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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 OSTI2024

Polarization-dependent photoemission electron microscopy for domain imaging of inorganic and molecular materials

Polarization-dependent photoemission electron microscopy (PD-PEEM) exploits spatial variation in the optical selection rules of materials to image domain formation and material organization on the nanoscale. In this Perspective, we discuss the mechanism of PD-PEEM that results in the observed image contrast in experiments and provide examples of a wide range of material domain structures that PD-PEEM has been able to elucidate, including molecular and polymer domains, local electronic structure and defect symmetry, (anti)ferroelectricity, and ferromagnetism. As a result, we discuss challenges and new directions that are possible with this tool for probing domain structure in materials, including investigating the formation of transient ordered states, multiferroics, and the influence of molecular and polymer order and disorder on excited state dynamics and charge transport.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Femtosecond photoemission electron microscopy of surface plasmon polariton beam steering via nanohole arrays

Directional control over surface plasmon polariton (SPP) waves is a prerequisite for the development of miniaturized optical circuitry. Here, the efficacy of single and dual component SPP steering elements is explored through photoemission electron microscopy. Our imaging scheme relies on two-color photoemission and counter-propagating SPP generation, which collectively allow SPPs to be visualized in real space. Wave-vector difference mixing between two-dimensional arrays of nanoholes and photon momenta enables SPP steering with directionality governed by the array lattice constant. The magnitude of grating momentum required to achieve counter-propagation guarantees efficient steering over the full range of the negative half-space. In our dual component configuration, separate SPP generation and Bragg diffraction based steering optics are employed. We find that array Bragg planes principally influence the SPP angles through the array band structure, which allows us to visualize both positive and negative refractory waves.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Modifications in the charge trap landscape in Hf 0.5 Zr 0.5 O 2 as a function of oxygen vacancy concentration observed with photoemission electron microscopy

Oxygen vacancies in Hf x Zr (1-x) O 2 (HZO) both contribute to stabilization of the ferroelectric orthorhombic phase and promote leakage pathways that limit the endurance of devices based on the material. Here, for this reason, the defect states of oxygen vacancies were investigated using photoemission electron microscopy (PEEM) and photoluminescence spectroscopy (PL), as their concentration was varied via ex situ laser exposure. Following a controlled oxygen vacancy reduction via visible (2.54 eV) laser dosing of HZO, deep-ultraviolet (DUV, 5.82 eV) PEEM was used to spatially probe the resulting mid-gap defect states and work function. Work function was found to increase monotonically with the laser-induced reduction in oxygen vacancy concentration culminating in a total increase near 70 meV. The change implies a Fermi level shift toward the valence band as the total available electron-filled charge states are reduced with the removal of oxygen vacancies. A reduction in charge states is corroborated by the observed lessening of both photoemission and photoluminescence intensities after laser dosing. The deduced position of the Fermi level is within a band of near-conduction band defect states produced by oxygen vacancies that are linked to endurance limiting leakage currents. Together, these results directly identify the primary role of oxygen vacancies on the defect states in HZO while demonstrating that laser exposure can be used for their modification.

42 ENGINEERING↗
DOE OSTI2025

Investigation of the Anisotropy of Y-Ba-Cu-O Thin Films With Photoemission Electron Microscopy

Understanding the anisotropy in the electrical properties of YBa2Cu3O7-δ (YBCO) is important for understanding the fundamental mechanism of superconductivity in unconventional superconductors. Additionally it is also essential for achieving uniform and controllable critical currents and resistances in YBCO Josephson junctions. Here, this study correlates work function measurements of different intrinsic regions on YBCO thin films, obtained through PhotoEmission Electron Microscopy (PEEM), with in plane tunneling data and helium ion imaging. YBCO thin films, 40 nm in thickness, were selectively irradiated with 300 keV helium using a Pelletron to investigate the effects of irradiation compared to unirradiated regions. Post-irradiation PEEM images revealed distinct contrasts between irradiated and non-irradiated regions, suggesting a metal-to-insulator transition. In non-irradiated areas, a domain pattern was detected, showing a 25 meV difference in work function, attributed to CuO and BaO rich surface regions. A similar domain structure was observed using high-resolution helium ion imaging; however, the helium ion beam can damage the YBCO, making PEEM a valuable non-destructive alternative. This work highlights the correlation between PEEM measurements and in-plane tunneling properties of YBCO, providing insights into material orientation and its impact on Josephson junction performance. Furthermore, it offers a non-destructive approach to understanding the anisotropy of cuprate materials, its superconducting properties, and the factors affecting Josephson junction performance.

