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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 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Three-dimensional nanoscale metal, metal oxide, and semiconductor frameworks through DNA-programmable assembly and templating

Controlling the three-dimensional (3D) nanoarchitecture of inorganic materials is imperative for enabling their novel mechanical, optical, and electronic properties. Here, by exploiting DNA-programmable assembly, we establish a general approach for realizing designed 3D ordered inorganic frameworks. Through inorganic templating of DNA frameworks by liquid- and vapor-phase infiltrations, we demonstrate successful nanofabrication of diverse classes of inorganic frameworks from metal, metal oxide and semiconductor materials, as well as their combinations, including zinc, aluminum, copper, molybdenum, tungsten, indium, tin, and platinum, and composites such as aluminum-doped zinc oxide, indium tin oxide, and platinum/aluminum-doped zinc oxide. The open 3D frameworks have features on the order of nanometers with architecture prescribed by the DNA frames and self-assembled lattice. Structural and spectroscopic studies reveal the composition and organization of diverse inorganic frameworks, as well as the optoelectronic properties of selected materials. The work paves the road toward establishing a 3D nanoscale lithography.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Technical Report: Final

The objective of this work was to develop catalyzed nanoporous materials that have superior hydrogen uptake between 300K and 400K and moderate pressures. Platinum nanoparticles were introduced to both activated carbons (ACs) and microporous metal organic frameworks (MMOFs) in order to dissociate molecular hydrogen into an active hydrogen species that diffuses from the catalyst to weakly chemisorbs to the AC/MMOF support; this combined sequence is referred to as the hydrogen spillover mechanism. For all materials studied, maximum excess hydrogen uptake was 1-1.4 wt% (excess) at 300K, falling short of DOE storage goals (5.5 wt% by 2015). Select Pt/AC materials (after in situ catalyst activation) had high uptake (up to 1.4 wt%) at low pressure which significantly exceeded that expected for physisorption. The uptake was not correlated to size of Pt catalyst, but appeared to be associated with high surface activity of the AC support and the methodology of catalyst doping. Multiple techniques were explored to introduce Pt nanoparticles into MMOFs, but most led to significant structural degradation. Ultimately, a ‘pre-bridge’ (PB) technique was used to introduce Pt/AC catalysts into MMOFs, as the PB technique led to virtually non-detectable changes in structure. At high pressure, hydrogen spillover of ~1 wt% (excess) to a PB-MMOF was very slow (i.e. >80 hours at 70-80 bar), which can be attributed to high diffusion barriers in a complex three-surface domain material (Pt, AC, MMOF) as well as unexpected evidence for mechanical instability of the undoped MMOF precursor. In a low-pressure comparison study of three PB-MMOFs, we found evidence that the doping technique may introduce defects which may contribute to enhanced adsorption at 300K. However, we could not rule out the effect of active Pt sites, as common predictors of adsorption generally favored the materials without Pt. Furthermore, spectroscopic evidence provided definitive evidence of weak hydrogen chemisorption to two MMOFs and AC, and was found only for materials containing Pt catalyst. Overall, high uptake via hydrogen spillover requires high catalytic activity and an energy neutral surface landscape for ready diffusion, with little to no correlation to the size of the Pt nanoparticle or textural properties (i.e. surface area or porosity) of the AC or MMOF support.

08 HYDROGEN↗
NASA NTRS1983

High voltage v-groove solar cell

A high voltage multijunction solar cell comprises a number of discrete voltage generating regions, or unit cells, which are formed in a single semiconductor wafer and are connected together so that the voltages of the individual cells are additive. The unit cells comprise doped regions of opposite conductivity types separated by a gap. The method includes forming V-shaped grooves in the wafer and orienting the wafer so that ions of one conductivity type can be implanted in one face of the groove while the other face is shielded. A metallization layer is applied and selectively etched away to provide connections between the unit cells.

