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Results for “diffractive optics”

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 1,441 records · Page 80
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Modulation of microstructure and optical properties of Mo-doped ZnO thin films by substrate temperature

Highlights: • Mo-doped ZnO films are obtained by sputtering at various substrate temperatures. • High-quality MZO thin films with good crystalline have been obtained at 200 °C. • Deposition temperature affects the amount of defects in the crystalline structure - Abstract: Mo-doped ZnO(MZO) films were deposited on Si (1 1 1) substrates by radio frequency sputtering at different substrate temperatures of 200, 300 and 400 °C. The effect of the substrate temperature on the structural and optical properties of the MZO films has been investigated. X-ray diffraction results reveal that all the films are polycrystalline with a hexagonal wurtzite structure with a preferential orientation according to the direction (0 0 2) plane. The crystallinity and surface morphologies of the films are strongly dependent on the growth temperature, which in turn exerts a great effect on microstructural and optical properties of the MZO films. The optical absorption measurements show high ultraviolet (UV) absorbance property of MZO with sharp and intense absorption band in this region and the optical band gap (E{sub g}) are 3.18, 3.22, 3.25 and 3.21 eV for the films deposited at room temperature, 200, 300 and 400 °C. The photoluminescence (PL) intensity of a strong broad violet–blue emission from MZO nanostructures with increasing deposited temperature was also observed. X-ray photoelectron spectroscopy (XPS) was employed to investigate the surface chemical composition of growth products.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Influence of bias voltage on structural and optical properties of TiN{sub x} thin films

In the present work, Ti thin films were deposited on Si substrate using DC sputtering technique. Indigenous hot cathode arc discharge plasma system was used for nitriding over these samples, where the plasma parameters and work piece can be controlled independently. A mixture of H{sub 2} and N{sub 2} gases (in the ratio of 80:20) was supplied into the plasma chamber. The effect of bias voltage on the crystal structure, morphology and optical properties was investigated by employing various physical techniques such as X-ray Diffraction, Atomic Force Microscopy and UV-Vis spectrometry. It was found that bias voltage affects largely the crystal structure and band gap which in turn is responsible for the modifications in optical properties of the deposited films.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Formation of wide-blocky calcite veins by extreme growth competition

Liassic limestones on the coast of Somerset in the UK contain dense arrays of calcite microveins with a common, but poorly understood microstructure, characterized by laterally wide crystals that form bridges across the vein. We investigated the mechanisms of formation and evolution of these ‘wide-blocky’ vein microstructures using a combination of high-resolution analytical methods, including virtual petrography, optical cathodoluminescence and scanning electron microscopy techniques (e.g. energy-dispersive X-ray spectrometry, back-scattered electron imaging, cathodoluminescence and electron back-scattered diffraction), laboratory experiments and multiphase field modelling. Our results indicate that the studied veins formed in open, fluid-filled fractures, each in a single opening and sealing episode. As shown by the optical and electron back-scattered diffraction images, the vein crystals grew epitaxially on grains of the wall rock and we hypothesize that their growth rates differed depending on whether the crystals were on a wall rock grain substrate that fractured intergranularly (slow growth rates) or transgranularly (rapid growth rates). Our multiphase field models support this hypothesis, showing that wide, blocky crystals only form where there are significant differences in the growth rate and are dependent on the type of seed grain. These results provide strong evidence for extreme growth competition, a process that we propose controls vein-filling in many micritic carbonate reservoirs, as well as demonstrate that the characteristics of the fracture wall can affect the filling processes in syntaxial veins. Supplementary material: The description and images of the studied thin sections are available at https://doi.org/10.6084/m9.figshare.c.5172371 . High-resolution optical microscopy mosaics (under plane-polarized- and crossed polarized light) of the thin section collection in PetroScan file format are available on request from the authors.

Geology↗
NASA NTRS1991

Quasi-Optical Millimeter-Wavelength Resonator

Quasi-optical reflection cavity serves as prototype resonator for oscillators at millimeter and submillimeter wavelengths. Exploits diffraction and reflection effects to achieve high Q. Useful mainly at wavelengths too short for conventional waveguide techniques but too long for optical techniques.

