Influence of PH, Doping and Annealing on Structural and Optical Properties of Chemical Bath Deposited Cobalt (iii) Oxide (CO3O4) Thin films

Influence of PH, Doping and Annealing on Structural and Optical Properties of Chemical Bath Deposited Cobalt (iii) Oxide (CO3O4) Thin films.

ABSTRACT

Cobalt (III) oxide (Co3O4) thin films were deposited on glass substrates at a temperature of 70°C with continuous stirring and heating of the alkaline bath of various pH of 8, 10, 12 and 14. Cobalt (II) chloride hexahydrate (CoCl2·6H2O) was used as source of Co2+ and to make it alkaline, 25% aqueous ammonia solution was added as the complexing agent with constant heating and stirring.

The bath was doped with zinc nitrate (Zn(NO3)2 and later, some samples were annealed at 200°C for 30 minutes. X-ray diffraction method was used to confirm the depositions.

The structural features obtained from the x-ray diffraction showed the peaks of Co3O4 and increase in crystallinity as pH increases which was confirmed by SEM. It also shown improvement in crystallinity after doping and annealing.

The optical studies showed a variation of absorbance, reflectance, direct band gap energy and refractive index as pH varies and changes after doping and annealing. The range of direct band gap energy and refractive index obtained are 1.34eV – 2.85eV and 1.38 – 2.07 respectively.

The values of the band gap energy and refractive index obtained indicate possible applications in photovoltaic systems, optoelectronics, laser diodes and light emitting diodes.

TABLE OF CONTENTS

Title Page i
Certification ii
Dedication iii
Acknowledgement iv
Table of content v – vii
List of tables viii
List of figures ix – x
Abstract xi

CHAPTER ONE

1.0 Introduction 1
1.1 Cobalt: The Technology Empowering Element 1
1.2 Cobalt in Electronics 2
1.3 Sources of Cobalt 19
1.4 Properties of Cobalt 19
1.5 Applications of Thin Films 20
1.6 Motivations 23
1.7 Purpose of Study 24

CHAPTER TWO

2.0 Literature Review 25
2.1 Review Studies of Cobalt Oxide Thin Film 25
2.2 History of Photovoltaics 26
2.3 Photovoltaic Technology 28
2.4 Solar Cells 35
2.5 X-Ray Diffraction (XRD) 42
2.6 Scanning Electron Microscope (SEM) 43
2.7 Energy Dispersive Spectroscopy (EDS) 44
2.8 Photo Spectrometer or UV-SPEC 45
2.9 Characterization Techniques 46

CHAPTER THREE

3.0 Experimental Details 47
3.1 Substrate Preparation 47
3.2 Synthesis of Co3O4 Thin Films 47
3.3 Equations of Reaction for Formation of Co3O4 Thin Films 48
3.4 Synthesis of Co3O4 Thin Films Doping The Bath With Zn(NO3)2 49
3.5 Annealing of Synthesized Films 49

CHAPTER FOUR

4.0 Results and Discussion 50
4.1 Structural Analysis 50
4.2 X- Ray Diffraction (XRD) Analysis of Co3O4 Films 50
4.3 Surface Morphology Analysis 53
4.4 Optical Analysis 55

CHAPTER FIVE

5.0 Conclusion 68
5.1 Conclusion 68
References 69 – 75

INTRODUCTION

1.1 Cobalt: The Technology Empowering Element

Cobalt oxide thin films have attracted significant research work in modern years because of their prospective application in various technological areas.

Cobalt has been at the service of man, the celebrated blue mixture in glazes back in ancient Egypt but now accepted as an important technology-improving element where energy, efficiency and environmental benefits are the order of the day.

Cobalt has many uses from aircraft engines to rechargeable batteries, which are very important in the improvement of energy for the future.

Cobalt play an important role in industrial chemical processes where its exceptional catalytic properties can be used for such applications as desulphurisation of hydrocarbons, which is crucial in cleaning fuel technology, and removal of nitrous oxide to ensure that emissions of greenhouse gases are reduced.

Its catalytic potentials are also used in the emerging technology of converting natural gas to liquid hydrocarbons, hence using carbon based resources more efficiently.

They can be used as high temperature solar selective absorber [1], electrochemical capacitors [2], optical gas sensors [3], heterogeneous catalysts [4], anodic electrochromic materials in smart window device [5], negative electrodes in lithium-ion batteries [6] and magnetic materials.

Industries also employs the advantages that cobalt can bring to the hard metal industry where hard wearing metals and alloys allow the manufacturer of highly effective cutting tools for a broad range of industrial applications.

REFERENCES

E. Barrera, L. Huerta, S. Muhl, A. Avila, (2005), Journal of Solar Energy Materials and Solar Cells, 88, 179 – 186.

Y. Li, K. Huang, Z. Yao, S. Liu, X. Qing, (2011), Electrochemical Acta, 56, 2140 – 2144.

 X. Liu, G. Qiu, X. Li, (2005), Journal of Nanotechnology, 16, 3035.

X. W. Xie, Y. Li, Z.Q. Liu, M. Haruta, W. J. Shen, (2009), Journal of Nature, 458, 746.

X. H. Xia, J. P. Tu, J. Zhang, X. H. Huang, X. L. Wang, W. K. Zhang, H. Huang, (2008) Electrochemistry Communications 10, 1815 – 1818.

K. M Shaju, F. Jiao, A. Debart, P. G. Bruce, (2007), Journal of Physical Chemistry, 9, 1837.

O. S. Heavens, (1970), Thin Film Physics, Methuen and Co Ltd., London.

E. Pentia, , V. Draghici, G. Sarua, B. Mereu, L. Pintilie, F. Sava and M. Popescu, (2004), Journal of Electrochemical Society, 151 (11), 729 – 733.