Development of a Hybrid Scanning Near-field Optical/Tunneling Microscope (SNOM/STM) System

Scanning near-field optical microscope (SNOM) is hybridized with a scanning tunneling microscope (STM) to investigate nanoscopic optical phenomena in both the near-field region and its proximity. The system is realized by introducing a doubly metal-coated optical fiber tip with an extremely small aperture (<100 nm), where the metal is coated on the aperture to obtain a half-transparent conducting tip after the fabrication of an “aperture probe.” A simultaneous SNOM/STM observation is performed for an Au (111) surface, where the evanescent field at the tip vicinity through the aperture is scattered by the local structures of the sample and the far-field component of the scattered light is collected as an optical signal. The distance control is carried out under the constant-current condition in order to separate the optical properties from surface topography. An optical resolution of λ/ 100 and identical channel transport for both electrons and photons are achieved. The intensity changes, as a function of the gap distance, are also measured in the far-field and the near-field regions and the proximity.