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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Matter-wave interference of a native polypeptide

The de Broglie wave nature of matter is a paradigmatic example of quantum physics and it has been exploited in precision measurements of forces and fundamental constants. However, matter-wave interferometry has remained an outstanding challenge for natural polypeptides, building blocks of life, which are fragile and difficult to handle. Here, we demonstrate the wave nature of gramicidin, a natural antibiotic composed of 15 amino acids. Its center of mass is delocalized over more than 20 times the molecular size in our timedomain Talbot-Lau interferometer. We compare the observed interference fringes with a model that includes both a rigorous treatment of the peptide’s quantum wave nature as well as a quantum chemical assessment of its optical properties to distinguish our result from classical predictions. The realization of quantum optics with this prototypical biomolecule paves the way for quantum-assisted measurements on a large class of biologically relevant molecules.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Gapless Dirac magnons in CrCl3

Abstract Bosonic Dirac materials are testbeds for dissipationless spin-based electronics. In the quasi two-dimensional honeycomb lattice of CrX 3 (X = Cl, Br, I), Dirac magnons have been predicted at the crossing of acoustical and optical spin waves, analogous to Dirac fermions in graphene. Here we show that, distinct from CrBr 3 and CrI 3 , gapless Dirac magnons are present in bulk CrCl 3 , with inelastic neutron scattering intensity at low temperatures approaching zero at the Dirac K point. Upon warming, magnon-magnon interactions induce strong renormalization and decreased lifetimes, with a ~25% softening of the upper magnon branch intensity from 5 to 50 K, though magnon features persist well above T N . Moreover, on cooling below ~50 K, an anomalous increase in the a -axis lattice constant and a hardening of a ~26 meV phonon feature are observed, indicating magnetoelastic and spin-phonon coupling arising from an increase in the in-plane spin correlations that begins tens of Kelvin above T N .

36 MATERIALS SCIENCE↗
DOE OSTI2020

Optically pumped spin polarization as a probe of many-body thermalization

Disorder and many body interactions are known to impact transport and thermalization in competing ways, with the dominance of one or the other giving rise to fundamentally different dynamical phases. Here we investigate the spin diffusion dynamics of 13 C in diamond, which we dynamically polarize at room temperature via optical spin pumping of engineered color centers. We focus on low-abundance, strongly hyperfine-coupled nuclei, whose role in the polarization transport we expose through the integrated impact of variable radio-frequency excitation on the observable bulk 13 C magnetic resonance signal. Unexpectedly, we find good thermal contact throughout the nuclear spin bath, virtually independent of the hyperfine coupling strength, which we attribute to effective carbon-carbon interactions mediated by the electronic spin ensemble. In particular, observations across the full range of hyperfine couplings indicate the nuclear spin diffusion constant takes values up to two orders of magnitude greater than that expected from homo-nuclear spin couplings.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Exceptional points in a passive strip waveguide

Abstract Exceptional points (EPs) in non‐Hermitian systems have attracted significant interest due to their unique behaviors, including novel wave propagation and radiation. While EPs have been explored in various photonic systems, their integration into standard photonic platforms can expand their applicability to broader technological domains. In this work, we propose and experimentally demonstrate EPs in an integrated photonic strip waveguide configuration, exhibiting unique deep wave penetration and uniform‐intensity radiation profiles. By introducing the second‐order grating on one side of the waveguide, forward and backward propagating modes are coupled both directly through second‐order coupling and indirectly through first‐order coupling via a radiative intermediate mode. To describe the EP behavior in a strip configuration, we introduce modified coupled‐mode equations that account for both transverse and longitudinal components. These coupled‐mode formulas reveal the formation of EPs in bandgap closure, achieved by numerically optimizing the grating’s duty cycle to manipulate the first‐ and second‐order couplings simultaneously. Experimental observations, consistent with simulations, confirm the EP behavior, with symmetric transmission spectra and constant radiation profiles at the EP wavelength, in contrast to conventional exponential decay observed at detuned wavelengths. These results demonstrate the realization of EPs in a widely applicable strip waveguide configuration, paving the way for advanced EP applications in nonlinear and ultrafast photonics, as well as advanced sensing technologies.

