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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Synthesis and Photoluminescent Properties of Arylethynyl substituted 9,10-Anthraquinones

A series of arylethynyl substituted anthraquinones were synthesized via Sonogashira coupling reactions of 2,7- dibromo-, 2,6-dibromo- and 2-bromoanthraquinone with para-substituted phenylacetylenes. While the redox properties of those compounds are almost insensitive to substitution, their absorption maxima are linearly related to the Hammett constants for electron donating and electron withdrawing groups separately. All compounds are photoluminescent both in solution (quantum yield of emission approximately 2%) and as solids. X-ray crystallographic characterization of 2,7-bisphenylethynyl anthraquinone indicates a monoclinic p2(l/n) space group and no indication for pi-overlap that would promote self-quenching. The emission maxima are red- shifted by both electron donating and electron withdrawing groups alike. The Stokes shifts of all compounds are significant and are correlated to the electronic properties of the substituents. The reduced forms of these compounds are also photoluminescent and the emission originates from the dihydroanthraquinone core.

Yang, Jin-Hua↗
NASA NTRS2016

Nanomaterial Based Sensors for NASA Missions

Nanomaterials such as carbon nanotubes (CNTs), carbon nanofibers (CNFs), graphene and metal nanowires have shown interesting electronic properties and therefore have been pursued for a variety of space applications requiring ultrasensitive and light-weight sensor and electronic devices. We have been pursuing development of chemical and biosensors using carbon nanotubes and carbon nanofibers for the last several years and this talk will present the benefits of nanomaterials these applications. More recently, printing approaches to manufacturing these devices have been explored as a strategy that is compatible to a microgravity environment. Nanomaterials are either grown in house or purchased and processed as electrical inks. Chemical modification or coatings are added to the nanomaterials to tailor the nanomaterial to the exact application. The development of printed chemical sensors and biosensors will be discussed for applications ranging from crew life support to exploration missions.

sensors↗
NASA NTRS1972

Average thermal characteristics of solar wind electrons

Average solar wind electron properties based on a 1 year Vela 4 data sample-from May 1967 to May 1968 are presented. Frequency distributions of electron-to-ion temperature ratio, electron thermal anisotropy, and thermal energy flux are presented. The resulting evidence concerning heat transport in the solar wind is discussed.

Montgomery, M. D.↗
NASA NTRS2006

Carbon-Nanotube Schottky Diodes

Schottky diodes based on semiconducting single-walled carbon nanotubes are being developed as essential components of the next generation of submillimeter-wave sensors and sources. Initial performance predictions have shown that the performance characteristics of these devices can exceed those of the state-of-the-art solid-state Schottky diodes that have been the components of choice for room-temperature submillimeter-wave sensors for more than 50 years. For state-of-the-art Schottky diodes used as detectors at frequencies above a few hundred gigahertz, the inherent parasitic capacitances associated with their semiconductor junction areas and the resistances associated with low electron mobilities limit achievable sensitivity. The performance of such a detector falls off approximately exponentially with frequency above 500 GHz. Moreover, when used as frequency multipliers for generating signals, state-of-the-art solid-state Schottky diodes exhibit extremely low efficiencies, generally putting out only micro-watts of power at frequencies up to 1.5 THz. The shortcomings of the state-of-the-art solid-state Schottky diodes can be overcome by exploiting the unique electronic properties of semiconducting carbon nanotubes. A single-walled carbon nanotube can be metallic or semiconducting, depending on its chirality, and exhibits high electron mobility (recently reported to be approx.= 2x10(exp 5)sq cm/V-s) and low parasitic capacitance. Because of the narrowness of nanotubes, Schottky diodes based on carbon nanotubes have ultra-small junction areas (of the order of a few square nanometers) and consequent junction capacitances of the order of 10(exp -18) F, which translates to cutoff frequency >5 THz. Because the turn-on power levels of these devices are very low (of the order of nano-watts), the input power levels needed for pumping local oscillators containing these devices should be lower than those needed for local oscillators containing state-of-the-art solid-state Schottky diodes.

Manohara, Harish↗
NASA NTRS1995

Applications of Silicon Carbide for High Temperature Electronics and Sensors

Silicon carbide (SiC) is a wide bandgap material that shows great promise in high-power and high temperature electronics applications because of its high thermal conductivity and high breakdown electrical field. The excellent physical and electronic properties of SiC allows the fabrication of devices that can operate at higher temperatures and power levels than devices produced from either silicon or GaAs. Although modern electronics depends primarily upon silicon based devices, this material is not capable of handling may special requirements. Devices which operate at high speeds, at high power levels and are to be used in extreme environments at high temperatures and high radiation levels need other materials with wider bandgaps than that of silicon. Many space and terrestrial applications also have a requirement for wide bandgap materials. SiC also has great potential for high power and frequency operation due to a high saturated drift velocity. The wide bandgap allows for unique optoelectronic applications, that include blue light emitting diodes and ultraviolet photodetectors. New areas involving gas sensing and telecommunications offer significant promise. Overall, the properties of SiC make it one of the best prospects for extending the capabilities and operational regimes of the current semiconductor device technology.

