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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 973 records · Page 54
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Formation of Surface Impurities on Lithium–Nickel–Manganese–Cobalt Oxides in the Presence of CO 2 and H 2 O

Surface impurities involving parasitic reactions and gas evolution contribute to the degradation of high Ni content LiNi x Mn y Co z O 2 (NMC) cathode materials. The transient kinetic technique of Temporal Analysis of Products (TAP), density functional theory, and infrared spectroscopy have been used to study the formation of surface impurities on varying nickel content NMC materials (NMC811, NMC622, NMC532, NMC433, NMC111) in the presence of CO 2 and H 2 O. CO 2 reactivity on a clean surface as characterized by CO 2 conversion rate in the TAP reactor follows the order: NMC811 > NMC622 > NMC532 > NMC433 > NMC111. The capacity of CO 2 uptake follows a different order: NMC532 > NMC433 > NMC622 > NMC811 > NMC111. Moisture pretreatment slows down the direct CO 2 adsorption process and creates additional active sites for CO 2 adsorption. Electronic structure calculations predict that the (012) surface is more reactive than the ($10\bar{1}4$) surface for CO 2 and H 2 O adsorption. CO 2 adsorption leading to carbonate formation is exothermic with formation of ion pairs. The average CO 2 binding energies on the different materials follow the CO 2 reactivity order. Water hydroxylates the (012) surface and surface OH groups favor bicarbonate formation. Water creates more active sites for CO 2 adsorption on the ($10\bar{1}4$) surface due to hydrogen bonding. The composition of surface impurities formed in ambient air exposure is dependent on water concentration and the percentage of different crystal planes. Different surface reactivities suggest that battery performance degradation due to surface impurities can be mitigated by precise control of the dominant surfaces in NMC materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2009

Evolved Gas Measurements Planned for the Lower Layers of the Gale Crater Mound with the Sample Analysis at Mars Instrument Suite

The lower mound strata of Gale Crater provide a diverse set of chemical environments for exploration by the varied tools of the Curiosity Rover of the Mars Science Laboratory (MSL) Mission. Orbital imaging and spectroscopy clearly reveal distinct layers of hydrated minerals, sulfates, and clays with abundant evidence of a variety of fluvial processes. The three instruments of the MSL Sample Analysis at aMars (SAM) investigation, the Quadrupole Mass Spectrometer (QMS), the Tunable Laser Spectrometer (TLS), and the Gas Chromatograph (GC) are designed to analyze either atmospheric gases or volatiles thermally evolved or chemically extracted from powdered rock or soil. The presence or absence of organic compounds in these layers is of great interest since such an in situ search for this type of record has not been successfully implemented since the mid-60s Viking GCMS experiments. However, regardless of the outcome of the analysis for organics, the abundance and isotopic composition of thermally evolved inorganic compounds should also provide a rich data set to complement the mineralogical and elemental information provided by other MSL instruments. In addition, these evolved gas analysis (EGA) experiments will help test sedimentary models proposed by Malin and Edgett (2000) and then further developed by Milliken et al (2010) for Gale Crater. In the SAM EGA experiments the evolution temperatures of H2O, CO2, SO2, O2, or other simple compounds as the samples are heated in a helium stream to 1000 C provides information on mineral types and their associations. The isotopic composition of O, H, C, and S can be precisely determined in several evolved compounds and compared with the present day atmosphere. Such SAM results might be able to test mineralogical evidence of changing sedimentary and alteration processes over an extended period of time. For example, Bibring et al (2006) have suggested such a major shift from early nonacidic to later acidic alteration. We will illustrate through a variety of evolved gas experiments implemented under SAM-like gas flow and temperature ramp conditions on terrestrial analog minerals on high fidelity Sam breadboards the type of chemical information we expect SAM to provide.

