 158 American Academic Scientific Research Journal for Engineering, Technology, and Sciences ISSN (Print) 2313-4410, ISSN (Online) 2313-4402 http://asrjetsjournal.org/ Baby Incubation in Ebonyi State University Abakaliki Using the Physical Properties of Iron-doped Copper Sulphide (CuS) and Lead Sulphide(PbS) Thin Films Made by SILAR Method Victoria N. Udeajah a *, Daniel U. Onah b a,b Department of Industrial Physics, Ebonyi State University Abakaliki, Ebonyi State,PMB 053, Abakaliki, Nigeria a Email: vakadujah45@gmail.com b Email: d_onah@yahoo.co.uk Abstract The influence of iron on lead sulphide(PbS) and Copper Sulphide (CuS) thin films deposited on glass substrates via successive ionic layer adsorption (SILAR) Technique using lead acetate, Pb(CH 3 COO) 2, Cupric Acetate Cu(CH 3 COO) 2, thioacetamide ( S 2 H 5 NS), Iron (II) Chloride dehydrate(Fe Cl 2. 2H 2 O), ethanol and ammonia by in alkaline medium annealed between 283K and 500K was investigated. The structural and morphological studies were performed by X-ray diffraction (XRD) Analysis and scanning electron microscopy(SEM) respectively. The XRD showed films of cubic crystalline PbS thin films, cubic and face- centred crystalline PbSFe thin films, cubic CuS thin film, hexagonal Cu 2 S thin films and cubic and hexagonal crystalline natured CuSFe thin films with the preferential (111),(002)(004) (311) orientations. From the structural and morphological studies, the iron lead sulphide, and iron copper sulphide thin films can be good materials for baby incubation in neo-natal unit of hospitals and adapted in Ebonyi State University Abakaliki - Nigeria due to their new characteristics. Keywords: Baby incubation; copper sulphide(CuS); iron-doping; lead sulphide(PbS); structural and morphological studies. ------------------------------------------------------------------------ * Corresponding author. http://asrjetsjournal.org/ American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2021) Volume 81, No 1, pp 158-166 159 1. Introduction The world energy crisis gave rise to the thin film growth research as a way to cushion problems associated with it. The continuous increase in population and industrialisation in almost every country in the world, has been very responsible for the ever growing or increasing energy demand. In Nigeria, less than 40% of the country is connected to the national electric grid and less than 60% of the energy demand by this group is generated and distributed [1-3]. The advantage of energy is facilitation of the provision of those things which are necessary for the welfare of human existence: health, heat, food, light, clothing, shelter and transport, etc. Energy availability improves the standard of living [4]. Solar energy, an energy obtained from the sun, is the world’s most abundant and cheapest source of energy available from Nature [5]. It is free and automatically renewable every day. In the world over, emphasis has shifted from the use of hydro and fossil-powered electricity generation to renewable energy such as solar source through nanotechnology involving growing of thin films from the abundant transition metals, resulting in getting ones with excellent properties that will be useful in solving the problem of energy crisis [6-9]. In the present study, lead sulphide and copper sulphide are studied to ascertain the structural and morphological properties when doped with iron. These new assumed properties will help determine their best areas of applicability. Lead sulphide (PbS) and Copper Sulphide (Cu 2 S) are groups IV- VI and I-VI compounds of semiconducting materials respectively[10- 14] that have drawn attention of many researchers because of its properties that have been applied widely in optoelectronic devices, photoconductors, sensors, infra-red detector devices solar cells, solar control and solar absorber coatings [15-18]. The present study describes successive ionic layer adsorption and reaction method for the synthesis and deposition of PbS, (PbS)x(Fe)1−x , CuS and (CuS)x(Fe) 1−x ternary thin films and the influence of iron added to the halide thin films