SURFACE MORPHOLOGICAL, STRUCTURAL AND OPTICAL PROPERTIES ON CADMIUM ZINC SULPHIDE (CdZnS) TERNARY COMPOUND PREPARED BY ELECTRODEPOSITION TECHNIQUE

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1 NIGERIAN ANNALS OF NATURAL SCIENCES, VOLUME 16 (1) 2017 (pp ) ISSN: SURFACE MORPHOLOGICAL, STRUCTURAL AND OPTICAL PROPERTIES ON CADMIUM ZINC SULPHIDE (CdZnS) TERNARY COMPOUND PREPARED BY ELECTRODEPOSITION TECHNIQUE Ikhioya, I.L. 1, Jonah, N.J. 1 and Okanigbuan, O.R. 2* 1 Department of Physics and Industrial Physics, Nnamdi Azikiwe University, Awka, Anambra State, Nigeria 2 Department of Physics and Geophysics, Ambrose Alli University, Ekpoma, Edo State. *Corresponding author. ikhioyalucky@gmail.com, Tel: ABSTRACT Cadmium Zinc sulphide (CdZnS) ternary compound have been deposited onto gla ss substrate fluorine doped tin oxide (FTO) by electrodeposition technique. Surface morphological studies revealed a polycrystalline nature of the deposited films and the deposited film s were found to be non - homogeneous. Structural analysis showed that the Cadmium Zinc sulphide (CdZnS) thin films, so deposited, exhibit hexagonal structure with a preferred orientation along (111) plane. The optical absorbance was mea sured using M501 UV-vi sible spectrophotometer in the wavelength range of nm. Cadmium Zinc sulphide (CdZnS) ternary compound were investigated at room temperature. Key words: CdZnS, Thin Films, Electrodeposition, Surface morphology, Structural and Optical Properties. INTRODUCTION Cadmium zinc sulphide (CdZnS) thin film is one of the promising materials due to their application in high efficiency thin film transistors, electron-beam pumped lasers, LED, electroluminescent devices, photovoltaic, photoelectrochemical energy conversion and photoconductors (Patil et al., 2013). Other areas of successful applications include photo-detectors, light amplifiers, lasers, gas sensors, large-screen liquid crystal display. Cadmium zinc sulphide thin films have been widely used as a wide band gap window material in heterojunction solar cells and in photoconductive devices (Ilican et al., 2006). Cadmium zinc sulphide (CdZnS) thin films have been prepared by several techniques including sputtering (Ahn et al., 2012; Hwang et al., 2012), molecular beam epitaxy (Bosco et al., 2012), pulsed laser deposition (Yano et al., 2003), chemical vapor deposition (Huang et al., 2012), successive ionic layer adsorption and reaction (Xu et al., 2012), spray pyrolysis (Nagamani et al., 2012), chemical bath deposition (CBD) (Agawane et al., 2013) and electrodeposition (Ikhioya et al., 2015; Ikhioya and Agbakwuru, 2016), etc. Among these techniques, electrodeposition offers several advantages: it is relatively economical; it can be used on a large scale; and it is conducted at low-temperature. Although there has recently been a growing interest in the electrodeposition of cadmium zinc sulphide film due to these advantages, two issues have concerned us. The first is that heat-treatment is necessary after deposition in order to adjust the cadmium zinc sulphide stoichiometry, thus forfeiting the advantages of a low-temperature process. The second is that electrodeposition is often performed at a relatively negative potential, indicating that a sub-reaction of hydrogen evolution reduction could arise, leading to a reduction in current efficiency (Ikhioya, 2015). For these reasons, we have been strongly interested in achieving a single electrodeposition of cadmium zinc sulphide film at a low over potential (a more positive potential) and without heat-treatment. According to various authors, the properties of films can be controlled by varying different deposition parameters such as deposition time and voltage, concentration of solution, ph of the solution, bath temperature, annealing temperature. In this study, an investigation was carried out to study the surface morphological, structural and optical properties on the electrodeposited films. EXPERIMENTAL PROCEDURES Cadmium zinc sulphide (CdZnS) thin films were prepared

