Vibrational properties of Cu(100)-c(2x2)-Pd surface and subsurface alloys

Using interaction potentials from the embedded-atom method we investigated the structural and vibrational properties of a Cu(100)-c(2x2)-Pd surface alloy and an underlayer c(2x2) alloy with a mixed CuPd second layer. The calculated surface phonon frequencies are in agreement with the experimental values obtained by electron energy-loss spectroscopy. From the calculated local phonon densities of states we find that surface effects are most pronounced in the first two layers for both systems studied. The results also indicate a very strong Pd-Cu bonding accompanied by a weaker bonding of the Cu surface atoms to their nearest neighbors. This has considerable influence on the surface phonon frequencies