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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Fabrication and efficiency measurement of a Mo/C/Si/C three material system multilayer Laue lens

In this letter we report on the manufacturing of a multilayer Laue lens (MLL) consisting of a multilayer stack with three materials: molybdenum and silicon as absorber and spacer layer, respectively, and carbon as transition layers. The design has four layers per period: Mo/C/Si/C. It yields 6000 zones, and provides an aperture of 50 μm. This allows the MLL structure to accept a large portion of the coherent part of the beam and achieving a small spot size. The MLL deposition was made by magnetron sputtering at the Fraunhofer IWS, the sectioning was done by laser cutting and subsequent focused ion beam milling to a thickness that provides a good efficiency for a photon energy of 12 keV. The diffraction efficiency as a function of the tilting angle has been measured at beamline 1-BM of the Advanced Photon Source. An efficiency of almost 40% has been achieved. This shows that the material system performs well compared to MLLs made of two-materials and that it is in an excellent agreement with the numerically calculated efficiency for a comparable molybdenum/silicon bilayer system lens. Here, we conclude that the three material system offers high efficiencies and is advantageous for stress reduction in MLLs.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Generation and stability of structurally imprinted target skyrmions in magnetic multilayers

In this work, Target Skyrmions (TSks) are extended topological spin textures with a constant chirality where the rotation of the z component of the magnetization is larger than π. TSks have topological charge 1 or 0, if the z component of the magnetization M z goes through a rotation of nπwhere n is an odd or even integer, respectively. TSks with a rotation of the z component of up to 4πhave been imaged via high spatial resolution element-specific X-ray imaging. The TSks were generated by weakly coupling 30 nm thin Permalloy (Ni 80 Fe 20 , PY) disks with a 1 μm diameter to asymmetric (Ir 1 nm/Co 1.5 nm/Pt 1 nm) × 7 multilayers that exhibit Dzyaloshinskii-Moriya interaction. The PY disks stabilize the TSks in the multilayers due to reduced stray field energy and enforced circular symmetry from pinning of domain walls at the edges of the disks. Upon applying external magnetic fields, it is the skyrmion core at the center that ensures stability of the TSk, whereas the collapse of the extended structures in the TSk does not depend on the topological charge.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

On the redistribution of charge in La 0.7 Sr 0.3 CrO 3 /La 0.7 Sr 0.3 MnO 3 multilayer thin films

The atomic and electronic structures of La 0.7 Sr 0.3 MnO 3 (LSMO)/La 0.7 Sr 0.3 CrO 3 (LSCO) multilayer thin films are investigated using aberration corrected scanning transmission electron microscopy (STEM) imaging and spectroscopy. Atomic resolution high angle annular dark-field reveals that LSMO layers have an expanded out-of-plane lattice parameter compared to compressed LSCO layers, contrasting with x-ray diffraction measurements. The expansion is found to result from preferential oxygen vacancy formation in LSMO during STEM sample preparation as determined by electron energy-loss spectroscopy. The La/Sr atom column intensity is also found to oscillate by about 4% between the LSMO and LSCO layers, indicative of La/Sr concentration variation. Using energy-dispersive x-ray spectroscopy in combination with image simulations, we confirm the La/Sr inhomogeneity and elucidate the origin of charge redistribution within the multilayer. These results illuminate the sensitivity of the technique to subtle structural, chemical, and electronic features that can arise to compensate charge imbalances in complex oxide heterostructures.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Thermal shock resistance of multilayer silicon carbide receiver tubes for 800°C molten salt concentrating solar power application

CSP power tower receiver systems during rapid transient weather periods can be vulnerable to thermal shock conditions from rain that which can facilitate the onset of leaks and failures that can have catastrophic consequences. Silicon carbide (SiC) materials have attractive receiver application characteristics for being light weight, having high-strength and excellent thermal shock resistance performance which make them a particularly good fit for receiver absorber materials in CSP. In this investigation, the performance characteristics of Ceramic Tubular Products (CTP) SiC ceramic matrix composite (CMC), multilayered tubes were explored with respect to thermal shock performance for solar receiver applications in next generation CSP plants. Here, thermal shock testing was performed at the Sandia National Laboratories (SNL) Solar Furnace facility using a dynamic stage and thermal shock tube test setup. The tubes tested under incident solar heat flux of 100 W/cm2 were heated with inner tube temperatures reaching approximately 800 °C, with outer temperatures exceeding or just reaching 1000 El for the multilayer and monolithic SiC tubes respectively. The tubes were then quenched with simulated rain. The tubes were then cooled and subjected to hoop stress analysis using an Instron device to assess their subsequent mechanical strength. Furthermore, the on-sun study experimental results indicate an average of 24.2% and 97% higher hoop strength for the CMC tubes than those composed of monolithic SiC and aluminum oxide (A1203) respectively.

