In most cases, analyses of experimental field emission I-V characteristics (FE current vs voltage variation) for extracting information about the cold cathode emission behavior and the work function Φ of the emitting surface, use the conventional analytic Fowler-Nordheim (FN) relation [1] I = 1.54×10{sup}(-6)×[(β{sup}2V{sup}2 A)/(Φ t{sup}2(y))]×exp {-6.83×10{sup}7 [(Φ{sup}(3/2) v(y))/(βV)]} where I is the FE current in A, Φ is the cathode work function in eV, V is the applied FE voltage in V, A is the FE surface area in cm{sup}2, β is a geometrical factor in cm{sup}(-1) determined by the geometry of the electron emitter and other electrodes and gives the applied local field F = βV. v(y) and t(y) are the Nordheim functions of the Nordheim parameter y = 3.7947×10{sup}(-4) F{sup}(1/2)/Φ, which take into account the lowering of the potential barrier due to the image potential, also called the Schottky effect. It's one property is the simplicity related to an analytical relation and the possibility to state, with high probability, on a tunnelling mechanism for the emission when its ln(I/V{sup}2) vs 1/V plot is a straight line. However, many new experimental measurements have stimulated another look on the relevance of the FN approach for low values of Φ [2,3] for which electron emission no longer takes place solely by tunnelling, through the triangular barrier, but occurs partly or dominantly by direct emission over the top of the barrier that has been pulled down below the Fermi level by the Schottky effect.
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