Size-dependent dissociation of small cobalt clusters on ultrathin NaCl films

Mass-selected anionic cobalt clusters of two different sizes (Co2 and Co13) were deposited onto ultrathin NaCl films grown on an Au(111) substrate. Using scanning tunneling microscopy experiments and density functional theory simulations, we show that the deposited Co2 cluster dissociates and that the resulting Co atoms dope the NaCl surface by substituting Na ions. In contrast, the larger Co13 cluster does not dissociate and remains stable on top of the NaCl film. The size-dependent fragmentation of clusters is an important aspect in the understanding of the chemical interaction between size-selected small aggregates of atoms and supporting surfaces.