Left: DC16-14-309-b AFMIR maps recorded at 1710 cm⁻¹ (green), 1600 cm⁻¹ (red), and 1470 cm⁻¹ (blue), composite (red, green blue) image of the three maps, AFM height, and back-scattered electrons (BSE) image (the bottom-right bright spots are associated with a contamination, with recorded spectra shown in Fig. 9). The orange square delineates the region analysed by EDX. Top right: far-field spectrum. Vertical lines in the inset indicate the laser settings used to map the sample. Bottom right: sulphur, silicon, iron, magnesium and oxygen X-ray maps. The bright spot in Si, Mg and Fe corresponds to silicates. The more extended sulphur spots probably include some elemental sulphur from the sample preparation. The AFMIR 1710 cm⁻¹ map is shown at the same scale.