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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 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Simulating dust grain-radiation coupling on a moving mesh

ABSTRACT We present a model for the interaction between dust and radiation fields in the radiation hydrodynamic code arepo-rt, which solves the moment-based radiative transfer equations on an unstructured moving mesh. Dust is directly treated using live simulation particles, each of which represent a population of grains that are coupled to hydrodynamic motion through a drag force. We introduce methods to calculate radiation pressure on and photon absorption by dust grains. By including a direct treatment of dust, we are able to calculate dust opacities and update radiation fields self-consistently based on the local dust distribution. This hybrid scheme coupling dust particles to an unstructured mesh for radiation is validated using several test problems with known analytic solutions, including dust driven via spherically symmetric flux from a constant luminosity source and photon absorption from radiation incident on a thin layer of dust. Our methods are compatible with the multifrequency scheme in arepo-rt, which treats UV, optical photons as single scattered and IR photons as multi scattered. At IR wavelengths, we model heating of and thermal emission from dust. Dust and gas are not assumed to be in local thermodynamic equilibrium but transfer energy through collisional exchange. We estimate dust temperatures by balancing these dust-radiation and dust-gas energy exchange rates. This framework for coupling dust and radiation can be applied in future radiation hydrodynamic simulations of galaxy formation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Growth and characterization of large (Y,La)TiO 3 and (Y,Ca)TiO 3 single crystals

The Mott-insulating rare-earth titanates ( R TiO 3 , with R being a rare-earth ion) are an important class of materials that encompasses interesting spin-orbital phases as well as ferromagnet-antiferromagnet and insulator-metal transitions. The growth of these materials has been plagued by difficulties related to overoxidation, which arises from a strong tendency of Ti 3 + to oxidize to Ti 4 + . We describe our efforts to grow sizable single crystals of YTiO 3 , Y 1 - x La x TiO 3 ( x ≤ 0.25 ), and Y 1 - y Ca y TiO 3 ( y ≤ 0.35 ) with the optical traveling-solvent floating-zone technique. Finally, we present sample characterization via chemical composition analysis, magnetometry, charge transport, neutron scattering, x-ray absorption spectroscopy, and x-ray magnetic circular dichroism to understand macroscopic physical property variations associated with overoxidation. Furthermore, we demonstrate a good signal-to-noise ratio in inelastic magnetic neutron scattering measurements of spin-wave excitations. A superconducting impurity phase, found to appear in Ca-doped samples at high doping levels, is identified as TiO.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Direct dark matter searches with metal halide perovskites

Polar materials with optical phonons in the meV range are excellent candidates for both dark matter direct detection via dark photon-mediated scattering and light dark matter absorption. In this study, we propose, for the first time, the metal halide perovskites MAPbI 3 , MAPbCl 3 , and CsPbI 3 for these purposes. Our findings reveal that CsPbI 3 is the best material, significantly improving exclusion limits compared to other polar materials. For scattering, CsPbI 3 can probe dark matter masses down to the keV range. For absorption, it enhances sensitivity to detect dark photon masses below ∼10 meV. The only material that has so far been investigated and that could provide competitive bounds is CsI, which, however, demonstrates lower stability as device platform compared to CsPbI 3 . Moreover, CsI is isotropic while the anisotropic structure of CsPbI 3 enables daily modulation analysis, showing that a significant percentage of daily modulation exceeding 1% is achievable for dark matter masses below 40 keV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

On the prospects of optical cycling in diatomic cations: effects of transition metals, spin–orbit couplings, and multiple bonds

Molecules with optical cycling centers (OCCs) are highly desirable in the context of fundamental studies as well as applications (e.g., quantum computing) because they can be effectively cooled to very low temperatures by repeated absorption and emission (hence, cycling). Charged species offer additional advantages for experimental control and manipulation. Here, we present a systematic computational study of a series of diatomic radical-cations made of a d-block metal and a p-block ligand, that are isoelectronic (in their valence shell) to the successfully laser-cooled neutral molecules. Using high-level electronic structure methods, we characterize state and transition properties of low-lying electronic states and compute Franck-Condon factors. The computed branching ratios and radiative lifetimes reveal that the electronic transitions analogous to those successfully used in the laser cooling of neutral molecules are less than optimal in the cations. We propose alternative transitions suitable for optical cycling and highlight trends that could assist future designs of OCCs in charged or neutral molecules.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2026

