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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 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Optically tunable mesoscale CdSe morphologies via inorganic phototropic growth

Inorganic phototropic growth using only spatially conformal illumination generated Se–Cd films that exhibited precise light-defined mesoscale morphologies including highly ordered, anisotropic, and periodic ridge and trench nanotextures over entire macroscopic substrates. Growth was accomplished via a light-induced electrochemical method using an optically and chemically isotropic solution, an unpatterned substrate, and unstructured, incoherent, low-intensity illumination in the absence of chemical directing agents or physical templates and masks. The morphologies were defined by the illumination inputs: the nanotexture long axes aligned parallel to the optical E-field vector, and the feature sizes and periods scaled with the wavelength. Optically based modeling of the growth closely reproduced the experimental results, confirming the film morphologies were fully determined by the light–matter interactions during growth. Solution processing of the Se–Cd films resulted in stoichiometric, crystalline CdSe films that also exhibited ordered nanotextures, demonstrating that inorganic phototropic growth can effect tunable, template-free generation of ordered CdSe nanostructures over macroscopic length scales.

36 MATERIALS SCIENCE↗
DOE OSTI2012

VUV 157nm laser ablation of spherical particles and modelling of whispering gallery mode optical antenna structures

We report on VUV 157nm F{sub 2} laser irradiation of CR-39 polymer substrates that have been intentionally seeded with spherical glass particles. We discuss the importance of adhesive forces for realizing spherical cavity structures by laser ablation. Strong optical absorption at 157nm in CR-39 enables precise control of pedestal height by controlling the laser fluence and the number of laser pulses. Resonant modes for free-standing spherical cavities have been calculated and we discuss briefly the potential applications for use as optical sources on-board lab-on-chip devices.

36 MATERIALS SCIENCE↗
DOE OSTI2012

The role of couplings in nuclear rainbow formation at energies far above the barrier

A study of the {sup 16}O+{sup 28}Si elastic and inelastic scattering is presented in the framework of Coupled Channel theory. The Sao Paulo Potential is used in the angular distribution calculations and compared with the existing data at 75 MeV bombarding energy. A nuclear rainbow pattern is predicted and becomes more clear above 100 MeV.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2013

A large-acceptance beam-deceleration module for retrofitting into ion-source beam lines

We describe a large-acceptance deceleration module capable of decelerating large-emittance full-intensity ion beams typical of ECR ion sources to very low energies with high efficiency. The deceleration module is designed to permit convenient retrofitting into an existing beam line to replace, e.g., the first Faraday cup after magnetic analysis of the beam extracted from the ion source. For starting energies of 10 keV, and incident ion currents as large as 300 {mu}A, deceleration efficiencies have been measured to be greater than 80% for final energies as low as 70 eV. The decelerated beam intensity can be monitored either by insertion of a beam catcher floating at the final deceleration voltage or from the current to the exit grid itself, with suitable correction applied for the grid transparency factor. The behavior of the deceleration optics was modeled using SIMION, incorporating the effects of intra-beam space charge repulsion. We describe a recent application of this deceleration module to study near-surface He bubble and blister formation of a W target heated to 1250 K and irradiated with a 98 eV He ion beam with a flux of {approx}10{sup 16} cm{sup -2} s{sup -1}.

43 PARTICLE ACCELERATORS↗
DOE OSTI2013

Effect of plasmonic losses on light emission enhancement in quantum-wells coupled to metallic gratings

Recent experimental work has shown significant luminescence enhancement from near-surface quantum-well (QW) structures using metallic grating to convert surface plasmon (SP) modes into radiative modes. This work introduces a detailed theoretical study of plasmonic losses and the role of SPs in improving light extraction from grated light-emitting QW structures, using the fluctuational electrodynamics method. The method explains experimental results demonstrating emission enhancement, light scattering, and plasmonic coupling in the structures. We study these effects in angle-resolved reflectometry and luminescence setups in InGaN QW structures with silver grating. In contrast to experiments, our model allows direct calculation of the optical losses. The model predicts that the plasmonic coupling and scattering increases light emission by a factor of up to three compared to a flat semiconductor structure. This corresponds to reducing the absorption losses from approximately 93% in the ungrated metallic structure to 75% in the grated structure. Lower losses are associated with a significant emission enhancement enabled by the SPs of silver/GaN interfaces, which are present in the blue/green wavelength range, and can be optimized by carefully nanostructuring the metal layer and by the positioning of the QW. In general, the enhancement results from the interplay of mode scattering, conversion of SP energy directly into light, and losses in the metallic grating. The reported losses are very high when compared to the losses present in modern light-emitting diodes (LEDs). Albeit, our work provides tools needed for further optimization of plasmonic light extraction, eventually leading to highly efficient LEDs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Coupling of Er light emissions to plasmon modes on In{sub 2}O{sub 3}: Sn nanoparticle sheets in the near-infrared range

