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 CNT yarns 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 CNT yarns. Nanocrystalline Au particle distributions in the cases of untreated and acid treated CNT yarns were sparse and the particle sizes were larger (10–20 nm). In all cases the introduction of Au to the yarns 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 ∼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.