Synthesis and Characterization of Nanostructured Zinc Oxide Thin Films Using Aqueous Chemical Method

ABSTRACT In this work, we report on the synthesis of Zinc Oxide (ZnO), by a cost effective and low temperature aqueous chemical method on conducting glass substrates. The grown nanostructures have been characterized by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), optical absorption techniques and Raman spectroscopy. Resistivity of the films was studied with I-V data for the ZnO samples. SEM images show the formation of flower, bud, star, spindle and blades-like morphologies at different deposition time ranging from 15 to 40 minutes. The AFM analysis reveals that the films are dominated by voids with regard to surface topography. The XRD results showed that all films crystallized under hexagonal wurtzite structure and presented a preferential orientation along the c-axis with the maximum crystallite size of 86.33 nm. The average transmittance of all the films increase in the visible region from 32 -75% in a long wavelength domain from 300 – 1100nm. The extinction coefficient decreases with an increase in wavelength and the band gap energy increases from 3.24 to 3.98eV due to increase in phonon energy. In addition to the vibrational modes from ZnO, the Raman spectra are dominated by the longitudinal optics (LO) between 480 – 580cm-1 . The resistivity of the films decreases as deposition time increases, this shows that ZnO thin films is a good conductor.

TABLE OF CONTENTS

Title Page - - - - - - - - - - i

Certification - - - - - - - - - - ii

Dedication - - - - - - - - - - iii

Acknowledgement - - - - - - - - - iv

Table of Contents - - - - - - - - - v

Abstract - - - - - - - - - - viii

CHAPTER ONE: INTRODUCTION

1.1 Why Nanomaterials? - - - - - - - - 2

1.1.1 Increase in surface area to volume ratio - - - - - 2

1.1.2 Quantum Comfinement Effect - - - - - - 2

1.2 Nanostructured Zinc Oxide - - - - - - - 3

1.3 Growth Mechanisms of ZnO - - - - - - - 4

1.4 Nucleation and Growth - - - - - - - - 5

1.5 Crystal Structure of Zinc Oxide - - - - - - - 6

1.6 Band Structure of Zinc Oxide - - - - - - - 7

1.7 Objectives of the Study - - - - - - - - 7

1.8 Research Methodology - - - - - - - - 8

1.9 Aqueous Chemical Method - - - - - - - 9

CHAPTER TWO: LITERATURE REVIEW

2.1 Studies on Zinc Oxide - - - - - - - - 11

2.2 X-Ray Diffraction Technique (XRD) - - - - - - 12

2.3 Identifications of Phases - - - - - - - - 14

2.4 Scanning Electron Microscopy (SEM) - - - - - - 16

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2.5 Principles of SEM - - - - - - - - 17

2.6 Raman Spectroscopy - - - - - - - - 18

2.7 Semi Conductor Characteristics System (SCS) - - - - - 24

2.8 Basic Photovoltaic Cell Circuit and Device Parameter - - - - 25

CHAPTER THREE: EXPERIMENTAL SET UP

3.1 Preparation of Seed Solution - - - - - - - 29

3.2 Seed Layer Deposition - - - - - - - - 30

3.3 Deposition of ZnO Thin Films - - - - - - - 30

CHAPTER FOUR: RESULTS AND DISCUSSIONS

4.1 Scanning Electron Microscopy (SEM) - - - - - - 31

4.2 Atomic Force Microscopy (AFM) - - - - - - 32

4.3 X-Ray Diffraction (XRD)- - - - - - - - 33

4.4 Optical Properties - - - - - - - - 35

4.5 Microstructural Properties - - - - - - - 37

4.6 Resistivity Studies- - - - - - - - - 38

CHAPTER FIVE: CONCLUSION - - - - - - - 42

 REFERENCES - - - - - - - 43