Frerking, Margaret A.↗
DOE OSTI2016

The synthesis and characterization of Mg-Zn-Ca alloy by powder metallurgy process

Known for its biodegradation and biocompatible properties, magnesium alloys have gained many interests to be researched as implant material. In this study, Mg-3Zn-1Ca, Mg-29Zn-1Ca, and Mg-53Zn-4.3Ca (in wt%) were synthesized by means of powder metallurgy method. The compression strength and corrosion resistance of magnesium alloy were thoroughly examined. The microstructures of the alloy were characterized using optical microscopy, Scanning Electron Microscope, and also X-ray diffraction analysis. The corrosion resistance were evaluated using electrochemical analysis. The result indicated that Mg- Zn- Ca alloy could be synthesized using powder metallurgy method. This study showed that Mg-29Zn-1Ca would make the highest mechanical strength up to 159.81 MPa. Strengthening mechanism can be explained by precipitation hardening and grain refinement mechanism. Phase analysis had shown the formation of α Mg, MgO, and intermetallic phases: Mg2Zn11 and also Ca2Mg6Zn3. However, when the composition of Zn reach 53% weight, the mechanical strength will be decreasing. In addition, all of Mg-Zn-Ca alloy studied here had better corrosion resistance (Ecorr around -1.4 VSCE) than previous study of Mg. This study indicated that Mg- 29Zn- 1Ca alloy can be further analyzed to be a biodegradable implant material.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Structural, optical, dielectric and magnetic investigation on mixed valance Pb{sub 3}Mn{sub 7}O{sub 15}

Polycrystalline Pb{sub 3}Mn{sub 7}O{sub 15} has been prepared by the solid state reaction route. The Rietveld refinement of the X-ray diffraction (XRD) data reveals that the compound possesses orthorhombic structure with space group ‘Pnma’. Optical characterization has been done to determine the band gap of the material which was found to be 2.95 eV. Temperature dependent dielectric measurements revealed an anomaly above 70 K which can be attributed to localized polaron hopping between the lattice sites. DC Magnetization measurement at 1 kOe showed an antiferromagnetic transition at ~70 K (T{sub N}). M-H measurement up to 9 T at low temperature shows unsaturated hysteresis loop which can be relayed to short range magnetic correlation present between various Mn oxidation states.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

To study the effect of doping concentration of silver on structural and optical properties of cadmium oxide (CdO) nanostructure

The present work deals with study of structural and optical properties of Silver (Ag) doped Cadmium oxide (CdO) nanostructured synthesized by Chemical Co-precipitation Techniques followed by calcinations at small temperature. The doping concentrations were changing from 0.1 to 10 at% respectively. Structural analysis study of these calcined materials is carried out by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The optical properties of calcined samples were investigating by Fourier transformation infrared (FTIR)spectroscopy, UV-Visible Spectroscopy (UV-Vis). The structural properties analysis results revels that crystallite size are in the range of nano region and TEM results are quite in accordance with XRD results.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

The visible laser absorption property of chromium-doped polyvinyl alcohol films: synthesis, optical and dielectric properties

New films for visible laser filter were fabricated from poly(vinyl alcohol), PVA, and various levels of chrome(III) chloride, CrCl{sub 3}, by a known simple process named casting. The structure order degree, complex interaction, as well as optical filtering characteristic of the PVA + xCrCl{sub 3} (x = 0.037, 0.37, 3.7, 18.5 and 37 wt%) samples were investigated via the diffraction of the X-ray, Fourier transform infrared spectroscopy and UV/Vis/NIR spectrum, respectively, while the behavior of optical limiting was tested by set-up laser limiting measurement. The increment of Cr{sup 3+}-doping level in the PVA gives some results as, (I) a marked increase in the degree of random structure of the samples, and (II) two clearly absorption peaks are seen around 428 nm and 608 nm with a progressive increase in the intensity and a slight shift to a higher wavelength. (III) Three distinguished energy gaps were clearly observed, as well as, (IV) the dielectric spectroscopy of the samples was decreased with increasing the Cr{sup 3+}-doping, which contributes to the strong interaction among the mixtures. Furthermore, at concentrations above 0.37 wt% of Cr{sup 3+}-doping, a notable decrease in the output detected laser power was observed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1973

Spectral line absorption measurement using optical cavities.

A simple technique using a conventional gas laser with spherical mirrors having identical radii of curvature in the nonoscillating regime for spectral line absorption measurements is described and applications for laser work are suggested. The theory of the measurement carried out in the geometrical optical approach for Doppler-broadened lines was checked experimentally and conditions are specified for which measurement inaccuracies of the order of 1% for the peak value of the line absorption coefficient can be obtained. Since the device provides a fine adjustment of the cavity losses, formation of the diffraction modes could be observed in the preoscillating regime of the optical cavity.

