The kinetics of desorption for Cs and Cs+ from basal graphite surfaces at surface temperatures of 1220 to 1530K was studied by the field reversal method. In this case, the peak ion signal after a period with retarding field, in the range 1 micros to 2ms, was measured. This peak signal was directly related to the surface density of Cs at the end of the retarding period. An analytical description, which included rapid diffusion into the bulk, was shown to give good agreement at relatively short times, while a normal desorption pattern applied at longer times. Under the present high temperature conditions, diffusion via the grain boundaries was generally a relatively slow process. A detailed kinetic model agreed well with the results. A few rate parameters were re-determined independently and were shown to agree within error limits. The diffusion process connecting the upper and lower migrating states was shown to have a small pre-exponential factor, indicating a grain boundary coverage of 10-3. The very rapid diffusion into the bulk was once more found to have a pre-exponential of 1025/s. It was proposed that this process involved the ionization of a Rydberg state outside the surface.

Rate Constants for Cesium Bulk Diffusion and Neutral Desorption on Pyrolytic Graphite Basal Surfaces: a Field Reversal Kinetic Study. Möller, K., Holmlid, L.: Surface Science, 1988, 204[1-2], 98-112