Structural and Optical Properties of ZnO Nano-Powder Synthesized by Combustion and Sol-gel Method

Abstract Nowadays, ZnO is considered as the most important chemical compounds due their distinctive properties owing to its wide band gab and large exciton binding energy. It is well known that the structural and the optical properties of ZnO differ by different methods of preparation. Therefore, in this work, ZnO power was prepared by two methods, namely sol-gel and combustion method with the aim of comparison. The obtained samples from both methods were investigated by many techniques for considerable comparison. The obtained results from ZnO synthesized by the sol- gel method showed that the crystallite size of ZnO was increases by increasing of the annealing temperature. Also little change in the lattice parameter was observed when the annealing temperature increased. It is observed also that similar structure of ZnO prepared by sol-gel and combustion can be obtained at particular conditions. TEM studies showed that the ZnO nanocrystals are irregularly spherical with average diameter of 32 nm, which is similar to the calculated crystallite size from the XRD data. The calculated energy band gab of ZnO prepared by combustion method is found to be 3.2 eV while for samples prepared by sol-gel method is found to be increased with increasing the annealing temperature. There was a clear difference between the two PL spectra obtained from ZnO synthesized by sol-gel and combustion method which is assigned to be due to complicated defect chemistry relevant to the experimental process.

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Dedication Ii

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Abstract Iv

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No Chapter One (Introduction)

1.1 Overview 1

1.2 Literature review 3

1.3 Problem statement 4

1.4 Research Objectives 4

1.4.1 General Objective 4

1.4.2 Specific Objectives 5

1.5 Dissertation layout 5

Chapter Two (Theoretical background)

2.1 Overview 6

2.2 Structural properties 6

2.2.1 Scherrer's equation 10

2.2.2 Lattice parameters 10

2.3 Optical properties of ZnO 11

2.3.1 Determination of Energy gabs from reflectance spectra 11

2.4 Mechanical properties of ZnO 12

2.5 Electrical properties 13

2.6 Native type of Defects in ZnO 13

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2.7 Applications of ZnO 14

Chapter Three (Experimental and Characterization techniques)

3.1 Experimental 15

3.1.1 Sol-gel method 15

3.1.2 Combustion method 16

3.2 Characterization techniques 17

3.2.1 X-ray Diffraction (XRD) 17

3.2.1.1 Bragg's law 18

3.2.2 Transmission Electron Microscopy (TEM) 19

3.2.3 Ultraviolet Visible Spectroscopy (UV-Vis) 21

3.2.4 Photoluminescence spectroscopy (PL) 23

Chapter Four (Result and Discussion)

4.1 Structure properties 25

4.1.1 X-rays diffraction studies 25

4.1.2 TEM studies 28

4.2 Optical studies 30

4.2.1 UV-Vis studies 30

4.2.2 Photoluminescence studies 33

Chapter Five(Conclusion and future works)

5.1 Conclusion 36

5.2 Future works 37

5.3 References 38