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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Probing elemental diffusion and radiation tolerance of perovskite solar cells via non-destructive Rutherford backscattering spectrometry

Mixed organic–inorganic halide perovskite-based solar cells have attracted interest in recent years due to their potential for both terrestrial and space applications. Analysis of interfaces is critical to predicting device behavior and optimizing device architectures. Most advanced tools to study buried interfaces are destructive in nature and can induce further degradation. Ion beam techniques, such as Rutherford backscattering spectrometry (RBS), is a useful non-destructive method to probe an elemental depth profile of multilayered perovskite solar cells (PSCs) as well as to study the inter-diffusion of various elemental species across interfaces. Additionally, PSCs are becoming viable candidates for space photovoltaic applications, and it is critical to investigate their radiation-induced degradation. RBS can be simultaneously utilized to analyze the radiation effects induced by He+ beam on the device, given their presence in space orbits. In the present work, a 2 MeV He+ beam was used to probe the evidence of elemental diffusion across PSC interfaces with architecture glass/ITO/SnO2/Cs0.05(MA0.17FA0.83)0.95Pb(I0.83Br0.17)3/spiro-OMeTAD/MoO3/Au. During the analysis, the device active area was exposed to an irradiation equivalent of up to 1.62 × 1015 He+/cm2, and yet, no measurable evidence (with a depth resolution ∼1 nm) of beam-induced ion migration was observed, implying high radiation tolerance of PSCs. On the other hand, aged PSCs exhibited indications of the movement of diverse elemental species, such as Au, Pb, In, Sn, Br, and I, in the active area of the device, which was quantified with the help of RBS.

14 SOLAR ENERGY↗
DOE OSTI2021

Spatially Resolved Potential and Li-Ion Distributions Reveal Performance-Limiting Regions in Solid-State Batteries

The performance of solid-state electrochemical systems is intimately tied to the potential and lithium distributions across electrolyte–electrode junctions that give rise to interface impedance. Here, we combine two operando methods, Kelvin probe force microscopy (KPFM) and neutron depth profiling (NDP), to identify the rate-limiting interface in operating Si-LiPON-LiCoO 2 solid-state batteries by mapping the contact potential difference (CPD) and the corresponding Li distributions. The contributions from ions, electrons, and interfaces are deconvolved by correlating the CPD profiles with Li-concentration profiles and by comparisons with first-principles-informed modeling. Furthermore, we find that the largest potential drop and variation in the Li concentration occur at the anode–electrolyte interface, with a smaller drop at the cathode–electrolyte interface and a shallow gradient within the bulk electrolyte. Correlating these results with electrochemical impedance spectroscopy following battery cycling at low and high rates confirms a long-standing conjecture linking large potential drops with a rate-limiting interfacial process.

25 ENERGY STORAGE↗
DOE OSTI2021

Evidence of lithium mobility under neutron irradiation

Understanding the evolution of intermetallic materials in high-radiation environments is of great importance for fusion science and national security. Tritium ( 3 H) and lithium ( 6 Li, 7 Li) transport within neutron irradiated claddings coated with aluminide (FeAl3) has been investigated using state-of-the-art multimodal imaging. Specifically, scanning electron microscopy – focused ion beam (SEM-FIB) was used to prepare irradiated coating lift-out samples for follow-on microanalysis. Here, scanning transmission electron microscopy (STEM) was used to acquire atomic-scale information on the carbonaceous structure and elemental mapping. Atomic force microscopy (AFM) was used to determine lift-out dimensions nondestructively. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) spectral and depth profiling show unexpected lithium isotopic distributions in the irradiated cladding, raising an important evidence of possible light isotope mobility within the cladding under elevated temperature and irradiation. ToF-SIMS three-dimensional chemical mappings of mid- and bottom-cladding coatings show light isotopic (e.g., 3 H, 6 Li, 7 Li) distributions in the irradiated coating and give new insights into the fundamental mechanism related to transport mechanisms within the cladding. Multimodal imaging is power to link microstructure, chemistry, and nanoscale defects that impact reliability of these materials. Furthermore, chemical mapping offers observations of the microstructural evolution due to irradiation and provides insights into unexpected material transport under extreme conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Three-dimensional hard X-ray ptychographic reflectometry imaging on extended mesoscopic surface structures

