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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 757 records · Page 42
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Strain-tunable metamagnetic critical endpoint in Mott insulating rare-earth titanates

Rare-earth titanates are Mott insulators whose magnetic ground state—antiferromagnetic (AFM) or ferromagnetic (FM)—can be tuned by the radius of the rare-earth element. We combine phenomenology and first-principles calculations to shed light on the generic magnetic phase diagram of a chemically substituted titanate on the rare-earth site that interpolates between an AFM and a FM state. Octahedral rotations present in these perovskites cause the AFM order to acquire a small FM component—and vice-versa—removing any multicritical point from the phase diagram. However, for a wide parameter range, a first-order metamagnetic transition line terminating at a critical endpoint survives inside the magnetically ordered phase. Like the liquid-gas transition, a Widom line emerges from the endpoint, characterized by enhanced fluctuations. In contrast to metallic FMs, this metamagnetic transition involves two symmetry-equivalent and insulating canted spin states. Moreover, instead of a magnetic field, we show that uniaxial strain can be used to tune this transition to zero temperature, inducing a quantum critical endpoint.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Turn‐on Circularly Polarized Luminescence in Chiral Indium Chlorides by 5s 2 Metal Centers

Abstract Introducing chirality into the metal‐halide hybrids has enabled many emerging properties including chiroptical activity, spin‐dependent transport, and ferroelectricity. However, most of the chiral metal‐halide hybrids to date are non‐emissive, and the underlying mechanism remains elusive. Here, we show a new strategy to turn on the circularly polarized luminescence (CPL) in chiral metal‐halide hybrids. We demonstrate that alloying Sb 3+ into chiral indium‐chloride hybrids dramatically increases the photoluminescence quantum yield in two new series of chiral indium‐antimony chlorides. These materials exhibit strong CPL signals with tunable energy and a high dissymmetry factor up to 1.5×10 −2 . Mechanistic studies reveal that the emission originates from the self‐trapped excitons centered in 5s 2 Sb 3+ . Moreover, near‐ultraviolet pumped white light is demonstrated with a polarization up to 6.0 %. Our work demonstrates new strategies towards highly luminescent chiral metal‐halide hybrids.

Wang, Zhiyu↗
DOE OSTI2016

Monobenzoporphyrins as Sensitizers for Dye‐Sensitized Solar Cells: Observation of Significant Spacer‐Group Effect

Abstract A series of monobenzoporphyrins ( WH1 – WH4 ) bearing different conjugated spacer groups were designed and synthesized as sensitizers for dye‐sensitized solar cells. Although a phenyl spacer only has a minimal impact on the absorption bands of the monobenzoporphyrin, an ethynylphenyl ( WH3 ) or a vinyl ( WH4 ) spacer redshifts and broadens the absorption bands of the dyes to result in much enhanced light‐harvesting ability. Dye‐sensitized solar cells based on these monobenzoporphyrin dyes displayed remarkable differences in power conversion efficiencies (PCEs). The monobenzoporphyrin bearing no spacer ( WH1 ) resulted in a PCE of only 0.5 %; in contrast, the monobenzoporphyrin bearing vinyl spacers ( WH4 ) achieved a PCE of 5.2 %. The high efficiency of the WH4 cell is attributed to the higher light‐harvesting ability, the lesser extent of aggregation on the TiO 2 surface, and the more favorable electron‐density distributions of the HOMO and LUMO for electron injection and collection. This work demonstrates the exceptional tunability of benzoporphyrins as sensitizers for dye‐sensitized solar cells.

Jinadasa, R. G. Waruna↗
DOE OSTI2021

Direct Optical Lithography of CsPbX 3 Nanocrystals via Photoinduced Ligand Cleavage with Postpatterning Chemical Modification and Electronic Coupling

Microscale patterning of solution-processed nanomaterials is important for integration in functional devices. Colloidal lead halide perovskite (LHP) nanocrystals (NCs) can be particularly challenging to pattern due to their incompatibility with polar solvents and lability of surface ligands. Here, we introduce a direct photopatterning approach for LHP NCs through the binding and subsequent cleavage of a photosensitive oxime sulfonate ester (-C=N-OSOO-). The photosensitizer binds to the NCs through its sulfonate group and is cleaved at the N-O bond during photoirradiation with 405 nm light. This bond cleavage decreases the solubility of the NCs, which allows patterns to emerge upon development with toluene. Postpatterning ligand exchange results in photoluminescence quantum yields of up to 79%, while anion exchange provides tunability in the emission wavelength. Finally, the patterned NC films show photoconductive behavior, demonstrating that good electrical contact between the NCs can be established.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