Materials Science↗
DOE OSTI2021

Degradation mechanisms of 1.3 μm C-doped quantum dot lasers grown on native substrate

Here, the aim of this paper is to analyse the degradation modes of 1.3 μm InAs quantum dot laser diodes (QD LDs) grown by using carbon as a p-type dopant, as an alternative to beryllium. The devices were stressed at high current densities, to favor the onset of excited-state (ES) emission, and to study the related degradation phenomena. The study of QD LDs is of fundamental importance for the photonic integrated circuits (PICs). The investigation is based on two types of stress tests: 1) a current step stress and 2) a constant current stress. With these experiments we demonstrate that a) the current is a determining factor for the onset of the ES during the operation of such devices. b) the onset of ES is responsible for a rapid quenching of the ground state (GS) emission. c) stress induces a significant increase in the threshold current of the devices, that is ascribed to the lowering of the injection efficiency, which in turn can be explained by the easier escape of carriers from quantum dots (QDs) from ES energy levels. d) the contribution of defects on the optical and electrical degradation is also discussed.

42 ENGINEERING↗
DOE OSTI2025

Pressure-Modulated Energy Transfer Dynamics in Mn 2+ -Doped CdS/ZnS Core/Shell Quantum Dots

Transition metal doping in semiconductor quantum dots (QDs) significantly impacts their optical properties, thus expanding the range of their potential optoelectronic applications. This study investigates the pressure-dependent energy transfer dynamics in Mn 2+ -doped CdS/ZnS core/shell QDs, focusing on how external hydrostatic pressure modulates these dynamics and optical properties. By synthesizing Mn 2+ -doped QDs with varying Mn 2+ doping concentrations, we explore the effects of the pressure on photoluminescence (PL) spectra and energy transfer efficiency. Our study reveals that increasing pressure induces a blueshift in the QD host bandgap PL and a redshift in the Mn 2+ dopant PL. The pressure-induced shifts highlight a unique modulation mechanism where the energy transfer efficiency decreases with pressure due to reduced wave function overlap between host excitons and Mn 2+ dopants. Detailed analysis of the PL quantum yields and energy transfer rate constants provides insights into these dynamics, suggesting that the pressure can effectively and reversibly regulate the energy transfer efficiencies and rates. In conclusion, these results have implications for developing pressure-sensitive configurable devices and exploring pressure-induced phenomena in doped nanomaterials.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Space-time crystals from particle-like topological solitons

Time crystals are unexpected states of matter that spontaneously break time-translation symmetry either in a discrete or continuous manner. However, spatially mesoscale space-time crystals that break both space and time symmetries have not been reported. Here we report a continuous space-time crystal in a nematic liquid crystal driven by ambient-power, constant-intensity unstructured light. Our numerically constructed four-dimensional configurations exhibit good agreement with these experimental findings. Although meeting the established criteria to identify time-crystalline order, both experiments and computer simulations reveal a space-time crystallization phase formed by particle-like topological solitons. The robustness against temporal perturbations and spatiotemporal dislocations shows the stability and rigidity of the studied space-time crystals, which relates to their locally topological nature and many-body interactions between emergent spontaneously twisted, particle-like solitonic building blocks. Their potential technological utility includes optical devices, photonic space-time crystal generators, telecommunications and anti-counterfeiting designs, among others.

Liquid crystals↗
DOE OSTI2021

Chemical Control of Spin‐Orbit Coupling and Charge Transfer in Vacancy‐Ordered Ruthenium(IV) Halide Perovskites

Abstract Vacancy‐ordered double perovskites are attracting significant attention due to their chemical diversity and interesting optoelectronic properties. With a view to understanding both the optical and magnetic properties of these compounds, two series of Ru IV halides are presented; A 2 RuCl 6 and A 2 RuBr 6 , where A is K, NH 4 , Rb or Cs. We show that the optical properties and spin‐orbit coupling (SOC) behavior can be tuned through changing the A cation and the halide. Within a series, the energy of the ligand‐to‐metal charge transfer increases as the unit cell expands with the larger A cation, and the band gaps are higher for the respective chlorides than for the bromides. The magnetic moments of the systems are temperature dependent due to a non‐magnetic ground state with J eff =0 caused by SOC. Ru‐ X covalency, and consequently, the delocalization of metal d ‐electrons, result in systematic trends of the SOC constants due to variations in the A cation and the halide anion.

