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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

GaAs-oxide interface states - Gigantic photoionization via Auger-like process

Spectral and transient responses of photostimulated current in MOS structures were employed for the study of GaAs-anodic oxide interface states. Discrete deep traps at 0.7 and 0.85 eV below the conduction band were found with concentrations of 5 x 10 to the 12th/sq cm and 7 x 10 to the 11th/sq cm, respectively. These traps coincide with interface states induced on clean GaAs surfaces by oxygen and/or metal adatoms (submonolayer coverage). In contrast to surfaces with low oxygen coverage, the GaAs-thick oxide interfaces exhibited a high density (about 10 to the 14th/sq cm) of shallow donors and acceptors. Photoexcitation of these donor-acceptor pairs led to a gigantic photoionization of deep interface states with rates 1000 times greater than direct transitions into the conduction band. The gigantic photoionization is explained on the basis of energy transfer from excited donor-acceptor pairs to deep states.

Lagowski, J.↗
NASA NTRS1983

Apparatus for accurately preloading auger attachment means for frangible protective material

Apparatus for preloading a spring loaded threaded member is described. The apparatus is formed of three telescoping tubes. The innermost tube has means to prevent rotation of the threaded member. The middle tube is threadedly engaged with the threaded member and by axial movement applies a preload thereto. The outer tube engages a nut which may be rotated to retain the threaded member in axial position to maintain the preload.

Wood, K. E.↗
NASA NTRS1990

Characterization of interfacial failure in SiC reinforced Si3N4 matrix composite material by both fiber push-out testing and Auger electron spectroscopy

AES depth profiling and a fiber push-out test for interfacial shear-strength determination have been used to ascertain the mechanical/chemical properties of the fiber/matrix interface in SiC-reinforced reaction-bonded Si3N4, with attention to the weak point where interfacial failure occurs. In the cases of both composite fracture and fiber push-outs, the interfacial failure occurred either between the two C-rich coatings that are present on the double-coated SiC fibers, or between the inner C-rich coating and the SiC fiber. Interface failure occurs at points of very abrupt concentration changes.

Eldridge, J. I.↗
NASA NTRS1975

Widths of atomic 4s and 4p vacancy states, 46 less than or equal to Z less than or equal to 50

Auger and X-ray photoelectron spectra involving N1, N2, and N3 vacancy states of Pd, Ag, Cd, In, and Sn were measured and compared with results of free atom calculations. As previously observed in Cu and Zn Auger spectra that involve 3d-band electrons, free-atom characteristics with regard to widths and structure were found in the Ag and Cd M4-N4,5N4,5 and M5-N4,5N4,5 Auger spectra that arise from transitions of 4d-band electrons. Theoretical N1 widths computed with calculated free-atom Auger energies agree well with measurements. Theory however predicts wider N2 than N3 vacancy states (as observed for Xe), while the measured N2 and N3 widths are nearly equal to each other and to the average of the calculated N2 and N3 widths. The calculations are made difficult by the exceedingly short lifetime of some 4p vacancies and by the extreme sensitivity of super-Coster-Kronig rates, which dominate the deexcitation, to the transition energy and to the fine details of the atomic potential.

Hsiungchen, M.↗
NASA NTRS1976

Widths of atomic 4s and 4p vacancy states, Z between 46 and 50

X-ray photoelectron and Auger spectra involving N sub 1, N sub 2, and N sub 3 vacancy states of Pd, Ag, Cd, In, and Sn were measured and compared with results of free-atom calculations. As previously observed in Cu and Zn Auger spectra that involve 3d-band electrons, free-atom characteristics are found, with regard to widths and structure, in the Ag and Cd M sub 4-N sub 4,5 N sub 4,5 and M sub 5-N sub 4,5 N sub 4,5 Auger spectra that arise from transitions of 4d-band electrons. Theoretical N sub 1 widths computed with calculated free-atom Auger energies agree well with measurements. Theory, however, predicts wider N sub 2 than N sub 3 vacancy states (as observed for Xe), while the measured N sub 2 and N sub 3 widths are nearly equal to each other and to the average of the calculated N sub 2 and N sub 3 widths. The calculations are made difficult by the exceedingly short lifetime of some 4 p vacancies and by the extreme sensitivity of super-Coster-Kronig rates, which dominate the deexcitation to the transition energy and to the fine details of the atomic potential.

Chen, M. H.↗
NASA NTRS2002

Atomic Data for the K-Vacancy States of Fe XXIV

As part of a project to compute improved atomic data for the spectral modeling of iron K lines, we report extensive calculations and comparisons of atomic data for K-vacancy states in Fe XXIV. The data sets include: (i) energy levels, line wavelengths, radiative and Auger rates; (ii) inner-shell electron impact excitation rates and (iii) fine structure inner-shell photoionization cross sections. The calculations of energy levels and radiative and Auger rates have involved a detailed study of orbital representations, core relaxation, configuration interaction, relativistic corrections, cancellation effects and semi-empirical corrections. It is shown that a formal treatment of the Breit interaction is essential to render the important magnetic correlations that take part in the decay pathways of this ion. As a result, the accuracy of the present A-values is firmly ranked at better than 10% while that of the Auger rates at only 15%. The calculations of collisional excitation and photoionization cross sections take into account the effects of radiation and spectator Auger dampings. In the former, these effects cause significant attenuation of resonances leading to a good agreement with a simpler method where resonances are excluded. In the latter, resonances converging to the K threshold display symmetric profiles of constant width that causes edge smearing.

