Ammonia sensing characteristics of carbon-nanotube yarns decorated with nanocrystalline gold

Ammonia-gas-sensing characteristics for gold-decorated carbon-nanotube yarns (CNT yarns) at room temperature are presented. CNT yarns were fabricated from vertically aligned multi-walled carbon-nanotube forests. The CNTyarns were first treated either with strong acid or in a pulsed direct-current plasma containing Ar and either oxygen or hydrogen. Self-fuelled electrodeposition method was used and is shown to be a useful method for incorporating nanocrystalline Au particles onto the surfaces of CNT yarns. The plasma treatments lead to surface modification resulting in dense and uniformly-distributed Au particles smaller than 3 nm along the lengths of CNTyarns. Nanocrystalline Au particle distributions in the cases of untreated and acid treated CNTyarns were sparse and the particle sizes were larger (10-20 nm). In all cases the introduction of Au to the yams increased the sensitivity (measured as a change in resistance in a chemiresistor arrangement) to NH3 by about a factor 10 in comparison to yarns with no Au. The lowest concentration of NH3 that was detectable using this method was similar to 500 ppb. Plasma-treated and Au decorated samples showed stable, reproducible response and recovery. Recovery in general was poor and non reproducible in the cases of acid-treated and Au coated samples. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.