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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Evolution from topological Dirac metal to flat-band-induced antiferromagnet in layered K x Ni 4 S 2 (0 ≤ x ≤ 1)

Condensed matter systems with coexisting Dirac cones and flat bands and a switchable control between them within a single system are desirable but remarkably uncommon. Here, we report a layered quantum material system, K x Ni 4 S 2 (0 <= x <= 1), that simultaneously hosts both characteristics without involving typical Kagome/honeycomb lattices. Enabled by a topochemical K-deintercalation process, the Fermi surface can be fine-tuned continuously over a wide range of energies. Consequently, a non-magnetic Dirac-metal state with a topological nontrivial Z 2 index of 1;(000), supported by first-principles calculations and high mobility up to 1,471 cm 2 V -1 s -1 , is observed on the K-rich x = 1 side, whereas a flat-band-induced antiferromagnetic state with T N up to 10.1 K emerges as the K-content approaches 0. The K x Ni 4 S 2 system offers a versatile platform for exploring emerging phenomena and underscores aviable pathway for in situ control of quantum materials dominated by Dirac cones, flat bands, and their interplay.

dirac metal↗
DOE OSTI2025

Phonon lifetimes and mode softening in cubic Cs 2 AgBiBr 6

Metal halide perovskites (MHPs) have emerged as noteworthy candidates for photovoltaic applications in recent years. Their high power-conversion efficiency is largely attributed to the structure-function relationship, which is not well understood. In this study, we examine the low-frequency phonons of the double perovskite Cs 2 AgBiBr 6 using neutron inelastic scattering. We find that the acoustic phonon lifetimes decrease from 16 to 3 ps along Γ to X, which is indicative of significant anharmonicity that contributes to the ultralow thermal conductivity. Additionally, we observe a linear temperature dependence of the square of the zone-center soft optical phonon energy, which is consistent with a weakly first-order displacive cubic-tetragonal structural phase transition. These results provide a deeper understanding of the lattice dynamics and phase transitions in MHPs as well as the effects of anharmonicity by comparison with prototypical hybrid organic-inorganic MHPs, (CH 3 NH 3 ) PbX 3 (X = Br, I).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Absorber Clamp for Microcalorimeter Decay Energy Spectrometry

Microcalorimeter Decay Energy Spectrometry (DES) is of interest to nuclear safeguards due to its ability to provide high precision isotopic compositions of nanogram-to microgram-scale samples of Pu and U and related daughter products. The DES method is able to record decay energy of each alpha-decay event in a sample that is embedded in a metal matrix (absorber) and thermally linked to a microcalorimeter detector. This work optimizes the DES technique used to thermally link the absorber and microcalorimeter detector element to allow for more rapid assembly and to increase detector performance and operating life. Optimized attachment methods are crucial for enhancing the viability of DES in high-sample-throughput facilities, such as those that support international nuclear safeguards measurements. Here, in this study, we designed and implemented a pressure-based absorber clamp and evaluated the performance of this new attachment method relative to pressed indium bond attachment. Results using the absorber clamp demonstrate a streamlined detector assembly procedure that minimizes accidental damage to detectors, as well as increasing detector pulse speeds by 57%. Spectral comparison shows the clamp preserves detector performance relative to indium attachment.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

PV backsheets survey protocol: A framework for geo-spatial field surveys for bulk material characterization and reliability analysis applied across 41 PV systems

