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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Lorentz factor for time-of-flight neutron Bragg and total scattering

We report the three fundamental origins of the Lorentz factor for neutron time-of-flight powder diffraction are revisited. A detailed derivation of the Lorentz factor is presented in the context of diffuse scattering modelling in reciprocal space when perfect periodicity is assumed, and the total scattering pattern is constructed in its discrete form – the factor in this case becomes 1/Q 2 (or d 2 ). Discussion is also presented with respect to practical data reduction where a vanadium measurement is usually taken as the normalization factor (to account for various factors such as detector efficiency), and it is shown that the existence of the Lorentz factor is independent of such a normalization process.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Liquid–Solid Mixtures of Ga Metal Infused with Cu Microparticles and Nanoparticles for Microscale and Nanoscale Patterning of Solid Metals at Room Temperature

This paper demonstrates and characterizes a simple ink for nanopatterning of solid metallic structures under ambient conditions by taking advantage of the low melting point of gallium and its affinity to form intermetallics with other metals. Bare copper micro- and nanoparticles readily mix with liquid gallium near room temperature to form a paste that ultimately amalgamates into a dense solid when mixed at the appropriate concentration ratios. The paste has sufficient shelf life that can be extruded from a nozzle at modest temperatures to form solid three-dimensional (3D) shapes. Additionally, the paste can be molded at room temperature to replicate feature sizes ranging from a few millimeters down to hundreds of nanometers. In situ X-ray diffraction (XRD) and thermo-mechanical analysis (TMA) data show gallium and copper readily interdiffuse to form the thermodynamically expected intermetallic phase. We describe the capabilities and limitations of a simple way to pattern solid metals in an additive fashion (syringe-based extrusion) and with high resolution (molding) at or near room temperature. Here, the use of a paste that solidifies provides a novel route for 3D printing of solid metals at ambient temperatures as well as the creation of micro- and nanostructured metallic surfaces that may be useful for optics, non-wetting surfaces, or electronic microcomponents.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Examining Infrasound Propagation at High Spatial Resolution Using a Nodal Seismic Array

Infrasound—acoustic waves in the atmosphere below 20 Hz—is a useful monitoring tool. Topography and atmospheric structure strongly control infrasound propagation, and at common source–receiver distances neither of these effects can be ignored when quantitative source constraints are sought. Detailed spatial measurements of the infrasound wavefield would inform propagation models and improve source estimates. However, the “large-N” deployment strategy now well-known in seismology has not yet been realized for infrasound studies. Here, we use the 900-node seismic array from the 2014 Imaging Magma Under St. Helens (iMUSH) experiment as a proxy for a large-N infrasound network, by leveraging acoustic–seismic coupled arrivals. The active-source component of iMUSH consisted of 23 shallowly buried explosions around Mount Saint Helens volcano; these explosions produced epicentral infrasound recorded on the nodes. We find that the bulk presence of ground-coupled infrasound on the nodes is controlled by wind noise and source–receiver distance, with observed arrivals for eight explosions. Explosions with the most extensive coupling produce complex spatial waveform patterns across the array. These patterns are related to both topographic and atmospheric propagation effects, as well as spatially variable site (coupling) effects. We compare our observations to simple topographic diffraction and high-resolution wind advection models, and full-wave numerical simulations. We find strong spatial correlations between (a) coupled arrival strength and modeled topographic obstruction and (b) coupled arrival time and along-path winds. Our seismoacoustic analyses and results are applicable to other existing and future nodal seismic data sets and can expand the utility of such deployments.