Near-infrared Er photoluminescence (PL) is markedly modified using a plasmonic In{sub 2}O{sub 3}: Sn nanoparticle (NP) sheet. Modeling and optical measurements reveal the presence of different electric fields (E-field) in the NP sheet. The local E-field excited at the interface between the NP sheet and Er-emitting layer of ZnO contributes significantly towards the spectral modifications of Er PL due to matching with the photon energy of Er PL. We also determine the critical temperature for Er PL modifications, which is related to the energy transfer efficiency between Er transition dipoles in ZnO and the plasmon modes on the NP sheet.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Bifacial Si heterojunction-perovskite organic-inorganic tandem to produce highly efficient (η T * ~ 33%) solar cell

As single junction photovoltaic (PV) technologies, both Si heterojunction (HIT) and perovskite based solar cells promise high efficiencies at low cost. Intuitively, a traditional tandem cell design with these cells connected in series is expected to improve the efficiency further. Using a self-consistent numerical modeling of optical and transport characteristics, however, we find that a traditional series connected tandem design suffers from low J SC due to band-gap mismatch and current matching constraints. Furthermore, a traditional tandem cell with state-of-the-art HIT (η = 24%) and perovskite (η = 20%) sub-cells provides only a modest tandem efficiency of η T ~ 25%. Instead, we demonstrate that a bifacial HIT/perovskite tandem design decouples the optoelectronic constraints and provides an innovative path for extraordinary efficiencies. In the bifacial configuration, the same state-of-the-art sub-cells achieve a normalized output of η T * = 33%, exceeding the bifacial HIT performance at practical albedo reflections. Unlike the traditional design, this bifacial design is relatively insensitive to perovskite thickness variations, which may translate to simpler manufacture and higher yield.

14 SOLAR ENERGY↗
DOE OSTI2022

Transducerless time domain reflectance measurement of semiconductor thermal properties

The dominant techniques for laser-based thermal measurement, time-domain thermoreflectance (TDTR) and frequency-domain thermoreflectance, generally require that samples be coated with a metal transducer layer. The properties of the transducer and its interface to the sample are then important to the interpretation of results, and heat conduction in the transducer layer can limit measurements of ultra-thin samples or in-plane conductivity. Here, we demonstrate the feasibility of measuring semiconductor samples using standard TDTR instrumentation, without the use of a metal transducer. A mathematical model accounting for non-zero laser penetration depth as well as both thermal and charge carrier effects is presented, and the ability of the model to describe and fit to experimental data for silicon and germanium samples is demonstrated. Though at this stage measurement uncertainties are larger than for traditional TDTR, we anticipate that the use of this technique will expand the range of samples that can be measured with existing TDTR setups.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Online quantitative analysis of multispectral images of human body tissues

A method is developed for online monitoring of structural and morphological parameters of biological tissues (haemoglobin concentration, degree of blood oxygenation, average diameter of capillaries and the parameter characterising the average size of tissue scatterers), which involves multispectral tissue imaging, image normalisation to one of its spectral layers and determination of unknown parameters based on their stable regression relation with the spectral characteristics of the normalised image. Regression is obtained by simulating numerically the diffuse reflectance spectrum of the tissue by the Monte Carlo method at a wide variation of model parameters. The correctness of the model calculations is confirmed by the good agreement with the experimental data. The error of the method is estimated under conditions of general variability of structural and morphological parameters of the tissue. The method developed is compared with the traditional methods of interpretation of multispectral images of biological tissues, based on the solution of the inverse problem for each pixel of the image in the approximation of different analytical models. (biomedical optics)

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

New laser technologies in ophthalmology for normalisation of intraocular pressure and correction of refraction

We present the results of recent studies that develop principally new approaches to solving the problem of visual impairment and provide the basis for new laser technologies in ophthalmology for the treatment of glaucoma, myopia and hypermetropia. The considered theoretical models and optical methods for detecting laser-induced structural changes in eye tissues pave the way to the invention of control systems with feedback, providing efficient and safe laser treatment. (laser medicine)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

Investigation of the effect of noise parameters of a 3D lidar on the error in estimating relief signatures of distant objects from 2D field intensity distributions of reflected radiation

We consider the influence of noise parameters of a 3D lidar and external background radiation on the error in estimating the relief signatures of distant objects from 2D field intensity distributions of the reflected radiation. A physical and mathematical model is developed to analyse the effect of noise. The dependence of the error in estimating the relief signatures at various signal-to-noise ratios is investigated taking into account the parameters of real multi-element photodetectors (MEPDs). The obtained results indicate the possibility of evaluating relief signatures of distant objects with high accuracy based on standard MEPDs simultaneously for a large number of points on the object’s surface with a signal-to-noise ratio of more than 4. (paper)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Hyperspectral interference tomography of nacre

