Active and passive control of nanogaps for optical and electrochemical applications

국문 초록 (Abstract)

본 논문에서는 원자층 리소그래피 방식을 활용하여 내부가 빈 금속 나노갭을 제작하여 광학적 및 전기화학적으로 활용하는 방법에 대해서 탐구하였다. 먼저 나노갭 내부의 유전체 박막을 화학적으로 식각하고 에너지분산형 분광분석법 및 테라헤르츠파 분석을 통해 갭 내부가 완전히 비어 있음을 확인하였다. 다음으로 속이 빈 나노갭을 온도 변화에 따라 테라헤르츠파 투과특성 변화를 관측하여 능동적인 나노안테나로써 활용하였으며 그 원인이 온도 변화에 따른 금속의 열팽창으로 인한 것임을 확인하였다. 한편, 나노갭 내부의 유전체 박막을 식각하는 과정에서 물이 갭 내부에 채워질 수 있다는 사실을 발견하고 가장 폭이 작은 나노 전극으로 활용하여 산화환원반응의 증폭을 유도하였다. 본 연구에서 제시하는 나노갭 제작 방식을 통해 나노광학, 전기화학, 전기분광학 등 매우 다양한 분야에서 이러한 나노갭을 활용할 수 있는 가능성을 기대할 수 있다.

다국어 초록 (Multilingual Abstract)

In this thesis, I studied the utilization of air-filled metallic nanogaps for optical and electrochemical applications. Using atomic layer lithography, spacer-filled nanogaps are fabricated and the dielectric spacer filled in the gaps is chemically etched. Full-access into the gaps is demonstrated by measuring terahertz (THz) transmission through nanogaps and energy dispersive spectroscopy (EDS) in a scanning transmission electron microscope (STEM) setup. After etching the dielectric spacer, air-filled nanogaps are first utilized as active nano-antennas for the thermal control of optical properties of THz waves, originating from the reduction of the gap width due to thermal expansion of metals. Meanwhile, water-filled nanogaps fabricated during the chemical etching process can be served as nano-electrodes for electrochemical amplification. I fabricated the narrowest nano-electrodes with 10 nm electrode distance for redox cycling and observed amplified Faradaic current which is inversely proportional to the electrode distance. These works provide useful applications in the active thermal control of the optical responses in the nanostructures and electrochemical sensing with excellent detection sensitivity.

목차 (Table of Contents)

• Chapter 1. Introduction 1
• Chapter 2. Full-access into the nanogaps fabricated via a spacer-based technique 4
• 2.1 Fabrication of spacer- and air-filled nanogaps via atomic layer lithography 4
• 2.2 Demonstration of full-etching of a dielectric spacer filled in nanogaps 9
• Chapter 3. Active thermal control of THz nano-antennas 13
• 3.1 Introduction: Modulation of electromagnetic waves through nanostructures combined with active materials 13
• 3.2 Thermal control of THz optical responses of air-filled nano-antennas 18
• 3.3 Effect of a dielectric spacer on the thermal control of air-filled nanoantennas 24
• 3.4 Effect of the gap width on the thermal control of air-filled nano-antennas 27
• 3.5 Theoretical study on the thermal control of air-filled nano-antennas 30
• 3.6 Various factors related to the thermal control of air-filled nano-antennas 34
• 3.7 Durability of air-filled nano-antennas according to the thermal control of air-filled nano-antennas 37
• Chapter 4. Electrochemical amplification in 10 nm wide nano-electrodes 40
• 4.1 Introduction: Electrochemical cells and redox cycling 40
• 4.2 Calculation of Faradaic limiting current during redox cycling 43
• 4.3 Fabrication of 10 nm wide nano-electrodes using modified atomic layer lithography 48
• 4.4 Fabrication issue: Electrostatic damage (ESD) of nano-electrodes 52
• 4.5 Measurement of Faradaic current with 10 nm wide nano-electrodes 55
• Chapter 5. Conclusion 60
• Chapter 6. Appendix 62
• 6.1 Terahertz time-domain spectroscopy 62
• Bibliography 64
• Abstract in Korean 78