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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 919 records · Page 51
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Atomic-Scale Behavior of Radiation-Resistant ZnO under High-Energy Electron Bombardment

Understanding the atomic structure and defect characteristics of ZnO thin films is crucial for optimizing their electronic properties and performance in advanced applications. Here, we investigate the atomic structure and defect characteristics of atomic layer deposition (ALD)-grown ZnO thin films by using aberration-corrected scanning transmission electron microscopy (STEM). Atomic-resolution imaging identifies prevalent stacking faults, dipole disorder, and various grain boundary types, which are believed to influence the electronic properties of ZnO. Additionally, real-time electron beam exposure experiments demonstrate structural transformations, including crystal growth and surface rearrangements. These findings provide insights into the growth mechanisms of ALD ZnO under high-energy electron irradiation conditions, an important finding for the use of polycrystalline ZnO wide bandgap semiconductors in space-like conditions. In conclusion, our results underscore the capability of STEM in directly visualizing and quantifying atomic-scale defects and beam-induced transformations in radiation-resistant ZnO.

Defects↗
NASA NTRS1985

A slewing control experiment for flexible structures

A hardware set-up has been developed to study slewing control for flexible structures including a steel beam and a solar panel. The linear optimal terminal control law is used to design active controllers which are implemented in an analog computer. The objective of this experiment is to demonstrate and verify the dynamics and optimal terminal control laws as applied to flexible structures for large angle maneuver. Actuation is provided by an electric motor while sensing is given by strain gages and angle potentiometer. Experimental measurements are compared with analytical predictions in terms of modal parameters of the system stability matrix and sufficient agreement is achieved to validate the theory.

Juang, J.-N.↗
DOE OSTI2013

Effect of build geometry on the β-grain structure and texture in additive manufacture of Ti-6Al-4V by selective electron beam melting

With titanium alloys, the solidification conditions in Additive Manufacturing (AM) frequently lead to coarse columnar β-grain structures. The effect of geometry on the variability in the grain structure and texture, seen in Ti-6Al-4V alloy components produced by Selective Electron Beam Melting (SEBM), has been investigated. Reconstruction of the primary β-phase, from α-phase EBSD data, has confirmed that in bulk sections where in-fill “hatching” is employed growth selection favours columnar grains aligned with an <001> {sub β} direction normal to the deposited powder layers; this results in a coarse β-grain structure with a strong < 001 > {sub β} fibre texture (up 8 x random) that can oscillate between a near random distribution around the fibre axis and cube reinforcement with build height. It is proposed that this behaviour is related to the highly elongated melt pool and the raster directions alternating between two orthogonal directions every layer, which on average favours grains with cube alignment. In contrast, the outline, or “contour”, pass produces a distinctly different grain structure and texture resulting in a skin layer on wall surfaces, where nucleation occurs off the surrounding powder and growth follows the curved surface of the melt pool. This structure becomes increasingly important in thin sections. Local heterogeneities have also been found within different section transitions, resulting from the growth of skin grain structures into thicker sections. Texture simulations have shown that the far weaker α-texture (∼ 3 x random), seen in the final product, arises from transformation on cooling occurring with a near random distribution of α-plates across the 12 variants possible from the Burgers relationship. - Highlights: • Distinctly different skin and bulk structures are produced by the contour and hatching passes. • Bulk sections contain coarse β-grains with a < 001 > fibre texture in the build direction. • This oscillates between a random distribution around the axis and cube reinforcement. • In the skin layer nucleation occurs off the surrounding powder bed and growth occurs inwards. • Simulations show that a weak α-texture results from a random distribution across habit variants.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Development of High-QE GaN Photodectors for Liquid Noble Particle Detectors

