Fig. 4

ETRs induced by 1 L edge and 1–2 L step. a, b Plots of normalized intensities of TERS peaks with the tip positions across the 1 L edge (a) and 1–2 L step (b). The solid lines are the fitted results. See Supplementary Note 2 for details about the data fitting. Note that these spectra are the pure near-field signals and have been subtracted with the far-field signals. Supplementary Fig. 20b, cshows more data sets for the corresponding line-trace TERS spectra. Enhanced TERS intensity profiles of the ETR in 1 L edge (c) and 1–2 L step (d) after the deconvolution of the EM field intensity distribution (see Supplementary Note 2 for more details).