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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 1,711 records · Page 95
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Non destructive neutron diffraction measurements of cavities, inhomogeneities, and residual strain in bronzes of Ghiberti's relief from the Gates of Paradise

Quantitative neutron studies of cultural heritage objects provide access to microscopic, mesoscopic, and macroscopic structures in a nondestructive manner. In this paper we present a neutron diffraction investigation of a Ghiberti Renaissance gilded bronze relief devoted to the measurement of cavities and inhomogeneities in the bulk of the sample, along with the bulk phase composition and residual strain distribution. The quantitative measurements allowed the determination of the re-melting parts extension, as well as improving current knowledge about the manufacturing process. The study provides significant and unique information to conservators and restorators about the history of the relief.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Electron back scattered diffraction characterization of Sm(CoFeCuZr){sub z} magnets

In permanent magnets based on the Sm{sub 2}Co{sub 17} phase, the high coercivity depends on the presence of a complex microstructure, consisting of a Sm{sub 2}(Co,Fe){sub 17} cell phase, a cell boundary phase Sm(Co,Cu){sub 5}, and a Zr-rich platelet or lamellae phase. The aim of this work is to use electron back scatter diffraction (EBSD) in order to identify the different phases present in the isotropic magnets produced from cast alloys with the composition of Sm(Co{sub bal}Fe{sub 0.2}Cu{sub 0.1}Zr{sub x}){sub 8}, where x = 0, 0.02, or 0.06, and correlate them with the different phases observed in scanning electron microscopy (SEM) images. Due to the combination of careful surface preparation and high resolution microscopy, it was possible to observe the cellular structure characteristic of the 2:17 magnets in the SEM images. Until now, only transmission electron microscopy (TEM) had been used. Composition maps, energy dispersive spectroscopy (EDS), and EBSD measurements were used for doing the phase identification.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Temperature dependent x-ray diffraction study of lightly doped Na{sub x}WO{sub 3}

Temperature dependent x-ray diffraction studies have been carried out on nonstoichiometric lightly doped sodium tungsten bronze (Na{sub x}WO{sub 3} for x=0.025). The investigation reveals a structural modification around 230 K. Although the high and low temperature phases are monoclinic but at low temperature the corner sharing WO{sub 6} octahedra get significantly distorted due to displacement of tungsten and oxygen atoms from its mean position. This structural modification induces polaron formation in Na{sub 0.025}WO{sub 3} below 230 K.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Time-resolved resonant soft x-ray diffraction with free-electron lasers: Femtosecond dynamics across the Verwey transition in magnetite

Resonant soft x-ray diffraction (RSXD) with femtosecond (fs) time resolution is a powerful tool for disentangling the interplay between different degrees of freedom in strongly correlated electron materials. It allows addressing the coupling of particular degrees of freedom upon an external selective perturbation, e.g., by an optical or infrared laser pulse. Here, we report a time-resolved RSXD experiment from the prototypical correlated electron material magnetite using soft x-ray pulses from the free-electron laser FLASH in Hamburg. We observe ultrafast melting of the charge-orbital order leading to the formation of a transient phase, which has not been observed in equilibrium.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Residual Stresses in DC cast Aluminum Billet: Neutron Diffraction Measurements and Thermomechanical Modeling

Thermally-induced residual stresses, generated during the industrial Direct Chill casting process of aluminum alloys, can cause both significant safety concerns as well as the formation of defects during down-stream processing. Although these thermally induced strains can be partially relieved by permanent deformation, cracks will be generated either during solidification (hot tears) or post-solidification cooling (cold cracks) when stresses exceed the deformation limit of the alloy. Furthermore, the thermally induced strains result in the presence of large internal stresses within the billet before further processing steps. Although numerical models have been previously developed to compute these residual stresses, most of the computations have been validated only against measured surface distortions. In the present work, the variation in residual elastic strains and stresses in the steady state regime of casting has been measured as a function of radial position using neutron diffraction in an AA6063 grain-refined cylindrical billet. These measurements have been carried out on the same billet section at Poldi at PSI-Villigen and at Salsa at ILL-Grenoble and compare favorably. The results are used to validate a thermo-mechanical finite element casting model and to assess the level of stored elastic energy within the billet.

