INTERFACE STUDIES USING VARIABLE ENERGY POSITRON BEAMS

The use of low energy positron beams to study interfaces and layered structures is reviewed. Measurement techniques are described, with emphasis on the Doppler broadening of the pair annihilation 511 KeV gamma ray peak, and the information that it carries about the electronic structure of the annihilation site. Theoretical descriptions of positron implantation and thermalisation are discussed. The equations of positron diffusion after thermalisation are presented and solved for several simple cases, and a computer code for handling more complex cases is briefly discussed. A sampling of experimental results is presented to demonstrate the range of problems to which low energy positron beams can be applied and to indicate the quality of current results. Some possible future directions for the use of this technique are discussed.