Figure 3.

(a) SERS intensity recorded for the Raman peak at 1378 cm${}^{-1}$ at ten positions taken randomly on the substrate (the black dashed line represents the average value of the SERS intensity with a RSD value of 5.4%). (b) SERS spectra for four positions of (a): in red at the position 8, in black at the position 6, in blue at the position 3 and in pink at the position 2. (c) SERS intensity distribution of the 1378 cm${}^{-1}$ peak for three distinct samples with an average RSD < 9%. (d) SERS spectra associated to three samples: in red for the sample 2, in black for the sample 1 and in blue for the sample 3.