The positron diffusion process studied in multilayer systems

Results of positron annihilation measurements in multilayer systems with stacking sequence of copper, silver or nickel layers are presented. The layers were produced by dc electrodeposition. Great attention was paid to the positron diffusion in homogeneous areas. The results of experiments with solely copper layers meet the predictions of the so-called diffusion trapping model (DTM). When a thin layer of another metal separated the copper layers, only qualitative agreement with this model was found. The author was successful in establishing the value of the positron diffusion length in a layer of electrodeposited copper, i.e. (102 ± 20) nm, being close to that of positron beam experiments. From the analysis of the experiment it was concluded that the grain boundary in copper contains voids which effectively localized positrons. The type of voids depends on the type of metal separating the copper layers.