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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Multi-range free-electron laser with a pair of dielectric multilayer mirrors

We report the experimental achievement of a free-electron laser in three wavelength regions, mid-infrared, near-infrared, and visible, using a pair of dielectric multilayer mirrors in the storage ring NIJI-IV. Dielectric multilayer mirrors can have high reflectivity at wavelength regions corresponding to higher-diffraction orders of the target wavelength. A narrowing of the relative bandwidth of the dielectric multilayer mirrors was observed in the higher-diffraction orders of the target wavelength and was found to be caused by high diffraction and carbon contamination. Our experimental results will be applied to development of a multi-rang laser that have a gain in a wade wavelength region.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

Phase constitution and interface structure of nano-sized Ag-Cu/AlN multilayers: Experiment and ab initio modeling

Nano-sized Ag-Cu{sub 8nm}/AlN{sub 10nm} multilayers were deposited by reactive DC sputtering on {alpha}-Al{sub 2}O{sub 3}(0001) substrates. Investigation of the phase constitution and interface structure of the multilayers evidences a phase separation of the alloy sublayers into nanosized grains of Ag and Cu. The interfaces between the Ag grains and the quasi-single-crystalline AlN sublayers are semi-coherent, whereas the corresponding Cu/AlN interfaces are incoherent. The orientation relationship between Ag and AlN is constant throughout the entire multilayer stack. These observations are consistent with atomistic models of the interfaces as obtained by ab initio calculations.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Spin transport parameters in metallic multilayers determined by ferromagnetic resonance measurements of spin-pumping

We measured spin-transport in nonferromagnetic (NM) metallic multilayers from the contribution to damping due to spin pumping from a ferromagnetic Co{sub 90}Fe{sub 10} thin film. The multilayer stack consisted of NM{sub 1}/NM{sub 2}/Co{sub 90}Fe{sub 10}(2 nm)/NM{sub 2}/NM{sub 3} with varying NM materials and thicknesses. Using conventional theory for one-dimensional diffusive spin transport in metals, we show that the effective damping due to spin pumping can be strongly affected by the spin transport properties of each NM in the multilayer, which permits the use of damping measurements to accurately determine the spin transport properties of the various NM layers in the full five-layer stack. We find that due to its high electrical resistivity, amorphous Ta is a poor spin conductor, in spite of a short spin-diffusion length of 1.0 nm, and that Pt is an excellent spin conductor by virtue of its low electrical resistivity and a spin diffusion length of only 0.5 nm. Spin Hall effect measurements may have underestimated the spin Hall angle in Pt by assuming a much longer spin diffusion length.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Deformation-induced nanoscale mixing reactions in Cu/Ni and Ag/Pd multilayers

During the repeated cold rolling of Cu/Ni and Ag/Pd multilayers, a solid solution forms at the interfaces as nanoscale layer structure with a composition that replicates the overall multilayer composition. The interfacial mixing behavior was investigated by means of X-ray diffraction and scanning transmission electron microscopy. During deformation induced reaction, the intermixing behavior of the Cu/Ni and Ag/Pd multilayers is in contrast to thermally activated diffusion behavior. This distinct behavior can provide new kinetic pathways and offer opportunities for microstructure control that cannot be achieved by thermal processing.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Tailoring dielectric properties of ferroelectric-dielectric multilayers

We develop a nonlinear thermodynamic model for multilayer ferroelectric heterostructures that takes into account electrostatic and electromechanical interactions between layers. We concentrate on the effect of relative layer fractions and in-plane thermal stresses on dielectric properties of Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3}-, BaTiO{sub 3}-, and PbZr{sub 0.2}Ti{sub 0.8}O{sub 3} (PZT)-SrTiO{sub 3} (STO) multilayers on Si and c-sapphire. We show that dielectric properties of such multilayers can be significantly enhanced by tailoring the growth/processing temperature and the STO layer fraction. Our computations show that large tunabilities (∼90% at 400 kV/cm) are possible in carefully designed barium strontium titanate-STO and PZT-STO even on Si for which there exist substantially large in-plane strains.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Multilayered gold/silica nanoparticulate bilayer devices using layer-by-layer self organisation for flexible bending and pressure sensing applications