Mahaffy, Paul↗
NASA NTRS2004

Atmospheric Trace Gas Abundances and Stable Isotope Ratios via IR-LIF

We propose to develop new technologies with support provided by PIDDP that will enable the in situ measurements of abundances and stable isotope ratios in important radiatively and biogenically active gases such as carbon dioxide, carbon monoxide, water, methane, nitrous oxide, and hydrogen sulfide to very high precision (0.1 per mil or better for the isotopic ratios, for example). Such measurements, impossible at present, could provide pivotal new constraints on the global (bio)geochemical budgets of these critical species, and could also be used to examine the dynamics of atmospheric transport on Mars, Titan, and other solar system bodies. We believe the combination of solid state light sources with imaging of the IR laser induced fluorescence (IR-LIF) via newly available detector arrays will make such in situ measurements possible for the first time. Even under ambient terrestrial conditions, the LIF yield from vibrational excitation of species such as water and carbon dioxide should produce emission measures well in excess of ten billion photons/sec from samples volumes of order 1 c.c. These count rates can, in principle, yield detection limits into the sub-ppt range that are required for the in situ isotopic study of atmospheric trace gases. While promising, such technologies are relatively immature, but developing rapidly, and there are a great many uncertainties regarding their applicability to in situ IR-LIF planetary studies. We therefore feel PIDDP support will be critical to developing these new tools, and propose a three-year program to combine microchip near-IR lasers with low background detection axes and state-of-the-art HgCdTe detectors developed for astronomical spectroscopy to investigate the sensitivity of IR-LIF under realistic planetary conditions, to optimize the optical pumping and filtering schemes for important species, and to apply the spectrometer to the non-destructive measurement of stable isotopes in a variety of test samples. These studies form the necessary precursors to the development of compact, lightweight stable isotope/trace gas sensors for future planetary missions.

Blake, Geoffrey A.↗
DOE OSTI2021

Electronic and catalytic engineering in two-dimensional vdW metal–organic frameworks through alloying

Bimetallic metal-organic framework (MOF s ) alloys, in which heterogeneous metal clusters are incorporated into their backbone, are capable of highly selective separations and catalysis. Due to limitations in our fundamental understanding of their alloying, however, established methods result in phase-separated or amorphous two-dimensional (2D) MOF s or lack precise control over alloy ratios. Here, our results demonstrate 2D MOF alloys where metal cation ratios (M 1 and M 2 ) in M 1 xM 2 1-x BDC (M 1 or M 2 = Zn, Cu, Ni, Co, Fe, Mn) can be engineered on demand by controlling the metal salt dissociation constants. Resulting MOF alloys exhibit a highly 2D nature with excellent crystallinity and minute control over metal cation ratios. Overall, our experimental and theoretical results show that their electronic bandgaps and photoexcited carrier lifetimes can be engineered by metal cation alloying. Interestingly, 2D alloyed MOF s enable high-efficiency photo-catalytic water reduction performance in Co/Ni MOF alloys owing to the spatially separated metal clusters in 2D MOF alloys.

2D materials↗
DOE OSTI2023

Electronic nematic order in the normal state of strontium ruthenate

Despite significant achievements in characterizing the properties of Sr 2 ⁢RuO 4 over the last three decades, the precise nature of its electronic ground state is still unresolved. In this work, we provide a missing piece of the puzzle by uncovering evidence of electronic nematic order in the normal state of Sr 2 ⁢RuO 4 , revealed by ultrafast time-resolved optical dichroism measurements of uniaxially strained thin films. This nematic order, whose domains are aligned by the strain, spontaneously breaks the fourfold rotational symmetry of the crystal. The temperature dependence of the dichroism resembles an Ising-like order parameter, and optical pumping induces a coherent oscillation of its amplitude mode. The existence of electronic nematic order in the normal state of Sr2⁢RuO4 may have consequences for the form and mechanism of superconductivity in this material.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2013

Put X-Ray Polarimetry on the MAP!

