a1 Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455
a2 Hysitron, Inc., Minneapolis, Minnesota 55344
a3 Characterization Facility, University of Minnesota, Minneapolis, Minnesota 55455
a4 Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455
Thin native oxide layers can dominate the mechanical properties of metallic thin films. However, to date there has been little quantification of how such overlayers affect yield and fracture during indentation in constrained film systems. To gain insight into such processes, electrical contact resistance was measured in situ during nanoindentation on constrained thin films of epitaxial Cr and polycrystalline Al, both possessing a native oxide overlayer. Measurements during loading of the films show both increases and decreases in current, which can then be used to distinguish between various sources of plasticity. Ex situ measurements of the oxide thickness are used to provide a starting point for elasticity simulations of stress in both systems. The results show that dislocation nucleation in the metal film can be differentiated from oxide fracture during indentation.
(Received October 21 2011)
(Accepted December 06 2011)
(Online publication January 05 2012)