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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 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Interlayer coupling in Fe/Cr/Gd multilayer structures

The effect of the chromium layer thickness on the magnetic state of an [Fe/Cr/Gd/Cr]{sub n} multilayer structure is studied. A series of Fe/Cr/Gd structures with Cr spacer thicknesses of 4–30 Å is studied by SQUID magnetometry and ferromagnetic resonance in the temperature range 4.2–300 K. The obtained experimental results are described in terms of an effective field model, which takes into account a biquadratic contribution to the interlayer coupling energy and a nonuniform magnetization distribution inside the gadolinium layer (which was detected earlier). Depending on the magnetic field and temperature, the following types of magnetic ordering are identified at various chromium layer thicknesses: ferromagnetic, antiferromagnetic, and canted ordering. A comparison of the experimental and calculated curves allowed us to determine the dependence of the bilinear (J{sub 1}) and biquadratic (J{sub 2}) exchange constants on chromium layer thickness t{sub Cr}. Weak oscillations at a period of about 18 Å are detected in the J{sub 1}(t{sub Cr}) dependence in the range 8–30 Å. The interlayer coupling oscillations in the system under study are assumed to be related to the RKKY exchange interaction mechanism via the conduction electrons of Cr.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Multilayer Semiconductor Charged-Particle Spectrometers for Accelerator Experiments

The current state of studies in the field of development of multilayer semiconductor systems (semiconductor detector (SCD) telescopes), which allow the energy to be precisely measured within a large dynamic range (from a few to a few hundred MeV) and the particles to be identified in a wide mass range (from pions to multiply charged nuclear fragments), is presented. The techniques for manufacturing the SCD telescopes from silicon and high-purity germanium are described. The issues of measuring characteristics of the constructed detectors and their impact on the energy resolution of the SCD telescopes and on the quality of the experimental data are considered. Much attention is given to the use of the constructed semiconductor devices in experimental studies at accelerators of PNPI (Gatchina), LANL (Los Alamos) and CELSIUS (Uppsala).

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

Thermal evolution of the morphology, structure, and optical properties of multilayer nanoperiodic systems produced by the vacuum evaporation of SiO and SiO{sub 2}

The alternate vacuum evaporation of SiO and SiO{sub 2} from separate sources is used to produce amorphous a-SiO{sub x}/SiO{sub 2} multilayer nanoperiodic structures with periods of 5-10 nm and a number of layers of up to 64. The effect of annealing at temperatures T{sub a} = 500-1100 Degree-Sign C on the structural and optical properties of the nanostructures is studied. The results of transmission electron microscopy of the samples annealed at 1100 Degree-Sign C indicate the annealing-induced formation of vertically ordered quasiperiodic arrays of Si nanocrystals, whose dimensions are comparable to the a-SiO{sub x}-layer thickness in the initial nanostructures. The nanostructures annealed at 1100 Degree-Sign C exhibit size-dependent photoluminescence in the wavelength range 750-830 nm corresponding to Si nanocrystals. The data on infrared absorption and Raman scattering show that the thermal evolution of structural and phase state of the SiO{sub x} layers with increasing annealing temperature proceeds through the formation of amorphous Si nanoinclusions with the subsequent formation and growth of Si nanocrystals.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Synchrotron study of the formation of nanoclusters in Al{sub 2}O{sub 3}/SiO{sub x}/Al{sub 2}O{sub 3}/SiO{sub x}/ Horizontal-Ellipsis /Si(100) multilayer nanostructures

Al{sub 2}O{sub 3}/SiO{sub x}/Al{sub 2}O{sub 3}/SiO{sub x}/ Horizontal-Ellipsis /Si(100) multilayer nanoperiodic structures (MNS) are studied by X-ray absorption near-edge structure spectroscopy (XANES). Experimental XANES spectroscopy spectra are obtained using synchrotron radiation. The formation of Si nanoclusters in the surface layers of the structures during their high-temperature annealing is observed. The structures featured intense size-dependent photoluminescence in the wavelength region near 800 nm. At the same time, it is shown that the formation of aluminum silicates is possible. The inversion effect of the intensity of the XANES spectra during the interaction of synchrotron radiation with MNSs is revealed.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Time-resolved photoluminescence from self-assembled Ge(Si) islands in multilayer SiGe/Si and SiGe/SOI structures

