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Characterization of Single Nanoparticles Characterization of Single Nanoparticles by Steven Jones BSc, University of Victoria, 2015 A Thesis Submitted in Partial Fulfillment of the Requirements for the Degree of MASTER OF APPLIED SCIENCE in the Department of Electrical and Computer Engineering Steven Jones, 2016 University of Victoria All rights reserved. This thesis may not be reproduced in whole or in part, by photocopy or other means, without the permission of the author. ii Supervisory Committee Characterization of Single Nanoparticles by Steven Jones BSc, University of Victoria, 2015 Supervisory Committee Dr. Reuven Gordon, (Department of Electrical and Computer Engineering) Supervisor Dr. Geoffrey Steeves, (Department of Physics and Astronomy) Outside Member iii Abstract Supervisory Committee Dr. Reuven Gordon, (Department of Electrical and Computer Engineering) Supervisor Dr. Geoffrey Steeves, (Department of Physics and Astronomy) Outside Member Optical trapping is a method which uses focused laser light to manipulate small objects. This optical manipulation can be scaled below the diffraction limit by using interactions between light and apertures in a metal film to localize electric fields. This method can trap objects as small as several nanometers. The ability to determine the properties of a trapped nanoparticle is among the most pressing issues to the utilization of this method to a broader range of research and industrial applications. Presented here are two methods which demonstrate the ability to determine the properties of a trapped nanoparticle. The first method incorporates Raman spectroscopy into a trapping setup to obtain single particle identification. Raman spectroscopy provides a way to uniquely identify an object based on the light it scatters. Because Raman scattering is an intrinsically weak process, it has been difficult to obtain single particle sensitivity. Using localized electric fields at the trapping aperture, the Raman integrated trapping setup greatly enhances the optical interaction with the trapped particle enabling the required sensitivity. In this work, the trapping and identification of 20 nm titania and polystyrene nanoparticles is demonstrated. The second method uses an aperture assisted optical trap to detect the response of a magnetite nanoparticle to a varying applied magnetic field. This information is then used to determine the magnetic susceptibility, remanence, refractive index, and size distribution of the trapped particle. iv Table of Contents Supervisory Committee ...................................................................................................... ii Abstract .............................................................................................................................. iii Table of Contents ............................................................................................................... iv List of Figures .................................................................................................................... vi Acknowledgments.............................................................................................................. xi Dedication ......................................................................................................................... xii Chapter 1 – Introduction ..................................................................................................... 1 1.1 Optical Sensing ......................................................................................................... 2 1.1.1 Dynamic Light Scattering .................................................................................. 2 1.1.2 Surface Plasmon Resonance Sensors ................................................................. 3 1.1.3 Spectroscopy ...................................................................................................... 5 1.2 Nanostructured Enhancements.................................................................................. 6 1.2.1 Localised Surface Plasmon Resonance Sensors ................................................ 7 1.2.2 Surface Enhanced Raman Spectroscopy ............................................................ 8 1.2.3 Extraordinary Optical Transmission .................................................................. 8 1.3 Optical Trapping ....................................................................................................... 9 1.4 Contributions of this Thesis .................................................................................... 10 Chapter 2 – Theory ........................................................................................................... 12 2.1 Introduction ............................................................................................................. 12 2.2 Rayleigh Scattering ................................................................................................. 13 2.2.1 Scattering Force ............................................................................................... 13 2.2.2 Gradient Force ................................................................................................. 16 2.3 Plasmons ................................................................................................................. 18 2.3.1 Surface Plasmon Polaritons ............................................................................. 21 2.3.2 Localized Surface Plasmons Resonances ........................................................ 25 2.4 Optical Trapping ..................................................................................................... 27 2.4.1 Introduction ...................................................................................................... 27 2.4.2 Bethe’s Aperture Theory.................................................................................. 30 2.4.3 Aperture Trapping ............................................................................................ 33 2.5 Raman Spectroscopy ............................................................................................... 34 2.5.1 Surface Enhanced Raman Spectroscopy .......................................................... 44 Chapter 3 – Methods ......................................................................................................... 46 3.1 Introduction ............................................................................................................. 46 3.2 Experimental Setup ................................................................................................. 46 3.3 Aperture Fabrication ............................................................................................... 48 3.4 Sample Preparation ................................................................................................. 50 3.5 Experimentation and Data Acquisition ................................................................... 52 Chapter 4 – Single Nanoparticle Raman Spectroscopy .................................................... 54 4.1 Introduction ............................................................................................................. 54 4.2 Contributions........................................................................................................... 55 4.3 Optical Trapping and Raman Integration ............................................................... 55 4.4 Results ..................................................................................................................... 56 4.5 Discussion ............................................................................................................... 62 4.6 Summary ................................................................................................................. 64 Chapter 5 – Characterization of Magnetic Nanoparticles ................................................. 66 v 5.1 Introduction ............................................................................................................. 66 5.2 Contributions........................................................................................................... 66 5.3 Optical Trapping and Magnetic Field Integration .................................................. 66 5.4 Results and Analysis ............................................................................................... 67 5.5 Summary ................................................................................................................. 74 Chapter 6 – Conclusion ..................................................................................................... 75 Chapter 7 – Future Outlook .............................................................................................. 77 Bibliography ..................................................................................................................... 78 Appendix ........................................................................................................................... 89 Appendix A – Quantum Harmonic Oscillator .............................................................. 89 Appendix B – Fabrication of DNH at Different FIB Magnifications ........................... 93 Appendix C – C-shaped Trapping Aperture ............................................................... 100 Appendix D – Magnetic Nanoparticles ....................................................................... 102 Appendix E – Vibrating Sample Magnetometry
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