Vertically oriented, three-dimensionally tapered deep-subwavelength metallic nanohole arrays developed by photofluidization lithography

Various metallic nanostructural motifs have attracted significant interest due to their exotic ability to localize and manipulate light in the nanoscale regime far beyond the diffraction limit. The incident visible light can be resonantly squeezed and focused into a deep-subwavelength-scaled point with high coupling efficiency by taking advantage of the 3D tapered geometry; consequently, the EOT, enabled by nanofocusing, was achieved even with deep-subwavelength-scaled metallic nanohole. The top and bottom radii of the truncated nanocone were 300 nm and 250 nm, respectively, while its height was 250 nm. First, the vertically oriented metallic nanohole enables efficient optical excitation of relevant plasmonic mode simply by light irradiation in a normal direction. Second, the 3D tapered geometry, rather than a simple cylindrical shape, offers an attractive way to enhance the efficiency of light coupling and nanofocusing into the deep-subwavelength-scaled spatial point.