Yam Chi Tong = 懸浮顆粒之介電反應 / 任智堂. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (leaves 76-79). / Text in English; abstracts in English and Chinese. / Yam Chi Tong = xuan fu ke li zhi jie dian fan ying / Ren Zhitang. / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Spectral Representation of a Pair of Polydisperse Cylinders --- p.3 / Chapter 2.1 --- Introduction --- p.3 / Chapter 2.2 --- Multiple Image Method --- p.4 / Chapter 2.2.1 --- Polydispersity in Size --- p.6 / Chapter 2.2.2 --- Polydispersity in Permittivity --- p.7 / Chapter 2.3 --- Spectral Representation --- p.9 / Chapter 2.3.1 --- Polydisperse Size Cylinders --- p.10 / Chapter 2.3.2 --- Polydisperse Permittivity Cylinders --- p.12 / Chapter 2.4 --- Numerical Results --- p.13 / Chapter 2.4.1 --- Polydispersity in Size --- p.14 / Chapter 2.4.2 --- Polydispersity in Permittivity --- p.17 / Chapter 2.5 --- Conclusion --- p.22 / Chapter 3 --- Dielectric Behaviors of Polydisperse Colloidal Suspensions --- p.24 / Chapter 3.1 --- Introduction --- p.24 / Chapter 3.2 --- Dielectric Dispersion Spectral Representation --- p.26 / Chapter 3.3 --- Polydisperse Colloidal Suspensions --- p.28 / Chapter 3.4 --- Numerical Results --- p.30 / Chapter 3.4.1 --- Monodisperse Limit --- p.31 / Chapter 3.4.2 --- Influence of the Medium Conductivities --- p.32 / Chapter 3.4.3 --- Effect of Conductivity Contrasts --- p.34 / Chapter 3.4.4 --- Effect of Varying the Volume Fractions --- p.37 / Chapter 3.5 --- Conclusion --- p.41 / Chapter 4 --- Dielectric Behaviors of Shelled Cell Suspensions --- p.43 / Chapter 4.1 --- Introduction --- p.43 / Chapter 4.2 --- Shelled Spherical Particle Model --- p.46 / Chapter 4.2.1 --- Intrinsic Dispersions --- p.47 / Chapter 4.3 --- Numerical Results --- p.49 / Chapter 4.3.1 --- One Type of Shelled Cells --- p.51 / Chapter 4.3.2 --- Mixture of Two Types of Shelled Cells --- p.60 / Chapter 4.4 --- Conclusion --- p.62 / Chapter 5 --- Dielectric Behaviors of Compositionally Graded Films --- p.64 / Chapter 5.1 --- Introduction --- p.64 / Chapter 5.2 --- Discrete Layer Model --- p.65 / Chapter 5.2.1 --- Linear Profiles --- p.67 / Chapter 5.2.2 --- Gaussian Profiles --- p.67 / Chapter 5.3 --- Continuously Graded Model --- p.68 / Chapter 5.3.1 --- Linear Profiles --- p.68 / Chapter 5.3.2 --- Gaussian Profiles --- p.69 / Chapter 5.4 --- Conclusion --- p.72 / Chapter 6 --- Summary --- p.74 / Bibliography --- p.76 / Chapter A --- The Maxwell-Garnett Approximation --- p.80 / Chapter B --- The Bergman-Milton Spectral Representation --- p.82

Liquid dispersions of colloidal particles play a big role in nature and as industrial products or intermediates. Their material properties are largely determined by the liquid-mediated particle-particle interaction. In water-based systems, electric charge is ubiquitous and electrostatic particle interaction often is the primary factor in stabilizing dispersions against decomposition by aggregation and sedimentation. Very nonpolar liquids, by contrast, are usually considered free of charge, because their low dielectric constant raises the electrostatic cost of separating opposite charges above the available thermal energy. Defying this conventional wisdom, nonpolar solutions of certain ionic surfactants do support mobile ions and surface charges. Even some nonionic surfactants have recently been found to raise the conductivity of nonpolar oils and promote surface charging of suspended particles, but this counter-intuitive behavior is not yet widely acknowledged, nor is the mechanism of charging understood. The present study provides the first characterization of the electrostatic particle interaction caused by nonionizable surfactants in nonpolar oils. The methods used in this study are video microscopy experiments where particle positions of equilibrium ensembles are obtained and translated into particle interactions. Experimentally, equilibrium particle positions are monitored by digital video microscopy, and subjected to liquid structure analysis in order to find the energy of interaction between two particles. The observed interaction energy profiles agree well with a screened-Coulomb potential, thus confirming the presence of both surface charge and mobile ions in solution. In contrast to recently reported electrostatic particle interactions induced by ionic surfactants in nonpolar solution, the present study finds evidence of charge screening both above and below the surfactant's critical micelle concentration, CMC. Fitted Debye screening lengths are much larger than in aqueous systems, but similar to the Debye length in nonpolar oils reported for micellar solutions of ionic surfactants cite{hsu_charge_2005}. Radial distribution functions obtained from experiments are compared to Monte-Carlo simulations with input potentials obtained from a fit to the interaction measurement. The measured electrostatic forces and fitted surface potentials are fairly substantial and easily capable of stabilizing colloidal dispersions. Although few in number, surface charges formed on polymer particle surfaces submerged in nonpolar solutions of nonionizable surfactants create surface potentials comparable to those in aqueous systems.

