Polymers, by virtue of their chemical composition and molecular architecture, exhibit a diverse range of microstructural features and properties. As thin films, due primarily to effects associated with confinement and interfacial interactions, their properties may be film-thickness dependent. The significance of their thicknessdependent behavior is underscored by the fact that polymer films are of technological interest in areas that include, sensors, catalysts and organic electronics. One challenge associated with the use of thin film polymers is to understand the role of confinement and interfacial interactions on thermally induced transitions, such as vitrification and various morphological transitions. To this end, the work presented in this dissertation focuses on the behavior of thermally induced transitions in two thin film polymer-based systems: (1) an A-b-B diblock copolymer which can undergo a disorder-to-order transitions (ODT), wherein the ordered state exhibits varying geometrical symmetries, depending on the relative volume fractions of the A and B components; (2) an amorphous polymer filled with particles of nanoscale dimensions. The first of three problems examined is the influence of supercritical carbon dioxide (scCO₂) on the order-disorder transition of thin film symmetric A-b-B diblock copolymer systems. We show that the transition (xN)ODT, where x is the energetic A-B Flory-Huggins interaction parameter and N is the total degree of polymerization of the copolymer, of the thin film decreased ~ 20% compared to the bulk; the decrease was more significant in scCO₂ environments. The decrease of (xN)ODT in scCO₂ is contrary to observations in bulk copolymer-scCO₂ systems where the effective A-B interactions are weaker, hence the condition for the transition increases to higher (xN)ODT values. With regard to the second problem, we show for the first time experimentally that nanoparticles induced order into thin films of a symmetric A-b-B diblock copolymer at temperatures below the bulk ODT. Finally, we examine the influence of polystyrene (PS) grafted nanoparticles on the glass transition of PS films of varying molecular weight and thickness. We demonstrate that by controlling spatial distribution of nanoparticles, through driving forces of entropic origin, the glass transition temperature of the film can be changed drastically, as much as tens of degrees.

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Melting of elemental solids can be identified and appreciated as a particularly simple example of discontinuous phase transitions involving condensed phases. Motivated, on the one hand, by the need to improve the microstructural quality of laser-crystallized columnar-grained polycrystalline Si films for manufacturing advanced AMOLED displays and, on the other hand, to investigate the fundamental details associated with phase transformations transpiring in condensed systems, this thesis examines the initiation and evolution of melting in polycrystalline thin films. Distilling the essence of the classical nucleation theory and extending its description to address more general cases of phase initiation and evolution, a general thermodynamic method based on capillarity effect is developed and applied to determine the shape of solid/liquid interfaces that are in mechanical equilibrium. We first explicitly identify and build our analysis based on how the shape of solid/liquid interfaces must comply with the contact angle conditions at the junctions and also the property of constant mean curvature. Bi-crystal and tri-crystal models are presented to capture the microstructural features such as junctions and vertices of interfaces in polycrystalline thin films. At each of the potential melt initiating sites, the parameter space of contact angles is divided into domains depending on the shape of the solid/liquid interface that can be established in mechanical equilibrium. Melting initiation mechanisms are subsequently determined based on the permissible shape for each domain. This analysis is further extended to the edges and corners of embedded cubic crystals (with nonidentical contact angles at different faces). Secondly, in order to facilitate the thermodynamic analysis of the melting initiation and interface propagation, we extend our curvature-evolution-centric method to identify and develop what we consider as the central function for discontinuous phase transitions. Specifically, starting with a local governing condition, identifies and builds on two curvatures: ρ^E (𝑉) and ρ* (𝑇). ρ^E (𝑉) captures the evolution of the mean curvature of the solid/liquid interface as a function of liquid volume for the case in which the mechanical equilibrium condition is satisfied, whereas ρ* (𝑇) incorporates the temperature effect on the difference between the volumetric free energy of solid and liquid phases using the corresponding equilibrium mean curvature. We define and identify the interface driving stress function ƒ(𝑉,𝑇)=∂𝐺/∂𝑉=σ(ρ^E (𝑉)-ρ* (𝑇)) of the phase transition as being an important fundamental quantity, which can be directly derived by taking the difference of the two curvature terms. In contrast to the conventional analysis that requires integration of volumetric and interfacial free energy terms over various geometric domains to derive the total free energy as a function of volume for a given temperature, this formation completely disentangles geometry from the thermodynamic aspects of the phase transition and allows them to be treated separately. In addition to providing essentially all relevant thermodynamic information about the phase initiation and evolution, the above method readily permits the use of powerful general-purpose numerical tools to calculate the potentially complex geometry of the solid/liquid and other interfaces and obtain ρ^E (𝑉) directly as the output. Plotting the ρ^E (𝑉) function together with the temperature-dependent iso-curvature line, ρ* (𝑇), unveils the critical thermodynamic information regarding the melting transition at the temperature, such as whether equilibrium points exist, the number of equilibrium points, their stability, and their corresponding volumes. The change of free energy as a function of liquid volume can be derived through integration of the interface driving stress function. The velocity of the solid/liquid interface is simply proportional to the interface driving stress function. The application of this method is demonstrated in both shape-preserving (which we term as isomorphic) and shape-changing (which we term as non-isomorphic) examples. The analysis and findings presented in this thesis are relevant and useful for understanding discontinuous phase transitions, in general, and can be particularly so for small, confined, and embedded systems that are increasingly being utilized in modern technologies.

