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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Impact of dynamic specimen shape evolution on the atom probe tomography results of doped epitaxial oxide multilayers: Comparison of experiment and simulation

The experimental atom probe tomography (APT) results from two different specimen orientations (top-down and sideways) of a high oxygen ion conducting Samaria-doped-ceria/Scandia-stabilized-zirconia multilayer thin film solid oxide fuel cell electrolyte was compared with level-set method based field evaporation simulations for the same specimen orientations. This experiment-simulation comparison explains the dynamic specimen shape evolution and ion trajectory aberrations that can induce density artifacts in final reconstruction, leading to inaccurate estimation of interfacial intermixing. This study highlights the importance of comparing experimental results with field evaporation simulations when using APT to study oxide heterostructure interfaces.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Distance probes of dark energy

This document presents the results from the Distances subgroup of the Cosmic Frontier Community Planning Study (Snowmass 2013). We summarize the current state of the field as well as future prospects and challenges. In addition to the established probes using Type Ia supernovae and baryon acoustic oscillations, we also consider prospective methods based on clusters, active galactic nuclei, gravitational wave sirens and strong lensing time delays.

Cosmology↗
DOE OSTI2021

Perspectives in Scanning Probe Microscopy from the 2021 Joint International Scanning Probe Microscopy and Scanning Probe Microscopy on Soft and Polymeric Materials Conference

In March of 2020 we were well on our way to organizing and hosting one of the premier scanning probe microscopy (SPM) conferences in Breckenridge, Colorado, USA. For the first time, the meeting would synergistically combine International Scanning Probe Microscopy (ISPM) and Scanning Probe Microscopy on Soft and Polymeric Materials (SPMonSPM), to increase the breadth of audience expertise and experience. We coined the joint conference iSPM 3 – a moniker we hope will persist in future events. The plan for 2020 iSPM 3 screeched to a halt in mid-March, amidst the COVID-19 pandemic. Luckily, we were able to regroup and reimagine the conference for 2021 as a virtual experience. The conference took place June 28th to July 2nd with a mix of live and pre-recorded content. Spread throughout the week were 4 live panel discussions, 3 plenary talks, 23 invited talks, 75 contributed talks, 15 posters and 3 social events. The technical program represented much of the latest and most impactful research in the field. The panel discussions sought to step back from specific research findings and assess the state of SPM as it pertains to some of the most pressing opportunities and influential successes. The lively discussions painted a vibrant future for SPM in both breadth and detail, and we hope that similar discussion can be a mainstay of future SPM conferences. In this work, we attempt to distill some of that discussion to motivate researchers across the field of SPM in the coming years.

47 OTHER INSTRUMENTATION↗
DOE OSTI2015

Simulation of Heterogeneous Atom Probe Tip Shape Evolution during Field Evaporation Using a Level Set Method and Different Evaporation Models

Accurate reconstruction of spatial positions of field evaporated ions from detector patterns depends on a correct understanding of the tip shape evolution and evaporation laws of component atoms. Reconstruction artifacts introduced in the heterogeneous tip can be contributed by the assumption on homogeneous evaporation behavior. A level set method based specimen shape evolution model is developed in this study to simulate the evaporation of synthetic layered-structured atom probe tip. The simulation results of the shape evolution by the present level set model agree well with the literature data using other numerical approaches, i.e. finite difference method. The asymmetric evolving shape predicted by the level set model demonstrates that the complex evaporation behavior of heterogeneous tips and interface curvature can potentially lead to the tip reconstruction distortion. Compared with other shape evaporation methods the new method provides considerably higher resolution and computational efficiency with the aid of the intrinsic subgrid scale accuracy.

atom probe tomography, field evaporation, tip shap↗
DOE OSTI2016

Analysis of compositional uniformity in Al{sub x}Ga{sub 1−x}N thin films using atom probe tomography and electron microscopy

Calculated frequency distributions of atom probe tomography reconstructions (∼80 nm field of view) of very thin Al{sub x}Ga{sub 1−x}N (0.18 ≤ x ≤ 0.51) films grown via metalorganic vapor phase epitaxy on both (0001) GaN/AlN/SiC and (0001) GaN/sapphire heterostructures revealed homogeneous concentrations of Al and chemically abrupt Al{sub x}Ga{sub 1−x}N/GaN interfaces. The results of scanning transmission electron microscopy and selected area diffraction corroborated these results and revealed that neither superlattice ordering nor phase separation was present at nanometer length scales.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Effects of Laser Energy and Wavelength on the Analysis of LiFePO4 Using Laser Assisted Atom Probe Tomography