Vishnoi, Pratap↗
DOE OSTI2022

Design considerations for gallium arsenide pulse compression photoconductive switch

In this paper, we present the physics and design-space exploration of a novel pulse compression photoconductive switch (PCPS) using semi-insulating gallium arsenide (GaAs) operating in the negative differential mobility (NDM) regime of electron transport. We systematically quantify the relationship between the PCPS performance and various design options, including contact separation, laser energy and placement, and trap dynamics. Specifically, we report the full-width at half-maximum and the peak output current generated by the PCPS as a function of applied electrical and optical bias. We discuss the optimal spacing between the electrodes and the distance of the laser spot to the anode to achieve higher electron confinement and superior radio-frequency (RF) metrics. Reducing the laser energy is important to prevent the appearance of secondary peaks due to diffusive transport, but there exists a trade-off between the bandwidth and the maximum current of the PCPS. We also compare the PCPS response with and without trap dynamics and find that the electrostatic screening from the trap-induced space charge is time-independent when the trapping time constant is set larger than the recombination lifetime. Overall, trap dynamics are detrimental to performance, unless the compensation doping scheme to achieve semi-insulating GaAs is carefully selected. Results presented in this paper can be used by experimentalists to fine-tune the PCPS design parameters to meet the specifications of various RF applications. Moreover, our results will provide a strong theoretical basis to the measurements of PCPS devices using GaAs and other NDM materials under investigation.

42 ENGINEERING↗
DOE OSTI2026

Synthesis and composition control of epitaxial FeWO4 thin films using pulsed laser deposition

We report the growth of epitaxial FeWO4 thin films on c-plane sapphire via pulsed laser deposition using a Fe 2 O 3 /WO 3 target ablated in an O 2 atmosphere. At a constant O 2 pressure of 1 mTorr, x-ray diffraction (XRD) confirms FeWO 4 as the major crystalline phase for substrate temperatures from 500 to 800 °C. As temperature increases, x-ray fluorescence (XRF) shows the Fe/W ratio remains nearly constant at 0.90 ± 0.02, while x-ray photoelectron spectroscopy (XPS) shows Fe 3+ to Fe 2+ conversion increases from 20% to 35%. Morphological analysis reveals phase separation, likely of amorphous Fe 3+ oxide from crystalline FeWO 4 , increasing with Fe 3+ conversion. This is attributed to an O-rich laser ablated flux, where conversion is driven by the Arrhenius temperature dependence of Fe 3+ → Fe 2+ reduction on the film surface. At a constant substrate temperature of 750 °C, XRD confirms FeWO 4 formation for O 2 pressures from 0.5 to 10 mTorr. As pressure increases, XRF shows the Fe/W ratio decreases from 0.98 to 0.70, while XPS shows Fe 3+ conversion rises from 15% to 70%. Morphology shows phase separation decreasing with increasing Fe 3+ conversion. This is attributed to scattering, where higher O 2 pressure makes the laser ablated flux O-deficient relative to Fe and W, facilitating Fe 2+ formation. Films with Fe 3+ conversion above ∼30% and Fe/W ratios from 0.86 to 0.96 exhibit FeWO 4 optical and electronic properties suitable for photoanode applications.

36 MATERIALS SCIENCE↗
DOE OSTI2023

The Chocolate Chip Cookie Model: Dust-to-metal Ratio of H ii Regions

Using a sample of face-on star-forming galaxies selected from the Sloan Digital Sky Survey, we statistically derive the typical optical depth $\tau$ cl of individual H II regions based on the "Chocolate Chip Cookie" model of Lu et al. (2022). By binning galaxies into stellar mass and gas-phase metallicity bins and interpreting $\tau$ cl as the dust-to-gas ratio (DGR) of H II regions, we further investigate the correlations between DGR and stellar mass and between DGR and gas-phase metallicity, respectively. We find that DGR increases monotonically with the stellar mass of galaxies. At a given stellar mass, DGR shows a linear correlation with the gas-phase metallicity, which implies a constant dust-to-metal ratio (DTM) of galaxies at a given stellar mass. These results adequately indicate that the DTM of galaxies is simply a function of their stellar masses. In terms of gas-phase metallicity, because of the mass–metallicity relation, DTM increases with increasing metallicity with a power-law index 1.45 in the low-metallicity region, while it remains constant at the high-metallicity end.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

eROSITA Final Equatorial-Depth Survey (eFEDS) eFEDS X-ray view of WERGS radio galaxies selected by the Subaru/HSC and VLA/FIRST survey