As widespread adoption of photovoltaic (PV) technologies continues, understanding the lifetime of modules is paramount to the viability of the industry as an environmentally conscious alternative to traditional energy generation. Although power degradation can affect the total energy production of a module over its lifetime, module safety failures necessitate the removal of a module leading to a loss of not only the particular asset, but the earning potential of the device. Therefore, it is critical to ensure that the components that provide essential safety functions for PV module operate for their entire rated lifetime. PV backsheets provide necessary electrical insulation to the completed device and failure of this component is cause for a immediate removal of the module. Degradation of the PV module backsheet has led to module safety failures in large-scale installations, costing millions of dollars in damages and lost potential revenue. The spatio-temporal degradation of fielded PV modules is important to study in order to identify which modules within installations are experiencing the greatest exposure conditions and in turn have the highest chance of failure. This paper describes a comprehensive field survey protocol developed for monitoring PV module backsheet performance using solely non-destructive methods in commercial PV fields. The protocol establishes a field naming convention, sampling method, data handling requirements, and measurement procedures. By ensuring consistent data collection practices, the field survey protocol enables research groups to obtain data of uniform quality on backsheet performance over multiple years and locations. In this study, the developed protocol was implemented at forty-one PV sites. Eight different types of airside layer backsheet materials including poly(vinylidene fluoride) (PVDF), acrylic PVDF, poly(tetrafluoroethylene-co-hexafluoropropylene-co-vinylidene fluoride) (THV), poly(vinyl fluoride) (PVF), poly(ethylene terephthalate) (PET), fluoroethylene vinyl ether (FEVE), polyethylene naphthalate (PEN), and glass were identified using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. The field survey results show that the spatial distribution of degradation indicators are non-uniform within a particular module, individual site, and across site locations. The degradation of PV modules increased in severity for modules mounted at the edge of rows (across a field) and near the junction box (within a module). This study demonstrates the sensitivity of material performance to exposure length across different materials and climates.

14 SOLAR ENERGY↗
DOE OSTI2025

Investigation of electrode-electrolyte interfaces to enable non-flammable Li-ion batteries operating up to 125°C with liquid electrolyte

Non-flammable and high-temperature stable ionic liquid (IL)-based electrolytes could eliminate catastrophic battery failures and improve battery safety, but their poor electrochemical interaction with the LiNi x Mn y Co z O 2 (NMC) family of cathodes is a long-standing problem due to severe parasitic reactions at high temperature. Understanding surface and bulk structural mechanisms of NMC-type cathodes at elevated operational temperature is of paramount importance to facilitate stable electrochemical performance. Here, we report a non-flammable phosphonium IL-based cell chemistry that offers stable electrode-electrolyte interfaces, leading to electrochemical performance up to 125°C and high-temperature safety. We combine electrochemistry with multimodal X-ray spectroscopy methods to understand interfaces at elevated temperature (100°C). This nanoscale understating enables a proof-of-concept high-temperature cylindrical cell (14500), and the design achieves an average Coulombic efficiency of ≈99.5% up to 300 cycles at 100°C. The results ascertain the significance of depth-dependent degradation at the interface, guiding room-temperature Li-ion technology toward extreme-temperature applications.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Alumina Priming-Mediated Enhanced Binding of Diethylzinc with Carbonyl Groups in Poly(Methyl Methacrylate) during Vapor-Phase Infiltration

Vapor-phase infiltration (VPI) of inorganic materials in polymers is increasingly becoming popular for synthesizing various functional hybrid materials. While AlO x infiltration using trimethylaluminum (TMA) has been extensively studied, the mechanism of diethylzinc (DEZ)-based ZnO x infiltration, especially one that is initiated by AlO x priming, has not received much attention because highly reactive hydroxyl groups generated by AlO x -priming are expected to dominate the initial binding of DEZ, thus enabling the overall ZnO x VPI. Here, we interrogate the ZnO x infiltration mechanism in AlO x -primed poly(methyl methacrylate) (PMMA) in comparison to the control AlO x -only infiltration by utilizing a suite of complementary characterizations, including quartz crystal microbalance mass gain measurement, transmission electron microscopy, infrared reflection–absorption spectroscopy (IRRAS), and synchrotron X-ray absorption spectroscopy (XAS). The multivalent TMA precursor and associated hyperbranched AlO x network can quickly saturate the AlO x infiltration by clogging the polymer-free volume near the top. On the contrary, the ZnO x infiltration using divalent DEZ precursor, once activated via AlO x -priming, can lead to accelerated ZnOx infiltration. With the help of IRRAS, XAS, and density functional theory (DFT) simulations, we uncover that the AlO x -priming enhances the reactivity of neighboring carbonyl groups toward DEZ and opens up simultaneous reaction pathways, leading to accelerated high-fidelity infiltration of ZnO x .