58 GEOSCIENCES↗
DOE OSTI2022

Infrared nanospectroscopy characterization of metal oxide photoresists

Implementation of extreme ultraviolet (EUV) lithography in high-volume semiconductor manufacturing requires a reliable and scalable EUV resist platform. A mechanistic understanding of the pros and cons of different EUV resist materials is critically important. However, most material characterization methods with nanometer resolution use an x-ray photon or electron beam as the probe, which often cause damage to the photoresist film during measurement. Here, we illustrated the use of non-destructive infrared nanospectroscopy [or nano-Fourier-Transform infrared spectroscopy (nano-FTIR)] to obtain spatially resolved composition information in patterned photoresist films. Further, clear evidence of exposure-induced chemical modification was observed at a spatial resolution down to 40 nm, well below the diffraction limit of infrared light. With improvements, such a nano-FTIR technique with nanoscale spatial resolution, chemical sensitivity, and minimal radiation damage can be a promising candidate for the fundamental study of material properties relevant to EUV lithography.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Patterned OLEDs: effect of substrate corrugation pitch and height

Abstract An ongoing OLED challenge is cost-effective enhancement of light extraction, i.e., increasing the external quantum efficiency ( EQE ∼20% in conventional devices). OLEDs on corrugated substrates often show enhanced EQE s providing insight into light emission processes. In particular, patterned plastic substrates directly imprinted easily at room temperature and amenable to low-cost R2R production are ideal for studying/optimizing various structures, further elucidating the extraction process. We show new semi-quantitative data of the effect of the pitch ( a ) and height/depth ( h ) of plastic substrate patterns on the OLEDs’ stack and EQE , focusing on new designs, interestingly, some showing surprisingly enhanced EQE s that were neither reported nor discussed before. These includ e : ( i ) shallow ( h < 200 nm) convex polycarbonate with a ∼ 750 versus ∼400 nm, where the h gradually decreases as the OLED stack is built and ( ii ) concave PET/CAB with large a (∼2.8 and ∼7.8 μ m), where the EQE enhancement of conformal OLEDs may be due largely to scattering. EQE s of green, blue, and white phosphorescent OLEDs were measured. OLEDs on substrates with narrow a ∼ 400 nm and low h < 200 nm s h owed no enhancement, resembling flat devices. In contrast, OLEDs on substrates with comparable or smaller h , but larger a ∼ 750 nm show signific a nt EQE enhancement despite h reduction across the stack. Green OLEDs with a ∼ 750 nm and h ∼ 160 to ∼180 nm, showed EQE s ∼30%, reaching ∼58% with substrate mode extraction. Surprisingly, fully conformal OLEDs on a PET/CAB substrate with a ∼ 7.8 μ m showed blue a nd white EQE s reaching ∼33%, without substrate mode extraction. The enhancing patterns increase the OLEDs’ EQE by reducing surface plasmon excitation and internal waveguiding. The experimental results for OLEDs on substrates with a < 2 μ m are supported by scattering matrix simulations that assume conformal stacks, incorporating diffraction for internal losses reduction. EQE enhancement not predicted by simulations may be due additionally to scattering mostly for substrates with a signific a ntly larger than the emitting wavelength.

42 ENGINEERING↗
DOE OSTI2018

Tracing Phase Transformation and Lattice Evolution in a TRIP Sheet Steel under High-Temperature Annealing by Real-Time In Situ Neutron Diffraction

Real-time in situ neutron diffraction was used to characterize the crystal structure evolution in a transformation-induced plasticity (TRIP) sheet steel during annealing up to 1000 °C and then cooling to 60 °C. Based on the results of full-pattern Rietveld refinement, critical temperature regions were determined in which the transformations of retained austenite to ferrite and ferrite to high-temperature austenite during heating and the transformation of austenite to ferrite during cooling occurred, respectively. The phase-specific lattice variation with temperature was further analyzed to comprehensively understand the role of carbon diffusion in accordance with phase transformation, which also shed light on the determination of internal stress in retained austenite. These results prove the technique of real-time in situ neutron diffraction as a powerful tool for heat treatment design of novel metallic materials.