A review of materials used in tomographic volumetric additive manufacturing

Abstract Volumetric additive manufacturing is a novel fabrication method allowing rapid, freeform, layer-less 3D printing. Analogous to computer tomography (CT), the method projects dynamic light patterns into a rotating vat of photosensitive resin. These light patterns build up a three-dimensional energy dose within the photosensitive resin, solidifying the volume of the desired object within seconds. Departing from established sequential fabrication methods like stereolithography or digital light printing, volumetric additive manufacturing offers new opportunities for the materials that can be used for printing. These include viscous acrylates and elastomers, epoxies (and orthogonal epoxy-acrylate formulations with spatially controlled stiffness) formulations, tunable stiffness thiol-enes and shape memory foams, polymer derived ceramics, silica-nanocomposite based glass, and gelatin-based hydrogels for cell-laden biofabrication. Here we review these materials, highlight the challenges to adapt them to volumetric additive manufacturing, and discuss the perspectives they present. Graphical abstract

36 MATERIALS SCIENCE↗
NASA NTRS1990

Novel laser gain and time-resolved FTIR studies of photochemistry

Several techniques are discussed which can be used to explore laboratory photochemical processes and kinetics relevant to planetary atmospheres; these include time-resolved laser gain-versus-absorption spectroscopy and time-resolved Fourier transform infrared (FTIR) emission studies. The laser gain-versus-absorption method employed tunable diode and F-center lasers to determine the yields of excited photofragments and their kinetics. The time-resolved FTIR technique synchronizes the sweep of a commercial FTIR with a pulsed source of light to obtain emission spectra of novel transient species in the infrared. These methods are presently being employed to investigate molecular photodissociation, the yields of excited states of fragments, their subsequent reaction kinetics, Doppler velocity distributions, and velocity-changing collisions of translationally fast atoms. Such techniques may be employed in future investigations of planetary atmospheres, for example to study polycyclic aromatic hydrocarbons related to cometary emissions, to analyze acetylene decomposition products and reactions, and to determine spectral features in the near infrared and infrared wavelength regions for planetary molecules and clusters.

Leone, Stephen R.↗
NASA NTRS2012

The Sample Analysis at Mars Investigation and Instrument Suite

The Sample Analysis at Mars (SAM) investigation of the Mars Science Laboratory (MSL) addresses the chemical and isotopic composition of the atmosphere and volatiles extracted from solid samples. The SAM investigation is designed to contribute substantially to the mission goal of quantitatively assessing the habitability of Mars as an essential step in the search for past or present life on Mars. SAM is a 40 kg instrument suite located in the interior of MSL's Curiosity rover. The SAM instruments are a quadrupole mass spectrometer, a tunable laser spectrometer, and a 6-column gas chromatograph all coupled through solid and gas processing systems to provide complementary information on the same samples. The SAM suite is able to measure a suite of light isotopes and to analyze volatiles directly from the atmosphere or thermally released from solid samples. In addition to measurements of simple inorganic compounds and noble gases SAM will conduct a sensitive search for organic compounds with either thermal or chemical extraction from sieved samples delivered by the sample processing system on the Curiosity rover's robotic arm,

Mahaffy, Paul↗
NASA NTRS2008

Tailored Asymmetry for Enhanced Coupling to WGM Resonators

Coupling of light into and out of whispering- gallery-mode (WGM) optical resonators can be enhanced by designing and fabricating the resonators to have certain non-axisymmetric shapes (see figure). Such WGM resonators also exhibit the same ultrahigh values of the resonance quality factor (Q) as do prior WGM resonators. These WGM resonators are potentially useful as tunable narrow-band optical filters having throughput levels near unity, high-speed optical switches, and low-threshold laser resonators. These WGM resonators could also be used in experiments to investigate coupling between high-Q and chaotic modes within the resonators. For a WGM resonator made of an optically nonlinear material (e.g., lithium niobate) or another material having a high index of refraction, a prism made of a material having a higher index of refraction (e.g., diamond) must be used as part of the coupling optics. For coupling of a beam of light into (or out of) the high-Q resonator modes, the beam must be made to approach (or recede from) the resonator at a critical angle determined by the indices of refraction of the resonator and prism materials. In the case of a lithium niobate/diamond interface, this angle is approximately 22 .

