Tin selenide (SnSe) thin films were electrochemically deposited onto Au(1 1 1) substrates from an aqueous solution containing SnCl2, Na2SeO3, and EDTA at room temperature (25 °C). The electrochemical behaviors and the codeposition potentials of Sn and Se were explored by cyclic voltammetry. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and UV–vis absorption spectroscopy were employed to characterize the thin films. When the electrodeposition potential increased, the Se content in the films decreased. It was found that the stoichiometric SnSe thin films could be obtained at −0.50 V. The as-deposited films were crystallized in the preferential orientation along the (1 1 1) plane. The morphologies of SnSe films could be changed from spherical grains to platelet-like particles as the deposition potential increases. The SEM investigations show that the film growth proceeds via nucleation, growth of film layer and formation of needle-like particles on the overlayer of the film. The optical absorption study showed the film has direct transition with band gap energy of 1.3 eV.
TABLE OF CONTENT
Title Page
Approval Page
Dedication
Acknowledgement
Abstract
Table of Content
CHAPTER ONE
1.0 Introduction
1.1 objective of the study
1.3 scope of the study
CHAPTER TWO
2.0 Literature review
2.1 Overview of tin selenide
2.2 Structure of tin selenide
2.3 Synthesis of tin selenide
2.4 Chemistry of tin selenide
2.5 Uses of tin selenide
2.6 Chemical properties of tin selenide
2.7 Application of tin selenide
CHAPTER THREE
3.0 Methodology
3.1 Materials and methods
CHAPTER FOUR
4.0 Result analysis
4.1 Result and discussion
CHAPTER FIVE
5.1 Conclusion
5.2 Bibliography
CHAPTER ONE
1.1 INTRODUCTION
Considerable attention has been paid to prepare metal chalcogenide thin films by different techniques such as chemical bath deposition, chemical vapor deposition, electrodeposition and vacuum evaporation methods (Fujii et al.1988; John et al.1994; Pandey et al. 2000; Amaraj et al. 2004; Hilal et al. 2009; Chate et al.2010; Indirajith et al. 2010; Yunos et al. 2011). Among those, vacuum evaporation is the favorable method to prepare semiconductor thin films for photovoltaic solar cells (Fujii et al. 1988; Tomakin et al. 2011). This is a simple technique that involves easy to control processing parameters, without participation of other atoms or molecules and offers extremely clean interfaces during processing and subsequent consolidation by conducting the experiments under ultra high vacuum conditions (Hass et al. 1993).
However, the source material is crucial in electrodeposition technique. Thin film properties depend on the quality of the source material and preparation methodology. Motivated by the potential applications of tin chalcogenides, investigations on these compounds are becoming particularly active in the field of materials chemistry. Tin chalcogenides offer a range of optical band gaps suitable for various optical and optoelectronic applications. These compounds are also used as sensor and laser materials, thin films polarizers and thermoelectric cooling materials (Zweibel, 2000). Considerable attention has been given by various researchers in studying the properties of tin selenide (SnSe). SnSe is a narrow band gap binary IV-VI semiconductor with an orthorhombic crystal structure. Among the uses of tin selenide (SnSe) are as memory switching devices, holographic recording systems, and infrared electronic devices (Lindgren et al., 2002). SnSe has been studied in the form of both single crystal and thin films (Subramanian et al., 1999; Yu et al., 1981; Agnithothri et al., 1979). SnSe could also be used in the fabrication of photoelectrochemical cells. The use of SnSe for this purpose could suppress photocorrosion and enhance the fill factor in electrical switches and in junction devices (Terada et al., 1971).
The methods used to prepare SnSe thin films are chemical bath deposition (Suguna et al., 1996), vacuum evaporation, chemical vapour deposition (Pramanik et al., 1988; Bennouna et al., 1983; Dang Tran, 1985) and electrodeposition (Subramanian et al., 1999; Engelken et al., 1986). Among these methods, electrodeposition is widely used because it is a simple, economical and viable technique, which produces films of good quality for device applications (Riveros et al., 2001; Pattabi et al., 2000). The attractive features of the method are the convenience for producing large area devices, low temperature growth, enable morphological, compositional and film thickness control by readily adjusting the electrical parameters, as well as the composition of the electrolytic solution (Riveros et al., 2001). We report here the electrodeposition of SnSe thin films under aqueous conditions in the presence of ethylendiaminetetraacetate (EDTA) as a chelating agent.
1.2 OBJECTIVE OF THE STUDY
There are different methods of absorbing spectra of tin selenide thin films such as chemical bath deposition, chemical vapor deposition, electrodeposition and vacuum evaporation methods. However, the method of absorbance using electrodeposition method is the focus of this study – which is the aim.
1.3 SCOPE OF THE STUDY
In this study, an electrochemistry involved in the deposition of SnSe films is presented. The redox reactions and the polarization curves of Sn and Se were studied to fix the pH and potential values V (NHE) to get uniform deposition. Films were cathodically deposited at 55°C. XRD studies show an orthorhombic structure. Films showed an indirect band-gap of 1.05 eV. Surface morphological studies were carried out using SEM, and the stoichiometry was estimated from XPS analysis. Effect of annealing in air at 200°C has been reported.
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