Gas sensitivity and point defects in sonochemically grown ZnO nanowires

We fabricated ZnO nanowires on pre-patterned alumina substrates by using a sonochemical method with Zn(NO₃)₂ and ZnCl₄ precursors, and we studied the optical and the gas sensing properties with thermal treatment for these samples. The yellow emission was found to be decreased with thermal annealing, and the gas response time was reduced with annealing. The NO gas sensitivity of the sample made using ZnCl₄ precursors was almost independent of the sensing temperature whereas a significant decrease in the yellow emission was observed with thermal annealing. This can be explained if the oxygen interstitials responsible for the yellow emission do not influence the affinity of the gas molecules significantly because they are located inside the nanowires.