Vertically Aligned Carbon Nanotube Arrays for Room Temperature Gas Sensors
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1057-II20-08
Vertically Aligned Carbon Nanotube Arrays for Room Temperature Gas Sensors Suresh Rajaputra1, Raghu Mangu1, Ning Ma1, Patricia Clore1, Dali Qian2, Rodney Andrews2, Sovannary Phok1, Janet Lumpp1, and Vijay Singh1 1 Electrical & Computer Engneering, University of Kentucky, 453 Anderson Hall, Lexington, KY, 40506-0046 2 Center for Applied Energy Research, University of Kentucky, 2540 Research Park Drive, Lexington, KY, 40511-8479 ABSTRACT Vertically aligned multiwalled carbon nanotube (CNT) arrays were fabricated in anodized aluminum oxide (AAO) templates without the use of a catalyst, using xylene pyrolysis. The CNT arrays in AAO template were integrated into a resistive sensor design. The sensors were found to be highly responsive to NH3 and NO2 with steady state sensitivities of 5% and 10% for 100ppm of NH3 and NO2 respectively, at room temperature. Results were interpreted in terms of the CNTs acting as p-type semiconductors. A study was undertaken to elucidate the dependence of sensitivity on the thickness of the conducting amorphous carbon layers on top and bottom. Recovery of the MWNT gas sensor was studied for different types of desorption techniques. The thickness of the amorphous carbon layer (sheet resistance) was found to be critical in determining the sensor response. INTRODUCTION In recent years, there has been growing interest in carbon nanotubes [1-3] because of their unique structure, properties and potential applications in electronics. The carbon nanotubes (CNTs) can be either metallic or semiconducting, depending on the diameter and chirality [4].Recent reports of the gas sensing capabilities of carbon nanotubes through the charge transfer or capacitance change by gas absorption (e.g., NH3, NO2, DMMP) [5-9] is significantly important. Carbon nanotubes with their small size, high surface area, excellent mechanical and electronic properties offer many advantages for sensing applications. The usage of carbon nanotubes in the pristine form for gas sensing, often involves a cumbersome processes of integrating either single or bundles of carbon nanotubes into various sensor designs. Aligned carbon nanotube arrays, offer several advantages for the development of novel sensor designs without the need for direct manipulation of individual nanotubes. The aligned nanotube structure further provides a large well-defined surface area and the capacity for modifying the carbon nanotube surface with various transduction materials [10-12, 19] to effectively enhance the sensitivity and to broaden the scope of analytes to be detected. Our method allows for tuning the sensor response via the control of the outer/ inner core diameters of the nanotubes, tube density which can be achieved by controlling the pore size and inter-pore spacing in highly ordered AAO templates [24] and CVD conditions [25]. It has been demonstrated that CNTs can be used to detect small concentrations of molecules with high responsiveness under ambient conditions. The adsorption of electron donating (NH3) or electron-withdrawing (NO
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