Yu, Dunji [ORNL] (ORCID:0000000189467851)↗
DOE OSTI2020

Evolution of Microstructure, Residual Stress, and Tensile Properties of Additively Manufactured Stainless Steel Under Heat Treatments

This study investigated the microstructure, residual stress and tensile properties of the directed energy deposited stainless steel 316L (SS316L) under thermal annealing. Microstructure characterization shows the as-printed sample has laser-generated patterns where dendritic structure is observed at the edge of the patterns and cellular structure dominates the interior region. Here, the thermal annealing at 983 and 1093°C effectively removes the dendritic/cellular structures. Synchrotron X-ray diffraction reveals that the as-fabricated SS316L exhibits compressive residual stress of -197.4 MPa. The stress is greatly relieved to -53.8 MPa after annealing at 1093°C. The room temperature tensile testing indicates that the yield strength and ultimate tensile strength drop from 378 and 502 MPa in the as-printed sample to 258 and 446 MPa in the annealed samples (1093°C), respectively. Our study provides insights into the relationship between microstructure, residual stress, and tensile properties of laser additive manufactured SS316L.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Surface coating by mechanofusion modulates bulk charging pathways and battery performance of Ni-rich layered cathodes

Ni-rich layered oxides as high-capacity battery cathodes suffer from degradation at high voltages. Here, we utilize a dry surface modification method, mechanofusion (MF), to achieve enhanced battery stability. The simplicity, high yield, and flexibility make it cost-effective and highly attractive for processing at the industrial scale. The underlying mechanisms responsible for performance improvement are unveiled by a systematic study combining multiple probes, e.g., 3D nano-tomography, spectroscopic imaging, in situ synchrotron diffraction, and finite element analysis (FEA). MF affects the bulk crystallography by introducing partially disordered structure, microstrain, and local lattice variation. Furthermore, the crack initiation and propagation pattern during delithiation are regulated and the overall mechanical fracture is reduced after such surface coating. We validate that MF can alter the bulk charging pathways. Such a synergic effect between surface modification and bulk charge distribution is fundamentally important for designing next-generation battery cathode materials.

25 ENERGY STORAGE↗
DOE OSTI2022

Measurement of shock roughness due to phase plate speckle imprinting relevant for x-ray diffraction experiments on 3rd and 4th generation light sources

Laser-shock compression experiments at 3rd and 4th generation light sources generally employ phase plates, which are inserted into the beamline to achieve a repeatable intensity distribution at the focal plane. Here, the laser intensity profile is characterized by a high-contrast, high-frequency laser speckle. Without sufficient smoothing, these laser non-uniformities can translate to a significant pressure distribution within the sample layer and can affect data interpretation in x-ray diffraction experiments. Here, we use a combination of one- and two-dimensional velocity interferometry to directly measure the extent to which spatial frequencies within the laser focal spot intensity pattern are smoothed out during propagation within the laser plasma and a polyimide ablator. We find that the use of thicker polyimide layers results in spatially smoother shock fronts, with the greatest degree of smoothing associated with the highest spatial frequencies. Focal spots with the smallest initial speckle separation produce the most rapid smoothing. Laser systems that employ smoothing by spectral dispersion techniques to rapidly modulate the focal plane intensity distribution are shown to be the most effective ones in producing a spatially smooth shock front. We show that a simple transport model combined with the known polyimide Hugoniot adequately describes the extent of shock smoothness as a function of polyimide thickness. Finally, our results provide a description of spatial structure smoothing across a shock front, which can be used to design targets on x-ray free electron laser facilities.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Salt-Mediated Coarsening in Conversion-Reaction-Synthesized Nanoporous Metals and Nanocomposites Resolved through In Situ Synchrotron Diffraction Studies

High-energy synchrotron X-rays were used to probe the structural and microstructural evolution in Fe, Co, and Cu nanoporous metals (NPMs) and metal/salt nanocomposites (NCs) produced by recently developed conversion reaction synthesis (CRS) methods. Microstructure analysis of as-synthesized samples via whole pattern fitting showed that the NPMs exhibit domain sizes that increase as Co < Fe < Cu, with both Fe and Co having crystallite sizes below 3.0 nm. The as-synthesized metal/salt NCs had similar metal sizes, and additionally, the salt in the composite had unusually large lattice microstrain whose origin is attributed to chemical substitution of metal ions into the salt (e.g., Li $1–3x$ Fe $x$ Cl for Fe 3+ ). When thermal annealing is used to modify crystallite size, pore collapse often occurs in NPMs but NCs can be effectively tuned without this problem. While the NC coarsening occurs slowly at low temperatures, it was found that there is a drastic acceleration of the reaction rate at a specific onset temperature that results in the crystallite size increasing by an order of magnitude in about a minute. Curiously, there was no evidence in the diffraction data for salt melting at this onset temperature. However, there was a sharp reduction in the salt chemical lattice strain at the onset temperature, indicating that rapid metal coarsening is facilitated by the salt. Importantly, this behavior indicates an unexpectedly coupled reaction mechanism by which the metal ions needed for grain growth are supplied by the salt in a rate-limiting fashion.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

