Nanoscale Imaging And Spectroscopy

Near field manipulation in plasmonic nano cavities can provide various applications in nanoscale science and technology. But in some particular, a gap plasmon in a scanning tunneling microscope (STM) junction is of key interest to nanoscale imaging and spectroscopy.

But for spatial resolution of optical microscopy and spectroscopy; is determining by how much one can confine light in space; which is usually restricting to about half micrometer at the best due to the diffraction limit. However, light can be confining into nanometer scale by using the metallic nanostructures through excitation of localizing surface plasmon resonance (LSPR).

Spectroscopy for nanomaterials

But by having such “nanolight” at a sharp metallic tip; is particularly useful because it can be using in scanning tunneling luminescence (STL); and scattering type scanning near field optical microscopy (s-SNOM) performing nanoscale imaging;  and spectroscopy to look at nanomaterials and even single molecules.

However, precise manipulation of nanolight in nanoscale junction has remaining an outstanding problem. Because the nature of nanolight (LSPR) is determined by the nanoscopic structure of the tip; its manipulation requires a fine processing technique at the nanoscale; showing that spectral features of a plasmonic STM junction can be manipulated by nano fabrication of Au tips using focused ion beam.

Plasmonics and nanooptics

The STML spectra with the grooved tips exhibit a characteristic modulation resulting from Fabry Perot type interference of surface plasmon polaritons (SPPs) on the tip shaft; as the standing wave formation is visualizing in the electrodynamic simulation.

The spectral modulation can be precisely controlled by the groove position on the shaft. They also demonstrated that the SPP Fabry Perot interference can be improving by optimizing the overall tip shape; showing a great potential of the combination of scanning probe techniques and nano fabrication of plasmonic tips using FIB in order to study the nature of nanolight and light matter interactions in nanocavities; which are an important frontier of plasmonics and nano optics.