Post-deposition heat treatment effect on pH sensing behavior of chemical bath deposited nanostructured zinc oxide

The post-deposition heat treatment process was studied to improve zinc oxide (ZnO) 's pH sensing performance as the sensing electrode (SE) of extended-gate field effect transistor (EGFET) pH sensor. The low-temperature chemical bath deposited ZnO nanostructured thin film was heated from 200 to 400 degrees C before being applied as the SE. The heat treatment enhanced the agglomeration of ZnO nanoparticles, and the formation of nanonails was seen at the highest temperature of 400 degrees C. It was proven by XRD results that the crystallinity of ZnO samples were improved when the ZnO SE was heated at 300 degrees C and formed different growth orientations at (100), (002) and (101) before turning to (101) growth orientation at 400 degrees C heat treatment. The heat treatment process also increased the ZnO particle size from 15.47 nm to 260 nm at 300 degrees C. Further increasing the heat treatment up to 400 degrees C decreased the particle size to 44.30 nm. The ZnO morphology was correlated with the pH sensor per-formance. The clustered structure of the untreated ZnO sample exhibited a good pH sensi-tivity of 52.4 mV/pH with a linearity of 0.93 and a hysteresis value of 46.71 mV. On the other hand, almost similar pH sensitivity was obtained from the sample treated at 300 degrees C having poly-structure morphology, which was 52.9 mV/pH, but with a significantly improved line-arity of 0.99, and hysteresis values of 41.99 mV respectively. The 300 degrees C heat treatment also improved the stability of ZnO SE performance. The difference in the performance of these two samples can also be related to the crystalline quality of the film.(c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.