Synthesis and ultrafast humidity sensing performance of Sr doped ZnO nanostructured thin films: the effect of Sr concentration

In this study, the effect of strontium (Sr) concentration on the ultrafast humidity sensing performance of Sr doped zinc oxide (SrxZn1-xO) nanostructured thin films was reported. The sol gel method was used in the synthesis of undoped zinc oxide (ZnO) and SrxZn1-xO (x = 0.01, 0.02, 0.03, 0.04, and 0.10) nanoparticles. According to the x-ray diffraction analysis, all films had a hexagonal wurtzite structure. By doping Sr into the ZnO lattice, the preferential orientation changed from the (002) plane to the (101) plane. Scanning electron microscopy micrographs showed that all films had a structure containing nanosized grains and capillary-nanopores, and the nanosized grains were homogeneously and uniformly distributed on the surface of films. The presence of zinc, oxygen and Sr elements in nanostructured thin films was proved by energy dispersive x-ray spectra. The relative humidity sensing performances of undoped ZnO and SrxZn1-xO films were tested with electrical resistance measurements in the range of 40-90% RH at room temperature. SrxZn1-xO films had high sensitivity, excellent stability, reliable and reproducible character, and fast response and recovery times. Sr0.10Zn0.90O was accepted as the best sample in terms of having the highest humidity sensitivity (657.59x) and the fastest response (0.8 s) and recovery (9.8 s) times. This study clearly revealed that SrxZn1-xO nanostructured thin films have great potential for high performance humidity sensor applications due to their ultrafast humidity sensing performance.