14 SOLAR ENERGY↗
DOE OSTI2022

Enhanced electrical conductivity in graphene–copper multilayer composite

For many years, researchers have been trying to make a material more conductive than silver by incorporating carbon nanotubes or graphene into copper to form a composite material. However, after a decade-long effort, only a few groups reported successful results, raising concerns about the feasibility of this composite approach. Here, we report our effort to validate the multilayer graphene–copper composite approach for improving electrical conductivity. We demonstrate that, with an estimated 0.008 vol. % graphene addition, copper’s electrical conductivity was improved to 104.2% of International Annealed Copper Standard (IACS) at room temperature. If the copper substrate used to make the multilayer composite is discounted using the parallel resistance model, the conductivity is calculated to be 185% IACS. This result could be further improved if the thickness of the copper layers can be further reduced.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Gate-tunable modulation of the optical properties of multilayer graphene by the reversible intercalation of ionic liquid anions

We demonstrate a substantial modulation of the optical properties of multilayer graphene (~100 layers) using a simple device consisting of a multilayer graphene/polymer electrolyte membrane/gold film stack. Applying a voltage of 3–4 V drives the intercalation of anion [TFSI] - [ion liquid diethylmethyl(2-methoxyethyl)ammonium bis(trifluoromethylsulfonyl)imide [DEME][TFSI]] resulting in the reversible modulation of the properties of this optically dense material. Upon intercalation, we observe an abrupt shift of 35 cm -1 in the G band Raman mode, an abrupt increase in FTIR reflectance over the wavelength range from 1.67 to 5 $μ$m (2000–6000 cm -1 ), and an abrupt increase in luminescent background observed in the Raman spectra of graphene. Furthermore, all of these abrupt changes in the optical properties of this material arise from the intercalation of the TFSI - ion and the associated change in the free carrier density (Δ$n$ = 10 20 cm -3 ). Suppression of the 2D band Raman mode observed around 3 V corresponds to Pauli blocking of the double resonance Raman process and indicates a modulation of the Fermi energy of Δ$E$ F = 1.1 eV.

42 ENGINEERING↗
DOE OSTI2022

Nanomechanical and tribological properties of nickel–chromium multilayer coating on Inconel 617

Multilayer coatings of Ni and Cr were deposited onto Inconel 617, and multi-scale physical properties were characterized using high temperature tribological experiments, nanoindentation, and microscratch. The effect of high temperature aging (950 °C under helium environment) on two different Ni/Cr multilayer coatings with individual layer thicknesses of 50 and 200 nm denoted by Ni/Cr(50) and Ni/Cr(200) was investigated. Nanoindentation of original coatings showed a hardness of 6 GPa that increases to 14 GPa for both samples once aged. Microscratch results support the macro-tribology results where Ni/Cr(50) (without aging) was the only delaminated coating with significant wear. Additionally, aging in both cases reduced the in situ coefficient of friction and wear. Cross-section energy dispersive spectrometry confirmed that the aged oxide layer was two to three times thicker than the original coating. In conclusion, an abundance of chromium oxide was found in the main body of the coatings, which led to higher hardness and better wear resistance.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Design and simulation of multilayer coatings for a multi-channel Wolter-like x-ray imager with large field of view and high resolution

X-ray diagnostics are key instruments for understanding the physics behind inertial confinement fusion experiments. We report on the multilayer design optimization for the Toroidal X-ray Imager (TXI), a hard x-rays microscope instrument designed by Commissariat à l’énergie atomique (CEA) and Laboratoire Charles Fabry (LCF) to be installed on the National Ignition Facility. TXI includes six channels designed for three different energy bands centered on 8.7, 13, and 17.5 keV. Each channel is made up of two toroidal mirrors arranged in a Wolter-like configuration. The required field of view is 800 × 400 µm2, and the resolution should be better than 5 µm. In addition, we seek to estimate the spatial distribution of the temperature, which requires no spectral overlap of the different energy bands and a good spectral homogeneity of the image produced. The development of the multilayer coatings was performed in a two-step method. First, the coatings were optimized to obtain proper energy bands. Then, an x-ray tracing code was used to calculate the integrated optical response of each channel and adjust the response of the mirror to fulfill the requirements. To fulfill all the specifications, we propose an original design using a combination of two aperiodic coatings, one with a narrow bandwidth and the other one with a larger bandwidth.