Significance We invented an optical technique—hyperspectral interference tomography—that rapidly and nondestructively extracts nanoscale structural information across large samples of nacre (mother-of-pearl) and other layered materials by combining multiangle and polarization-resolved hyperspectral imaging with optical-interference modeling. We investigated nacre in mollusk shells from two different species, red abalone and rainbow abalone, and discovered a previously unknown relationship between the age of the mollusk and the thickness of aragonite tablets in nacre. Hyperspectral interference tomography will have applications in climate science, since nacre tablet thickness in fossil shells is a proxy for ancient seawater temperature, and in bioinspired mechanics, because the layered structure of nacre inspires engineered materials with exceptional strength and toughness.

47 OTHER INSTRUMENTATION↗
DOE OSTI2013

UV-BRIGHT NEARBY EARLY-TYPE GALAXIES OBSERVED IN THE MID-INFRARED: EVIDENCE FOR A MULTI-STAGE FORMATION HISTORY BY WAY OF WISE AND GALEX IMAGING

In the local universe, 10% of massive elliptical galaxies are observed to exhibit a peculiar property: a substantial excess of ultraviolet emission than what is expected from their old, red stellar populations. Several origins for this ultraviolet excess (UVX) have been proposed including a population of hot young stars and a population of old, blue horizontal branch or extended horizontal branch (BHB or EHB) stars that have undergone substantial mass loss from their outer atmospheres. We explore the radial distribution of UVX in a selection of 49 nearby E/S0-type galaxies by measuring their extended photometry in the UV through mid-infrared (mid-IR) with the Galaxy Evolution Explorer (GALEX), the Sloan Digital Sky Survey, and the Wide-field Infrared Survey Explorer (WISE). We compare UV/optical and UV/mid-IR colors with the Flexible Stellar Population Synthesis models, which allow for the inclusion of EHB stars. We find that combined WISE mid-IR and GALEX UV colors are more effective in distinguishing models than optical colors, and that the UV/mid-IR combination is sensitive to the EHB fraction. There are strong color gradients, with the outer radii bluer than the inner half-light radii by {approx}1 mag. This color difference is easily accounted for with an increase in the BHB fraction of 0.25 with radius. We estimated that the average ages for the inner and outer radii are 7.0 {+-} 0.3 Gyr, and 6.2 {+-} 0.2 Gyr, respectively, with the implication that the outer regions are likely to have formed {approx}1 Gyr after the inner regions. Additionally, we find that metallicity gradients are likely not a significant factor in the color difference. The separation of color between the inner and outer regions, which agrees with a specific stellar population difference (e.g., higher EHB populations), and the {approx}0.5-2 Gyr age difference suggests multi-stage formation. Our results are best explained by inside-out formation: rapid star formation within the core at early epochs (>4 Gyr ago) and at least one later stage starburst event coinciding with z {approx} 1.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

THE PROPERTIES OF THE 500 K DWARF UGPS J072227.51-054031.2 AND A STUDY OF THE FAR-RED FLUX OF COLD BROWN DWARFS

We present i and z photometry for 25 T dwarfs and 1 L dwarf. Combined with published photometry, the data show that the i - z, z - Y, and z - J colors of T dwarfs are very red, and continue to increase through to the late-type T dwarfs, with a hint of a saturation for the latest types with T{sub eff} Almost-Equal-To 600 K. We present new 0.7-1.0 {mu}m and 2.8-4.2 {mu}m spectra for the very late type T dwarf UGPS J072227.51-054031.2, as well as improved astrometry for this dwarf. Examination of the spectral energy distribution using new and published data, with Saumon and Marley models, shows that the dwarf has T{sub eff} = 505 {+-} 10 K, a mass of 3-11 M{sub Jupiter}, and an age between 60 Myr and 1 Gyr. This young age is consistent with the thin disk kinematics of the dwarf. The mass range overlaps with that usually considered to be planetary, despite this being an unbound object discovered in the field near the Sun. This apparently young rapid rotator is also undergoing vigorous atmospheric mixing, as determined by the IRAC and WISE 4.5 {mu}m photometry and the Saumon and Marley models. The optical spectrum for this 500 K object shows clearly detected lines of the neutral alkalis Cs and Rb, which are emitted from deep atmospheric layers with temperatures of 900-1200 K.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

