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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Electron-ion plasma modification of Al-based alloys

The paper reports on the study where we analyzed the surface structure and strength properties of coated Al alloys modified by electron-ion plasma treatment. The Al alloys were deposited with a thin (≈0.5 μm) TiCu film coating (TiCu-Al system) and with a hard TiCuN coating (TiCuN–AlSi system) on a TRIO vacuum setup in the plasma of low-pressure arc discharges. The temperature fields and phase transformations in the film–substrate system were estimated by numerical simulation in a wide range of electron energy densities (5–30 J/cm{sup 2}) and pulse durations (50–200 μs). The calculations allowed us to determine the threshold energy density and pulse duration at which the surface structure of the irradiated Al-based systems is transformed in a single-phase state (solid or liquid) and in a two-phase state (solid plus liquid). The elemental composition, defect structure, phase state, and lattice state in the modified surface layers were examined by optical, scanning, and transmission electron microscopy, and by X-ray diffraction analysis. The mechanical characteristics of the modified layers were studied by measuring the hardness and Young’s modulus. The tribological properties of the modified layers were analyzed by measuring the wear resistance and friction coefficient. It is shown that melting and subsequent high-rate crystallization of the TiCu–Al system makes possible a multiphase Al-based surface structure with the following characteristics: crystallite size ranging within micrometer, microhardness of more than 3 times that in the specimen bulk, and wear resistance ≈1.8 times higher compared to the initial material. Electron beam irradiation of the TiCuN–AlSi system allows fusion of the coating into the substrate, thus increasing the wear resistance of the material ≈2.2 times at a surface hardness of ∼14 GPa.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Microsized structures assisted nanostructure formation on ZnSe wafer by femtosecond laser irradiation

Micro/nano patterning of ZnSe wafer is demonstrated by femtosecond laser irradiation through a diffracting pinhole. The irradiation results obtained at fluences above the ablation threshold are characterized by scanning electron microscopy. The microsized structure with low spatial frequency has a good agreement with Fresnel diffraction theory. Laser induced periodic surface structures and laser-induced periodic curvelet surface structures with high spatial frequency have been found on the surfaces of microsized structures, such as spikes and valleys. We interpret its formation in terms of the interference between the reflected laser field on the surface of the valley and the incident laser pulse.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2004

Hot Structure Control Surface Progress for X-37 Technology Development Program

The NASA Marshall Space Flight Center (MSFC) has been leading the development of technologies that will enable the development, fabrication, and flight of the automated X-37 Orbital Vehicle (OV). With the Administration s recent announcement of the Vision for Space Exploration, NASA placed the X-37 OV design on hold while developing detailed requirements for a Crew Exploration Vehicle, but has continued funding the development of high-risk, critical technologies for potential future space exploration vehicle applications. Hot Structure Control Surfaces (HSCS) technology development is one of the high-priority areas being funded at this time. The goal of HSCS research is to mitigate risk by qualifying the lightest possible components that meet the stringent X-37 OV weight and performance requirements, including Shuttle-type reen- try environments with peak temperatures of 2800 OF. The small size of the X-37 OV (25.7-feet long and 14.9-foot wingspan) drives the need for advanced HSCS because the vehicle's two primary aerodynamic surfaces, the flaperons and ruddervators, have thicknesses ranging from approximately 5 in. down to 1 in. Traditional metallic or polymer-matrix composites covered with tile or blanket thermal protection system (TPS) materials cannot be used as there is insufficient volume to fabricate such multi-component structures. Therefore, carbon-carbon (C-C) and carbodsilicon-carbide (C-SiC) composite HSCS structures are being developed in parallel by two teams supporting the X-37 prime contractor (The Boeing Company). The Science Applications International Coy. (SAIC) and Carbon-Carbon Advanced Technologies, Inc. (C-CAT) team is developing the C-C HSCS, while the General Electric Energy Power Systems Composites (GE-PSC) and Materials Research and Design (MRD) team is developing the C-SiC HSCS. These two teams were selected to reduce the high level of risk associated with developing advanced control surface components. They have continued HSCS development work as part of the X-37 critical technology development contract. The SAIC/C-CAT team is using Advanced Carbon-Carbon (ACC) because its fabrication is very similar to the process used for Space Shuttle Reinforced Carbon-Carbon fabrication, including the Sic-based pack cementation conversion coating systems using with both materials. ACC was selected over RCC because it has much higher tension and compressions strengths, and because T-300 fiber is readily available, whereas RCC rayon fiber is no longer manufactured. The GE-PSC/MRD team is using a T-300 fiber-reinforced Sic matrix composite material densified by chemical vapor infiltration. The C-Sic material has an Sic-based environmental barrier coating. Major accomplishments have been made over the past year by both HSCS teams. C-C and C- SiC flaperon subcomponents, which are truncated full-scale versions of flight hardware, have been fabricated and are undergoing testing at the NASA Dryden Flight Research Center, NASA Langley Research Center, and U.S. Air Force Research Laboratory. By the end of 2004, ruddervator subcomponents also will be delivered and tested. As NASA moves forward in realizing the Vision for Space Exploration, it will continue to invest in advanced research and development aimed at making new generations of spacecraft safer, more reliable, and more affordable. The X-37 HSCS effort ultimately will benefit the Agency's vision and mission.