hard x-rays↗
DOE OSTI2012

Aperiodic multilayer structures in soft X-ray radiation optics

We review the works related to the development of aperiodic multilayer structures - optical elements for the soft X-ray range. The potentialities of aperiodic multilayer mirrors as regards reflection of soft X-ray radiation in a broad wavelength range, first and foremost at normal radiation incidence, as well as the capabilities of broadband polariser mirrors are investigated. The results of multiparametric optimisation and experimental results for Mo/Si aperiodic mirrors ({lambda} {>=} 12.5 nm) as well as calculations for several promising material pairs (Pd/Y, Ag/Y, etc.) for {lambda} {<=} 12.5 nm are outlined. The effect of transition layers on the reflectivity is considered, in particular by taking into account the smooth variation of the permittivity near interfacial boundaries. The use of broadband mirrors in laser-plasma spectroscopic experiments is discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Investigation of optical properties of multilayer dielectric structures using prism-coupling technique

A method based on resonant excitation of waveguide modes with a prism coupler is proposed for measuring the thickness and refractive index of thin-film layers in multilayer dielectric structures. The peculiarities of reflection of TE- and TM-polarised light beams from a structure comprising eleven alternating layers of zinc sulfide (ZnS) and magnesium barium fluoride (MgBaF{sub 4}), whose thicknesses are much less than the wavelength of light, are investigated. Using the mathematical model developed, we have calculated the coefficients of reflection of collimated TE and TM light beams from a multilayer structure and determined the optical constants and thicknesses of the structure layers. The refractive indices of the layers, obtained for TE and TM polarisation of incident light, are in good agreement. The thicknesses of ZnS and MgBaF{sub 4} layers, found for different polarisations, coincide with an accuracy of ±1%. Thus, we have demonstrated for the first time that the prism-coupling technique allows one to determine the optical properties of thin-film structures when the number of layers in the structure exceeds ten layers. (integrated optics)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Optical Elements: Effect of structural defects of aperiodic multilayer mirrors on the properties of reflected (sub)femtosecond pulses

The effect of structural defects (for example, of interlayer roughness, layer thickness fluctuations and departures of Mo film density from the tabular one) on the amplitude and phase of the complex reflection coefficient as well as on the amplitude and duration of reflected pulses is numerically studied by the example of a model aperiodic Mo/Si multilayer mirror intended for the compression of a chirped pulse with a spectrum lying in a 50 – 80 eV photon energy range. The departures of Mo film density from the tabular values and film thickness fluctuations are shown to exert the strongest effect on the amplitude and duration of the reflected pulses. The interlayer roughness has a comparable effect on the amplitude of the reflection coefficient, but its effect on the duration of reflected pulses is weaker. Even small film thickness fluctuations may give rise to additional reflected pulses of high intensity, which are delayed in time relative to the principal pulse. The Mo-film density in a Mo/Si mirror is shown to vary from 0.77 to 0.97 (in units of the tabular value for massive molybdenum) as the film thickness varies from 1.5 to 5.5 nm. We discuss the key problems that have to be solved in the development of the fabrication technology of multilayer mirrors with desired characteristics. (paper)

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Spectral characterisation of aperiodic normal-incidence Sb/B{sub 4}C multilayer mirrors for the λ < 124 Å range

Three broadband aperiodic Sb/B{sub 4}C multilayer mirrors were synthesised for the purposes of soft X-ray optics and spectroscopy in the wavelength range beyond the L-edge of Si (λ < 124 Å), and their reflection spectra were measured. The multilayer structures were optimised for maximum uniform reflectivity in the ranges 100 – 120 Å, 95 – 105 Å and 90 – 100 Å. The reflection spectra were recorded using a laboratory laser-plasma radiation source and an electronic detector with a 2D spatial resolution (a CCD matrix with 13 × 13 μm sized pixels). The experimental spectra are compared with theoretical calculations. The effect of lower antimony and B{sub 4}C layer densities on the reflection spectra is discussed. (invited paper)

36 MATERIALS SCIENCE↗
DOE OSTI2018

Optical nonlinear properties and dynamics of interband transitions in multilayer MoS{sub 2} structures under femtosecond excitation at a wavelength of 514 nm

The optical nonlinear absorption and bleaching of aqueous suspensions of multilayer MoS{sub 2} sheets (structural modification 2H) under excitation by a 400-fs pulse at a wavelength of 514 nm is investigated using longitudinal scanning. The sample exhibits nonlinear absorption at intensities up to 15 GW cm{sup −2}, while a further increase in intensity to 70 GW cm{sup −2} causes nonlinear bleaching with a relative change in transmission to 14 %. The dynamics of interband transitions in the picosecond range is studied by femtosecond laser photolysis. The relaxation time of photoexcited excitons is measured to be 20 ± 2 ps. The transition dynamics is calculated in the three-level approximation, and the absorption cross sections of photoinduced electron transitions from the valence band to the conduction band and from the first to the second conduction band are estimated. It is shown that the optical nonlinear properties of suspensions of multilayer 2H MoS{sub 2} sheets are mainly determined by the dynamics of single-photon interband transitions. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Numerical simulation of the divergence and optical confinement factor of a semiconductor laser with an asymmetric periodic multilayer AlGaInAs/InP waveguide