With Prof. R. Novick and others at the Columbia Astrophysics Laboratory I help found the field of X-ray polarimetry in the early 1970s. Currently I have more experience with the design, construction, calibration, and space flight of such instruments than anyone on the planet. The early probing beginnings saw only one definitive measurement (that of the integrated low-energy X-ray emission from the Crab Nebula sans pulsar) and a number of upper limits. The limited success did nevertheless inspire a number of detailed theoretical calculations, concentrating at first on neutron stars and black holes showing how precise measurements (e.g. degree of polarization and position angle as a function of pulse phase) would provide definitive limitations on otherwise equally plausible theoretical models. Over time the theoretical foundation has grown (e.g. the proceedings of the X-Ray Polarimetry Workshop held at SLAC in 2004). I will outline these foundations. It is important to understand the history of X-ray polarimetry beyond the early excitement. A polarimeter was at the focus of the original Einstein mission but was dropped during the restructuring. A polarimeter was successfully proposed (R. Novick PI, I was a Co-I) and built for the original Spectrum-X mission. During the years before the cancellation of Spectrum-X, the potential flight of this device stood in the way of other space flights for polarimeters --- "let us wait and see what it finds". This was unfortunate as there were a number of reasons why that polarimeter should not have been flown on the mission. Perhaps the most significant (but not only) reason was that a shared focal plane provided very little observing time. This is an extremely important point in considering the Roadmap. It is doubtful that there many 100%-polarized sources and so the "signal" is more typically a small fraction of the source flux. Thus, the source itself provides a substantial background, making continuum polarimetry even more difficult than narrow-line spectroscopy. X-ray polarimetry thus requires a dedicated mission that can, without programmatic pressures from other instruments/users, devote the integration time to perform meaningful measurements. The recently cancelled GEMS might have been such a mission. At least it was dedicated to polarimetry. Performing meaningful measurements is not going to be easy. In part because of the long hiatus and lack of experience, there appears to be too much pressure to "sell" polarimetry missions by the number of sources for which one might answer the simple question is, or is not, the integrated and time averaged emission from the source polarized at some confidence level? This was a fine question for the 1970 s but, I maintain, it is not today. One simply doesn't want to measure the time averaged polarization of the Crab s pulsar, but one wants to know the polarization as a function of energy and pulse phase to compare, e.g. to optical and radio measurements which divide even the primary pulse into dozens of phase bins. Such observations can distinguish amongst competing theories for the pulsed emission. The Roadmap should define what meaningful experiments are. I will pose some suggestions. Note that , because X-rays are usually believed originate in either non-thermal or highly aspherical situations we expect X-ray polarimetry to be much more important and rich in astrophysical information as opposed to the visible, where starlight often dominates the emission. One has often dreamt about an instrument that does polarimetry whilst it does other things, and I will discuss this. Even in this case, one needs to realize that the observing time will be driven by the polarimetry, otherwise no useful polarization measurements will be made. Finally, I will discuss some misconceptions that have appeared in the literature and at conferences which indicate to me that certain fundamental principles of polarimeter design and performance are not clearly understoodt is important for the Roadmap that we understand these principles and not advocate instruments that will not (or even worse cannot) accomplish the promised scientific return. I will discuss these principles.

Weisskopf, Martin C.↗
NASA NTRS2020

Utilizing Small Telescopes Operated by Citizen Scientists for Transiting Exoplanet Follow-up