Surface-Functionalized, Two-Dimensional Polymer Electrochromic Layers as Ultrafast, Multi-State Infrared Optical Gates

Electrochromic devices have widespread application potential, but the currently available switching speeds limit broad real-world implementation of this technology. Here, we report surface-engineered two-dimensional polymers with ionophilic pores that offer unprecedented switching speeds in solid-state, two-terminal, electrochromic devices. In particular, we demonstrate that a crystalline donor–acceptor 2DP functionalized with ethylene glycol oligomers exhibits multistate infrared absorption that is 4× faster (t c = 320 ms) with 3× coloration efficiency (491 cm 2 C –1 ) compared to an alkyl functionalized 2DP constructed from the same chromophores. The functionalized nanoporous surfaces enable rapid switching in these materials under either oxidative or reductive conditions, allowing us to access a range of robust, stable optical responses in a single electrochromic layer. These attributes led us to leverage surface-functionalized 2DPs as multistate infrared logic gates. Collectively, this work demonstrates that surface engineering of nanoporous crystalline lattices is a promising approach to co-optimize the electronic and ionic conductivities required to achieve rapidly switchable electrochromic layers. Beyond speed and efficiency, the demonstration of multistate infrared characteristics shows that electrochromic frameworks are useful in integrated optoelectronic circuits. This positions surface-engineered 2DPs as improved electrochromic coatings and a new material platform for photonic information processing and adaptive devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Distinguishing resonance symmetries with energy-resolved photoion angular distributions from ion-pair formation in O 2 following two-photon absorption of a 9.3 eV femtosecond pulse

We present a combined experimental and theoretical study on the photodissociation dynamics of ion-pair formation in O 2 following resonant two-photon absorption of a 9.3 eV femtosecond pulse, where the resulting O + ions are detected using 3-D momentum imaging. Ion-pair formation states of $^3\Sigma^-_g$ and $^3\Pi_g$ symmetry are accessed through predissociation of optically dark continuum Rydberg states converging to the B $^2\Sigma^-_g$ ionic state, which are resonantly populated via a mixture of both parallel-parallel and parallel-perpendicular two-photon transitions. This mixture is evident in the angular distribution of the dissociation relative to the light polarization, and varies with the kinetic energy release (KER) of the fragmenting ion-pair. The KER-dependent photoion angular distribution reveals the underlying two-photon absorption dynamics involved in the ion-pair production mechanism and indicates the existence of two nearly degenerate continuum resonances possessing different symmetries, which can both decay by coupling to ion-pair states of the same total symmetry through internal conversion.

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

Increased phase precision of spatial light modulators using irrational slopes: application to attosecond metrology

The ability of spatial light modulators (SLMs) to modify the amplitude and phase of light has proved them invaluable to the optics and photonics community. In many applications, the bit-depth of SLMs is a major limiting factor dictated by a digital processor. As a result, there is usually a compromise between refresh speed and bit-depth. Here, we present a method to increase the effective bit-depth of SLMs, which utilizes a linear slope, as is commonly applied to deal with the zeroth-order effect. This technique was tested using two interferometric transient absorption spectroscopy setups. Through the high harmonic generation in gases producing a train of attosecond pulses and harmonics from solids in the ultraviolet, two pulses are generated that interfere in the far field providing a measurement of the optical phase. An increase in the precision far beyond the limit dictated by the digital processor in the bit-depth was found.

