Internal friction in thin films and membranes

After a brief introduction into the essentials of thin film and membrane damping two topics are discussed. (1) The stress and microstructure of growing thin films. The parameters which control the kinetic growth processes of sputter deposited ultra thin Au, Cu and Al layers on Si membranes were established by monitoring the film stress and damping by a vibrating membrane technique. The related surface morphology was studied by scanning tunneling microscopy. Aging after each deposition causes stress evolution towards higher tension and the evolution of the stress with time follows an exponential law with a characteristic relaxation time of the order of tens of seconds. This time was found to depend strongly on the accumulated film thickness as well as the surface morphology. The intrinsic stress of the growing layer increases with the coverage of the film on substrate. Scanning Tunneling Microscopy shows that the film grows in a Volmer-Weber mode. The stress reaches a maximum as the film become continuous. (2) A magneto-mechanical instability in 1 μm thick nanocrystalline tensioned Terfenol-D films occurring in a transverse magnetic field of about 1.5KOe. The phenomenon is critically dependent on the orientation of the magnetic field and is the result of a magneto-mechanical instability in the Terfenol film.