Mohageg, Makan↗
DOE OSTI2020

Tunable Layer Circular Photogalvanic Effect in Twisted Bilayers

In this work, we develop a general theory of the layer circular photogalvanic effect (LCPGE) in quasi-two-dimensional chiral bilayers, which refers to the appearance of a polarization-dependent, out-of-plane static dipole moment induced by circularly polarized light. We elucidate the geometric origin of the LCPGE as two types of interlayer coordinate shift weighted by the quantum metric tensor and the Berry curvature, respectively. As a concrete example, we calculate the LCPGE in twisted bilayer graphene, and find that it exhibits a resonance peak whose frequency can be tuned from visible to infrared as the twisting angle varies. The LCPGE thus provides a promising route toward frequency-sensitive, circularly polarized light detection, particularly in the infrared range.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Improving a Multilevel Turbulence Closure Model for a Shallow Lake in Comparison With Other 1-D Models

Lakes differ from lands in water availability, heat capacity, albedo, and roughness, which affect local surface-atmospheric interactions. This study modified a multilevel upper ocean model (UOM) for lake applications and evaluated its performance in Lake Taihu (China) with comprehensive measurements against three popular one-dimensional (1-D) lake models. These models were based on different concepts, including the self-similarity (FLake), the wind-driven eddy diffusion (LISSS), the k-ε turbulence closure (SIMSTRAT), and a simplified turbulence closure (UOM). The surface flux scheme in these models was unified to exclude the discrepancies in representing air-lake exchanges. All models in their default formulations presented obvious cold water temperature biases and largely underestimated the lake surface temperature (LST) diurnal range. For each model, these deficiencies were significantly reduced by incorporating new physics schemes or calibrated tunable parameters based on systematic sensitivity tests. The primary modifications for UOM included (1) a new scheme of decreased surface roughness lengths to better characterize the shallow lake, (2) a solar radiation penetration scheme with increased light extinction coefficient and surface absorption fraction to account for the high water turbidity, and (3) turbulent Prandtl number increased by a factor of 20 to reduce the turbulent vertical mixing. All other models were improved in these three aspects (roughness, extinction, and mixing) within their original formulations. Given these improvements, UOM showed superior performance to other models in capturing LST diurnal cycle and daily to seasonal variations, as well as summer-autumn vertical stratification changes. The new UOM is well suited for application in shallow lakes.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Surface plasmons induce topological transition in graphene/α-MoO3 heterostructures

Abstract Polaritons in hyperbolic van der Waals materials—where principal axes have permittivities of opposite signs—are light-matter modes with unique properties and promising applications. Isofrequency contours of hyperbolic polaritons may undergo topological transitions from open hyperbolas to closed ellipse-like curves, prompting an abrupt change in physical properties. Electronically-tunable topological transitions are especially desirable for future integrated technologies but have yet to be demonstrated. In this work, we present a doping-induced topological transition effected by plasmon-phonon hybridization in graphene/α-MoO 3 heterostructures. Scanning near-field optical microscopy was used to image hybrid polaritons in graphene/α-MoO 3 . We demonstrate the topological transition and characterize hybrid modes, which can be tuned from surface waves to bulk waveguide modes, traversing an exceptional point arising from the anisotropic plasmon-phonon coupling. Graphene/α-MoO 3 heterostructures offer the possibility to explore dynamical topological transitions and directional coupling that could inspire new nanophotonic and quantum devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Building superlattices from individual nanoparticles via template-confined DNA-mediated assembly

