Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “molecular electronics”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

WF/PC internal molecular contamination during system thermal-vacuum test

During the recent system thermal vacuum test of the Wide-Field/Planetary Camera (WF/PC), instrumentation was added to the WF/PC to characterize the internal molecular contamination and verify the instrument throughput down to 1470 angstroms. Analysis of data elements revealed two contaminants affecting the far-ultraviolet (FUV) performance of the WF/PC. The one contaminant (heavy volatile) is correlated with the electronic and housing temperature, and the contamination is significantly reduced when the electronics are operated below plus 8 degrees to plus 10 degrees C. The other contaminant (light volatile) is controlled by the heat pipe temperature, and the contamination is significantly reduced when the Thermal Electric Cooler (TEC) hot-junction temperature is below minus 40 degrees to minus 50 degrees C. The utility of contamination sensors located behind instruments during system tests was demonstrated.

Taylor, Daniel M.↗
NASA NTRS2012

Negative Ion Chemistry in the Coma of Comet 1P/Halley

Negative ions (anions) were identified in the coma of comet 1P/Halley from in-situ measurements performed by the Giotto spacecraft in 1986. These anions were detected with masses in the range 7-110 amu, but with insufficient mass resolution to permit unambiguous identification. We present details of a new chemical-hydrodynamic model for the coma of comet Halley that includes - for the first time - atomic and molecular anions, in addition to a comprehensive hydrocarbon chemistry. Anion number densities arc calculated as a function of radius in the coma, and compared with the Giotto results. Important anion production mechanisms arc found to include radiative electron attachment, polar photodissociation, dissociative electron attachment, and proton transfer. The polyyne anions C4H(-) and C6H(-) arc found to be likely candidates to explain the Giotto anion mass spectrum in the range 49-73 amu. Thc CN(-) anion probably makes a significant contribution to the mass spectrum at 26 amu. Larger carbon-chain anions such as C8H(1) can explain the peak near 100 amu provided there is a source of large carbon-chain-bearing molecules from the cometary nucleus.

Cordiner, M. A.↗
NASA NTRS1989

Growth of single-crystal columns of CoSi2 embedded in epitaxial Si on Si(111) by molecular beam epitaxy

The codeposition of Si and Co on a heated Si(111) substrate is found to result in epitaxial columns of CoSi2 if the Si:Co ratio is greater than approximately 3:1. These columns are surrounded by an Si matrix which shows bulk-like crystalline quality based on transmission electron microscopy and ion channeling. This phenomenon has been studied as functions of substrate temperature and Si:Co ratio. Samples with columns ranging in average diameter from approximately 25 to 130 nm have been produced.

Fathauer, R. W.↗
NASA NTRS1993

Relation between bond-length alternation and second electronic hyperpolarizability of conjugated organic molecules

The solvent dependence of the second hyperpolarizability, gamma, of a variety of unsaturated organic compounds has been measured by third harmonic generation at 1907 nanometers. It is seen that the measured gamma is a function of solvent polarity. These solvent-dependent hyperpolarizabilities are associated with changes in molecular geometry from a highly bond-length alternated, polyenelike structure for a formyl-substituted compound in nonpolar solvents, to a cyaninelike structure, with little bond-length alternation, for a dicyanovinyl-substituted compound in polar solvents. By tuning bond-length alternation, gamma can be optimized in either a positive or negative sense for polymethine dyes of a given conjugation length.

Marder, Seth R.↗
NASA NTRS1981

Low-energy charged particles in Saturn's magnetosphere - Results from Voyager 1

The Voyager 1 low-energy charged particle instrument measured electrons and ions with energies below 26 and 40 kiloelectron volts, respectively, in the Saturn magnetosphere. Spectra of all ion species were found to have an energy cutoff at levels greater than 2 million electron volts. In contrast to the magnetospheres of Jupiter and earth, there are no lobe regions essentially devoid of particles in Saturn's nighttime magnetosphere. One novel feature of the Saturn magnetosphere is a pervasive population of energetic molecular hydrogen.

Krimigis, S. M.↗
NASA NTRS1982

An investigation of the kinetics of hydrogen chemisorption on iron metal surfaces

The isothermal kinetics of H2, H2S, and O2 chemisorption onto epitaxially grown (III) oriented Fe films were studied. The measurements were made using the techniques of chemisorption induced resistance change and Auger electron spectroscopy (for adsorbed sulfur and oxygen). Also the origin of the chemisorption induced resistance change for these systems and its applicability to kinetic measurements were established. The chemisorption kinetics were interpreted as dissociative chemisorption via an adsorbed molecular species. The applicable rate constants were established. In none of the studies were the rate constants observed to be coverage dependent. By comparing the temperature dependence of the rate constants with absolute rate theory, the binding energies and activation energies of all the kinetic processes were obtained for the H2/Fe system. The initial sticking coefficient was pressure dependent for both the H2/Fe and H2S/Fe systems. This results from the step between the adsorbed molecular state and the dissociated chemisorbed state being the rate limiting step for absorption at certain pressures and temperatures. Estimates were obtained for the temperature dependence of the rate constants for the O2/Fe system.

