THIN FILMS - Asia Pacific

Asia Pacific Journal of Research

Vol: I Issue XXI, January 2015

ISSN: 2320-5504, E-ISSN-2347-4793

SYNTHESIS AND CHARACTERIZATION OF CHEMICALLY DEPOSITED IRON COPPER SULPHIDE (FeCuS) THIN FILMS

Ezenwa I. A. Ezenwa and Okoli L. N. Department of Industrial Physics, Anambra State University, Uli, Nigeria. ABSTRACT Thin films of FeCuS were grown on glass substrates by the Chemical Bath Deposition (CBD) technique at room temperature. Iron (III) trioxonitrate nanohydrate, copper chloride dehydrate and thiourea were used as sources for iron, copper and sulphur ions respectively. The optical characterization was done by using a Janway UV- VIS spectrophotometer in the wavelength range of 300 nm – 1100 nm. The optical absorbance of the films was determined directly from the spectrophotometer. Other properties such as transmittance, reflectance refractive index and absorption coefficient squared were calculated. A band gap energy range between 2.5 eV to 2.8 eV was obtained. Introduction Thin films are crystalline or non-crystalline material developed two dimensionally on a substrate surface by physical or chemical method. The Chemical Bath Deposition (CBD) techniques has been in used for the deposition of both binary and ternary compounds. The preparation and study of physical properties of ternary chalcogenide compounds has increased in recent years due to their wide range of application [Ezema (2004)]. Some ternary compounds have been investigated for various application. Ternary compounds are found to be suitable material for optoelectronic device applications and good material for window layer solar cells [Woon – Jo and Gye – Choon (2003)]. There is considerable interest in the deposition of ternary derivative material, due to the potential of tailoring both the lattice parameters and the band gap by controlling depositions parameters [Sankapal and Lokhande (2002)]. Many techniques have been successfully employed for these purposes: Chemical Vapour Deposition (CVD) [Frigo et al (1989)], Successive Ionic Layer and Reaction (SILAR) [Nilolou et al., (1990)], and Sol-gel Methods [Seung and Byung, 2008]. Many researcher have deposited ternary transition metal thin films such

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ISSN: 2320-5504, E-ISSN-2347-4793

