Interplay of wrinkles, strain, and lattice parameter in graphene on iridium.

Following graphene growth by thermal decomposition of ethylene on Ir(111) at high temperatures we analyzed the strain state and the wrinkle formation kinetics as function of temperature. Using the moiré spot separation in a low energy electron diffraction pattern as a magnifying mechanism for the difference in the lattice parameters between Ir and graphene, we achieved an unrivaled relative precision of ±0.1 pm for the graphene lattice parameter. Our data reveals a characteristic hysteresis of the graphene lattice parameter that is explained by the interplay of reversible wrinkle formation and film strain. We show that graphene on Ir(111) always exhibits residual compressive strain at room temperature. Our results provide important guidelines for strategies to avoid wrinkling.