Surfactant-Induced Suppression of Twin Formation During Growth of fcc Co/Cu Superlattices on Cu(111)

Cu/Co bilayers grown by molecular beam epitaxy on Cu(111) present a peculiar defect: the Cu layers display a large fraction of fcc twins, giving rise to a lack of lateral continuity in the film and causing direct ferromagnetic coupling in Co/Cu superlattices. We show how the formation of twins in the epitaxial Cu layers can be suppressed by precovering the clean Cu(111) surface with a monolayer of Pb that floats at the surface of the growing film. The use of this surfactant results in a highly improved structural quality of Co/Cu superlattices.