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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 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Particle–hole asymmetry and quantum confinement effects on the magneto-optical response of topological insulator thin-films

Intrinsically broken symmetries in the bulk of topological insulators (TIs) are manifested in their surface states. Despite particle–hole asymmetry in TIs, it has often been assumed that their surface states are characterized by a particle–hole symmetric Dirac energy dispersion. In this work, we demonstrate that the effect of particle–hole asymmetry is essential to correctly describe the energy spectrum and the magneto-optical response in TIs thin-films. In thin-films of TIs with a substantial degree of particle–hole symmetry breaking, such as Sb 2 Te 3 , the longitudinal optical conductivity displays absorption peaks arising from optical transitions between bulk and surface Landau levels for low photon energies. The transition energies between the bulk and surface Landau levels exhibit clearly discernable signatures from those between surface Landau levels due to their distinct magnetic field dependence. Furthermore, bulk contributions to the magneto-optical conductivity in a TI thin-film are enhanced via one type of doping while being suppressed by the other. This asymmetric dependence on the type of doping aids in revealing the particle–hole asymmetry in TI thin-films.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Non-Equilibrium Plasma Interactions with Biomaterials, Biological Solutions and Tissues

Cold atmospheric pressure plasma discharges offer an abundant source of reactive oxygen and nitrogen species (RONS) at room temperature enabling unique interactions with biomaterials, biological solutions and tissues. These interactions particularly with living matter are presently an important intellectual frontier in plasma science with promising potential applications ranging from human health care to advanced biomaterial processing. Exciting case studies have been reported that illustrate the huge potential of cold atmospheric plasma technology in wound healing and cancer treatment. The interaction of plasma with conducting and dielectric biomaterials such as tissue strongly influences the plasma properties. In turn this changes the impact of the plasma on the biomaterial. Particularly in the case of living matter, liquid based solutions are ubiquitous which complicates interfacial processes. The lack of insight into the underlying mechanisms of the interaction of plasma with wounds and tumors is currently a bottleneck for the further development of the technology and gives rise to many interesting scientific questions. This project was focused on plasma properties and kinetics during plasma-biomaterial interactions. Both DC pulsed and RF driven atmospheric pressure plasma jets, extensively used by the plasma community were studied. The bio-interfaces included hydrogel as a tissue model, (saline) solutions, bacteria and virus. Plasma diagnostics used include Thomson scattering, Rayleigh scattering, Raman scattering, (two-photon absorption) laser induced fluorescence, optical emission spectroscopy, absorption spectroscopy, molecular beam mass spectrometry and fast imaging allowing to determine electron densities and temperatures, ionic species, reactive species including radicals, gas temperatures, gas composition, electric fields and solution components transferred to the gas phase.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Thermoacoustic and photoacoustic characterizations of few-layer graphene by pulsed excitations

We characterized the thermoacoustic and photoacoustic properties of large-area, few-layer graphene by pulsed microwave and optical excitations. Due to its high electric conductivity and low heat capacity per unit area, graphene lends itself to excellent microwave and optical energy absorption and acoustic signal emanation due to the thermoacoustic effect. When exposed to pulsed microwave or optical radiation, distinct thermoacoustic and photoacoustic signals generated by the few-layer graphene are obtained due to microwave and laser absorption of the graphene, respectively. Clear thermoacoustic and photoacoustic images of large-area graphene sample are achieved. A numerical model is developed and the simulated results are in good accordance with the measured ones. This characterization work may find applications in ultrasound generator and detectors for microwave and optical radiation. It may also become an alternative characterization approach for graphene and other types of two-dimensional materials.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1998

Investigation of Third Order Optical Nonlinearity and Reverse Saturable Absorption of Octa-alkoxy Metallophthalocyanines

In recent years, there has been a growing interest in the development of passive optical power limiters for the protection of the human eye and solid-state sensors from damage caused by energetic light pulses and also for other switching applications. One of the key issues involved is the search for appropriate materials that show effective reverse saturable absorption. Phthalocyanines seem to be good candidates for such applications because of their higher third order nonlinearity and the unique electronic absorption characteristics. A series of 1,4,8,11,15, 18,22,25-octa-alkoxy metallophthalocyanines containing various central metal atoms such as zinc, copper, palladium, cobalt and nickel were characterized for their third order nonlinearity and for their nonlinear absorptive properties to evaluate their suitability to function as reverse saturable absorbers.