36 MATERIALS SCIENCE↗
DOE OSTI2011

In-situ stoichiometry determination using x-ray fluorescence generated by reflection-high-energy-electron-diffraction

A major challenge in the stoichiometric growth of complex oxide compounds is the control of the relative compositions of the constituent materials. A potential avenue for compositional analysis during growth is the use of x-ray fluorescence generated during reflection high energy electron diffraction measurements. Using this technique, relative compositions of Y and Mn in molecular beam epitaxy grown YMnO{sub 3} samples were studied. Comparing the results with Rutherford back scattering spectroscopy suggests that the technique has the potential for real-time analysis of elemental fluxes and stoichiometry control during sample growth.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

High-resolution x-ray diffraction investigation of relaxation and dislocations in SiGe layers grown on (001), (011), and (111) Si substrates

This work presents a detailed characterization, using high-resolution x-ray diffraction, of multilayered Si{sub 1-x}Ge{sub x} heterostructures grown on (001), (011), and (111) Si substrates by reduced pressure chemical vapor deposition. Reciprocal space mapping has been used to determine both the strain and Ge concentration depth profiles within each layer of the heterostructures after initially determining the crystallographic tilt of all the layers. Both symmetric and asymmetric reciprocal space maps were measured on each sample, and the evaluation was performed simultaneously for the whole data set. The ratio of misfit to threading dislocation densities has been estimated for each individual layer based on an analysis of diffuse x-ray scattering from the defects.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Analyzing the growth of In{sub x}Ga{sub 1-x}N/GaN superlattices in self-induced GaN nanowires by x-ray diffraction

Self-induced GaN nanowires are grown by plasma-assisted molecular beam epitaxy, with In{sub x}Ga{sub 1-x}N quantum wells inserted to form an axial superlattice. From the {omega}-2{theta} scans of a laboratory x-ray diffraction experiment, we obtain the superlattice period, the thickness of the quantum wells, and the In content in this layer. The axial growth rate of the In{sub x}Ga{sub 1-x}N quantum wells is significantly enhanced, which we attribute to increased Ga diffusion along the nanowire sidewalls in the presence of In.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Use of Justified Constraints in Coherent Diffractive Imaging

We demonstrate the use of physically justified object constraints in x-ray Fresnel coherent diffractive imaging on a sample of nanoporous gold prepared by dealloying. Use of these constraints in the reconstruction algorithm enabled highly reliable imaging of the sample's shape and quantification of the 23- to 52-nm pore structure within it without use of a tight object support constraint.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Elimination of higher-order diffraction using zigzag transmission grating in soft x-ray region

We present a realization of the sinusoidal transmission function using a series of zigzag-profiled strips where the transmission takes on the binary values 0 and 1 in a two-dimensional distribution. A zigzag transmission grating of 1000 line/mm has been fabricated and demonstrated on the soft x-ray beam of synchrotron radiation. The axial single-order diffraction indicates that the zigzag transmission grating is adequate for spectroscopic application.

43 PARTICLE ACCELERATORS↗
DOE OSTI2012

Characterization of Ni/Al multilayer on Si substrate by diffraction and reflectometry techniques

An ion beam deposited multilayer film of nominal thickness [Ni(200 Angst )/Al(100 Angst )]x5 on Si substrate has been characterized by X-Ray Diffraction(XRD), X-Ray Reflectivity (XRR) and Polarized neutron reflectivity(PNR). The present paper attempts to identify presence of any intermetallic compounds at the interfaces of the as-deposited sample. Structural parameters obtained from XRR and PNR are close to design values.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Study of strain propagation in laser irradiated silicon crystal by time-resolved diffraction of K-{alpha} x-ray probe of different photon energies

An experimental study on the time resolved x-ray diffraction from laser shocked silicon crystal, carried out using a 10 TW Ti:sapphire laser system, is presented. The characteristic K{sub {alpha}} x-ray line radiation generated by 45 fs laser produced plasmas of two different target materials (iron and copper) is used as the probe, whereas the stretched pulse of sub-nanosecond duration (pump), derived from the same laser, is used to compress the sample. The use of x-ray probe of different photon energies yields information about the strain over a greater crystal depth. The dynamics of the strain propagation is inferred by monitoring the evolution of rocking curve width of the shocked sample at different time delays between the pump and the probe pulse. The shock velocity deduced from these measurements is {approx}10{sup 6} cm/s, consistent with the sound velocity in bulk silicon. The maximum elastic compression observed is 0.4%, indicating a pressure of 0.8 GPa.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Neutron diffraction studies on chemical and magnetic structure of multiferroic PbFe{sub 0.67}W{sub 0.33}O{sub 3}