Harrison, Geoffrey R. (ORCID:0000000152141866)↗
DOE OSTI2020

Enhanced tuneable rotatory power in a rotating plasma

We report that the gyrotropic properties of a rotating magnetized plasma are derived analytically. Mechanical rotation leads to a new cutoff for wave propagation along the magnetic field, and polarization rotation above this cutoff is the sum of the classical magneto-optical Faraday effect and the mechanico-optical polarization drag. Exploiting the very large effective group index near the cutoff, we expose here that polarization drag can be 10 4 larger than Faraday rotation at GHz frequency. The rotation leads to weak absorption while allowing direct frequency control, demonstrating the unique potential of rotating plasmas for nonreciprocal elements. The very large rotation frequency of a dense non-neutral plasma could enable unprecedented gyrotropy in the THz regime.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Gradient Field Detection Using Interference of Stimulated Microwave Optical Sidebands

Here, we demonstrate that stimulated microwave optical sideband generation using parametric frequency conversion can be utilized as a powerful technique for coherent state detection in atomic physics experiments. The technique has advantages over traditional absorption or polarization rotation-based measurements and enables the isolation of signal photons from probe photons. We outline a theoretical framework that accurately models sideband generation using a density matrix formalism. Using this technique, we demonstrate a novel intrinsic magnetic gradiometer that detects magnetic gradient fields between two spatially separated vapor cells by measuring the frequency of the beat note between sidebands generated within each cell. The sidebands are produced with high efficiency using parametric frequency conversion of a probe beam interacting with 87 Rb atoms in a coherent superposition of magnetically sensitive hyperfine ground states. Interference between the sidebands generates a low-frequency beat note whose frequency is determined by the magnetic field gradient between the two vapor cells. In contrast to traditional gradiometers the intermediate step of measuring the magnetic field experienced by the two vapor cells is unnecessary. We show that this technique can be readily implemented in a practical device by demonstrating a compact magnetic gradiometer sensor head with a sensitivity of 25 fT/cm/ √ Hz with a 4.4 cm baseline, while operating in a noisy laboratory environment unshielded from Earth’s field.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2024

Automated Gold Nanorod Spectral Morphology Analysis Pipeline

The development of a colloidal synthesis procedure to produce nanomaterials with high shape and size purity is often a time-consuming, iterative process. This is often due to quantitative uncertainties in the required reaction conditions and the time, resources, and expertise intensive characterization methods required for quantitative determination of nanomaterial size and shape. Absorption spectroscopy is often the easiest method for colloidal nanomaterial characterization. However, due to the lack of a reliable method to extract nanoparticle shapes from absorption spectroscopy, it is generally treated as a more qualitative measure for metal nanoparticles. This work demonstrates a gold nanorod (AuNR) spectral morphology analysis tool, called AuNR-SMA, which is a fast and accurate method to extract quantitative structural information from colloidal AuNR absorption spectra. To demonstrate the practical utility of this model, we apply it to three distinct applications. First, we demonstrate this model's utility as an automated analysis tool in a high-throughput AuNR synthesis procedure by generating quantitative size information from optical spectra. Second, we use the predictions generated by this model to train a machine learning model to predict the resulting AuNR size distributions under specified reaction conditions. Third, we apply this model to spectra extracted from the literature where no size distributions are reported and impute unreported quantitative information on AuNR synthesis. This approach can potentially be extended to any other nanocrystal system where absorption spectra are size dependent, and accurate numerical simulation of absorption spectra is possible. In addition, this pipeline could be integrated into automated synthesis apparatuses to provide interpretable data from simple measurements, help explore the synthesis science of nanoparticles in a rational manner, or facilitate closed-loop workflows.