Sanghadasa, Mohan↗
DOE OSTI2022

Monte Carlo calculations of the extraction of scintillation light from cryogenic $N$-type GaAs

We report the high scintillation luminosity of n-type GaAs at 10 °K is surprising because (1) with a refractive index of 3.5, escape is inhibited by total internal reflection and (2) narrow-beam experiments at 90 °K report infrared absorption coefficients of several per cm. This paper presents Monte Carlo calculations showing that the high luminosity at 10 °K can be explained if (1) the narrow-beam absorption is almost all optical scattering and (2) the absolute absorption coefficient is below 0.1 per cm. Sixteen surface reflector configurations are simulated for a range of internal scattering and absolute absorption coefficients, and these can guide the design of cryogenic scintillating GaAs targets for the direct detection of dark matter. The discussion section presents a possible infrared scattering mechanism based on the metallic nature of n-type GaAs. A supplement file describes (1) the Monte Carlo program steps in detail and (2) how narrow-beam and integrating sphere experiments can measure the cryogenic optical scattering and absolute absorption coefficients.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

Probing the Structural Evolution of the Hydrated Electron in Water Cluster Anions (H 2 O) n – , n ≤ 200, by Electronic Absorption Spectroscopy

Electronic absorption spectra of water cluster anions (H 2 O) n - , n ≤ 200, at T = 80 K are obtained by photodissociation spectroscopy and compared with simulations from literature and experimental data for bulk hydrated electrons. Two almost isoenergetic electron binding motifs are seen for cluster sizes 20 ≤ n ≤ 40, which are assigned to surface and partially embedded isomers. With increasing cluster size, the surface isomer becomes less populated, and for n ≥ 50, the partially embedded isomer prevails. The absorption shifts to the blue, reaching a plateau at n ≈ 100. In this size range, the absorption spectrum is similar to that of the bulk hydrated electron but is slightly red-shifted; spectral moment analysis indicates that these clusters are reasonable model systems for hydrated electrons near the liquid-vacuum interface.

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

Carrier-Specific Hot Phonon Bottleneck in CH 3 NH 3 PbI 3 Revealed by Femtosecond XUV Absorption

Femtosecond carrier cooling in the organohalide perovskite semiconductor CH 3 NH 3 PbI 3 is measured using extreme ultraviolet (XUV) and optical transient absorption spectroscopy. XUV absorption between 44 and 58 eV measures transitions from the I 4d core to the valence and conduction bands and gives distinct signals for hole and electron dynamics. The core-to-valence-band signal directly maps the photoexcited hole distribution and provides a quantitative measurement of the hole temperature. The combination of XUV and optical probes reveals that upon excitation at 400 nm, the initial hole distribution is 3.5 times hotter than the electron distribution. At an initial carrier density of 1.4 × 10 20 cm –3 both carriers are subject to a hot phonon bottleneck, but at 4.2 × 10 19 cm –3 the holes cool to less than 1000 K within 400 fs. Finally, this result places significant constraints on the use of organohalide perovskites in hot-carrier photovoltaics.

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

Excited-state structural dynamics of nickel complexes probed by optical and X-ray transient absorption spectroscopies: insights and implications

Excited states of nickel complexes undergo a variety of photochemical processes, such as charge transfer, ligation/deligation, and redox reactions, relevant to solar energy conversion and photocatalysis. The efficiencies of the aforementioned processes are closely coupled to the molecular structures in the ground and excited states. The conventional optical transient absorption spectroscopy has revealed important excited-state pathways and kinetics, but information regarding the metal center, in particular transient structural and electronic properties, remains limited. These deficiencies are addressed by X-ray transient absorption (XTA) spectroscopy, a detailed probe of 3d orbital occupancy, oxidation state and coordination geometry. The examples of excited-state structural dynamics of nickel porphyrin and nickel phthalocyanine have been described from our previous studies with highlights on the unique structural information obtained by XTA spectroscopy. Furthermore, we close by surveying prospective applications of XTA spectroscopy to active areas of Ni-based photocatalysis based on the knowledge gained from our previous studies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Using Lightning Flashes to Image Thunderclouds

