On Field-Evaporation End Forms of b. c. c. Metal Surfaces Observed by Field Ion Microscope

Abstract

The distinct differences in the field-evaporation end form of W, Ta, Mo and Nb are investigated by comparing the temperature dependence of their polarization energy and binding energy. At low temperatures the field-evaporation end form is mainly influenced by the polarization energy of the atom under a strong electric field. The influence decreases in the order Ta>Nb>W>Mo. As the field-evaporation temperature is raised the influence is gradually transferred from polarization energy to binding energy. Excepting the {001} planes the binding energy obtained from the Morse potential energy are in fair agreement with the experimental results. The field-evaporation end forms at high temperatures are mainly influenced by the magnitude of the activation energy due to the self migration of the atoms on the surface of each crystal plane. The influence of the residual gases, the change of field-evaporation mechanism and the anisotropy of elastic deformation are also described.