Atomic force microscope based infrared spectroscopy (AFM-IR, nanoIR) is an effective analytical technique for identifying the “chemical family” of a substance with high spatial resolution. Typically, organic and polymeric compounds (and, to a lesser degree, inorganic compounds) produce a unique “fingerprint” IR spectrum that is reflective of the chemical structure of the compound.

Similar to Fourier Transform Infrared Spectroscopy (FTIR), nanoIR measures the absorbance of infrared light by a sample and generates a spectrum based on the functional groups in the material. However, FTIR is typically limited to a spatial resolution on the order of tens of microns, and samples that are too thick cannot always be directly analyzed without additional preparation. These limitations are bypassed in nanoIR by utilizing the AFM cantilever as a near-field detector for infrared absorption in the sample. The detection of IR absorbance is localized to the cantilever tip (~30 nm radius), subsequently resulting in spatial resolutions down to tens of nanometers. Briefly, if a material absorbs infrared light at a particular frequency, there is a subsequent thermal excitation and expansion of the sample, which is detected by the AFM cantilever. Measuring the cantilever response as a function of laser frequency generates a spectrum that is proportional to the infrared absorption of the material. The resulting spectra are often highly similar to those obtained via FTIR, enabling compound/family identification via comparisons to EAG’s extensive reference database.