Figure 2. Mechanics of graphene membranes at room temperature.

(a) Stress (σ_r) versus strain (ɛ_r) dependence for a typical device. The in-plane stiffness E_2D is extracted from the slope of linear fit to these data (black line). Inset: Raw centre-point deflection, h, versus pressure, P, data used for calculation of stress and strain (red: loading cycle, blue: unloading cycle) along with a fit to the bulge-test equation (black line). (b) Histogram of E_2D for all measured CVD graphene devices. (c) A non-linear stress-strain curve seen in a minority of devices. The dashed line is a guide to the eye. (d) A cartoon view of a crumpled membrane.