Properties of gas sensor using CNTs thin film prepared by PLD/CVD method
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Properties of CNTs gas sensors prepared using PLD/CVD method T. Ueda, H. Norimatsu, M.M.H. Bhuiyan, T. Ikegami, K. Ebihara Graduate School of Science and Technology, Kumamoto University, 2-39-1, Kurokami, Kumamoto 860-8555, Japan Abstract Carbon nanotubes (CNTs) were grown on Si (with Si3N4 film on the surface ) and Al2O3 substrates with Pt electrodes using pulsed laser deposition (PLD) – and chemical vapor deposition (CVD) method in order to prepare a gas sensor which can operate at room temperature. To prepare a gas sensor which can operate at room temperature, CNTs were grown on Si substrate and Al2O3 substrate with interdigital Pt-electrodes (sensor substrate) using both PLD and CVD method. In this method, Fe thin film as catalyst was prepared by PLD method and then CNTs were grown on the Fe thin film by thermal CVD method. Surface images of prepared CNTs on the substrates were observed by SEM, and the gas sensing property specific to NO gas was measured. Resistance of the prepared CNTs gas sensor decreased with increase of sensor temperature, and it increased in NO ambient gas at room temperature. 1. Introduction In recent years, interest in air pollutants and its monitoring have been growing in our life. Nitrogen oxides (especially NO and NO2) are typical air pollutants that cause environmental problems. In light of these issues, it is necessary to develop highly sensitive NOx gas sensors of low cost for ambient air monitoring. CNTs are a promising material that has unique properties such as high electrical conductivity, mechanical strength and high aspect ratio. In particular, SWNTs show promise as effective material in light of their very thin diameter and of their subsequent large specific surface area, in addition to the properties of other types of CNTs. Some types of gas sensors using CNTs have been proposed. A gas ionization sensor, in which CNTs are used as field emission electrodes for the electrical breakdown of gas, has a high gas selectivity and sensitivity[1]. Another type of CNT gas sensor is based on the change of electrical conductance of CNT which adsorbed gas molecules. This type sensor is expected to have very high sensitivity and fast response at ambient temperatures and compatibility with the integrated circuits. The mechanism which underlies the deployment of single-walled CNTs (SWNTs) within gas sensors can be accounted for in terms of the dependence of conductivity of the SWNT on the adsorbance to oxidizers and on the charge transfer between the SWNT surface and gas molecules adsorbed (Fig.1)[2-3]. Many methods of preparing CNT have been reported, laser ablation, arc-discharge, thermal CVD, plasma-enhanced CVD, etc. In order to realize the practical application, including application to CNTs gas sensor, nanotubes need to be prepared in high quality and quantity at low cost. In this paper, we prepared CNTs thin film by PLD/CVD method on Si substrates. To prepare a sensor device, Al2O3 substrates with Pt interdigital electrodes (hereinafter called as “sensor substrate”) wer
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