Graphene strain tuning by control of the substrate surface chemistry

We show that the Raman spectrum of graphene is sensitive to the surface chemistry of the substrate where the atomic plane is deposited. Two types of functionalized $SiO2$ surface are experimentally compared: OH-terminated and $NH2$-terminated. In the case of $NH2$-terminated surface, the graphene Raman bands are significantly redshifted with respect to the peaks observed on the hydroxylated surface. The observed phonon softening can be ascribed to a biaxial strain induced into graphene by its interaction with the substrate. Therefore, the control of the substrate surface chemistry may be envisaged as a route to graphene strain engineering.