DNA programmable assembly has been combined with top-down lithography to construct superlattices of discrete, reconfigurable nanoparticle architectures on a gold surface over large areas. Specifically, the assembly of individual colloidal plasmonic nanoparticles with different shapes and sizes is controlled by oligonucleotides containing “locked” nucleic acids and confined environments provided by polymer pores to yield oriented architectures that feature tunable arrangements and independently controllable distances at both nanometer- and micrometer-length scales. These structures, which would be difficult to construct by other common assembly methods, provide a platform to systematically study and control light-matter interactions in nanoparticle-based optical materials. The generality and potential of this approach are explored by identifying a broadband absorber with a solvent polarity response that allows dynamic tuning of visible light absorption.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Exciton Transfer Between Extended Electronic States in Conjugated Inter-Polyelectrolyte Complexes

Artificial light harvesting, a process that involves converting sunlight into chemical potential energy, is considered to be a promising part of the overall solution to address urgent global energy challenges. Conjugated polyelectrolyte complexes (CPECs) are particularly attractive for this purpose due to their extended electronic states, tunable assembly thermodynamics, and sensitivity to their local environment. Importantly, ionically assembled complexes of conjugated polyelectrolytes can act as efficient donor-acceptor pairs for electronic energy transfer (EET). However, to be of use in material applications, we must understand how modifying the chemical structure of the CPE backbone alters the EET rate beyond spectral overlap considerations. In this report we investigate the dependence of the EET efficiency and rate on the electronic structure and excitonic wave function of the CPE backbone. To do so, we synthesized a series of alternating copolymers where the electronic states are systematically altered by introducing comonomers with electron withdrawing and electron-rich character while keeping the linear ionic charge density nearly fixed. We find evidence that the excitonic coupling may be significantly affected by the exciton delocalization radius, in accordance with analytical models based on the line-dipole approximation and quantum chemistry calculations. Our results imply that care should be taken when selecting CPE components for optimal CPEC EET. These results have implications for using CPECs as key components in water-based light-harvesting materials, either as standalone assemblies or as adsorbates on nanoparticles and thin films.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Enabling enhanced emission and low-threshold lasing of organic molecules using special Fano resonances of macroscopic photonic crystals

The nature of light interaction with matter can be dramatically altered in optical cavities, often inducing nonclassical behavior. In solid-state systems, excitons need to be spatially incorporated within nanostructured cavities to achieve such behavior. Although fascinating phenomena have been observed with inorganic nanostructures, the incorporation of organic molecules into the typically inorganic cavity is more challenging. We present a unique optofluidic platform comprising organic molecules in solution suspended on a photonic crystal surface, which supports macroscopic Fano resonances and allows strong and tunable interactions with the molecules anywhere along the surface. We develop a theoretical framework of this system and present a rigorous comparison with experimental measurements, showing dramatic spectral and angular enhancement of emission. We then demonstrate that these enhancement mechanisms enable lasing of only a 100-nm thin layer of diluted solution of organic molecules with substantially reduced threshold intensity, which has important implications for organic light-emitting devices and molecular sensing.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

High Extraction Phosphors for Solid State Lighting

We have developed high-index, high efficiency bulk luminescent materials and novel nano-sized phosphors for improved solid-state white LED lamps. These advances can potentially contribute to reducing the loss in luminous efficiencies due to scattering, re-absorption, and thermal quenching. The bulk and nanostructured luminescent materials investigated are index matched to GaN and have broad and size-tunable absorption bands, size and impurity tuned emission bands, size-driven elimination of scattering effects, and a separation between absorption and emission bands. These innovations were accomplished through the use of novel synthesis techniques suitable for high volume production for LED lamp applications. The program produced a full-color set of high quantum yield phosphors with high chemical stability. In the bulk phosphor study, the ZnSeS:Cu,Ag phosphor was optimized to achieve >91% efficiency using erbium (Er) and other activators as sensitizers. Detailed analysis of temperature quenching effects on a large number of ZnSeS:Cu,Ag,X and strontium- and calcium-thiogallate phosphors lead to a breakthrough in the understanding of the anti-quenching behavior and a physical bandgap model was developed of this phenomena. In a follow up to this study, optimized phosphor blends for high efficiency and color performance were developed and demonstrated a 2-component phosphor system with good white chromaticity, color temperature, and high color rendering. By extending the protocols of quantum dot synthesis, large nanocrystals, greater than 20 nm in diameter were synthesized and exhibited bulk-like behavior and blue light absorption. The optimization of ZnSe:Mn nanophosphors achieved ~85% QE The limitations of core-shell nanocrystal systems were addressed by investigating alternative deltadoped structures. To address the manufacturability of these systems, a one-pot manufacturing protocol was developed for ZnSe:Mn nanophosphors. To enhance the stability of these material systems, the encapsulation of ZnSeS particle phosphors and ZnSeS screens with Al 2 O 3 and TiO 2 using ALD was shown to improve the stability by >8X and also increased the luminescence efficiency due to improved surface passivation and optical coupling. A large-volume fluidized bed ALD system was designed that can be adapted to a commercial ALD or vapor deposition system. Throughout the program, optical simulations were developed to evaluate and optimize various phosphor mixtures and device configurations. For example, to define the scattering properties of nanophosphors in an LED device or in a stand-off screen geometry. Also this work significantly promoted and assisted in the implementation of realistic phosphor material models into commercial modeling programs.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2022