Qu, Rochelle Y. [Univ. of California, Riverside, C↗
DOE OSTI2022

Uncovering surface plasmon optical resonances in nanohole arrays through interferometric photoemission electron microscopy

In this work, the role of surface plasmon polaritons (SPPs) in nanohole array optical extinction spectra is explored using a time-resolved technique capable of isolating the air/metal interfacial SPP contribution to the typical Fano profile in optical transmission curves. A pair of interferometrically locked broad-band femtosecond pulses is used to launch SPPs from lithographically patterned plasmonic nanohole arrays. SPPs launched in the co- and counter-propagating directions are probed using a third probe pulse in a photoemission electron microscope. Using this approach, we record interferometric SPP–SPP linear autocorrelations that selectively report on the resonances of SPPs launched from arrays of varying pitches and hole diameters. Aside from advancing an approach to selective SPP spectroscopy, we illustrate that resonant coupling in the counter-propagating direction may be exploited to control the spatial, temporal, and spectral characteristics of SPPs. For the counter-propagating direction, we show that tuning the array pitch near the fundamental plasmon resonance generates color-tuned (~770–820 nm), narrow bandwidth SPPs, and the bandwidth may be controlled by changing the ratio of pitch to hole diameter. The SPP resonances we recover through Fourier transforms of the interferometric autocorrelations shed light on the classical problem of Fano interference in nanohole array extinction spectra.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Atomic structure of different surface terminations of polycrystalline ZnPd

The intermetallic compound ZnPd has been found to have desirable characteristics as a catalyst for the steam reforming of methanol. The understanding of the surface structure of ZnPd is important to optimize its catalytic behavior. However, due to the lack of bulk single-crystal samples and the complexity of characterizing surface properties in the available polycrystalline samples using common experimental techniques, all previous surface science studies of this compound have been performed on surface alloy samples formed through thin-film deposition. In this study, we present findings on the chemical and atomic structure of the surfaces of bulk polycrystalline ZnPd studied by a variety of complementary experimental techniques, including scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy (XPS), low energy electron microscopy (LEEM), photoemission electron microscopy (PEEM), and microspot low-energy electron diffraction ( μ -LEED). These experimental techniques, combined with density functional theory (DFT)-based thermodynamic calculations of surface free energy and detachment kinetics at the step edges, confirm that surfaces terminated by atomic layers composed of both Zn and Pd atoms are more stable than those terminated by only Zn or Pd layers. DFT calculations also demonstrate that the primary contribution to the tunneling current arises from Pd atoms, in agreement with the STM results. The formation of intermetallics at surfaces may contribute to the superior catalyst properties of ZnPd over Zn or Pd elemental counterparts. Published by the American Physical Society 2024

36 MATERIALS SCIENCE↗
DOE OSTI2024

Exploring the Mineral Composition, Structure, and Function of a Freshwater Bivalve Adhesive

Abstract Etheria elliptica is a freshwater oyster that produces an adhesive that hardens underwater, allowing them to attach to other oysters, rocks, wood, and other natural substrates, producing complex oyster bed communities. Despite the importance of the adhesive in oyster bed formation, little is known about its chemical composition, structure, or mechanical properties. Through a combination of scanning electron microscopy (SEM), x‐ray photoemission electron microscopy (X‐PEEM), infrared (IR) spectroscopy, microhardness testing, and nanoindentation, it is found that the oyster adhesive consists entirely of aragonite nanoparticles that clump together into crystallites of varied shape, size, and orientation. The crystallite clumping density varies from the exterior of the adhesive to the interior, with the adhesive closest to the prismatic layer generally being denser. With this variation in density comes a variation in material properties with the exterior adhesive layer being softer and more flexible and the interior adhesive layer being harder and less elastic, or more similar to the prismatic and nacre shell structures produced by the E. elliptica . The resultant material exhibits varied materials properties, despite similar mineral composition.

