Model calculations of tunnelling and thermal evaporation rate constants relating to field evaporation

Abstract

Tunnelling and thermal evaporation rate constants are compared for model potential barriers relating to field evaporation. Previous calculations of the temperature below which tunnelling becomes appreciable are shown to be model dependent. Distinctive features of different shaped barriers are found which might be experimentally observable and this could provide a means to distinguish between charge-hopping, charge-draining and image-hump models of field evaporation. The experimental results of Wada et al. (1980), who measured the temperature dependence of the evaporation field of W and Mo at constant evaporation rate, are shown to be consistent with the occurrence of ionic tunnelling below 60K.