Many nanodevices and quantum devices, with their sizes often spanning from millimeters down to sub-nanometer, have intricate low-dimensional, non-uniform, or hierarchical structures on surfaces and interfaces. Since their functionalities are dependent on these structures, high-resolution surface-sensitive characterization becomes imperative to gain a comprehensive understanding of the function–structure relationship. We thus developed hard x-ray ptychographic reflectometry imaging, a new technique that merges the high-resolution two-dimensional imaging capabilities of hard x-ray ptychography for extended objects, with the high-resolution depth profiling capabilities of x-ray reflectivity for layered structures. The synergy of these two methods fully leverages both amplitude and phase information from ptychography reconstruction to not only reveal surface topography and localized structures, such as shapes and electron densities, but also yields statistical details, such as interfacial roughness that is not readily accessible through coherent imaging solely. The hard x-ray ptychographic reflectometry imaging is well-suited for three-dimensional imaging of mesoscopic samples, particularly those comprising planar or layered nanostructures on opaque supports, and could also offer a high-resolution surface metrology and defect analysis on semiconductor devices, such as integrated nanocircuits and lithographic photomasks for microchip fabrications.

47 OTHER INSTRUMENTATION↗
DOE OSTI2024

Natural formation of linear defect structures in MoS 2

Near surface defects can significantly impact the quality of metallic interconnects and other interfaces necessary to create device structures incorporating two-dimensional materials. Furthermore, the impact of such defects can strongly depend on their organization. In this study, we present scanning tunneling microscopy images and tunneling spectroscopy of point and linear defects near the surface of natural MoS 2 . The point defects share similar structural and electronic characteristics and occur with comparable frequency as subsurface sulfur vacancies observed previously on natural MoS 2 . The linear defects observed here occur less frequently than the point defects but share the same depth profile and electronic structure. These data indicate that the linear defects are actually a one-dimensional organization of subsurface sulfur vacancies. Our density functional calculations agree with this assessment in that, for sufficient local defect concentrations, it is energetically more favorable for the defects to be organized in a linear fashion rather than as clusters or even isolated single point defects. Given these measurements were taken from naturally formed MoS 2 , this organization likely occurs during crystal formation. Considering the impact of one-dimensional organization on the local properties of layered materials, and the potential for them to be introduced purposefully during crystal formation, research into the formation mechanism and properties of these defects could enable new paths for defect engineering in MoS 2 -based systems.

2D materials↗
NASA NTRS1973

Nuclear microprobe analysis of solar proton implantation profiles in lunar rock surfaces

Discussion of the results of hydrogen (proton) depth profile concentration analyses conducted on selected Apollo 16 rocks. A modeling of solar particle implantation profiles in lunar rocks is shown to trace the evolvement of these profiles under the combined influence of diffusion of atomic particles implanted in the rock, and rock surface erosion. It is also demonstrated that such diffusion may have a significant effect on the shape of the implantation profiles in certain rock materials.

