Vibrations at Ni-Cu interfaces

Vibrational modes for the Ni(100)/Cu(100) and Ni(111)/Cu(111) interfaces in the relaxed configuration have been calculated using the embedded-atom method. The interface phonon modes localized on one side of the boundary between the constituent solids have been found for both interfaces studied. In all cases the interface modes are only observed near the two-dimensional Brillouin zone boundary and do not exist in the long wavelength limit. Such a behavior shows that the elastic properties of the superlattices are determined by vibrational phonon modes of constituent metals. The changes in interatomic force constants at the interfaces are discussed.