Search Menu
DOE PAGES title logo U.S. Department of Energy
Office of Scientific and Technical Information
Search Scholarly Publications

22 Search Results

Sorted by Relevance
Save Results
...

  1. Molecular Beam Epitaxy Growth of IrO2 Using Plasma-Only Oxidation

    Sacksteder, D. ; Dahl, S. ; Dorsey, J. ; ... - APL Materials
    Growth of IrO2 films via molecular beam epitaxy (MBE) using an oxygen plasma as the sole oxidant is demonstrated for the first time. We investigate the oxidizing conditions required for IrO2 by characterizing the species present in the plasma using optical emission spectroscopy and comparing the thermodynamic equilibrium between Ir/IrO2 under atomic and molecular oxygen. Across the pressure range accessible, monatomic oxygen was the primary reactive species present in the plasma. IrO2 films were grown under varying Ir flux, oxygen pressure, and substrate temperature to understand growth thermodynamics and kinetics. Structural characterization assessed film phase and composition, crystallinity, strain, andmore » surface morphology. The optimized films from this study validate plasma-only reactive growth by MBE as a successful method for growing IrO2.« less

  2. High-Power Impulse Magnetron Sputter Deposition of Ultrathick Amorphous Carbon

    Engwall-Holmes, A. M. ; Bayu Aji, L. B. ; Shin, S. J. ; ... - Fusion Science and Technology
    Diamond-like carbon (DLC) is a material of interest for inertial confinement fusion (ICF) ablators. However, the deposition of ultrathick DLC coatings, as required for ICF ablator fabrication, remains a challenge. Here, in this study, we use high-power impulse magnetron sputtering to deposit DLC and demonstrate a set of process parameters leading to high-purity, amorphous DLC coatings with a low compressive residual stress of <400 MPa. Coatings with thicknesses of up to 80 μm are demonstrated.

  3. Low leakage current in heteroepitaxial Al 0.7 Sc 0.3 N ferroelectric films on Ga N

    Yazawa, Keisuke ; Evans, Charles ; Dickey, Elizabeth C. ; ... - Physical Review Applied
    Wurtzite ( Al , Sc ) N ferroelectrics are attractive for microelectronics applications due to their chemical and structural compatibility with wurtzite semiconductors, such as Ga N and ( Al , Ga ) N . However, the leakage current in epitaxial stacks reported to date should be reduced for reliable device operation. Here, we demonstrate low leakage current in epitaxial Al 0.7 Sc 0.3 N filmsmore » on Ga N with well-saturated ferroelectric hysteresis loops that are orders of magnitude lower (i.e., 0.07 A cm − 2 ) than previously reported films (1–19 A cm − 2 ) having similar or better structural characteristics. We also show that, for these high-quality epitaxial ( Al , Sc ) N films, structural quality (edge and screw dislocations), as measured by diffraction techniques, is not the dominant contributor to leakage. Instead, the small leakage in our films is limited by thermionic emission across the interfaces, which is distinct from the large leakage due to trap-mediated bulk transport in the previously reported ( Al , Sc ) N films. To support this conclusion, we show that Al 0.7 Sc 0.3 N on lattice-matched In 0.18 Ga 0.82 N buffers with improved structural characteristics but higher interface roughness exhibit increased leakage characteristics. This demonstration of low leakage current in heteroepitaxial ( Al , Sc ) N films and understanding of the importance of interface barrier and surface roughness can guide further efforts toward improving the reliability of wurtzite ferroelectric devices. Published by the American Physical Society 2025« less

  4. Construction of a New MgB2 Coating System for 1.3-GHz Superconducting RF Cavities at LANL

    Tajima, T. ; Civale, L. ; Grumstrup, T. P. ; ... - IEEE Transactions on Applied Superconductivity
    After many years of evaluating MgB 2 films prepared with various techniques for the application to superconducting radio-frequency (SRF) cavities, we have decided to build a system to coat full-size 1.3-GHz elliptical cavities. This paper describes the design and construction of the system. Additionally, we briefly describe experimental results with a small system and first tests with the new large system. In conclusion, we were able to obtain superconducting samples with a T c of up to 38 K with the small system, but we have not been able to get any superconducting samples with the new system yet.