Stauber, M. C.↗
DOE OSTI2023

Three-dimensional structure of hybrid magnetic skyrmions determined by neutron scattering

Magnetic skyrmions are topologically protected chiral spin textures which present opportunities for next-generation magnetic data storage and logic information technologies. The topology of these structures originates in the geometric configuration of the magnetic spins, more generally described as the structure. While the skyrmion structure is most often depicted using a two-dimensional projection of the three-dimensional (3D) structure, recent works have emphasized the role of all three dimensions in determining the topology and their response to external stimuli. Here, grazing-incidence small-angle neutron scattering and polarized neutron reflectometry are used to determine the 3D structure of hybrid skyrmions. The structure of the hybrid skyrmions, which includes a combination of Néel-like and Bloch-like components along their length, is expected to significantly contribute to their notable stability, which includes ambient conditions. To interpret the neutron scattering data, micromagnetic simulations of the hybrid skyrmions were performed, and the corresponding diffraction patterns were determined using a Born approximation transformation. The converged magnetic profile reveals the magnetic structure along with the skyrmion depth profile, including the thickness of the Bloch and Néel segments and the diameter of the core.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Mechanisms of Retention and Transport of Fission Products in Virgin and Irradiated Nuclear Graphite

To fulfill the design and licensing requirements for advanced reactors, the U.S. Department of Energy (DOE) is specifically interested in targeted research to quantify the mechanisms of fission product transport and retention in graphitic grades that will likely be used in next-generation very/high temperature reactors, fluoride salt-cooled high temperature reactors and molten salt reactors. We have examined an integrated experimental-computational approach to determine the diffusivities of selected fission products – ruthenium (Ru) and silver (Ag) in five nuclear graphite grades – POCO AXF-5Q, POCO ZXF-5Q, PCEA, IG110, and NBG-18. Experimental investigation for diffusion of other fission products (iodine, cesium, and krypton) in graphite could not be carried out due to extreme evaporation due to high vapor pressure, despite several attempts incorporating various experimental schemes. Experimental investigation with irradiated graphite could not be carried out because necessary approval to transport irradiated graphite could not be obtained due to procedural reasons at ORNL and national policy change in UK. An effort was made to “produce” by ion sputtering, but it was discontinued because the outcome did not adequately represent irradiated graphite. Thin film and “cup-and-cap” methods were employed to deposit fission products, diffusion annealed were carried out in an argon atmosphere, and concentration profiles were determined by dynamic secondary ion mass spectroscopy depth profiling technique. Regardless of graphite type, anomalous diffusion behavior of Ru (i.e., lower than expected based on Arrhenius temperature dependence) at an intermediate temperature, around 600 to 700 °C, was observed. Diffusion behavior of silver on the other hand agreed well to the Arrhenius temperature dependence although the excessive evaporation of silver hampered the accurate determination of diffusivities at temperature higher than 900 °C. In general, silver was observed to diffuse faster than Ru in the temperature range compared from 500 to 900 °C, had consistently had higher pre-exponential factor corresponding to higher jump frequency. To understand the abnormal diffusional behavior of Ru in graphite in intermediate temperature range, a detailed microstructural analysis was carried out. Clustering of Ru into particles on the surface of graphite was observed around 700 °C corresponding to de-wetting and spheroidization. This change would influence the boundary condition of diffusion, although features of clustering was much smaller (<1 mm) than the SIMS raster size (120 x 120 mm). Raman spectroscopy also demonstrated that Raman peak intensity for Ru decreased significantly for samples annealed higher than 700 °C and presence of Ru in graphite altered the crystallinity of graphite. To further elucidate the abnormal diffusion behavior observed in intermediate temperature investigated, the vibrational properties of graphene, bilayer graphene and Kr atoms in bilayer graphene were investigated with molecular dynamics. Krypton, which is a fission product, was introduced between a bilayer graphene system to evaluate (i) whether the phonon dispersion curves change with high temperature in bilayer graphene (ii) whether the addition of Kr atoms between the bilayer introduces any significant change in the vibrational properties, and (iii) whether any change in the vibrational properties can be correlated to the diffusive behavior of Kr atoms. The results show that the Kr atoms indeed exhibit an anomalous diffusive behavior at 550°C. Phonon analysis shows that a few phonon frequencies are enhanced as much as 20 to 30 % with the addition of just 0.2 at.% Kr. So, this may explain the unexpected self-diffusivity of fission products.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Two-dimensional electron systems in perovskite oxide heterostructures: Role of the polarity-induced substitutional defects

