The modulus of a thin thin metallic (Cu, Ag, Cu/Ag multilayers; polycrystalline) or ceramic (alumina; amorphous) films has been measured by differential thermal expansion on an elastic substrate, and by tensile testing in a specially designed microtensile tester [1]. The differential thermal expansion technique has been used as well to monitor the evolution of the modulus in situ during vapor deposition [2].
Possible origins of the lower stiffness which these films compared to their bulk counterparts are reviewed: amorphization, texture, porosity, anelasticity, microplasticity and microcracking [3, 4]. In many cases several factors contribute together. In the case of alumina, the loss of stiffness is attributable to amorphization as well as porosity (measured by adsorption porosimetry). In the case of the metals, the contribution from dislocation anelasticity has been identified from stress relaxation measurements in the tensile tester [5].
References
1. J.A. Ruud, D. Josell, F. Spaepen and A.L. Greer, "A new method for tensile testing of thin films", Journal of Materials Research 8:112-117 (1993)
2. J. Proost and F. Spaepen, "Evolution of the growth stress, stiffness and microstructure of alumina thin films during vapor deposition", Journal of Applied Physics, 91:204-216 (2002)
3. H. Huang and F. Spaepen, "Tensile testing of free-standing Cu, Ag and Al thin films and Ag/Cu multilayers", Acta Materialia 48:3261-3269 (2000)
4. F. Spaepen, “Interfaces and Stresses in Thin Films”, Acta Materialia, Millenium Issue, 48:31-42 (2000)
5. D.Y.W. Yu and F. Spaepen, to be published