A pressure and bending sensor was fabricated using multilayer thin films fabricated on a flexible substrate based on layer-by-layer self-organization of 18 nm gold nanoparticles separated by a dielectric layer of 30 nm silica nanoparticles. 50, 75, and 100 gold-silica bi-layered films were deposited and the device characteristics were studied. A threshold voltage was required for electron conduction which increases from 2.4 V for 50 bi-layers to 3.3 V for 100 bi-layers. Upon bending of the device up to about 52°, the threshold voltage and slope of the I-V curves change linearly. Electrical characterization of the multilayer films was carried out under ambient conditions with different pressures and bending angles in the direct current mode. This study demonstrates that the developed multilayer thin films can be used as pressure as well as bending sensing applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Quantitative analysis of electron energy loss spectra and modelling of optical properties of multilayer systems for extreme ultraviolet radiation regime

Ruthenium capped multilayer coatings for use in the extreme ultraviolet (EUV) radiation regime have manifold applications in science and industry. Although the Ru cap shall protect the reflecting multilayers, the surface of the heterostructures suffers from contamination issues and surface degradation. In order to get a better understanding of the effects of these impurities on the optical parameters, reflection electron energy loss spectroscopy (REELS) measurements of contaminated and H cleaned Ru multilayer coatings were taken at various primary electron beam energies. Experiments conducted at low primary beam energies between 100 eV and 1000 eV are very surface sensitive due to the short inelastic mean free path of the electrons in this energy range. Therefore, influences of the surface condition on the above mentioned characteristics can be appraised. In this paper, it can be shown that carbon and oxide impurities on the mirror surface decrease the transmission of the Ru cap by about 0.75% and the overall reflectance of the device is impaired as the main share of the non-transmitted EUV light is absorbed in the contamination layer.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Induced spin-polarization of EuS at room temperature in Ni/EuS multilayers

Ni/EuS multilayers with excellent multilayer sequencing are deposited via e-beam evaporation on the native oxide of Si(100) wafers at 4 × 10{sup −9} millibars. The samples have very small surface and interface roughness and show sharp interfaces. Ni layers are nanocrystalline 4–8 nm thick and EuS layers are 2–4 nm thick and are either amorphous or nanocrystalline. Unlike for Co/EuS multilayers, all Eu ions are in divalent (ferromagnetic) state. We show a direct antiferromagnetic coupling between EuS and Ni layers. At room temperature, the EuS layers are spin-polarized due to the proximity of Ni. Therefore, Ni/EuS is a candidate for room-temperature spintronics applications.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Dual anisotropic character in Fe/Pt multilayer grown on (001) MgO substrate

The multilayers of [Fe(5Å)/Pt(25 Å)]{sub ×15} were prepared by dc magnetron sputtering on 50 Å Pt-buffered MgO substrates. The structural characterization of the multilayers was carried out using X-ray diffraction, X-ray reflectivity. The Secondary ion mass spectroscopy measurement reveals the depth profile and compositional modulations of the multilayer films as per our design specifications. Room temperature magnetic measurements were carried out by using SQUID both in-plane and out-of-plane sample geometry. Magnetization measurements show similar M-H loops for both in-plane and out-of-plane directions of external magnetic field with a coercivity of 190 Oe. These measurements indicate that our samples are magnetically soft and have multifunctional character which is important for making magnetic tunnel junctions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Operation of ohmic Ti/Al/Pt/Au multilayer contacts to GaN at 600 °C in air

