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Results for “Electron emission”

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 NTRS1972

Photon induced secondary electron emission

Numerical models for predicting photon-induced secondary electron emission are presented. The results are compared with experimental measurements made using a Co-60 gamma ray source.

Spencer, R. B.↗
DOE OSTI2025

General kinetic ion-induced electron emission model for metallic walls applied to biased Z-pinch electrodes

A kinetic ion-induced electron emission (IIEE) model for general applications is developed to obtain the emitted electron energy spectrum for a distribution of ion impacts on a metallic surface. We assume an ionization cascade mechanism and use empirical models for the ion and electron stopping powers. The emission spectrum and the secondary electron yield (SEY) are validated for a variety of materials. The IIEE model is used to study the effect of IIEE on the plasma-material interactions of Z-pinch electrodes. Un-magnetized Boltzmann-Poisson simulations are performed for a Z-pinch plasma doubly bounded by two biased copper electrodes with and without IIEE at bias potentials from 0 to 9 kV. At the anode, the SEY decreases from 0 to 1 kV, but then increases at higher bias potentials. At the cathode, the SEY is much larger due to higher energy ion bombardment and grows with bias potential. As the bias potential increases, the emitted cathode electrons are accelerated to higher energies into the domain, collisionally heating the plasma. Above 1 kV, the heating is strong enough to increase the plasma potential. Despite SEY greater than 1, only a classical sheath forms as opposed to a space-charge limited or inverse sheath due to the emitted electron flux not reaching the space charge current saturation limits. Furthermore, the current in the emissionless cases saturates to a value lower than experiment. With IIEE, the current does not saturate and continues to increase with the 4 kV case, matching most closely with the experiment.

Carbon based materials↗
NASA NTRS1978

Electron emission from nickel-alloy surfaces in cesium vapor

An experimental apparatus and measurement techniques are described for measuring the thermionic emission from cesium-activated materials having adequate high-temperature properties such as creep strength and corrosion resistance, which might ultimately reduce the cost of thermionic converters. The electron emission characteristics are measured for nickel, Inconel 600, and Hastelloy X probes with a 412 K cesium reservoir. It is found that the nickel alloys exhibit a peak electron emission 1.4 to 2.1 times greater than pure nickel. Both the Inconel and the Hastelloy samples have work functions of 1.64 eV at peak emission. The minimum cesiated work functions are estimated to be 1.37 eV for Inconel at a probe temperature of 750 K and 1.4 eV for Hastelloy at a probe temperature of 665 K. The bare work functions for both alloys is estimated to be about the same as for pure nickel, 4.8 eV.

Manda, M.↗
DOE OSTI2020

Evidence for trap-assisted Auger recombination in MBE grown InGaN quantum wells by electron emission spectroscopy

We report on the direct measurement of hot electrons generated in the active region of blue light-emitting diodes grown by ammonia molecular beam epitaxy by electron emission spectroscopy. The external quantum efficiency of these devices is <1% and does not droop; thus, the efficiency losses from the intrinsic, interband, electron-electron-hole, or electron-hole-hole Auger should not be a significant source of hot carriers. Here, the detection of hot electrons in this case suggests that an alternate hot electron generating process is occurring within these devices, likely a trap-assisted Auger recombination process.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Electrostatic Relativistic Fluid Models of Electron Emission in a Warm Diode

A semi-analytic fluid model has been developed for characterizing relativistic electron emission across a warm diode gap. Here we demonstrate the use of this model in (i) verifying multi-fluid codes in modeling compressible relativistic electron flows (the EMPIRE-Fluid code is used as an example; see also Ref. 1), (ii) elucidating key physics mechanisms characterizing the influence of compressibility and relativistic injection speed of the electron flow, and (iii) characterizing the regimes over which a fluid model recovers physically reasonable solutions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1998

Diamond Analyzed by Secondary Electron Emission Spectroscopy

Diamond is a promising semiconductor material for novel electronic applications because of its chemical stability and inertness, heat conduction properties, and so-called negative electron affinity (NEA). When a surface has NEA, electrons generated inside the bulk of the material are able to come out into the vacuum without any potential barrier (work function). Such a material would have an extremely high secondary electron emission coefficient o, very high photoelectron (quantum) yield, and would probably be an efficient field emitter. Chemical-vapor-deposited (CVD) polycrystalline diamond films have even more advantages than diamond single crystals. Their fabrication is relatively easy and inexpensive, and they can be grown with high levels of doping--consequently, they can have relatively high conductivity. Because of these properties, diamond can be used for cold cathodes and photocathodes in high-power electronics and in high-frequency and high-temperature semiconductor devices.

