On the thermally activated field evaporation of surface atoms

Abstract

The temperature dependence of the evaporation fields of various metals in a temperature range from 20 to 150 K is examined in terms of a thermally activated process. The charge-exchange model was considered for the evaporation process and the atomic potential curve was obtained for Ni, as an example, from the observed temperature dependence of the field. However, the obtained curve was quite different from the expected atomic curve. Furthermore, when activation energies for the evaporation process were estimated from the observed temperature dependences of all the metals examined, unreasonably large values were resulted. Thus, the correlation between the experimental results and the model was not satisfactory. This was found to be due to the observed large temperature of the applied field compared with that predicted by the model. The field-induced short-range migration of edge atoms on an atomic plane prior to the field evaporation is also considered. It will be shown that this thermally activated migration process is possibly the rate-controlling process of the field evaporation in a temperature range where the large temperature dependence of the evaporation field is observed.