Fig. 2
STM-TERS spectroscopic imaging of area A1 (23 × 14 nm2, 0.5 nm/pixel) and spatial resolution. a Representative TERS on graphene (red), TERS on bare Au(111) substrate (blue), and far-field (black, tip retracted) Raman spectra (exposure time = 0.3 s). STM-TERS spectroscopic imaging of D, G and 2D bands showing integrated intensity: b D, (ID), c G, (IG) and d 2D, (I2D); Raman shifts: e D, (ωD), f G, (ωG) and g 2D, (ω2D), and spectral widths: h D, (ΓD), i G, (ΓG) and j 2D, (Γ2D). Red “x” mark in d is the point where TERS and far-field (tip retracted) spectra in Fig. 4c were measured. Three NDs with characteristic Raman peak shift are labelled in g as NDs 1, 2 and 3. Black lines in g are a guide to the eye to identify the extent of the NDs. Scale bar indicates 5 nm. k Average TERS spectra from NDs 1 (blue), 2 (green) and 3 (red). l Line profile of step response taken at red line in b. STM-TERS spatial resolution is 0.7 nm based on the 10-90% distance. m Long exposure (300 s) measurement of far-field Raman taken at the same point as TERS measurements showing only G and 2D bands. Excitation laser of λ = 632.8 nm with a laser power of 0.35 mW at the sample was used (tunnelling current: 40 pA; bias voltage: 300 mV)