Due to the efforts by numerous ground-based surveys and NASA's Kepler and Transiting Exoplanet Survey Satellite (TESS), there will be hundreds, if not thousands, of transiting exoplanets ideal for atmospheric characterization via spectroscopy with large platforms such as James Webb Space Telescope and ARIEL. However their next predicted mid-transit time could become so increasingly uncertain over time that significant overhead would be required to ensure the detection of the entire transit. As a result, follow-up observations to characterize these exoplanetary atmospheres would require less-efficient use of an observatory's time—which is an issue for large platforms where minimizing observing overheads is a necessity. Here we demonstrate the power of citizen scientists operating smaller observatories (≤1 m) to keep ephemerides "fresh," defined here as when the 1σ uncertainty in the mid-transit time is less than half the transit duration. We advocate for the creation of a community-wide effort to perform ephemeris maintenance on transiting exoplanets by citizen scientists. Such observations can be conducted with even a 6 inch telescope, which has the potential to save up to ∼10,000 days for a 1000-planet survey. Based on a preliminary analysis of 14 transits from a single 6 inch MicroObservatory telescope, we empirically estimate the ability of small telescopes to benefit the community. Observations with a small-telescope network operated by citizen scientists are capable of resolving stellar blends to within 5''/pixel, can follow-up long period transits in short-baseline TESS fields, monitor epoch-to-epoch stellar variability at a precision 0.67% ± 0.12% for a 11.3 V-mag star, and search for new planets or constrain the masses of known planets with transit timing variations greater than two minutes.

Robert T. Zellem↗
DOE OSTI2023

Accuracy and precision of ESI-Orbitrap-IRMS observations of hours to tens of hours via reservoir injection

Here, orbitrap isotope ratio mass spectrometry (Orbitrap-IRMS) has recently been applied to high-precision, natural-abundance isotope ratio measurements of a diverse range of compounds, including amino acids, oxyanions, fatty acids, and metals. These measurements can characterize many isotope ratios simultaneously at high (≈1.0‰) precision. In a successful experiment, observed precision will track the shot-noise limit and be limited by experimental time. Some isotope ratios, for example those involving 17 O in organic compounds or multiply-substituted (‘clumped’) isotopologues, require experimental times of hours to tens of hours to achieve desired precision, while current sample introduction techniques focus on observations on the order of seconds to tens of minutes. In this study, we characterize Orbitrap-IRMS performance for three long duration measurements (individual acquisitions ≥1 h and as long as 24 h) using an automated reservoir injection system coupled to a Q Exactive HF Orbitrap with an electrospray ionization (ESI) source. First, we characterize long-term intra-measurement stability through a 24-h long measurement of acetone. We report the following isotope ratios and precisions (as acquisition errors, errors on the observed ratio within this measurement (σ AE )): 13 C/ 12 C (σ AE = 0.07‰), 17 O/ 16 O (σ AE = 1.1‰), 18 O/ 16 O (σ AE = 0.3‰), and 13 C 13 C/ 12 C (σ AE = 0.65‰). The σ AE of each tracks the shot noise limit throughout and is limited by the challenging conditions (high resolution and low numbers of ions per scan) required for 17 O/ 16 O measurement in the presence of 13 C via Orbitrap. Second, we characterize inter-measurement stability via a sequence of seven 75-min analyses of perchlorate. We observe the following ratios and acquisition errors: 37 Cl/ 35 Cl (σ AE = 0.09‰); 17 O/ 16 O (σ AE = 1.6‰); 18 O/ 16 O (σ AE = 0.7‰), 37 Cl 17 O/ 35 Cl 16 O (σ AE = 2.7‰), and 37 Cl 18 O/ 35 Cl 16 O (σ AE = 1.2‰). However, we find that inter-measurement drift between acquisitions limits our accuracy and precision for standardized measurements (i.e., error on reported δ values) to ≈1‰ for the 37 Cl/ 35 Cl measurement. Hence, the benefits of low σ AE may not be fully realized. Third, we demonstrate accuracy via sample/standard comparisons of a methionine sample with 13 C enrichment of ≈20‰ relative to a known standard. Using a sequence of seven 60-min analyses, we recover the following isotope ratios and standardized precisions (i.e., error on reported δ values, denoted propagated acquisition errors, σ PAE ): 33 S/ 32 S (σ PAE = 1.0‰), 34 S/ 32 S (σ PAE = 0.7‰), 15 N/ 14 N (σ PAE = 2.1‰), 2 H/ 1 H (σ PAE = 3.2‰), 13 C/ 12 C (σ PAE = 0.4‰), 18 O/ 16 O (σ PAE = 1.6‰), & 13 C 13 C/ 12 C (σ PAE = 2.8‰) with confirmation of accurate results for the known 13 C/ 12 C and 13 C 13 C/ 12 C enrichments. Together, our results demonstrate the viability of Orbitrap-IRMS for long duration measurements of diverse sample types via an automated reservoir injection system. Inter-measurement stability remains a challenge; we expect our methods to be most applicable to extended measurements of hard-to-observe properties, such as 17 O in organics and clumped isotopologues.

