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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Mass spectra of neutral particles released during electrical breakdown of thin polymer films

A special type of time-of-flight mass spectrometer triggered from the breakdown event was developed to study the composition of the neutral particle flux released during the electrical breakdown of polymer films problem. Charge is fed onto a metal-backed polymer surface by a movable smooth platinum contact. A slowly increasing potential from a high-impedance source is applied to the contact until breakdown occurs. The breakdown characteristics is made similar to those produced by an electron beam charging system operating at similar potentials. The apparatus showed that intense instantaneous fluxes of neutral particles are released from the sites of breakdown events. For Teflon FEP films of 50 and 75 microns thickness the material released consists almost entirely of fluorocarbon fragments, some of them having masses greater than 350 atomic mass units amu, while the material released from a 50 micron Kapton film consists mainly of light hydrocarbons with masses at or below 44 amu, with additional carbon monoxide and carbon dioxide. The apparatus is modified to allow electron beam charging of the samples.

Kendall, B. R. F.↗
DOE OSTI2012

Visual and Electrical Evidence Supporting a Two-Plasma Mechanism of Vacuum Breakdown Initiation

The energy available during vacuum breakdown between copper electrodes at high vacuum was limited using resistors in series with the vacuum gap and arresting diodes. Surviving features observed with SEM in postmortem samples were tentatively correlated with electrical signals captured during breakdown using a Rogowski coil and a high-voltage probe. The visual and electrical evidence is consistent with the qualitative model of vacuum breakdown by unipolar arc formation by Schwirzke [1, 2]. The evidence paints a picture of two plasmas of different composition and scale being created during vacuum breakdown: an initial plasma made of degassed material from the metal surface, ignites a plasma made up of the electrode material.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

IONIZATION IN ATMOSPHERES OF BROWN DWARFS AND EXTRASOLAR PLANETS. III. BREAKDOWN CONDITIONS FOR MINERAL CLOUDS

Electric discharges were detected directly in the cloudy atmospheres of Earth, Jupiter, and Saturn, are debatable for Venus, and indirectly inferred for Neptune and Uranus in our solar system. Sprites (and other types of transient luminous events) have been detected only on Earth, and are theoretically predicted for Jupiter, Saturn, and Venus. Cloud formation is a common phenomenon in ultra-cool atmospheres such as in brown dwarf and extrasolar planetary atmospheres. Cloud particles can be expected to carry considerable charges which may trigger discharge events via small-scale processes between individual cloud particles (intra-cloud discharges) or large-scale processes between clouds (inter-cloud discharges). We investigate electrostatic breakdown characteristics, like critical field strengths and critical charge densities per surface, to demonstrate under which conditions mineral clouds undergo electric discharge events which may trigger or be responsible for sporadic X-ray emission. We apply results from our kinetic dust cloud formation model that is part of the DRIFT-PHOENIX model atmosphere simulations. We present a first investigation of the dependence of the breakdown conditions in brown dwarf and giant gas exoplanets on the local gas-phase chemistry, the effective temperature, and primordial gas-phase metallicity. Our results suggest that different intra-cloud discharge processes dominate at different heights inside mineral clouds: local coronal (point discharges) and small-scale sparks at the bottom region of the cloud where the gas density is high, and flow discharges and large-scale sparks near, and maybe above, the cloud top. The comparison of the thermal degree of ionization and the number density of cloud particles allows us to suggest the efficiency with which discharges will occur in planetary atmospheres.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

Effects of He (90%)/H{sub 2} (10%) plasma treatment on electric properties of low dielectric constant SiCOH films

In microelectronics industry, integration of the low dielectric constant (low-k) material films is a continuing issue due to the decreasing device feature size. To improve electric properties, various post-deposition treatments of the low-k material films can be used. In this work, we used room temperature treatment of He/H{sub 2} plasma and investigated the effects of plasma treatment on the electrical properties of low-k SiOCH films. Plasma treatment time changed from 300 to 1800 s. After treatment, the dielectric constant was decreased from 2.9 to 2.48, and the thickness of the low-k SiCOH films changed by only ∼5%. The leakage current densities of the low-k SiCOH films were decreased to ∼10{sup −11} A/cm{sup 2}, with treatment time ≥600 s. The breakdown occurred only around 2 V for films plasma-treated for 600 and 900 s. However, for 1800 s treatment time, the breakdown voltage was enhanced dramatically and breakdown occurred at applied voltage higher than 40 V. The surface composition change of the films after treatment was investigated by X-ray photoelectron spectroscopy (XPS). As the plasma treatment time was increased, the intensities of C-C/C-H and C-Si peaks were decreased while the intensities of Si-O and C-O peaks were increased. It is thought that increase of oxygen content of the SiCOH film, after plasma treatment, contributed to leakage current reduction and breakdown voltage increase.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Lignin decomposition is sustained under fluctuating redox conditions in humid tropical forest soils