Synthesis, structure, linear and nonlinear optical properties of noncentrosymmetric quaternary diamond-like semiconductors, Cu 2 ZnGeSe 4 (CZGSe) and the novel Cu 4 ZnGe 2 Se 7

In this work, two quaternary diamond-like semiconductors (DLSs) in the Cu-Zn-Ge-Se system, the known Cu 2 ZnGeSe 4 (also referred to as CZGSe) and the new Cu 4 ZnGe 2 Se 7 , are compared in terms of their crystal structures, electronic structures and physicochemical properties. Both compounds were prepared by high-temperature, solid-state synthesis at 800 degrees C. Single crystal X-ray diffraction was used to determine the structure of Cu 4 ZnGe 2 Se 7 . The structures of both Cu 2 ZnGeSe 4 and Cu 4 ZnGe 2 Se 7 can be considered as derivatives of cubic diamond. Cu 4 ZnGe 2 Se 7 , with a reduced symmetry due to the cation ordering pattern, adopts the Cu 4 NiSi 2 S 7 structure type, with space group C2. The corner-sharing tetrahedra in Cu 4 ZnGe 2 Se 7 are slightly distorted because the charge for some of the S 2 - anions is not compensated by the first-nearest-neighbor cations. Rietveld refinements using synchrotron X-ray powder diffraction data were used to assess the phase purity of the samples and confirm the bulk structural behavior. Diffuse reflectance UV/Vis/NIR spectroscopy shows that Cu 2 ZnGeSe 4 and Cu 4 ZnGe 2 Se 7 have direct optical bandgaps of 1.38 and 0.91 eV, respectively. Electronic structure calculations implementing density functional theory confirm the direct bandgap for Cu 4 ZnGe 2 Se 7 , with a calculated value of 0.62 eV. Both compounds are air stable, thermally stable up to relatively high temperatures, undergo phase transitions and have wide windows of optical clarity. The Kurtz-Perry powder technique was used to determine the second harmonic generation (SHG) responses using a commercial AgGaSe 2 standard. While Cu 4 ZnGe 2 Se 7 displays a weak SHG response, Cu 2 ZnGeSe 4 exhibits a response that is greater than several benchmark materials, with a large SHG coefficient, χ (2) , of 43 ± 6 pm/V at λ = 2900 nm.

36 MATERIALS SCIENCE↗
DOE OSTI2026

A large interlaboratory electron diffraction study of monolayer graphene

Standardisation of data collection and analysis is essential to enable commercialisation of 2D materials in a wide range of technologies. Selected area electron diffraction (SAED) in the transmission electron microscope (TEM) is one of the key methods for distinguishing monolayer from bilayer and few-layer graphene by comparing the 1st and 2nd order diffraction spot intensities. Yet there are many factors that can affect the reliability of data collection and interpretation, causing the measurement of monolayer samples to deviate from the literature boundary condition of $I_{\{\bar{2}110\}}$$/$$I_{\{1\bar{1}00\}}$ < 1 for monolayer graphene (1LG). Here we present the results of a large interlaboratory SAED comparison study, where 15 international laboratories measured and analysed nominally identical samples of chemical vapour deposited graphene. Large variations were observed in the measured ratios of diffraction spot intensities, with the largest variance associated with poor quality SAED data resulting from inadequate specimen handling and storage. To inform the reliable determination of monolayer thickness from SAED patterns we provide a description of best practice for specimen handling, TEM operation, data collection and analysis. This work was undertaken within VAMAS Technical Working Area 41: Graphene and related 2D materials—Project 9, the results of which have been directly incorporated into ISO/TS 21356–2 for the characterisation of graphene sheets. We find that when this methodology is followed, 1LG can be distinguished from bilayer or thicker material with high confidence where analysis of a single SAED pattern gives $I_{\{\bar{2}110\}}$$/$$I_{\{1\bar{1}00\}}$ < 1.2, even in the absence of precise specimen tilting.

