Surface alloying of a Co film on the Cu(001) surface

Surface alloying during the growth of ultrathin Co film on Cu(001) surface was studied by employing Xe as a probing atom. Work functions and Xe 5p spectra for the clean Cu(001) surface and Co films deposited on the Cu(001) surface, both at room temperature and around 50 K, were taken as a function of Xe dosage. The pure Co film, represented by a thick Co film deposited on the Cu(001) surface at 50 K, showed little change of work function as the dosage of Xe increased. In contrast, a linear decrease of work function was observed on the Cu(001) surface as Xe coverage increased. The binding energy of the Xe 5p spectra on a Co film showed a shift toward higher binding energy with increasing Xe coverage, while that on clean Cu(001) surface is almost constant before completion of one Xe monolayer (ML). These two distinctive characteristics were taken as fingerprints of Co and Cu exposed surfaces, respectively. Then, a nominal 2 ML Co film was deposited on Cu(001) surface at room temperature and examined by the fingerprints. It is estimated that about 65% of the surface is made up of disordered CoCu alloy, while the rest of the surface is made up of Co atoms.