Shanabarger, M. R.↗
NASA NTRS1993

DSMC and continuum analyses of low-density nozzle flow

Two different approaches, the direct-simulation Monte Carlo (DSMC) method based on molecular gas dynamics and a finite-volume approximation of the Navier-Stokes equations, which are based on continuum gas dynamics, are employed in the analysis of a low-density gas flow in a small converging-diverging nozzle. The fluid experiences various kinds of flow regimes including continuum, slip, transition, and free-molecular. Results from the two numerical methods are compared with Rothe's experimental dam, in which density and rotational temperature variations along the centerline and at various locations inside a low density nozzle were measured by the electron-beam fluorescence technique. The continuum approach showed good agreement with the experimental data as far as density is concerned. The results from the DSMC method showed good agreement with the experimental data both in the density and the rotational temperature. It is also shown that the simulation parameters, such as the gas/surface interaction model, the energy exchange model between rotational and translational modes, and the viscosity temperature exponent, have substantial effects on the results of the DSMC method.

Chung, Chan-Hong↗
NASA NTRS2003

Polyimide Nanocomposites Prepared from High-Temperature, Reduced Charge Organoclays

Montmorillonite clays modified with the dihydrochloride salt of 1,3-bis(3-aminophenoxy)benzene (APB) were used in the preparation of polyimide/organoclay hybrid films. Organoclays with varying surface charge based upon APB were prepared and examined for their dispersion behavior in the polymer matrix. High molecular weight poly(amide acid) solutions were prepared in the presence of the organoclays. Films were cast and subsequently heated to 300C to cause imidization. The resulting nanocomposite films, containing 3 wt% of organoclay, were characterized by transmission electron microscopy and X-ray diffraction. The clay's cation exchange capacity (CEC) played a key role in determining the extent of dispersion in the polyimide matrix. Considerable dispersion was observed in some of the nanocomposite films. The most effective organoclay was found to have a CEC of 0.70 meq/g. Nanocomposite films prepared with 3-8 wt% of this organoclay were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and thin-film tensile testing. High levels of clay dispersion could be achieved even at the higher clay loadings. Results from mechanical testing revealed that while the moduli of the nanocomposites increased with increasing clay loadings, both strength and elongation decreased.

Delozier, D. M.↗
NASA NTRS2010

Radiation Environment and Surface Radiolytic Interactions at Mimas

Saturn's innermost principal moon Mimas shares the distinction with Europa at Jupiter of being the most irradiated icy moon in its respective planetary system, although the energetic electron energy flux at Mimas is forty times smaller than at Europa. High energy (> 10 MeV) proton fluxes are low in this moon's orbital corridor, likely since slowly diffusing protons from the weak but steady source of cosmic ray albedo neutron decay (CRAND) cannot accumulate without impacting the moon surface. Lower energy proton fluxes are also evidently suppressed in this orbital region. Plasma ion and electron fluxes are also low apparently due to cooling by interaction with E-ring dust and neutral gas from Enceladus. Due to energy-dependent effects of longitudinal gradient-curvature drift for the electrons, the trailing hemisphere is mainly irradiated by electrons at energies below 1 MeV that drift relative to Mimas in the prograde direction of orbital motion around Saturn, while higher energy electrons primarily impact the leading hemisphere. Plasma ions in the inner magnetosphere of Saturn are mainly pickup ions forming from the dissociation products of Enceladus plume water molecules, additionally including some contribution from photosputtering of the main rings, and do not introduce new elemental materials at Mimas via surface implantation from the corotating plasma. Thus the primary interaction at the surface is radiolytic chemistry induced in pure water ice by relatively deep penetration of the energetic electrons to millimeter and greater depths, as compared to the micron depths impacted by the corotating plasma ions. If surface erosion by sputtering from relatively low fluxes of the plasma and more energetic ions is indeed ineffective, then molecular products (OH, H2O2, 02, 03) of the radiolytic interactions may accumulate in the meters-deep impact regolith of the surface ices. An effect of regolith trapped gas accumulation could be to increase porosity and reduce thermal conductivity of the ice, potentially contributing to reported thermal anomalies from Cassini infrared map observations. Low amplitude of trailing-leading asymmetry in optical albedo and color maps at Mimas is suggestive of relative weakness of asymmetrical effects from low-energy ions. Greater induced asymmetries are expected and observed for the moons beyond Enceladus in the middle magnetospheric region of hot plasma ions at much greater fluxes than at Mimas. Low density (1.15 g/cc) of this moon indicates paucity of mineral salts and radiogenic heating to maintain subsurface liquids, so Enceladus-like cryovolcanism as a resurfacing process is unlikely despite closer proximity to Saturn, greater tidal forcing, and more intense surface irradiation than for Enceladus.