2D materials↗
DOE OSTI2025

Simulation driven adaptive sampling for neutron-diffraction based strain mapping of additively manufactured parts

Neutron diffraction based strain mapping is a useful technique for measuring residual strains in additively manufactured (AM) metal parts. The measurement is traditionally done by scanning the sample in a point-wise raster pattern to extract the strain at each position. Since the overall scan can span several hours, adaptive sampling approaches using Bayesian optimization based on Gaussian process (BO-GP) regression have been introduced—demonstrating that even with a fraction of the typically made measurements the dominant strain patterns in the sample can be reconstructed. However, the parameters of the BO-GP algorithm have to be carefully chosen for best performance, and the movement time between arbitrary points can offset the time savings from a reduced number of measurement locations. In this paper, we propose algorithms to refine the BO-GP based methods by using simulations of strain patterns in AM parts based on the materials and the process used to print them. We demonstrate that the simulated strain patterns can be used to help choose better parameters for the BO-GP based framework—leading to low reconstruction error for the final strain pattern. Furthermore, we show that the strain mapping experiment can be initialized with a sampling pattern learnt from the simulation data and ordered to reduce movement time, dramatically enabling reduction in the overall time required to run the baseline BO-GP method.

Gaussian process regression↗
DOE OSTI2025

Structural and Electronic Complexities of a Sulfur‐Bridged Di‐Iron Complex Composed of Mono‐ and Di‐Nitrosyl Units

The delocalized, thermodynamically stable cation, [(N 2 S 2 )Fe(NO)•Fe(NO) 2 ] + , an adduct of mono-nitrosyl and dinitrosyl iron units, is analyzed to address the unusual stability of the sulfur-bridged diiron complex in its three overall redox levels, +, 0, and −. X-ray diffraction and myriad spectroscopic techniques probe products of sequential electron uptake in the corresponding neutral and anionic species. Conundrums include unified blueshifts of the overall 3-band, ν(NO), pattern with added electrons. One-electron reduction changes the anti-ferromagnetically coupled, S = 0, cationic diiron species to the neutral analog, S = ½, with unpaired spin mainly localized on the MNIU, which decreases its ∠Fe–N–O angle by 10 degrees in response to the extra electron density. Subsequent reduction to the anionic species, S = 1, involves a major geometric change at the MNIU, which moves the Fe in {Fe(NO)} 8 out of the N 2 S 2 plane. Site-specific 15 N labeling of nitrosyl in the MNIU confirms the IR analysis and shows rapid NO exchange between the MNIU/DNIU (mono-nitrosyl iron unit/dinitrosyl iron unit) pairs during its synthesis at RT. Mössbauer spectroscopy, S K-edge XAS, and molecular orbital calculations confirm the ability of NO and the versatility of sulfur bridges to buffer and distribute electrons, a key to their major importance in metalloenzymes.

DNIC↗
DOE OSTI2024

Parameter development and characterization of laser powder directed energy deposition of Nb – Alloy C103 for thin wall geometries

