Thermal post-annealing and gas concentration effect on liquid petroleum gas sensing characteristics of nanocrystalline zinc oxide thin films

Chemical adsorption and sensing reactions of liquid petroleum gas over the surface and between grain boundaries of nanostructured zinc oxide thin films were investigated and monitored under the influence of various post-synthesis thermal annealing and target gas concentration conditions. Prior to sensing tests, zinc oxide thin films were synthesized in three steps: at first, zinc oxide nanoparticles were synthesized by a sol–gel method using zinc acetate dihydrate, ethanol and monoethanolamine as precursor, solvent and stabilizing agent, respectively. Then, untreated zinc oxide thin films were prepared from zinc oxide sol through spin coating procedure and finally, thermal post-annealing treatment with different temperatures was performed to yield heated thin films. The formation of the synthesized nanoparticles, morphology, crystalline size, porosity and transparency of final thin films were characterized by field emission-scanning electron microscopy, X-ray diffraction and ultraviolet–visible spectroscopy techniques. Sensing tests showed the dependence of the liquid petroleum gas detection on the thermal annealing process and gas concentration and indicated a maximum response of 75 % at the operation temperature of 300 °C for the zinc oxide film pre-annealed at 600 °C and 1,000 ppm gas. Moreover, the results exhibit excellent sensitivity for the sensor via short response and recovery times of 34 and 220 s, respectively.