structurally and morphologically. Variety of materials such as insulators, semiconductors, metals and temperature sensitive materials like polyester can be used as a substrate since the deposition is carried out at or near to room temperature. As it is a low temperature process, it avoids oxidation and corrosion of the substrate. In spite of this SILAR having a number of advantages as compared to other methods; it does not require vacuum at any stage, doping of any element can be achieved easily, film thickness can be easily controlled by adjusting the number of deposition cycles, operating at room temperature, no restrictions on substrate material, dimensions or its surface profile etc. The prime requisite for obtaining good quality thin film is the optimization of various preparative parameters viz. concentration of precursors, nature of complexing agent, pH of the precursor solutions and adsorption, reaction and rinsing time durations etc[19-25]. 2. Experimental procedure The layer-by-layer growth of the material is achieved by dipping the substrate alternately into separately placed cationic and anionic precursors. After every cationic and anionic immersion the substrate is rinsed in deionised water to remove the un-adsorbed ions from the surface. The synthesis and deposition of PbS and CuS involved four steps while that of PbSFe and CuSFe thin films involved six steps. After pre-treatment of the substrates, the synthesis were done using .05M lead acetate and thioacetamide solution. Ammonia was used to control the pH. It was done between pH between 8.5 and 11.5. The iron ions were got from iron(II) chloride dehydrate. The copper ions were got from cupric acetate. It was equally deposited in alkaline environment too[Udeajah, 2020]. The thickness of the composite (PbS)x(Fe)(1−x) thin film was measured using the transmittance[Allah and American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2021) Volume 81, No 1, pp 158-166 160 his colleagues 2007]. The density of PbS was taken as 4.9g/cm 3 and iron as 5.2g/cm 3. The densities of the composite (PbS)x(Fe)(1−x) thin films were estimated by considering compositional parameter ‘x’. In the present investigation thickness of (PbS)x(Fe)(1−x) films measured. The site for the research work was the crystal growth laboratory, Physics and Astronomy Department, University of Nigeria, Nsukka, Nigeria. The structural properties of the (PbS)x(Fe)(1−x) composite thin films were studied by X-ray diffractometer with CuKα radiation of wavelength 0.154 nm. The surface morphological investigations were performed using scanning electron microscopy analysis and energy dispersive spectrometry (EDS) analysis at the Department of Industrial Chemistry , The Technical University, Ibadan Nigeria. B. Copper Sulphide and Copper Sulphide Iron thin films. The substrates were pre-treated as in the case above. For the SILAR deposition of (CuS)(1−x) thin films, 0.05 M cupric acetate solutions were taken as cationic precursor and 0.05 M thioacetamide as anionic precursor. The pH of the anionic and cationic precursors was adjusted to 12 and 8 by ammonia addition. Substrate was immersed in the cupric acetate solution for 35 s to adsorb Cu 2+ ions. (a) The un-adsorbed Cu 2+ ions were removed from the substrate by rinsing it in deionised water for 35 s. (b) The substrate was then again immersed in thioacetamide solution for 35 s, where S 2− ions reacted with Cu 2+ to form a layer of CuS. After repeating a sufficient number of cycles. It was removed and dried in an oven to avoid dust and oxidation. . For the SILAR deposition of (CuS)(1−x) Fe (1-x) thin films, the pre-treated glass substrates were immersed into 0.05 M cupric acetate solutions taken as cationic precursor, then rinsed in deionised water for 35 seconds before immersing into 0.05 M thioacetamide , taken as anionic precursor for 35 seconds before rinsing in deionised water. This was repeated for several cycles before the substrate was immersed in iron(II) Chloride dehydrate solution to adsorb iron ions on the pre-adsorbed copper sulphide layer. Table 1: Deposition scheme for the growth of CuS x Fe (1-x) thin films The unadsorbed iron ions were removed from the substrate by rinsing in deionised water for 35seconds. It is worthy to note that the substrate was again immersed in thioactetamide solution where S 2− ions react with Cu 2+ to form a layer of CuS. After repeating a sufficient number of cycles, (Fe)1−x(CuS)(x) composite thin films were American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2021) Volume 81, No 1, pp 158-166 161 deposited. The number of deposition cycles for CuS and Fe was adjusted to obtain various compositions of (Fe) 1−x(CuS)x . 