Elastic stiffness of interfaces studied by Rayleigh waves

The properties of nanocrystalline materials are often dominated by the behavior of their interfaces. We use Rayleigh waves to measure in situ the elastic stiffness of elemental and alloy thin films while they are being deposited. Of special interest are changes in stiffness of the multilayer upon switching the deposition from one metal to another. For most film/substrate combinations, the stiffness changes abruptly, as found for Ir/Pd, Pd/Ag, Pd/Co, Au/Co, Ag/Pd, Ag/Co, and Pt/Pd interfaces. For other metal–metal combinations, the stiffness change shows transient effects. These changes reflect either an elastic softening, as found at Co/Pd, Co/Ag, Co/Au, Pd/Pt, and Ir/Pt interfaces, or an elastic stiffening, as found at Pd/Ir and Pt/Ir interfaces. The stiffening at Pd/Ir interfaces is studied in greater detail. X-ray photoelectron spectroscopy (XPS) data are used in the interpretation of the results.