Fabrication of a carbon nanotube-based gas sensor using dielectrophoresis and its application for ammonia detection by impedance spectroscopy

Abstract

This paper describes a new method for fabricating a gas sensor composed of multi-wall carbon nanotubes (MWCNTs) using dielectrophoresis (DEP). MWCNTs dispersed in ethanol were trapped and enriched in an interdigitated microelectrode gap under the action of a positive DEP force that drove the MWCNTs to a higher electric field region. During the trapping of MWCNTs, the electrode impedance varied as the number of MWCNTs bridging the electrode gap increased. After the DEP process, the ethanol was evaporated and the microelectrode retaining the MWCNTs was exposed to ammonia (NH3) gas while the electrode impedance was monitored. It was found that the electrode impedance was altered by ppm-levels of ammonia at room temperature. The ammonia exposure decreased the sensor conductance, while the capacitance increased. The sensor showed a reversible response with a time constant of a few minutes. The conductance change was proportional to ammonia concentration below 10 ppm and then gradually saturated at higher concentrations. Effects of the number of trapped MWCNTs on sensor response were also discussed.

Sensitive detection of Nitrogen Dioxide using gold nanoparticles decorated Single Walled Carbon Nanotubes

“…Among all harmful gasses, NO 2 is a well-known toxic gas and air pollutant and monitoring its concentration is crucial for air quality monitoring. Prolonged exposure to low concentration of NO 2 capable of causing several health hazards such as coronary artery disease as well as stroke [5][6]. The sensitivity of SWNTs towards NO 2 at atmospheric temperature as reported [1] is particularly interesting.…”

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“…Figure 3 gives the shape of the device. The detection of a clamped circular shape under a uniform pressure P is denoted by w and is given by [8]:…”

Gas Sensors Based on Decorated Carbon Nanotubes

“…However, the number of nanotubes is not well controlled and their orientations are random. Dielectrophoresis (DEP) technique using ac electric fields (Suehiro et al 2003), (Gelamo et al, 2009a) has proven to be a very efficient technique for deposition of aligned nanotubes in desired position between metallic electrodes. In a DEP process, elongated polarized objects are aligned and attracted to the area of strongest electric field (Pohl, 1978).…”

“…To improve sensitivity, large area interdigitated electrodes can be used, with the gaps filled with a big number of nanotubes. This kind of devices has been successfully used to detect gases and organic vapors, including at room temperature, at mW power consumption (Li et al 2003), (Suehiro, Zhou and Hara 2003). In principle, the MWCNTs based sensors must be less sensitive than those based on SWCNTs, as the measured current (and the associated noise) is supposed to pass through the whole volume of a MWCNT including all internal walls, whereas the reaction with gases should affect mainly the current fraction through the outermost wall.…”