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산화환원 활성 다공성 네트워크를 이용한 가스 센서 소자 제작

Title
산화환원 활성 다공성 네트워크를 이용한 가스 센서 소자 제작
Authors
김재준
Date Issued
2015
Publisher
포항공과대학교
Abstract
This thesis describes the synthesis, film device fabrication and gas sensing properties of redox-active porous coordination networks (PCNs) and its sensing mechanism based on X-ray crystallography. Our goals include the preparation of conductive PCN based on redox-active ligand and the understanding of charge transfer mechanism in PCN to develop selective, efficient and sensitive sensing material as electrical signal transduction sensor. The first part of the thesis describes the selective formation of conductive PCN films based on 2,5,8-tris(4’-pyridyl)-diazaphenalene (TPDAP) which is redox active ligand and cadmium nitrate by changing the rate of evaporation. The PCN film 1 which has π-staking columnar structure kept the crystallinity and showed clear intrinsic conductivity. However the PCN film 2 which has slipped 2-dimentional structure has low stability as shown in time-dependent current-voltage measurement. The simple evaporation method for crystallization also enabled to control the size of crystal by increasing the ratio of metal ions. The second part of thesis described the gas sensing ability of PCN film 1. The PCN film 1 showed air/vacuum dependent electrical property, which suggested electrical active property under humidity condition. Humidity sensing measurement showed that when only nitrogen gas containing small amount water by bubbling flowed to the PCN film 1, the current significantly increased with two order difference. However, if only nitrogen gas flow to the PCN film 1, it decreased with two order difference. In other words, PCN film 1 is capable of detecting water sensitively. Considering nitrogen gas doesn’t carry much amount of water by bubbling, we guess that sensitivity of PCN film 1 is also very high. The PCN film 1 showed electrical-inactive states under acetone/Ethanol vapour, which means that PCN film 1 has water selectivity. The mechanism of humidity sensing ability was proposed by x-ray structure analysis for the first time in this field by comparison between vacuum condition and hydrated condition. Hydration promotes the dissociation of NO3- because of solvation effect, inducing the positively charged network. The electron deficient state can naturally increase electronic interaction between the TPDAPs as evidence by electron density between them in single crystal x-ray analysis. This result suggested the number of water molecules changed the conductivity, which means this system be able to sense water concentration very finely. This research will help to realize the electron transfer mechanism in the redox-active PCNs and open the way for the practical use of redox active PCN as electrical sensors.
URI
http://postech.dcollection.net/jsp/common/DcLoOrgPer.jsp?sItemId=000002066943
https://oasis.postech.ac.kr/handle/2014.oak/93453
Article Type
Thesis
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