Growth morphology of ultra-thin Ni films on Pd(1Â 0Â 0)

A series of thin Ni films, with thicknesses between 0.2 ML to 13 ML, were deposited on a Pd(1 0 0) substrate (a = 3.89 Å) at room temperature (RT). The growth morphology was investigated using scanning tunneling microscopy (STM). STM images indicate the existence of three different growth modes as a function of increasing coverage. Up to 6.5 ML, the films grow pseudomorphically, consistent with a face-centered tetragonal (fct) structure. From 6.5 ML to 10.5 ML a new apparent interlayer distance of 1.0 ± 0.1 Å is established. The new structure is accompanied by the appearance of an arrangement of filaments on the top layer surface. These filaments are presumably related to a strain relief mechanism of the fct films. Finally above 10.5 ML the Ni films recover the face-centered cubic (fcc) lattice constants. The filaments evolve, as a function of coverage, to form a net-like structure over the whole surface.