An experimental method for measuring the Poisson's ratio in thin films andmultilayers using a tensile machine set up on an X-ray goniometer

A few years ago, some authors have observed by X-ray diffraction analysis i n metallic multilayers with small period an in plane expansion combined wit h a large perpendicular expansion. These trends differ from prediction base d on simple continuum elasticity theory. This unexpected result has been th e starting point of an experimental development in our laboratory for deter mining the Poisson's ratio in such systems. Applying the sin(2) psi method on firm-substrate set which is elastically deformed in an X-ray diffractome ter, it is possible to extract the Poisson's ratio of the film. In this pap er, we first detail the theoretical principles of the method and; we show i ts application on 150 nm thick tungsten films elaborated by ion beam assist ed deposition on duralumin substrate. The obtained results demonstrate the feasibility of the method and its good precision.