Low temperature ethanol response enhancement of ZnO nanostructures sensor decorated with gold nanoparticles exposed to UV illumination

To increase the ethanol sensing at low operating temperatures in ZnO nanostructure sensors, the gold nanoparticles were introduced to ZnO nanostructures (ZnO:AuNPs) by a sputtering technique. Then, the ethanol sensing characteristics were investigated under UV illumination at the temperatures in the range of 25-125 °C. It was found that the sensor response of ZnO:AuNPs sensor under UV illumination was remarkably improved. Moreover, the sensor based on ZnO:AuNPs under UV illumination exhibited the increasing of sensor response toward ethanol vapor with an increasing of UV illumination intensity from 0 to 4.1 mW/cm2. The sensor response enhancement mechanism can be explained by two main effects including sensor response enhancement due to an addition of AuNPs on ZnO nanostructures and UV illumination. The AuNPs added onto ZnO nanostructure strongly affect the chemical reaction change in the oxygen adsorption reaction resulting in a larger depletion layer width. As a result, the sensor response is enhanced to higher than that of ZnO nanostructure sensor. The sensor response enhancement due to UV illumination is explained by the formation of weakly bound oxygen ions from electron carriers being excited from band to band and oxygen molecule in air. This produces a thinner depletion layer width with the weakly bound oxygen ions due to the photo activation which are easily removed from the ZnO surface resulting in high sensor response with lower resistance.