Field Emission Through Dielectric Layers

Abstract

Field emission experiments on the adsorption of inert gases on tungsten have shown the presence of stepwise multilayer adsorption. It is possible to obtain emission data through these layers. It turns out; that after suitable corrections for the reduction in field by dielectric effects a thinning of the field emission barrier remains. This is attributed to the fact that individual inert gas atoms represent short-range but deep potential holes (as in ordinary scattering) and so make the barrier more transparent. It is possible to treat the effect quantitatively in two approximations. One is due to Fermi and yields scattering lengths. The other consists of neglecting electronic motion transverse to the barrier, thereby making the problem one-dimensional and results in potential well dimensions. It is possible to calculate theoretical Fermi leugths for various assumed well shapes and dimensions. This is done for square wells and used to compare the results of the two approximations, in terms of the effective nuclear charges required to produce matching of the experimental Fermi lengths with the experimental well dimensions. Reasonable values of Z result for neon, argon, krypton, and xenon_ Since the zero of the potential wells lies above that of the tunnelling electrons these experiments represent in fact scattering of negative energy electrons.