The high-temperature characteristics (at 600 °C) of Ti/Al/Pt/Au multilayer contacts to gallium nitride (GaN) in air are reported. Microfabricated circular-transfer-line-method test structures were subject to 10 h of thermal storage at 600 °C. Intermittent electrical characterization during thermal storage showed minimal variation in the contact resistance after 2 h and that the specific contact resistivity remained on the order of 10{sup −5} Ω-cm{sup 2}. In addition, the thermally stored multilayer contacts to GaN showed ohmic I-V characteristics when electrically probed at 600 °C. The microstructural analysis with atomic force microscopy showed minimal changes in surface roughness after thermal storage. Observations of the thermochemical reactions after thermal storage using Auger electron spectroscopy chemical depth profiling showed diffusion of Pt and minimal additional Al oxidation. The results support the use of Ti/Al/Pt/Au multilayer metallization for GaN-based sensors and electronic devices that will operate within a high-temperature and oxidizing ambient.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Interfacial electronic structure-modulated magnetic anisotropy in Ta/CoFeB/MgO/Ta multilayers

We have observed several unexpected phenomena when a trace amount of Fe atoms is deposited onto the CoFeB/MgO interface in Ta/CoFeB/MgO/Ta multilayers. With the nominal thickness of the introduced Fe atoms (t{sub Fe}) varying from 0 to 0.1 Å, the effective magnetic anisotropy energy (K{sub eff}) of annealed multilayers is remarkably enhanced from 1.28 × 10{sup 6 }erg/cm{sup 3} to 2.14 × 10{sup 6 }erg/cm{sup 3}. As t{sub Fe} further increasing, the K{sub eff} decreases and even becomes negative when t{sub Fe} > 1 Å, indicating the change from perpendicular magnetic anisotropy to in-plane magnetic anisotropy. The analysis by X-ray photoelectron spectrometer reveals that the Fe atoms at annealed CoFeB/MgO interface show different electronic structures as t{sub Fe} increasing, which combine with O atoms to form FeO{sub x} (x < 1), Fe{sub 2}O{sub 3}, and Fe{sub 3}O{sub 4}, respectively, leading to modulation of Fe 3d-O 2p orbital hybridization and thus the K{sub eff}. On the other hand, we find that the introduction of Fe atoms also helps to reduce the multilayers' magnetic damping.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Self-consistent iteration procedure in analyzing reflectivity and spectroscopic ellipsometry data of multilayered materials and their interfaces

For multilayered materials, reflectivity depends on the complex dielectric function of all the constituent layers, and a detailed analysis is required to separate them. Furthermore, for some cases, new quantum states can occur at the interface which may change the optical properties of the material. In this paper, we discuss various aspects of such analysis, and present a self-consistent iteration procedure, a versatile method to extract and separate the complex dielectric function of each individual layer of a multilayered system. As a case study, we apply this method to LaAlO{sub 3}/SrTiO{sub 3} heterostructure in which we are able to separate the effects of the interface from the LaAlO{sub 3} film and the SrTiO{sub 3} substrate. Our method can be applied to other complex multilayered systems with various numbers of layers.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Design and development of an in-line sputtering system and process development of thin film multilayer neutron supermirrors

Neutron supermirrors and supermirror polarizers are thin film multilayer based devices which are used for reflecting and polarizing neutrons in various neutron based experiments. In the present communication, the in-house development of a 9 m long in-line dc sputtering system has been described which is suitable for deposition of neutron supermirrors on large size (1500 mm × 150 mm) substrates and in large numbers. The optimisation process of deposition of Co and Ti thin film, Co/Ti periodic multilayers, and a-periodic supermirrors have also been described. The system has been used to deposit thin film multilayer supermirror polarizers which show high reflectivity up to a reasonably large critical wavevector transfer of ∼0.06 Å{sup −1} (corresponding to m = 2.5, i.e., 2.5 times critical wavevector transfer of natural Ni). The computer code for designing these supermirrors has also been developed in-house.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Optimized aperiodic multilayer structures for use as narrow-angular absorbers