Evans, J. C., Jr.↗
DOE OSTI2022

Tunable, Homoepitaxial Hyperbolic Metamaterials Enabled by High Mobility CdO

We report propagating light exhibits hyperbolicity in strongly anisotropic materials where the principal components of the dielectric tensor are opposite in sign. While hyperbolicity occurs naturally in anisotropic polar dielectrics, wherein optical phonons along orthogonal crystal axes are nondegenerate, such optical anisotropy can also be engineered in hyperbolic metamaterials (HMMs): thin film superlattices of alternating dielectric and metallic layers. Contrasted with the severely limited tunability of natural hyperbolic materials, the hyperbolic behavior of HMMs can be tailored significantly both through superlattice design and material selection. However, so far HMMs have suffered from high optical losses, hindering their performance. In this report, broadly tunable (λ = 2–5 µm) Type I and II hyperbolic modes with low losses (quality (Q)-factors up to 19.7) are observed through attenuated total reflectance measurements of monolithic, homoepitaxial superlattices of high- and low-doped cadmium oxide (CdO). Further, the low losses offered by CdO enable the first demonstration of real-space imaging of hyperbolic plasmon polaritons in nanoresonators by scattering-type scanning near-field optical microscopy—previously only possible for hyperbolic phonon polariton materials. Tunable, low-loss CdO HMMs promise designability for applications such as on-chip photonics, super-resolution imaging (hyperlensing), enhanced emission, novel emitter designs, and possibly quantum nanophotonic and time variant metasurfaces.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Direct solar-to-hydrogen conversion via inverted metamorphic multi-junction semiconductor architectures

Solar water splitting via multi-junction semiconductor photoelectrochemical cells provides direct conversion of solar energy to stored chemical energy as hydrogen bonds. Economical hydrogen production demands high conversion efficiency to reduce balance-of-systems costs. For sufficient photovoltage, water-splitting efficiency is proportional to the device photocurrent, which can be tuned by judicious selection and integration of optimal semiconductor bandgaps. Here, we demonstrate highly efficient, immersed water-splitting electrodes enabled by inverted metamorphic epitaxy and a transparent graded buffer that allows the bandgap of each junction to be independently varied. Voltage losses at the electrolyte interface are reduced by 0.55 V over traditional, uniformly p-doped photocathodes by using a buried p-n junction. Lastly, advanced on-sun benchmarking, spectrally corrected and validated with incident photon-to-current efficiency, yields over 16% solar-to-hydrogen efficiency with GaInP/GaInAs tandem absorbers, representing a 60% improvement over the classical, high-efficiency tandem III-V device.

14 SOLAR ENERGY↗
NASA NTRS1982

Method of making a high voltage V-groove solar cell

A method is provided for making a high voltage multijunction solar cell. The cell comprises a plurality of discrete voltage generating regions, or unit cells, which are formed in a single semiconductor wafer and are connected together so that the voltages of the individual cells are additive. The unit cells comprise doped regions of opposite conductivity types separated by a gap. The method includes forming V-shaped grooves in the wafer and thereafter orienting the wafer so that ions of one conductivity type can be implanted in one face of the groove while the other face is shielded. A metallization layer is applied and selectively etched away to provide connections between the unit cells.

Evans, J. C., Jr.↗
NASA NTRS2010

Using Whispering-Gallery-Mode Resonators for Refractometry

A method of determining the refractive and absorptive properties of optically transparent materials involves a combination of theoretical and experimental analysis of electromagnetic responses of whispering-gallery-mode (WGM) resonator disks made of those materials. The method was conceived especially for use in studying transparent photorefractive materials, for which purpose this method affords unprecedented levels of sensitivity and accuracy. The method is expected to be particularly useful for measuring temporally varying refractive and absorptive properties of photorefractive materials at infrared wavelengths. Still more particularly, the method is expected to be useful for measuring drifts in these properties that are so slow that, heretofore, the properties were assumed to be constant. The basic idea of the method is to attempt to infer values of the photorefractive properties of a material by seeking to match (1) theoretical predictions of the spectral responses (or selected features thereof) of a WGM of known dimensions made of the material with (2) the actual spectral responses (or selected features thereof). Spectral features that are useful for this purpose include resonance frequencies, free spectral ranges (differences between resonance frequencies of adjacently numbered modes), and resonance quality factors (Q values). The method has been demonstrated in several experiments, one of which was performed on a WGM resonator made from a disk of LiNbO3 doped with 5 percent of MgO. The free spectral range of the resonator was approximately equal to 3.42 GHz at wavelengths in the vicinity of 780 nm, the smallest full width at half maximum of a mode was approximately equal to 50 MHz, and the thickness of the resonator in the area of mode localization was 30 microns. In the experiment, laser power of 9 mW was coupled into the resonator with an efficiency of 75 percent, and the laser was scanned over a frequency band 9 GHz wide at a nominal wavelength of approximately equal to 780 nm. Resonance frequencies were measured as functions of time during several hours of exposure to the laser light. The results of these measurements, plotted in the figure, show a pronounced collective frequency drift of the resonator modes. The size of the drift has been estimated to correspond to a change of 8.5 x 10(exp -5) in the effective ordinary index of refraction of the resonator material.