The results of a study of the spectral and temporal characteristics of the photoluminescence (PL) from multilayer structures with self-assembled Ge(Si) islands grown on silicon and 'silicon-on-insulator' substrates in relation to temperature and the excitation-light wavelength are presented. A substantial increase in island-related PL intensity is observed for structures with Ge(Si) islands grown on silicon substrates upon an increase in temperature from 4 to 70 K. This increase is due to the diffusion of nonequilibrium carriers from the silicon substrate into the active layer with the islands. In this case, a slow component with a characteristic time of {approx}100 ns appears in the PL rise kinetics. At the same time, no slow component in the PL rise kinetics and no rise in the PL intensity with increasing temperature are observed for structures grown on 'silicon-on-insulator' substrates, in which the active layer with the islands is insulated from the silicon substrate. It is found that absorption of the excitation light in the islands and SiGe wetting layers mainly contributes to the excitation of the PL signal from the islands under sub-bandgap optical pump conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Study of multilayered SiGe semiconductor structures by X-ray diffractometry, grazing-incidence X-ray reflectometry, and secondary-ion mass spectrometry

In this publication, we report the results of studying a multilayerd nonperiodic SiGe/Si structure by the methods of X-ray diffractometry, grazing-angle X-ray reflectometry, and secondary-ion mass spectrometry (SIMS). Special attention is paid to the processing of the component distribution profile using the SIMS method and to consideration of the most significant experimental distortions introduced by this method. A method for processing the measured composition distribution profile with subsequent consideration of the influence of matrix effects, variation in the etching rate, and remnants of ion sputtering is suggested. The results of such processing are compared with a structure model obtained upon combined analysis of X-ray diffractometry and grazing-angle reflectometry data. Good agreement between the results is established. It is shown that the combined use of independent techniques makes it possible to improve the methods of secondary-ion mass spectrometry and grazing-incidence reflectometry as applied to an analysis of multilayered heteroepitaxial structures (to increase the accuracy and informativity of these methods)

36 MATERIALS SCIENCE↗
DOE OSTI2015

Formation of Si nanocrystals in multilayered nanoperiodic Al{sub 2}O{sub 3}/SiO{sub x}/Al{sub 2}O{sub 3}/SiO{sub x}/.../Si(100) structures: Synchrotron and photoluminescence data

The results of X-ray absorption near-edge structure spectroscopy data obtained with synchrotron radiation for multilayered nanoperiodic Al{sub 2}O{sub 3}/SiO{sub x}/Al{sub 2}O{sub 3}/SiO{sub x}/.../Si(100) structures annealed at temperatures of 500–1100°C are reported. The data show that, upon high-temperature annealing (∼1100°C), the structures are modified. The modification is attributed to the formation of Si nanocrystals in deep layers of the structures. At the same time, the structures exhibit size-dependent high-intensity photoluminescence in the photon-energy range 1.4–1.52 eV.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Optical phonons in PbTe/CdTe multilayer heterostructures

The infrared reflection spectra of PbTe/CdTe multilayer nanostructures grown by molecular-beam epitaxy are measured in the frequency range of 20–5000 cm{sup −1} at room temperature. The thicknesses and high-frequency dielectric constants of the PbTe and CdTe layers and the frequencies of the transverse optical (TO) phonons in these structures are determined from dispersion analysis of the spectra. It is found that the samples under study are characterized by two TO phonon frequencies, equal to 28 and 47 cm{sup −1}. The first frequency is close to that of TO phonons in bulk PbTe, and the second is assigned to the optical mode in structurally distorted interface layers. The Raman-scattering spectra upon excitation with the radiation of an Ar{sup +} laser at 514.5 nm are measured at room and liquid-nitrogen temperatures. The weak line at 106 cm{sup −1} observed in these spectra is attributed to longitudinal optical phonons in the interface layers.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Multilayer photosensitive structures based on porous silicon and rare-earth-element compounds: Study of spectral characteristics

