Theoretical arguments against the Muller-Schottky mechanism of field evaporation

Abstract

In a theoretical investigation of the Muller-Schottky mechanism of field evaporation, an 'extended' image-hump formalism has been developed that includes a term relating to the repulsive ion-surface interaction. This formalism is used to calculate the field at which the Schottky hump disappears. It is then shown that: (i) the conventional simple image-hump formalisms are invalid because they predict evaporation fields higher than the hump-disappearance field; (ii) the ability of the simple formalisms to roughly predict observed evaporation fields is a numerical coincidence rather than a meaningful test of the formalisms; (iii) observed evaporation fields are in most cases higher than the fields at which the Schottky hump disappears. It is concluded that normal metal field evaporation at low temperatures cannot be described by any image-hump formalism yet considered, and that such evaporation almost certainly takes place via a Gomer-type surface charge-exchange mechanism.