Growth of ZnO Nanostructures by Wet Oxidation of Zn Thin Film Deposited on Heat-Resistant Flexible Substrates at Low Tem

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EMICONDUCTOR STRUCTURES, LOW-DIMENSIONAL SYSTEMS, AND QUANTUM PHENOMENA

Growth of ZnO Nanostructures by Wet Oxidation of Zn Thin Film Deposited on Heat-Resistant Flexible Substrates at Low Temperature O. F. Farhata,*, M. Hishamb, M. Bououdinac, Ammar A. Oglatd, and Nyan J. Mohammede a Physics

Department, Faculty of Sciences, Al-Asmarya Islamic University, Zliten, Libya Department, Faculty of Education, Tishk International University (TIU), Erbil, KRG, Iraq c Department of Physics, College of Science, University of Bahrain, Manama, 32038 Kingdom of Bahrain d Department of Medical Imaging, Faculty of Applied Medical Sciences, The Hashemite University, Zarqa, Jordan e Department of Pathological analysis, College of Science, University of Knowledge, Erbil, KRG, Iraq *e-mail: [email protected] b Physics

Received March 20, 2020; revised March 20, 2020; accepted May 27, 2020

Abstract—Coral-like ZnO nanostructures were successfully grown onto heat-resistant flexible substrates by the oxidation of Zn thin films. At a relatively low temperature (100°C), Zn thin film was oxidized using a horizontal furnace under the flow of water vapour. The obtained results revealed well-defined aggregates of ZnO nanostructures grown on the flexible films. XRD patterns exhibited a strong and sharp diffraction along the (002) plane suggesting a well-crystallized ZnO phase. Field emission scanning electron microscopy observations showed high-density ZnO nanostructures aggregated in coral-like shape. The present study introduced a cost-effective and simple approach to grow high-quality ZnO nanostructures with controlled shape and size, offering a promising candidate for nano-based devices such as fast-response photodiodes and gas sensors. Keywords: ZnO, nanostructures, low temperature, wet oxidation DOI: 10.1134/S1063782620100103

1. INTRODUCTION Zinc oxide (ZnO) material has attractive properties, such as a broad direct band gap (3.37 eV) at room temperature and high binding energy of free excitation (60 meV), being in addition transparent conductive metal oxide with important piezoelectric characteristics [1, 2]. Accordingly, ZnO offers potential applications in various electronic and optoelectronic devices. Various preparation techniques have been reported to produce ZnO films with variety of nanostructures (NSs) such as thermal evaporation [3], hydrothermal processing [4], chemical vapour deposition [5], metalorganic [6], and carbothermal reduction. The synthesis of Zn nanoparticles followed by thermal oxidation process is considered as an effective technique to grow ZnO nanowires (NWs) [7]. This process can be achieved through two approaches; namely, wet and dry oxidations. In addition, it offers outstanding features compared to other techniques such as low preparation cost and simplicity of deposition onto different substrates including polymeric materials, without the need of catalysts. Numerous studies have been carried out to grow ZnO NSs by oxidation of Zn films [8–10]. Zn metal was successfully transformed into ZnO nanoparticl