Turn-on Circularly Polarized Luminescence in Chiral Indium Chlorides by 5s 2 Metal Centers

Introducing chirality into the metal-halide hybrids has enabled many emerging properties including chiroptical activity, spin-dependent transport, and ferroelectricity. However, most of the chiral metal-halide hybrids to date are non-emissive, and the underlying mechanism remains elusive. Here, in this study, we show a new strategy to turn on the circularly polarized luminescence (CPL) in chiral metal-halide hybrids. We demonstrate that alloying Sb 3+ into chiral indium-chloride hybrids dramatically increases the photoluminescence quantum yield in two new series of chiral indium-antimony chlorides. These materials exhibit strong CPL signals with tunable energy and a high dissymmetry factor up to 1.5×10 -2 . Mechanistic studies reveal that the emission originates from the self-trapped excitons centered in 5s 2 Sb 3+ . Moreover, near-ultraviolet pumped white light is demonstrated with a polarization up to 6.0 %. Our work demonstrates new strategies towards highly luminescent chiral metal-halide hybrids.

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

Tailored Frequency Conversion in Nonlinear Subwavelength Grating Metaslabs

The use of metaslab waveguides consisting of subwavelength gratings (SWGs) is proposed as a highly flexible approach to obtain phase‐matched frequency conversion in nonlinear integrated devices. Control over the phase matching (PM) condition is achieved through modification of the linear modal propagation constants by the SWG. The method is experimentally demonstrated by fabrication of 0.4 mm‐long GaAs metaslabs designed for second harmonic generation of near‐infrared light. A controlled spectral shift of up to 100 nm in the PM condition, relative to a uniform slab is observed. Excellent agreement is found between the experimental results and finite‐difference eigenmode simulations, which predict a tunable frequency conversion bandwidth of ∼300 nm for the design parameters. The different regimes of PM control supported by the structure are discussed. This work highlights the potential of SWGs as building blocks for tailored frequency conversion in nonlinear integrated devices.

Form birefringence↗
DOE OSTI2022

Protein Vesicles with pH-Responsive Disassembly

We report protein biomaterials offer several advantages over those made from other components because their amino acid sequence can be precisely controlled with genetic engineering to produce a diverse set of material building blocks. In this work, three different elastin-like polypeptide (ELP) sequences were designed to synthesize pH-responsive protein vesicles. ELPs undergo a thermally induced hydrophobic transition that enables self-assembly of different kinds of protein biomaterials. The transition can be tuned by the composition of the guest residue, X, within the ELP pentapeptide repeat unit, VPGXG. When the guest residue is substituted with an ionizable amino acid, such as histidine, the ELP undergoes a pH-dependent hydrophobic phase transition. We used pH-responsive ELPs with different levels of histidine substitution, in combination with leucine zippers and globular, functional proteins, to fabricate protein vesicles. We demonstrate pH-dependent self-assembly, diameter, and disassembly of the vesicles using a combination of turbidimetry, dynamic light scattering, microscopy, and small angle X-ray scattering. As the ELP transition is dependent on the sequence, the vesicle properties also depend on the histidine content in the ELP building blocks. These results demonstrate the tunability of protein vesicles endowed with pH responsiveness, which expands their potential in drug-delivery applications.

59 BASIC BIOLOGICAL SCIENCES↗