36 MATERIALS SCIENCE↗
DOE OSTI2024

X-ray dichroism as a probe of orbital quenching and unquenching induced by optically excited Jahn-Teller modes

The use of soft-X-ray spectroscopy to probe changes in the ground-state due to vibronic excitations is studied. The changes in L-edge X-ray absorption on divalent cobalt in the presence of a vibrating Jahn-Teller distortion are calculated. For linear dichroism, a strong dependence on the distortion is obtained reflecting the change in the local quadrupole moment due to the changes in the xy versus yz/zx hole densities during the oscillation. Here, in the presence of a magnetic moment, significant variations in the circular dichroic signal are obtained related to the quenching and unquenching of the orbital angular momentum.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Understanding the Benefit of Hybrid Electrolytes towards Vanadium Dissolution Suppression and Improved Capacity Retention in Zinc‐Aqueous Batteries Using NaV 3 O 8 Cathodes

Vanadate cathodes used in aqueous Zn-ion batteries with ZnSO 4 are hindered by capacity loss from V dissolution into the electrolyte. However, studies pinpointing the onset of dissolution as a function of electrochemical redox state and quantifying the amount of associated active material are lacking. To prevent dissolution of the NaV 3 O 8 active material, Na + ions are introduced into the electrolyte. Specifically, a hybrid ZnSO 4 + Na 2 SO 4 electrolyte is investigated in concert with NaV 3 O 8 (NVO) cathodes of varied crystallinity to determine the resulting impacts on cathode dissolution and functional electrochemistry. The use of Na + -containing hybrid electrolyte shows no significant change in Zn 2+ diffusion coefficients yet improved capacity retention. Time-resolved quantitative optical emission spectroscopy demonstrates the suppression of V dissolution with the hybrid electrolyte in both pristine and cycled electrodes. Operando synchrotron X-ray diffraction and absorption provide mechanistic insights. Hydrated NVO with wider interplanar spacing exhibits much higher H + /Zn 2+ capacity, while the Na 2 SO 4 mitigates the formation of irreversible side products. Furthermore, this study demonstrates that the use of hybrid electrolytes and control of crystallite size in the parent material can significantly improve electrochemical behavior of layered V-based cathodes in Zn-ion batteries, providing a general strategy toward safe and resilient aqueous battery systems.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Polariton Formation from Soret Band Excitons in Metal–Organic Frameworks and Plasmonic Lattices

This Letter describes strong coupling between a plasmonic nanoparticle (NP) lattice cavity and Soret excitons in a metal–organic framework (MOF) film. In optical transmission measurements, we observed a lower polariton mode that can be spectrally tuned by infiltrating MOF pores with solvents of different refractive index. Using transient absorption spectroscopy, both the lower and upper polariton modes can be resolved, with an estimated Rabi splitting of ~300 meV, nearly twice that of other plasmonic cavity–organic emitter systems. The polariton modes decay more rapidly than that of the uncoupled exciton. Furthermore, this hybrid system highlights the advantages of open plasmonic cavities for tunable coupling and the use of transient absorption spectroscopy to identify polariton modes.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

Understanding the dopant induced effects on SFX-MeOTAD for perovskite solar cells: a spectroscopic and computational investigation

SFX-MeOTAD [2,2',7,7'-tetrakis(N,N-di(4-methoxyphenyl)amino)-spiro-(fluorene-9,9'-xanthene)] (also known as X60) has emerged as a cost-effective alternative to the ubiquitous, but excessively-expensive, spiro-MeOTAD hole transport material (HTM) in perovskite solar cells. Using its pre-oxidised dicationic salt, SFX-(TFSI) 2 , a controlled concentration dependent conductivity tuning of this HTM without the requirement of air (oxygen) exposure has been carried out. This study details the modifications in the optical and electrical properties of this low cost HTM as a function of the concentration of the dicationic salt (0–100 mol%) using UV-vis absorption and electrical conductivity measurements. X-ray absorption and photoelectron spectroscopy investigations have been carried out to elucidate the role of the dicationic salt in the enhanced electronic properties of SFX-MeOTAD. By incorporating the dicationic SFX-(TFSI) 2 it has been shown that the conductivity of SFX-MeOTAD increased by 4 orders of magnitude from 2.55 × 10 –8 S cm –1 to 9.4 × 10 –4 S cm –1 when using an optimal dopant concentration of 20.5 mol%. The degree of oxidation of SFX-MeOTAD was determined through UV-vis absorption and consolidated using the computational calculations. The XPS study reveals that doping SFX-MeOTAD with SFX(TFSI) 2 not only results in the oxidation of the HTM but also leads to a variation in the local chemistry around carbon and nitrogen which directly influences the conductivity of the doped films. NEXAFS studies indicate that doping enhances the aromatic nature of the molecule initially but increasing the dopant concentration further affects the aromaticity and possibly the π stacking, similar to the trend seen in dopant concentration dependent conductivity of the SFX-MeOTAD films. These findings have implications on the choice of dopant concentration and counterions more generally for triarylamine based HTMs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Broadband 2DES detection of vibrational coherence in the S x state of canthaxanthin

