Nucleation and growth of transition metals on a thin alumina film

We have studied the growth of various metals (Pd, Rh, Co and Ir) on a thin well-ordered alumina film in order to elucidate the influence of film structure and deposition conditions on nucleation and growth behaviour. All metals exhibit a three-dimensional growth mode in agreement with thermodynamic considerations. The nucleation is, however, dominated by the defects of the substrate. At a deposition temperature of 90 K, point defects are the primary nucleation centres. At 300 K, the situation is different for some metals (such as Pd and Rh) since decoration of steps and film domain boundaries is favoured under these conditions. This temperature dependence points to a stronger interaction of the diffusing metal atoms with the line defects which, however, can only play a role if the thermal energy is sufficiently high to reach them. Metals which are expected to interact more strongly with the support (such as Ir and Co) do not show such a diversity with respect to their nucleation behaviour.