SYNTHESIS OF METAL SELENIDE SEMICONDUCTOR NANOCRYSTALS USING SELENIUM DIOXIDE AS PRECURSOR By XIAN CHEN A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2007 1 © 2007 Xian Chen 2 To my parents 3 ACKNOWLEDGMENTS Above all, I would like to thank my parents for what they have done for me through these years. I would not have been able to get to where I am today without their love and support. I would like to thank my advisor, Dr. Charles Cao, for his advice on my research and life and for the valuable help during my difficult times. I also would like to thank Dr. Yongan Yang for his kindness and helpful discussion. I learned experiment techniques, knowledge, how to do research and so on from him. I also appreciate the help and friendship that the whole Cao group gave me. Finally, I would like to express my gratitude to Dr. Ben Smith for his guidance and help. 4 TABLE OF CONTENTS page ACKNOWLEDGMENTS ...............................................................................................................4 LIST OF FIGURES .........................................................................................................................7 ABSTRACT.....................................................................................................................................9 CHAPTER 1 SEMICONDUCTOR NANOCRYSTALS ............................................................................11 1.1 Introduction..................................................................................................................11 1.2 General Synthetic Methods for Nanocrystals ..............................................................11 1.2.1 Injection-Based Synthetic Method.....................................................................13 1.2.2 One-Pot Synthetic Method.................................................................................14 1.3 Applications of Semiconductor Nanocrystals..............................................................16 1.3.1 Biological Detection ..........................................................................................16 1.3.2 Hybrid Electroluminenscent Device..................................................................17 1.3.3 Photovoltaic Device...........................................................................................18 2 SYNTHESIS OF CADMIUN SELENIDE NANOCRYSTALS USING SELENIUM DIOXIDE AS PRECURSOR .................................................................................................19 2.1 Introduction..................................................................................................................19 2.2 Experimental Section...................................................................................................20 2.2.1 Materials ............................................................................................................20 2.2.2 Instrumentation ..................................................................................................20 2.2.3 Preparation of Cd-Precursors.............................................................................22 2.2.3.1 Cadmium myristate (CdC14)....................................................................22 2.2.3.2 Cadmium stearate (CdC18) ......................................................................22 2.2.3.3 Cadmium docosanate (CdC22).................................................................22 2.2.4 Preparation of CdSe Nanocrystals .....................................................................23 2.3 Results and Discussion ................................................................................................23 2.3.1 Diol Effect..........................................................................................................23 2.3.2 Precursor Effect .................................................................................................32 2.3.3 Multiple-Addition Method.................................................................................36 2.4 Conclusion ...................................................................................................................37 3 SYNTHESIS OF METAL SELENIDE NANOCRYSTALS USING SELENIUM DIOXIDE AS PRECURSOR .................................................................................................39 3.1 Introduction..................................................................................................................39 3.2 Experimental Section...................................................................................................40 3.2.1 Materials ............................................................................................................40 3.2.2 Instrumentation ..................................................................................................41 5 3.2.3 Preparation of Precursors...................................................................................41 3.2.3.1 Gallium myristate....................................................................................41 3.2.3.2 Silver oleate.............................................................................................41 3.2.3.3 Copper oleate...........................................................................................41 3.2.3.4 Nickel oleate............................................................................................42 3.2.4 Preparation of Nanocrystals...............................................................................42 3.2.4.1 Gallium selenide nanocrystals.................................................................42 3.2.4.2 Lead selenide nanocrystals......................................................................42 3.2.4.3 Silver selenide nanocrystals ....................................................................43 3.2.4.4 Copper selenide nanocrystals ..................................................................43 3.2.4.5 Nickel selenide nanocrystals ...................................................................43 3.2.5 Purification of Nanocrystals ..............................................................................43 3.3 Results and Discussion ................................................................................................44 3.4 Conclusion ...................................................................................................................48 4 SUMMARY AND FUTURE WORK...................................................................................50 4.1 Summary......................................................................................................................50 4.2 Future work..................................................................................................................50 4.2.1 Injection-Synthetic Method for CdSe ................................................................50 4.2.2 Improvement of Other Metal Selenide Nanocrystals.........................................51 4.2.3 Mechanism Study...............................................................................................51 LIST OF REFERENCES...............................................................................................................52 BIOGRAPHICAL SKETCH .........................................................................................................56 6 LIST OF FIGURES Figure page 1-1 Scheme of the formation of nanocrystals. ..........................................................................12 1-2 LaMer Curve.......................................................................................................................13 1-3 Representation of the synthetic apparatus employed in the injection-based method.........14 1-4 Absorption spectrum of CdS nanocrystals (d = 3.5 nm). ...................................................15 1-5 Representation of the synthetic apparatus employed in the one-pot synthetic method......16 2-1 Sizing curve of CdSe nanocrystals .....................................................................................19 2-2 HWHF and peak sharpness used for size distribution determination.................................20 2-3 Schematic diagram of a UV-Vis microscope. ....................................................................21 2-4 Schematic diagram of a Fluorolog-3 Model FL3-12 spectrofluorometer. .........................21 2-5 Molecular structures of organic solvents used. ..................................................................23 2-6 Temporal evolution of the absorption spectra during the CdSe synthesis .........................24 2-7 Characterization of CdSe nanocrystals synthesized in ODE with reaction time of 40 minutes...............................................................................................................................25 2-8 Temporal evolution of CdSe nanocrystal concentration synthesized in ODE with different C16-diol/SeO2 ratios............................................................................................26 2-9 CdSe particle growth rate in the synthesis with different C16-diol/SeO2 ratios ................27 2-10 CdSe particle size and normalized nuclei number in the synthesis with different C16-diol/SeO2 ratios. .........................................................................................................28 2-11 Temporal evolution