as CuInS2 [Tang et al (2005)], PbCdS [Mohammed et al (2009)], ZnNiS [Ottih (2014)], Cd1-xPbxSe [Hankare et al (2005)], ZnxCd(1-x)Te [Umeshkumar et al (2011)] for various applications. In this paper, FeCuS thin films were deposited using chemical bath method, pH as a bath parameter was optimized. The possible applications of the films were discovered from their properties. The optical properties investigated include; absorbance (A), transmittance (T) and reflectance (R), which were used to calculate other properties such as refractive index (n), extinction coefficient (K) and the band gap energy of the as – grown films. These properties were determined based on the equations found in the literature of some researchers on thin films like that of [Ezema and Okeke (2004), Jae – Hyeong et al (2003)]. Experimental Details The growth of FeCuS thin films on glass slides was carried out using chemical bath deposition technique. The glass slides used were previously degreased in trioxonitrate (V) acid for 48 hours, washed with detergent, rinsed in distilled water and dried in air. The degreased cleaned surface provide nucleation centre for the growth of the films onto the substrate surface hence will result to highly adhesive and uniformly deposited films on the surface of the substrate. The slides for deposition of FeCuS were labelled 𝐹𝐶7 , 𝐹𝐶8 , 𝐹𝐶9 , 𝐹𝐶10 𝑎𝑛𝑑 𝐹𝐶11 . Deposition of FeCuS thin films of slides 𝐹𝐶7 , 𝐹𝐶8 , 𝐹𝐶9 , 𝐹𝐶10 𝑎𝑛𝑑 𝐹𝐶11 were carried out using 100 ml glass beaker at an average room temperature of 300 K. 3 𝑚𝑙𝑠 of Iron (III) trioxonitrate nanohydrate and Copper chloride dihydrate were measured, transferred into the beaker. The mixture was stirred for 2 minutes after which 2 𝑚𝑙 of thiourea was added and stirred to have a homogeneous mixture. Addition of thiourea formed a sky blue jelly – like solution. Followed by addition of 1.0 𝑚𝑙 of EDTA, 1.0 𝑚𝑙 of TEA. The solution was stirred for 5 minutes followed by addition of 35 𝑚𝑙 of distilled water. The final solution was stirred to have a homogeneous mixture. The five beakers were prepared in the same manner. The varying bath parameter is the pH of the medium which was achieved by varying the volume concentration of ammonium solution used. Volumes of ammonium solution used were 2 𝑚𝑙, 3 𝑚𝑙, 4 𝑚𝑙, 5 𝑚𝑙 and 6 𝑚𝑙 at a constant time of 48 hours. After 48 hours, the substrates were removed, rinsed in distilled water, and dried in open air at room temperature of (300K). pH of deposition baths were obtained using a pH meter of accuracy ±0.1. the values of the pH are 7.9, 8.3, 9.0, 9.4 and 9.9 respectively. TEA and EDTA served as complexing agents. Ammonia solution was used as a pH adjuster. The function of the complexing agent is to slow down the reaction in order to eliminate spontaneous precipitation of cations in the reacting medium. The bath composition of the five depositions made with different pH values is shown in the Tab. 1 below. The chemical equation of the reaction for the deposition is given below: 𝐹𝑒(𝑁𝑂3 )3 . 9𝐻2 𝑂 + 𝐸𝐷𝑇𝐴 ⟶ [𝐹𝑒(𝐸𝐷𝑇𝐴)]+ + 𝑁𝑂3 ¯ [𝐹𝑒(𝐸𝐷𝑇𝐴)]+ ⟶ 𝐹𝑒 3+ + 𝐸𝐷𝑇𝐴2− 𝐶𝑢𝐶𝑙2 . 2𝐻2 𝑂 + 𝑇𝐸𝐴 ⟶ [𝐶𝑢(𝑇𝐸𝐴)]+ + 𝐶𝑙¯ [𝐶𝑢(𝑇𝐸𝐴)]+ ⟶ 𝐶𝑢2+ + 𝑇𝐸𝐴 (𝑁𝐻2 )2 𝐶𝑆 + 𝑂𝐻 − ⟶ (𝑁𝐻2 )2 𝐶𝑂 + 𝐻𝑆 − 𝐻𝑆 − + 𝑂𝐻 − ⟶ 𝐻2 𝑂 + 𝑆 2− 𝐹𝑒 3+ + 𝐶𝑢2+ + 𝑆 2− ⟶ 𝐹𝑒𝐶𝑢𝑆3 The sulphide ions are released by the hydrolysis of thiourea, 𝐹𝑒 3+ and 𝐶𝑢2+ ions are from complexes which the solution of 𝐹𝑒(𝑁𝑂3 )3 . 9𝐻2 𝑂 and 𝐶𝑢𝐶𝑙2 . 2𝐻2 𝑂 formed with EDTA and TEA. The 𝐹𝑒 3+ , 𝐶𝑢2+ and 𝑆 2− present in the solution combined to form FeCuS molecules which were deposited on the glass substrate. The

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ISSN: 2320-5504, E-ISSN-2347-4793

films grown were characterized for optical absorbance using Janway 6405 UV – VIS spectrophotometer. From the values of absorbance obtained, other properties such as film transmittance, reflectance, thickness and band gap energy were determined through theoretical calculations. These optical properties were obtained in the wavelength range of 300 nm– 1100 nm. Table 1: Optimization of Iron Copper sulphide (FeCuS) with pH at room temperature Reacti on bath

Fe(NO3)3.9H2 O

CuCl.2H2 O

EDTA

Mol. (m)

Vol. (ml)

Mol. Vol. Mol (m) (ml) . (m)

TEA

(NH2)2CS

NH4OH

Vol. (ml)

Mol . (m)

Mol. (m)

Vol. (ml)

