Fig. 7: Illustration of the peak height ratio criterium. | Nature Communications

Fig. 7: Illustration of the peak height ratio criterium.

From: Subsurface chemical nanoidentification by nano-FTIR spectroscopy

Fig. 7

ac Schematic of the nano-FTIR experiment employing different higher harmonic demodulation orders n = 3 (red) and n = 4 (blue) for three samples with different geometries: a bulk material, b thin surface layers, and c subsurface layers. Gray areas mark the absorbing material. Ellipses below the tip illustrate the probing volumes. Graphs illustrate the exponential decay of near fields Ez for different demodulation orders. df Sketch of qualitative nano-FTIR phase spectra, corresponding to panels ac. For a given n, all φn spectra are normalized to \(\varphi _n^{{\mathrm{max}}}\) of bulk.

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