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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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The experimental phase diagram for liquid–liquid phase separation in submicrometer aerosol particles converges with theory as equilibration time is increased.
With their shielded 4f orbitals, rare-earth ions (REIs) offer optical and electron spin transitions with good coherence properties even when embedded in a host crystal matrix, highlighting their utility as promising quantum emitters and memories for quantum information processing. Among REIs, trivalent erbium (Er 3+ ) uniquely has an optical transition in the telecom C-band, ideal for transmission over optical fibers, making it well suited for applications in quantum communication. The deployment of Er 3+ emitters into a thin film TiO 2 platform has been a promising step toward scalable integration; however, like many solid-state systems, the deterministic spatial placement of quantum emitters remains an open challenge. Here, we investigate laser annealing as a means to locally tune the optical resonance of Er 3+ emitters in TiO 2 thin films on Si. Using both nanoscale x-ray diffraction measurements and cryogenic photoluminescence spectroscopy, we show that tightly focused below-gap laser annealing can induce anatase to rutile phase transitions in a nearly diffraction-limited area of the films and improve local crystallinity through grain growth. As a percentage of Er:TiO 2 is converted to rutile, the Er 3+ optical transition blueshifts by 13 nm. We explore the effects of changing laser annealing time and show that the amount of optically active Er:rutile increases linearly with laser power. We additionally demonstrate local phase conversion on microfabricated Si structures, which holds significance for quantum photonics.
We report on fabrication and performance of sub-micrometer Ni/Au/Ge contacts to a two-dimensional electron gas in an AlGaAs/GaAs heterostructure. Utilizing scanning transmission electron microscopy, energy dispersive x-ray spectroscopy, and low temperature electrical measurements, we investigate the relationship between contact performance and the mechanical and chemical properties of the annealed metal stack. Contact geometry and crystallographic orientation significantly impact performance. Our results indicate that the spatial distribution of germanium in the annealed contact plays a central role in the creation of high transmission contacts. We characterize the transmission of our contacts at high magnetic fields in the quantum Hall regime. Our work establishes that contacts with an area of 0.5 μm2 and resistance less than 400 Ω can be fabricated with high yield.
Soft X-ray tomography (SXT) is an invaluable tool for quantitatively analyzing cellular structures at suboptical isotropic resolution. However, it has traditionally depended on manual segmentation, limiting its scalability for large datasets. Here, we leverage a deep learning-based autosegmentation pipeline to segment and label cellular structures in hundreds of cells across three Saccharomyces cerevisiae strains. This task-based pipeline uses manual iterative refinement to improve segmentation accuracy for key structures, including the cell body, nucleus, vacuole, and lipid droplets, enabling high-throughput and precise phenotypic analysis. Using this approach, we quantitatively compared the three-dimensional (3D) whole-cell morphometric characteristics of wild-type, VPH1-GFP, and vac14 strains, uncovering detailed strain-specific cell and organelle size and shape variations. We show the utility of SXT data for precise 3D curvature analysis of entire organelles and cells and detection of fine morphological features using surface meshes. Our approach facilitates comparative analyses with high spatial precision and statistical throughput, uncovering subtle morphological features at the single-cell and population level. This workflow significantly enhances our ability to characterize cell anatomy and supports scalable studies on the mesoscale, with applications in investigating cellular architecture, organelle biology, and genetic research across diverse biological contexts.
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Poly-Si/SiO2 passivating contacts have shown great potential for industry-relevant next-generation solar cells. Previous work has demonstrated an improved Jsc from dry reactive ion etching in an SF6 environment, using front metal grids as a self-aligned mask. Here, we show an effective method to measure the front poly-Si thickness on an alkaline textured surface using X-ray diffraction. The calculated thicknesses are compared with cross-section SEM analysis and Quokka simulation. We show that by thinning the front poly-Si from 200 nm to 60 nm, Jsc increases by 2.4 mA/cm2, leading to an absolute efficiency gain of 1.73%. Finally, we discuss possible reasons for the premature loss of passivation before the removal of all poly-Si.
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Three (3) items of errata are submitted for our recently published paper [ Opt. Express 28 , 36505 ( 2020 ) 10.1364/OE.405566 ]. One is a clarifying extension to the Fig. 3 caption. Two are typographical corrections. The scientific results and conclusions are unaffected.