58 GEOSCIENCES↗
NASA NTRS2011

AXIOM: Advanced X-Ray Imaging of the Magnetosphere

Planetary plasma and magnetic field environments can be studied in two complementary ways by in situ measurements, or by remote sensing. While the former provide precise information about plasma behaviour, instabilities and dynamics on local scales, the latter offers the global view necessary to understand the overall interaction of the magnetospheric plasma with the solar wind. Some parts of the Earth's magnetosphere have been remotely sensed, but the majority remains unexplored by this type of measurements. Here we propose a novel and more elegant approach employing remote X-ray imaging techniques, which are now possible thanks to the relatively recent discovery of solar wind charge exchange X-ray emissions in the vicinity of the Earth's magnetosphere. In this article we describe how an appropriately designed and located X-ray telescope, supported by simultaneous in situ measurements of the solar wind, can be used to image the dayside magnetosphere, magnetosheath and bow shock, with a temporal and spatial resolution sufficient to address several key outstanding questions concerning how the solar wind interacts with the Earth's magnetosphere on a global level. Global images of the dayside magnetospheric boundaries require vantage points well outside the magnetosphere. Our studies have led us to propose AXIOM: Advanced X-ray Imaging Of the Magnetosphere, a concept mission using a Vega launcher with a LISA Pathfinder-type Propulsion Module to place the spacecraft in a Lissajous orbit around the Earth Moon L1 point. The model payload consists of an X-ray Wide Field Imager, capable of both imaging and spectroscopy, and an in situ plasma and magnetic field measurement package. This package comprises a Proton-Alpha Sensor, designed to measure the bulk properties of the solar wind, an Ion Composition Analyser, to characterize the minor ion populations in the solar wind that cause charge exchange emission, and a Magnetometer, designed to measure the strength and direction of the solar wind magnetic field. We also show simulations that demonstrate how the proposed X-ray telescope design is capable of imaging the predicted emission from the dayside magnetosphere with the sensitivity and cadence required to achieve the science goals of the mission.

Branduardi-Raymont, G.↗
NASA NTRS2012

AXIOM: Advanced X-ray Imaging of the Magnetosphere

Planetary plasma and magnetic field environments can be studied in two complementary ways - by in situ measurements, or by remote sensing. While the former provide precise information about plasma behaviour, instabilities and dynamics on local scales, the latter offers the global view necessary to understand the overall interaction of the magnetospheric plasma with the solar wind. Some parts of the Earth's magnetosphere have been remotely sensed, but the majority remains unexplored by this type of measurements. Here we propose a novel and more elegant approach employing remote X-ray imaging techniques. which are now possible thanks to the relatively recent discovery of solar wind charge exchange X-ray emissions in the vicinity of the Earth's magnetosphere. In this article we describe how an appropriately designed and located. X-ray telescope, supported by simultaneous in situ measurements of the solar wind, can be used to image the dayside magnetosphere, magnetosheath and bow shock. with a temporal and spatial resolution sufficient to address several key outstanding questions concerning how the solar wind interacts with the Earth's magnetosphere on a global level. Global images of the dayside magnetospheric boundaries require vantage points well outside the magnetosphere. Our studies have led us to propose 'AXIOM: Advanced X-ray Imaging Of the Magnetosphere', a concept mission using a Vega launcher with a LISA Pathfinder-type Propulsion Module to place the spacecraft in a Lissajous orbit around the Earth - Moon Ll point. The model payload consists of an X-ray Wide Field Imager, capable of both imaging and spectroscopy, and an in situ plasma and magnetic field measurement package. This package comprises a Proton-Alpha Sensor, designed to measure the bulk properties of the solar wind, an Ion Composition Analyser, to characterize the minor ion populations in the solar wind that cause charge exchange emission, and a Magnetometer, designed to measure the strength and direction of the solar wind magnetic field. We also show simulations that demonstrate how the proposed X-ray telescope design is capable of imaging the predicted emission from the dayside magnetosphere with the sensitivity and cadence required to achieve the science goals of the mission.