Valentine, P. G.↗
NASA NTRS2005

Lunar and Martian Sub-surface Habitat Structure Technology Development and Application

NASA's human exploration initiative poses great opportunity and great risk for manned missions to the Moon and Mars. Subsidace structures such as caves and lava tubes offer readily available and existing in-situ habitat options. Sub-surface dwellings can provide complete radiation, micro-meteorite and exhaust plume shielding and a moderate and constant temperature environment; they are, therefore, excellent pre-existing habitat risk mitigation elements. Technical challenges to subsurface habitat structure development include surface penetration (digging and mining equipment), environmental pressurization, and psychological environment enhancement requirements. Lunar and Martian environments and elements have many beneficial similarities. This will allow for lunar testing and design development of subsurface habitat structures for Martian application; however, significant differences between lunar and Martian environments and resource elements will mandate unique application development. Mars is NASA's ultimate exploration goal and is known to have many very large lava tubes. Other cave types are plausible. The Moon has unroofed rilles and lava tubes, but further research will, in the near future, define the extent of Lunar and Martian differences and similarities. This paper will discuss Lunar and Martian subsurface habitation technology development challenges and opportunities.

Boston, Penelope J.↗
DOE OSTI2025

PySIDT: Subgraph Isomorphic Decision Trees for Molecular Property Prediction

Accurate molecular property prediction is important across all fields of chemistry. Deep neural networks (DNNs) have become increasingly popular due to their ability to train automatically, avoiding the incredibly tedious process of constructing and extending traditional property estimation schemes. However, DNNs require large amounts of training data, are challenging to interpret, require large amounts of memory to load even during inference, and have severe difficulties incorporating qualitative chemical knowledge, which are often desired for molecular property prediction tasks. Here, in this study, we present PySIDT (https://github.com/zadorlab/PySIDT), a software for training and running inference on Subgraph Isomorphic Decision Trees (SIDTs). SIDTs are graph-based decision trees made of nodes associated with molecular substructures. Inference is done by descending target molecular structures down the decision tree to nodes with matching subgraph isomorphic substructures and making predictions based on the final (most specific) nodes matched. SIDTs scale down well to dataset sizes much smaller than is feasible for DNNs. As trees of molecular substructures, SIDTs are inherently readable and easy to visualize, making them easy to analyze. They are also straightforward to extend and retrain, facilitate uncertainty estimation, and enable easy integration of expert knowledge. We demonstrate the SIDT approach discussing its application to a diverse range of molecular prediction tasks: rate coefficient estimation, diffusion coefficient estimation, thermochemistry estimation, transition state bond stretch prediction, p K a prediction, stability of molecular structures, stability of surface structures, and prediction of surface lateral interaction energetics. Additionally, we demonstrate the power of the SIDT algorithms in two direct learning curve vanilla comparisons with the popular DNN-based software Chemprop and the popular gradient boosted trees-based software XGBoost on enthalpy of formation and rate coefficient prediction tasks. In particular, in the enthalpy of formation case, vanilla PySIDT is able to outperform vanilla Chemprop and XGBoost across the full range of training/validation set sizes out to 11,560 data points.

