AES Studies of Saturation in Surfactant Segregation Process in Co/Cu Multilayers

The chemical composition of successive layers in a Co/Cu multilayered system was studied during growth with Auger electron spectroscopy. Experiments were carried out on a sample with 10 repetitions of Co(1 nm)/Cu(2 nm) evaporated at a very low deposition rate in ultrahigh vacuum. A very small amount of Bi or Pb (0.06 nm) was deposited on each Cu film in the system. The experimental data have shown that the concentration of Bi and Pb increases with the number of deposited trilayers up to coverage corresponding to 5 trilayers. At that point the concentration of the surfactant saturated. The changes in the surfactant concentrations are described with a simple model depicting the interaction of the surfactant atoms with the system and how the evolution of the segregation processes. It allows the prediction of the saturation concentration and helps to explain the behaviour of various elements used as a surfactant. The comparison between the theoretical predictions and the experimental results is also discussed.