Thin Cu/Ag(111) and Ag/Cu(111) structures studied with monoenergetic positrons.

Abstract

The early stages of crystal growth have been studied with variable-energy positrons in conjunction with low-energy electron diffraction and Auger-electron spectroscopy. We report measurements of positron branching ratios for (0.1--10)-monolayer (ML) Cu overlayers grown on Ag(111) and for (0.1--100)-ML Ag overlayers grown on Cu(111). The results are discussed in terms of the structural and electronic properties of the surfaces as well as positron-interaction mechanisms at the surfaces. Our method is not sensitive to open-volume defects created during the early stages of crystal growth. Information on positron implantation at small incident energies, positron surface processes, and positron thermalization properties is extracted from experimental data.