Figure 2

Subtraction Raman spectra of (a) the average CTRL signal versus the average signal of COV+ , (b) the average CTRL signal versus the average COV- spectrum and c) the average COV+ signal versus the average COV− signal. The ± 0.005 ∆I interval is indicated in the graphs, confirmed by the error propagation from the spectra standard deviation. d) Overlapped average spectra of CTRL, COV+ and COV− with the main different regions highlighted.