Matsko, Andrey↗
DOE OSTI2016

Methods and apparatus for transparent display using up-converting nanoparticles

Disclosed herein are transparent color displays with nanoparticles made with nonlinear materials and/or designed to exhibit optical resonances. These nanoparticles are embedded in or hosted on a transparent substrate, such as a flexible piece of clear plastic or acrylic. Illuminating the nanoparticles with invisible light (e.g., infrared or ultraviolet light) causes them to emit visible light. For example, a rare-earth doped nanoparticle may emit visible light when illuminated simultaneoulsy with a first infrared beam at a first wavelength .lamda..sub.1 and a second infrared beam at a second wavelength .lamda..sub.2. And a frequency-doubling nanoparticle may emit visible light when illuminated with a single infrared beam at the nanoparticle's resonant frequency. Selectively addressing these nanoparticles with appropiately selected pump beams yields visible light emitted from the nanoparticles hosted by the transparent substrate in a desired pattern.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Elastomeric reflection suppressor

Various embodiments of the present technology generally relate to reflection suppressors. More specifically, some embodiments use elastomeric materials doped with optical absorbers for temporary suppression of Fresnel reflections for multiple substrates spanning wide spectral and angular bandwidth. The refractive index of the elastomer can be tuned to match a substrate and thereby minimize reflection. Some embodiments can use the addition of different absorptive dopants to allow for either broadband or wavelength-selective reflection suppression. As performance is limited only by index mismatch, both spectral and angular performance significantly exceed that of anti-reflection coatings. After use, these light traps may be removed and reused without damaging the substrate. These films have uses in spectroscopic ellipsometry, holography, and lithography.

Miller, David↗
DOE OSTI2021

Structure-property relationships and mobility optimization in sputtered La-doped BaSn O 3 films: Toward 100cm 2 V -1 s -1

he wide band gap semiconducting perovskite BaSnO 3 is of high current interest due to outstanding room temperature mobility at high electron density, fueled by potential applications in oxide, transparent, and power electronics. Due in part to a lack of lattice-matched substrates, BaSnO 3 thin films suffer from high defect densities, however, limiting electron mobility. Additionally, the vast majority of BaSnO 3 thin film research has focused on pulsed laser deposition or molecular beam epitaxy. In this work, we present an exhaustive optimization of the mobility of Ba 0.98 La 0.02 SnO 3 films grown by a scalable, high-throughput method: high-pressure-oxygen sputter deposition. Considering target synthesis conditions, substrate selection, buffer layer structure, deposition temperature, deposition rate, thickness, and postdeposition annealing conditions, and by combining high-resolution x-ray diffraction, reciprocal space mapping, rocking curve analysis, scanning transmission electron microscopy, atomic force microscopy, and temperature-dependent electronic transport measurements, detailed understanding of synthesis-structure-property relationships is attained. Optimized room temperature mobility of 96 cm 2 V –1 s –1 is achieved in vacuum-annealed GdScO 3 (110)/BaSnO 3 (120 nm)/Ba 0.98 La 0.02 SnO 3 (200 nm) heterostructures, as well as 92 cm 2 V –1 s –1 on unbuffered substrates and 87 2 V –1 s –1 without postdeposition annealing. These results, including important trends in defect densities and a surprising dependence of mobility on lattice mismatch, substantially expand the understanding of the interplay between deposition conditions, microstructure, and transport in doped BaSnO 3 films, establishing competitive mobilities in films fabricated via a scalable, high-throughput, industry-standard technique.

36 MATERIALS SCIENCE↗
DOE OSTI2019

DLTS Investigation of the Energy Spectrum of Si:Mg Crystals

Electrically active centers in n-type magnesium-doped silicon crystals are studied by deep-level transient spectroscopy (DLTS). Magnesium is introduced by diffusion from a metal film on the surface at 1100°C. It is found that two levels with a similar concentration of ~6 × 10{sup 14} cm{sup –3} dominate in the DLTS spectrum; the value approximately corresponds to the interstitial magnesium (Mg{sub i}) concentration expected from diffusion conditions and published data on the Hall effect. The dependence of the electron emission rate from these levels on the electric-field strength agrees qualitatively with the Poole–Frenkel effect, which indicates the donor nature of both levels, although the absolute value of the effect differs from theoretical value. The activation energies of these levels found by the extrapolation of emission rates measured at various temperatures to zero field are 112 and 252 meV, which coincides within the accuracy with energies of ground states of the first and second donor levels of Mg determined previously from optical absorption. Thus, it is shown that when using high-quality initial material and the selected diffusion mode, interstitial magnesium atoms are the dominant centers with levels in the upper half of the band gap.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