36 MATERIALS SCIENCE↗
DOE OSTI2025

Vitamin E Acetate Causes Softening of Pulmonary Surfactant Membrane Models

The popularity of electronic cigarettes and vaping products has launched the outbreak of a condition affecting the respiratory system of users, known as electronic-cigarette/vaping-associated lung injury (EVALI). The build-up of vitamin E acetate (VEA), a diluent of some illicit vaping oils, in the bronchoalveolar lavage of patients with EVALI provided circumstantial evidence as a target for investigation. In this work, we provide a fundamental characterization of the interaction of VEA with lung cells and pulmonary surfactant (PS) models to explore the mechanisms by which vaping-related lung injuries may be present. We first confirm the localization and uptake of VEA in pulmonary epithelial cells. Further, as PS is vitally responsible for the biophysical functions of the lungs, we explore the effect of added VEA on three increasingly complex models of PS: dipalmitoylphosphatidylcholine (DPPC), a lipid-only synthetic PS, and the biologically derived extract Curosurf. Using high-resolution techniques of small-angle X-ray scattering, small-angle neutron scattering, neutron spin–echo spectroscopy, and neutron reflectometry, we compare the molecular-scale behaviors of these membranes to the bulk viscoelastic properties of surfactant monolayer films as studied by Langmuir monolayer techniques. While VEA does not obviously alter the structure or organization of PS membranes, a consistent softening of membrane systems—regardless of compositional complexity—provides a biophysical explanation for the respiratory distress associated with EVALI and yields a new perspective on the behavior of the PS system.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Following CO and H Insertion into Ru–C Bonds with X-ray Photoelectron and Absorption Spectroscopies

Insertion reactions play a central role in the catalytic synthesis of ethanol and higher alcohols. X-ray photoelectron and absorption spectroscopies have been used to follow migratory CO insertion and C─C coupling in a cis-[Ru(2,2′-bipyridine) 2 (CO)(CH 3 )] + complex heated in a vacuum or exposed to CO. Heating of the Ru complex in a vacuum to temperatures above 50 °C induced spontaneous migration of CO into the Ru─CH 3 bond to yield a ─COCH 3 ligand. In conclusion, after adding CO to the background gas, the CO insertion reaction was seen at room temperature, opening the door for the synthesis of ethanol and more energy dense liquids.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Speed of Sound Measurements of Binary Mixtures of trans -1,2-Difluoroethylene (R-1132(E)) with Difluoromethane (R-32) or 2,3,3,3-Tetrafluoropropene (R-1234yf)

The speed of sound of two binary mixtures containing 0.336 mole fraction trans-1,2- difluoroethylene (R-1132(E)) with difluoromethane (R-32) and 0.435 mole fraction R-1132(E) with 2,3,3,3-tetrafluoropropene (R-1234yf) were measured with a dual-path pulse-echo instrument. The speed of sound was measured along several pseudo-isochores for each blend at temperatures ranging from 230 K to 325 K for blends with R-32 and to 342 K for blends with R- 1234yf. Measurements started at pressures just above each mixtures bubble point pressure and were limited to 8 MPa to avoid potential disproportionation reactions of the R-1132(E). The data were compared to multi-fluid models incorporating Helmholtz-energy-explicit equations of state (EOS) for each pure fluid.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Strain-Modulated Exciton Localization and Enhanced Emission in Multilayer GaSe

Strain engineering is one of the most effective routes for tuning the electrical and optical properties of two-dimensional layered materials. Besides reproducing the results of other groups on the tunability and photoluminescence (PL) enhancement of free and bound excitons under mechanical deformation or thermal effects, we systematically studied the mechanical strain (wrinkle) and local thermal strain (laser heating) effects on the PL lifetime and polarization in GaSe multilayers and their interplay, revealing their coupled impact on excitonic dynamics. Here, the PL intensity of localized excitons in the wrinkle region of GaSe increases superlinearly with the excitation laser power. The polarization effect has been observed for the bound exciton in GaSe under mechanical strain, but not in GaSe under thermal strain. Fluorescence lifetime imaging (FLIM) measurements reveal strain-tunable lifetimes for both free and bound excitons, and the lifetime of the bound exciton is longer than the free exciton in the mechanical strain region, correlating with the enhanced emission of the bound exciton. These results highlight previously uncharacterized optoelectronic tunability in GaSe and broaden the design space for strain (or thermally)-controlled 2D layered devices.

