Thin films of Co on Pt(111): Strain relaxation and growth

The growth, structure and morphology of thin Co layers with a thickness ran ging from 1 to 15 monolayers deposited at room temperature on Pt(111) have been studied by the use of scanning tunneling microscopy. We demonstrate th at the first Co layer grows preferably in the Pt fee lattice sites, with a high density of defects due to the lattice mismatch. The second Co layer is found to exhibit a moire structure, with the Co in-plane lattice distance close to that of bulk Co. The growth of thin Co films is observed to be mos tly in terms of flat layers (two dimensional) up to a Co coverage of about 3.5 ML. At higher coverages, we find that the Co grows in (three dimensiona l) islands and we show that the growth is characterized by a mainly twinned fee-like stacking. We argue that the reason for the two dimensional growth mode at lower Co coverages is due to the strained interface between the Co overlayers and the Pt(111) surface resulting in a large number of kinks an d corners which facilitate interlayer diffusion. For higher coverage such s ites become less common, due to the decreasing influence of the strained in terface. resulting in no interlayer diffusion leading to a three dimensiona l growth mode. The implications by these observations on the magnetic prope rties of the Co/Pt(111) interface system are discussed.