DESIGN AND FABRICATION OF A PORTABLE SPECTROMETER TO INVESTIGATE OPTICAL PROPERTIES OF THIN FILMS BENARD RIRO MORUMBWA [B.Ed. (Sc)] I56/10991/2006 ` A thesis submitted in partial fulfillment of the requirements for the award of the degree of Master of Science (Electronics and Instrumentation) in the School of Pure and Applied Sciences of Kenyatta University June, 2013 ii DECLARATION This thesis is my original work and has not been presented for the award of a degree or any other award in any other University Benard Riro Morumbwa …………………………. ……………………….. Department of Physics Signature Date Kenyatta University P.O. BOX 43844 - 00100 NAIROBI- KENYA We confirm that the work reported in this thesis was carried out by the candidate under our supervision. Dr. Patrick M. Karimi ………………………….. …………………………. Department of Physics Signature Date Kenyatta University P.O. BOX 43844 - 00100 NAIROBI- KENYA Dr. Daniel M. Wamwangi ……… ……10.06.2013…… School of Physics Signature Date University of Witswatersrand PRIVATE BAG 3, 2050 JOHANNESBERG - SOUTH AFRICA iii DEDICATION This thesis is dedicated to my wife Stellah Kemunto and my daughters, Brenda and Mitchell. iv ACKNOWLEDGEMENTS I thank in a special way Dr. P.M. Karimi and Dr. D. Wamwangi for their invaluable support, guidance and advice which enabled successful completion of this research. I do appreciate the attention and timely response they gave whenever I was in need of help. Their wide and in-depth knowledge in material science, electronics and instrumentation gave me the courage and ability I needed most in doing this work. I once more thank them for the great efforts and sacrifice they made to ensure that this work was a success. I am grateful to Dr. Migwi, former and Dr. Njoroge the current head of physics department who gave conducive learning environment during my stay as a student at Kenyatta University. I also acknowledge the physics laboratory technical staff, particularly the chief technician Mr. Simon Njuguna who made it possible for me to carry out thin film sample preparations in the laboratory. I will also not forget the encouragement and support I got from my colleagues Omayio, Agumba, Tuwei, Namasaka and Ogaro to mention a few. Appreciation to my family for being patient and understanding during the time I was away because of my studies. Most importantly I thank almighty lord for making this work possible. v TABLE OF CONTENTS TITLE……………………………………………………………………………………..i DECLARATION………………………………………………………………………...ii DEDICATION…………………………………………………………………………..iii ACKNOWLEDGEMENTS…………………………………………………………….iv TABLE OF CONTENTS…………………………………………………………..........v LIST OF TABLES……………………………………………………………………….x LIST OF FIGURES……………………………………………………………………..xi ABBREVIATIONS AND ACRONYMS……………………………………………...xiv LIST OF SYMBOLS…………………………………………………………………...xv ABSTRACT…………………………………………………………………………….xvi CHAPTER 1……………………………………………………………………………...1 INTRODUCTION………………………………………………………………….........1 1.1 Background to the Study……………………………………………………………..1 1.2 Statement of Research Problem………………………………………………………2 1.3 Objectives of the Research Project…………………………………………………...3 1.3.1 Main Objective…………………………………………………………….3 1.3.2 Specific Objectives……………………………………….……………….3 1.4 Rationale………………………………………………………………....…………...4 CHAPTER 2……………………………………………………………………………...5 LITERATURE REVIEW……………………………………………………………….5 2.1 Introduction..…………………………………………………………………….........5 2.2 Historical Background of Spectroscopy……………………………………………..5 vi 2.3 Development of Optical Spectrometers………………………………………………8 2.4 Types of Optical Spectrometers……………………………………………………....9 2.4.1 Ellipsometers………………………………………………………………9 2.4.2 Spectrophotometers……………………………………………………....10 CHAPTER 3…………………………………………………………………………….11 THEORY………………………………………………………………………………..11 3.1 Introduction………………………………………………………………………….11 3.2 Spectroscopy………………………………………………………………………...11 3.3 Optical Spectrometers……………………………………………………………….12 3.3.1 Ellipsometers……..………………………………………………………13 3.3.2 Visible Range Optical Spectrophotometers………………..…………….15 3.4 Spectrometer Automation…………………...………………………………………17 3.5 Enhanced Parallel Port (EPP)………………………………………………..……...18 3.6 Deposition of Thin Films……………..……………………………………………..20 3.6.1 Deposition of Thin Films by Thermal Evaporation…………..………….21 3.6.2 DC Magnetron Sputtering……………….……………………………….22 3.7 Optical Properties of Thin Films…………………..………………………………...24 3.7.1 Reflectance, (R)……………………...…………………………………..24 3.7.2 Real Refractive Index, (n)………………………………………………..25 3.7.3 Extinction Coefficient, (k)……………………………………………….26 3.7.4 Real Dielectric Constant, (ε1)…………….………………………………26 3.7.5 Imaginary Dielectric Constant, (ε2)…………….………………………..26 3.7.6 Absorption Coefficient, (α)……….……………………………………...27 vii 3.7.7 Determination of Thickness of a Thin Film, (x)……….