The spectral characteristics of the specular reflectance, photosensitivity, and photoluminescence (PL) of multilayer structures based on porous silicon with rare-earth-element (REE) ions are investigated. It is shown that the photosensitivity of these structures in the wavelength range of 0.4–1.0 μm is higher than in structures free of REEs. The structures with Er{sup 3+} ions exhibit a luminescence response at room temperature in the spectral range from 1.1 to 1.7 μm. The PL spectrum of the erbium impurity is characterized by a fine line structure, which is determined by the splitting of the {sup 4}I{sub 15/2} multiplet of the Er{sup 3+} ion. It is shown that the structures with a porous layer on the working surface have a much lower reflectance in the entire spectral range under study (0.2–1.0 μm).

36 MATERIALS SCIENCE↗
DOE OSTI2018

Optical Properties of Multilayered Sol–Gel Zinc-Oxide Films

Study of structural, optical and photocatalytic properties of multilayered (1–8 layers) zinc oxide films deposited on glass substrates by sol-gel method showed, that after thermal treatment at 500°C they consist of random oriented hexagonal crystalline grains with size of 34–40 nm, forming larger particles with sizes of 100–150 nm, which do not depend on number of layers. With an increase in the number of layers, the intensity of exciton photoluminescence decreases by a factor of 10, the absorption of light in the visible and near IR ranges increases, and the efficiency of photocatalytic decomposition of the test organic dye rhodamine B increases by 10–12%. The observed changes are related to the increase in the total area of grain boundaries and to the change in the integral amount of oxygen vacancies and interstitial atoms as the number of layers increases, which makes it possible to control the properties of zinc oxide films for applications in optoelectronics, photovoltaics and photocatalysis.

36 MATERIALS SCIENCE↗
DOE OSTI2019

On the Combined Application of Raman Spectroscopy and Photoluminescence Spectroscopy for the Diagnostics of Multilayer Heterostructures

The results of studying GaInAs/GaInP/GaAs photodiode structures grown by metal–organic vapor-phase epitaxy are reported. A procedure for the diagnostics of such multilayer structures is developed. The procedure is based on the application of Raman spectroscopy in combination with photoluminescence spectroscopy in the mode of the lateral scanning of transverse cleavages. The compositions of the GaInAs and GaInP solid solutions are determined.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Structural and Magnetic Characteristics of Nanogranular Co–Al{sub 2}O{sub 3} Single- and Multilayer Films Formed by the Solid-State Synthesis

The results of structural and magnetic investigations of nanogranular Co–Al{sub 2}O{sub 3} films formed from Co{sub 3}O{sub 4}/Al thin-film layered structures upon vacuum annealing are reported. The Co{sub 3}O{sub 4}/Al films have been obtained by sequential reactive magnetron sputtering of a metallic cobalt target in a medium consisting of the Ar + O{sub 2} gas mixture and magnetron sputtering of an aluminum target in the pure argon atmosphere. It is shown that such a technique makes it possible to obtain nanogranular Co–Al{sub 2}O{sub 3} single- and multilayer thin films with a well-controlled size of magnetic grains and their distribution over the film thickness.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Formation of a Domain Structure in Multilayer CoPt Films by Magnetic Probe of an Atomic Force Microscope

Abstract—A possibility of changing the magnetic type structure of multilayer CoPt films under action of the magnetic field of the atomic force microscope probe is demonstrated. A new method of non-contact magnetic-force measurements based on artificial increase in the electrostatic interaction between the probe and the film is proposed. This method enables one to controllably change the distance between a probe and a film, thus changing the strength of the magnetic interaction. Using it, one can create from a uniformly magnetized state both a labyrinth domain structure and isolated domains, which are apparently magnetic skyrmions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Influence of Beryllium Barrier Layers on the Properties of Mo/Si Multilayer Mirrors

