FIELD-BASED MANIPULATION OF MICRO- AND NANO- PARTICLES IN FLUIDS: TUNABLE MACROSCOPIC MATERIAL PROPERTIES AND CHARACTERIZATION OF INDIVIDUAL NANOPARTICLES by WUHAN YUAN A dissertation submitted to the School of Graduate Studies Rutgers, The State University of New Jersey In partial fulfillment of the requirements For the degree of Doctor of Philosophy Graduate Program in Mechanical and Aerospace Engineering Written under the direction of Jerry W. Shan and Liping Liu And approved by New Brunswick, New Jersey May, 2019 ABSTRACT OF THE DISSERTATION Field-Based Manipulation of Micro- and Nano- Particles in Fluids: Tunable Macroscopic Material Properties and Characterization of Individual Nanoparticles By WUHAN YUAN Dissertation Directors: Jerry W. Shan and Liping Liu Field-based particle manipulation has provided us unique opportunities to remotely manipulate fluid-suspended micro- and nano- particles in a highly efficient and control- lable manner. Specifically, an external electric/magnetic field can be used to control (1) the macroscopic physical properties of the materials and (2) the microscopic movement of micro- or nano- particles in a suspending fluid, both of which have given rise to a wide variety of novel applications. In terms of controlling the macroscopic material properties, we have investigated a novel type of smart material with anisotropic and tunable acoustic properties. To elaborate, the microstructure (e.g., particle orientation and chaining) of suspensions of non-spherical ferromagnetic particles can be controlled by an external magnetic field, making it possible to change the acoustic properties of the suspension. Here, we experi- mentally demonstrate that dilute suspensions of subwavelength-sized oblate-spheroidal nickel particles exhibit up to a 35% change in attenuation coefficient at MHz frequencies upon changing the direction of an external magnetic field, for particle volume fractions ii of only 0:5%. Comparison is made to suspensions of spherical particles, in which the attenuation is smaller and nearly isotropic. Optical transmission measurements and analysis of the characteristic timescales of particle alignment and chaining are also per- formed to investigate the reasons for this acoustic anisotropy. The alignment of the oblate-spheroidal particles is found to be the dominant mechanism for the anisotrop- ic and tunable acoustic attenuation of these suspensions. A mathematical model has also been developed to describe the acoustic properties of the above mentioned mi- crostructured suspensions using effective medium theory as well as Eshelby's analytical solutions for ellipsoidal inclusions. For individual micro- or nano- particles, we take advantage of the strong depen- dence between AC-field induced particle rotation and particle properties to effectively characterize individual particles. In detail, we utilize the contactless, high-throughput electro-orientation spectroscopy (EOS) technique to measure the electrical conductivity of Si nanowires with atomic-layer-deposition- (ALD-) induced Al2O3 layers in a statis- tically meaningful manner. Initial surface treatments with HF and chemical-induced oxide (SC1) before ALD passivation were both investigated. We show that nanowire properties and variability are dominated by the surfaces, given that the ALD-induced Al2O3 layer changes the electrical conductivity by 5-orders-of-magnitude while reduc- ing the variation in conductivity by half. These changes in the nanowire conductivity are believed to be due to a combination of chemical passivation and the field-effect passivation introduced by the ALD treatment. Finally, we extend the EOS technique to enable characterization of nanowires with more complex structures. Specifically, we show that the EOS technique can determine the conductivity and dimensions of two distinct segments in individual Si nanowires with axially encoded dopant profiles. Our analysis combines experimental measure- ments and computational simulations to determine the electrical conductivity of the nominally undoped segment of two-segment Si nanowires, as well as the ratio of the segment lengths. We demonstrate the efficacy of our approach by comparing results gen- erated by EOS with conventional four-point-probe measurements. Our work provides iii new insights into the control and variability of semiconductor nanowires for electron- ic applications and is a critical first step toward the high-throughput interrogation of complete nanowire-based devices. iv Preface Much of the content in Chapters 2, 4 and 5 is taken verbatim from published or soon- to-be-submitted papers with collaborators, and other chapters contain wording similar or identical to that found in these papers. Permissions have been obtained from the collaborators to