Field evaporation rates of tungsten

Essential parameters of the theory of field evaporation are the higher ionization potentials of the metal {article}{empty}{document}∑ₙ Iₙ{document} In, the surface atom's distance x0 from the effective electronic surface plane of the metal, the polarizability α of the surface atom in its site, the energy difference An between the atomic and the ionic states of the surface atom, the rate and temperature dependent activation energy Qn, and the pre-exponential factor v of the Arrhenius equation. It is shown how these data can be obtained from field evaporation rate measurements. Experiments with the (110) plane of tungsten were carried out in a range from 10−2 to 107 layers/s using both dc and pulsed field evaporation techniques. The following data are obtained: .It is also shown that the well known reduction of the evaporation field by the imaging gas is to a considerable extent due to the field induced adsorption of the gas.