A sample resembling the simulated structure using FEM and PSF model was prepared using PMMA beads with diameters of approximately 140 nm. These beads were suspended in a PE matrix and subsequently microtomed into thin slices with a thickness of 1 µm (refer to the Methods section for more details). The buried absorber (see Fig- ) was detected using the 1730 cm -1 carbonyl band of PMMA (see Figure ) which can be clearly distinguished from the matrix spectrum. The AFM-IR absorption image (also referred to as "chemical image") at 1730 cm -1 shows a single PMMA bead (see Figure ) with a FWHM determined from the cross section through the chemical image of 121 nm.