We describe two acoustical methods to evaluate the mechanical properties of thin films and nanoscale structures: atomic force acoustic microscopy and surface acoustic wave spectroscopy. The elastic properties of an 800-nm-thick nickel film were examined with both methods as well as nanoindentation and microtensile testing techiques. Values for the indentation modulus M measured in the film's out-of-plane direction and Young's modulus E measured in the in-plane direction were lower than expected for an isotropic, polycrystalline film. The reduction in stiffness was attributed to grain-boundary effects in the nanocrystalline film. Agreement between the measured and predicted values was improved by reducing the Ni elastic moduli by 10-15 %. Using the measured elastic properties to interpret the surface-wave data, we found that the film density was 1-2 % lower than bulk values. Our results illustrate how complementary methods can provide a more complete and physically realistic picture of a film's properties.
Citation: Journal of Materials Research
Pub Type: Journals
atomic force microscopy, elastic properties, microtensile testing, nanoindentation, surface acoustic waves, thin films