Cooper, J. F.↗
NASA NTRS2012

Low-Cost, Rugged High-Vacuum System

A need exists for miniaturized, rugged, low-cost high-vacuum systems. Recent advances in sensor technology have led to the development of very small mass spectrometer detectors as well as other analytical instruments such as scanning electron microscopes. However, the vacuum systems to support these sensors remain large, heavy, and power-hungry. To meet this need, a miniaturized vacuum system was developed based on a very small, rugged, and inexpensive-to-manufacture molecular drag pump (MDP). The MDP is enabled by a miniature, very-high-speed (200,000 rpm), rugged, low-power, brushless DC motor optimized for wide temperature operation and long life. The key advantages of the pump are reduced cost and improved ruggedness compared to other mechanical hig-hvacuum pumps. The machining of the rotor and stators is very simple compared to that necessary to fabricate rotor and stator blades for other pump designs. Also, the symmetry of the rotor is such that dynamic balancing of the rotor will likely not be necessary. Finally, the number of parts in the unit is cut by nearly a factor of three over competing designs. The new pump forms the heart of a complete vacuum system optimized to support analytical instruments in terrestrial applications and on spacecraft and planetary landers. The MDP achieves high vacuum coupled to a ruggedized diaphragm rough pump. Instead of the relatively complicated rotor and stator blades used in turbomolecular pumps, the rotor in the MDP consists of a simple, smooth cylinder of aluminum. This will turn at approximately 200,000 rpm inside an outer stator housing. The pump stator comprises a cylindrical aluminum housing with one or more specially designed grooves that serve as flow channels. To minimize the length of the pump, the gas is forced down the flow channels of the outer stator to the base of the pump. The gas is then turned and pulled toward the top through a second set of channels cut into an inner stator housing that surrounds the motor. The compressed gas then flows down channels in the motor housing to the exhaust port of the pump. The exhaust port of the pump is connected to a commercially available diaphragm or scroll pump.

Sorensen, Paul↗
NASA NTRS2014

Modeling Materials: Design for Planetary Entry, Electric Aircraft, and Beyond

NASA missions push the limits of what is possible. The development of high-performance materials must keep pace with the agency's demanding, cutting-edge applications. Researchers at NASA's Ames Research Center are performing multiscale computational modeling to accelerate development times and further the design of next-generation aerospace materials. Multiscale modeling combines several computationally intensive techniques ranging from the atomic level to the macroscale, passing output from one level as input to the next level. These methods are applicable to a wide variety of materials systems. For example: (a) Ultra-high-temperature ceramics for hypersonic aircraft-we utilized the full range of multiscale modeling to characterize thermal protection materials for faster, safer air- and spacecraft, (b) Planetary entry heat shields for space vehicles-we computed thermal and mechanical properties of ablative composites by combining several methods, from atomistic simulations to macroscale computations, (c) Advanced batteries for electric aircraft-we performed large-scale molecular dynamics simulations of advanced electrolytes for ultra-high-energy capacity batteries to enable long-distance electric aircraft service; and (d) Shape-memory alloys for high-efficiency aircraft-we used high-fidelity electronic structure calculations to determine phase diagrams in shape-memory transformations. Advances in high-performance computing have been critical to the development of multiscale materials modeling. We used nearly one million processor hours on NASA's Pleiades supercomputer to characterize electrolytes with a fidelity that would be otherwise impossible. For this and other projects, Pleiades enables us to push the physics and accuracy of our calculations to new levels.

Supercomputing↗
NASA NTRS2003

Bacillus nealsonii sp. nov., isolated from a spacecraft-assembly facility, whose spores are gamma-radiation resistant

One of the spore-formers isolated from a spacecraft-assembly facility, belonging to the genus Bacillus, is described on the basis of phenotypic characterization, 16S rDNA sequence analysis and DNA-DNA hybridization studies. It is a Gram-positive, facultatively anaerobic, rod-shaped eubacterium that produces endospores. The spores of this novel bacterial species exhibited resistance to UV, gamma-radiation, H2O2 and desiccation. The 18S rDNA sequence analysis revealed a clear affiliation between this strain and members of the low G+C Firmicutes. High 16S rDNA sequence similarity values were found with members of the genus Bacillus and this was supported by fatty acid profiles. The 16S rDNA sequence similarity between strain FO-92T and Bacillus benzoevorans DSM 5391T was very high. However, molecular characterizations employing small-subunit 16S rDNA sequences were at the limits of resolution for the differentiation of species in this genus, but DNA-DNA hybridization data support the proposal of FO-92T as Bacillus nealsonii sp. nov. (type strain is FO-92T =ATCC BAAM-519T =DSM 15077T).