Silicon Carbide↗
NASA NTRS2002

Effects of Structural Deformation and Tube Chirality on Electronic Conductance of Carbon Nanotubes

A combination of large scale classical force-field (UFF), density functional theory (DFT), and tight-binding Green's function transport calculations is used to study the electronic properties of carbon nanotubes under the twist, bending, and atomic force microscope (AFM)-tip deformation. We found that in agreement with experiment a significant change in electronic conductance can be induced by AFM-tip deformation of metallic zigzag tubes and by twist deformation of armchair tubes. The effect is explained in terms of bandstructure change under deformation.

Svizhenko, Alexei↗
NASA NTRS1979

A theory of local and global processes which affect solar wind electrons. 2: Experimental support

The microscopic characteristics of the Coulomb cross section show that there are three natural subpopulations for plasma electrons: the subthermals with local kinetic energy E kT sub c; the transthermals with kT sub c E 7 kT sub c and the extrathermals E 7 kT sub c. Data from three experimental groups on three different spacecraft in the interplanetary medium over a radial range are presented to support the five interrelations projected between solar wind electron properties and changes in the interplanetary medium: (1) subthermals respond primarily to local changes (compression and rarefactions) in stream dynamics; (2) the extrathermal fraction of the ambient electron density should be anti-correlated with the asymptotic bulk speed; (3) the extrathermal "temperature" should be anti-correlated with the local wind speed at 1 AU; (4) the heat flux carried by electrons should be anti-correlated with the local bulk speed; and (5) the extrathermal differential 'temperature' should be nearly independent of radius within 1 AU.

Scudder, J. D.↗
NASA NTRS1994

Geometry and Unoccupied Electronic States of Ba and BaO on W(001)

A study aimed at understanding the geometrical and electronic properties of barium and oxygen coadsorbed on the tungsten(001) surface has been carried out by means of work-function measurements (Delta-phi), Auger-electron spectroscopy, low-energy electron diffraction, inverse photoelectron spectroscopy, and relativistic-electronic-structure calculations. A report of the experimental measurements and a comparison with theoretical results from embedded-cluster-model calculations are presented. Our experimental studies show that the work function of the W(001) surface (phi = 4.63 eV) is lowered to approximately 2.3-2.4 eV by coadsorption of 1 ML of Ba and O regardless of the order of deposition of these two species. The technique of IPS in the isochromat mode was used to determine the unoccupied electronic-energy band structure for ordered c (2 X 2) Ba and O layers on W(001). Several spectral features are observed above the Fermi level (E(F)), which we assign to transitions into Ba and W d-states. The measured two-dimensional electronic band structure is independent of the order of Ba and O deposition. Using embedded-cluster-model calculations, we investigated two possible adsorption configurations of an ordered c(2 X 2) adlayer of Ba and O on W(001): 'tilted,' where Ba and O are placed on alternate fourfold-hollow sites, and 'upright,' where the adsorbed atoms lay above the same site with Ba outer-most. The calculated densities of states for the tilted geometry show distinct peaks above E(F) originating from Ba and W d-orbitals and are in good agreement with the experimental results.

Lamouri, A.↗
NASA NTRS2005

Thermal Characterization of Fe3O4 Nanoparticles Formed from Poorly Crystalline Siderite

Increasing interest in environmental geochemistry has led to the recognition that crystals with sizes in the nanometer range (e.g., colloids and nanoscale precipitates) and poorly crystalline compounds (e.g., ferrihydrites) may comprise the majority of reactive mineral surface area near the Earth s surface. When the diameters of individual particles are in the range of 100 nm or less, the surface energy contribution to the free energy modifies phase stability. This results in stabilization of polymorphs not normally encountered in the macrocrystal domain. These phases potentially have very different surface-site geometries, adsorptive properties, and growth mechanisms, and exhibit size-dependent kinetic behavior. Thus nanophases dramatically modify the physical and chemical properties of soils and sediments. In a more general sense, the characteristics of nanocrystals are of intense technological interest because small particle size confers novel chemical, optical, and electronic properties. Thus, nanocrystalline materials are finding applications as catalytic substrates, gas phase separation materials, and even more importantly in the field of medicine. This is an opportune time for mineral physicists working on nanocrystalline materials to develop collaborative efforts with materials scientists, chemists, and others working on nanophase materials of technological interest (e.g., for magnetic memories). Our objective in this study was to synthesize submicron (<200 nm) magnetite and to study their thermal and particle size properties.

