Effect of inserting Ni and Co layers on the quantum well states of a thin Cu film grown on Co/Cu(001)

The effect of Ni and Co inserting layers on the quantum well (QW) states of a Cu film grown on Co/Cu(001) is systematically investigated using angle-resolved photoemission spectroscopy. For electron energy E- EF <-0.5 eV, we find that both Ni and Co inserting layers behave similarly to serve as a potential-energy barrier to divide the Cu film into two Cu QWs. For energy near the Fermi energy, the Ni and Co inserting layers have different effects on the Cu QW states while the Co thin layer still perturbs the Cu QW states, the Ni inserting layer behaves as if it were a Cu layer, especially at the Fermi energy, even up to 10 ML thickness. Such different effects of the Ni and Co inserting layers are attributed to their different electronic band matching with the Cu energy band. The first-principles calculation confirms that the electron reflectivity near the Fermi level is indeed very different at the Cu/Ni and Cu/Co interfaces, supporting the experimental results.