We report the optical energy emitted by lightning flashes interacts with the surrounding cloud medium through scattering and absorption. The optical signals recorded by space-based lightning imagers describe a convolution of lightning flash energetics and radiative transfer effects in the intervening cloud layer. A thundercloud imaging technique is presented that characterizes cloud regions based on how they are illuminated by lightning. This technique models the spatial distribution of optical energy in radiant lightning pulses to determine whether and to what extent each illuminated cloud pixel behaves like a homogeneous planar cloud layer. A gridded product is constructed that differentiates flashes that illuminate convective cells from stratiform flashes with long horizontal channels and anvil flashes whose optical emissions reflect off of nearby cloud surfaces. Lastly, producing this imagery with a rolling 15-min window allows us to visualize changes in convection with a rapid (20 s) update cycle.

58 GEOSCIENCES↗
DOE OSTI2019

Investigation of the Photoinduced axial ligation process in the excited state of nickel (II) phthalocyanine

Photoinduced axial ligation process in the excited state of nickel(II) octabutoxyphthalocyanine (NiPcOBu8) in pyridine solvent has been investigated by ultrafast optical transient absorption and X-ray transient absorption spectroscopies. Although Ni phthalocyanine complexes have been reported to have no tendency to form sixcoordinate structure, the (d(z2),d(x2-y2)) state of NiPcOBu8 generated by photoexcitation of Q-band was discovered to axially ligate with the pyridine molecule very rapidly, on a timescale of (similar to)100 ps. Although the presence of an excited unligated (d,d) state cannot be confirmed due to the time resolution limit of the synchrotron X-ray probe pulse with (similar to)80 ps FWHM, the biexponential kinetics of the ground state recovery detected by the is 1s -> 4pz feature suggests the decay of the unligated (d,d) species with an 82ps time constant, while that of the ligated NiPcOBu8 species is 3-5 ns. The photoinduced ligation dynamics of NiPcOBu8 is vastly different compared to that of Ni porphyrin complexes. This study provides a structural basis on the ligation chemistry in both the ground and excited states of nickel complexes based on their electronic and nuclear structures.

Excited state structural dynamics↗
DOE OSTI2023

Mapping the Ultrafast Mechanistic Pathways of Co Photocatalysts in Pure Water through Time‐Resolved X‐ray Spectroscopy

Abstract Nanosecond time‐resolved X‐ray (tr‐XAS) and optical transient absorption spectroscopy (OTA) are applied to study 3 multimolecular photocatalytic systems with [Ru(bpy) 3 ] 2+ photoabsorber, ascorbic acid electron donor and Co catalysts with methylene ( 1 ), hydroxomethylene ( 2 ) and methyl ( 3 ) amine substituents in pure water. OTA and tr‐XAS of 1 and 2 show that the favored catalytic pathway involves reductive quenching of the excited photosensitizer and electron transfer to the catalyst to form a Co II square pyramidal intermediate with a bonded aqua molecule followed by a Co I square planar derivative that decays within ≈8 μs. By contrast, a Co I square pyramidal intermediate with a longer decay lifetime of ≈35 μs is formed from an analogous Co II geometry for 3 in H 2 O. These results highlight the protonation of Co I to form the elusive hydride species to be the rate limiting step and show that the catalytic rate can be enhanced through hydrogen containing pendant amines that act as H−H bond formation proton relays.