3. Results and discussion 3.1 Structural Characterisation The structural characterizations of (PbS)x(Fe)(1−x) and (CuS)x(Fe)(1−x) thin films were carried out using X-ray diffraction (XRD) technique. The peaks of XRD patterns have been assigned from the x-ray diffraction files ref. numbers : INEL/EZEMA/18-162115 and INEL/EZEMA/18-171343 respectively. Using the CuSFe as case study, detailed analyses are given in Table1 . The crystallite size of the deposited material was calculated by using Debye- Scherer’s formula (equation 1) D = Kλ / Βcos θ, (1) where D is the average crystallite size, k is the particle shape factor that varies with the method of taking the breadth and shape of crystallites , λ is the X-ray wavelength used(0.1542 nm), β is the angular line width of half- maximum intensity (FWHM) of the diffraction peak, and θ is the Bragg’s angle in degrees. Figure 1: XRD of (PbS)x(Fe)(1−x) composite thin films: (A) PbS, (B) (PbS)0.80(Fe)0.20, (C) (PbS)0.5(Fe)0.5, (D) (PbS)0.20(Fe)0.80 and (E) (PbS)0.10(Fe)0.90.(Source: udeajah,2020) Figure 1: XRD of (CuS)x(Fe)(1−x) composite thin films: (a) (CuS)0.50(Fe)0.50 (b) (CuS)0.20(Fe)0.80, (c) (CuS)0.1(Fe)0.9, (D) CuS (source: Udeajah, 2021) American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2021) Volume 81, No 1, pp 158-166 162 Table 2: Thickness, grain size, strain and dislocation density of (PbS)x ( Fe)(1−x) thin films. Film composition Thickness (nm) Grain Size (nm) Dislocation density (δ × 10 10 ) lines/cm 2 Strain (ε × 10 −4 ) A PbS 375 34 10.91 10.17 B (PbS)0.80(Fe)0.20 301 26 14.26 14.30 C (PbS)0.5(Fe)0.5 290 25 15.99 14.77 D (PbS)0.20(Fe )0.80 285 18 16.87 14.90 E (PbS)0.10(Fe 0.90 280 16 32.47 21.03 3.2 Morphological Studies The morphological characterisation of CuS, CuSFe, PbS and PbSFe thin films were done using the scanning electron microscopy analysis(SEM) and Energy Dispersive spectrometry analysis . 3.2.1 Scanning electron microscopy(SEM) analysis The SEM Micrographs of the doped and undoped PbS and CuS thin films are show in Fig.2 and 3 below: (A) (B) Figure 2: SEM images of (PbS)x(Fe)(1−x) composite thin films: (A) PbS)0.20( Fe)0.80 , at 10 µm(HFW=125 µm) (B) (PbS)0.8(Fe)0.2 . at 10 µm(HFW=124 µm)[udeajah, 2020] SEM of doped CuS thin film SILAR (deposited at 90cycles) is shown below in Fig.3 below. American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2021) Volume 81, No 1, pp 158-166 163 (A) (B) Figure 3: SEM Micrograph of CuSFe (A) micrograph at 15µm (B) micrograph at 20µm 3.2.2 Energy Dispersive Spectrometry (EDS) Analysis : These are show in Figures 4 and 5 below. Figure 4: EDS of (PbS)x(Fe)(1−x) composite thin films[Udeajah, 2020] Figure 5: EDS of (CuS)x(Fe)(1−x) composite thin films [Udeajah,2020] The X-ray diffraction patterns of CuSFe and (PbS)x(Fe)1−x composite films were shown in Figures 1 and 2 above. The peaks of XRD patterns have been assigned from the x-ray diffraction files ref. numbers : INEL/EZEMA/18-162115 and INEL/EZEMA/18-171343 respectively. Lead sulphide thin film has ten diffraction peaks (111)(200 (220) (311) (222)(400) (331)(420)(422)(511), which corresponds to 2θ angles ranging from10.098-85.846. The XRD of doped PbS and CuS annealed at about 650K has been included. These had thirteen and seven peaks ranging from angles 2θ ranging from 10.429-85.9645 and 18.012-80.012 respectively. The (0 0 2) and (0 0 4) orientations due to hexagonal lattice are prominent in CuSFe and (1 1 1) and (2 0 0) orientations due to cubic lattice are distinct in pure PbS and CuS thin films. The PbSFe