Detection of the handful of photons generated when a dark matter particle interacts in a liquid Xenon detector requires a new type of photodetector with very high detection efficiency at ultraviolet wavelengths, very low radioactive backgrounds, and essentially no measureable readout noise (achieved with devices with high intrisic gain). Such devices would find wide applicability to not only high energy physics experiments, but to a number of commercial applications including, e.g., biomedical imaging of fluorescent tags. We developed photodetectors based on amorphous GaN thin film structures (photocathodes) grown by molecular beam epitaxy on quartz windows. We also developed approaches to integrate these photocathode device structures with vacuum electron multipliers. All materials and fabrication techniques were developed to minimize radioactive backgrounds in materials, so these detectors could be used for very low count rate experiments, such as the future liquid-Xenon dark matter detectors, and future liquid-Argon neutrino detectors. We demonstrated growth of very high quantum efficiency amorphous GaN cathodes grown on a number of different substrates (Stainless steel, p-Silicon) reaching detection efficiencies of 80% at 220nm. The key to this growth was to use nitrogen plasma-assistend MBEs and very low growth temperatures. We also discovered that thinner structures (e.g.,40nm a-GaN thin films) had the best performance. We successfully demonstrated techniques for the vacuum transfer of these photocathode structures to a novel chamber that used hydraulics and bellow to form a cold indium bond needed to integrate these cathodes into sealed-tube devices. A complete, stand-along, device could not be completed during this proposal period due to difficulties in growing structures on the thick quartz window. Subsequent work is aimed at addressing this difficulty, by growing a buffer layer on the quartz substrate.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2023

Framework for Characterizing the Performance of High-Early Strength, High-Volume Fly Ash (HVFA) Concrete Structures

This presentation will highlight the development of a comprehensive framework to characterize the performance of high-volume fly ash (HVFA) concretes at early ages and discuss the resulting implications for concrete structures built using such materials. Achieving high-early compressive and/or flexural strength is often of particular importance for precast and/or prestressed concrete components – due to early age loading demands resulting from lifting, handling, or application of initial prestress – or other types of concrete structures that can significantly benefit from rapid strength development - such as for bridge deck repairs. The framework first includes a methodology for optimizing the strength of HVFA cementitious binders before subsequently scaling up the technology to evaluation of fresh and hardened HVFA concrete performance. A series of trial mix designs will be presented to demonstrate the effectiveness of the framework to achieve not only the desired high-early strength targets but also satisfactory workability, often in the form of self-consolidating concrete. Mechanical performance was evaluated at several age-dependent milestones and, in conjunction with estimating concrete strength using the maturity method, was ultimately used to facilitate the development of novel strength development history curves. By way of these datasets, concrete mechanical properties were utilized in the design of prototype structural components, such as beams and wall panels, for subjection to larger-scale experimental testing. Implications for other pertinent HVFA concrete performance attributes, such as shrinkage or creep, will also be discussed. The framework also includes a comprehensive methodology for evaluating the environmental life-cycle performance of HVFA concrete structures focused on mitigating any unwarranted environmental consequences resulting from beneficial HVFA reuse in concrete. Strategies for more widespread implementation of HVFA concrete materials into construction practice will also be presented. Lastly, the role of the HVFA concrete framework towards the development of new provisions for building codes and/or design standards, and recommendations for future research needs will also be discussed.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2014

Structural anisotropic properties of a-plane GaN epilayers grown on r-plane sapphire by molecular beam epitaxy

Heteroepitaxial non-polar III-Nitride layers may exhibit extensive anisotropy in the surface morphology and the epilayer microstructure along distinct in-plane directions. The structural anisotropy, evidenced by the “M”-shape dependence of the (112{sup ¯}0) x-ray rocking curve widths on the beam azimuth angle, was studied by combining transmission electron microscopy observations, Raman spectroscopy, high resolution x-ray diffraction, and atomic force microscopy in a-plane GaN epilayers grown on r-plane sapphire substrates by plasma-assisted molecular beam epitaxy (PAMBE). The structural anisotropic behavior was attributed quantitatively to the high dislocation densities, particularly the Frank-Shockley partial dislocations that delimit the I{sub 1} intrinsic basal stacking faults, and to the concomitant plastic strain relaxation. On the other hand, isotropic samples exhibited lower dislocation densities and a biaxial residual stress state. For PAMBE growth, the anisotropy was correlated to N-rich (or Ga-poor) conditions on the surface during growth, that result in formation of asymmetric a-plane GaN grains elongated along the c-axis. Such conditions enhance the anisotropy of gallium diffusion on the surface and reduce the GaN nucleation rate.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Beam Dynamics Simulations of Optically-Enhanced Field Emission from Structured Cathodes

Structured cathodes - cathodes with a segmented emission surface - are finding an increasing number of applications and can be combined with a variety of emission mechanisms, including photoemission and field emission. These cathodes have been used to enhance the quantum efficiency of metallic cathodes when operated as plasmonic cathodes, have produced high-current electron bunches though field emission from multiple tips, and can be used to form beams with transverse segmentations necessary for improving the performance of accelerator-based light sources. In this report we present recent progress towards the development of finite-difference time-domain particle-in-cell simulations using the emission process in structured cathodes based on the WARP framework. The simulations give further insight on the localized source of the emitted electrons which could be used for additional high-fidelity start-to-end simulations of electron accelerators that employ this type of electron source.

