Hybrid scanning near-field optical/tunneling microscopy with indium-tin-oxide/Au coated optical fiber probe

As widely known, the spatial resolution of a scanning near-field optical microscope (SNOM) is strongly limited by its aperture size (50-200 nm). However, as reported by the authors [Jpn. J. Appl. Phys. 38 (1999) 3949], a hybrid system of a SNOM with a scanning tunneling microscope (STM) using a "doubly metal-coated optical fiber probe" could be used to overcome this limitation, resulting in a high-resolution feature (λ/50 ≃ 10 nm). However, the throughput of such a probe was extremely low because of the metal coating on the aperture. In this study, we developed a novel probe to overcome this disadvantage, where the metal coating on the aperture was replaced with an indium-tin-oxide (ITO) coating. The performance of this probe was evaluated by examining isolated CdSe nanoparticles on an ITO substrate. The fluorescence from each nanoparticle was observed as a bright spot with the full-width at half-maximum of about 20 nm, indicating high spatial resolution beyond the aperture size without sacrificing single-molecular-level high sensitivity.