35.0 0 35.0 0 35.0 0 35.0 0 35.0 0

2.00

14.0 0 14.0 0 14.0 0 14.0 0 14.0 0

2.00

H2 O

Ph

FC7

7.90

2.00

3.00

2.00

3.00 0.50

FC8

8.30

2.00

3.00

2.00

3.00 0.50

FC9

9.00

2.00

3.00

2.00

3.00 0.50

FC10

9.40

2.00

3.00

2.00

3.00 0.50

FC11

9.90

2.00

3.00

2.00

3.00 0.50

Vol . (ml ) 1.0 0 1.0 0 1.0 0 1.0 0 1.0 0

Mol . (m) 7.40 7.40 7.40 7.40 7.40

Vol . (ml ) 1.0 0 1.0 0 1.0 0 1.0 0 1.0 0

2.00 2.00 2.00 2.00

Vol . (ml ) 2.0 0 2.0 0 2.0 0 2.0 0 2.0 0

3.00 4.00 5.00 6.00

Figure 1 shows the variation of film thickness with pH of deposition. A critical analysis of the graph indicates that thickness decreases as the pH of the baths increases. The film with lowest pH value of 7.9 has the highest thickness value of 0.9 μm. Figures 2, 3 and 4 show the graphs of spectral absorbance, transmittance and reflectance of the deposited Iron Copper Sulphide thin films respectively. The optical properties considered in the figures mentioned above revealed high absorbance but low transmittance and reflectance in the UV region, low values of absorbance and reflectance accompanied with high transmittance in the VIS – NIR region. It can be seen that absorbance decreases as pH increases and transmittance increases as pH decrease. The plot of absorption coefficient times (hυ) squared against the photon energy is shown in Figure 5. From the graph, the band gap energy of the films was determined. Its value ranges from 2.5 eV to 2.8 eV. This is done by extrapolating the straight part of the graph to a point where 𝛼 2 = 0. The value of the photon energy at that point is the energy gap of the thin film. This implies that FeCuS is a wide band gap energy material and can be used as an absorber layer of a solar cell.

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Thickness (μm)

ISSN: 2320-5504, E-ISSN-2347-4793 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 7.9

8.4

8.9

9.4

pH Variation of Thickness (μm) versus pH of Deposition

9.9

Fig. 1:

Fig. 2: Absorbance Spectra versus Wavelength of FeCuS Thin Films

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ISSN: 2320-5504, E-ISSN-2347-4793

Fig. 3: Transmittance Spectra versus Wavelength of FeCuS Thin Films FC8 FC9 FC10 FC11

0.25

Reflectance R

0.2 0.15 0.1 0.05 0 400

500

600

700

800

900

1000

Wavelength (nm)

1100

1200

(αhυ)2 ×1012 (eV)2m-2

Fig. 4: Reflectance Spectra versus Wavelength of FeCuS thin films

16

FC8

14

FC9

12

FC10

10 8 6 4 2 0 0

0.5

1

1.5

2

Photon Energy (eV)

2.5

3

3.5

Fig 5: Graph of (αhυ)2 versus Photon Energy (eV)

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ISSN: 2320-5504, E-ISSN-2347-4793

Fig. 6: Graph of Refractive Index ƞ versus wavelength (nm) of FeCuS Thin Films

Fig. 7: Graph of Extinction Coefficient K versus wavelength (nm) of FeCuS Thin Films

Fig. 8: Micrograph of 𝑭𝒆𝑪𝒖𝑺 for Slide 𝑭𝑪𝟕

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ISSN: 2320-5504, E-ISSN-2347-4793