Johnson, Matthew Sean [Sandia National Laboratorie↗
NASA NTRS2011

High-Temperature Modal Survey of a Hot-Structure Control Surface

Ground vibration tests are routinely conducted for supporting flutter analysis for subsonic and supersonic vehicles; however, for hypersonic vehicles, thermoelastic vibration testing techniques are neither well established nor routinely performed. New high-temperature material systems, fabrication technologies and high-temperature sensors expand the opportunities to develop advanced techniques for performing ground vibration tests at elevated temperatures. When high-temperature materials, which increase in stiffness when heated, are incorporated into a hot-structure that contains metallic components that decrease in stiffness when heated, the interaction between those materials can affect the hypersonic flutter analysis. A high-temperature modal survey will expand the research database for hypersonics and improve the understanding of this dual-material interaction. This report discusses the vibration testing of the carbon-silicon carbide Ruddervator Subcomponent Test Article, which is a truncated version of a full-scale hot-structure control surface. Two series of room-temperature modal test configurations were performed in order to define the modal characteristics of the test article during the elevated-temperature modal survey: one with the test article suspended from a bungee cord (free-free) and the second with it mounted on the strongback (fixed boundary). Testing was performed in the NASA Dryden Flight Research Center Flight Loads Laboratory Large Nitrogen Test Chamber.

Spivey, Natalie D.↗
DOE OSTI2015

Surface electronic structure of polar NiO thin film grown on Ag(111)

The growth and structure of NiO thin films on top of Ag(111) substrate were studied where the formation of faceted surface was confirmed by Low Energy Electron Diffraction. The electronic structure of polar NiO(111) surface has been probed using photoemission techniques. The core energy levels and the valence band electronic structure were excited by x-ray and ultraviolet photons respectively. The modifications in physical structure and valence band electronic structure of the film under vacuum annealing have also been enlightened.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1972

An observation of the Gulf Stream surface front structure by ship, aircraft, and satellite.

Evaluation of observations of surface temperature and salinity along the western edge of the Gulf Stream made from a ship and of concurrent temperature observations obtained by instrumented aircraft at six altitudes. The major feature along a five-kilometer line normal to the Stream's edge is a temperature gradient of about 0.75 C/kilometer within which are embedded two abrupt temperature increases of about 1.5 C. Temperature variations were compensated by salinity variations, yielding nearly constant density through the frontal zone; a sharp lateral current shear was associated with the thermohaline mixing region between the steps. The attenuation of surface temperature measured by the airborne radiometer was compared with a theoretical model. The analysis supports the view that a two-part correction technique is required: one part for bulk-skin temperature differences, and another for atmospheric attenuation of sea surface emission due to the mass and temperature of interfering gases.

Maul, G. A.↗
DOE OSTI2025

Tuning effect of vanadium substitution on the structural and electronic properties of potassium hollandite surfaces

Metal oxide surfaces possess unique properties that are crucial for a wide variety of applications. Herein, density functional theory calculations are performed to study surfaces of potassium hollandite, KMn 8 O 16 , a promising cathode material for electrochemical energy storage, and the vanadium-substituted analog KMn 7 VO 16 . The results show that there is a clear increase in the stability of KMn 8 O 16 with (001) < (110) < (100) or (010), apt to adopt an elongated rod-like morphology. The vanadium (V)-substitution lowers the crystal symmetry and prefers to occupy the surface sites, resulting in electron redistribution and selective tuning of surface energy depending on the surface structures. In particular, the higher stability of substituted V 4+ compared with Mn 4+ ions leads to stabilization of the (001) surface due to the direct interaction of reduced Mn δ+ ions on the surface, while such tuning effect decreases with the increase in surface stability, (110) > (100) and (010). As a result, the KMnO 16 rod is shortened upon V-substitution as observed experimentally, effectively facilitating the ion transport during discharge. The V substituents also introduce stabilization to the defect surfaces resulting from Mn 2+ dissolution during cycling, thereby hindering further structural decay. In conclusion, our study demonstrates the potential tuning effect of V-substitution to promote the ion transport and mitigate the capacity degradation of α-MnO 2 -based materials.