We report on the single phase synthesis and room temperature structural characterization of PbFe{sub 0.67}W{sub 0.33}O{sub 3} (PFW) multiferroic. The PFW was synthesized by low temperature sintering, Columbite method. Analysis of powder XRD pattern exhibits single phase formation of PFW with no traces of pyrochlore phase. Detailed analysis of room temperature neutron diffraction (ND) reveals cubic phase at room temperature, space group Pm-3m. The ND pattern clearly reveals magnetic Bragg peak at 2θ = 18.51° (Q = 1.36Å{sup −1}). The refinement of magnetic structure reveals G-type antiferromagnetic structure in PFW at room temperature. The dielectric constant and loss tangent decreases with increasing frequency. The room temperature P-E measurements shows a non-linear slim hysteresis, typical nature of relaxor multiferroics, with saturation and remnant polarizations of P{sub s} = 1.50 μC/cm{sup 2} and P{sub r} = 0.40 μC/cm{sup 2}, respectively.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Time-resolved X-ray diffraction studies of laser-induced acoustic wave propagation in bilayer metallic thin crystals

Phonon propagation across the interface of a Cu/Ag(111) bilayer and transient lattice disorder, induced by a femtosecond 267 nm pulse, in Ag(111) crystal have been measured by means of time resolved X-ray diffraction. A “blast” force due to thermal stress induced by suddenly heated electrons is formed within two picoseconds after excitation and its “blast wave” propagation through the interface and Ag (111) crystal was monitored by the shift and broadening of the rocking curve, I vs. ω, as a function of time after excitation. Lattice disorder, contraction and expansion as well as thermal strain formation and wave propagation have also been measured. The experimental data and mechanism proposed are supported by theoretical simulations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Polarity of semipolar wurtzite crystals: X-ray photoelectron diffraction from GaN(101⁻1) and GaN(202⁻1) surfaces

Polarity of semipolar GaN(101⁻1) (101⁻1⁻) and GaN(202⁻1) (202⁻1⁻) surfaces was determined with X-ray photoelectron diffraction (XPD) using a standard MgKα source. The photoelectron emission from N 1s core level measured in the a-plane of the crystals shows significant differences for the two crystal orientations within the polar angle range of 80–100° from the (0001) normal. It was demonstrated that XPD polar plots recorded in the a-plane are similar for each polarity of the GaN(101⁻1) and GaN(202⁻1) crystals if referred to (0001) crystal axes. For polarity determinations of all important GaN(h0h⁻l) semipolar surfaces, the above given polar angle range is suitable.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Mathematical and computational modeling of the diffraction problems by discrete singularities method

The main objective of this study is reduced the boundary-value problems of scattering and diffraction waves on plane-parallel structures to the singular or hypersingular integral equations. For these cases we use a method of the parametric representations of the integral and pseudo-differential operators. Numerical results of the model scattering problems on periodic and boundary gratings and also on the gratings above a flat screen reflector are presented in this paper.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Performance enhancement of thin film silicon solar cells based on distributed Bragg reflector and diffraction grating

The influence of various designing parameters were investigated and explored for high performance solar cells. Single layer grating based solar cell of 50 μm thickness gives maximum efficiency up to 24 % whereas same efficiency is achieved with the use of three bilayers grating based solar cell of 30 μm thickness. Remarkably, bilayer grating based solar cell design not only gives broadband absorption but also enhancement in efficiency with reduced cell thickness requirement. This absorption enhancement is attributed to the high reflection and diffraction from DBR and grating respectively. The obtained short-circuit current were 29.6, 32.9, 34.6 and 36.05 mA/cm{sup 2} of 5, 10, 20 and 30 μm cell thicknesses respectively. These presented designing efforts would be helpful to design and realize new generation of solar cells.

36 MATERIALS SCIENCE↗
DOE OSTI2015

A short note on physical properties to irradiated nuclear fuel by means of X-ray diffraction and neutron scattering techniques

For nuclear reactor applications, understanding the evolution of the fuel materials microstructure during irradiation are of great importance. This paper reviews the physical properties of irradiated nuclear fuel analysis which are considered to be of most importance in determining the performance behavior of fuel. X-rays diffraction was recognize as important tool to investigate the phase identification while neutron scattering analyses the interaction between uranium and other materials and also investigation of the defect structure.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