, GaSe, Exciton localization↗
DOE OSTI2025

Scalable Bottom-Up Synthesis of Nanoporous Hexagonal Boron Nitride ( h -BN) for Large-Area Atomically Thin Ceramic Membranes

Nanopores embedded within monolayer hexagonal boron nitride (h-BN) offer possibilities of creating atomically thin ceramic membranes with unique combinations of high permeance (atomic thinness), high selectivity (via molecular sieving), increased thermal stability, and superior chemical resistance. However, fabricating size-selective nanopores in monolayer h-BN via scalable top-down processes remains nontrivial due to its chemical inertness, and characterizing nanopore size distribution over a large area remains extremely challenging. Here, we demonstrate a facile and scalable approach of exploiting the chemical vapor deposition (CVD) process temperature to enable direct incorporation of subnanometer/nanoscale pores into the monolayer h-BN lattice, in combination with manufacturing compatible polymer casting to fabricate centimeter-scale nanoporous atomically thin ceramic membranes. We leverage diffusive transport of analytes including size-selective Ficoll sieving to characterize subnanometer-scale and nanoscale defects that manifest as pores in centimeter-scale h-BN membranes, overcoming previous limitations in large-area characterization of nanoscale defects in h-BN. Our approach opens a new frontier to advance atomically thin membranes to 2D ceramic materials, such as h-BN via facile and direct formation of nanopores, for size-selective separations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Two-Dimensional Siloxene Nanosheets: Understanding the Effect of Heat Treatment on the Surface Chemistry and Resulting Electrochemistry in Lithium-Based Batteries

Two-dimensional (2D) silicon materials are conceptually appealing as negative electrode materials in lithium-ion batteries due to their layered morphology, which can accommodate (de)lithiation-induced volume changes. Herein, heat treatment of 2D Siloxene materials was used to modify the surface functional groups to determine the impact on the electrochemical behavior. Spectroscopic characterization of the heat-treated nanosheets confirmed the loss of oxygenated and hydride surface functional groups with an increased annealing temperature. Formation and disproportionation of the amorphous suboxides with increasing heat treatment were affirmed with lab and synchrotron-based measurements. A reduced irreversible capacity was observed for Siloxene with a higher temperature heat treatment consistent with the formation of a more favorable surface electrolyte interphase (SEI). A Siloxene-400||NMC622 full cell (prepared with 400 °C-annealed Siloxene (Siloxene-400) and LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622)) showed significantly enhanced capacity and rate capability compared to a nano Si||NMC622 cell. Finally, these results illustrate the ability of thermal annealing to modify the surface functional groups of Siloxene and highlight the favorable impact of the appropriate surface functionality on the electrochemistry of Siloxene in lithium cells.

25 ENERGY STORAGE↗
DOE OSTI2025

UV-Enabled Defect Engineering in Multilayer GaSe and InSe and UV Writing of the Grating Pattern

III–VI post-transition-metal chalcogenides are layered semiconductor materials that exhibit direct band gaps in multilayers. Defect engineering is essential in 2D layered semiconductors for functional devices. Here, in this work, we report defect engineering in multilayer gallium selenide (GaSe) and indium selenide (InSe), where defects generated by ultraviolet (UV, 325 nm) laser irradiation result in an additional photoluminescence (PL) line. The additional PL line is due to defect-bound excitons. Characteristics of the defect emission are similar in GaSe and InSe samples subjected to UV irradiation, air annealing, and hydrostatic pressure. Two-beam UV interference was applied to create grating patterns with a periodic array of low and high densities of defects in GaSe. Density functional theory has identified the defect type in GaSe. The results provide valuable insights into defect generation and UV scribing of photonic circuits in 2D Se-based multilayers for optical integration in a 2D platform.