Chemistry↗
DOE OSTI2025

Initiation of dusting corrosion in high-temperature alloys under CO exposure

Carbon monoxide is commonly encountered in energy systems, yet its reactivity with structural alloys—critical heat-resistant components in these systems—has been largely overlooked compared to the well-documented effects of oxidizing gases. In contrast, we demonstrate the high-temperature reaction of CO with NiAl using in-situ low-energy electron microscopy and X-ray photoemission electron microscopy. Our results show that CO dissociates into atomic oxygen and carbon, resulting in two concurrent reactions: selective oxidation of aluminum to form Al 2 O 3 and the initiation of dusting corrosion through carbon dissolution into the alloy and subsequent carbon deposition on the surface. These reactions produce spatially distinct surface products, preventing the formation of a continuous protective Al oxide layer. These results reveal a preference for the dissociative pathway of CO over the classic Boudouard disproportionation reaction that forms CO 2 . These insights not only advance our understanding of CO-induced alloy degradation but also highlight the practical implications for managing alloy stability and optimizing catalysis in carbon-rich environments, such as those in petrochemical processing and hydrocarbon combustion.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Modulating above-room-temperature magnetism in Ga-implanted Fe 5 GeTe 2 van der Waals magnets

The creation of van der Waals (vdW) ferromagnets with tunable Curie temperature (T C ) and magnetic anisotropy is essential in developing vdW magnet-based devices. Here, we report an effective and reliable method for modulating the magnetic properties of vdW Fe 5 GeTe 2 by site-specific Ga + implantation. In this study, we report an easy axis in the ab-plane for bulk Fe 5 GeTe 2 (T C = 310 K) and an axis out of the plane for thin Fe 5 GeTe 2 flakes (T C = 290 K). Combining element-resolved photoemission electron microscopy and spatially resolved magneto-optic Kerr microscopy, we find that the implantation of a tiny amount of 10 –3 Ga + ·Å –3 in Fe 5 GeTe 2 greatly enhances the T C from 290 to 360 K and switches the magnetic easy axis from the out-of-plane c axis to the ab-plane. The room-temperature x-ray magnetic circular dichroism signal is enhanced from 0% to 9% at an implantation level of 10 –2 Ga + ·Å –3 . These results provide new opportunities for tailoring the magnetic properties of vdW materials beyond room temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Analysis of X-ray images and spectra (aXis2000): A toolkit for the analysis of X-ray spectromicroscopy data

Spectromicroscopy refers to analytical methods that combine imaging and spectroscopy to provide detailed, spatially resolved analytical information about a sample, such as the type and quantitative spatial distributions of chemical components, geometric or magnetic alignment information, crystal structure, etc. The analysis of X-ray images and spectra (aXis2000) software described in this work provides a set of routines within a single, integrated, graphical-oriented package to read, display, manipulate and analyze spectromicroscopy data, with particular focus on soft X-ray spectromicroscopy methods such as scanning transmission X-ray microscopy (STXM), X-ray photoemission electron microscopy (XPEEM), scanning photoelectron X-ray microscopy (SPEM) and transmission X-ray microscopy (TXM). Here, this free software is described and compared to other software that can provide similar or complementary capabilities. Examples of spectromicroscopic analyses using advanced features of aXis2000 are provided.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Imaging the spin chirality of ferrimagnetic Néel skyrmions stabilized on topological antiferromagnetic Mn 3 Sn

