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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Ballistic-electron-emission microscopy of subsurface defects at the Au-GaAs(100) interface

The application of ballistic-electron-emission microscopy (BEEM) to a study of the influence of GaAs(100) substrate conditions on the formation of a multidefect structure at the Au-GaAs(100) Schottky barrier interface is described. Interfaces prepared on both melt-grown GaAs(100) wafer substrates and MBF-deposited GaAs(100) buffer layers are considered. As a comparison to the study of Au-GaAs(100) interfaces, BEEM imaging is performed on Au-Si(100) interfaces. It is noted that Au-GaAs(100) interface formation is relatively insensitive to the effects of substrate surface condition and substrate bulk defect density, and that the combination of BEEM imaging and BEEM spectroscopy indicates that the heterogeneous interface defects are the result of diffusion between the Schottky barrier electrodes.

Hecht, M. H.↗
NASA NTRS2006

Secondary Electron Emission and the Exploration of Space

The emission of secondary electrons from surfaces exposed to the space plasma and radiation environment is a process of great importance to space system engineering design and operations. A spacecraft will collect charge until it reaches an equilibrium potential gov,erned by the balance of incoming electron and ion currents from the space environment with outgoing secondary, backscattered, and photoelectron currents. Laboratory measurements of secondary electron yields are an important parameter for use in spacecraft charging analyses because the magnitude and sign of the equilibrium potential depends on both the energy spectrum of electrons and ions in the space environment and the electrical properties of the surface materials (including the energy dependent secondary electron yields). Typical benign equilibrium potentials range &om a few tens of volts positive in interplanetary space to a few volts negative in low Earth orbit. However, spacecraft are known to charge to negative potentials exceeding one to ten kilovolts in some environments and anomalies or system failures due to electrostatic discharges originating from highly charged surfaces becomes a serious concern. This presentation will provide a review of the spacecraft charging process with special emphasis on the role of secondary electrons in controlling the current balance process. Charging examples will include spacecraft in Earth orbit and interplanetary space as well as dust charging on the lunar surface, a phenomenon of importance to future lunar surface operations.

Minow, Joseph I.↗
NASA NTRS2012

Laboratory Measurements on Charging of Individual Micron-Size Apollo-11 Dust Grains by Secondary Electron Emissions

Observations made during Apollo missions, as well as theoretical models indicate that the lunar surface and dust grains are electrostatically charged, levitated and transported. Lunar dust grains are charged by UV photoelectric emissions on the lunar dayside and by the impact of the solar wind electrons on the nightside. The knowledge of charging properties of individual lunar dust grains is important for developing appropriate theoretical models and mitigating strategies. Currently, very limited experimental data are available for charging of individual micron-size size lunar dust grains in particular by low energy electron impact. However, experimental results based on extensive laboratory measurements on the charging of individual 0.2-13 micron size lunar dust grains by the secondary electron emissions (SEE) have been presented in a recent publication. The SEE process of charging of micron-size dust grains, however, is found to be very complex phenomena with strong particle size dependence. In this paper we present some examples of the complex nature of the SEE properties of positively charged individual lunar dust grains levitated in an electrodynamic balance (EDB), and show that they remain unaffected by the variation of the AC field employed in the above mentioned measurements.

Tankosic, D.↗
NASA NTRS1976

Resolution of electron emission mechanisms in an argon arc with a hot tungsten cathode

The regenerative nature of the interaction between the electron emission processes at the cathode surface and the ion-, excited-atom-, and photon-production processes in the plasma was examined. Semiquantitative estimates of the thickness of the species production layer, the current partition, and the time constants were made. These results were used to interpret experimental measurements of the current decay of an argon arc at 46.7 kPa, 3.2-7.9 A, and 28-18 V, with a self-sustained hot tungsten cathode. After the discharge is suddenly connected to a voltage clamp, the disparity of decay rates for different emission processes permits the separation of thermionic emission from the faster-decaying components. The observed thermionic current constitutes about 30% of the total emission. The high nonthermionic portions of the current could not be explained in terms of the present understanding of the emission processes.

