Raman spectroscopy of four epitaxial graphene layers: Macro-island grown on 4H-SiC 0001¯ substrate and an associated strain distribution

•Finding giant graphene macro-islands•Mapping Raman spectroscopy of the macro-island surface•Discovery of various strain effects on the four-layer islands•Temperature dependence of strain in epitaxial graphene•Theoretical approach of strain effects

Using Raman spectroscopy, we have characterised the optical and mechanical properties of a large macro-island area (150 μm2) of four layer epitaxial graphene grown on a 4H-SiC 0001¯ substrate. Local Raman mapping showed an inhomogeneously stressed macro-island. There, the 2D and G Raman modes revealed a large frequency red-shift in this island with a decreasing temperature. An unexpected change appeared in the Raman spectra due to the inhomogeneous strain effect which was described in detail. Uniaxial and biaxial strains have been identified.