The discovery of a two-dimensional electron system (2DES) at the interfaces of perovskite oxides such as LaAlO 3 and SrTiO 3 has motivated enormous efforts in engineering interfacial functionalities with this type of oxide heterostructures. However, the fundamental origins of the 2DES are still not understood, e.g., the microscopic mechanisms of coexisting interface conductivity and magnetism. In this paper, we report a comprehensive spectroscopic investigation on the depth profile of 2DES-relevant Ti 3d interface carriers using depth- and element-specific techniques like standing-wave excited photoemission and resonant inelastic scattering. We found that one type of Ti 3d interface carriers, which give rise to the 2DES are located within three unit cells from the n-type interface in the SrTiO 3 layer. Unexpectedly, another type of interface carriers, which are polarity-induced Ti-on-Al antisite defects, reside in the first three unit cells of the opposing LaAlO3 layer (~10 Å). Our findings provide a microscopic picture of how the localized and mobile Ti 3d interface carriers distribute across the interface and suggest that the 2DES and 2D magnetism at the LaAlO 3 /SrTiO 3 interface have disparate explanations as originating from different types of interface carriers.

36 MATERIALS SCIENCE↗
NASA NTRS1986

In situ production of terrestrial cosmogenic helium and some applications to geochronology

The concentrations of cosmogenic He-3 have been measured in a series of basaltic drill core samples from Hawaiian volcanoes Haleakala and Mauna Loa. The He-3 concentration in the surface of a radiocarbon dated Mauna Loa flow (20,000 years) gives reasonable agreement with a theoretical production rate of 140 atoms/g/yr, and suggests that the uncertainty in this rate is roughly 10 percent. The results illustrate the feasibility of using He-3 to measure exposure ages of young basaltic lava flows and for measuring erosion rates. Erosion rates calculated from the three Haleakala cores range from 7 to 11 meters/million years. The drill core data demonstrate that accurate depth control is crucial to the use and evaluation of cosmogenic helium. Depth profiles from several of the older cores display a nonexponential depth dependence of He-3(c) below 170 g/sq cm, which is attributed to the contribution from Li-6(n, alpha)T, where the neutrons are from stopped muons. This has important implications for depth dependence of cosmogenic He-3 because muons are weakly attenuated compared to the nucleonic component that produces spallation.

Kurz, Mark D.↗
NASA NTRS1974

Measurement of the lunar neutron density profile

An in situ measurement of the lunar neutron density from 20 to 400 g/sq cm depth between the lunar surface was made by the Apollo 17 Lunar Neutron Probe Experiment using particle tracks produced by the B10(n, alpha)Li7 reaction. Both the absolute magnitude and depth profile of the neutron density are in good agreement with past theoretical calculations. The effect of cadmium absorption on the neutron density and in the relative Sm149 to Gd157 capture rates obtained experimentally implies that the true lunar Gd157 capture rate is about one half of that calculated theoretically.

Woolum, D. S.↗
DOE OSTI2024

Oxide dissolution and oxygen diffusion scenarios in niobium and implications on the Bean–Livingston barrier in superconducting cavities

We generalize a native Nb2O5 dissolution model [G. Ciovati, Appl. Phys. Lett. 89, 022507 (2006)] to sequential overlayer dissolutions, multilayer dissolution, and realistic temperature profiles, which may be applicable to other materials. The model is applied to secondary ion mass spectrometry depth profile measurements for varying temperature profiles and two-step oxide dissolution in Nb and found to agree well. In the context of the Meissner screening response due to impurity profiles on the length scale of the London penetration depth, the shallow diffusion of O impurities results in a substantial decrease in the peak supercurrent density near the surface. In this framework, oxide dissolution and oxygen diffusion can account for a rise in peak supportable magnetic field in SRF cavities with baking time and a suppression after the optimal baking time is reached, in good agreement with peak-field baking temperatures and times as well as recent quench field measurements.

