Nanomechanical properties of graphene on poly(ethylene terephthalate) substrate

A graphene film was synthesized using chemical vapor deposition and then transferred to a flexible poly(ethylene terephthalate) (PET) substrate. The nanomechanical properties of the graphene/PET (G/PET) system were investigated by nanoindentation. The hardness (H) and reduced modulus (Er) of PET and G/PET were calculated using the Oliver–Pharr method with corrections for creep and material pile-up around the contact. The H and Er of the G/PET were 97% and 16% higher respectively than on the PET substrate. The increase in Er can be attributed to the high in-plane elastic modulus of graphene, the smaller increase in Er than H merely reflecting the far-field nature of the elastic stress field compared to the plastic stress field. The creep behavior of the PET is strongly hindered by the presence of the graphene overlayer. A simple volume contribution model was adopted to calculate the elastic modulus of the graphene overlayer and the computed values were of the right magnitude for graphene film.