Abstract
Field evaporation of iron in neon and hydrogen between 20 and 200 K has been examined with a field-ion microscope (FIM). From the temperature dependence of an applied field at a constant evaporation rate and the field dependence of the evaporation rate, activation energies and pre-exponential factors have been determined. The pre-exponential factor is quite small compared to the vibrational frequency of metal atoms and the possibility of a tunnelling effect is examined. It is shown that below 100 K in neon, a small pre-exponential can be explained by a tunnelling effect; however, the small pre-exponential in neon at higher temperatures and that in hydrogen are believed to be characteristic of the field evaporation of iron. It is shown that the rate-controlling process in neon below 100 K is not the field evaporation itself but the short-range migration of atoms prior to the evaporation. The reduction in the binding energy of surface atoms by hydrogen is estimated to be about 1 eV.