25 ENERGY STORAGE↗
DOE OSTI2021

First-principles calculations of metal surfaces. II. Properties of low-index platinum surfaces toward understanding electron emission

The stability of low-index platinum surfaces and their electronic properties is investigated with density functional theory, toward the goal of understanding the surface structure and electron emission, and identifying precursors to electrical breakdown, on nonideal platinum surfaces. Propensity for electron emission can be related to a local work function, which, in turn, is intimately dependent on the local surface structure. The (1×N) missing row reconstruction of the Pt(110) surface is systematically examined. The (1×3) missing row reconstruction is found to be the lowest in energy, with the (1×2) and (1×4) slightly less stable. In the limit of large (1×N) with wider (111) nanoterraces, the energy accurately approaches the asymptotic limit of the infinite Pt(111) surface. Furthermore, this suggests a local energetic stability of narrow (111) nanoterraces on free Pt surfaces that could be a common structural feature in the complex surface morphologies, leading to work functions consistent with those on thermally grown Pt substrates.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2010

High-Temperature Modal Survey of a Hot-Structure Control Surface

Ground vibration tests or modal surveys are routinely conducted for supporting flutter analysis for subsonic and supersonic vehicles; however, for hypersonic vehicle applications, thermoelastic vibration testing techniques are not well established and are not routinely performed for supporting hypersonic flutter analysis. New high-temperature material systems, fabrication technologies and high-temperature sensors expand the opportunities to develop advanced techniques for performing ground vibration tests at elevated temperatures. High-temperature materials have the unique property of increasing in stiffness when heated. When these materials are incorporated into a hot-structure, which includes metallic components that decrease in stiffness with increasing temperature, the interaction between the two materials systems needs to be understood because that interaction could ultimately affect the hypersonic flutter analysis. Performing a high-temperature modal survey will expand the research database for hypersonics and will help build upon the understanding of the dual material interaction. This paper will discuss the vibration testing of the Carbon-Silicon Carbide Ruddervator Subcomponent Test Article which is a truncated version of the full-scale X-37 hot-structure control surface. In order to define the modal characteristics of the test article during the elevated-temperature modal survey, two series of room-temperature modal test configurations had to be performed. The room-temperature test series included one with the test article suspended from a bungee cord (free-free) and the second with it mounted on the strongback (fixed boundary condition) in NASA Dryden's Flight Loads Lab large nitrogen test chamber.

Spivey, Natalie Dawn↗
DOE OSTI2021

The impact of surface composition on the interfacial energetics and photoelectrochemical properties of BiVO{sub 4}.

The ability to engineer a photoelectrode surface is pivotal for optimizing the properties of any photoelectrode used for solar fuel production. Altering crystal facets exposed on the surface of photoelectrodes has been a major strategy to modify their surface structure. However, there exist numerous ways to terminate the surface even for the same facet, which can considerably alter the photoelectrode properties. Here we report tightly integrated experimental and computational investigations of epitaxial BiVO4 photoelectrodes with vanadium- and bismuth-rich (010) facets. Our study demonstrates that even for the same facet the surface Bi:V ratio has a remarkable impact on the interfacial energetics and photoelectrochemical properties. We also elucidate the microscopic origins of how the surface composition can affect the photoelectrochemical properties. This study opens an unexplored path for understanding and engineering surface energetics via tuning the surface termination/composition of multinary oxide photoelectrodes.

Lee, Dongho↗
DOE OSTI2014

Realizing in-plane surface diffraction by x-ray multiple-beam diffraction with large incidence angle

Based on rigorous dynamical-theory calculations, we demonstrate in this paper the principle of an x-ray multiple-beam diffraction (MBD) scheme that overcomes the long-lasting difficulties of high-resolution in-plane diffraction from crystal surfaces. This scheme only utilizes symmetric reflection geometry with large incident angles but activates the out-of-plane and in-plane diffraction processes simultaneously and separately in the continuous MBD planes. The in-plane diffraction is realized by detoured MBD, where the intermediate diffracted waves propagate parallel to the surface, which corresponds to an absolute Bragg surface diffraction configuration that is extremely sensitive to surface structures. Finally, a series of MBD diffraction and imaging techniques may be developed from this principle to study surface/interface (misfit) strains, lateral nanostructures, and phase transitions of a wide range of (pseudo)cubic crystal structures, including ultrathin epitaxial films and multilayers, quantum dots, strain-engineered semiconductor or (multi)ferroic materials, etc.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Catalytic activity and stability of oxides: The role of near-surface atomic structures and compositions