Chen, M. M.↗
NASA NTRS1995

A study of secondary electron emission effects for suppressing passive intermodulation interference in high power communication satellites

In this paper a study of secondary electron emission effects for suppressing passive intermodulation interference in high power communications satellites is studied. The test facility is described and the test results are provided. The effects of environmental factors on the secondary emission coefficient are given. It is found that certain refractory compounds are very promising in eliminating some of the passive intermodulation in satellite communications.

Bosisio, Renato G.↗
NASA NTRS1998

A Review of the Suppression of Secondary Electron Emission from the Electrodes of Multistage Collectors

A review is presented of more than 20 years of research conducted at NASA Lewis Research Center on the suppression of secondary electron emission (SEE) for the enhancement of the efficiency of vacuum electron devices with multistage depressed collectors. This paper will include a description of measurement techniques, data from measurements of SEE on a variety of materials of engineering interest and methods of surface treatment for the suppression of SEE. In the course of this work the lowest secondary electron yield ever reported was achieved for ion textured graphite, and, in a parallel line of research, the highest yield was obtained for chemical vapor deposited thin diamond films.

Dayton, James A., Jr.↗
NASA NTRS2010

Lunary Dust Grain Charging by Electron Impact: Complex Role of Secondary Electron Emissions in Space Environments

Dust grains in various astrophysical environments are generally charged electrostatically by photoelectric emissions with radiation from nearby sources, or by electron/ion collisions by sticking or secondary electron emissions (SEES). The high vacuum environment on the lunar surface leads to some unusual physical and dynamical phenomena involving dust grains with high adhesive characteristics, and levitation and transportation over long distances. Knowledge of the dust grain charges and equilibrium potentials is important for understanding a variety of physical and dynamical processes in the interstellar medium, and heliospheric, interplanetary/ planetary, and lunar environments. It has been well recognized that the charging properties of individual micron-/submicron-size dust grains are expected to be substantially different from the corresponding values for bulk materials. In this paper, we present experimental results on the charging of individual 0.2-13 m size dust grains selected from Apollo 11 and 17 dust samples, and spherical silica particles by exposing them to mono-energetic electron beams in the 10-200 eV energy range. The dust charging process by electron impact involving the SEES discussed is found to be a complex charging phenomenon with strong particle size dependence. The measurements indicate substantial differences between the polarity and magnitude of the dust charging rates of individual small-size dust grains, and the measurements and model properties of corresponding bulk materials. A more comprehensive plan of measurements of the charging properties of individual dust grains for developing a database for realistic models of dust charging in astrophysical and lunar environments is in progress.

Abbas, M. M.↗
DOE OSTI2021

Electron emission from fluorene (C 13 H 10 ) upon 3.5 MeV/u Si 8+ ion impact: double differential distributions

In this work, we have studied the electron emission from one of the polycyclic aromatic hydrocarbon (PAH) molecules namely, fluorene (C13H10), upon 3.5 MeV/u Si8+ ion impact. The experimentally measured absolute double differential cross sections (DDCS) are compared with the continuum distorted wave-eikonal initial state (CDW-EIS) model and the first Born approximation including correct boundary conditions (CB1). The measurements are carried out in the ejected e⁻-energy range of 1 eV–400 eV and in the angular range of 20°–160°. We have obtained the single differential and the total cross sections (TCSs) of e⁻-emission as well. The CB1 calculation largely underestimates the data. The CDW-EIS model, which is applied for the PAH molecule for the first time, provides an overall better agreement with the double differential, single differential and TCS data. The DDCS data for fluorene has also been compared with that for CH4 molecule, at a few angles. The forward–backward angular asymmetry shows a relatively flatter distribution compared to the theoretical predictions. The contribution due to the giant plasmon resonance could not be clearly observed except a mild indication in the asymmetry parameter. The angular distribution of the carbon KLL Auger electron cross section shows certain variations. The study of the KLL hyper-satellite component indicates the double K-ionization cross section is about 8.6% of the single K-ionization one.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS1993

