Elsevier

Applied Surface Science

Volume 288, 1 January 2014, Pages 76-82
Applied Surface Science

Effect of complexing agent TEA: The structural, morphological, topographical and optical properties of FexSx nano thin films deposited by SILAR technique

https://doi.org/10.1016/j.apsusc.2013.09.118Get rights and content

Highlights

Abstract

Iron sulfide thin films (FexSx) (x = 0.05 M, 0.10 M, 0.15 M, 0.20 M and 0.25 M) were deposited by SILAR method from equimolar and equivolume aqueous solutions of ferrous nitrate and sodium sulfide with the addition of complexing agent TEA. The structural, morphological and optical characteristics of the films were derived from X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and UV–vis spectral techniques. The mixed characteristics (crystalline and amorphous) of the deposited films and the increasing crystalline qualities with the concentrations were understood from the XRD analysis. The grain sizes and roughness of the films were decreases with the increasing concentration and also at the higher concentration films are shown by the same images presence of hexagonal like crystallite structure. The influence of complexing agent TEA on the surface roughness and morphological properties are confirmed by the atomic force microscope (AFM) results. The effect of increasing substrate concentration on the absorption and transmission measurements and its impact on the optical band-gap energy were enumerated from the UV–vis analysis.

Introduction

The research work of thin film materials that focus on alternative solar cell, photovoltaic, photo catalysis and photo electrochemical applications are growing exponentially [1], [2], [3], [4]. The substrate and reagent materials used for making thin films are cheap, abundant, without sulfuration and nontoxic natured, hence the thin films are having versatile applications. A variety of processes such as spray pyrolysis [5], [6], low pressure metal organic chemical vapour deposition [7], atmospheric pressure chemical vapour deposition [8], molecular beam deposition [9], sol–gel [10], [11], electrodeposition [12], [13], [14], chemical bath deposition [15] and sputtering [16], [17], [18] are employed to produce thin films.

The ratio between iron and sulfide in FeS thin films are varying at different levels. Depends on the concentration of sulfur/iron, the material will exist in several distinct forms viz., pyrrhotite (Fe1−xS), troilite (FeS), mackinawite (Fe1+xS), greigite (Fe2S3) and pyrite (FeS2) and hence these materials has different crystalline structures [19]. Pyrites are greatly creating interest because of the prospect of fabricating inexpensive, large-area photovoltaics by the roll-to-roll deposition of nano thin films on substrates. The nano crystalline films processed from solution may offer excellent manufacturing scalability at very low cost thin-film approaches [1], [4].

The FeS materials have exhibited a direct band gap energy in the range of Eg = 2.07–0.95 eV [20], [21]. The increasing concentration of sulfur in FeS reduces the band gap energy of the thin film. Now a day, many researchers concentrate on these kinds of absorber materials of thin film that have the suitability for solar cells [22], [23], [24], [25], [26].

However, till now there is no effective attempt have made on the SILAR (successive ionic layer adsorption and reaction) method, to prepare FeS thin films at room temperature. This research work aimed to prepare the FeS thin film with the equimolar and equivolume concentrations of substrates by SILAR technique in the aqueous medium with the addition of complexing agent TEA, also considered the influence of concentrations on the structural, optical and morphological properties [27].

Section snippets

Preparation of thin films

Microscope glass slides of 26 mm × 76 mm × 1 mm dimension were used as substrates. The substrates were ultrasonically cleaned with 15% nitric acid and ethanol, washed in detergent solution to clean the dirts, and purified with deionised water (conductivity ∼1 Ω−1) for 30 min and then dried in a hot air oven.

In SILAR method concentration, pH and temperature of precursor solutions and the time duration are important parameters for adsorption and reaction thus effective film coating.

The analytical reagent

XRD analysis

The prepared films were analysed for X-ray diffraction studies using Cu-Kα radiation (λ = 0.15406 nm) to understand the crystalline properties of the films. The diffractogram of the films were displayed in Fig. 2(a)–(c) for the concentrations 0.05 M, 0.10 M, and 0.15 M, respectively. The film of lower concentration is having amorphous character; while the concentration increases the crystalline nature of the FeS films also increases. The crystalline nature of the coated film was identified by

Conclusion

Thin films of iron sulfide (FexSx) (x = 0.05 M, 0.10 M, 0.15 M, 0.02 M and 0.25 M) were prepared by the SILAR technique using TEA as complexing agent. The population of material, grain sizes and roughness of the deposited film were improved at the higher concentrated material. The surface, morphological, optical and crystalline properties are interconnected with each other and the properties are modified while altering the substrate concentrations. The band gap energy of the materials also changed

Acknowledgements

We thank Dr. M. Sivakumar, Coordinator, Department of Nanoscience and Technology of our institution for providing us AFM and UV–visible spectra facilities, also we acknowledge National Institute of Technology, Tiruchirappalli, 620024 for providing XRD & SEM facilities to this research.

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