43 PARTICLE ACCELERATORS↗
NASA NTRS1988

Composite transport wing technology development: Design development tests and advanced structural concepts

Numerous design concepts, materials, and manufacturing methods were investigated for the covers and spars of a transport box wing. Cover panels and spar segments were fabricated and tested to verify the structural integrity of design concepts and fabrication techniques. Compression tests on stiffened panels demonstrated the ability of graphite/epoxy wing upper cover designs to achieve a 35 percent weight savings compared to the aluminum baseline. The impact damage tolerance of the designs and materials used for these panels limits the allowable compression strain and therefore the maximum achievable weight savings. Bending and shear tests on various spar designs verified an average weight savings of 37 percent compared to the aluminum baseline. Impact damage to spar webs did not significantly degrade structural performance. Predictions of spar web shear instability correlated well with measured performance. The structural integrity of spars manufactured by filament winding equalled or exceeded those fabricated by hand lay-up. The information obtained will be applied to the design, fabrication, and test of a full-scale section of a wing box. When completed, the tests on the technology integration box beam will demonstrate the structural integrity of an advanced composite wing design which is 25 percent lighter than the metal baseline.

Griffin, Charles F.↗
DOE OSTI2015

Enhanced traveling wave amplification of co-planar slow wave structure by extended phase-matching

The electron beam co-propagating with slow waves in a staggered double grating array (SDGA) efficiently amplifies millimeter and sub-millimeter waves over a wide spectrum. Our theoretical and numerical analyses show that the power amplification in the fundamental passband is enhanced by the extended beam-wave phase-matching. Particle-in-cell simulations on the SDGA slow wave structure, designed with 10.4 keV and 50–100 mA sheet beam, indicate that maintaining beam-wave synchronization along the entire length of the circuit improves the gain by 7.3% leading to a total gain of 28 dB, corresponding to 62 W saturated power at the middle of operating band, and a 3-dB bandwidth of 7 GHz with 10.5% at V-band (73.5 GHz center frequency) with saturated peak power reaching 80 W and 28 dB at 71 GHz. These results also show a reasonably good agreement with analytic calculations based on Pierce small signal gain theory.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Radiation defect dynamics in 3 C -, 4 H -, and 6 H -SiC studied by pulsed ion beams

Radiation damage behavior of SiC depends on its lattice structure. Here, we use a pulsed-ion-beam method to study defect interaction dynamics in 6H-SiC and damage buildup in 4H- and 6H-SiC irradiated at 100 °C with 500 keV Ar ions. These results are compared with previously reported data for Ar-ion-irradiated 3C- and 4H-SiC. We find that, for these irradiation conditions, damage buildup in 3C- and 6H-SiC is statistically indistinguishable and is significantly more efficient than in 4H-SiC. Within a stimulated amorphization model, 4H-SiC is described by a reduced amorphization cross-section constant, while the point defect cluster production cross-section is the same (within experimental errors) for the three polytypes studied. Moreover, 4H-SiC exhibits slower defect relaxation dynamics than 3C- and 6H-SiC. These results clearly demonstrate the importance of the lattice structure in damage buildup and defect interaction dynamics in SiC.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Atomic-Scale Dynamic Mechanisms of Embedded MoS 2 Wires

Nanowires composed of a 1:1 stoichiometry of transition metals and chalcogen ions can be fabricated from two-dimensional transition metal dichalcogenides (TMDs) by using electron beam irradiation. Wires fabricated through in situ experiments can be geometrically connected to TMD sheets in various ways, and their physical properties can vary accordingly. Understanding the structural transformation caused by electron beams is critical for designing wire-sheet structures for nanoelectronics. In this study, we report the behavior of nanowires formed inside a monolayer MoS 2 sheet by combining phase-contrast images and large-scale atomistic modeling. Here we investigate the effect of vacancies on the dynamic evolution of wires, such as rotations with different edge structures and breaking, by considering the interactions between MoS wires and MoS 2 nanosheets. The obtained insights can be applied to other monolayer TMDs to guide the behavior of TMD wires and fabricate favorable geometries for various applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRSDate not supplied

Precision in Assembled Discrete Lattice Space Structures for Next-Generation ISAM Applications

