Rapid and ultrahigh ethanol sensing based on Au-coated ZnO nanorods.

Rapid and ultrahigh sensing is realized from Au-coated ZnO rods with diameters down to 15 nm. Both the small diameters and the Au coating make the surface-depletion effect more pronounced for gas sensing. Such enhanced surface depletion increases the sensitivity, lowers the operation temperature and decreases the response time. A sensitivity of 89.5-100 ppm ethanol is obtained with response time shorter than 2 s at 300 °C, and the operation temperature can be as low as 150 °C. It is found that the Au coating improves the sensitivity by three times; this is much higher than that of noble metal-doped metal oxide sensors controlled by a grain-boundary barrier. Our results imply that the surface-depletion model is very helpful in fabricating high performance gas sensors.