………………...27 3.7.8 Transmittance, (T)………………………………………………………..28 3.7.9 Band Gap, (Eg)……………….…………………………………………..28 3.7.10 Direct Band Gap…………………………………………………………28 3.7.11 Indirect Band Gap………….…………………………………………….29 3.7.12 Band Gap of Amorphous Semiconductor Thin Films…………………...30 3.7.13 Energy Absorption Factor…………………….………………………….30 CHAPTER 4………………………………………………………………..…………...31 EXPERIMENTAL PROCEDURES………………………………………….……….31 4.1 Introduction………………………………..………………………………………....31 4.2 Hardware Design……………………………………...………………………..........32 4.2.1 Powering System………………………………………………………...32 4.2.2 Diffraction System………………………………………………….........34 4.2.3 Stepper Motor……………………………………………………………35 4.2.4 Photo – detectors…………………………………………………………37 4.2.5 Analog to Digital Converter (ADC 0809CCN)………………………….38 4.3 Software Design……………………………………………………………………...40 4.3.1 Hardware Interfacing………………………….…………………………40 4.3.2 MSVC++ 6.0 Portable Spectrometer Driver Program Designed in this Work……………………………………………………………………..42 4.4 Preparation of Sample Thin Films……………………………………..…………….45 4.4.1 Preparation of CuO Thin Film…………………………………………...45 4.4.2 Deposition of SnSe……………………………………………………....46 viii 4.5 Measurement Procedure of a Portable Spectrometer Designed in this Work………..48 CHAPTER 5………………………………………………...…………………………..50 RESULTS AND DISCUSSIONS……………………………...……………………….50 5.1 Introduction………………………...………………………………………………...50 5.2 Instrument Calibration………………………...………………………………..........50 5.3 Optical Properties of Copper Oxide (CuO)………………………...………………..52 5.3.1 Reflectance, (R) of CuO…………………….………...…………………52 5.3.2 Phase Angle, (Φ) of CuO………………………………………………...53 5.3.3 Real Refractive Index, (n) of CuO…………………………………...…..54 5.3.4 Imaginary Refractive Index, (k) of CuO.……………………………..….55 5.3.5 Real Permittivity, (ε1) of CuO.…………………………………………..56 5.3.6 Imaginary Permittivity, (ε2) of CuO……………………………………..57 5.3.7 Energy Absorption Factor of CuO.………………………………………57 5.3.8 Absorption Coefficient, (α) of CuO…..……………………………….…58 5.3.9 Band Gap, (Eg) of CuO……………………………………...…………...59 5.3.10 Validation of CuO Results………………….……………………………59 5.4 Optical Properties of Tin Selenide (SnSe)………………………...………………....61 5.4.1 Reflectance, (R) of SnSe……………………………….………………...61 5.4.2 Phase Angle, (Φ) of SnSe………………………………………………..62 5.4.3 Real Refractive Index, (n) of SnSe………………………….…………...62 5.4.4 Imaginary Refractive Index, (k) of SnSe………………………….……..63 5.4.5 Real Permittivity, (ε1) of SnSe…………………………………………...63 ix 5.4.6 Imaginary Permittivity, (ε2) of SnSe…………………….……………….64 5.4.7 Energy Absorption Factor of SnSe……………………….……………...65 5.4.8 Absorption Coefficient, (α) of SnSe……………………………….…….65 5.4.9 Band Gap, (Eg) of SnSe……………………………………………...…..65 5.4.10 Validation of SnSe Results………………………………………………66 CHAPTER 6………………………………..…………………………………………...69 CONCLUSION AND RECOMMENDATIONS FOR FURTHER WORK………...69 6.1 Conclusion……………...……………………………………………………............69 6.2 Recommendations for Further Work…………………..………………………….....70 REFERENCES……………...…………………………..………………………………71 APPENDICES………………..…………………………………………………………74 Appendix I: How to Run MSVC++ 6.0 Portable Spectrometer Driver Program Designed in this Work………………………………………………………………..74 Appendix II: Picture of Hardware Components of the Portable Spectrometer designed in this Work………..........................................................................................78 Appendix III: Specification Chart for Stepper Motor used in the Portable Spectrometer Designed in this Work…...........................................................................79 Appendix IV: MSVC++ 6.0 Portable Spectrometer Driver Program………..…………..80 x LIST OF TABLES Table 3.1: Pin Assignment for D-type 25 pin Female Connector of Enhanced Parallel Port (EPP)………………………………………………………………………….19 Table 4.1: Unipolar Stepper Motor Half Stepping Mode Procedure….…………………36 Table 4.2: Input States for the Address lines (A, B and C) used to Select Analog Input Channel into Analog to Digital Converter (ADC08090CCN)………………..40 Table 4.3: Binary Code generated by Half Stepping Mode of the Uni-polar Stepper Motor………………………………………………………………………….45 Table 4.4: Deposition Parameters for CuO Thin Film used to test Portable Spectrometer Designed in this Work..………………………………………………………46 Table 4.5: Deposition Parameters for SnSe Thin Film used to test Portable Spectrometer Designed in this work………………………………………………………...47 Table 5.1: Comparison between Reflectance of CuO Using Portable Spectrometer Designed in this Work and Spectrophotometer (SolidSpec-3700)…………...61 Table 5.2: Reflectance of SnSe using Portable spectrometer Designed in this Work and Spectrophotometer (SolidSpec-3700)………………………………………...67 Table 5.3: Band Gap of SnSe using Portable spectrometer Designed in this Work and Spectrophptometer (SolidSpec-3700)………………………………………...68