Young's modulus of thin films by speckle interferometry

Speckle interferometry has been applied to the measurement of Young's modulus in thin films. The present study has two novel aspects: the specimens used were approximately 1 mu m thick and less than 1 mm long, so the speckle images were obtained by photomicroscopy; and the digital images were analysed by quantitative treatment at intense speckles, rather than by the more standard techniques. Displacements and strains within the gauge length were obtained with low statistical uncertainties. Young's modulus values for three varieties of copper thin films were obtained. All were lower than the polycrystalline bulk average value and the electrodeposited film's modulus was lower than those of both the vapour-deposited films.