In this paper, we investigate aperiodic multilayer structures for use as narrow-angular absorbers. The layer thicknesses and materials are optimized using a genetic global optimization algorithm coupled to a transfer matrix code to maximize the angular selectivity in the absorptance at a single or multiple wavelengths. We first consider structures composed of alternating layers of tungsten and silicon or silica, and find that it is not possible to achieve angular selectivity in the absorptance with such structures. We next consider structures composed of alternating layers of silicon and silica, and show that when optimized they exhibit high angular selectivity in absorptance. In addition, as the angular selectivity in absorptance increases, the wavelength range of high angular selectivity also decreases. Optimizing the material composition of the multilayer structures, in addition to optimizing the layer thicknesses, leads to marginal improvement in angular selectivity. Finally, we show that by optimizing the absorptance of the multilayer structures at multiple wavelengths, we can obtain structures exhibiting almost perfect absorptance at normal incidence and narrow angular width in absorptance at these wavelengths. Similar to the structures optimized at a single wavelength, the wavelength range of high angularly selective absorptance is narrow.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Formation of multilayered magnetic nanotracks with perpendicular anisotropy via deoxidization using ion irradiation on ultraviolet-imprinted intaglio nanostructures

We proposed a method to fabricate perpendicular magnetic nanotracks in the cobalt oxide/palladium multilayer films using UV-nanoimprinting lithography and low-energy hydrogen-ion irradiation. This is a method to magnetize UV-imprinted intaglio nanotracks via low-energy hydrogen ion irradiation, resulting the irradiated region are magnetically separated from the non-irradiated region. Multilayered magnetic nanotracks with a line width of 140 nm, which were fabricated by this parallel process without additional dry etching process, exhibited a saturation magnetization of 290 emu cm{sup −3} and a coercivity of 2 kOe. This study demonstrates a cost-effective mass production of multilayered perpendicular magnetic nanotracks and offers the possibility to achieve high density storage and memory devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Magneto-transport anisotropy in epitaxially grown hybrid MnAs/GaAs multilayer

Using molecular-beam epitaxy, we grew a MnAs/GaAs multilayer on a GaAs(100) substrate and compared its magneto-transport characteristics to those of a single-layer MnAs thin film. The crystal orientation of the MnAs layers in both samples was type-B. M–H measurements revealed two-fold symmetric magnetic anisotropy on the surface with the easy and hard direction of magnetization. When the current flowed along the hard direction, the MnAs/GaAs multilayer exhibited negative magnetoresistance below Curie temperature; when the current flowed along the easy direction, it turned positive. We suggest that this peculiar anisotropic magneto-transport behavior in the multilayer originated from two-dimensional carrier confinement and spin-orbit coupling.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Laboratory-based x-ray reflectometer for multilayer characterization in the 15–150 keV energy band

A laboratory-based X-ray reflectometer has been developed to measure the performance of hard X-ray multilayer coatings at their operational X-ray energies and incidence angles. The instrument uses a sealed-tube X-ray source with a tungsten anode that can operate up to 160 kV to provide usable radiation in the 15–150 keV energy band. Two sets of adjustable tungsten carbide slit assemblies, spaced 4.1 m apart, are used to produce a low-divergence white beam, typically set to 40 μm × 800 μm in size at the sample. Multilayer coatings under test are held flat using a vacuum chuck and are mounted at the center of a high-resolution goniometer used for precise angular positioning of the sample and detector; additionally, motorized linear stages provide both vertical and horizontal adjustments of the sample position relative to the incident beam. A CdTe energy-sensitive detector, located behind a third adjustable slit, is used in conjunction with pulse-shaping electronics and a multi-channel analyzer to capture both the incident and reflected spectra; the absolute reflectance of the coating under test is computed as the ratio of the two spectra. The instrument’s design, construction, and operation are described in detail, and example results are presented obtained with both periodic, narrow-band and depth-graded, wide-band hard X-ray multilayer coatings.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Investigation of optical and interfacial properties of Ag/Ta{sub 2}O{sub 5} metal dielectric multilayer structure

One-dimensional periodic metal-dielectric multilayer thin film structures consisting of Ag and Ta{sub 2}O{sub 5} alternating layers are deposited on glass substrate using RF magnetron sputtering technique. The spectral property of the multilayers has been investigated using spectrophotometry technique. The optical parameters such as refractive index, extinction coefficient, band gap etc., along with film thickness as well as the interfacial layer properties which influence these properties have been probed with spectroscopic ellipsometry technique. Atomic force microscopy has been employed to characterize morphological properties of this metal-dielectric multilayer.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