Branduardi-Raymont, G.↗
DOE OSTI2024

Understanding the deficiency in inertial confinement fusion hohlraum x-ray flux predictions using experiments at the National Ignition Facility

The predicted implosion performance of deuterium-tritium fuel capsules in indirect-drive inertial confinement fusion experiments relies on precise calculations of the x-ray drive in laser-heated cavities (hohlraums). This requires accurate, spectrally dependent simulations of laser to x-ray conversion efficiencies and x-ray absorption losses to the hohlraum wall. A set of National Ignition Facility experiments have identified a cause for the long-standing hohlraum “drive deficit” as the overprediction of gold emission at ~2.5 keV in nonlocal thermodynamic equilibrium coronal plasma regions within the hohlraum. Finally, reducing the emission and absorption opacity in this spectral region by ~20% brings simulations into agreement with measured x-ray fluxes and spectra.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Algorithms for coordinate reconstruction in position-sensitive virtual Frisch-grid detectors

Arrays of position-sensitive virtual Frisch-grid (VFG) CdZnTe (CZT) detectors provide a cost-effective solution for integrating large-area arrays for gamma-ray imaging and spectroscopy. These detectors employ high-aspect ratio CZT crystals (bars) with thicknesses up to 50 mm and cross-sections of up to 10 × 10 mm 2 . Despite the long drift distances of charge carriers in such crystals, the detectors have demonstrated excellent performance, achieving energy resolutions better than 1 % full width at half maximum (FWHM) at 662 keV and 3D position resolutions finer than 1 mm. The high spatial resolution is a critical feature of these detectors, as it enables correction of response non-uniformities caused by crystal defects, which remain present even in the highest-quality CZT material. Dislocations and dislocation walls are the primary defects responsible for variations in charge carrier losses as they drift from the interaction points toward the charge-collecting electrodes. The mechanism by which these defects affect carrier transport is generally well understood. Dislocations and sub-grain boundaries act as sinks for carrier-trapping centers, primarily impurities and secondary phases such as tellurium inclusions and precipitates. Here, these regions exhibit significantly higher carrier-trapping rates, leading to variations in the μτ-products. Because the locations of these micron-sized regions are fixed within the detector volume, fluctuations in the total collected charge arise from the random distribution of interaction sites. This results in non-uniform detector responses and degradation of energy resolution. However, by measuring the interaction-site locations with sufficient precision, charge-loss variations can be accurately corrected, allowing recovery of nearly intrinsic energy resolution.

47 OTHER INSTRUMENTATION↗
DOE OSTI2022

Strong-Field Control of Plasmonic Properties in Core–Shell Nanoparticles

Utilization of the plasmonic response in nanosystems is a key component of nanophotonics that is typically altered by varying the incident optical frequency or the material configuration. However, in this work we demonstrate that employing intense, femtosecond laser fields unlock nonlinear light–matter interactions such that precise control of the optical response is achieved solely by adjusting the incident intensity. The plasmonic properties of Au/SiO 2 nanoshells are manipulated by exploiting the nonlinear index of refraction of gold and experimentally observed by employing photoelectrons emitted during the interaction as a sensitive, sub-wavelength probe. A striking transition seen in the photoelectron energy spectrum between the weak and strong-field regime is verified by a modified Mie theory simulation that incorporates the nonlinear dielectric nanoshell response. The exhibited intensity-dependent optical control of the plasmonic response in prototypical core–shell nanoparticles paves the way toward ultrafast switching and opto-electronic signal modulation with more complex nanostructures.

