Small-scale plasticity in thin Cu and Al films

Flow stresses in thin metal films significantly exceed the flow stresses of their bulk counterparts. In order to identify the underlying deformation mechanisms and correlate them with microstructure, we analysed epitaxial and polycrystalline Cu and Al thin films. The films (100-2000 nm thickness) were magnetron sputtered on (0001) alpha-Al2O3 single crystals or on nitrided and oxidised (001) Si substrates. For epitaxial films, the flow stress measurements, which were obtained from substrate-curvature tests, agree with predictions from a dislocation-based model [1,2], whereas for polycrystalline films the stresses measured for film thicknesses down to 400 nm are much higher than predicted. However, thinner films reveal a plateau in room temperature flow stress. This behavior, as well as the stress-temperature evolution of the various films will be discussed in terms of existing theories for plasticity in thin metal films, and under consideration of recent in situ transmission electron microscopy studies. (C) 2003 Published by Elsevier B.V.