2D multilayered materials↗
DOE OSTI2024

Structural, Electrochemical, and (De)lithiation Mechanism Investigation of Cation-Disordered Rocksalt and Spinel Hybrid Nanomaterials in Lithium-Ion Batteries

Significant demand for lithium-ion batteries necessitates alternatives to Co- and Ni-based cathode materials. Cation-disordered materials using earth-abundant elements are being explored as promising candidates. Here, in this paper, we demonstrate a coprecipitation synthetic approach that allows direct preparation of disordered rocksalt Li 2.4 Fe 1.0 Ti 1.0 O 4.7 (r-LFTO·C) and spinel structured hybrid Li 0.5 Fe 1.0 Ti 0.9 O 3.2 ·C (s-LFTO·C) nanoparticles with a conformal conductive carbon coating. High-angle annular dark-field imaging coupled with electron energy loss spectroscopy mapping shows uniform Fe/Ti distribution with minor compositional variation among particles. Cation disorder was confirmed for both of the materials at an atomic level, with a short-range order more pronounced in r-LFTO·C. Operando X-ray absorption spectroscopy, ex situ hard X-ray photoelectron spectroscopy, ex situ soft X-ray absorption spectroscopy, and ex situ synchrotron X-ray diffraction were used to investigate (de)lithiation in the bulk and at the surface. Structurally, the r-LFTO·C demonstrated reversible partial Fe center migration between octahedral and tetrahedral sites during (de)lithiation. The r-LFTO·C evidenced that the redox of O was coincident with iron redox during initial electrochemical cycling, while iron redox dominated later cycling. In contrast, s-LFTO·C electrochemistry involved iron redox throughout the cycling process. The findings rationalize the differences in the electrochemistry where r-LFTO·C shows higher initial capacity yet poorer capacity retention over a voltage window where O redox can be accessed, while the s-LFTO·C shows lower initial capacity yet improved capacity retention.

25 ENERGY STORAGE↗
DOE OSTI2026

Magnetic Response of Excitons and Excitonic Complexes in Defective Hexyl Ammonium Lead Iodide Self-Assembled Quantum Wells

Correlating the magnetic behavior of low-dimensional semiconductors with the chemistry used to form these excitonic materials remains crucial to the development of devices applied to quantum technologies. In this study, we apply large magnetic fields during the collection of low-temperature photoluminescence (PL) to assess the magnetic properties of excitons in hexyl ammonium lead iodide (HA 2 PbI 4 ) self-assembled quantum wells (SAQWs) formed at liquid−liquid interfaces. The effect of incident laser power and temperature was used to assign lower energy features in these samples’ PL spectra to both excitons trapped at defect sites and trions. Measured peaks shifts allow us to estimate coupling between the applied magnetic fields and the charged defect excitons. Our conclusions are supported by density functional theory calculations on supercells of the proposed defective HA 2 PbI 4 SAQW structure. Additionally, we find an anomalous magnetic response from trion states that resembles the behavior of interacting excitonic complexes in similar, quantum-confined materials at low temperatures. These results highlight the crucial role that chemical conditions can play in the magnetic response of 2D semiconductors applied in quantum technologies.

defect chemistry↗
DOE OSTI2025

Local Inversion Symmetry Breaking and Thermodynamic Evidence for Ferrimagnetism in Fe 3 GaTe 2