Lechner, Eric↗
NASA NTRS1977

Auger profiling of 'abrupt' LPE Al/x/Ga/1-x/As-GaAs heterojunctions

Auger analysis in conjunction with ion milling was used to study depth profiles of 'abrupt' Al/x/Ga/1-x/As-GaAs heterojunctions grown by liquid-phase epitaxial (LPE) techniques. Results are presented on samples with x = 0.43, 0.60, and 0.85. The interface widths obtained are listed in a table together with the growth conditions and the layer thicknesses. The values for the layer thicknesses are in the range from 125 to 950 A. It is found that for thin layers the interface widths do not differ greatly from the average value of 110A.

Garner, C. M.↗
DOE OSTI2022

Pulsed Thermal Tomography Nondestructive Examination of Additively Manufactured Reactor Materials and Components (Final Technical Report)

Metal Additive Manufacturing (AM) is a promising method for cost-efficient fabrication of complex shape structures for applications in harsh environment, such as in a nuclear reactor. However, internal defects (pores) occur in high-strength AM alloys, which are manufactured with Laser Powder Bed Fusion (LPBF) AM method. Pulsed Infrared Thermography (PIT) is an efficient nondestructive evaluation (NDE) method to examine actual structures, because this method offers one-sided non-contact measurements, and fast processing of large sample areas. However, imaging of material defects, particularly defects with sizes at microscopic level, is challenging. In this report, we benchmark the performance of several Unsupervised Learning (UL) algorithms designed to enhance imaging of microscopic defects in metals with PIT. UL aims to learn the latent principal patterns (dictionaries) in PIT data to detect defects with minimal human supervision. Performance of Independent Component Analysis (ICA), Sparse Coding (SC), Principal Component Analysis (PCA) and Exploratory Factor Analysis (EFA) was compared using F-score, UL model training time and defects reconstruction time. We obtained the average F-score of 0.75, and a highest F-score of 0.89 for the EFA algorithm. Overall, EFA outperforms other UL algorithms considered in this study. In another approach, we investigate Thermal Tomography (TT), which is a computational method for reconstruction of depth profile of internal material defects from PIT nondestructive evaluation (NDE). TT algorithm obtains depth reconstructions of thermal effusivity, which has been shown to provide visualization of subsurface internals defects in metals. In many applications, one needs to determine the defect shape and orientation from reconstructed effusivity images. Interpretation of TT images is non-trivial because of blurring, which increases with depth due to heat diffusion-based nature of image formation. We have developed a deep learning convolutional neural network (CNN) to classify size and orientation of subsurface material defects in TT images. CNN was trained with TT images produced with computer simulations of 2D metallic structures (thin plates) containing elliptical subsurface voids. Performance of CNN was investigated using test TT images developed with computer simulations of plates containing elliptical defects, and defects with shape imported from scanning electron microscopy (SEM) images. CNN demonstrated the ability to classify radii and angular orientation of elliptical defects in previously unseen test TT images. We have also demonstrated that CNN trained on TT images of elliptical defects is capable of classifying shape and orientation of irregular defects. Training the CNN on irregular defect shapes instead of on elliptical shapes would make the resulting classifications more descriptive of actual defect shapes. However, this requires a much higher volume of SEM images of material defects, which are difficult to obtain because of random occurrence of defects in LPBF. To address this challenge, we developed a generative adversarial network (GAN) to augment the existing dataset of SEM defect images. The GAN model is demonstrated to create novel yet realistic defect shapes that can be used as input for simulated PTT images to train CNN. We also investigate several approaches based on Gaussian Random Circle and Bezier Curves for constructing parametric models of irregular-shape defects.