The nonadiabatic mechanism that mediates nonradiative decay of the bright S 2 state to the dark S 1 state of carotenoids involves population of a bridging intermediate state, S x , in several examples. The nature of S x remains to be determined definitively, but it has been recently suggested that S x corresponds to conformationally distorted molecules evolving along out-of-plane coordinates of the isoprenoid backbone near a low barrier between planar and distorted conformations on the S 2 potential surface. Here, the electronic and vibrational dynamics accompanying the formation of S x in toluene solutions of the ketocarotenoid canthaxanthin (CAN) are characterized with broadband two-dimensional electronic spectroscopy (2DES) with 7.8 fs excitation pulses and detection of the linear polarization components of the third-order nonlinear optical signal. A stimulated-emission cross peak in the 2DES spectrum accompanies the formation of S x in <20 fs following excitation of the main absorption band. S x is prepared instantaneously, however, with excitation of hot-band transitions associated with distorted conformations of CAN’s isoprenoid backbone in the low frequency onset of the main absorption band. Vibrational coherence oscillation maps and modulated anisotropy transients show that S x undergoes displacements from the Franck–Condon S 2 state along out-of-plane coordinates as it passes to the S 1 state. The results are consistent with the conclusion that CAN’s carbonyl-substituted β-ionone rings impart an intramolecular charge-transfer character that frictionally slows the passage from S x to S 1 compared to carotenoids lacking carbonyl substitution. Despite the longer lifetime, the S 1 state of CAN is formed with retention of vibrational coherence after passing through a conical intersection seam with the S x state.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Constraining dark matter-proton scattering from molecular cloud ionization

Optically dense clouds in the interstellar medium composed predominantly of molecular hydrogen, known as molecular clouds, are sensitive to energy injection in the form of photon absorption, cosmic-ray scattering, and dark matter (DM) scattering. The ionization rates in dense molecular clouds are heavily constrained by observations of abundances of various molecular tracers. Recent studies have set constraints on the DM-electron scattering cross section using measurements of ionization rates in dense molecular clouds. Here we calculate the analogous bounds on the DM-proton cross section using the molecular Migdal effect, recently adapted from the neutron scattering literature to the DM context. These bounds may be the strongest limits on a strongly coupled DM subfraction, and represent the first application of the Migdal effect to astrophysical systems. Published by the American Physical Society 2024

Astronomy & Astrophysics↗
DOE OSTI2026

Errors in reconstruction of dichroic X-ray orientation tomography due to polarization rotation of the incident beam

Dichroic X-ray tomography is a technique in which the crystal orientation or magnetization of a sample is resolved in three dimensions. The best-known uses of this technique are for observation of magnetic moments via circular dichroism, using left- and right-handed circularly polarized X-ray beams. Another variant uses linear dichroism to resolve the crystal orientation. In both these techniques, it is assumed that the absorption of X-rays along a path inside a material can be computed as a line integral of a local absorption coefficient along the ray path. For linear dichroism, this assumption is inaccurate because the polarization of the beam changes along the propagation direction when the optic axis of the material is not aligned along the polarization. In this work, a finite-element Maxwell solver is used to simulate tomography and reconstructions. The propagation effect can lead to significant errors in the reconstructed orientations. These errors may be mitigated by taking data at additional angles or by operating at energies at which the dichroism is weak. An iterative approach is proposed which may allow accurate reconstruction with fewer data than would otherwise be required.

X-ray linear dichroism↗