Mixed layer formation on the copper-deposited Ni(110) surface

We studied initial Cu overlayer formation on the Ni(110) surface by scanning tunneling microscopy (STM) in an ultrahigh vacuum. Initially, deposited Cu displaces the top Ni layer, forming two-dimensional Cu-Ni alloy on the substrate. The Cu atom embedded into the top layer was depressed in the STM image. The depression due to the lack of Ni 3d-derived surface local density of states was confirmed by the first-principles calculation. Ni atoms squeezed out from the top substrate layer agglomerated in the anisotropic Ni island along the close-packed (1 (1) over bar0) direction. Further Cu deposition resulted in a Cu-Ni mixed island. Quantitative measurement of the Cu fraction on the substrate showed that 0.71 +/- 0.04 of deposited Cu was embedded in the top Ni layer, whereas significant Cu enrichment was seen on the island.