36 MATERIALS SCIENCE↗
NASA NTRS1989

Simulation of collisional transport processes and the stability of planetary rings

The utility of the phase-space fluid method for the study of planetary ring dynamics is presently demonstrated through the numerical solution of a model kinetic equation for a flattened Keplerian disk. Attention is given to ringlets composed of single-sized particles, as well as to ringlets composed of two different-sized particles; in the latter case, the ringlets evolve in such a way that the lighter particles are confined by the heavier ones. The results obtained indicate that some natural process may sharpen the optical depth profile of edges even without an external forcing mechanism, and that intermediate optical depths are dynamically preferred in some cases.

Brophy, Thomas G.↗
NASA NTRS1995

Saturn's central flash from the 3 July 1989 occultation of 28 Sgr

We present observations of Saturn's central flash obtained from Palomar and McDonald Observatories during the 3 July 1989 occultation of 28 Sgr. As the star passed close to the geometric center of Saturn's shadow, the focusing of the incident starlight by the planet's atmosphere formed multiple stellar images along the limb which were detected in infrared images obtained at wavelengths of 3.9 (Palomar) and 2.1 microns (McDonald). These are the first reported observations of a central flash due to Saturn, and the first of any planet in which the signal flash from each stellar image could be determined separately, permitting a comparison of both intensity and position for each image with model predictions. Four separate flashes were observed from each observatory, corresponding to points on the limb where the starlight passed through the Cassini Division and the relatively transparent C Ring, with maximum brightness reaching 1-2% of the unocculted stellar intensity. The timing of the flashes is quite sensitive to the shape of Saturn's limb, which depends in turn on the planet's zonal gravity harmonics and on the zonal wind profile in the lower stratosphere, near the 2.5-mbar pressure level. The locations of the images along the limb, as well as the timing, shapes, and amplitudes of the individual flash light curves, are well matched by a smoothed model based on a tropospheric zonal wind profile obtained from tracking cloud features in Voyager images and the Saturn ring optical depth profile obtained from the Voyager Photopolarimeter experiment. The smoothing required to give the best match to the data exceeds that attributable to the finite angular extent of the occulted star and may be due to refractive scattering by turbulence or wave structure in Saturn's atmosphere. There is no evidence of significant atmospheric absorption at the observed wavelengths, which correspond to spectral regions of weak methane absorption.

Nicholson, Philip D.↗
DOE OSTI2025

Understanding the limitations and potential of micro tensile testing of tungsten and needs for crystal plasticity modelling

Tungsten is the leading plasma facing material candidate due to its exceptional properties. Understanding the response to neutron irradiation is crucial for the lifetime evaluation of tungsten. The limited space in nuclear reactors and the high levels of radioactivity of the specimens after irradiation are significant barriers to accurately measuring the mechanical properties after neutron irradiation. Testing of micro tensile specimens is one approach to reduce the total amount of irradiated material needed for a set of mechanical testing experiments. However, micro samples are not necessarily measuring the bulk material properties, as size effects produce higher measured mechanical properties than is observed in engineering size counterparts. Determining the minimal sample size for reliable bulk property measurement, combined with modeling efforts, is essential. We conducted room temperature tensile tests on tungsten micro tensile specimens fabricated with focused ion beam, plasma focused ion beam and femto-second laser ablation system to dimension of 2×2×7?µm³, 7×7×18?µm³, and 80×100×233?µm³ (width×thickness×gauge-length), respectively. Elevated tensile testing was performed up to 475°C on 5×5×18?µm³ specimens fabricated with focused ion beam. The smallest specimens exhibited a high degree of ductility and strength, whereas the largest specimens demonstrated behavior akin to bulk tungsten. To investigate the effects introduced by the micro specimen fabrication processes and to obtain the necessary bulk dislocation density for the crystal plasticity model, we employed X-ray diffraction depth profiling. This measurement was performed using different X-ray sources with varying penetration depths. Finally, the potential and limitations of micro mechanical tests for tungsten will be discussed.

36 - MATERIALS SCIENCE↗