Stretchable graphene: a close look at fundamental parameters through biaxial straining

Tunable biaxial stresses, both tensile and compressive, are applied to a single layer graphene by utilizing piezoelectric actuators. The Grneisen parameters for the phonons responsible for the D, G, 2D and 2D′ peaks are studied. The results show that the D peak is composed of two peaks, unambiguously revealing that the 2D peak frequency (ω_2D) is not exactly twice that of the D peak (ω_D). This finding is confirmed by varying the biaxial strain of the graphene, from which we observe that the shift of ω_2D/2 and ω_D are different. The employed technique allows a detailed study of the interplay between the graphene geometrical structures and its electronic properties.