NO Gas Sensing Characteristics of Wire-Like Layered Composites Between Zinc Oxide and Carbon Nanotube

We report on the NO gas sensing properties of Al-doped zinc oxide-carbon nanotube (ZnO-CNT) wire-like layeredcomposites fabricated by coaxially coating Al-doped ZnO thin films on randomly oriented single-walled carbon nanotubes. Wewere able to wrap thin ZnO layers around the CNTs using the pulsed laser deposition method, forming wire-like nanostructuresof ZnO-CNT. Microstructural observations revealed an ultrathin wire-like structure with a diameter of several tens of nm. Gassensors based on ZnO-CNT wire-like layered composites were found to exhibit a novel sensing capability that originated fromthe genuine characteristics of the composites. Specifically, it was observed by measured gas sensing characteristics that the gassensors based on ZnO-CNT layered composites showed a very high sensitivity of above 1,500% for NO gas in dry air at anoptimal operating temperature of 200 o C; the sensors also showed a low NO gas detection limit at a sub-ppm level in dry air.The enhanced gas sensing properties of the ZnO-CNT wire-like layered composites are ascribed to a catalytic effect of Alelements on the surface reaction and an increase in the effective surface reaction area of the active ZnO layer due to the coatingof CNT templates with a higher surface-to-volume ratio structure. These results suggest that ZnO-CNT composites made ofultrathin Al-doped ZnO layers uniformly coated around carbon nanotubes can be promising materials for use in practical high-performance NO gas sensors.Key wordsoxide gas sensor, zinc oxide, carbon nanotube, ZnO-CNT composite.