Enhanced NO Gas Performance of (002)-Oriented Zinc Oxide Nanostructure Thin Films

(002)-oriented ZnO nanostructure for NO gas sensing application was successfully grown on glass substrates by two-step processes, which are seeding process via dip-coating method using diethanolamine (DEA) as chelating agent and growth process via chemical bath deposition (CBD). The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Two ZnO film samples, named samples A and B, were fabricated without and with DEA addition in the seeding process, respectively. XRD observation results show that ZnO film was successfully deposited on both samples, where sample A has a random crystal orientation; while sample B has a very dominant (002) orientation. Further, the selected area electron diffraction (SAED) observation with TEM confirmed that sample A has a random orientation indicated by a ring-shaped diffraction pattern; while sample B has a hexagonal crystalline structure diffraction pattern which is oriented towards the normal direction of the substrate surface, indicated that ZnO film was grown along this (002) orientation for sample B. SEM images of both samples showed that the ZnO film is ZnO nanorods with hexagonal wurtzite structure shape and sample A is clearly more randomly oriented than sample B. During the investigation of NO gas sensing performance, it is found that the highest response towards NO gas was occurred at a lower operating temperature of 200°C for sample B compared to a higher operating temperature of 300°C for sample A. Furthermore, sample B has a higher dynamic gas response and sensitivity than sample A. These results indicate that the (002) oriented ZnO film has a better performance than the randomly oriented ZnO film as NO gas sensor.