The effect of surfactants on the growth of Co/Cu multilayers

The effect on the interface structure of multilayers of a pre-deposited ultrathin film of Bi and Pb surfactants introduced into Co/Cu multilayers has been studied. The [Co(1 nm)/Cu(2 nm)] multilayers were thermally evaporated at very low deposition rates with a small amount of Bi and Pb surfactant (about 0.2 ML) introduced at each Cu layer. Auger spectra were taken after subsequent steps of evaporation of Co and Cu, and also after evaporation of surfactants. The evolution of Auger peaks showed that on both Co and Cu surfaces a surfactant peak was always visible. Its intensity continuously increased with the number of Co/Cu repetitions. This shows that the surfactant already segregates to the surface of Co/Cu multilayers during the deposition process. The structure of Co/Cu multilayers with added surfactant has been studied using low-angle X-ray reflectivity. We have found that surfactant addition leads to well-ordered structures with small roughness (a few A). The results demonstrate that the application of a surfactant during deposition process allows the fabrication of atomically smooth multilayers via a surface segregation mechanism. (C) 2007 Elsevier B.V. All rights reserved.