Point defects assisted NH₃ gas sensing properties in ZnO nanostructures

In this report, the NH₃ gas sensing properties of ZnO nanostructures fabricated by radio frequency magnetron sputtering under various argon sputtering pressures have been investigated under various temperatures. The morphological transitions occur from vertical standing nanorods to inclined and tapered nanostructures with increasing the argon sputtering pressure. The dominant green emission at around 2.28 eV in the photoluminescence spectra signifies the presence of oxygen vacancies in the ZnO nanostructures which increases as a function of argon sputtering pressure. Despite low surface area, the nanostructures grown under higher argon sputtering pressure of 10 Pa exhibit excellent NH₃ gas response magnitude since it is exhibiting more oxygen vacancies as compared to other counterparts. For 25 ppm NH₃ gas at room temperature, a response time of 49 s and a fast recovery time of 19 s are attributed to the modification in the intermediate defect states induced by the oxygen vacancies through the adsorption and desorption of gas molecules on the surface of ZnO nanostructures.