This work focuses on the parameter development and microstructural characterization of Nb-based alloy C103 for thin wall structures produced via laser powder – directed energy deposition (LP – DED). Laser power and scanning speeds were varied as part of a design of experiments to identify adequate print parameters. Combinations were evaluated for relative density, porosity, and geometrical accuracy. A combination of a laser power of 1420 W and scanning speed of 14 mm/s resulted in a relative density >99%, exhibited a consistent weld bead profile and was used for further microstructural evaluation. A mix of optical and scanning electron microscopy (SEM) revealed small, slightly elongated grains along the edges and large epitaxial grains in the central region along the Build – Transverse view. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analysis revealed Hf rich columnar cells in the center that transition into an evenly spaced cellular structure towards the edges of the built sample. Electron backscatter diffraction (EBSD) scans show a sharp [001] texture when looking at the cross section of the sample along the build direction. The Build – Scan view revealed a zig – zag pattern that follows the back – and – forth deposition strategy that was used. Finally, microhardness measurements were taken in the as – built (AB) and stress relieved (SR) conditions to baseline preliminary mechanical properties. The AB condition exhibited a large amount of scatter in the data and averages up to 11% larger than the SR condition. The reduction in scatter upon applying the SR cycle are indicative of a large concertation of dislocations present in the AB condition.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Electronic and magnetic structures of a mixed triple perovskite: Ba 3 NiRuIrO 9

In search of spin-orbit coupling driven nonmagnetic J = 0 ground state and excitonic magnetism, various pentavalent iridates have been studied in recent years. However, a finite moment was observed in most of the cases due to solid state effects. Here, in this work, we investigate the electronic and magnetic structure of 6H hexagonal compound Ba 3 NiRuIrO 9 , where Ir 5+ is present along with magnetic Ni 2+ and Ru 5+ ions. Magnetic susceptibility measurements and neutron powder diffraction (NPD) experiments demonstrate the appearance of short-range magnetic ordering below 170 K and a long-range antiferromagnetic ordering below 80 K. The refinement of the NPD pattern further shows that the Ru and Ir moments interact antiferromagnetically within the dimer and interact ferromagnetically with the Ni sublattice. These experimental findings have been complemented by first-principles density functional theory calculations incorporating spin-orbit coupling effects and electronic correlations for the transitional metal d states. The computed magnetocrystalline anisotropy is also found to be significant and the crystallographic c axis comes out to be the easy axis of magnetization, consistent with the spin alignment direction found from NPD. This study shows that the mixed ruthenate iridate triple perovskite series is a promising family to study the interplay among spin-orbit coupling, electron correlation, and electron filling as a variety of Ba 3 M RuIrO 9 with M as a transition metal ion, rare-earth ion, and alkali metal ions can be synthesized.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

X-Ray Performance of Critical-angle Transmission Grating Prototypes for the Arcus Mission

Arcus is a proposed Explorer Class soft X-ray grating spectrometer. It aims to explore cosmic feedback by mapping hot gases within and between galaxies and galaxy clusters and characterizing jets and winds from supermassive black holes and to investigate the dynamics of protoplanetary disks and stellar accretion. Arcus features 12 m focal-length grazing-incidence silicon pore optics (SPO) developed for the Athena mission. Critical-angle transmission (CAT) gratings efficiently disperse high diffraction orders onto CCDs. We report new and improved X-ray performance results for Arcus-like CAT gratings, including a record resolving power for two coaligned CAT gratings. Multiple Arcus prototype grating facets were illuminated by an SPO at the PANTER facility. The facets consist of 32 × 32.5 mm 2 patterned silicon membranes, bonded to metal frames. The bonding angle is adjusted according to the measured average tilt angle of the grating bars in the membrane. Two simultaneously illuminated facets show a minor broadening of the Al-K α doublet in the 18th and 21st orders with the best-fit record effective resolving power of ${R}_{G}\approx {1.3}_{-0.5}^{+\infty }\times {10}^{4}$ (3σ), about three to four times the Arcus requirement. We measured the diffraction efficiency of quasi-fully illuminated gratings at O-K wavelengths in orders 4–7 in an Arcus-like configuration and compare results with synchrotron spot measurements. After corrections for geometrical effects and bremsstrahlung continuum, we find agreement between full and spot illumination at the two different facilities, as well as with the models used for Arcus effective area predictions. We find that these flight-like gratings meet the diffraction efficiency and greatly exceed the resolving power Arcus requires.

79 ASTRONOMY AND ASTROPHYSICS↗