The performance of multilayer Mo/Si mirrors with B{sub 4}C and Be spacers near a wavelength of 13.5 nm has been studied. It has been shown that four-component Mo/Be/Si/B{sub 4}C mirrors outperform Mo/Si and Mo/Si/B{sub 4}C mirrors in reflection coefficient by 2.0 and 1.3%, respectively. In addition, Mo/Si mirrors offer the widest transmission band width at half maximum (Δλ{sub 1/2} = 0.535 nm). An explanation for these findings has been given.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Evaluation of the SEI using a multilayer spectroscopic ellipsometry model

A multilayer spectroscopic ellipsometry (SE) model has been developed to characterize SEI formation. The model, which consists of two Cauchy layers, is constructed with an inner layer meant to model primarily inorganic compounds adjacent to an electrode and an outer layer which mirrors polymeric, organic constituents on the exterior of the SEI. Comparison of 1:1 EC:EMC and 1:4 EC:EMC with 1.0 M LiPF₆ shows distinct differences in the two modeled layers. The data suggest that the thickness of both layers change over a wide potential range. These changes have been linked with other reports on the growth of the SEI.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Femtosecond-laser–induced modifications in Co/Pt multilayers studied with tabletop resonant magnetic scattering

We characterize the magnetic domain structure of Co/Pt multilayer fi lms on length scales below one hundred nanometers using resonant magnetic scattering and magnetic force microscopy. The extreme ultraviolet light for the scattering experiment is created by a laser- based high-order harmonic generation source. After illumination with intense ultrashort laser pulses, we observe pronounced changes in the magnetic structure and morphology. Furthermore, this study points out the importance of a detailed analysis of the different laser-induced modifications of a magnetic thin fi lm that influence the scattering patterns.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Quantitative analysis of multilayer organization of proteins and RNA in nuclear speckles at super resolution

Nuclear speckles are self-assembled organelles composed of RNAs and proteins. They are proposed to act as structural domains that control distinct steps in gene expression, including transcription, splicing and mRNA export. Earlier studies identified differential localization of a few components within the speckles. It was speculated that the spatial organization of speckle components might contribute directly to the order of operations that coordinate distinct processes. Here, by performing multi-color structured illumination microscopy, we characterized the multilayer organization of speckles at a higher resolution. We found that SON and SC35 (also known as SRSF2) localize to the central region of the speckle, whereas MALAT1 and small nuclear (sn)RNAs are enriched at the speckle periphery. Coarse-grained simulations indicate that the non-random organization arises due to the interplay between favorable sequence-encoded intermolecular interactions of speckle-resident proteins and RNAs. Finally, we observe positive correlation between the total amount of RNA present within a speckle and the speckle size. These results imply that speckle size may be regulated to accommodate RNA accumulation and processing. Accumulation of RNA from various actively transcribed speckle-associated genes could contribute to the observed speckle size variations within a single cell.

Fei, Jingyi↗
DOE OSTI2013

Improving the performance of high-laser-damage-threshold, multilayer dielectric pulse-compression gratings through low-temperature chemical cleaning

A low-temperature chemical cleaning approach has been developed to improve the performance of multilayer dielectric pulse-compressor gratings for use in the OMEGA EP laser system. X-ray photoelectron spectroscopy results guided the selection of targeted cleaning steps to strip specific families of manufacturing residues without damaging the grating's fragile 3D profile. Grating coupons that were cleaned using the optimized method consistently met OMEGA EP requirements on diffraction efficiency and 1054 nm laser-damage resistance at 10 ps. The disappearance of laser-conditioning effects for the highest-damage-threshold samples suggests a transition from a contamination-driven laser-damage mechanism to defect-driven damage for well-cleaned components.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