Thermal post-annealing and gas concentration effect on liquid petroleum gas sensing characteristics of nanocrystalline zinc oxide thin films Hamed Aleebrahim Dehkordi • Kamran Dastafkan • Ahmad Moshaii • Ali Mokhtari Received: 19 November 2014 / Accepted: 2 February 2015 Ó Springer Science+Business Media New York 2015 Abstract 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 concen- tration 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 tem- peratures 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 elec- tron microscopy, X-ray diffraction and ultraviolet–visible spectroscopy techniques. Sensing tests showed the depen- dence 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. 1 Introduction As in the last two decades interests have been converted toward the application of nanomaterials and nanotech- nology, more nanocrystalline inorganics including metals and metal oxides with unique and fascinating properties were assayed as solid surfaces in a wide range of tech- nologies. Down to the nanoscale, key reasons such as large surface area, unsaturated and increased number of surface atoms and highly accessed surface energy fraction together result in high chemical activity and high rate of chemical reaction. This is subjected to combination with other ele- ments and substances including metals and polar organic compounds [1]. Zinc oxide (ZnO) is usually recognized as a n-type semiconductor compound with a wide band gap of 3.2–3.4 eV at room temperature, hexagonal wurtzite structure and a large excitation binding energy of about 60 MeV [2, 3]. ZnO has been subjected to a broad area of research due to interested and potential physical, electrical, mechanical, optical and chemical characteristics such as piezoelectric nature, high voltage-current nonlinearity, optical transparency in visible region, light emitting in blue and ultraviolent ranges, chemical stability and biocom- patibility [4–7], etc. Within recent years, significant pro- gress has been made in the nanostructures of ZnO and morphologies like nanoparticles, nanotubes, nanorods, nanowalls, nanofibers, nanopellets, undoped and doped thin films [7–11] were fabricated and intended for applied fields of surface acoustic wave devices (SAW), varistors, H. A. Dehkordi (&)  A. Moshaii Department of Physics, Tarbiat Modares University, P.O. Box 14115-175, Tehran, Iran e-mail: h.aleabrahim@modares.ac.ir K. Dastafkan Young Researchers and Elite Club, Karaj Branch, Islamic Azad University, Karaj, Iran e-mail: kamrandastafkan@gmail.com A. Mokhtari Department of Physics, Faculty of Science, Shahrekord University, P. B. 115, Shahrekord, Iran 123 J Mater Sci: Mater Electron DOI 10.1007/s10854-015-2808-7