The effects of laser wavelength (355 nm and 532 nm) and laser pulse energy on the quantitative accuracy of atom probe tomography (APT) examinations of LiFePO4 (LFP) are considered. A systematic investigation of ultraviolet (UV, 355 nm) and green (532 nm) laser assisted APT of LFP has revealed distinctly different behaviors. With the use of UV laser the major issue was identified as the preferential loss of oxygen (up to 10 at. %) while other elements (Li, Fe and P) were observed to be close to nominal ratios. Lowering the laser energy per pulse to 1 pJ increased the observed oxygen concentration to near its correct stoichiometry and was well correlated with systematically higher concentrations of 16O2+ ions. This observation supports the premise that lower laser energies lead to a higher probability of oxygen molecule ionization. Conversely, at higher laser energies the resultant lower effective electric field reduces the probability of oxygen molecule ionization. Green laser assisted field evaporation led to the selective loss of Li (~50% deficiency) and correct ratios of the remaining elements, including the oxygen concentration. The loss of Li is explained by selective dc evaporation of lithium between laser pulses and relatively negligible oxygen loss as neutrals during green-laser pulsing. Lastly, plotting of multihit events on a Saxey plot for the straight-flight path data (green laser only) revealed a surprising dynamic recombination process for some molecular ions mid-flight.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2014

On the reliable analysis of indium mole fraction within In x Ga 1-x N quantum wells using atom probe tomography

Surface crystallography and polarity are shown to influence the detection probability of In, Ga, and N ions during atom probe tomography analysis of In x Ga 1-x N m -plane, c -plane, and ($20\overline{21}$) quantum wells. A N deficit is observed in regions of the reconstruction generated from Ga-polar surfaces, and the probability of detecting group-III atoms is lower in In x Ga 1-x N quantum wells than in GaN barrier layers. Finally, despite these artifacts, the detected In mole fraction is consistent throughout a given quantum well regardless of the crystal orientation of the quantum well or the evaporation surface from which the reconstruction was generated.

36 MATERIALS SCIENCE↗
DOE OSTI2015

A polarized Drell-Yan experiment to probe the dynamics of the nucleon sea

In QCD, nucleon spin comes from the sum of the quark spin, gluon spin, and the quark and gluon orbital angular momentum, but how these different components contribute and the interplay among them is not yet understood. For instance, sea quark orbital contribution remains largely unexplored. Measurements of the Sivers function for the sea quarks will provide a probe of the sea quark orbital contribution. The upcoming E1039 experiment at Fermilab will measure the Sivers asymmetry of the sea quarks via the Drell-Yan process using a 120 GeV unpolarized proton beam directed a transversely polarized ammonia target. We report on the status and plans of the E1039 polarized Drell-Yan experiment.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Developing a bright 17 keV x-ray source for probing high-energy-density states of matter at high spatial resolution

A set of experiments were performed on the National Ignition Facility (NIF) to develop and optimize a bright, 17 keV x-ray backlighter probe using laser-irradiated Nb foils. High-resolution one-dimensional imaging was achieved using a 15 μm wide slit in a Ta substrate to aperture the Nb He{sub α} x-rays onto an open-aperture, time integrated camera. To optimize the x-ray source for imaging applications, the effect of laser pulse shape and spatial profile on the target was investigated. Two laser pulse shapes were used—a “prepulse” shape that included a 3 ns, low-intensity laser foot preceding the high-energy 2 ns square main laser drive, and a pulse without the laser foot. The laser spatial profile was varied by the use of continuous phase plates (CPPs) on a pair of shots compared to beams at best focus, without CPPs. A comprehensive set of common diagnostics allowed for a direct comparison of imaging resolution, total x-ray conversion efficiency, and x-ray spectrum between shots. The use of CPPs was seen to reduce the high-energy tail of the x-ray spectrum, whereas the laser pulse shape had little effect on the high-energy tail. The measured imaging resolution was comparably high for all combinations of laser parameters, but a higher x-ray flux was achieved without phase plates. This increased flux was the result of smaller laser spot sizes, which allowed us to arrange the laser focal spots from multiple beams and produce an x-ray source which was more localized behind the slit aperture. Our experiments are a first demonstration of point-projection geometry imaging at NIF at the energies (>10 keV) necessary for imaging denser, higher-Z targets than have previously been investigated.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Overestimation of Mach number due to probe shadow

Comparisons of the plasma ion flow speed measurements from Mach probes and laser induced fluorescence were performed in the Controlled Shear Decorrelation Experiment. We show the presence of the probe causes a low density geometric shadow downstream of the probe that affects the current density collected by the probe in collisional plasmas if the ion-neutral mean free path is shorter than the probe shadow length, L g = w 2 V drift /D ⊥ , resulting in erroneous Mach numbers. We also present a simple correction term that provides the corrected Mach number from probe data when the sound speed, ion-neutral mean free path, and perpendicular diffusion coefficient of the plasma are known. The probe shadow effect must be taken into account whenever the ion-neutral mean free path is on the order of the probe shadow length in linear devices and the open-field line region of fusion devices.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Influence of surface relaxation on solute atoms positioning within atom probe tomography reconstructions

