Extended Data Fig. 3: Nano-FTIR analysis of Particle 33.

A, SEM image of Particle 33 showing where the FIB was used to mill through the protective Pt (box in red). The location FIBed for 3D reconstruction (Fig. 3) and STXM/TEM can also be seen in the upper left quadrant. B, Nano-FTIR map showing the sample height as a function of position. The ion beam milled deeper on the right side of the patch and exposed subsurface carbonates. Spectra from four locations (orange circles) were averaged to produce the orange spectrum shown in D. Spectra from two locations (blue circles) were averaged to produce the blue spectrum in D. C, S₂, the integrated infrared scattering intensity. The regions coated in Pt are brighter than the organic material. D, Spectra showing carbonate-rich (orange) and carbonate-poor (blue) organic spectra. The bold lines are the mean spectra with the 1σ standard deviation of the averaged spectra is plotted in a lighter shade. The N–H bend and amide C=O stretch peaks are visible at 1540 cm⁻¹ and 1650 cm⁻¹, respectively, with a blue-shift of several cm⁻¹ from the near-field interaction. A carbonate peak at 1465 cm⁻¹ and overtones near 2800 cm⁻¹ are visible in the orange spectrum. The N–H stretch at 3285 cm⁻¹ is visible in both spectra. The Si–O feature at 1015 cm⁻¹ is absent in both spectra.