Effect of Zn/S non-stoichiometric ratio on the structural, optical and electronic properties of nano-ZnS
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Effect of Zn/S non‑stoichiometric ratio on the structural, optical and electronic properties of nano‑ZnS Zein K. Heiba1 · A. A. Albassam2 · Mohamed Bakr Mohamed1,3 Received: 17 March 2020 / Accepted: 22 May 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Non-stoichiometric ZnS nanomaterials were prepared using a thermolysis procedure by decreasing the stoichiometric amount of thiourea relative to the amount of zinc acetate as starting precursors: Zn(Ac)/(1−x) thiourea (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5). The high-resolution transmission electron microscope revealed the nanonature of the obtained samples. The X-ray diffraction analysis applying Rietveld method was carried out to explore the influence of Zn/S non-stoichiometry on the structural and microstructural properties of the crystalline phases in the samples. ZnO phase appeared for x ≥ 0.2 forming ZnS1–x/ ZnO heterostructures; its percentage increased with increasing non-stoichiometric parameter (x). Incorporation of oxygen ions into the ZnS lattice compensating the sulfur deficiency was manifested by Fourier transform infrared spectroscopy. The UV–Vis analysis revealed the decrease in the bandgap of ZnS from 3.42 eV for x = 0.0 to 2.71 eV for x = 0.5, making these materials suitable for new applications. The influence of non-stoichiometric parameter (x) on the photoluminescence emissions of formed samples was examined; results indicated the spectrum shift towards higher wavelengths. Density function calculations were performed in order to compare the electronic and optical properties of sulfur-deficient Z nS0.9 (single phase) with the ZnS sample. Keywords Non-stoichiometric · Zn/s ratio · Structure · Optical · Electronic
1 Introduction Zinc sulfide, non-toxic material, is a very important member of the II–VI chalcogenides that has new characteristics in fundamental research and enormous technological uses in numerous quantum devices [1–5]. Zinc sulfide (ZnS) has a wide direct bandgap and can crystallize in two different modifications: zinc blende-type cubic structure with lattice constant a = 5.409 Å and optical bandgap Eg = 3.6 eV and wurtzite-type hexagonal structure with lattice constants a = b = 3.812 Å, c = 6.26 Å and Eg = 3.77 eV [6]. ZnS has * Mohamed Bakr Mohamed [email protected] 1
Physics Department, Faculty of Science, Ain Shams University, Cairo, Egypt
2
Research Chair of Exploitation of Renewable Energy Applications in Saudi Arabia, Physics and Astronomy Department, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia
3
Physics Department, Faculty of Science, Taibah University, Al‑Madina al Munawarah, Saudi Arabia
been used in different applications such as detectors, optical windows for visible and ultraviolet light, light-emitting laser diodes and modulators in optoelectronics devices [7]. ZnS can be doped by various elements for modifying and tailoring its properties for new applications [1–5]. The bandgap of Fe/Cd-doped ZnS nanocrystal showed non-monotonic dependen
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