Defects in Heteroepitaxial Structures Studied with Monoenergetic Positrons: Large Lattice Mismatch Systems Cu/Ag(111) and Ag/Cu(111)

摘要

In positron beam experiments the backdiffusion probability of positrons is analyzed as a function of implantation energy to non-destructively extract depth distributions of open-volume defects in the near-surface region. The authors are reporting on the first quantitative studies of this type for metallic heteroepitaxial structures. Silver and copper layers have been grown on Cu(111) and Ag(111) substrates in-situ under ultra-high vacuum conditions with an effusion cell system. The overlayer thickness varies from 250 A to 2800 A. Large lattice mismatch between silver and copper is expected to result in a large amount of lattice defects. In Cu/Ag(111)-structures a vacancy concentration of the order of 1000 ppm or, alternatively, a dislocation density 10 to the 11 power/sq cm, is observed near the interface. When silver is grown on Cu(111) the corresponding densities are smaller by a factor of three.