Highly sensitive ammonia gas sensors based on semiconductor-enriched carbon nanotube networks
- 주제(키워드) carbon nanotube , gas sensors , impedancemetric
- 발행기관 고려대학교 대학원
- 지도교수 민남기
- 발행년도 2015
- 학위수여년월 2015. 2
- 학위구분 박사
- 학과 일반대학원 제어계측공학과
- 원문페이지 121 p
- 실제URI http://www.dcollection.net/handler/korea/000000057237
- 본문언어 영어
- 제출원본 000045827884
초록/요약
Recently, nanostructures, such as carbon nanotubes (CNTs), have begun to attract wide attention in the study of their application to various sensors. The gas sensors based on single-walled carbon nanotubes (SWCNTs) show extreme sensitivity towards changes in their local chemical environment that stems from the susceptibility of their electronic structure to interacting molecules. So far, CNT-based gas sensors have been investigated for the detection of elements such as H2, N2, NO2, and NH3. For preventing an unexpected accident, such as a gas explosion or suffocation, very sensitive sensors are needed. Therefore, we developed a high-performance gas sensor based on highly semiconductor-enriched SWCNTs. The operating principles of the CNT based gas sensor can be classified into two major categories: the conductivity change of the CNT channels and the variation of the Schottky barrier between the electrode and the CNT film. Although the sensing mechanisms are different, the most effective component of the sensor sensitivity is the semiconductor/metallic tube ratio of CNT films. Typical SWCNTs consist of 66% semiconducting tubes and 33% metallic tubes. Purification technology has evolved; high purity semiconducting SWCNTs have been developed, and some SWCNTs consist of 99% semiconducting tubes. In this study, we fabricated 99% semiconducting SWCNT gas sensors. For comparison, we used semienriched 90% SWCNTs and typical SWCNT gas sensors that were also fabricated using solution-deposition and spray deposition, respectively. To enhance the sensitivity and the response time of sensors, oxygen plasma treatment was performed on the 66%-SWCNT and 90%-SWCNT gas sensors. We also demonstrated the effect of oxygen plasma treatment on the highly semiconductor-enriched SWCNT device. The sensor response to NH3 gas was characterized by a resistance increase at the moment of NH3 exposure. A general linear response was observed with an increasing NH3 concentration with a significantly greater responsiveness for the semiconductor-enriched 99% sensor compared with the 66% and 90% sensors. Furthermore, plasma treated 66% and 90% sensors (p-66% and p-90%, respectively) showed a higher performance than NH3 sensing due to the fact that oxygen functional groups were formed on the CNT film and the electrical structure of SWCNT was changed from metallic to semiconducting[1]. This suggested that a large semiconducting/metallic ratio is the most important factor for achieving a high sensitivity in mixed SWCNT-networked-based gas sensors.
more목차
Chapter 1 INTRODUCTION 1
1.1 OBJECTIVE 1
1.2 OUTLINE OF THE THESIS 7
Chapter 2 LITERATURE SURVEY 8
2.1 CARBON NANOTUBE BASED SENSORS 8
2.1.1 Semiconducting/metallic carbon nanotubes 8
2.1.2 Semiconducting single-walled carbon nanotube sensors 13
2.2 PLASMA TREATMENT ON CARBON NANOTUBE NETWORKS 18
2.2.1 Functionalization 18
2.2.2 Changes in the electrical properties in carbon nanotube networks 21
Chapter 3 EXPERIMENTAL DETAILS 24
3.1 DESIGN AND FABRICATION OF CARBON NANOTUBE GAS SENSORS 24
3.1.1 Basic structure of a gas sensor 24
3.1.2 Preparation of carbon nanotube networks and sensor fabrication 25
3.1.3 Oxygen plasma treatment on the carbon nanotube networks 30
3.2 GAS SENSORS MEASUREMENTS AND CHARACTERIZATION 31
3.2.1 Measurements 31
3.2.2 X-ray photoelectron spectroscopy 33
Chapter 4 RESULTS AND DISSCUSSION 35
4.1 MORPHOLOGIES OF CARBON NANOTUBE NETWORKS 35
4.2 GAS SENSING CHARACTERISTICS 37
4.2.1 Contact properties between Pd and SWCNT networks 37
4.2.2 Static characteristics of gas sensors 40
4.2.3 Dynamic characteristics of gas sensors 45
4.2.4 Electrical impedance spectroscopic analysis of gas sensors 49
4.3 EFFECT OF OXYGEN PLASMA FUNCTIONALIZATION ON CARBON NANOTUBE GAS SENSORS 65
4.3.1 X-ray photoelectron spectroscopy analysis 65
4.3.2 Sensing performance of the plasma treated gas sensors 71
4.3.3 Effect of xygen plasma treatment on semiconductor-enriched SWCNT networks gas sensors 83
Chapter 5 CONCLUSIONS AND FUTURE WORKS 87
References 89