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

Neutron-Resonance Transmission Analysis with a Compact Deuterium-Tritium Neutron Generator

Neutron Resonance Transmission Analysis (NRTA) is a spectroscopic technique which uses the resonant absorption of neutrons in the epithermal range to infer the isotopic composition of an object. This spectroscopic technique has relevance in many traditional fields of science and nuclear security. NRTA in the past made use of large, expensive accelerator facilities to achieve precise neutron beams, significantly limiting its applicability. Here, we describe a series of NRTA experiments where we use a compact, low-cost deuterium-tritium (DT) neutron generator to produce short neutron beams (2.6 m) along with a 6 Li-glass neutron detector. The time-of-flight spectral data from five elements – silver, cadmium, tungsten, indium, and 238 U – clearly show the corresponding absorption lines in the 1-30 eV range. The experiments show the applicability of NRTA in this simplified configuration, and prove the feasibility of this compact and low-cost approach. This could significantly broaden the applicability of NRTA, and make it practical and applicable in many fields, such as material science, nuclear engineering, and arms control.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Sub-quarter micrometer periodically poled Al 0.68 Sc 0.32 N for ultra-wideband photonics and acoustic devices

In this study, we demonstrate the ability of polarity inversion of sputtered aluminum scandium nitride thin films through post-fabrication processes with domain widths as small as 220 nm at a periodicity of 440 nm. An approach using photo- and electron-beam lithography to generate sub-quarter micrometer feature size with adjustable duty cycle through a lift-off process is presented. Here, the film with a coercive field $E_c^+$ of 5.35 MV/cm was exercised first with a 1 kHz triangular double bipolar wave and ultimately poled with a 0.5 kHz double monopolar wave using a Radiant Precision Premier II tester. The metal polar (M-polar) and nitrogen polar (N-polar) domains were identified and characterized through potassium hydroxide wet etching as well as piezoresponse force microscopy (PFM). Well-distinguished boundaries between the oppositely polarized domain regions were confirmed through the phase diagram of the PFM results. The relationship between the electrode width, poling voltage, and domain growth was experimentally studied and statistically analyzed, where 7.96 nm/V domain width broadening vs escalating poling voltage was observed. This method produces extremely high domain spatial resolution in III-nitride materials via poling and is transferable to a CMOS-compatible photolithography process. The spatial resolution of the periodically poled Al 0.68 Sc 0.32 N is suitable for second-harmonic generation of deep ultraviolet through quasi-phase-matching and RF MEMS operating in the X-Band spectrum.

36 MATERIALS SCIENCE↗
NASA NTRS2018

Laser Ablation Surface Treatment of Structural Aerospace Composites and Metal Alloys for Adhesive Bonding

