Vertically aligned multi-walled carbon nanotube (MWCNT) arrays fabricated by xylene pyrolysis in anodized aluminum oxide (AAO) templates without the use of a catalyst were integrated into a resistive sensor design. Steady state sensitivities as high as 5% and 10% for 100 ppm of NH(3) and NO(2), respectively, at a flow rate of 750 sccm were observed. A thin layer of amorphous carbon (5-50 nm), formed on both sides of the template during xylene pyrolysis, was part of the sensor design. The thickness of the conducting amorphous carbon layers was found to play a crucial role in determining the sensitivity of the resistive sensor. A study was undertaken to elucidate (i) the dependence of sensitivity on the thickness of amorphous carbon layers, (ii) the effect of UV light on gas desorption characteristics and (iii) the dependence of room temperature sensitivity on different NH(3) flow rates. Variations in sensor resistance with exposure to oxidizing and reducing gases are explained on the basis of charge transfer between the analytes and the CNTs which were modeled as p-type semiconductors.
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.
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