Indiana University-Purdue University Indianapolis (IUPUI) / Fabrication and analysis of Copper Indium Gallium di-Selenide (CIGS) nanoparticles-based thin film solar cells are presented and discussed. This work explores non-traditional fabrication processes, such as spray-coating for the low-cost and highly-scalable production of CIGS-based solar cells. CIGS nanoparticles were synthesized and analyzed, thin CIGS films were spray-deposited using nanoparticle inks, and resulting films were used in low-cost fabrication of a set of CIGS solar cell devices. This synthesis method utilizes a chemical colloidal process resulting in the formation of nanoparticles with tunable band gap and size. Based on theoretical and experimental studies, 100 nm nanoparticles with an associated band gap of 1.33 eV were selected to achieve the desired film characteristics and device performances. Scanning electron microcopy (SEM) and size measurement instruments (Zetasizer) were used to study the size and shape of the nanoparticles. Electron dispersive spectroscopy (EDS) results confirmed the presence of the four elements, Copper (Cu), Indium (In), Gallium (Ga), and Selenium (Se) in the synthesized nanoparticles, while X-ray diffraction (XRD) results confirmed the tetragonal chalcopyrite crystal structure. The ultraviolet-visible-near infra-red (UV-Vis-NIR) spectrophotometry results of the nanoparticles depicted light absorbance characteristics with good overlap against the solar irradiance spectrum. The depositions of the nanoparticles were performed using spray-coating techniques. Nanoparticle ink dispersed in ethanol was sprayed using a simple airbrush tool. The thicknesses of the deposited films were controlled through variations in the deposition steps, substrate to spray-nozzle distance, size of the nozzle, and air pressure. Surface features and topology of the spray-deposited films were analyzed using atomic force microscopy (AFM). The deposited films were observed to be relatively uniform with a minimum thickness of 400 nm. Post-annealing of the films at various temperatures was studied for the photoelectric performance of the deposited films. Current density and voltage (J/V) characteristics were measured under light illumination after annealing at different temperatures. It was observed that the highest photoelectric effect resulted in annealing temperatures of 150-250 degree centigrade under air atmosphere. The developed CIGS films were implemented in solar cell devices that included Cadmium Sulfide (CdS) and Zinc Oxide (ZnO) layers. The CdS film served as the n-type layer to form a pn junction with the p-type CIGS layer. In a typical device, a 300 nm CdS layer was deposited through chemical bath deposition on a 1 $mu$m thick CIGS film. A thin layer of intrinsic ZnO was spray coated on the CdS film to prevent shorting with the top conductor layer, 1.5 μm spray-deposited aluminum doped ZnO layer. A set of fabricated devices were tested using a Keithley semiconductor characterization instrument and micromanipulator probe station. The highest measured device efficiency was 1.49%. The considered solar cell devices were simulated in ADEPT 2.0 solar cell simulator based on the given fabrication and experimental parameters. The simulation module developed was successfully calibrated with the experimental results. This module can be used for future development of the given work.