시분해 테라파 분광학을 이용한 고전도성 탄소나노튜브 박막의 광학계수 측정
Optical Constants Measurements of Highly Conductive Carbon Nanotube Films by Using Time-domain Terahertz Spectroscopy
- 발행기관 아주대학교
- 지도교수 안영환
- 발행년도 2010
- 학위수여년월 2010. 2
- 학위명 석사
- 학과 및 전공 일반대학원 에너지시스템학부
- 실제URI http://www.dcollection.net/handler/ajou/000000010684
- 본문언어 한국어
- 저작권 아주대학교 논문은 저작권에 의해 보호받습니다.
초록/요약
단일벽 탄소나노튜브 (single-walled carbon nanotube) 는 뛰어난 기계적, 전기적, 광학적 특성들로 인하여 다양한 소자로써 이용할 수 있는 물질로 연구되어 왔다. 특히 단일벽 탄소나노튜브 박막은 구부리기 쉬운 물질로써 가공에 용이하여 그 잠재성이 매우 크다. 또한 점증하는 고속, 고집적 회로에 대한 기술적 수요가 증가하는 추세에서, 경량의 전자기 간섭 차폐 물질의 필요성이 주목되고 있다. 이와 관련하여 본 연구그룹에서는 선행연구를 통하여 탄소나노튜브 필름이 테라파 (Terahertz waves) 의 효과적 차폐 물질로 작동될 수 있음을 증명한 바 있다. 그러나 높은 테라파 차폐 효율 (Shielding effectiveness) 을 달성하기 위해서는 더 두꺼운 단일벽 탄소나노튜브 박막의 제작이 필수적임이 밝혀졌으며, 따라서 선행 연구에서 활용해왔던 스핀 코팅 (spin-coating) 의 방법으로는 한계가 있다. 본 연구에서는 두꺼운 탄소나노튜브 박막 제작을 위하여 진공여과방법을 채택하였다. 박막 제작에 앞서 아크 방전법 (Arc discharge) 으로 성장시킨 단일벽 탄소나노튜브를 사용해 초음파 분해 방법으로 분산용액을 제작했다. 이 분산용액을 니트로셀룰로오스막 (Nitrocellulose membrane) 위에 진공여과방법으로 여과시켜 단일벽 탄소나노튜브 박막을 제작하였다. 탄소나노튜브 박막의 두께는 분산용액의 양으로 조절이 가능하며, 이를 통하여 30 nm 에서부터 800 nm 까지 다양한 두께를 가지는 탄소나노튜브 박막을 제작하였다. 이렇게 제작된 단일벽 탄소나노튜브 박막에 테라파를 입사시켜 시분해분광학 (terahertz time-domain spectroscopy) 방법으로 투과 스펙트럼을 검출하였다. 테라파 시분해 실험을 위해 836 nm 파장의 펨토초 레이저를 ZnTe 결정에 입사시켜 테라파를 생성하였고, 전광 표본추출 방법을 이용하여 시료를 투과한 테라파를 검출하였다. 그 결과 투과된 파는 박막의 두께가 증가 할수록 극적으로 줄어드는 것을 확인할 수 있었다. 특히 800 nm 두께의 단일벽 탄소나노튜브 박막의 경우, 1 % 내외의 투과율을 보였다. 또한 박막의 두께가 30 nm 에서 800 nm 로 달라짐에 따라 차폐 효율이 2 dB 에서 40 dB 로 변화함이 측정되었다. 또한 우리의 단일벽 탄소나노튜브 박막의 유전함수는 정확하게 전도성 금속에서 관찰할 수 있는 간단한 드루드 모형 (Drude model) 을 따른다는 것을 확인할 수 있었다. 제작된 모든 박막들은 비슷한 주파수 응답을 보이는데, 이는 상대적으로 얇은 박막의 경우에서조차 전도성 금속의 성질을 띰을 의미한다. 단일벽 탄소나노튜브 박막을 원자힘현미경 (AFM) 으로 측정한 결과 대부분 좋은 네트워크 구조를 보였다. 이러한 결과들은 박막의 두께와 전기적 특성 사이의 상호관계에 대한 연구에 테라파 분광학이 효과적으로 이용될 수 있는 가능성을 시사한다.
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제 5 절. 테라파 분광과 고속 푸리에 변환 ·························································· 16
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