Lauer, H. V., Jr.↗
NASA NTRS2003

5' modification of duplex DNA with a ruthenium electron donor-acceptor pair using solid-phase DNA synthesis

Incorporation of metalated nucleosides into DNA through covalent modification is crucial to measurement of thermal electron-transfer rates and the dependence of these rates with structure, distance, and position. Here, we report the first synthesis of an electron donor-acceptor pair of 5' metallonucleosides and their subsequent incorporation into oligonucleotides using solid-phase DNA synthesis techniques. Large-scale syntheses of metal-containing oligonucleotides are achieved using 5' modified phosporamidites containing [Ru(acac)(2)(IMPy)](2+) (acac is acetylacetonato; IMPy is 2'-iminomethylpyridyl-2'-deoxyuridine) (3) and [Ru(bpy)(2)(IMPy)](2+) (bpy is 2,2'-bipyridine; IMPy is 2'-iminomethylpyridyl-2'-deoxyuridine) (4). Duplexes formed with the metal-containing oligonucleotides exhibit thermal stability comparable to the corresponding unmetalated duplexes (T(m) of modified duplex = 49 degrees C vs T(m) of unmodified duplex = 47 degrees C). Electrochemical (3, E(1/2) = -0.04 V vs NHE; 4, E(1/2) = 1.12 V vs NHE), absorption (3, lambda(max) = 568, 369 nm; 4, lambda(max) = 480 nm), and emission (4, lambda(max) = 720 nm, tau = 55 ns, Phi = 1.2 x 10(-)(4)) data for the ruthenium-modified nucleosides and oligonucleotides indicate that incorporation into an oligonucleotide does not perturb the electronic properties of the ruthenium complex or the DNA significantly. In addition, the absence of any change in the emission properties upon metalated duplex formation suggests that the [Ru(bpy)(2)(IMPy)](2+)[Ru(acac)(2)(IMPy)](2+) pair will provide a valuable probe for DNA-mediated electron-transfer studies.

Non-NASA Center↗
NASA NTRS2013

Energy Band Gap Study of Semiconducting Single Walled Carbon Nanotube Bundle

The electronic properties of multiple semiconducting single walled carbon nanotubes (s-SWCNTs) considering various distribution inside a bundle are studied. The model derived from the proposed analytical potential function of electron density for na individual s-SWCNT is general and can be easily applied to multiple nanotubes. This work demonstrates that regardless the number of carbon nanotubes, the strong coupling occurring between the closet neighbors reduces the energy band gap of the bundle by 10%. As expected, the coupling is strongly dependent on the distance separating the s-SWCNTs. In addition, based on the developed model, it is proposed to enhance this coupling effect by applying an electric field across the bundle to significantly reduce the energy band gap of the bundle by 20%.

semiconducting single-wall carbon nanotube↗
NASA NTRS1987

Plasma properties in electron-bombardment ion thrusters

The paper describes a technique for computing volume-averaged plasma properties within electron-bombardment ion thrusters, using spatially varying Langmuir-probe measurements. Average values of the electron densities are defined by integrating the spatially varying Maxwellian and primary electron densities over the ionization volume, and then dividing by the volume. Plasma properties obtained in the 30-cm-diameter J-series and ring-cusp thrusters are analyzed by the volume-averaging technique. The superior performance exhibited by the ring-cusp thruster is correlated with a higher average Maxwellian electron temperature. The ring-cusp thruster maintains the same fraction of primary electrons as does the J-series thruster, but at a much lower ion production cost. The volume-averaged predictions for both thrusters are compared with those of a detailed thruster performance model.

Matossian, J. N.↗
NASA NTRS1987

Observations of polar rain at low and high altitudes

Data from the low-altitude DMSP spacecraft were used to compare polar rain electron intensities, energy spectra, and time variations at low altitudes with concurrent bidirectional electron properties in the magnetotail measured by ISEE 3. The DMSP-measured polar rain phase space densities near the polar cap agreed well with the field-aligned magnetotail lobe electron phase space densities above about 200 eV. Below 100-200 eV, a thermal electron population was observed (by ISEE) in the distant tail which is absent at the DMSP altitudes. The results suggest that the suprathermal tail lobe electrons can move freely along field lines to form polar rain, whereas the thermal electrons are bound to the tailward flowing lobe ion population far down the tail and thus cannot reach the polar cap regions.