An Effective Secondary Electron Emission Suppression Treatment For Copper MDC

Untreated oxygen-free, high-conductivity (OFHC) copper, commonly used for MDC electrodes, exhibits relatively high secondary electron emission characteristics. This paper describes a specialized ion-bombardment procedure for texturing copper surfaces which sharply reduces the emission properties relative to untreated copper. The resulting surface is a particle-free, robust, uniformly highly-textured all-metal structure. The use of this process requires no modifications to copper machining, brazing, or other MDC normal fabrication procedures. The flight TWT for a planned NASA deep space probe, the Cassini Mission, will incorporate copper MDC electrodes treated with the method described here.

Curren, Arthur N.↗
DOE OSTI2026

Intrinsic emittance properties of an Fe-doped β-Ga 2 O 3 (010) photocathode: Ultracold electron emission at 300 K and the polaron self-energy

Measurements of the spectral emission properties of an iron-doped a β-Ga 2 O 3 (010) photocathode at 300 K reveal the presence of an ultracold contribution to the total electron beam emission with a 6 meV mean transverse energy (MTE) in the 3.5–4.4 eV photon energy range (282–354 nm). This extreme sub-thermal photoemission signal is consistent with direct emission of electrons photoexcited from the Fe dopant states into the low effective mass and positive electron affinity primary conduction band, and it is superimposed on a stronger signal with a larger MTE associated with an (optical)phonon-mediated momentum-resonant Franck–Condon (FC) emission process from a thermally populated and negative electron affinity upper conduction band. For photon energies above 4.5 eV, a transition from a long to a short transport regime is forced by an absorption depth reduction to below 100 nm and both MTE signals exhibit spectral trends consistent with phonon-mediated FC emission if the polaron formation self-energy is included in the temperature of the initial thermalized photoexcited electron distribution.

Angeloni, Louis A. [University of Illinois, Chicag↗
NASA NTRS1981

Effects of secondary electron emission on charging

Laboratory charging studies using two electron sources with different energies show that the charging behaviors of typical spacecraft thermal control dielectric surface are extremely sensitive to the shape of their secondary emission curves. The results also suggest that the electron spectrum in a natural charging environment can be separated into three distinct regions (noninteracting, discharging, and charging) depending on the kinetic energy of the incident electron relative to the charged surface, and on the secondary emission characteristics of the material. To a first order approximation, the relative number of electrons in these different regions determines the potential of the charged surface. Detailed measurements of the secondary electron emission characteristics of Kapton, the effects of bulk conductivity and secondary emission on surface charging of these materials is reported.

Leung, M. S.↗
NASA NTRS1996

A Portable Surface Contamination Monitor Based on the Principle of Optically Stimulated Electron Emission (OSEE)

Many industrial and aerospace processes involving the joining of materials, require sufficient surface cleanliness to insure proper bonding. Processes as diverse as painting, welding, or the soldering of electronic circuits will be compromised if prior inspection and removal of surface contaminants is inadequate. As process requirements become more stringent and the number of different materials and identified contaminants increases, various instruments and techniques have been developed for improved inspection. One such technique, based on the principle of Optically Stimulated Electron Emission (OSEE), has been explored for a number of years as a tool for surface contamination monitoring. Some of the benefits of OSEE are: it is non-contacting; requires little operator training; and has very high contamination sensitivity. This paper describes the development of a portable OSEE based surface contamination monitor. The instrument is suitable for both hand-held and robotic inspections with either manual or automated control of instrument operation. In addition, instrument output data is visually displayed to the operator and may be sent to an external computer for archiving or analysis.