thin films American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2021) Volume 81, No 1, pp 158-166 164 annealed at temperature less than 500K were crystals that was cubic and face-centred. However, at x = 0.5 i.e. for (PbS)0.5(Fe)0.5, and (CuS)0.5(Fe)0.5 strong orientations disappear showing the non-formation of crystals due to the sp-d orientation. The crystallite sizes of the deposited materials were calculated using Debye-Scherer’s formula [udeajah,2021]. Thickness for PbS , (PbS)0.8(Fe)0.2 , (PbS)0.5(Fe)0.5, (PbS)0.2(Fe)0.8, (PbS)0.1(Fe)0.9 were 375nm,301nm, 290nm, 285nm and 280nm while their grain sizes were 34, 26, 25, 18,16 . The thickness for CuS, (CuS)0.8(Fe)0.2 , (CuS)0.5(Fe)0.5, (CuS)0.2(Fe)0.8, (CuS)0.1(Fe)0.9 . were 386, 300, 298,287, 273 while their grain sizes were 35, 33, 30, 27, 17. The variation in the strain and dislocation density may influence the properties of the nanostructures. From literature, the lead Sulphide thin films have been reported as having thermal stability as observed in this study. The samples(doped and undoped) were annealed between temperatures of 293K and 493K and from the XRD, the intensity ratio some diffractions changed but no additional peaks were observed up to 475K; This showed that the PbS nanofilm was not oxidized. The change in the diffraction reflection intensities was attributed to the fact that the phase transition to cubic structure takes place in the PbS film at 375K (26).The copper sulphide behaved in a similar manner. The presence of oxygen atoms as shown by the EDS studies showed that the proportion ofiron to lead sulphide and iron to copper sulphide were not in equal proportion and also oxidation must have taken place because of their large surface area(27). Based on this finding, the lead sulphide and copper sulphide thin films (doped and undoped ) can be used in devices as fire alarm sensors, flame sensors, heat source detection systems and baby incubators as in Ebonyi State University - Abakaliki, Nigeria. 4. Conclusions A simple, cheap and convenient SILAR method was be employed to deposit good quality CuSFe and (PbS)x (Fe)1−x composite thin films. The deposited films were uniform and adherent to the substrate. Their structural and morphological properties of those composite thin films were studied. The compositional analysis was done using energy dispersive spectroscopy(EDS). EDS Studies showed that in (PbS)x (Fe)1−x composite thin films, the composition of iron was 21.8wt%, while in (CuS)x (Fe)1−x composite thin films, iron composition was 20.8wt%. The XRD and morphological studies revealed that CuSFe and PbSx(Fe)(1−x) thin films were nanocrystalline in nature depending on film composition. The average crystallite size was found to vary for the CuSFe thin films between 35 and 17 nm and for PbSFe thin films 34 and 16 depending on film composition. The variation in thickness, strain and dislocation densities were also composition dependent. Similar observation has been reported by Wang and his colleagues. The samples annealed at different temperatures (383K-500K) never showed any prominent peaks structurally and morphologically as confirmed by studies done[8, 12] . From literature, considerable changes can be seen for temperatures up to 700 0 K [28-29]. The high absorbance displayed by PbSFe films may be used as spectrally selective coating for solar thermal applications. Solar collectors for heating fluids require increasing the reception area of the solar radiation, and/or to increase the absorbance of the surface coating in order to improve thermal efficiency. The relatively high transmittance of PbSFe and CuSFe thin films in the infrared region suggest that they may be used for coating the walls and roofs of baby incubators to facilitate the transmission of infrared radiation in order to generate the heat required for warming neo-nates as adapted in the Faculty of Health Sciences of the Ebonyi State University, Abakaliki, Nigeria.[30]. These properties can be well used in solar energy conversion devices and optoelectronics[31-33]. 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