Increased dissociation probability of CH4 on Co/Cu(111)

this paper, the reactivity of Co films deposited on Cu(111) is investigated, and the results show that a few layers of Co on Cu are more reactive than pure Co itself. This counter intuitive conclusion is based on measurements of the dissociation probability of CH4 using a molecular beam source. The Co grows in islands on the Cu(111) surface. The structure is unstable since Cu segregates to the surface of the Co islands, lowering the total energy of the system. The rate for this process depends critically on the temperature of the system, and the result is easily seen with temperature programmed desorption of CO. A change in the bonding strength of CO to a few Co layers on Cu compared to pure Co, as measured in a thermal desorption experiment, is not observed. The origin of the observed enhanced reactivity is discussed with a starting point in the structure of the surface and theory of metallic reactivity. (C) 1998 Elsevier Science B.V. All rights reserved.