Metal-on-Metal Heteroepitaxy and the Influence of a Surfactant: Cu/O/Ru(0001)

Cu-on-Ru(OOOl) has been a suitable model system for metal-on-metal heteroepitaxy for many years because of the immiscibility of the two components. In contrast to most ex-situ studies the present work emphasizes dynamical work function change (ΔO) measurements using a special KELVIN-capacitor probe as being a sensitive method to monitor the film morphology in-situ , that is during film growth. In particular, it is demonstrated that preadsorbed oxygen on the Ru(0001) substrate permanently “floats out” to the Cu surface and acts as a surfactant for layer-by- layer growth at a temperature of 400 K, at which in the absence of oxygen non-ergodic growth leads to the formation of pyramidal clusters and, hence, a very rough film. The mechanistic influence of the surfactant oxygen is discussed in detail and may certainly be carried over to other metal-on-metal systems.