Electrical and lattice vibrational behaviors of graphene devices on flexible substrate under small mechanical strain

We present systematic experimental study on the electrical response and two-phonon Raman scattering mode of graphene under small uniaxial strain. The graphene, which was initially grown by chemical vapor deposition, was transferred to a transparent-flexible-polyethylene-terephthalate substrate. It was found that the electrical resistance increases as the stain is increased after a slight decrease in very small strain regimes of <0.20%. This is due to a relaxation of intrinsic ripples created during the transfer of the graphene to the polyethylene-terephthalate substrate. The gauge factor in the linear response regime was found to be about 22. Also, the 2D Raman bands of the strained graphene showed a distinct red-shift of -37 cm ^-1 per 1% strain for the 2D ⁺ mode and -46 cm ^-1 per 1% strain for the 2D ^- mode. Finally, we determined the Gruneisen parameters of γ _2Δ+ ∼ 2.05 and γ _2Δ-∼ 2.55 for the phonons in free-standing graphene without a substrate. Our results provide electro-mechanical parameters for graphene-based flexible devices and show the potential of graphene for measuring strain in future flexible electronics.