NASA Langley Research Center (LaRC) has been involved over the past decade in the development of laser ablation as a method to surface treat aerospace structural fiber reinforced composites (CFRPs) and metal alloys. [1- 18] Laser surface treatment has been shown to be a rapid, high precision, and reproducible method for surface treatment of these materials, and is amenable to automation. The laser ablation process removes surface contamination such as silicones, creates surface roughness, and chemically activates a surface for bonding. The degree of ablation is controllable by adjusting laser parameters. In the case of CFRPs, ablation can be performed without damage to any underlying carbon fibers. In the case of metal alloys, ablation is possible without surface embrittlement, heat damage or creation of undesirable grain structures or morphologies. The optimum laser treatment conditions are substrate dependent and generally are influenced by laser wavelength and pulse duration (typically fixed for a laser system), and laser power. In the case of metal alloys such as Ti-6Al-4V, the laser ablation process eliminates the need for several steps of the conventional processes, including hydrofluoric (HF) acid and caustic treatment. These steps are often conducted in dip tanks and require costly facilities and environmentally unfriendly liquids. In addition, the laser can create nano-porosity on the Ti-6Al-4V alloy surface allowing for sol-gel penetration and thereby creating a gradient interface with improved temperature and mechanical performance. NASA LaRC has also been involved with the development of in-line characterization methods compatible with the laser treatment process to rapidly determine the presence of key contaminates such as silicones that, even at very low concentrations, are a threat to adhesive bonding. A spectroscopic technique called micro-laser induced breakdown spectroscopy (u-LIBS) has been developed to rapidly detect silicones at concentrations below those known to cause bonding problems. This technique requires no sample preparation, vacuum or inert atmosphere, has no practical size limitations, and provides nearly instantaneous feedback to the operator. This presentation will give an overview and update of these developments with specific examples highlighted.

Connell, John W.↗
DOE OSTI2020

Spectroscopic study and lifetime measurement of the 6d7p 3 F 2 o state of radium

We report a method for the precision measurement of the oscillator strengths and the branching fractions of the decay channels of the 6d7p 3 F 2 o state in 226 Ra. Here, this method exploits a set of metastable states present in Ra, allowing a measurement of the oscillator strengths that does not require knowledge of the number of atoms in the atomic beam. We measure the oscillator strengths and the branching fractions for decays from the 6d7p 3 F 2 o state to the 7s6d 3 D 1 , 7s6d 3 D 2 , and 7s6d 1 D 2 states and constrain the branching fraction to the 7s6d 3 D 3 state to be less than 0.4% (68% confidence limit). The lifetime of the 3 F 2 o state is determined to be 15 ± 4 ns.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS2001

HgCdTe Photoconductive Mixers for 2-8 THz

Heterodyne spectroscopy has been taken to wavelengths as short as 63 micrometers with Schottky-diode mixers. Schottkys, however, are relatively insensitive compared to superconducting mixers such as the hot-electron microbolometer (HEB), which has an effective quantum efficiency of 3% at 120 micrometers (2.5 THz). Although HEB sensitivities are bound to improve, there will always be losses associated with antenna coupling of radiation into sub-micron size devices. Another approach to far infrared (FIR) mixer design is to use a photoconductive device which can be made much larger than a wavelength, and thus act as its own antenna. For example, HgCdTe photodiodes have been used as mixers in the lambda = 10 micrometers band for over 25 years, with sensitivities now only a factor of 2 from the quantum-noise-limit. HgCdTe can also be applied at FIR wavelengths, but surprisingly little work has been done to date. The exception is the pioneering work of Spears and Kostiuk and Spears, who developed HgCdTe photomixers for the 20-120 micrometer region. The spectral versatility of the HgCdTe alloy is well recognized for wavelengths as long as 8-20 micrometers. What is not so recognized, however, is that theoretically there is no long wavelength limit for appropriately composited HgCdTe. Although Spears successfully demonstrated a photoconductive response from HgCdTe at 120 micrometers, this initial effort was apparently never followed up, in part because of the difficulty of controlling the HgCdTe alloy composition with liquid-phase-epitaxy (LPE) techniques. With the availability of precise molecular-beam-epitaxy (MBE) since the early 1990's, it is now appropriate to reconsider HgCdTe for detector applications longward of lambda = 20 micrometers. We recently initiated an effort to fabricate detectors and mixers using II-VI materials for FIR wavelengths. Of particular interest are device structures called superlattices, which offer a number of advantages for high sensitivity direct detectors and very long wavelength heterodyne mixers.

Betz, A. L.↗