ATF material model development and validation for priority fuel concepts

Development, implementation, and validation of material and behavior models for accident tolerant fuel (ATF) concepts in the Bison fuel performance code began in 2014 in response to the events that occurred at the Fukushima Daichii nuclear power plant in March 2011. Early on the focus was on U 3 Si 2 fuel and FeCrAl cladding as part of a high impact problem through the Nuclear Energy and Advanced Modeling Simulation (NEAMS) program. Then, developments for Cr 2 O 3 -doped UO 2 fuel, and SiC-SiC and Cr-coated zirconium-based claddings began based upon industry interests. In late fiscal year 2018 the Consortium for Advanced Simulation of Light Water Reactors (CASL) took over further ATF work in Bison in support of the Nuclear Regulatory Commission (NRC) engagement. Discussions with the NRC identified their list of priority fuel and cladding concepts, which included Cr 2 O 3 -doped UO 2 and U 3 Si 2 fuels, and Cr-coated zirconium-based and FeCrAl claddings. In particular, the NRC suggested that reports similar in form to NUREG/CR-7024 [1] that was developed for traditional LWR materials UO 2 and zirconium-based claddings (i.e., Zircaloy-4, M5®, ZIRLO) be created for the priority ATF concepts. The approach to ATF capability development in Bison since the beginning has been two-fold: (1) empirical correlations and (2) multiscale model development. Both approaches have uncertainty inherent to them. Uncertainty in empirical correlations is bounded by the experimental data upon which with the correlation was developed. Models developed through a multiscale approach have uncertainty associated with the lower length scale calculations and input parameters that must be propagated to the engineering scale model in Bison. In this report, the recommended models, their range of applicability (e.g., temperature, burnup), and associated uncertainty for the NRC priority fuel concepts Cr 2 O 3 -doped UO 2 and U 3 Si 2 are presented in a manner similar to the aforementioned NUREG. In addition, the Cr 2 O 3 -doped UO 2 models are validated to the Halden Reactor tess IFA-677.1 rods 1 and 5 and IFA-716.1 rod 1. For U 3 Si 2 the models are validated to the recent post-irradiation examination (PIE) data ATF-13 and ATF-15 rods that were irradiated in the Advanced Test Reactor (ATR) at Idaho National Laboratory. Finally, an uncertainty quantification (UQ) and sensitivity analysis (SA) is completed on a single rod for each fuel concept that takes into account the defined uncertainty in select models. The results of the UQ and SA analyses indicate that given the large uncertainty in some of the input ATF models that the uncertainty on the Bison predictions of fuel performance metrics of interest bound the available experimental data. Correlation coefficients are also reported that identified the uncertain inputs with the strongest correlation (positive or negative) with the outputs of interest. Fuel performance metrics investigated include fuel elongation, rod internal pressure, fuel centerline temperature, and fission gas release.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2024

Infrared-Transparent Semiconductor Membranes for Electromagnetic Interference Shielding of Millimeter Waves

Here, it is demonstrated that single-crystalline and highly doped GaAs membranes are excellent candidates for realizing infrared-transparent shields of electromagnetic interference at millimeter frequencies. Measured optical transmittance spectra for the semiconductor membranes show resonant features between 750 and 2500 nm, with a 100% maximum transmittance. The shielding effectiveness of the membranes is extracted from measured scattering parameters between 65 and 85 GHz. Selected GaAs membranes and membranes/polyamide films exhibit shielding effectiveness ranging from 22 to 40 dB, which are suitable values to ensure the safe operation of infrared devices for commercial applications. Theoretical calculations based on a plane wave model show that the interplay of primary reflection and multiple internal reflections of the radio-frequency waves results in broadband shielding capabilities of the membrane between 10 and 300 GHz.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

Tunable Oxygen Reduction Electrocatalysis by Phenazine-Modified Carbons (Final Report)

This project aims to systematically investigate the fundamental interfacial chemistry that underlies the four-electron, four-proton oxygen reduction reaction (ORR) mediated by heteroatom-doped graphitic carbon electrodes. Heteroatom-doped (Fe, N, etc.) graphitic carbons have emerged as a rich class of materials that are promising ORR catalysts in low temperature fuel cells because of their earth-abundant elements, extremely low cost, environmental harmlessness, and high tolerance to impurities in the fuel stream. However, despite decades of research, systematic efforts to improve the activity, selectivity, and durability of these catalysts has been hampered both by a complex heterogeneous distribution of potential N- and Fe-dopant active sites and by the inability to tune the local electronic structure and environment of the active site with molecular precision. Understanding the fundamental chemistry that influences the turnover-limiting and selectivity determining steps for ORR and other multielectron/multiproton electrocatalytic transformations requires new and innovative methods to prepare heteroatom active sites with molecular precision on carbon surfaces.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Pyrolyzed Triazine-Based Nanoporous Frameworks Enable Electrochemical CO 2 Reduction in Water

