Size control and characterization of colloidal magnetic cobalt nanoparticles

Abstract

SIZE CONTROL AND CHARACTERIZATION OF COLLOIDAL MAGNETIC COBALT NANOP ARTICLES by Abhishek Singh The overall goals of this research were to synthesize magnetic cobalt nanoparticles and characterize their structural and magnetic properties. Cobalt nanoparticles were synthesized via high temperature reduction of cobalt chloride utilizing two different surfactants, tributylphosphine and trioctylphosphine, and varying the surfactant-to-reagent molar concentration for each. X-ray diffraction results indicate that each synthesis condition yielded nanoparticles with an e-cobalt crystal structure, a resemblance to the P-manganese structure. Transmission electron micrographs indicate the formation of discrete hexagonal networks among the particles with inter-particle spacing of 2-5 nm. Sizing analysis found that utilizing a bulkier surfactant yields smaller mean particle size. Furthermore, utilizing a surfactant at a higher surfactant-to-reagent molar ratio also yields a smaller mean particle size with a tighter distribution. Normalized vibrating sample magnetometer results indicate synthesized cobalt nanoparticles exhibit ferromagnetic behavior at room temperature and increasing coercivity with mean particle size. To my parents, Dharam and Yashodhara, my family, friends, and all of my teachers, Thank you for loving, caring, educating, and inspiring. TABLE OF CONTENTS LIST OF FIGURES viii LIST OF TABLES x LIST OF EQUATIONS xii CHAPTER ONE: INTRODUCTION 1 1.1 THE PROMISE OF NANOTECHNOLOGY 1 1.2 SIGNIFICANCE 3 CHAPTER TWO: LITERATURE REVIEW 5 2.1 NANO-PARTICLE SYNTHESIS METHODOLOGIES 5 2.1.1 TOP-DOWN VERSUS BOTTOM-UP APPROACH 5 2.1.2 BOTTOM-UP SYNTHESIS: THERMAL DECOMPOSITION OF ORGANOMETALLIC AND POLYMER COMPOUNDS 6 2.1.3 BOTTOM-UP SYNTHESIS: REDUCTION OF METAL-SALTS 7 2.1.3.1 ISOLATION OF SYNTHESIZED NANO-P ARTICLES 11 2.2 STRUCTURAL CHARACTERIZATION 12 2.2.1 X-RAY DIFFRACTION (XRD) 12 2.2.2 TRANSMISSION ELECTRON MICROSCOPY (TEM) 15 2.3 MAGNETIC ANALYSIS 17 2.3.1 VIBRATING SAMPLE MAGNETOMETER (VSM) 17 2.3.2 HYSTERESIS 19 2.4 SUMMARY 22 CHAPTER THREE: EXPERIMENTAL METHODS 23 3.1 RESEARCH OBJECTIVES 23