Bautista, M. A.↗
NASA NTRS2003

Atomic Data for the K-vacancy States of Fe XXIV

As part of a project to compute improved atomic data for the spectral modeling of iron K lines, we report extensive calculations and comparisons of atomic data for K-vacancy states in Fe XXIV. The data sets include: (i) energy levels, line wavelengths, radiative and Auger rates; (ii) inner-shell electron impact excitation rates and (iii) fine structure inner-shell photoionization cross sections. The calculations of energy levels and radiative and Auger rates have involved a detailed study of orbital representations, core relaxation, configuration interaction, relativistic corrections, cancellation effects and semi-empirical corrections. It is shown that a formal treatment of the Breit interaction is essential to render the important magnetic correlations that take part in the decay pathways of this ion. As a result, the accuracy of the present A-values is firmly ranked at better than 10% while that of the Auger rates at only 15%. The calculations of collisional excitation and photoionization cross sections take into account the effects of radiation and spectator Auger dampings. In the former, these effects cause significant attenuation of resonances leading to a good agreement with a simpler method where resonances are excluded. In the latter, resonances converging to the K threshold display symmetric profiles of constant width that causes edge smearing.

Bautista, M. A.↗
NASA NTRS2009

The Orbiting Wide-Angle Light Collectors (OWL) Mission for Charged-Particle Astronomy

The space-based OWL mission is designed to perform high-statistics measurements of ultra-high-energy cosmic rays (UHECR) using the Earth's atmosphere as a vast particle calorimeter, furthering the field of charged-particle astronomy. OWL has been developed in formal NASA instrument and mission studies and is comprised of two large telescopes separated by approx.600 km in 1000 km, near-equatorial orbits to stereoscopically image the near-UV air fluorescence emitted by UHECR-induced particle cascades. The High Resolution Fly's Eye (HiRes) Collaboration, and subsequently the Pierre Auger Observatory, recently reported confirmation of the expected Greisen-Zatsepin-Kuzmin (GZK) suppression of the UHECR flux above a few times 10(exp 19) eV. This observation is consistent with the majority of UHECR originating in astrophysical objects and reduces the need to invoke exotic physical processes. Particles observed above the GZK threshold energy must have come from sources within about 100 Mpc from the Earth. The small particle deflection angles expected at UHECR energies, with standard assumptions of extragalactic magnetic fields, are on the order of 1 degree. Thus by observing particles above the GZK threshold with sufficient exposure, there is the potential of identifying and characterizing individual UHECR sources. Auger has reported significant anisotropy in the arrival directions of UHECR at energies above about 6 10(exp 19) eV observed in the South, and a correlation to AGN in the 12th VCV catalog, suggesting that the sources of UHECR are traced by the distribution of luminous matter in the Universe. However, with similar statistics and the same event selection criteria, HiRes observations in the North are consistent with isotropy. Extended observations by Auger-South, by Telescope Array in the North, and possibly by the proposed Auger-North, will further these investigations. However, much greater exposures will be required to fully identify individual sources and measure their cosmic ray spectra. A five-year OWL mission would deliver approximately 10(exp 6)sq km/sr/yr of exposure with full aperture reached at approx. 10(exp 19) eV. The baseline 3 m optical aperture OWL telescopes with 45 degree full field-of-view are easily accomodated on a single conventional launch vehicle. On orbit, the simultaneous viewing of the same volume of atmosphere allows for precise stereo event reconstruction, which is nearly independent of the inclination of the particle track and tolerant of atmospheric conditions. The availability of monocular operation provides increased reliability or can be employed to increase the instantaneous aperture. In stereo mode, OWL is also capable of fully reconstructing horizontal or upward-moving showers and so has unmatched sensitivity to neutrino-induced events. The details of the OWL mission will he presented and its science capabilities will be discussed.

Mitchell, John↗
NASA NTRS1972

Evaluation of plasma cleaning and electron spectroscopy for reduction of organic contamination

The use of Auger spectroscopy to evaluate the effectiveness of plasma cleaning procedures in decontaminating Viking spacecraft is examined. Also investigated was the use of Auger spectroscopy to monitor organic contamination. Results show plasma cleaning can be used effectively to remove organic films and that Auger spectroscopy can be used to monitor organic contamination.

Source record↗
NASA NTRS1976

Surface studies of thermionic cathodes and the mechanism of operation of an impregnated tungsten cathode

The surface properties of conventional impregnated cathodes were investigated by the use of Auger spectroscopy and work function measurements, and these were compared with a synthesized barium or barium oxide coated tungsten surface. The barium and barium oxide coated surfaces were prepared by evaporating barium onto a tungsten surface that can be heated to elevated temperatures. Multilayer or monolayer coverages can be investigated using this technique. The results of this study show that the surface of an impregnated tungsten cathode is identical to that observed for a synthesized monolayer or partial monolayer of barium on partially oxidized tungsten, using the criteria of identical Auger patterns and work functions. Desorption measurements of barium from a tungsten surface were also made. These results in conjunction with Auger and work function data were interpreted to show that throughout most of its life an impregnated cathode operating in the range of 1100 C has a partial monolayer rather than a monolayer of barium on its surface.

Forman, R.↗