented IBAD MgO films. The results have been corroborated with extensive grazing-incidence X-ray diffraction (GID). Results of these analyses have allowed us to deposit films on metallic substrates with in-plane mosaic spread less than 7°.

Ion-beam assisted deposition of bi-axially aligned MgO template films for YBCO coated conductors

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/.