Microwave field enhancement by deep subwavelength metallic gaps down to five nanometers

Abstract

In this dissertation, I describe experimental demonstrations of strong field enhancements in microwave regime achieved by deep subwavelength metallic gaps down to 5 nanometers. I built a Ku band (12~18 GHz) free-space setup to measure transmittances and electric field enhancement factors of the samples. I prepared λ/400-width slot antennas by punching aluminum foils with a razor blade and the hand-made antennas exhibited good agreements to the previous studies of terahertz nanoantennas which have a similar aspect ratio of the incident wavelength and the widths of slots. To investigate deeper subwavelength regime, λ/10,000,000-width nanogaps were fabricated by high-throughput atomic layer lithography. I built three open-ended waveguide pair setups to cover Ku, K (18~26.5 GHz), and Ka (26.5~40 GHz) band spectra and observed giant electric field enhancement factors up to 5,000 with the nanogaps. I also performed terahertz time-domain spectroscopy with the same sample and confirmed a convergence to the microwave range. As a potential application of subwavelength microwave optics, I exhibited a λ/2000-width microwave switch based on insulator-metal transition. The aforementioned researches would open up a way to enhance nonlinearities and detection sensitivities of microwave and millimeter-wave optics applications and enable non-invasive molecule trappings and designed fluidic controls by light.