2 Nigerian Annals of Natural Sciences 083 Table1. Variation of Parameters CdZnS Ternary compound. Samples of H 2 SO 4 of K 2 SO 4 of Zinc Zn 2+ of Na 2 S.6H 2 O 0f Cd 2+ of SeO 2 Voltage (V) Time (minute s) CdZnS 2V CdZnS 4V CdZnS 6V CdZnS 8V CdZnS 10V by electrodeposition Technique on the glass substrates Fluorine doped Tin Oxide (FTO). The substrates were cleaned ultrasonically by detergent solution, acetone, and deionized water, respectively, to ensure the complete cleanness. The reaction bath for the deposition of cadmium zinc sulphide (CdZnS) was composed of different electrolyte selenium IV Oxide (SeO 2 ), Cd 2+, Zn 2+, Sodium Sulphide (Na 2 S.H 2 O), Potassium tetraoxosulphate VI (K 2 SO 4 ) and Tetraoxosulphate VI acid (H 2 SO 4 ) (Table 1). The growth of cadmium zinc sulphide (CdZnS) films were determined with respect to the different bath parameters which includes time of deposition and substrate for the deposition. 10cm 3 each of SeO 2, Cd 2+ Na 2 S.H 2 O and Zn 2+ was measured into 250cm 3 beaker using burette. 2cm 3 of K 2 SO 4 was measured into the same 250cm 3 beaker containing SeO 2, Cd 2+ Na 2 S.H 2 O and Zn 2+ respectively to serve as the inert electrolyte which hel ps to dissociate the cadmium, zinc and sulphide to form the required cadmium zinc sulphide (CdZnS) film on the substrate and the solution was acidified with 3cm 3 of dilute H 2 SO 4 which serves to adjust the P H value. The entire mixture was stirred with the glass rod to achieve uniformity. In each of the reaction baths prepared, a glass substrate and platinum electrode were connected to a DC power supply source and the time was maintained at 2minutes for different voltages. The optical absorbance was measured using M501 UV-visible spectrophotometer in the wavelength range of nm. Figure 1. SEM micrograph for sample CdZnS 2V. compared with the sample deposited at 2V with thickness of 299nm. It is also showed that the micrograph were spherical in shape. Cracks observed on the surface region indicate that the films were less compact on glass substrate, as the kinetics of film formation on the substrate was not uniform. It can be eliminated by increasing the time and voltage of the deposited films. RESULTS AND DISSCUSSIONS Surface Morphology Figures 1 and 2 show the surface morphology prepared of CdZnS at room temperature on the deposited films. The deposited CdZnS ternary compound analyzed with Scanning Electron Microscopy. The micrograph revealed a polycrystalline nature and the deposited films were found to be non-homogeneous. The micrograph of the sample deposited with 6V has a thickness of 487nm Structural Analysis of CdZnS Ternary Compound Figures 3 and 4 show the XRD using CuKal radiation (λ = Ǻ) and the XRD patterns of CdZnS ternary compound respecitively. The XRD patterns show hexagonal structure which correspond to (111) planes. The diffraction angle 2ϴ value is and with d = 3.334Å and 3.494Å. The preferred orientation lies along the (111) plane (Table 2). The lattice constant was given in the XRD analysis is found to be a = 5.665Ǻ. The

3 Nigerian Annals of Natural Sciences 084 Figure 2. SEM micrograph for sample CdZnS 6V. Figure 3. XRD pattern of CdZnS for sample 2V. crystallite size was determined by means of the X-ray line broadening method using Scherer equation (Abeles, 1988). δ = lines/m 2 (2) D = (1) Where λ is the wavelength of CuKal radiation (λ = Ǻ), is the full width of half β maximum FW HM of the (hkl) peak of the diffracting angle hkl 2θ. The average grain size D, the dislocation density δ is calculated using the following relation (Harbeke, 1972). Optical Analysis of CdZnS Ternary compound The optical characterization of cadmium zinc sulphide was carried out using M501 UV -visible spectrophotometer, where the absorbance was obtained and others optical parameters such as transmittance (t) and reflectance (r). CdZnS ternary compound were study at