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

Tracking the Light-Induced Excited-State Dynamics and Structural Configurations of an Extraordinarily Long-Lived Metastable State at Room Temperature

Time-resolved X-ray (Tr-XAS) and optical transient absorption (OTA) spectroscopy in the pico-microsecond time scale coupled with Density Functional theory calculations are applied to study the light-induced spin crossover processes of a Fe-based macrocyclic complex in solution. Tr-XAS analysis after light illumination shows the formation of a seven-coordinated high spin quintet metastable state which relaxes to a six-coordinated high spin configuration before decaying to ground state. Kinetic analysis of the macrocyclic complex reveals an unprecedented long-lived decay lifetime of ~42.6 µs. Comparative studies with a non-macrocyclic counterpart illustrate a significantly shortened ~568-old decay lifetime of ~75 ns, and highlight the importance of the ligand arrangement in stabilizing the reactivity of the excited state. Lastly, OTA analysis shows the seven-coordinated high spin state to be formed within ~6.2 ps. Finally, these findings provide a complete understanding of the spin crossover reaction and relaxation pathways of the macrocyclic complex, and reveal the importance of a flexible coordination environment for their rational design.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Effect of Thermodenuding on the Structure of Nascent Flame Soot Aggregates

The optical properties (absorption and scattering) of soot particles depend on soot size and index of refraction, but also on the soot complex morphology and the internal mixing with materials that can condense on a freshly emitted (nascent) soot particle and coat it. This coating can affect the soot optical properties by refracting light, or by changing the soot aggregate structure. A common approach to studying the effect of coating on soot optical properties is to measure the absorption and scattering coefficients in ambient air, and then measure them again after removing the coating using a thermodenuder. In this approach, it is assumed that: (1) most of the coating material is removed; (2) charred organic coating does not add to the refractory carbon; (3) oxidation of soot is negligible; and, (4) the structure of the pre-existing soot core is left unaltered, despite the potential oxidation of the core at elevated temperatures. In this study, we investigated the validity of the last assumption, by studying the effect of thermodenuding on the morphology of nascent soot. To this end, we analyzed the morphological properties of laboratory generated nascent soot, before and after thermodenuding. Our investigation shows that there is only minor restructuring of nascent soot by thermodenuding

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS2019

Retrieving Aerosol Characteristics From the PACE Mission, Part 1: Ocean Color Instrument

NASA’s Plankton, Aerosol, Clouds, ocean Ecosystem (PACE) satellite mission is scheduled to launch in 2022, with the Ocean Color Instrument (OCI) on board. For the first time reflected sunlight from the Earth across a broad spectrum from the ultraviolet (UV: 350 nm) to the short wave infrared (SWIR: 2260 nm) will be measured from a single instrument at 1 km spatial resolution. While seven discrete bands will represent the SWIR, the spectrum from 350 to 890 nm will be continuously covered with a spectral resolution of 5 nm. OCI will thus combine in a single instrument (and at an enhanced spatial resolution for the UV) the heritage capabilities of the Moderate resolution Imaging Spectroradiometer (MODIS) and the Ozone Monitoring Instrument (OMI), while covering the oxygen A-band (O2A). Designed for ocean color and ocean biology retrievals, OCI also enables continuation of heritage satellite aerosol products and the development of new aerosol characterization from space. In particular the combination of MODIS and OMI characteristics allows deriving aerosol height, absorption and optical depth along with a measure of particle size distribution. This is achieved by using the traditional MODIS visible-to-SWIR wavelengths to constrain spectral aerosol optical depth and particle size. Extrapolating this information to the UV channels allows retrieval of aerosol absorption and layer height. A more direct method to derive aerosol layer height makes use of O2A absorption methods, despite the relative coarseness of the nominal 5 nm spectral resolution of OCI. Altogether the PACE mission with OCI will be an unprecedented opportunity for aerosol characterization that will continue climate data records from the past decades and propel aerosol science forward toward new opportunities.

PACE↗
NASA NTRS2001

Asymptotic Solutions for Optical Properties of Large Particles with Strong Absorption

The transverse wave condition is not applicable to the refracted electromagnetic wave within the context of geometrical optics when absorption is involved. Either the transverse magnetic (TM) or the transverse electric (TE) wave condition can be assumed for the wave to locally satisfy the electromagnetic boundary condition in a ray-tracing calculation. The assumed wave mode affects both the reflection and the refraction coefficients. As a result, nonunique solutions for these coefficients are inevitable. In this study the appropriate solutions for the Fresnel reflection-refraction coefficients are identified in light-scattering calculations based on the ray-tracing technique. In particular, a 3x2 refraction or transmission matrix is derived to account for the inhomogeneity of the refracted wave in an absorbing medium. An asymptotic solution that completely includes the effect of medium absorption on Fresnel coefficients is obtained for the scattering properties of a general polyhedral particle. Numerical results are presented for hexagonal plates and columns with both preferred and random orientations.