We constructed the eROSITA X-ray catalog of radio galaxies discovered by the WERGS survey, made by cross-matching the wide area Subaru/Hyper Suprime-Cam (HSC) optical survey and VLA/FIRST 1.4 GHz radio survey. We report finding 393 eROSITA detected radio galaxies in the 0.5-2 keV band in the eFEDS field covering 140 deg 2 . Thanks to the wide and medium depth eFEDS X-ray survey down to f 0.5 - 2 keV = 6.5 × 10 -15 erg s -1 cm -2 , the sample contains the rare and most X-ray luminous radio galaxies above the knee of the X-ray luminosity function, spanning 44 < log(L 0.5-2 keV (abs,corr) /erg s -1 ) < 46.5 at 1 < z < 4. The sample also contains the sources around and below the knee for the sources 41 < log(L 0.5-2 keV (abs,corr) /erg s -1 ) < 45 at z < 1. Based on the X-ray properties obtained by the spectral fitting, 37 sources show obscured active galactic nucleus (AGN) signatures with log(N H /cm -2 ) > 22. These obscured and radio AGN reside in 0.4 < z < 3.2, indicating that they are obscured counterparts of the radio-loud quasar, which were missed in the previous optical quasar surveys. By combining radio and X-ray luminosities, we also investigated the jet production efficiency η jet = η rad P jet /L AGN,bol by utilizing the jet power of P jet . We find that there are 14 sources with extremely high jet production efficiency at η jet ≈ 1. This high η jet value might be a result of the decreased radiation efficiency of η rad < 0.1, due to the low accretion rate for those sources, and/or of the boosting due to the decline of L AGN,bol by a factor of 10-100 by keeping P jet constant in the previous Myr, indicating the experience of the AGN feedback. Finally, inferring the BH masses from the stellar mass, we find that X-ray luminous sources show the excess of the radio emission with respect to the value estimated from the fundamental plane. This radio emission excess cannot be explained by the Doppler boosting alone, and therefore the disk–jet connection of X-ray luminous eFEDS-WERGS is fundamentally different from the conventional fundamental plane which mainly covers the low-accretion regime.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Numerical modeling of hydrogen mixing in a direct-injection engine fueled with gaseous hydrogen

Hydrogen is considered as one of the most promising options to achieve effective decarbonization of the energy and transportation sectors. As such, it has recently been receiving increasing attention because of its promising potential as an energy carrier for advanced energy and propulsion systems. With a focus on internal combustion engines, direct injection (DI) of gaseous hydrogen during the compression stroke offers great potential for high engine efficiency and specific power while reducing the risk of backfiring and pre-ignition issues. Therefore, many experimental and numerical efforts have recently been dedicated to understanding the physical and chemical behaviors of hydrogen in engine during mixing and combustion. This study focuses on computational fluid dynamics (CFD) modeling of the hydrogen DI process in a hydrogen optical research engine. Under the conditions studied, gaseous hydrogen is injected into the combustion chamber via a centrally located single-hole injector at a pressure of 100 bar. Two configurations, namely low-and high-tumble, are investigated to understand the impact of different in-cylinder flow patterns on the fuel-air mixture preparation. Simulations are carried out using the commercial CFD software CONVERGE. Here, the in-cylinder turbulence is modeled with an unsteady Reynolds-averaged Navier-Stokes (URANS) formulation closed by the renormalization group (RNG) k-ε model. Several numerical methods and model constants, including but not limited to turbulent Schmidt number, are evaluated. The numerical results are systematically compared against experimental measurements of velocity and hydrogen concentration fields on the vertical center plane to assess the performance of the CFD model, unveil the physics of hydrogen mixing, and establish best practices for modeling hydrogen DI under relatively high injection pressure conditions.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2022