Blanaru, D. L.↗
DOE OSTI2018

Tensile Deformation Temperature Impact on Microstructure and Mechanical Properties of AISI 316LN Austenitic Stainless Steel

Uniaxial tensile tests were conducted on AISI 316LN austenitic stainless steel from − 40 to 300 °C at a rate of 0.5 mm/min. Microstructure and mechanical properties of the deformed steel were investigated by optical, scanning and transmission electron microscopies, x-ray diffraction, and microhardness testing. The yield strength, ultimate tensile strength, elongation, and microhardness increase with the decrease in the test temperature. The tensile fracture morphology has the dimple rupture feature after low-temperature deformations and turns to a mixture of transgranular fracture and dimple fracture after high-temperature ones. The dominating deformation microstructure evolves from dislocation tangle/slip bands to large deformation twins/slip bands with temperature decrease. The deformation-induced martensite transformation can only be realized at low temperature, and its quantity increases with the decrease in the temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructural Characteristics and Mechanical Properties of an Electron Beam-Welded Ti/Cu/Ni Joint

Electron beam welding experiments of TA15 titanium alloy to GH600 nickel superalloy with and without a copper sheet interlayer were carried out. Surface appearance, microstructure and phase constitution of the joint were examined by optical microscopy, scanning electron microscopy and x-ray diffraction analysis. Mechanical properties of Ti/Ni and Ti/Cu/Ni joint were evaluated based on tensile strength and microhardness tests. The results showed that cracking occurred in Ti/Ni electron beam weldment for the formation of brittle Ni-Ti intermetallics, while a crack-free electron beam-welded Ti/Ni joint can be obtained by using a copper sheet as filler metal. The addition of copper into the weld affected the welding metallurgical process of the electron beam-welded Ti/Ni joint significantly and was helpful for restraining the formation of Ti-Ni intermetallics in Ti/Ni joint. The microstructure of the weld was mainly characterized by a copper-based solid solution and Ti-Cu interfacial intermetallic compounds. Ti-Ni intermetallic compounds were almost entirely suppressed. The hardness of the weld zone was significantly lower than that of Ti/Ni joint, and the tensile strength of the joint can be up to 282 MPa.

36 MATERIALS SCIENCE↗
DOE OSTI2020

On residual stress analysis and microstructural evolution for stainless steel type 304 spent nuclear fuel canisters weld joint: Numerical and experimental studies

Chloride-induced stress corrosion cracking (CISCC) in the weldments of austenitic stainless steel canisters is one of the primary safety concerns during the dry storage of used nuclear fuel at Independent Spent Fuel Storage Installations in coastal areas. In order to evaluate the CISCC behavior in the canister, a 3D sequentially coupled thermo-mechanical finite element model was built to simulate the residual stresses induced by two intersecting longitudinal and circumferential multi-pass welds in austenitic stainless steel mockup canister. Weld-induced residual stresses from simulation were in good agreement with the experimental measurement results by deep-hole drilling and contour methods. Through-wall high tensile axial and hoop stresses were observed in both the fusion zone and heat affected zone (HAZ) in the longitudinal and circumferential weld, respectively. On the other hand, the microstructure within the weldments of 304 stainless steel mockup was characterized using optical microscopy, scanning electron microscopy, electron back-scattered diffraction and energy dispersive X-ray spectroscopy methods. A few amount of MnS inclusions in both the base metal and HAZ, and a lot of (Mn,Si) x O y inclusions in the fusion zone were found. Meanwhile, there is some α'-martensite in the base metal, while the martensite was reversed in the HAZ. In the fusion zone, there is a lot of δ-ferrite. The martensite reversion phenomenon was also verified by the combination of Feritscope test and thermal simulation, which could predict a martensite reversion temperature as 400C°. The welding residual stresses and microstructure analysis results could offer the instructive information for the prediction of CISCC behavior of the spent nuclear fuel canisters.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Microstructural evolution of Mo-UO 2 cermets under high temperature hydrogen environments

Ceramic-metallic (cermet) materials show promise for use in nuclear thermal propulsion applications due to attractive thermophysical properties including high temperature stability and high thermal conductivity. In this work, molybdenum-uranium dioxide (Mo-UO 2 ) cermet fuel elements were fabricated by means of spark plasma sintering (SPS) and were subsequently exposed to hydrogen at high temperatures (2500 K). Mo-UO 2 samples pre- and post-exposure were characterized by means of optical microscopy, scanning electron microscopy, and X-ray diffraction (XRD). Microscopy analyses of the as-produced material displayed microscopic cracking on the interior of the spherical UO 2 fuel particles but confirmed that the fuel particles were fully encapsulated in the Mo matrix. The results further showed mass loss, macroscopic swelling, and cracking in the cermet samples which occurred during high temperature hydrogen testing. Nanoscale swelling was evidenced by XRD in the Mo matrix and UO 2 fuel structure due to the incorporation of defects and accompanied microstrain.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The role of titanium and vanadium based precipitates on hydrogen induced degradation of ferritic materials