Fig. 9: Micrograph of 𝑭𝒆𝑪𝒖𝑺 for Slide 𝑭𝑪𝟗 The real part of the refractive index ranged from 1.7 to 2.6 as seen in fig. 6. In Fig. 7, the extinction coefficient ranged from 5.20 × 10−3 to 1.23 × 10−1 . Fig. 8 and 9 show micrograph of FeCuS thin films for slides 𝐹𝐶7 and 𝐹𝐶9 . Critical observations of the micrographs reveal that the films are polycrystalline and has small grain sizes. Conclusion Ternary thin films of Iron Copper Sulphide have been grown on glass substrate using Chemical Bath Method and characterized using a spectrophotometer to determine its optical properties. These results above suggest that the thin films can suitably be applied in the following: (i) solar cell fabrication, (ii) for the screening off UV radiation that is harmful to human beings and animals due to its high absorbance, low transmittance and low reflectance in UV region, (iii) optoelectronic devices, (iv) architectural design for cooling or heating buildings, (v) coating of windscreen and driving mirrors to reduce the effect of dazzling of light into driver’s eyes etc. This deduction agrees with the findings of other researchers on similar films [Ezema, 2003, Uhuegbu, 2010]. Reference [1] Ezema F.I., (2004), Optical Properties of Chemical Bath Deposited FeCdS3 Thin Films, Academic Open Internet Journal, Vol. 11. [2] Woon–Jo, Jeong and Gye–Choon, Park. 2003. “Structural and Electrical Properties of CuGaS2 Thin Films by Electron Beam Evaporation”. Solar Energy Materials and Solar Cells. 75:93–100. [3] Sankapal B. R. and Lokhande C. D., (2002), Effect of annealing on chemically deposited Bi2Se3-Sb2Se3 composite thin films, Materials Chemistry and Physics, 74, 126-133. [4] Frigo D. M., Khan O. F. Z. and O'Brien P., (1989), Growth of Epitaxial and Highly Oriented Thin Films of Cadmium and Cadmium Zinc Sulphide by Low – Pressure Metalorganic Chemical Vapour Deposition Using Diethyldithiocarbamates, Journal of Crystal Growth, , Vol. 96, p. 989. [5] Nicolau Y. F. Dupuy M. and Brunel M., (1990), ZnS, CdS and Zn1-xcdxS Thin Films Deposited by the Successive Ionic Layer Adsorptionand Reaction Process, Journal of Elecrochemical Society, Vol. 137, p. 2915. [6] Seung – Yup Lee and Byung – Ok Park, (2008), CuInS2 Thin Films Deposited by Sol – gel Spin Coating Method, Thin Solid Films, Vol. 516(12), pp. 3862 – 2664. [7] Tang H. X, Yan M., Zhang H., Ma X. Y., Wang L. And Yang D., (2005), Preparation and Characterization of CuInS2 Thin Films for Solar Cells by Chemical Bath Deposition, Chem. Res. Chinese U. 2005, 21( 2), 236 – 239.

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[8] Mohammed M. A., Mousa A.M., and Ponpon J. P., (2009), Optical and Optoelectric Properties of PbCdS Ternary Thin Films Deposited by CBD, Journal of Semiconductor Technology and Science, Vol.9, No.2. pp. 111 – 117. [9] Ottih I. E., (2014), Studies of Chemical Bath Anti – reflection Thin Film of ZnNiS, Pelagia Research Library, Advances in Applied Science Research, 5(1) pp. 91 – 96. [10] Hankare P. P., Delekar S. D., Chate P.A, Sabane S. D., Garadkar K. M. and Bhuse V. M., (2005), A Novel Route to Synthesize Cd1-xPbxSe Thin Films from Solution Phase, Semiconductor Science and Technology, 20, p. 257 – 264. [11] Umeshkumar P. K., Sulakshana S.B. and Pawar P. H., (2011), The Optical Parameters of ZnxCd(1-x)Te Chalcogenide Thin Films, Journal of Surface Engineered Materials and Advanced Technology, Vol. 1, pp. 5155. [12] Ezema F. I., (2004), Effect of Some parametric Variations on the Optical Properties of Chemical Bath Deposited BiClO Thin Films, Journal of University of Chemical Technology and Metallurgy, Vol. 39, 225 – 238. [13] Jae – Hyeong, Lee, Woo–Chang, Song, Jun–sin, Yi, and Yeong–Sik, Yoo. 2003. “Characteristics of CdZnS Thin Film Doped by Thermal Diffusion of Vacuum Evaporated Indium Films”. Solar Energy Materials and Solar Cells. 75 (1-2):227 – 234. [14] Ezema F. I. and Okeke C. E., (2003), Chemical Bath Deposition of Bismuth Oxide (Bi 2O3) Thin Films and its Application, Greenwich Journal of Science and Technology, Vol. 3(2), p. 90. [15] Uhuegbu, C. C., (2010), Solution Growth Technique for FeCuS2 Ternary Thin Film and its Optical Characteristics, American Journal Scientific and Industrial Research, Vol. 1(3), pp. 392 – 396.

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