An examination of field evaporation theory

Contrary to opinions expressed by earlier investigators, thorough examination of the existing models for field evaporation indicates that they are capable of predicting changes in the relative abundance of ionic species as temperature is changed and evaporation rate is held constant, without assuming atomic tunneling or slowness of electronic transition. However, this need not imply that atomic tunneling and slowness of electronic transition do not exist. Furthermore, the inclusion of energy level shifts in field evaporation theory results in the prediction of higher charge states than would be otherwise expected. This is in agreement with the observations of various investigators on copper and other metals. The examination further reveals that very significant differences in the predicted variation of evaporation rate with field exist between the image-hump and intersection models. This suggests a means by which one can attempt to determine experimentally the “correct” model to apply in a given situation. Furthermore, rigorous interpretation of the intersection model in conjunction with the experimental data of Tsong and Müller can result in significantly different values for the distance of the equilibrium position of the surface atom from the metal surface and the polarizability of the surface atom, than obtained using linear approximations.