The layered compound Fe 3 GaTe 2 is attracting attention due to its high Curie temperature, low dimensionality, and the presence of topological spin textures above room temperature, making Fe 3 GaTe 2 a good candidate for applications in spintronics. Here, in this study, we show, through transmission electron microscopy (TEM) techniques, that Fe 3 GaTe 2 single crystals break local inversion symmetry while maintaining global inversion symmetry according to X-ray diffraction. Coupled to the observation of Néel skyrmions via Lorentz-TEM, our structural analysis provides a convincing explanation for their presence in centrosymmetric materials. Magnetization measurements as a function of the temperature displays a sharp first-order thermodynamic phase-transition leading to a reduction in the magnetic moment. This implies that the ground state of Fe 3 GaTe 2 is globally ferrimagnetic and not a glassy magnetic state composed of ferrimagnetic, and ferromagnetic domains as previously claimed. Neutron diffraction studies indicate that the ferromagnetic to ferrimagnetic transition upon reducing the external magnetic field is associated with a change in the magnetic configuration/coupling between Fe1 and Fe2 moments. We observe a clear correlation between the hysteresis observed in both the skyrmion density and the magnetization of Fe 3 GaTe 2 . This indicates that its topological spin textures are affected by the development of ferrimagnetism upon cooling. Observation, via magnetic force microscopy, of magnetic bubbles at the magnetic phase boundary suggests skyrmions stabilized by the competition among magnetic phases and distinct exchange interactions. Our study provides an explanation for the observation of Néel skyrmions in centrosymmetric systems, while exposing a correlation between the distinct magnetic phases of Fe 3 GaTe 2 and topological spin textures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Efficient Measurement of Length Distribution of 1D Nanoparticles in Solution via Optical Polarimetry

The efficient measurement of the length distribution of nanotubes, nanowires, and other one-dimensional (1D) nanoparticles in solution is important to enable their incorporation into materials and devices and to optimize their processing for properties of interest, such as thermal/electrical conductivity or mechanical strength, in suspensions and composites. We report an electric-field (E-field)-assisted optical-polarimetry technique to measure the length distribution of ensembles of high-aspect-ratio particles in dilute suspension. The degree of alignment of polarizable 1D particles suspended in a fluid under Brownian motion explicitly depends on the E-field strength and the particle length. We show that it is possible to extract the length distribution of 1D nanoparticles suspended in an insulating fluid by applying a range of E-fields and using optical polarimetry to measure the corresponding alignment order parameter. Notably, the method is relatively insensitive to the diameter of the 1D particles, which can be poorly known or vary within a sample. The technique is validated with silver nanowires and carbon nanotubes of known lengths, as well as polymer-depletion-length-separated single-wall carbon nanotube samples with length distributions independently measured with analytical ultracentrifugation. Finally, we demonstrate the ability of the optical-polarimetry technique to quantify changes in the length distribution of ultranarrow, sub-nanometer-diameter single-wall carbon nanotubes under different types and durations of ultrasonication. Within its range of applicability (polarizable 1D nanoparticles in the 0.5 to 15 μm length range, constrained by the voltage stability of the media and the suspended particles), the E-field-assisted optical-polarimetry method is a particularly efficient and accurate method to measure the length distribution of nanowires and nanotubes in suspension.

1D nanoparticles↗
DOE OSTI2025

Quantum Emitters Induced by High Pressure and UV Laser Irradiation in Multilayer GaSe

In this work, we report on defect generation in multilayer GaSe through hydrostatic pressure quenching and UV laser irradiation. The Raman line width from the UV 266 nm irradiated sample is much wider than that in pressure-quenched GaSe, corresponding to a wider defect energy distribution range in the former sample than the latter. After quenching from 11.2 GPa, three photoluminescence (PL) peaks from defect states are observed at 657, 681, and 695 nm at a low temperature of 93 K. Defect-related peaks at 649, 694, 750, and 774 nm also appear in low-temperature PL spectra after UV laser irradiation, with a nonmonotonous intensity dependence on irradiation duration. There are common features in defects produced by these two methods: the PL peaks with the lowest energy are sharp, and their PL intensities increase linearly with the excitation laser power and saturate above a certain excitation laser power. These two features are similar to those in defects for single-photon emission (SPE) in other 2D materials at even lower temperatures. Fluorescence lifetime imaging shows distinguished short (2.3 ns) and long (75.6 nm) lifetimes of the 695 nm PL line in pressure-quenched GaSe. The density functional theory predicts defect energy levels related to Se vacancy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