Anomalous elastic properties of metal-metal interfaces

We use Rayleigh waves to measure in situ the elastic modulus of elemental and alloy thin films prepared by e-beam evaporation in an ultra-high vacuum. A high-resolution surface-acoustic-wave velocity technique (I part in 10 7) enables us to measure the film modulus while it is being deposited. We investigate several metal-metal thin-film combinations. Many metal interfaces (e.g. Pd, Au or Ag on Co) show no change in modulus, even for mono-layer thickness. However, a 0.7-nm thick Pd film deposited onto Ir shows an up to threefold increase in modulus. We propose that the modulus increase is not due to a stiff 0.7 rim Pd film, but is due to the repairing effect that this I'd film has on the topmost 5 rim of the underlying Ir layer. Conditions that favor this effect are film combinations of high and low melting point materials. This study sheds new light on the controversial Supermodulus effect in metallic multilayers.