Non-programmatic↗
NASA NTRS1978

A theoretical study of the electronic transition moment for the C2 Swan band system

Large-scale self-consistent-field plus configuration-interaction calculations have been performed for the a 3Pi u and d 3Pi g states of C2. The theoretical potential curves are in good agreement with those found by a Klein-Dunham analysis of measured molecular constants in terms of shape and excitation energy. The sum of the squares of the theoretical transition moments between the states at 2.44 bohr is 4.12 a.u. which agrees with the results of shock tube measurements. The variation in the sum of the squares of the theoretical moments with internuclear separation agrees with the values of Danylewych and Nicholls (1974). Based on the data for C2 and mother molecules, it is suggested that CI calculations using near Hartree-Fock quality Slater basis sets produce highly reliable transition moments.

Arnold, J. O.↗
NASA NTRS1975

Theoretical and experimental studies in ultraviolet solar physics

The processes and parameters in atomic and molecular physics that are relevant to solar physics are investigated. The areas covered include: (1) measurement of atomic and molecular parameters that contribute to discrete and continous sources of opacity and abundance determinations in the sun; (2) line broadening and scattering phenomena; and (3) development of an ion beam spectroscopic source which is used for the measurement of electron excitation cross sections of transition region and coronal ions.

Parkinson, W. H.↗
NASA NTRS1985

Development of an apparatus for obtaining molecular beams in the energy range from 2 to 200 eV

The formation and detection of molecular beams obtained by charge exchange from a low-energy ion source is discussed. Dispersion in energy of the ion source was measured and problems concerning detection of neutral beams were studied. Various methods were used, specifically secondary electron emissivity of a metallic surface and ionization of a gas target with a low ionization voltage. The intensities of neutral beams as low as 10 eV are measured by a tubular electron multiplier and a lock-in amplifier.

Clapier, R.↗
NASA NTRS1993

Fabrication of photovoltaic laser energy converterby MBE

A laser-energy converter, fabricated by molecular beam epitaxy (MBE), was developed. This converter is a stack of vertical p-n junctions connected in series by low-resistivity, lattice matched CoSi2 layers to achieve a high conversion efficiency. Special high-temperature electron-beam (e-beam) sources were developed especially for the MBE growth of the junctions and CoSi2 layers. Making use of the small (greater than 1.2 percent) lattice mismatch between CoSi2 and Si layers, high-quality and pinhole-free epilayers were achieved, providing a capability of fabricating all the junctions and connecting layers as a single growth process with one pumpdown. Well-defined multiple p-n junctions connected by CoSi2 layers were accomplished by employing a low growth temperature (greater than 700 C) and a low growth rate (less than 0.5 microns/hour). Producing negligible interdiffusion, the low growth temperature and rate also produced negligible pinholes in the CoSi2 layers. For the first time, a stack of three p-n junctions connected by two 10(exp -5) Ohm-cm CoSi2 layers was achieved, meeting the high conversion efficiency requirement. This process can now be optimized for high growth rate to form a practical converter with 10 p-n junctions in the stack.

Lu, Hamilton↗
NASA NTRS1994

Low-Density Nozzle Flow by the Direct Simulation Monte Carlo and Continuum Methods

Two different approaches, the direct simulation Monte Carlo (DSMC) method based on molecular gasdynamics, and a finite-volume approximation of the Navier-Stokes equations, which are based on continuum gasdynamics, are employed in the analysis of a low-density gas flow in a small converging-diverging nozzle. The fluid experiences various kinds of flow regimes including continuum, slip, transition, and free-molecular. Results from the two numerical methods are compared with Rothe's experimental data, in which density and rotational temperature variations along the centerline and at various locations inside a low-density nozzle were measured by the electron-beam fluorescence technique. The continuum approach showed good agreement with the experimental data as far as density is concerned. The results from the DSMC method showed good agreement with the experimental data, both in the density and the rotational temperature. It is also shown that the simulation parameters, such as the gas/surface interaction model, the energy exchange model between rotational and translational modes, and the viscosity-temperature exponent, have substantial effects on the results of the DSMC method.

Chung, Chang-Hong↗