Elastic property characterization of soft substrate-supported thin films using multiscale digital image correlation

Abstract

We present an original experimental approach to characterizing the Young’s modulus of nanoscale thin films on a soft substrate. A microtester is developed to permit pre-stretching of the polymer substrate and symmetric film deposition on both sides of its half surface. During compression and tensile tests related to the as-deposited residual stress state, the full-field macrostrains of the film-substrate composite and the uncoated substrate can be measured simultaneously with the film microstrains using multiscale digital image correlation. The macrostrain difference allows extraction of the elastic properties of thin films. Combined with microstrains, a perfect strain transfer at the film-substrate interface, minus buckling of the composite, is evidenced. No film delamination or cracking phenomena are observed, and the measured Young’s modulus agrees well with the literature. Our approach could potentially be used to explore the mechanical properties and behaviors of emerging functional thin films, both crystalline and amorphous.