  5. Epitaxial Electrodeposition of Wide Bandgap Cuprous Bromide on Silver via a Silver Bromide Buffer Layer

    Luo, Bin ; Zhang, Xiaoting ; Tubbesing, John Z. ; ... - Journal of the Electrochemical Society
    Cuprous halides are an important class of wide bandgap p-type semiconductors used in opto-electronics. Cuprous bromide (CuBr) shows potential for short-wavelength devices due to a large exciton binding energy (108 meV) and near-ultraviolet bandgap (3.1 eV). However, the growth of high-quality epitaxial CuBr films by electrodeposition has remained a challenge. Here, we introduce a low-cost electrochemical procedure for producing epitaxial CuBr(111) on a Ag(111) substrate by a [111]-oriented silver bromide (AgBr) buffer layer. The AgBr buffer layer forms during the electrodeposition of the CuBr. The mismatch between CuBr(111) and AgBr(111) is –1.3%. A plausible mechanism for nucleation and growth ofmore » the epitaxial CuBr is proposed. X-ray techniques including high resolution X-ray diffraction and X-ray pole figures are used to determine the epitaxial relationship. CuBr(100) is also produced on a Ag(100) surface by a AgBr(100) buffer layer that is rotated in-plane 45° relative to the Ag(100) surface. In conclusion, this in-plane rotation reduces the lattice mismatch from +39.5% for an unrotated film to –1.4% for a 45° rotated film.« less

  6. Pseudocapacitive Charge Storage in Electrochromic Transition-Metal Oxide Thin Films

    Dong, Dongmei ; DeForest, Tinsley Benhaddouch ; Metler, Christopher Lloyd ; ... - Journal of the Electrochemical Society
    Electrochromic pseudocapacitive transition-metal oxide materials, such as tungsten oxide, which combine fast response, high energy density, and optical effects, can play a significant role as energy storage materials. Here we investigate the electrochemical kinetics of thin films of tungsten oxide, which turn transparent to sky-blue color in the lithiated state due to the reduction of W6+ to W5+. In this study, we investigated the charge density, charge transfer, ion diffusion, and interfacial behavior upon Li+ insertion/de-insertion in WO3. The electrochromic thin film's pseudocapacitive and electrical double layer mechanism was differentiated based on the power-law. Faradaic diffusion-controlled process dominates over themore » surface capacitive behavior at scan rates below 40 mV s–1. These films exhibit an areal charge density of around 100 mC cm–2 and a capacitance of 80 mF cm–2, superior to most comparable electrochromic materials and supercapacitors. This work combines electrochromics and energy storage properties and provides a fundamental understanding of pseudocapacitive and electrochromic mechanisms in WO3.« less

  7. Crystalline Orientation–Dependent Spin Hall Effect in Epitaxial Platinum

    Xiao, Yuxuan ; Wang, Hailong ; Fullerton, Eric E. - Frontiers in Physics
    We report on the spin Hall effect in epitaxial Pt films with well-defined crystalline (200), (220), and (111) orientations and smooth surfaces. The magnitude of the spin Hall effect has been determined by spin–torque ferromagnetic resonance measurements on epitaxial Pt/Py heterostructures. We observed a 54% enhancement of the charge-to-spin conversion efficiency of the epitaxial Pt when currents are applied along the in-plane <002> direction. Temperature-dependent harmonic measurements on epitaxial Pt/Co/Ni heterostructures compared to a polycrystalline Pt/Co/Ni suggest the extrinsic mechanism underlying spin Hall effect in epitaxial Pt. Our work contributes to the development of energy-efficient spintronic devices by engineering themore » crystalline anisotropy of non-magnetic metals.« less

