Defects in Cu and Ag overlayers epitaxially grown on a Ru(0001) substrate studied by slow positrons

Slow positrons were used to study buried open-volume defects in epitaxially grown Cu and Ag overlayers on Ru(0001). Vacancy complexes (voids) were found after cryo-condensation of thick (100 nm) Cu and Ag films. These complexes anneal below room temperature. An Ar-sputtered Ru(0001) surface was covered with a 32 nm Cu overlayer (deposition at 300K). The buried defect layer was studied in the as-deposited and as-annealed state as well. It was found that the defect concentration in the Cu layer is distinctly increased after annealing at 500 K. Thus, migration of sputter defects towards the surface through the epitaxially grown metallic overlayer is directly observed.