Effect of Mg Doping on the Structural, Optical and NO₂-sensing Properties of ZnO Thin Films Prepared by Modified SILAR Method

Abstract

In this report, we have prepared undoped and Mg-doped ZnO thin films by a modified successive ionic layer adsorption and reaction (SILAR) method. The structural, surface morphological, chemical compositional, and optical properties of pure and Mg-doped ZnO thin films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), ultraviolet-visible (UV-VIS) spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy. The XRD patterns of undoped and doped films have wurtzite crystal structures with preferential orientation along the (101) plane, without any secondary phases. Addition of Mg into host ZnO influenced surface morphology of the film. Predominant nanorods-like surface morphology of undoped ZnO turned to be predominant nanoflowers-like surface morphology after addition of Mg. UV-VIS spectra showed that the energy band gap of films increased with increase Mg doping concentration. EDS and FT-IR spectroscopy confirmed the successful Mg doping. Gas sensing properties of the undoped and Mg-doped ZnO thin films were tested based on the electrical resistance changes upon exposure to different concentrations of a NO 2 gas at 200°C operating temperature. Mg-doped ZnO (3 wt%) showed higher response compared to other wt% and exhibited the highest responses of 2.95, 9.51, and 9.93 when exposed to 25, 50, and 100 ppm concentrations of the NO 2 gas at 200°C, respectively. The response/recovery time of the Mg-doped ZnO thin film were 6/75, 14/88, and 14/89 s at 25, 50, and 100 ppm, respectively. Keywords Modified SILAR; Mg-doped ZnO; Flowers-like; NO 2 gas sensor 42 Chemical gas sensors based on semiconducting metal ox-43 ides play a pivotal role in detecting toxic and dangerous 44 substances, where considered promising alternatives to 45 measuring and detecting the amount of environmental pollu-46 tion due to their advantages such as low cost, high sensitivi-47 ty, and fast response [1, 2, 4]. 48 Zinc oxide nanostructures are the best metal oxides, due 49 to their interesting properties such as a wide band gap (ap-50 proximately 3.37 eV), a high exciton binding energy (60 51 meV), non-toxicity, and chemical stability. ZnO nanostruc-476 477 478 479 480 481 All articles published on e-J. Surf. Sci. Nanotechnol. are licensed 482 under the Creative Commons Attribution 4.0 International (CC BY 483 4.0). You are free to copy and redistribute articles in any medium 484 or format and also free to remix, transform, and build upon articles 485 for any purpose (including a commercial use) as long as you give 486 appropriate credit to the original source and provide a link to the 487 Creative Commons (CC) license. If you modify the material, you 488 must indicate changes in a proper way.489