Highlights: • Hydrogen induced damage is studied in Fe-C-Ti and Fe-C-V ferritic alloys. • Fe-C-Ti is less susceptible to hydrogen embrittlement than Fe-C-V. • Fe-C-V is less susceptible to blistering than Fe-C-Ti. • The role of diffusible hydrogen depends on the damage mechanism. - Abstract: The hydrogen induced damage of generic Fe-C-Ti and Fe-C-V ferritic alloys was investigated to assess the influence of precipitates on the hydrogen sensitivity of a material. The precipitates, formed during heat treatment, were evaluated by scanning transmission electron microscopy (STEM). The hydrogen/material interaction was evaluated by: 1) melt and hot extraction to determine the total and diffusible hydrogen content, respectively, 2) permeation experiments to calculate the diffusion coefficient, 3) thermal desorption spectroscopy to determine the hydrogen trapping characteristics of the materials. Furthermore, two different types of hydrogen induced damage were evaluated, i.e. hydrogen assisted cracking and blistering, resulting from electrochemical hydrogen charging with and without the application of an external load, respectively. Evaluation of the hydrogen induced damage and the role of the precipitates was performed by combining optical microscopy, scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). An important though divertive role of diffusible hydrogen is observed in both damage mechanisms for the investigated microstructures. On the one hand, a large amount of diffusible hydrogen compared to strongly trapped hydrogen promotes hydrogen assisted cracking of materials, while on the other hand, the blistering phenomenon is delayed under such conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effects of in-process cryocooling on metallurgical and mechanical properties of friction stir processed Al7075 alloy

Highlights: • For in-process cryocooling (IPC) during FSP, an efficient cooling fixture was designed & fabricated. • FSP of Al7075 alloy with IPC setup suppressed precipitate coarsening as well as grain growth. • Nanosize η′ precipitates (20–30 nm) in IPC condition increased work hardening capacity & strength. • Simultaneous improvement in ductility & strength occurred for sample FSPed with IPC. - Abstract: Friction stir processing (FSP) of heat treatable aluminum alloys is reported to deteriorate strength and hardness properties in spite of huge grain size refinement. The improvement in strength due to the grain size refinement after FSP could not be able to offset the reduction in strength due to coarsening or dissolution of the strengthening precipitate(s). To overcome this, the present work investigates an effective way of heat rejection from the FSP zone to control the precipitate evolution besides the grain size refinement during FSP of Al7075 alloy. The FSP was carried out with standardized process parameters (i.e. 720 rpm, 65 mm/min traverse speed) under two different cooling environments: (i) at normal air cooling and (ii) by rushing a chilled mixture (−30 °C) of liquid nitrogen and methanol through the bottom of the backing plate. Microstructural evolution was examined through optical, scanning and transmission electron microscopy and electron backscatter diffraction to confirm the grain size and morphology of precipitate(s) formed. The in-process cryocooling during the FSP led to 65 and 72% improvement in the Vickers hardness and tensile strength, respectively, in comparison to the solutionized base metal. The results have been analyzed in terms of precipitate interface characteristics and its strengthening effect, Hall–Petch strengthening due to grain size reduction and tradeoff between them.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Surface grain refinement of casting A380 aluminum alloy by ultrasonic-assisted surface mechanical grinding treatment

A novel surface processing technique, ultrasonic-assisted surface mechnical grinding treatment (U-SMGT), was proposed and applied to modify the surface micriostructure of the casting aluminum alloy (A380). Comprehensive post-process chracterization techniques including 3D profilometry, optical microscope, scanning electric microscopy (SEM), and electron backscatter diffraction (EBSD) were carried out to investigate the surface morphology and microstructure of the processed region (PR). It was found that a surface layer of grain refinement with a thickness of about 50 µm was formed. In the as-received base material (BM), large clusters of dendritic eutectic phase with a size of approximately 20 µm were isolated by α-Al matrix. Nano-indentation tests showed that hardness of the eutectic and α-Al in the as-received BM was 2.15 GPa and 1.2 GPa respectively. After U-SMGT, the large dendritic eutectic phase was broken down into much fine particles with an average size of 0.57 µm. These fine particles were uniformly distributed into the α-Al matrix. Nano-indentation measurement exhibited a hardness of 2.27 GPa within the processed region. The overall high hardness in the processed region is a result of the pinning effect of uniformly distributed fine dendrites and grain refinement of Al-matrix.

36 MATERIALS SCIENCE↗
DOE OSTI2020

The importance of temporal and spatial incoherence in quantitative interpretation of 4D-STEM

Recent developments in pixelated detectors, when combined with aberration correction of probe forming optics have greatly enhanced the field of scanning electron diffraction. Differential phase contrast is now routine and deep learning has been proposed as a method to extract maximum information from diffraction patterns. This study examines the effects of temporal and spatial incoherence on convergent beam electron diffraction patterns and demonstrates that simple center of mass measurements cannot be naively interpreted. The inclusion of incoherence in deep learning data sets is also discussed.

36 MATERIALS SCIENCE↗