Another Look at the Classical Calculation of Evaporation Fields

摘要

This paper reports: an improved classical methodology for estimating the field F{sup}E at which the field evaporation (FEV) activation energy become zero, including a classification of different theoretical approaches; new comparisons between experiment and theory, that show that unexplained discrepancies still exist after corrections are made to existing theory; and suggestions as to causes of the discrepancy. The condition that FEV activation energy be zero yields an "energy-balance" equation with seven terms. The simplest analysis ("level 0") starts with two terms; different "levels" of theory are then defined by adding terms. The simplest useful approximation is the standard "level 2" formula: (K{sub}n){sup}0 - ne(F{sub}n){sup}e(x{sub}n){sup}e - n{sup}2e{sup}2/16πε{sub}0(x{sub}n){sup}e = 0 where (K{sub}n){sup}0 is the usual thermodynamic term, ε{sub}0 the electric constant, e the elementary positive charge, ne the ion charge immediately after escape, (F{sub}n){sup}e the "escape field" at which the activation energy Q{sub}n for an ion of charge ne becomes zero, and the "escape distance" (x{sub}n){sup}e is the distance at which Q{sub}n=0.