Super-Resolution Photothermal Infrared Imaging and Its Applications in Materials Science

This PhD thesis highlights recent advances in super-resolution, mid-infrared imaging and spectroscopy. It provides an overview of the different near field microscopy techniques developed to address the problem of chemically imaging specimens in the mid-infrared “fingerprint” region of the spectrum with high spatial resolution. It then focuses on a recently developed far-field all-optical technique, called infrared photothermal heterodyne imaging (IR-PHI), and discusses the technique in great detail. A significant part of the thesis devoted towards understanding the technique’s signal generation mechanism through the means of analytical modeling. Its practical implementation in terms of the best practices, equipment used, optical geometries employed are also described. The thesis further summarizes the milestones where IR-PHI allowed to achieve notable advances in materials science. It describes the greater understanding of local photophysical and photochemical properties of mixed-cation hybrid organic-inorganic perovskites. Importantly, it also studies dynamics of different organic cation within the perovskite layers during the operational conditions. This has led to better understanding of fundamental physical and chemical ions-related phenomena inside the working perovskite solar cells. Finally, the thesis shows a potential future application of IR-PHI in environmental science, where it can solve a long-standing problem of simultaneous chemical identification and concentration estimation of plastic micro- and nanoparticulates inside environmentally-relevant matrices.