THE GROWTH OF COBALT ON A RHENIUM (0001)-SURFACE AT 300 K

We report on combined LEED and scanning tunneling microscopy (STM) res ults of the initial growth of thin cobalt films on a Re(0001) surface at 300 K, whereby the coverage range 0<Theta(Co)<2 monolayers was inve stigated. At Theta(Co)approximate to 0.1 homogeneous nucleation of Co on the flat terraces of the Re(0001) surface and heterogeneous nucleat ion at defect (step) sites can be distinguished: Individual Co nuclei grow to dendritic islands with 'arms' extending preferentially in the [(1) over bar 2 (1) over bar 0], [2<(11)over bar>0] and [<(11)over bar >20] directions. At medium and high coverages kinetic limitations in t he diffusivity of the impinging Co atoms provide additional growth in the second layer, while the first Co layer still remains incomplete: c oalescence of individual first-layer islands only occurs close to the monolayer coverage. Accordingly, we observe an incomplete layer-by-lay er or 'pseudo-Frank-van-der-Merwe' growth for Co on the Re(0001) surfa ce at room temperature.