Pressure-dependent mechanical properties of thin films under uniaxial strain via the layer compression test

Amorphous materials can exhibit strong non-linear mechanical properties in comparison to ordered solids, which can depend on sample preparation history and the means of applied stress. This non-linearity remains unexplored in the case of thin film materials where current mechanical testing techniques struggle to apply and monitor well-characterised stress and strain, a critical gap given the importance of thin film materials across modern technologies. In this work, we present elastic and yield pressure dependence during aligned flat punch nanoindentation of amorphous thin films. Supported by finite element simulations of a pressure-dependent material, we show continuous in-situ stiffening of polystyrene and sprayed graphene nanosheet network films throughout uniaxial strain compression, on the order of 45