  8. Epitaxial Thin Films of a Chalcogenide Perovskite

    Surendran, Mythili ; Chen, Huandong ; Zhao, Boyang ; ... - Chemistry of Materials
    Chalcogenide perovskites have emerged as a new class of optoelectronic materials, especially for photovoltaic applications, but fundamental properties and applications of chalcogenide perovskites remain limited due to the lack of high-quality thin films. In this paper, we report direct epitaxial thin film growth of BaZrS3, a prototypical chalcogenide, by pulsed laser deposition. X-ray diffraction studies show that the films are strongly textured out-of-plane and have a clear in-plane epitaxial relationship with the substrate. Electron microscopy studies confirm the presence of epitaxy for the first few layers of the film at the interface, even though away from the interface, the filmsmore » are polycrystalline with many extended defects, suggesting the potential for further improvement in growth. X-ray reflectivity and atomic force microscopy show smooth film surfaces and interfaces between the substrate and the film. The films show strong light absorption near the band edge and photoluminescence in the visible region, validating BaZrS3 as a suitable candidate for ultrathin front absorbers in tandem solar cells. The photodetector devices show fast and efficient photo response with the highest ON/OFF ratio reported for BaZrS3 films thus far. Our study opens up opportunities to use high quality thin films of chalcogenide perovskites to probe fundamental physical phenomena in thin films and heterostructures and also in photovoltaic and optoelectronic applications.« less

  9. Scale Up of High-Performance REBCO Tapes in a Pilot-Scale Advanced MOCVD Tool With In-Line 2D-XRD System

    Chen, Siwei ; Majkic, Goran ; Jain, Rohit ; ... - IEEE Transactions on Applied Superconductivity
    We have reported the development of an Advanced Metal-Organic Chemical Vapor Deposition (AMOCVD) method featuring ohmic heating of the substrate for REBCO film growth, direct tape temperature monitoring, and laminar precursor flow. This A-MOCVD method has been used to fabricate 4 – 5 m thick film REBCO tapes with record high performance: critical currents exceeding 8700 A/12 mm at 30 K, 3 T; and engineering current density of 5200 A/mm2 at 4.2 K, 15 T. Recently, we constructed a pilot-scale reel-to-reel A-MOCVD system to scale up the technology to long tapes. Preliminary batches of tapes exhibit consistent performance and goodmore » uniformity along the length. An in-line 2D X-ray Diffraction (XRD) system has been integrated into the pilot A-MOCVD tool to monitor the REBCO texture and composition, RE2O3 content, and the dimensions of BaMO3 (BMO, M=Zr,Hf) nanorods that act as artificial pinning centers. Specifically, the streaking angle between REBCO (103) and BZO (101) has been found to correlate well with (Ba+M)/Cu of the film, lift factor in critical current over a range of temperatures and magnetic fields, and the size of the BMO nanorods. Furthermore, the in-line 2D-XRD is expected to serve as a valuable quality measuring tool supporting realtime feedback control for the process to yield uniform and consistent manufacturing of high performance REBCO tapes by Advanced MOCVD.« less

  10. Electrochemically active surface area controls HER activity for FexNi100–x films in alkaline electrolyte

    Bakovic, Sergio I. Perez ; Acharya, Prashant ; Watkins, Morgan ; ... - Journal of Catalysis
    We report the synthesis and electrocatalytic activity of FexNi100-x electrochemically deposited films were investigated. Films were evaluated for the hydrogen evolution reaction (HER) in alkaline media with respect to composition and electrochemically active surface area (ECSA). Results demonstrate that films of higher or equal Fe content had an ECSA tenfold greater than films with higher Ni. When normalized by geometric surface area, Fe50Ni50 films required the lowest overpotential of -390 mV to reach a current density of -10 mA cm-2. However, when normalized by the ECSA, intrinsic HER activity increases as Ni content increases. Tafel slope, ECSA, microscopy, and impedancemore » spectroscopy analyses allow a decoupled analysis of surface area versus activity effects on overall measured HER activity. Furthermore, these analyses collectively demonstrate that the increase in electrocatalytic activity is attributed to the increase in ECSA and not to an enhancement in the intrinsic activity by Fe and Ni component interactions.« less
...
Search for:
All Records
Subject
epitaxial thin films
Refine by:
Article Type
Availability
Journal
more less
Creator / Author
more less
Publication Date
Research Organization
more less