Peak force infrared microscopy for label-free chemical imaging at sub 10 nm spatial resolution

Chemical characterization of materials at the nanoscale provides insights into their compositions and organizations. Infrared spectroscopy has been a powerful tool that directly indicates the identity and amount of functional groups of molecules by measuring the absorption of infrared light. However, nanoscale spatial resolution is hard to achieve for conventional Fourier-transform infrared (FTIR) spectroscopy because of the optical diffraction limit. Herein we reported a recently developed infrared microscopy and spectroscopy technique also based on infrared absorption of molecules - peak force infrared microscopy - that combines atomic force microscopy and infrared laser illumination. Sub 10 nanometer spatial resolution has been demonstrated on various samples, including block copolymers, hexagonal boron nitride flakes, and amyloid fibrils. Simultaneous chemical and mechanical mapping can be obtained with peak force infrared microscopy in that both information is encoded in the cantilever deflection curves during peak force tapping cycles. The high spatial resolution and multimodal measurement capability render peak force infrared microscopy a label-free chemical imaging technique for explorations of nanoscale across broad disciplines.