Abstract Lignin mineralization represents a critical flux in the terrestrial carbon (C) cycle, yet little is known about mechanisms and environmental factors controlling lignin breakdown in mineral soils. Hypoxia is thought to suppress lignin decomposition, yet potential effects of oxygen (O 2 ) variability in surface soils have not been explored. Here, we tested the impact of redox fluctuations on lignin breakdown in humid tropical forest soils during ten‐week laboratory incubations. We used synthetic lignins labeled with 13 C in either of two positions (aromatic methoxyl or propyl side chain C β ) to provide highly sensitive and specific measures of lignin mineralization seldom employed in soils. Four‐day redox fluctuations increased the percent contribution of methoxyl C to soil respiration relative to static aerobic conditions, and cumulative methoxyl‐C mineralization was statistically equivalent under static aerobic and fluctuating redox conditions despite lower soil respiration in the latter treatment. Contributions of the less labile lignin C β to soil respiration were equivalent in the static aerobic and fluctuating redox treatments during periods of O 2 exposure, and tended to decline during periods of O 2 limitation, resulting in lower cumulative C β mineralization in the fluctuating treatment relative to the static aerobic treatment. However, cumulative mineralization of both the C β ‐ and methoxyl‐labeled lignins nearly doubled in the fluctuating treatment relative to the static aerobic treatment when total lignin mineralization was normalized to total O 2 exposure. Oxygen fluctuations are thought to be suboptimal for canonical lignin‐degrading microorganisms. However, O 2 fluctuations drove substantial Fe reduction and oxidation, and reactive oxygen species generated during abiotic Fe oxidation might explain the elevated contribution of lignin to C mineralization. Iron redox cycling provides a potential mechanism for lignin depletion in soil organic matter. Couplings between soil moisture, redox fluctuations, and lignin breakdown provide a potential link between climate variability and the biochemical composition of soil organic matter.

Hall, Steven J.↗
DOE OSTI2020

Chemical Modeling of the Capture of Radioiodine Species

Iodine is a common fission product resulting from the transmutation of uranium fuel in nuclear power reactors. The short-lived radioactive isotope, 131 I, with a half-life of around eight days, would be a particular health concern if released into the environment. Capture materials, such as activated carbon, are used routinely in nuclear power plants and medical isotope production facilities to remove this hazard during normal operations to reduce emissions to acceptable levels. Iodine, unlike other common fission products such as noble gases, is challenging because of the wide range of molecular forms and oxidation states (from +VII in IF 7 to -I in iodide) that it displays, which can interconvert both in the gas phase and in the solution phase for example. The work in this project is focused on three computational tasks. In the first, we consider the binding of iodine-containing molecules of varying oxidation states to the major component of activated carbon – pristine graphene-like sheets. The second task focused on molecular binding and possible chemical transformations resulting from the reaction of molecular iodine with chemical functional groups on the edge of the graphene sheets or surface defects in the sheet itself. The final task was associated with radiolytic breakdown of 131 I to 131 Xe in iodine containing molecules and investigated the resulting molecular fragmentation process both in the gas phase and on the graphene-like surface. For each of the tasks, the intent was to learn about the thermodynamics and kinetics of the chemical transformations and use the calculations to provide parameters for input into kinetic models describing these processes for interpretation of experimental data in future work.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2010

Nonstationary statistical theory for multipactor

This work presents a new and general approach to the real dynamics of the multipactor process: the nonstationary statistical multipactor theory. The nonstationary theory removes the stationarity assumption of the classical theory and, as a consequence, it is able to adequately model electron exponential growth as well as absorption processes, above and below the multipactor breakdown level. In addition, it considers both double-surface and single-surface interactions constituting a full framework for nonresonant polyphase multipactor analysis. This work formulates the new theory and validates it with numerical and experimental results with excellent agreement.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Structural properties of relaxed thin film germanium layers grown by low temperature RF-PECVD epitaxy on Si and Ge (100) substrates

