Field Ionization and Field Ion Microscopy

Abstract

This chapter elaborates the various aspects of the field ionization and field ion microscopy. The ionization of a free atom by the tunnel effect in a high electric field is called field ionization. An analysis of the energy distribution can be used to localize the origin of the ions, and the best resolution in energy can be obtained by applying the retarding potential method with spherical symmetry. This arrangement has proved its usefulness in the measurements of energy distribution of field-emitted electrons. The case of field emission of positive ions that originate from a bound state at the metal surface, either in the form of adsorbed atoms and ions is considered. A general feature of field desorption of electropositive adsorbates is the increase of desorption field with increasing degree of coverage, as seen for barium. The results obtainable from field desorption measurements promise to present a valuable supplement for the investigation of adsorption phenomena by providing a new range of data beyond the conventional measurements of activation energies for surface migration and thermal desorption. The technique of field ion microscopy is also described.