Hot electron emission from composite metal-insulator micropoint cathodes

Abstract

Field electron emission measurements have been made on composite emitters consisting of electrolytically etched tungsten micropoint cathodes overlayed by a 40-200 nm thick layer of epoxy resin. Their emission properties include (a) an initial switch-on effect at threshold fields of approximately 109 V m-1, (b) a subsequent reversible I-V characteristic that gives a linear FN plot at low fields (<or approximately=108 V m-1) and saturated emission at high fields >or approximately=4*108 V m-1, (c) electron spectra whose FWHM and energy shift is strongly field dependent, (d) single-spot emission images. This unusual pattern of behaviour has been interpreted in terms of a hot electron emission mechanism resulting from field penetration in the dielectric overlayer. Consideration is also given to the technological significance of such composite microemitters.

Epoxylite Influece on Field Electron Emission Properties of Tungsten and Carbon Fiber Tips

“…It is found that the field emission characteristics of these micro-emitters are intrinsically changed by coating the emitters with a thin layer of dielectric material, this is in line with the results from previous investigations (AlQudah et al, 2015;Bajic et al, 1989;Latham & Mousa, 1986;Moran Meza et al, 2015;Mousa, 1987Mousa, , 1988Mousa, , 1992Mousa, , 1994Mousa, , 2007Mousa & Kelly, 2003;Mussa et al, 2012). By comparing the effects of different coating materials, we find the following effects.…”

“…Procedures for coating a tungsten (W) tip have been described elsewhere (Al-Qudah et al, 2015;Latham & Mousa, 1986;Madanat et al, 2015;Mousa et al, 2015). The micropoint emitters used were electrolytically etched from 0.1 mm diameter tungsten wires (99.95% purity), using a 2 M solution of NaOH and for carbon fiber tip were using a 0.1 M solution of sodium hydroxide solution .…”

The Effects of Dielectric Coatings on Electron Emission from Tungsten

“…This technology now makes it possible to prepare a cathode tip with a diameter of several nanometers. Composite micro-point cathodes have been prepared, with the aims of improving the emission characteristics needed for small bright electron sources, and reducing degradation of the electron emitter due to ion sputtering during emission (hence improving lifetime) (AlQudah et al, 2015;Latham & Mousa, 1986;Mousa, 1990;Mousa et al, 1994Mousa et al, , 2012Mousa & Al Share, 1999). The research reported here continues this work on composite micro-point cathodes.…”

“…The procedures used for coating tungsten emitters in the present work are the same as those described previously (AlQudah et al, 2015;Latham & Mousa, 1986). In all cases, the micro-point, nano-apex metallic emitters used were electrolytically etched from 0.1 mm diameter tungsten wires of 99.95% purity (Goodfellow Metals, England), using a 2 M solution of NaOH, and were then ultrasonically cleaned.…”

“…This procedure was repeated 12 times, leading to a coating about 150 to 200 nm thick. The emitter was then carefully transferred to an oven and subjected to a resin-curing cycle of thirty minutes at 100°C to drive off the solvents, followed by another thirty minutes at 185°C to complete the curing (Al-Qudah et al, 2015;Latham & Mousa, 1986). The emitters were studied in a FEM pumped with a diffusionpump system having an additional liquid nitrogen trap.…”