Single-Walled Carbon Nanotube Rope for Gas Sensor Application
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Single-Walled Carbon Nanotube Rope for Gas Sensor Application J.W.Lee, Y.M.Choi, K.J.Kong, H.J.Chang, and B.H.Ryu Advanced materials division, Korea Research Institute of Chemical Technology, Jangdong 100, Yuseong, Daejeon 305-600, Korea ABSTRACT A chemical gas sensor with a novel pad pattern applicable to NH3, NO2, and H2 gas was developed based on single-walled carbon nanotube ropes. In this pattern named BCE (Barricade confronting electrode), several electrodes were located at the circumference of a sample and each pair of electrode tips was designed to confront to each other with a narrow interval. Several single -walled carbon nanotubes were shifted to the interval by the centrifugal force generated through the rapid rotation of a sample equipped on the spinner. Our device showed improved performance for NO2, NH3, and H2 gases compared with others in references. INTRODUCTION One of interesting and important applications of single-walled carbon nanotubes is chemical gas sensors. Nanotubes have shown rapid response and very good sensitivity for various gas molecules such as NO21,2,3, NH32,4, or oxygen-based gaseous species4 than any existing metal oxide sensors5,6. In addition, nanotube-based sensors for carbon dioxide4, methane7, ethanol8, and even hydrogen9,10 have also been reported, respectively. For nanotube sensor applications, various types of electrode geometries have been suggested. Among them, IDE (interdigitated electrode) pattern was frequently applied for device fabrication for the simplicity of process. However, IDE offers multiple sites for electric connections between electrodes and nanotubes simultaneously and may cause the depletion of sensitivity for low resistance. Therefore, the performance of gas sensors fabricated with nanotube suspension cannot reach those of individual nanotube based FET(Field Effect Transister) type sensors1. In this report, to overcome the low sensitivity of IDE geometry, a novel electrode pad pattern, named BCE(barricade type confronting electrodes) was introduced. In addition, nanotubes were shifted, for the first time, to the narrow intervals between electrodes by centrifugal force without direct handing. The physical connection between nanotubes and BCE electrodes was explored by a high resolution FE-SEM(Field Emission Scanning Electron Microscope) and we showed how effective is our new method for sensor fabrication.
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EXPERIMENTAL DETAILS Single-walled carbon nanotubes(SWNTs) were dispersed in DMF(N,N-Dimethylform amide) solution and sonicated for more than 10 h without pause. The BCE pad pattern for our gas sensor was fabricated using the conventional photolithographic method. Gold electrode pattern was deposited on the oxidized Si substrate by Lift-off process. A SEM(Scanning Electron Microscope) image of the BCE pattern is shown in Fig. 1. In the figure, the interval between the electrodes is approximately 2 ~ 3 µm, which is a limitation of conventional lithography technology. The sample was equipped at the center of the conventional spin coater
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