Néel skyrmions are generally realized in asymmetric multilayers made of heavy metals (HMs) and ultrathin ferromagnets possessing strong interfacial Dzyaloshinskii-Moriya interactions (iDMIs). Depending on the relative strengths of iDMIs at the interfaces, various types of Néel skyrmions have been suggested, which are typified with characteristically different topological properties and current-driven dynamics. This suggests the importance of a precise quantification of their spin chiralities. In this paper, we explore the possibility of realizing Néel skyrmions in magnetic multilayers without the direct usage of standard HMs. Specifically, through depositing a thin layer of ferrimagnetic (FIM) CoTb layer on top of an antiferromagnetic (AFM) quantum material of composition Mn 3 Sn, the AFM exchange interaction at the asymmetric interface provides an equivalent iDMI for stabilizing FIM Néel skyrmions. Secondly, through using advanced four-dimensional Lorentz scanning transmission electron microscopy (4D LSTEM), in combination with x-ray magnetic circular dichroism photoemission electron microscopy (XMCD-PEEM), we can directly determine the spin chirality of FIM Néel skyrmions. Finally, the present findings not only broaden the phase space for chiral interfacial magnetism but also provide a possibility for future applications of heavy-metal-free skyrmionic devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Imaging Phase Segregation in Nanoscale Li x CoO 2 Single Particles

Li x CoO 2 (LCO) is a common battery cathode material that has recently emerged as a promising material for other applications including electrocatalysis and as electrochemical random access memory (ECRAM). During charge– discharge cycling LCO exhibits phase transformations that are significantly complicated by electron correlation. While the bulk phase diagram for an ensemble of battery particles has been studied extensively, it remains unclear how these phases scale to nanometer dimensions and the effects of strain and diffusional anisotropy at the single-particle scale. Understanding these effects is critical to modeling battery performance and for predicting the scalability and performance of electrocatalysts and ECRAM. Here we investigate isolated, epitaxial LiCoO 2 islands grown by pulsed laser deposition. After electrochemical cycling of the islands, conductive atomic force microscopy (c-AFM) is used to image the spatial distribution of conductive and insulating phases. Above 20 nm island thicknesses, we observe a kinetically arrested state in which the phase boundary is perpendicular to the Li-planes; we propose a model and present image analysis results that show smaller LCO islands have a higher conductive fraction than larger area islands, and the overall conductive fraction is consistent with the lithiation state. Thinner islands (14 nm), with a larger surface to volume ratio, are found to exhibit a striping pattern, which suggests surface energy can dominate below a critical dimension. When increasing force is applied through the AFM tip to strain the LCO islands, significant shifts in current flow are observed, and underlying mechanisms for this behavior are discussed. The c-AFM images are compared with photoemission electron microscopy images, which are used to acquire statistics across hundreds of particles. Finally, the results indicate that strain and morphology become more critical to electrochemical performance as particles approach nanometer dimensions.

25 ENERGY STORAGE↗
DOE OSTI2022

Formation of Complex Spin Textures in Thermally Demagnetized La 0.7 Sr 0.3 Mn O 3 Artificial-Spin-Ice Structures

Artificial spin ices (ASIs) have traditionally been designed such that each nanomagnet possesses a single-domain magnetic configuration that is assumed to be minimally perturbed by interisland dipolar interactions. Using x-ray photoemission electron microscopy to perform magnetic domain imaging, we study thermally demagnetized La 0.7 Sr 0.3 MnO 3 -based brickwork ASI arrays and showed that complex spin textures (CSTs) can be stabilized through an appropriate selection of nanoisland width and interisland spacing. While the width dependence can be explained through the dominance of shape anisotropy in isolated nanoislands, the ASIs we investigate demonstrate a complex dependence on both the nanoisland width and interisland spacing. Micromagnetic simulations reveal that interisland dipolar interactions play a role in the formation of CSTs, which are composed of single- and double-vortex states. Furthermore, energy analysis of the simulations provides an understanding of the system energetics that arises from a delicate balance between intraisland effects (i.e., shape anisotropy and exchange energy) and interisland effects (i.e., dipolar interactions between nearest-neighbor nanoislands).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Topological spin memory of antiferromagnetically coupled skyrmion pairs in Co/Gd/Pt multilayers

