Raman spectroscopy of strained monolayer graphene modulated by monodispersed Au nanoparticles

Abstract

Due to its inherent exceptional mechanical flexibility and strength, graphene provides an ideal platform for strain engineering, enabling versatile modulation and significant enhancement of their optical properties. Both uniaxial and biaxial strain have been achieved by transferring monolayer graphene onto monodispersed Au nanoparticles with negligible charge doping. We present a study on the phonon frequency and crystallographic orientation in graphene monolayer wrinkles under uniaxial and biaxial strain. The G and 2D peaks of graphene exhibit significant red shifts under tensile strain. The doubly degenerate G peak splits in two sub-peaks G− and G+ under larger uniaxial strain because of symmetry breaking, while this phenomenon does not occur in the 2D peak. But the 2D peak is much more sensitive to strain. Further, Raman spectra of the unsplit G and 2D peaks have been proved to show a distinctive polarization dependence. We proposed polarized Raman spectroscopy to determine the crystallographic orientation with respect to the strain of graphene by the unsplit G mode. The polarization dependence of 2D mode offers a unique opportunity to examine the anisotropic modifications of the phonon dispersion and changes in electronic structures. This result is of significant in strain engineering of graphene and other two-dimensional materials.