Baker, D. N.↗
NASA NTRS2013

Energy Band Gap Study of Semiconducting Single Walled Carbon Nanotube Bundle

The electronic properties of multiple semiconducting single walled carbon nanotubes (s-SWCNTs) considering various distribution inside a bundle are studied. The model derived from the proposed analytical potential function of the electron density for an individual s-SWCNT is general and can be easily applied to multiple nanotubes. This work demonstrates that regardless the number of carbon nanotubes, the strong coupling occurring between the closest neighbours reduces the energy band gap of the bundle by 10%. As expected, the coupling is strongly dependent on the distance separating the s-SWCNTs. In addition, based on the developed model, it is proposed to enhance this coupling effect by applying an electric field across the bundle to significantly reduce the energy band gap of the bundle by 20%.

potential function↗
NASA NTRS1991

Chemistry of electronic ceramic materials. Proceedings of the International Conference on the Chemistry of Electronic Ceramic Materials

The conference was held at Jackson Hole, Wyoming from August 17 to 22, 1990, and in an attempt to maximize the development of this rapidly moving, multidisciplinary field, this conference brought together major national and international researchers to bridge the gap between those primarily interested in the pure chemistry of inorganic solids and those interested in the physical and electronic properties of ceramics. With the many major discoveries that have occurred over the last decade, one of the goals of this meeting was to evaluate the current understanding of the chemistry of electronic ceramic materials, and to assess the state of a field that has become one of the most important areas of advanced materials research. The topics covered include: crystal chemistry; dielectric ceramics; low temperature synthesis and characterization; solid state synthesis and characterization; surface chemistry; superconductors; theory and modeling.

Davies, P. K.↗
NASA NTRS1987

Study of the production of some superconducting and magnetic materials by solidification in the drop tube and drop tower

A systematic study on the relationship between the microstructure and physical properties of several superconducting materials prepared by solidification in low gravity was conducted. Further study of the materials, such as the applications of hydrostatic pressure which is known to be an effective mean to vary the electronic structure of materials, in conjunction with the detailed microstructure analysis of the samples was also performed to better understand the low gravity effects on the enhancement of the electronic properties. Results of the studies on the directionally solidified AlInSn alloys processed in the KC-135 aircraft and immiscible GaBi alloy prepared during free fall in the Marshall Space Flight Center Drop Tower are presented.

Wu, M. K.↗
NASA NTRS1972

Some surface characteristics and gas interactions of Apollo 14 fines and rock fragments.

Comprehensive survey of the physical surface characteristics of Apollo 14 fines, two fragments of a breccia (14321), and a crystalline rock (14310). The survey was carried out with optical and both scanning and transmission electron microscopy and by studying the adsorption of a variety of gases including nitrogen, hydrogen, and water vapor. Our objective in the optical microscope study was to relate the visible geological and petrological features to the surface properties. Electron microscopy particularly helped relate surface roughness and particle fusion to gas adsorption and pore structure. The fine sample (14163,111) had a surface area of 0.210 sq m/g and a helium density of 2.9 g/cc. Similar values have been observed with breccia fragments. Other observations include physical adsorption of molecular hydrogen at low temperatures and of water vapor at ambient temperatures. It is concluded that these particular lunar materials, while capable of adsorbing water vapor, do not retain it for any significant time at low pressures, nor, under lunar conditions, is there any indication of absorption or penetration.

Cadenhead, D. A.↗
NASA NTRS1996

Scanning Tunneling Microscopy Studies of Diamond Films and Optoelectronic Materials

We present a summary of the research, citations of publications resulting from the research and abstracts of such publications. We have made no inventions in the performance of the work in this project. The main goals of the project were to set up a Chemical Vapor Deposition (CVD) diamond growth system attached to an UltraHigh Vacuum (UHV) atomic resolution Scanning Tunneling Microscopy (STM) system and carry out experiments aimed at studying the properties and growth of diamond films using atomic resolution UHV STM. We successfully achieved these goals. We observed, for the first time, the atomic structure of the surface of CVD grown epitaxial diamond (100) films using UHV STM. We studied the effects of atomic hydrogen on the CVD diamond growth process. We studied the electronic properties of the diamond (100) (2x1) surface, and the effect of alkali metal adsorbates such as Cs on the work function of this surface using UHV STM spectroscopy techniques. We also studied, using STM, new electronic materials such as carbon nanotubes and gold nanostructures. This work resulted in four publications in refereed scientific journals and five publications in refereed conference proceedings.

Perez, Jose M.↗