Perey, D. F.↗
NASA NTRS2012

Charging of Individual Micron-Size Interstellar/Planetary Dust Grains by Secondary Electron Emissions

Dust grains in various astrophysical environments are generally charged electrostatically by photoelectric emissions with UV/X-ray radiation, as well as by electron/ion impact. Knowledge of physical and optical properties of individual dust grains is required for understanding of the physical and dynamical processes in space environments and the role of dust in formation of stellar and planetary systems. In this paper, we discuss experimental results on dust charging by electron impact, where low energy electrons are scattered or stick to the dust grains, thereby charging the dust grains negatively, and at sufficiently high energies the incident electrons penetrate the grain leading to excitation and emission of electrons referred to as secondary electron emission (SEE). Currently, very limited experimental data are available for charging of individual micron-size dust grains, particularly by low energy electron impact. Available theoretical models based on the Sternglass equation (Sternglass, 1954) are applicable for neutral, planar, and bulk surfaces only. However, charging properties of individual micron-size dust grains are expected to be different from the values measured on bulk materials. Our recent experimental results on individual, positively charged, micron-size lunar dust grains levitated in an electrodynamic balance facility (at NASA-MSFC) indicate that the SEE by electron impact is a complex process. The electron impact may lead to charging or discharging of dust grains depending upon the grain size, surface potential, electron energy, electron flux, grain composition, and configuration (e.g. Abbas et al, 2010). Here we discuss the complex nature of SEE charging properties of individual micron-size lunar dust grains and silica microspheres.

Tankosic, D.↗
NASA NTRS1993

Ballistic-Electron-Emission Microscopy Techniques for Nanometer-scale Characterization of Interfaces

Semiconductor interface properties are among the most important phenomena in materials science and technology. The study of metal/semiconductor Schottky barrier interfaces has been the primary focus of a large research and development community for decades. Throughout the long history of interface investigation, the study of interface defect electronic properties have been seriously hindered by the fundamental experimental difficulty of probing subsurface structures. A new method, Ballistic-Electron-Emission Microscopy (BEEM), has been developed which not only enables spectroscopic probing of subsurface interface properties, but also, provides nanometer-resolution imaging capabilities. BEEM employs Scanning Tunneling Microscopy (STM) and a unique spatially localized ballistic electron spectroscopy method...

Bell, L. D.↗
DOE OSTI2020

High current density electron emission from an electrodeposited metal nanowire array

High-current electron field emitters are of interest for many applications, but state-of-the-art devices suffer from limitations such as high turn-on macroscopic field, low macroscopic current density, poor emission stability, and short lifetime. Field emitter arrays with a high spatial density of uniform emitters have the potential to address these problems. This work presents the process development, fabrication, and testing of a novel field emitter array. The authors employed electron beam lithography and templated electrodeposition to fabricate a high spatial density array of metallic nanowires, resulting in electron emission with high macroscopic current density (2 A/cm 2 ) and low turn-on macroscopic field (4.35 V/ μ m). Templated electrodeposition of metallic nanowire arrays is a promising method for producing high performance field emitters.

42 ENGINEERING↗
NASA NTRS2009

Characterization of a Carbon Nanotube Field Emission Electron Gun for the VAPoR Miniaturized Pyrolysis-Time-of-Flight Mass Spectrometer

We are developing the VAPoR (Volatile Analysis by Pyrolysis of Regolith) instrument towards studying soil composition, volatiles, and trapped noble gases in the polar regions of the Moon. VAPOR will ingest a soil sample and conduct analysis by pyrolysis and time-of-flight mass spectrometry (ToF-MS). Here, we describe miniaturization efforts within this development, including a carbon nanotube (CNT) field emission electron gun that is under consideration for use as the electron impact ionization source for the ToF-MS.

Getty, Stephanie↗
NASA NTRS1986

Process Produces Low-Secondary-Electron-Emission Surfaces

Textured carbon layer applied to copper by sputtering. Carbon surface characterized by dense, random array of needle-like spires or peaks that extend perpendicularly from local copper surface. Spires approximately 7 micrometers in height and spaced approximately 3 micrometers apart, on average. Copper substrate essentially completely covered by carbon layer, is tenacious and not damaged by vibration loadings representative of multistage depressed collector (MDC) applications. Process developed primarily to provide extremely low-secondary-electron-emission surface for copper for use as highefficiency electrodes in MDC's for microwave amplifier traveling-wave tubes (TWT's). Tubes widely used in space communications, aircraft, and terrestrial applications.

Curren, A. N.↗