LINE PROFILES OF CORES WITHIN CLUSTERS. I. THE ANATOMY OF A FILAMENT

Observations are revealing the ubiquity of filamentary structures in molecular clouds. As cores are often embedded in filaments, it is important to understand how line profiles from such systems differ from those of isolated cores. We perform radiative transfer calculations on a hydrodynamic simulation of a molecular cloud in order to model line emission from collapsing cores embedded in filaments. We model two optically thick lines, CS(2-1) and HCN(1-0), and one optically thin line, N{sub 2}H{sup +}(1-0), from three embedded cores. In the hydrodynamic simulation, gas self-gravity, turbulence, and bulk flows create filamentary regions within which cores form. Though the filaments have large dispersions, the N{sub 2}H{sup +}(1-0) lines indicate subsonic velocities within the cores. We find that the observed optically thick line profiles of CS(2-1) and HCN(1-0) vary drastically with viewing angle. In over 50% of viewing angles, there is no sign of a blue asymmetry, an idealized signature of infall motions in an isolated spherical collapsing core. Profiles that primarily trace the cores, with little contribution from the surrounding filament, are characterized by a systematically higher HCN(1-0) peak intensity. The N{sub 2}H{sup +}(1-0) lines do not follow this trend. We demonstrate that red asymmetric profiles are also feasible in the optically thick lines, due to emission from the filament or one-sided accretion flows onto the core. We conclude that embedded cores may frequently undergo collapse without showing a blue asymmetric profile, and that observational surveys including filamentary regions may underestimate the number of collapsing cores if based solely on profile shapes of optically thick lines.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Stellar parameters and accretion rate of the transition disk star HD 142527 from X-shooter

HD 142527 is a young pre-main-sequence star with properties indicative of the presence of a giant planet and/or a low-mass stellar companion. We have analyzed an X-Shooter/Very Large Telescope spectrum to provide accurate stellar parameters and accretion rate. The analysis of the spectrum, together with constraints provided by the spectral energy distribution fitting, the distance to the star (140 ± 20 pc), and the use of evolutionary tracks and isochrones, led to the following set of parameters: T{sub eff} = 6550 ± 100 K, log g = 3.75 ± 0.10, L{sub *}/L{sub ☉} = 16.3 ± 4.5, M{sub *}/M{sub ☉} = 2.0 ± 0.3, and an age of 5.0 ± 1.5 Myr. This stellar age provides further constraints to the mass of the possible companion estimated by Biller et al., being between 0.20 and 0.35 M{sub ☉}. Stellar accretion rates obtained from UV Balmer excess modeling and optical photospheric line veiling, and from the correlations with several emission lines spanning from the UV to the near-IR, are consistent with each other. The mean value from all previous tracers is 2 (±1) × 10{sup –7} M{sub ☉} yr{sup –1}, which is within the upper limit gas flow rate from the outer to the inner disk recently provided by Cassasus et al.. This suggests that almost all gas transferred between both components of the disk is not trapped by the possible planet(s) in between but fall onto the central star, although it is discussed how the gap flow rate could be larger than previously suggested. In addition, we provide evidence showing that the stellar accretion rate of HD 142527 has increased by a factor ∼7 on a timescale of 2 to 5 yr.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Metal-poor, strongly star-forming galaxies in the DEEP2 Survey: The relationship between stellar mass, temperature-based metallicity, and star formation rate

We report on the discovery of 28 z≈0.8 metal-poor galaxies in DEEP2. These galaxies were selected for their detection of the weak [O iii] λ4363 emission line, which provides a “direct” measure of the gas-phase metallicity. A primary goal for identifying these rare galaxies is to examine whether the fundamental metallicity relation (FMR) between stellar mass, gas metallicity, and star formation rate (SFR) holds for low stellar mass and high SFR galaxies. The FMR suggests that higher SFR galaxies have lower metallicity (at fixed stellar mass). To test this trend, we combine spectroscopic measurements of metallicity and dust-corrected SFR with stellar mass estimates from modeling the optical photometry. We find that these galaxies are 1.05 ± 0.61 dex above the z∼1 stellar mass–SFR relation and 0.23 ± 0.23 dex below the local mass–metallicity relation. Relative to the FMR, the latter offset is reduced to 0.01 dex, but significant dispersion remains (0.29 dex with 0.16 dex due to measurement uncertainties). This dispersion suggests that gas accretion, star formation, and chemical enrichment have not reached equilibrium in these galaxies. This is evident by their short stellar mass doubling timescale of ≈100{sub −75}{sup +310} Myr, which suggests stochastic star formation. Combining our sample with other z∼1 metal-poor galaxies, we find a weak positive SFR–metallicity dependence (at fixed stellar mass) that is significant at 94.4% confidence. We interpret this positive correlation as recent star formation that has enriched the gas but has not had time to drive the metal-enriched gas out with feedback mechanisms.

79 ASTRONOMY AND ASTROPHYSICS↗