Review on robot-assisted polishing: Status and future trends

Nowadays, precision components have been extensively used in various industries such as biomedicine, photonics, and optics. To achieve nanometric surface roughness, high-precision polishing is mandatory. Compared with the conventional polishing techniques, the robot-assisted polishing has the advantages of flexible working ranges and low cost. Therefore, it has been more widely deployed in demanding polishing tasks. However, few review articles were found on this topic to provide a general progress on the development of the robot-assisted polishing technology. Here in this paper reviews the recent advancement of the robot-assisted polishing. Firstly, the integration of robots with various polishing techniques is overviewed, followed by the introduction of the research status of constant force control in robot-assisted polishing. Then, the errors in typical robot-assisted polishing systems are analyzed, together with the corresponding compensation methods. At last, the future trends in the development of robot-assisted polishing are discussed. This review is intended as a roadmap for researchers or engineers who are interested in robot-assisted polishing or machining.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Miscibility and Cocrystallization in Ethylene–Vinyl Alcohol Copolymer Blends

The compatibility among different ethylene−vinyl alcohol (EVOH) copolymer grades plays a crucial role in determining how easily they can be recycled when present together in a mixed waste stream. In this work, melt miscibility and cocrystallization in 50/50 wt/wt binary blends of EVOH copolymers with differing ethylene content were studied. Blends with up to a 21 mol % difference in composition were analyzed. Thin films of miscible blends appeared homogeneous in the melt as observed under an optical microscope, whereas AFM height images showed that immiscible blends underwent surface roughening due to phase separation. For copolymers with modest composition differences, the blend behaved as a single component, showing single, narrow melting and crystallization peaks in DSC thermograms, indicating cocrystallization at the level of crystal stems. Interestingly, even phase-separated blends demonstrated partial cocrystallization due to partial miscibility of the components in the molten phase-separated domains. The extent of cocrystallization is governed by the difference in freezing points of the components; rapid cooling increased cocrystallization in the blends. The maximum compositional difference allowed for miscibility is not constant but depends on the blend’s average comonomer content, in agreement with the “miscibility window” calculated from literature pressure−volume−temperature behavior for the individual EVOH copolymers and regular mixing theory. This study helps illuminate the effect of copolymer composition on miscibility, as well as cocrystallization behavior in blends of random copolymers with cocrystallizable units.

Cocrystallization↗
DOE OSTI2025

Pressure-induced structural phase transitions in CrSBr

There is growing interest in combining chemical complexity with external stimuli like pressure, field, and light for property control in van der Waals solids. This is because extreme conditions trigger the development of new states of matter and functionality. In this work, we bring together synchrotron-based infrared absorption, Raman scattering, and diamond anvil cell techniques with first-principles calculations of the lattice dynamics and energy landscape to reveal the series of structural phase transitions in CrSBr. By tracking how the phonons change under pressure, we uncover a remarkable chain of complex symmetry modifications, interlayer interactions, and chemical reactions. A group-subgroup analysis suggests that CrSBr undergoes an orthorhombic Pmmn → monoclinic P2/m transition at 7.6 GPa, and based upon a comparison with model oxychlorides like FeOCl and CrOCl, we propose that changes in the pendant halide groups drive the system to a P2 1 /m-like space group above 15.3 GPa. Compression above 20.2 GPa is irreversible, resulting in the formation of an entirely new compound that is metastable for months. This work opens the door to the use of pressure and possibly strain to control the properties of CrSBr.

Microscopy↗
DOE OSTI2022

3D velocity map imaging of electrons with TPX3CAM

In this report we demonstrate three-dimensional velocity map imaging of low energy electrons using a TPX3CAM, where the three-dimensional momentum information [$p_x, p_y, p_z$] is encoded in position and timing [x, y, t] of hits on the camera sensor. We make use of the camera sensor for the [x, y] information and a constant fraction discriminator and fast time to digital converter in the camera for the time information. We illustrate the capabilities of our apparatus by presenting above threshold ionization measurements of xenon, which produces well defined structures in the momentum resolved photoelectron yield.

79 ASTRONOMY AND ASTROPHYSICS↗