Fig. 4

G band and D’ band splitting due to biaxially anisotropic strain. a Far-field spectrum measured with 300 s exposure time showing single G and 2D bands. This spectrum was taken at the same point where TERS spectra was measured to serve as a reference spectrum for enhancement calculations. b Single Raman peak G band from a measured in the far-field and fitted with a single Voigt. c Representative TERS (red line) and far-field (black) spectra measured with 10 s exposure time at point x in Fig. 2d. d Multiple Raman peaks from c consisting of G⁻, G⁺, D’⁻ and D’⁺ bands measured using TERS (tunnelling current: 40 pA; bias voltage: 300 mV) and fitted with a quadruple Voigt. Background has been subtracted in b, d. During the experiments, an excitation laser wavelength of 632.8 nm with a laser power of 0.35 mW at the sample was used