Highlights: • APT measurement of Al/Cu alloy is simulated with a combined electrostatics and molecular dynamics (MD) approach. • Results show segregation of dilute Cu at [111] poles in correspondence to experimental measurements. • No temperature is involved. The effect originates in both disparate evaporation field and bond-energies in the alloy. While thermal or field-induced surface migration has been invoked often in past literature to rationalize the experimental observations of solute and impurity atoms segregation to specific poles and zones lines in atom probe tomography (APT) reconstructions, it does not satisfactorily explain all experimental results. Using a combined finite-element and molecular dynamics simulation approach that models the field evaporation process from mechanically relaxed emitter structures, we show that an additional mechanism, athermal relaxation, can also drive significant solute migration. The mechanism is illustrated for Cu in solid solution in Al, which exhibits segregation of Cu to 111 poles and along [110] zone lines in reconstructed APT data. The higher bonding energy of Cu atoms on the surface, confirmed using density-functional theory calculations, causes longer retention on the surface and preferential evaporation of neighboring Al atoms with subsequent athermal relaxation of Cu into higher-neighbor-count sites left vacant by evaporating Al neighbors. This in turn results in barrier-free long-range migration of the Cu atoms by a series of relaxation events that follow the receding terrace ledges towards high-neighbor count poles and zone lines. This mechanism fundamentally limits spatial resolution in the limit of zero temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Optimization of a low noise detection circuit for probing the structure of damage cascades with IBIC

Optimal detector / pre-amplifier combinations have been identified for the use of light ion IBIC (ion beam induced charge) to probe the physical structure of electrically active defects in damage cascades caused by heavy ion implantation. The ideal detector must have a sufficiently thin dead layer that incident ions will produce the majority of damage cascades in the depletion region of the detector rather than the dead layer. Detector and circuit noise must be low enough to detect the implantation of a single heavy ion as well as the decrease in the light ion IBIC signal caused by Shockley-Read-Hall recombination when the beam scans regions of the detector damaged by the heavy ion. The IBIC signals from three detectors irradiated with 750 keV He⁺ ions are measured with commercial and bespoke charge sensitive pre-amplifiers to identify the combination with the lowest noise.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Comparative analyses of plasma probe diagnostics techniques

The subject of this paper is a comparative analysis of the plasma parameters inferred from the classical Langmuir probe procedure, from different theories of the ion current to the probe, and from measured electron energy distribution function (EEDF) obtained by double differentiation of the probe characteristic. We concluded that the plasma parameters inferred from the classical Langmuir procedure can be subjected to significant inaccuracy due to the non-Maxwellian EEDF, uncertainty of locating the plasma potential, and the arbitrariness of the ion current approximation. The plasma densities derived from the ion part of the probe characteristics diverge by as much as an order of magnitude from the density calculated according to Langmuir procedure or calculated as corresponding integral of the measured EEDF. The electron temperature extracted from the ion part is always subjected to uncertainty. Such inaccuracy is attributed to modification of the EEDF for fast electrons due to inelastic electron collisions, and to deficiencies in the existing ion current theories; i.e., unrealistic assumptions about Maxwellian EEDFs, underestimation of the ion collisions and the ion ambipolar drift, and discounting deformation of the one-dimensional structure of the region perturbed by the probe. We concluded that EEDF measurement is the single reliable probe diagnostics for the basic research and industrial applications of highly non-equilibrium gas discharge plasmas. Examples of EEDF measurements point up importance of examining the probe current derivatives in real time and reiterate significance of the equipment technical characteristics, such as high energy resolution and wide dynamic range.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Investigation of Sampling-Probe Distorted Temperature Fields with X-Ray Fluorescence Spectroscopy

Flame-sampling experiments, especially in conjunction with laminar low-pressure premixed flames, are routinely used in combustion chemistry studies to unravel the identities and quantities of key intermediates and their pathways. In many instances, however, an unambiguous interpretation of the experimental and modeling results is hampered by the uncertainties about the probe-induced, perturbed temperature profile. To overcome this limitation, two-dimensional perturbations of the temperature field caused by sampling probes with different geometries have been investigated using synchrotron-based X-ray fluorescence spectroscopy. In these experiments, which were performed at the 7-BM beamline of the Advanced Photon Source (APS) at the Argonne National Laboratory, a continuous beam of hard X-rays at 15 keV was used to excite krypton atoms that were added in a concentration of 5 vol.-% to the unburnt gas mixture and the resulting krypton fluorescence at 12.65 keV was subsequently collected. The highly spatially resolved signal was converted into the local flame temperature to obtain temperature fields at various burner-probe separations as functions of the distance to the burner surface and the radial distance from the centerline. Multiple measurements were performed with different probe geometries and because of the observed impact on the temperature profiles the results clearly revealed the need to specify the sampling probe design to enable quantitative and meaningful comparisons of modeling results with flame-sampled mole fraction data. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Hansen, N.↗