Antiferromagnetically (AFM) coupled skyrmions offer potential advantages for spintronic devices, including reduced dipolar fields that may enable smaller skyrmion sizes and a reduction of the skyrmion Hall effect. However, the topological stability of AFM-coupled skyrmions subjected to dramatic spin deformation through low-temperature cycling has not been investigated. We report the discovery of a topological spin memory effect for AFM-coupled skyrmion pairs in [Co/Gd/Pt](10) multilayered films. Photoemission electron microscopy imaging shows that bubble skyrmions in the multilayer that are stable at room temperature evolve into complex in-plane spin textures as the temperature is lowered and reform completely when the sample is warmed back up. Simulations demonstrate that Dzyaloshinskii-Moriya interactions play a key role in this spin memory effect, and furthermore reveal that the topological charge is preserved throughout the dramatic spin texture rearrangement and recovery. These results highlight a key aspect of topological protection-the preservation of the topological properties under continuous deformation-and also provide a promising avenue for information encryption and recovery.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Dipolar Aleppo lattice: Ground state ordering and ergodic dynamics in the absence of vertex frustration

We introduce the Aleppo spin ice geometry, another variation of decimated square ice patterns, which in contrast to similar systems previously studied, does not exhibit vertex frustration. Using synchrotron-based photoemission electron microscopy, we directly visualize low-energy states achieved after thermal annealing, in addition to temperature-dependent moment fluctuations. The results reveal the observation of ground state patterns and the absence of ergodicity-breaking dynamics. Our observations further confirm vertex frustration to be an important criterion for the emergence of ergodicity transitions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Surface and grain boundary carbon heterogeneity in CH 3 NH 3 PbI 3 perovskites and its impact on optoelectronic properties

Rivaling state-of-the-art crystalline silicon, organic-inorganic hybrid perovskites have been intensely studied in recent years. Surface and interfacial engineering have been a focus for performance improvement. Even though significant progress has been made during the last decade in terms of the diversity and capability of perovskite-based devices, the structure-property relationship, particularly at the surface, which governs the real-world performance of these applications, is still unresolved. In the article, this issue was addressed by employing synchrotron-related experimental measurements, and a mechanism that correlates microstructure with surface chemistry was resolved. As a powerful and highly sensitive spectromicroscopy, soft x ray photoemission electron microscopy (X-PEEM) was used to probe the surface of perovskite films varying in post solvent annealing. Furthermore, static and in situ grazing incidence hard x ray diffraction (GIXD) was used to track the grain growth dynamics during the film formation process. It was found that the nature of the surfaces was dictated by the local chemistry that varied due to mass flow during the development of the microstructure. Combining optical and electronic characterizations, it was confirmed that a more homogenous chemistry, i.e., uniform chemical components and properties, along with reduced strain and grain boundary energies, yielded more defect-tolerant films. Grain boundaries were more favorable for screening carriers than those in the control film. Our findings underscore the importance of the uniformity in the surface for developing a chemistry-structure-property relationship in perovskite materials, as well as engineering local chemistry toward high-performance and stable devices.

42 ENGINEERING↗
DOE OSTI2024

Voltage-induced magnetic domain evolution in a phase-change material

Applying voltage to metal–insulator transition (MIT) materials allows electrical actuation of the local electronic phase state. In MIT systems that have the electronic order coupled with the magnetic order, voltage switching of the electronic phase state can also enable the electrical manipulation of magnetic properties. In this work, we utilized x-ray magnetic circular dichroism photoemission electron microscopy (XMCD-PEEM) to investigate the control of magnetic domain configurations in ferromagnetic MIT electrical switches. For applied voltages above a threshold value, the XMCD-PEEM images show that the magnetic domains separate into two distinct regions: one with a high contrast (white/black), indicating well-defined micrometer-scale magnetic domains with a component of their magnetization aligned parallel/antiparallel to the x-ray helicity, and the other with different shades of intermediate contrast (gray). Significant changes in magnetic domain configurations upon voltage biasing were only observed in these gray regions. Furthermore, the voltage-induced magnetic domain separation was found to be bias polarity-dependent, with the gray regions expanding from the opposite sample edge when the applied voltage polarity was reversed. This polarity-dependent electrical control of magnetic domain configurations during the MIT switching opens alternative opportunities in memory applications for magnetic MIT switching materials.

42 ENGINEERING↗