Fig. 3

Subnanometre strain analysis of Gr/Au(111) from TERS data. a Correlation plot of ω_2D vs. ω_G of NDs 1 (blue), 2 (green) and 3 (red) found in Fig. 2g of A1. All data points of A1 are also plotted in b as red crosses. The red star represents the Raman frequencies for undoped and unstrained graphene on SiO₂/Si substrate using 632.8 nm excitation^35,37 and serves as the origin for the pure strain (consisting of biaxially isotropic strain and of biaxially anisotropic strain that less than 1%)^28,38 and pure p-doping slopes. The maroon dashed line represents the expected Raman frequencies for pure strain with slope (∂ω_2D/∂ω_G) of 2.2^28,38 while the grey dashed line is for pure p-doping with ∂ω_2D/∂ω_G of 0.55.³⁴ The black solid line is the fitted data from NDs 1, 2 and 3 with ∂ω_2D/∂ω_G of 1.1. b Correlation plot of ω_2D vs. ω_G of areas A1 (red cross), A2 (orange hollow circle), A3 (green asterisk) and A4 (blue ×’s). Yellow hexagons represent average ω_2D and ω_G frequencies for each area. Error bars indicate one standard deviation from the average. Correlation plot of ω_2D vs. ω_G of micro-Raman data from Fig. 1 (green pound sign, excitation wavelength: 532 nm). Green star indicates unstrained and undoped Raman peak of monolayer graphene on SiO₂/Si substrate using 532 nm illumination (ω_G,SiO2,532 = 1580.8 cm⁻¹, ω_2D,SiO2,532 = 2676.2 cm⁻¹). Red line represents the expected Raman frequencies for pure strain at the 2.2 slope