The divergence and optical confinement factor of a semiconductor laser with an asymmetric periodic (multilayer) waveguide are numerically simulated. The reasons for the choice of the given heterostructure design are explained, and the consequences of choosing other layer structures are considered. It is shown how to choose the active waveguide thickness, the active region position on the waveguide, and the multilayer waveguide grating period. (lasers)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Design and fabrication of a high-density multilayer metal-insulator-metal capacitor based on selective etching

This paper presents a novel and cost-effective method for fabricating high-density multilayer metal-insulator-metal (MIM) integrated capacitors. To eliminate the usage of numerous photolithography steps when parallel stacking multiple capacitors layers, a unique process has been developed based on depositing the MIM layers onto a substrate with two protruding pillars, polishing down the pillars to expose the multilayer cross sections and then selectively etching the metal layers on each pillar to form the alternating capacitor plate electrodes. For demonstration purpose, only capacitors with two dielectric layers were fabricated, and the measurement results were verified by a compact analytical model together with finite element simulations. With 200 nm thick silicon nitride/oxide dielectric layers, a capacitance density of 0.6 fF mu m(-2) was achieved, which can be easily increased by scaling down the layer thicknesses and/or stacking more layers. A low equivalent series resistance (ESR) of 300-700 m Omega was measured, and the self-resonance frequency was above measurement limits (> 100 MHz). Further design optimization shows that the ESR can be reduced to below 80 m Omega, while the operation frequency extended to above 2.6 GHz.

Tseng, VFG↗
DOE OSTI2025

Positron stopping in multilayer materials

Positron annihilation spectroscopy provides a sensitive toolset for defect characterization. In beam based studies of single-layer targets, the form of implantation profiles is well established, depending on the kinetic energy and angle of incident positrons relative to the target surface and the density and average atomic number of the target. For multilayer systems, the difference in density and across the layers makes derivation of an analytical form difficult. To date, the determination of positron stopping profiles in multilayer targets has primarily involved Monte Carlo simulations. We present here an alternative approach that estimates the energy distribution dN/dE of those positrons transmitted past each layer boundary, by fitting the remaining tail of the stopping profile after each layer with a basis set comprised of calculated stopping profiles in the same material they are transmitted through. The stopping profile in the next layer is then found by summing a series of stopping profiles in the new medium in proportion to the determined distribution dN/dE. The results of our model are compared with simulation results in a system of alternating layers of Al and Au and find reasonable agreement in the predicted profile and excellent agreement in the predicted mean implantation depth. Finally, we derived a simple formula-based approach for the calculation of the mean implantation depth in two-layer systems that provides results in excellent agreement with the full model.

Jones, A. C. L. [Arizona State University, Tempe, ↗
DOE OSTI2020

Effect of layer thickness on structural, morphological and superconducting properties of Nb 3 Sn films fabricated by multilayer sequential sputtering

Superconducting Nb3Sn films can be synthesized by controlling atomic concentration of Sn. Multilayer sequential sputtering of Nb and Sn thin films followed by high temperature annealing is considered as a method to fabricate Nb3Sn films where Sn composition of deposited films can be controlled by controlling the thickness of alternating Nb and Sn layers. We report on the structural, morphological and superconducting properties of Nb3Sn films fabricated by multilayer sequential sputtering of Nb and Sn films on sapphire substrates with ex-situ annealing at 950 °C for 3 h. We have investigated the effect of Nb and Sn layer thickness on the properties of Nb3Sn films. The thicknesses of Nb and Sn layers were varied in two ways: (1) varied Nb:Sn thickness ratio (1:1, 2:1, 3:1, 4:1), and (2) varied layer thickness of both Nb and Sn layers, while keeping constant Nb:Sn thickness ratio of 2:1. The crystal structure, surface morphology, topography, and film composition were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and energy dispersive X-ray spectroscopy (EDS) respectively. The results showed Sn loss from the surface due to evaporation during annealing. Superconducting Nb3Sn films of critical temperature up to 17.93 K have been achieved.

Sayeed, M. N.↗
DOE OSTI2020

Landau quantization of multilayer graphene on a Haldane sphere

Here, we consider the problem of multilayer graphene on a Haldane sphere and determine the Landau level spectrum for this family of systems. This serves as a generalization of the Landau quantization problem of ordinary nonrelativistic Haldane sphere and spherical graphene, or Dirac-like particles on a sphere. The Hamiltonian is diagonalized in a concise algebraic fashion exploiting two mutually commuting SU(2) algebras of the problem. Additionally, using exact wave functions we demonstrate computation of Haldane pseudopotentials in the second Landau level. These exact solutions add to the current toolkits of the numerical studies on fractional quantum Hall effects in systems of graphite multilayers.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