Abstract
Vertically aligned multi-walled carbon nanotube (MWCNT) arrays fabricated by xylene pyrolysisin anodized aluminum oxide (AAO) templates without the use of a catalyst were integratedinto a resistive sensor design. Steady state sensitivities as high as 5% and 10% for 100 ppm ofNH3 and NO2, 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 thesensor design. The thickness of the conducting amorphous carbon layers wasfound 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 thethickness of amorphous carbon layers, (ii) the effect of UV light on gas desorptioncharacteristics and (iii) the dependence of room temperature sensitivity on differentNH3 flow rates. Variations in sensor resistance with exposure to oxidizing and reducing gases areexplained on the basis of charge transfer between the analytes and the CNTs which weremodeled as p-type semiconductors.
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