Electrocatalysts play an important role in catalyzing the kinetics for oxygen reduction and oxygen evolution reactions for many air-based energy storage and conversion devices, such as metal$-$air batteries and fuel cells. Although noble metals have been extensively used as electrocatalysts, their limited natural abundance and high costs have motivated the search for more cost-effective catalysts. Oxides are suitable candidates since they are relatively inexpensive andhave shown reasonably high activity for various electrochemical reactions. However, a lack of fundamental understanding of the reaction mechanisms has been a major hurdle toward improving electrocatalytic activity. Here, detailed studies of the oxide surface atomic structure and chemistry (e.g.,cation migration) can provide much needed insights for the design of highly efficient and stable oxide electrocatalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1998

Broadband Infrared Antireflection Structured Silicon Surfaces

Silicon and germanium are materials often used for IR windows and optical elements. However they have a very high index of refraction, in the order of three to four, which causes large reflection losses on each surface. These losses are especially high under large angles of incidence which are often desirable if signals are faint and fast optics are to be used. Solid antireflection coatings are either not available because materials with appropriate index of refraction do not exist, or their use is limited to a small wavelength range and small angles of incidence. We will present the status of our work to calculate, create, and test the performance of graded structures in Si to reduce its surface reflection. The structures are expected to work over the very broad wavelength range of 10 microns to 1000 microns and a wide range of angle of incidence. We have identified several high aspect ratio MEMS process techniques to create the structures and have done 3D electromagnetic modeling, which predicts significant effects. Measurements on different samples have validated our modeling.

Stewart, Kenneth↗
NASA NTRS1999

Broadband Infrared Antireflection Structured Silicon Surfaces

Silicon and germanium are materials often used for IR windows and optical elements. However they have a very high index of refraction, in the order of three to four, which causes large reflection losses on each surface. These losses are especially high under large angles of incidence which are often desirable if signals are faint and fast optics are to be used. Solid antireflection coatings are either not available because materials with appropriate index of refraction do not exist, or their use is limited to a small wavelength range and small angles of incidence. We will present the status of our work to calculate, create, and test the performance of graded structures in Si to reduce its surface reflection. The structures are expected to work over the very broad wavelength range of 10 to 1000 micrometers and a wide range of angle of incidence. We have identified several high aspect ratio MEMS process techniques to Create the structures and have done 3D electromagnetic modeling, which predicts significant effects. Measurements on different samples have validated our modeling.

Stewart, Kenneth↗
NASA NTRS1999

Broadband Infrared Antireflection Structured Silicon Surfaces

Silicon and germanium are materials often used for infrared (IR) windows and optical elements. However they have a very high index of refraction, in the order of three to four, which causes large reflection losses on each surface. These losses are especially high under large angles of incidence which are often desirable if signals are faint and fast optics are to be used. Solid antireflection coatings are either not available because materials with appropriate index of refraction do not exist, or their use is limited to a small wavelength range and small angles of incidence. We will present the status of our work to calculate, create, and test the performance of graded structures in Si to reduce its surface reflection. The structures are expected to work over the very broad wavelength range of 10 micron to 1000 micron and a wide range of angle of incidence. We.have identified several high aspect ratio MEMS process techniques to create the structures and have done 3D electromagnetic modeling, which predicts significant effects. Measurements on different samples have validated our modeling.

Stewart, Kenneth↗
DOE OSTI2026

Locating the atoms at the hard-soft interface of gold nanoparticles

Surface structure affects the growth, shape and properties of nanoparticles. In wet chemical syntheses, metal additives and surfactants are used to modify surfaces and guide nanocrystal growth. To understand this process, it is critical to understand how the surface structure, and hence its energy, is modified. However, measuring the type and arrangement of atoms at hard-soft interfaces on nanoscale surfaces, especially in the presence of surfactants, is extremely challenging. Here, we determine the atomic structure of the hard-soft interface in a metallic nanoparticle by developing low-dose imaging conditions in four-dimensional scanning transmission electron microscopy that are preferentially sensitive to surface adatoms. By revealing experimentally the copper additives and bromide surfactant counterion at the surface of a gold nanocuboid and quantifying their interatomic distances, our direct, low-dose imaging method provides atomic-level understanding of chemically sophisticated nanomaterial surface structures. These measurements of the atomic structure of the hard-soft interface provide the information necessary to understand and quantify surface chemistries and energies and their pivotal role in nanocrystal growth.

Li, Weilun [Monash University, Melbourne, VIC (Aus↗