include the content in this thesis. References [1] W. Yuan, L. Liu, and J. W. Shan. Tunable acoustic attenuation in dilute suspensions of subwavelength, non-spherical magnetic particles. Journal of Applied Physics, 121(4):045110, 2017. [2] W. Yuan, G. Tutuncuoglu, A. T. Mohabir, L. Liu, L. C. Feldman, M. A. Filler, and J. W. Shan. Contactless electrical and structural characterization of semiconductor nanowires with axially modulated doping profiles. Small, 15(15):1805140, 2019. [3] W. Yuan, G. Tutuncuoglu, A. T. Mohabir, L. Liu, L. C. Feldman, M. A. Filler, and J. W. Shan. Contactless, high-throughput analysis on electrical conductivity of si nanowires with surface passivation. in preparation, 2019. v Acknowledgements I would like to start by expressing my sincere gratitude to my advisors, Prof. Jerry W. Shan and Prof. Liping Liu, for their valuable guidance and never-ending support. I thank Prof. Shan for offering me the opportunity to work in a multidisciplinary en- vironment and allowing me to grow as an experimental researcher. I could not have accomplished my research goals without him sharing his experience and wisdom with me. I would also like to thank Prof. Liu, as he helped me greatly with his intelligence and knowledge in shaping the theoretical end of my research. His patience and encour- agement throughout my PhD studies are invaluable. It is truly a privilege for me to have both Prof. Shan and Prof. Liu as my advisors, as they will be my role models through my life. I want to extend my gratitude to the rest of my dissertation committee members, Prof. Leonard C. Feldman and Prof. Stephen D. Tse, for their insightful comments and brilliant suggestions on my research. I am also very grateful for the assistance from Prof. Michael Filler and Dr. Gozde Tutuncuoglu at GA Tech on our collaborative project. I would like to recognize some of my previous and current colleagues, Cevat Akin, Richard J. Castellano, Semih Cetindag, Yasir Demiryurek, Gabriel Giraldo, Lixin Hu, Xin Liu, Hanxiong Wang and Kaiyan Yu, for their kind assistance and counseling in my research work. I also want to thank John Petrowski for helping me build my experimental setups. Finally, I want to express my deepest gratitude to my mother, Jun Zhou and my grandparents, Huanzhi Bao and Wenbin Zhou. I could not have done it without their unconditional love and support. I also want to thank my girlfriend, Xin Ai, for always being there for me and believing in me. vi Special thanks to my father, Naichao Yuan, who passed away during the second year of my PhD. Thank you, dad, for everything. vii Table of Contents Abstract :::::::::::::::::::::::::::::::::::::::: ii Preface ::::::::::::::::::::::::::::::::::::::::: v Acknowledgements ::::::::::::::::::::::::::::::::: vi List of Tables ::::::::::::::::::::::::::::::::::::: xi List of Figures :::::::::::::::::::::::::::::::::::: xii 1. Introduction ::::::::::::::::::::::::::::::::::: 1 1.1. Particle manipulation by electric/magnetic fields . 1 1.1.1. Electric/magnetic field responsive smart materials . 2 1.1.2. Microscopic particle manipulation and characterization using elec- tric/magnetic field . 4 1.2. Electrical characterization of semiconductor nanowires . 5 1.3. Dissertation outline . 6 2. Tunable Acoustic Attenuation in Dilute Suspensions of Non-spherical Magnetic Particles: Experiments :::::::::::::::::::::::: 10 2.1. Introduction . 10 2.2. Experiment . 12 2.3. Results and discussion . 15 2.4. Conclusions . 25 3. Acoustic Properties of Microstructured Suspensions: Theory :::: 27 3.1. Introduction . 27 3.2. Acoustic properties of a homogeneous viscoelastic medium . 29 viii 3.3. Homogenization limit of mixtures of viscoelastic materials . 32 3.4. Effective viscoelastic properties of two-phase suspensions . 36 3.4.1. Suspensions in the dilute limit . 37 3.4.2. Non-dilute suspensions . 39 3.4.3. Suspensions with random particle directions . 40 3.5. Effective acoustic properties of a two-phase medium with spheroidal in- clusions . 41 3.5.1. Influence of particle aspect ratio . 41 3.5.2. Influence of particle volume fraction . 43 3.5.3. Comparison with the experimental results . 43 3.6. Conclusions . 47 4. Contactless, High-throughput Analysis on Electrical Conductivity of Si Nanowires with Surface Passivation ::::::::::::::::::::: 48 4.1. Introduction . 48 4.2. Method . 50 4.2.1. Electro-orientation . 50 4.2.2. Electro-orientation Spectroscopy . 53 4.2.3. EOS measurements . 54 4.2.4. Nanowire processing . 54 4.3. Results and discussion . 56 4.4. Conclusions . 62 5. Contactless Electrical and Structural Characterization of Semiconduc- tor Nanowires with Axially Modulated Doping Profiles :::::::::: 65 5.1. Introduction . 65 5.2. Methods . 66 5.3. Results and discussion . 69 5.4. Conclusions . 74 ix 6. Conclusions