Gas sensing property of ZnO NR arrays stabilized by high-temperature annealing and the mechanism of detecting reduce gases

Abstract

Due to the high sensitivity and lithographic compatibility, gas sensors prepared with ZnO nanorod (NR) arrays in-situ grown on substrates receive much attention. In this work, ZnO NR arrays are grown on ITO glass by a solution method and the thermal stability is studied. It is found that the instability of as-grown sample can be associated with the metastable defects formed during the growth of ZnO NR arrays and the variation of surface states during the measurement. After high-temperature annealing, the thermal stability of ZnO NR arrays are improved, while the best working temperature is shifted to ∼350 °C. By studying the effects of annealing temperature on the thermal stability, the lowest annealing temperature is suggested to be 400 °C for stabilizing ZnO NR arrays. After annealing at 400 °C in air, the ZnO NR arrays exhibit sufficiently good reproducibility with the gas response of ∼45. Based on the dependences of electric currents on working temperature and O2 partial pressure, chemisorbed O− is suggested to play a predominant role in detecting reducing gases for the ZnO NR arrays and the best working temperature is probably in association with the conversion from irreversible to reversible chemisorption of O−.