Theoretical and experimental analysis of subwavelength bowtie-shaped antennas

Recently, bowtie-shaped apertures have received significant attention due to their extraordinary ability to generate dramatic field enhancement and light confinement in nanometer scale. In this article, we investigate both experimentally and theoretically nearfield and farfield responses of bowtie-shaped apertures in detail. We study the role of bowtie gap in creating large and highly accessible local electromagnetic fields. In order to experimentally excite strong local fields, we introduce a high-resolution and lift-off free fabrication method which enables bowtie apertures with gap sizes down to sub-10nm. We also show that for identical geometries, bowtie-shaped apertures support much stronger local electromagnetic fields compared to particle-based bowtie-shaped antennas. We investigate the role of polarization on the gap effect, which plays the dominant role for creating strong nearfield intensities. Finally, we introduce a mechanism to fine-tune the optical response of bowtie apertures through geometrical parameters.