4 Nigerian Annals of Natural Sciences 085 Figure 4. XRD pattern of CdZnS for sample 6V. Table 2. Structural parameters of CdZnS ternary compound. Sample thickne ss and voltage 299nm 2V 487nm 6V 2θ (degree) d (spacing) Å (β) FWHM (hkl) Lattice (a) Å Grain Size(D) nm density (δ) x10 13 lines/m 2 Micro strain (ε) x room temperature. Figure 5 shows the optical properties of films deposited on a glass substrate; the plot of optical absorbance as a function of wavelength reveal that the absorption in the visible infrared regions with a value of and the absorption in ultra violet region with a value of the optical absorption spectral of cadmium zinc sulphide reveal that the films grown at room temperature and at varying deposition voltage of 2V, 4V, 6V, 8V and 10V have high absorbance in the visible and infrared and ultraviolet region it was observed that cadmium zinc sulphide 2V, 4V and 6V are relatively constant, cadmium zinc sulphide 8V has high absorbance in the visible and near infrared region of about 0.5 and also high absorbance in the ultraviolet (Ilican et al., 2006; Xu et al., 2012; Nagamani et al., 2012). This high absorbance in the UV region makes cadmium zinc sulphide useful in p-n junction formation of solar cells with other suitable thin film materials for photovoltaic applications which is also useful for window coatings in cold temperate regions of the world. The transmittance as a function of wavelength of the CdZnS films is shown in Figure 5. The transmittance spectral reveals transmission of above 0.29% in the infrared region and transmission of about 0.52% in the ultraviolet region. It was observed that CdZnS 4V, 6V and 8V are relatively constant while CdZnS 2V and 10V maintain the same increment to some extent, when CdZnS 10V later increase with 0.10% from 0.40% to 0.50%. The general observation shows that the overall films demonstrate more than 20% transmittance (Ilican et al., 2006, Xu et al., 2012; Nagamani et al., 2012). Films of low transmittance in the infrared region is used in window coatings in hotter regions

5 Nigerian Annals of Natural Sciences 086 Figure 5. Plot of absorbance as a function of wavelength. of the world like Nigeria while films with high transmittance in the ultraviolet region is useful in photosynthetic coatings because they exhibit selective transmittance of photosynthetic active radiation (PAR) and also used as reflector and dielectric filter. The reflectance as function photon energy of the deposited CdZnS films showed a high absorption in the visible and IR region (Figure 5). The high reflectance of the entire sample in the infrared region makes the material useful in formation of p-n junction solar cells with other suitable thin films materials for photovoltaic application. These optical properties make CdZnS thin films nice glazing material for maintaining cool interior in buildings in warm climate regions. CONCLUSION Cadmium zinc sulphide has been prepared using electrodeposition technique. It has been showed from the surface morphological analysis that the micrograph revealed a polycrystalline nature and the deposited films were found to be non-homogeneous. The micrograph of the sample deposited with 6V has a thickness of 487nm compared with the sample deposited at 2V with thickness of 299nm. The XRD patterns show hexagonal structure which correspond to (111) planes. The diffraction angle 2ϴ value is and with d = 3.334Å and 3.494Å. The preferred orientation lies along the (111) plane. The lattice constant was given in the XRD analysis is found to be a = 5.665Ǻ. The plot of optical absorbance as a function of wavelength reveal that the absorption in the visible infrared regions with a value of and the absorption in ultra violet region with a value of The transmittance spectral reveals transmission of above 0.29% in the infrared region and transmission of about 0.52% in the ultraviolet region. The entire sample in the infrared region makes the material useful in formation of p-n junction solar cells with other suitable thin films materials for photovoltaic application. These optical properties make CdZnS thin films nice glazing material for maintaining cool interior in buildings in warm climate regions. ACKNOWLEDGEMENTS The authors are grateful to the Staff of Engineering and Material Development Institute (EMDI) and National Agency for Science and Engineering Infrastructure (NASENI) Akure, Ondo State were the characterization was done. REFERENCES Abeles, F. (1988) (Ed). Optical Properties of Solid, Nort h- Holland Pub.Co. Amsterdam. Agawane, G.L., Shin, S.W. and Kim, M.S. (2013). Green route fast synthesis and characterization of chemical bath deposited nanocrystalline ZnS buffer layers, Current Applied Physics, 13(5): Ahn, K., Jeon, J.H. and Jeong, S.Y. (2012). Chemical bonding states and atomic distribution within Zn(S,O) film prepared on CIGS/Mo/glass substrates by chemical bath deposition, Current Applied Physics, 12(6) Bosco, J.P., Demers, S.B., Kimball, G.M., Lewis, N.S. and Atwater, H.A. (2012). Band alignment of epitaxial ZnS/Zn3P2 heterojunctions, Journal of Applied

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