Yang, Ping↗
DOE OSTI2018

Major improvements on the longwave radiative interactions between surface and clouds in the Polar Regions in atmospheric global circulation model (GCM). Final Project Report

1. Summary of Work and Accomplishments in Year 1 (01/15/2015-01/14/2016). We developed new ice cloud parameterizations based on state-of-the-art MODIS Collection 6 (MC6) ice particle model. Features of the model include the consideration of surface roughness of ice crystals and spectral consistency in cloud property retrievals. Using more than 14,000 particle size distributions (PSDs) from in-situ measurements and the latest ice particle single-scattering property library, our parameterizations provide band-averaged bulk-scattering properties. According to statistics of fittings, the parameterization schemes represent the band-averaged bulk-scattering properties very well. Compared to the ice particle model developed by Fu (1998), flux simulations with the MC6 particle model result in larger upward flux at the top of the atmosphere (TOA) and smaller at the surface for typical cirrus clouds. In the assessment of the effect of longwave light scattering, our results also support the conclusions of previous studies. The error in flux calculations reaches about 10 W/m 2 when a cirrus cloud is thin and its particle size is small. 2. Summary of Work and Accomplishments in Year 2 (01/15/2016-01/14/2017) Clouds are a major modulator of the global radiation budgets. However, representations of clouds in general circulation models (GCMs) neglect many important processes, particularly those related to ice clouds. One major uncertainty source is the radiative transfer scheme in GCMs. To reduce the computational burden in most GCMs, absorption is the only radiative transfer process considered in longwave spectral bands. Recently, a state-of-the-art MC6 ice model has been available, which provides spectral consistency in ice cloud retrievals. With an advanced light scattering library for ice particles, we performed sensitivity studies of the potential impacts on the climate including light scattering for MC6 model and other 11 ice cloud models. Specifically, we modified RRTMG_LW (the GCM version of Longwave Rapid Radiative Transfer Model), a radiative transfer module widely used in GCMs and numerical prediction models, to identify flux simulation differences with and without considering light scattering processes. The simulations with light scattering come from a rigorous radiative solver, DISORT (Discrete Ordinates Radiative Transfer Program for a Multi-Layered Plane-Parallel Medium), are used as benchmarks. The results show that the weighted annual mean biases of RRTMG_LW for the upward flux at the top of the atmosphere, the downward flux at the surface, and the net flux into the atmosphere are about 0.8 ± 0.3, -0.1 ± 0.05, and -0.7 ± 0.3 W m-2, respectively. According to the different the ice crystal shapes, the weighted annual mean bias for heating rate is about -0.006 ± 0.02 to 0.04 K/day. 3. Summary of Work and Accomplishments in Year 3 (01/15/2017-01/14/2018) Since absorption dominates optical properties of clouds in the longwave (LW) spectrum, most of general circulation models (GCMs) only take absorption properties of clouds into account in the radiative transfer modules in order to reduce computational costs. To quantify the biases of excluding LW scattering when clouds exist, we simulated fluxes and heating rates by using satellite data from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), CloudSat, Clouds and the Earth’s Radiant Energy System (CERES) and Moderate Resolution Imaging Spectrometer (MODIS) merged products (CCCM) in 2010. In annual global average, neglecting LW scattering causes overestimation by 2.6 W/m 2 for the top-of-atmosphere (TOA) upward fluxes and underestimation by 1.2 W/m 2 for surface downward fluxes. In particular, regional extreme biases are approximately 12 W/m 2 for TOA upward fluxes and are approximately -3.6 W/m 2 for surface downward fluxes, or are approximately 5% of the global averaged outgoing longwave radiation (OLR) and 1% of the global averaged surface downward fluxes, respectively. In terms of heating rates, on average, LW scattering heats the whole atmosphere column by 0.0045 K/day, heats the cloud layers by 0.0420 K/day, heats the surface by 0.028 K/day, and cools the tropopause by 0.018 K/day.

58 GEOSCIENCES↗