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

학위논문(박사)--서울대학교 대학원 :자연과학대학 물리·천문학부,2017. 2. 김대식.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.Chapter 1. Introduction 1 Chapter 2. Preparation of subwavelength gaps 4 2.1 Perforation by razor blade 5 2.2 Photolithography 8 2.3 Focused ion beam 12 2.4 Atomic layer lithography 14 Chapter 3. Experimental setups 17 3.1 Horn antenna pair 18 3.2 Open-ended waveguide pair 21 3.3 Terahertz time-domain spectroscopy 24 Chapter 4. Microwave field enhancement by λ/400-width hand-made gaps 26 4.1 Anomalous band formation in antenna arrays 27 4.2 Selective enhanced transmittances of asymmetric antenna pairs 31 4.3 Effects of fabrication errors 33 4.4 Summary 35 Chapter 5. Microwave field enhancement by λ/10,000,000-width nanogaps 36 5.1 Field enhancement by λ/2,000-width gaps 37 5.1 Details on the nanogap sample 39 5.2 Microwave transmission measurements 42 5.3 Comparison with terahertz time-domain spectroscopy 44 5.4 Summary 50 Chapter 6. Conclusions 51 Bibliography 54 요약 (국문초록) 65 List of publications 66 Conferences 67Docto