Tip-Based Plasmonic Nanofocusing: Vector Field Engineering and Background Elimination

Nearly thirty years ago, Specht et al. proposed a new optical near-field microscope based on the interaction of surface plasmons and a sharp metal tip. Since then, the tip-based plasmonic nanofocusing has been widely studied. When the tip-based plasmonic nanofocusing integrated with scanning probe microscopy, it not only forms highly localized enhanced electric field to boost the spectral signal but also simultaneously provides morphological information. These amazing properties provide a new detection method to understand the nano-world, including spatial structures of chemicals and physical, electronic and catalytic properties of substance. Upon growing demand for background-free nanofocusing, more and more attention is being drawn to developing new technologies for it. Hitherto, owing to the salient properties, tip-based background-free nanofocusing have tremendous advanced applications such as ultrafast optics, nonlinear optics, and even electron emission. This article reviews the historical developments from fundamentals to the techniques for tip-based plasmonic nanofocusing and then to their advanced applications.