Robust autonomous robotic assembly of large-scale space structures has been a long-term and challenging goal to enable higher quality in-space communication and science instrumentation. For optical observatory support structures and antenna structures, the challenge is the strict dimensional precision requirements (generally RMS surface error) driven by the operational radiation wavelength. Early theoretical work in the area linked RMS surface error of a reflector support truss plate to the natural passive dynamic mode frequencies of the structure, as well as to the error distribution in dimensions of constituent structural elements. Prior robotic truss assembly demonstrations focused on designing ultra-high precision structural elements, joints, and robotic actuators. Recently, an alternative space structure assembly strategy based on a programmable matter approach (NASA ARMADAS) was demonstrated. This approach uses lattice building blocks (voxels) that are reversibly, mechanically joined into a bulk lattice structure by robots that locomote in and on the structure itself. Such a system can achieve high-level autonomy with low computation, robustly assemble utilizing inexpensive and imprecise robots, and efficiently build structures several orders of magnitude larger than the assembly robots. However, for instrumentation support structure applications, the resulting precision of these building block-based lattice structures is not well studied. Since they are demonstrated with many more assembly units than prior art trusses, it is unclear whether the same precision design approaches apply. In this work, we study in simulation the effects of voxel geometry, error in distribution, assembly resolution (module size), and assembly geometry on the error of both beam and plate lattice structures. While average RMS error of a plate increases with plate size, increasing plate thickness quickly collapses RMS error towards a limit that is on the order of the error of the constituent parts. We validate our models against previously published precision measurements of built systems. Results from this study will guide manufacturing precision requirements, as well as designs, for future robotically assembled structural applications and establish feasibility for different applications.

Christine E Gregg↗
NASA NTRS1983

Parameter estimation in truss beams using Timoshenko beam model with damping

Truss beams with members having viscous damping are modeled with a Timoshenko beam. Procedures for deriving the equivalent bending rigidity, transverse shear rigidity, and damping are presented. Explicit expressions for these equivalent beam properties are obtained for a specific truss beam. The beam model thus established is then used to investigate the effect of damping in free vibration. Finally, the beam is employed in the estimation of structural parameters in a simply-supported truss beam using a random search algorithm.

Sun, C. T.↗
NASA NTRS1986

Synchronously Deployable Truss Structures

Structure lightweight, readily deployed, and has reliable joints. New truss concept, designated as "pac truss," developed. Features easy deployment without need for complex mechanisms. Structures of this type deployed in free flight by controlled release of stored energy in torsional springs at selected hinges located throughout structure. Double-folding technique used in beam model applicable to flat planar trusses, allowing structures of large expanse to fold into compact packages and be deployed for space-platform applications.

Rhodes, M. D.↗
DOE OSTI2019

Identification of interstratified mica and pyrophyllite monolayers within chlorite using advanced scanning/transmission electron microscopy

Interstratified clay minerals reflect the weathering degree and record climatic conditions and the pedogenic processes in the soil. It is hard to distinguish a few layers of interstratified clay minerals from the chlorite matrix, due to their similar two-dimensional tetrahedral-octahedral-tetrahedral (TOT) structure and electron-beam sensitive nature during transmission electron microscopy (TEM) imaging. In this study, we used multiple advanced TEM techniques including low-dose high-resolution TEM (HRTEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) imaging combined with energy-dispersive spectroscopic (EDS) mapping to study interstratified layers in a chlorite sample from Changping, Beijing, China. We demonstrated an interstratified mica or pyrophyllite monolayer could be well distinguished from the chlorite matrix by projected atomic structures, lattice spacings, and chemical compositions with advanced TEM techniques. Further investigation showed two different transformation mechanisms from mica or pyrophyllite to chlorite: either a 4 A increase or decrease in the lattice spacing. Lastly, this characterization approach can be extended to the studies of other electron-beam sensitive minerals.

36 MATERIALS SCIENCE↗
NASA NTRS1986

Vibration of a large space beam under gravity effect

Future space structures will have a low mass density and high flexibility, with ground test dynamic behavior differing significantly from that in zero-G orbit. Attention is presently given to the vibration behavior of a beam deformed by its own weight; the results obtained by the differential equations for both the static and dynamic responses of a large, simply supported beam, which are derived and solved analytically, allow ground test experiment measurements to be used for orbital dynamic characteristics verification efforts.

Shih, C.-F.↗