Aerosol properties were characterized at a rural site southwest of Houston from May to September 2022 during the intensive operation periods (IOPs) of the Tracking Aerosol Convection Interactions ExpeRiment (TRACER). Backward trajectory analysis reveals three major air mass types: marine air mass from the Gulf, urban air mass influenced by urban emissions, and regional air mass. Marine aerosols typically show a bimodal size distribution and have the lowest particle number and mass concentrations of PM 1 (particulate matter with an aerodynamic diameter of less than 1 µm), while aerosols from air masses strongly influenced by urban emissions exhibit the highest concentrations. Organic aerosol (OA) accounts for more than 50 % of PM 1 for urban and regional air masses, whereas sulfate is comparable to OA in marine air masses. Positive matrix factorization (PMF) analysis of aerosol mass spectra identifies 6 OA factors: hydrocarbon-like OA (HOA), OA from the oxidation of monoterpenes (MT-SOA), OA from the reactive uptake of isoprene epoxydiols by acidic sulfate particles (isoprene-SOA), oxygenated OA arising from shipping emissions (shipping-OOA), and two oxygenated OA factors with high O : C ratios (OOA1 and OOA2). OOA2 has the highest O : C ratio and exhibits elevated mass concentration in the afternoon. Similar diurnal variation of highly oxidized OA factors was commonly observed in the Houston area during previous studies and attributed to the SOA formation by photochemistry and mixing from aloft. Here, using air mass backward trajectories and a 1-D box model, we show the diurnal trend of OOA2 mass concentration is instead driven by changes in air mass arriving at the rural site. The air mass changes are likely caused by the shift between land breezes and sea/bay breezes. Within the same air mass type (e.g., either urban or marine air mass), OOA2 mass concentration is largely independent of wind direction and shows essentially no diurnal variation, suggesting OOA2 is related to aged OA with minimal influence by local emissions. This study helps identify the major sources of OA in the Houston region and highlights the impacts of both atmospheric chemistry and meteorology on aerosol properties in the coastal–rural environment.
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Series of electron micrographs at successively lower magnifications can localize the substrate area sufficiently for a particle to be picked up by the beam of the electron microprobe. This approach could be modified to apply to fractographic studies, particularly of oxidation products stripped from fractures.
The differential scattering parameter has been measured for 0.04-micron tungsten particles in hydrogen and nitrogen at temperatures to 1080 K. The differential scattering parameter has also been measured for 0.1 micron tungsten, three types of carbon particles, and fly ash in nitrogen at temperatures to 1000 K. The 0.04 micron tungsten shows a temperature dependent total scattering parameter varying from around 4000 sq cm per g at room temperature to 7000 sq cm per g at 1088 K. The temperatures over which data were obtained are not high enough to confirm the temperature dependence of the total scattering parameter of tungsten.
The (7-2), (8-3), (5-1) and (6-2) bands of OH were observed from NASA's CV-990 aircraft during the Spacelab Simulation Mission. Both the average intensity and the fluctuations in intensity of each band were found to be strongly correlated to those of all other bands observed, suggesting that the excitation mechanisms for these bands are not independent processes. No significant correlation was observed between airglow intensity and latitude, azimuth, or local time for the ranges accessible during these flights. An additional ground-based experiment revealed a comparable correlation between the (6-0) and (8-3) bands.
Molten-silicon pool receives fine silicon powder and melts it. After stable molten layer forms, pedestal is lowered at rate equal to siliconpowder feed rate. If silane is directly decomposed on silicon pool, powder feeder is replaced by jet of silane on silicon surface, and hydrogen produced in decomposition of solane is pumped from bottom end of chamber.
Process for making metal-oxide/semiconductor field-effect transistors (MOSFET's) results in gate-channel lengths of only few hundred angstroms about 100 times as small as state-of-the-art devices. Gates must be shortened to develop faster MOSFET's; proposed fabrication process used to study effects of size reduction in MOS devices and eventually to build practical threedimensional structures.
Powder synthesis by thermally induced vapor phase reactions is described. The powder generated by this technique consists of spherical, nonagglomerated particles of high purity. The particles are uniform in size, in the 0.1-0.2-micron size range. Most of the particles are crystalline spheres. A small fraction of the spheres are amorphous. Chain agglomerates account for less than 1 percent of the spherules.
A real-time laser reflectivity method and Pt ribbon targets are used to obtain experimental data on the initial deposition rate of MgO(s) particles of approximately 700 nm diameter from otherwise clean combustion products as a function of target temperature (about 950-1450 K) and mainstream gas temperature (about 1500-1600 K). These preliminary data are used to demonstrate the dominant role of thermophoresis (particle drift down a temperature gradient) and to assess the utility of recently developed theoretical methods for predicting and correlating the temperature dependence of thermophoretically augmented convective-diffusion 'dust' deposition rates from flowing hot gases.