Highly ordered Pd, Fe, and Co clusters on alumina on Ni3Al(111)

Template-mediated growth of metals has attracted much interest due to the remarkable magnetic and catalytic properties of clusters in the nanometer range and provides the opportunity to grow clusters with narrow size distributions. We have grown well-ordered Fe and Co clusters on the ultrathin aluminum oxide on Ni3Al(111), a template with a 4.1 nm lattice. The structure of the approximate to 0.5-nm-thick oxide film exhibits holes reaching down to the metal substrate at the corners of the (67x67)R12.2 degrees unit cell. Pd atoms trapped in these corner holes create metallic nucleation sites where Fe as well as Co clusters can nucleate and form a well-ordered hexagonal arrangement on the oxide nanomesh. We have studied these Fe and Co clusters and applied different methods such as scanning tunneling microscopy and surface x-ray diffraction to determine the morphology and crystallography of the clusters. For Fe, we found cluster growth in either bcc[110] or bcc[100] direction, depending on the deposition temperature and for Co we found close-packed planes on top of the clusters and random stacking of close-packed planes. Pd clusters grow with fcc(111) orientation.