To show how the field reduction factor and the emission current ratio vary with the space-charge strength .
To show how the factor varies with .
Plots, in FN coordinates, showing how the Laplace , Poisson , and Child’s law current densities , , and vary with the Laplace field , for the parameter values and . This value corresponds to a tungsten emitter of moderate to large apex radius, in a conventional field electron microscope configuration. Curve is marked with dots and is terminated at the point where the Poisson field becomes equal to the value at which the top of the tunneling barrier goes below the emitter Fermi level. The numbers 0.90, 0.95, and 0.98 are -values corresponding to different possible criteria for the onset of FEVSC effects, and label points on the Poisson curve where approximately has these values.
Enlarged version of the turn-over region in Fig. 3, for values (1) and (2) . The latter value corresponds to a sharp emitter, as might be used in a Spindt array. The Laplace and Poisson curves are terminated when the top of the relevant tunneling barrier goes below the emitter Fermi level. For the high- Poisson curve this occurs before turn over. Theoretically, the Poisson curves continue into the ballistic emission regime and eventually merge with the relevant Child’s law curve, but this part of the Poisson curve may not normally be experimentally accessible. Figure 4 suggests that, for sharp emitters, FEVSC effects become significant at higher current densities than for blunter emitters, if other things are equal.
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