Krainsky, Isay L.↗
NASA NTRS1985

Electron emission and acoustic emission from the fracture of graphite/epoxy composites

In past studies it has been shown that the fracture of materials leads to the emission of a variety of species, including electrons, ions, neutral molecules, and photons, all encompassed by the term 'fractoemission' (FE). In this paper, electron emission (EE) from the fracture of single graphite fibers and neat epoxy resin is examined. Measurements of EE are also combined with the detection of acoustic emission (AE) during the testing of graphite-epoxy composite specimens with various fiber orientation. The characteristics of these signals are related to known failure mechanisms in fiber-reinforced plastics. This study suggests that by comparing data from AE and FE measurements, one can detect and distinguish the onset of internal and external failure in composites. EE measurements are also shown to be sensitive to the locus of fracture in a composite material.

Dickinson, J. T.↗
NASA NTRS1989

Ballistic-electron-emission microscopy investigation of Schottky barrier interface formation

Ballistic-electron-emission microscopy (BEEM) has been used to investigate the origin of defects at the Au/GaAs(100) Schottky barrier interface. In addition, molecular beam epitaxy (MBE) and in situ fabrication methods have been employed to control Schottky barrier interface properties. BEEM characterization combined with MBE methods has enabled the development of a near-ideal Schottky barrier interface with drastically reduced defect density.

Hecht, M. H.↗
NASA NTRS1962

Estimation of Critical Temperature for Surface Ion Currents from Electron Emission Data

A method of calculating a relation for the critical surface temperature for ion current emission is presented. The method is based on the S-shaped electron emission curves for surfaces in the presence of ionizable vapors and upon the assumptions of thermodynamic equilibrium involved in the Saha-Langmuir relation. A comparison of the critical temperatures so calculated with the relation obtained from actual ion emission data on the cesium-tungsten system shows good agreement over a wide current density range. Critical temperatures for cesium ion current densities of 0.21 and 1.9 amperes per square centimeter calculated by this method are presented for surfaces of rhenium, molybdenum, tantalum, and niobium. Tentative relations of the form log j equals A (sub p) plus (B (sub p) over T) are presented for these same systems, where j is the ion current density, A (sub p) and B (sub p) are constants, and T is the temperature.

ELECTRON EMISSION↗
DOE OSTI2023

Secondary electron emission of reticulated foam materials

Complex material surfaces can reduce secondary electron emission (SEE) and sputtering via geometric trapping. In this work, the SEE yields for a range of open-cell reticulated carbon foam geometries are characterized using scanning electron microscopy. The total reduction in the SEE yield from carbon foams with a 3% volume fill density and 10–100 pores per inch (PPI) is shown to be between 23.5% and 35.0%. Contributions of a foam backplate are assessed by experimentally and analytically defining the critical parameter, transparency. The transparency of a foam is quantified and is shown to affect the primary electron angular dependence on the SEE yield. For the same thickness of 6 mm, it is found that higher PPI decreases foam transparency from 32% to 0% and reduces the SEE yield. The SEE yield from carbon foams is also shown to have weaker dependence on the morphology of the surface compared with fuzzes and velvets and less variation across individual sample surfaces due to the rigidity of their ligament structures and isotropic geometries.

Physics↗
DOE OSTI2024

Theoretical Assessment of the Transition Between Electron Emission Mechanisms for Nonplanar Diodes

Theoretically and computationally describing the operation of nanodiodes requires characterizing the transitions between multiple electron emission mechanisms for nanodiodes with complicated geometries. This motivates our development of techniques to determine when simplified theories for individual mechanisms suffice compared to more complete, but more computationally expensive, models. Leveraging recent theories that define a canonical gap distance to translate planar theory to nonplanar diodes, we derive the conditions for the transitions among thermal emission, field emission, and space-charge-limited current density (SCLCD) in vacuum and with collisions for non-Cartesian coordinate systems, including spherical, cylindrical, and prolate spheroidal coordinate systems. Particle-in-cell (PIC) simulations of the current density as a function of applied voltage for a tip-to-plate geometry in vacuum agreed qualitatively with the asymptotes for thermal emission at low voltage and SCLCD at higher voltage using the canonical gap distance. As a result, this demonstrates the utility of this approach for guiding system design and suggests future extensions to save simulation time for more realistic geometries that are more computationally expensive.

Conformal mapping↗
NASA NTRS1978

Electron emission from nickel-alloy surfaces in cesium vapor

The cesiated electron emission was measured for three candidate electrodes for use as collectors in thermionic converters. Nickel, Inconel 600 and Hastelloy were tested with a 412 K cesium reservoir. Peak emission from the alloys was found to be comparable to that from pure nickel. Both the Inconel and the Hastelloy samples had work functions of 1.64 eV at peak emission. The minimum work functions were estimated to be 1.37 eV at a probe temperature of 750 K for Inconel and 1.40 eV for Hastelloy at 665 K. The bare work function for both alloys is estimated to be approximately the same as for pure nickel, 4.8 eV.

Manda, M.↗