Figure 4: Nano-FTIR mapping of PM.

(a) Topography image of PM on a silicon substrate. Scale bar, 100 nm. (b) Infrared spectroscopic line scan recorded while the tip was scanned in 10 nm steps along the line of red and blue dots in a. At the position of each dot, a spectrum was taken (each spectrum is an average of 17 interferograms; 2.3 min acquisition time; 16 cm⁻¹ resolution; × 6 zero filling). (c) Absorption signal a₃ at 1,660 cm¹ as a function of position x. (d) Twenty nano-FTIR spectra recorded at the positions P1–P20 marked by red and blue dots in a. The spectra are the same as those presented in b. For better visibility, each spectrum is vertically offset. All spectra have been normalized to the reference spectrum recorded at the position marked by the yellow dot and R in a.