Nanoscale imaging and spectroscopy is of increasing importance in a wide range of research fields over physics, chemistry, biology, and medical applications. With conventional optics the spatial resolution of optical microscopy and spectroscopy is limited to be a few hundreds of nanometers due to the diffraction limit. We try to overcome this limitation and to achieve even atomic-scale spectromicroscopy by combining state-of-the-art scanning probe microscopy with plasmonics. To this end, we have developed a sophisticated method to control “nanolight” that can be generated by localized surface plasmon resonance at the apex of a scanning probe microscope tip. The plasmonic properties can be manipulated by nanoscale structures of the tip and we use nano-fabrication technique with focused ion beam. As a simple demonstration, we have recently showed that plasmonic Fabry-Pérot resonance can be controlled by making a single groove on the tip shaft . This technique in combination with low-temperature scanning probe microscopy has a great potential for studying the nature of nanolight and atomic-scale light–matter interactions as well as for applying to many types of scanning near-field optical microscopies, thus paving the way for novel nanoscale imaging and spectroscopy. Furthermore, spectral control of the intense near-field at the apex of plasmonic tips may open up new opportunities for the realization of coherent laser-triggered electron point sources for low-energy electron microscopy and holography techniques.
 S. Liu, H. Böckmann et al. Nano Lett. 19, 3597 (2019).