IR near-field nanoscopy and nanospectroscopy

Scattering-type scanning near-field optical microscopy (s-SNOM) and nanoscale Fourier transform infrared spectroscopy (nano-FTIR) open a new era in modern nanoanalytics, including the chemical identification of organic and inorganic materials, protein secondary structure mapping, free-carrier profiling in semiconductors, or mapping of plasmon polaritons in 2D materials such as graphene, all with a spatial resolution of about 10 - 20 nm. s-SNOM and nano-FTIR are based on elastic light scattering at an atomic force microscope tip, employing either monochromatic laser illumination or broadband illumination from a glow bar, a supercontinuum laser or a synchrotron. Acting as an optical antenna, the tip converts the illuminating field into a strongly concentrated near field at the very tip apex (nanofocus), which provides a means for local excitation of molecule vibrations, plasmons or phonons in the sample surface. Recording of the tip-scattered field as a function of sample position (employing monochromatic illumination) yield nanoscale-resolved IR and THz images, while Fourier-transform spectroscopy of the tip-scattered field (employing broadband illumination) allows for nanoscale IR point spectroscopy and IR hyperspectral nanoimaging. In this talk, recent developments, trends and applications in materials sciences and nanophotonics will be discussed.