We report on unusual low temperature (175 °C) heteroepitaxial growth of germanium thin films using a standard radio-frequency plasma process. Spectroscopic ellipsometry and transmission electron microscopy (TEM) reveal a perfect crystalline quality of epitaxial germanium layers on (100) c-Ge wafers. In addition direct germanium crystal growth is achieved on (100) c-Si, despite 4.2% lattice mismatch. Defects rising from Ge/Si interface are mostly located within the first tens of nanometers, and threading dislocation density (TDD) values as low as 10{sup 6} cm{sup −2} are obtained. Misfit stress is released fast: residual strain of −0.4% is calculated from Moiré pattern analysis. Moreover we demonstrate a striking feature of low temperature plasma epitaxy, namely the fact that crystalline quality improves with thickness without epitaxy breakdown, as shown by TEM and depth profiling of surface TDD.

36 MATERIALS SCIENCE↗
NASA NTRS1969

Effects of high-pressure hydrogen on storage vessel materials

Tensile tests on welded plates of three grades of steel indicate an appreciable decrease of tensile strength and ductility of notched specimens and a decrease in ductility of unnotched samples. Surface cracking, evident in unnotched specimens, is conducive to breakdown in tensile strength and ductility.

Chandler, W. T.↗
NASA NTRS1976

Time-dependent MOS breakdown

A general model for time-dependent breakdown in metal-oxide-silicon (MOS) structures is developed and related to experimental measurements on samples deliberately contaminated with Na. A statistical method is used for measuring the breakdown probability as a function of log time and applied field. It is shown that three time regions of breakdown can be explained respectively in terms of silicon surface defects, ion emission from the metal interface, and lateral ion diffusion at the silicon interface.

Li, S. P.↗
NASA NTRS1988

Navier-Stokes computation of flow around a round-edged double-delta wing

Computations of three-dimensional vortical flows over a thin round-edged double-delta wing with an aspect ratio of 2.05 are performed using an implicit upwind-relaxation finite-difference scheme. The effects of grid and angle of attack on the Navier-Stokes computations are studied. Coarse-grid calculations can not predict the detailed structures of the vortical flowfields for lack of grid resolution. On the contrary, fine-grid computations show that key features of vortex formation, interaction, and breakdown are simulated. Furthermore, computed lift coefficients and spanswise surface static pressure distributions are in good agreement with the experimental data up to alpha = 25 deg.

Hsu, C.-H.↗
NASA NTRS1989

An experimental investigation of delta wing vortex flow with and without external jet blowing

A visual and quantitative study of the vortex flow field over a 70-deg delta wing with an external jet blowing parallel to and at the leading edge was conducted. In the experiment, the vortex core was visually marked with TiCl4, and LDA was used to measure the velocity parallel and normal to the wing surface. It is found that jet blowing moved vortex breakdown farther downstream from its natural position and influenced the breakdown characteristics.

Iwanski, Kenneth P.↗
DOE OSTI2015

Progressive failure site generation in AlGaN/GaN high electron mobility transistors under OFF-state stress: Weibull statistics and temperature dependence

Gate leakage degradation of AlGaN/GaN high electron mobility transistors under OFF-state stress is investigated using a combination of electrical, optical, and surface morphology characterizations. The generation of leakage “hot spots” at the edge of the gate is found to be strongly temperature accelerated. The time for the formation of each failure site follows a Weibull distribution with a shape parameter in the range of 0.7–0.9 from room temperature up to 120 °C. The average leakage per failure site is only weakly temperature dependent. The stress-induced structural degradation at the leakage sites exhibits a temperature dependence in the surface morphology, which is consistent with a surface defect generation process involving temperature-associated changes in the breakdown sites.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2018

Determination of Trace Silicone Contamination on Composites by Quantitative XPS and LIBS

Surface treatment and surface characterization techniques are critical to ensure that adherends are chemically activated and free of contaminants prior to adhesive bonding. Silicone contamination from mold-release agents and other sources can interfere with interfacial bonding, decreasing the durability and performance of bonded composite structures. Tools and methods are needed that can be used in a production environment to reliably detect low levels of contaminants in a rapid, simple, and cost-effective manner to improve bond reliability. In this work, surface characterization of carbon fiber reinforced polymer (CFRP) composites was performed using laser induced breakdown spectroscopy (LIBS) and the results were compared with those obtained from X-ray photoelectron spectroscopy (XPS). The objective was to investigate the ability to quantify the surface species measured by LIBS since it offers many advantages over XPS in terms of ease of use, sample preparation, and real-time results. The as-processed CFRP panels had trace surface silicone contamination from the fabrication process, the source of which was not investigated. The composites were laser treated at select average laser power levels, resulting in varying levels of contamination reduction. The Si atomic percentage measurements using XPS were conducted both before and after laser ablation. The XPS results were compared with those obtained from LIBS to assess the reliability of each technique for surface contaminant characterization. The results showed an excellent correlation in Si atomic concentration between the two techniques.

