ON FIELD-EVAPORATION END FORMS OF A BCC METAL SURFACE OBSERVED BY A FIELD ION MICROSCOPE

Distinct differences in the field-evaporation end forms of W, Ta, and Mo are investigated by comparing the temperature dependence of the contribution of polarization energy and binding energy to the field-evaporation energy. The field-evaporation end form at low temperature is influenced mainly by the polarization energy of atoms under the influence of a strong field; its magnitude decreases in the following sequence: Ta, W and Mo. As the field-evaporation temperature is raised the influence is gradually transferred from polarization energy to binding energy. Binding energies except for the {001} planes, which are estimated from the Morse potential energy, are in fair agreement with the experimental results. The field-evaporation end forms at high temperature are mainly influenced by the magnitude of the activation energy due to the self-migration of the atoms on the surface of each crystal planes. The influence of residual gases and the change of field-evaporation mechanism are discussed. © 1969.