The first study of rational synthesis of triazine-based nanoporous frameworks as electrocatalysts for CO 2 reduction reaction (CO 2 RR) was presented. The resulting optimized framework with rich pyridinic nitrogen-containing sites can selectively reduce CO 2 to CO in water with a high Faradic efficiency of ca. 82% under a moderate overpotential of 560 mV. The key of our success lies in the use of pyridine-based backbones as sacrificial groups inside the triazine framework for in situ generation of CO 2 RR-active pyridinic N-doped sites during the high-temperature ZnCl 2 -promoted polymerization process. We anticipate that this study may facilitate new possibilities for the development of porous organic polymers for electrochemical conversion of CO 2 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Ultrafast band engineering and transient spin currents in antiferromagnetic oxides

Here, we report a dynamic structure and band engineering strategy with experimental protocols to induce indirect-to-direct band gap transitions and coherently oscillating pure spin-currents in three-dimensional antiferromagnets (AFM) using selective phononic excitations. In the Mott insulator LaTiO 3 , we show that a photo-induced nonequilibrium phonon mode amplitude destroys the spin and orbitally degenerate ground state, reduces the band gap by 160 meV and renormalizes the carrier masses. The time scale of this process is a few hundreds of femtoseconds. Then in the hole-doped correlated metallic titanate, we show how pure spin-currents can be achieved to yield spin-polarizations exceeding those observed in classic semiconductors. Last, we demonstrate the generality of the approach by applying it to the non-orbitally degenerate AFM CaMnO 3 . These results advance our understanding of electron-lattice interactions in structures out-of-equilibrium and establish a rational framework for designing dynamic phases that may be exploited in ultrafast optoelectronic and optospintronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Distance dependent quenching and gamma-ray spectroscopy in tin-loaded polystyrene scintillators

In this study, we report the synthesis and inclusion of rationally designed organotin compounds in polystyrene matrices as a route towards plastic scintillators capable of gamma-ray spectroscopy. Tin loading ratios of up to 15% w/w have been incorporated, resulting in photopeak energy resolution values as low as 10.9% for 662 keV gamma-rays. Scintillator constituents were selected based upon a previously reported distance-dependent quenching mechanism. Data obtained using UV-Vis and photoluminescence measurements are consistent with this phenomenon and are correlated with the steric and electronic properties of the respective organotin complexes. We also report fast scintillation decay behavior that is comparable to the quenched scintillators 0.5% trans-stilbene doped bibenzyl and the commercial plastic scintillator BC-422Q-1%. These observations are discussed in the context of practical considerations such as optical transparency, ease-of-preparation/scale-up, and total scintillator cost.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Manipulating cobalt oxide on N-doped aligned electrospun carbon nanofibers towards instant electrochemical detection of dopamine secreted by living cells

A demand exists for the development of miniaturized biosensors with high sensitivity and a wide dynamic range for rapid detecting dopamine (DA) levels. Here, an electrochemical sensor is created by decorating closely packed cobalt oxide (Co 3 O 4 ) nanograins on nitrogen-doped electrospun carbon nanofibers (NECNFs) via a facile electrodeposition method. The carbon nanofiber matrix provides both a scaffold with ultrahigh surface area for homogeneous dispersion of cobalt oxide nanostructures and facilitates the electrochemical conductivity for the hybrid electrode. The sensing principle is based on the redox reaction between DA and DA quinone that generates electrical signal, which is detectable via differential pulse voltammetry (DPV) and chronoamperometry (CA). Owing to a high electroactive surface area and facilitating electron transfer between electrode surface and the target molecule, the electrical sensing platform exhibits superior sensitivity and selectivity toward DA, with an excellent limit of detection (9 nM) over a wide range of concentrations (0.01 to 100 μM). Moreover, based on its excellent sensing properties and biocompatibility, the sensor has been used for the real-time monitoring exogeneous DA released from pheochromocytoma (PC12) cells. This work demonstrates promise of a novel sensor technology that may render rapid point-of-care testing of DA towards early clinical diagnosis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