Field-evaporation from first-principles

Under the application of a strong electric field, atoms from a metal surface can rupture their bonds and escape, leading to ‘field-evaporation’. We present a firstprinciples description of this phenomenon, taking as an example the evaporation of Al adatoms from an Al(111) surface. The ‘charged-plane’ method [A.Y. Lozovoi and A. Alavi, Phys Rev B 68, 246416 (2003)], has been implemented in the context of a localised-basis code (SIESTA). This enables appreciable fields to be stably and efficiently applied to surfaces, represented using slab geometries. We quantify details of the evaporation process as a function of the applied field strength. The field at which the zero-temperature barrier disappears (evaporation field) is predicted, and possible scenarios of the evaporation of surface atoms are discussed. Results are compared to the ‘image-hump’ model for this process. The field dependence of the barrier is described by this model surprisingly well, despite the potential energy surface not being satisfactorily reproduced.