Figure 6: (a) The relative SERS intensities 1 mM benzoic acid obtained on dual-layer coated substrates separated by different types of self-assembled monolayers (MAA, UDA, and HXDA represent 2, 11, and 16 carbon chains, resp.) and optimized SFON substrates. (b) The spectra showing the 1000 cm−1 band of 1 mM benzoic acid used for the measurement.