Ledesma, Rodolfo↗
DOE OSTI2010

Analysis of material collected on swipes using laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) was evaluated to determine elements collected on swipes as surface contamination. A series of long laser plasmas formed along the swipe surface (Post-it paper) interrogated the collected contamination. LIBS detection limits, determined for the elements Ag, As, Ba, Be, Cd, Cr, Cu, Hg, Mn, Ni, Pb, Sr, and Zn on swipes (2 cm{sup 2} area), ranged from 0.002 {mu}g (Be) to 1.46 {mu}g (Pb). The elements were introduced as constituents of synthetic silicate particles serving as a contaminant dust stimulant. The average predicted mass was within 16% of the actual mass on the swipe. The efficiency of collecting particles from surfaces including plastic, Formica, and Al metal was also evaluated. The ability to detect and differentiate two amino acids on a swipe from each other and from the swipe using chemometric modeling techniques was also demonstrated.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2010

Experimental Study of Local Micro-forming for Bi-HTS

The Bi-HTS (BSCCO high temperature superconductor) tape now has become the product in an industrial way, which has been available to apply in electric and electron fields. The main way to manufacture Bi-HTS tape is to use the technique of oxide powder in silver tube (OPIT), which involves the multi-step drawing and rolling with plastic deformation, which obviously belongs to a type of the micro-forming in macro-scale processing. There are two main characteristics founded: (a) contact and friction between silver and BSCCO surfaces, (b) interface between two materials. A series of micro-tensile experiments of silver foil with thicknesses of 0.03, 0.06 and 0.1 mm are designed to investigate the behaviors of silver with various scale of sizes. And the surface topography measurements have been carried out to analyze the changes in surface topography. Based upon experiments, some topics are researched which are referred to inhomogeneous, local effect, size effect, grain and micro-structure affecting, surface roughness, long-distance sausage phenomenon. Further the local breakdown of silver by Bi-HTS powder during process is analyzed through failure criterion. The results of this work will bring out an important exploration value to the theory and computation of micro-forming.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Properties of polycarbonate containing BaTiO{sub 3} nanoparticles

The real part of the relative permittivity, ε′, and dielectric loss, tan δ, have been determined at audio frequencies at temperatures from about 5 K to 350 K for nano-composites composed of BaTiO{sub 3} nanoparticles and polycarbonate. The room temperature breakdown strength was also measured and thermal analysis, nuclear magnetic resonance and scanning electron microscopy studies were carried out. For some films the nanoparticles were surface-treated (STNP) while for others they were not (UNP). For concentrations of UNP greater than about 3.4 vol. %, ε′ is much larger than expected on the basis of laws of mixing. On the other hand, ε′ for materials made using STNP is well-behaved. Correspondingly, increased loss (ε″ or tan δ) in the vicinity of room temperature is observed for the materials made from UNP. The anomalously large values of relative permittivity and increased loss are attributed to the presence of large aggregates in the materials made using the UNP. For both UNP-and STNP-based materials, the breakdown strength is found to decrease as nanoparticle concentration increases. The breakdown strength for the materials made using STNP is found to be larger for all concentrations than for those containing UNP despite the presence of large aggregates in some of the STNP-based materials. This shows that breakdown is strongly affected by the nanoparticle surfaces and/or the interface layer. It is also found that the breakdown strength for materials made using UNP increases as particle size increases. Finally, variable temperature and pressure proton nuclear magnetic resonance relaxation measurements were made to assess the effect of nanoparticle inclusion on polymer motion, and the effects were found to be very minor.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Photoemission Induced Plasma Breakdown (Update)

Laser-induced photoemission of electrons offers opportunities to trigger and control plasmas and discharges. However, the underlying mechanisms are not sufficiently characterized to be fully utilized. Photoemission is highly nonlinear, achieved through multiphoton absorption, above threshold ionization, photo-assisted tunneling, etc., where the dominant process depends on the work function of the material, photon energy and associated fields, surface heating, background fields, etc. To characterize the effects of photoemission on breakdown, breakdown experiments were performed and interpreted using a 0D plasma discharge circuit model and quantum model of photoemission.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