Optical imaging of nanosized structures by using plasmonically excited cascade near-field coupling with a carbon nanotube probe

Abstract

Near-field scanning optical microscopy (NSOM) overcomes the diffraction limit, thereby realizing a spatial resolution far beyond the wavelength of light used. However, NSOM still has a problem in repeatable imaging at the high spatial resolution and high contrast with conventional aperture or apertureless probes that are needed for practical applications. Here, we describe an optical imaging technique based on plasmonically excited cascade near-field coupling that has the potential to achieve single-nanometer spatial resolution with high imaging repeatability. This technique makes use of a plasmon waveguide coupled with a high-stiffness carbon nanotube optical probe. Through the action of surface plasmon polaritons, the input far-field light is converted into an optical near field that is used as an excitation source. This excitation near field is strongly enhanced and concentrated on the probe tip such that it generates a second near field as a nanosized probe spot on the apex of the tip. Extremely high-resolution optical imaging is accomplished by scanning the sample surface with the probe spot. At a wavelength of 850 nm, a 5-nm-wide metallic striped pattern on a cross-sectional superlattice sample was clearly resolved as a permittivity distribution.