Effect of annealing temperature on the structural, optical, magnetic and electrochemical properties of NiO thin films pr
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Effect of annealing temperature on the structural, optical, magnetic and electrochemical properties of NiO thin films prepared by sol–gel spin coating N. R. Aswathy1 · Jiji Varghese1 · R. Vinodkumar1 Received: 10 April 2020 / Accepted: 10 August 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract The effect of annealing temperature on the structural, morphological, optical, magnetic and electrochemical properties of spin coated NiO thin films were studied. The XRD analysis shows that all the annealed NiO thin films are cubic structure with (200) preferred orientation. The XPS spectrum indicates that the main peak and satellite peaks of Ni (2P) and O (1S) show the presence of N i2+ cation and O2− anions. Raman spectra show (1P) 1LO and (2P) 2LO modes for annealed NiO thin films. The SEM result shows that, increase in annealing temperature increases the grain size. UV–Visible spectrum exhibits high transmittance for annealed NiO thin films. The band gap energy decreases from 3.72 to 2.89 eV with increasing annealing temperature. The room temperature PL spectrum of NiO thin film has blue and violet emission in addition to UV emission. VSM studies revealed that a weak ferromagnetic behavior has shown by films annealed upto 400 °C and thereafter the magnetic behavior changes to paramagnetic nature. The NiO thin film annealed at 600 °C shows high specific capacitance by cyclic voltammetry analysis. Equivalent series resistance of NiO thin films were measured using electrochemical impedance spectrum and it decreases with increasing annealing temperature.
1 Introduction Most of the researchers are looking for transition metal oxide based electrode material for pseudocapacitors due to their high specific capacitance, excellent reversibility, low sheet resistance, low toxicity, high stability and non reactivity to surrounding atmosphere [1–5]. However among the various transition metal oxides, NiO has been considered as the promising electrode material for pseudocapacitors because of its unique characteristics such as low cost, low toxicity, environmental friendly, high theoretical specific capacitance (2573 Fg−1), high surface area and high cyclic stability [1, 5, 6]. NiO is a p-type semiconducting metal oxide with a wide band gap of about 3–4 eV. NiO exhibit face centered cubic structure [1, 5–7]. In bulk form NiO is antiferromagnetic in nature. But at room temperature NiO thin films exhibit ferromagnetic behavior [7, 8]. NiO thin film has high chemical * R. Vinodkumar [email protected] 1
Department of Physics, University College, University of Kerala, Thiruvananthapuram, Kerala 695034, India
and thermal stability with excellent electrical, optical, magnetic, electrochromic and electrochemical properties [1, 5, 7, 8]. Hence it has many applications in memory devices, gas sensors, UV photo detectors, solar cells, display and defrosting windows, supercapacitor, electrochromic device, catalysts and spintronic devices [9–20]. NiO thin films can be fabricated using different techniq
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