Applications of Field-Evaporation Theory

Abstract

This thesis is concerned with the application of the theory of the evaporation of metal atoms from a surface under the influence of a strong electric field. The theory of field evaporation under discussion, put forward by Forbes, assumes that the shape of the atomic bonding-well is parabolic and also that a Gomer-type mechanism operates. When this theory is combined with a standard Arrhenius-type emission equation, we predict linear relationships between T½and 1/F and also between xcr and Q½, where T is the temperature, F the electric field necessary for evaporation, xcr the crossing point of the atomic and ionic curves and Q the activation energy. Experimental results obtained by various workers using Tungsten, Molybdenum and Rhodium tips in an electric field, are compared with this theory over a limited temperature range. The employment of other forms for the atomic bonding-well has also been investigated, in order to improve the performance of the theory at high temperatures. In the case of Rhodium, values have been derived for some surface atomic parameters, namely, the electrical bonding distance of a surface atom nucleus and the vibrational force-constant and frequency of a typical surface atom.