by Yeung Mei Ki. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (leaves 122-127). / Text in English; abstracts in English and Chinese. / by Yeung Mei Ki. / Abstract --- p.i / 論文摘要 --- p.iii / Acknowledgements --- p.iv / Table of Contents --- p.v / List of Figures --- p.viii / List of Tables --- p.xi / Abbreviations --- p.xii / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Polymer light emitting devides --- p.1 / Chapter 1.1.1 --- Development history of PLEDs --- p.3 / Chapter 1.1.2 --- Basic structure of the PLEDs --- p.4 / Chapter 1.1.3 --- Operation principle of the PLEDs --- p.7 / Chapter 1.1.4 --- Electroluminescent (EL) polymers --- p.9 / Chapter 1.2 --- Research motivation and aim of study --- p.11 / Chapter 1.3 --- Thesis outline --- p.16 / Chapter Chapter 2 --- Instrumentation / Chapter 2.1 --- Thermal analysis --- p.18 / Chapter 2.1.1 --- Thermogravimetry (TG) --- p.19 / Chapter 2.1.2 --- Differential scanning calorimetry (DSC) --- p.22 / Chapter 2.2 --- Spectroscopic analysis --- p.27 / Chapter 2.2.1 --- Fourier transform infrared spectroscopy (FTIR) --- p.27 / Chapter 2.2.2 --- X-ray photoelectron spectroscopy (XPS) --- p.32 / Chapter 2.2.3 --- Photoluminescence spectroscopy (PL) --- p.36 / Chapter Chapter 3 --- Experimental metods to charaterize the elimination of / Chapter 3.1 --- Introduction --- p.41 / Chapter 3.2 --- Synthesis of the PPV precursor polymer --- p.43 / Chapter 3.3 --- Average molecular weight of the PPV precursor --- p.46 / Chapter 3.4 --- Thermal elimination of the precursor polymer --- p.48 / Chapter 3.5 --- Thermal stability of the PPV precursor polymer --- p.50 / Chapter 3.5.1 --- Sample preparation --- p.50 / Chapter 3.5.2 --- Experimental --- p.51 / Chapter 3.5.3 --- Results and discussion --- p.52 / Chapter 3.6 --- Structural changes of the precursor polymer during elimination --- p.57 / Chapter 3.6.1 --- Sample preparation --- p.57 / Chapter 3.6.2 --- Experimental --- p.58 / Chapter 3.6.3 --- Results and discussion --- p.58 / Chapter 3.7 --- Chemical composition of the precursor polymer upon elimination --- p.67 / Chapter 3.7.1 --- Sample preparation --- p.67 / Chapter 3.7.2 --- Experimental --- p.67 / Chapter 3.7.3 --- Results and discussion --- p.68 / Chapter 3.8 --- Effect of the conjugation length of the polymer on photoluminescence --- p.74 / Chapter 3.8.1 --- Sample preparation --- p.76 / Chapter 3.8.2 --- Experimental --- p.78 / Chapter 3.8.3 --- Results and discussion --- p.79 / Chapter 3.9 --- Conclusions --- p.89 / Chapter Chapter 4 --- Experimental methods to characterize the water absorption by PEDOT:PSS / Chapter 4.1 --- Introduction --- p.90 / Chapter 4.2 --- Determination of the water content of PEDOT:PSS at different relative humidity using TG --- p.93 / Chapter 4.2.1 --- Experimental --- p.94 / Chapter 4.2.2 --- Results and discussion --- p.96 / Chapter 4.3 --- Determination of bounded water content of PEDOT:PSS at different RH by DSC --- p.98 / Chapter 4.3.1 --- Experimental --- p.98 / Chapter 4.3.2 --- Results and discussion --- p.100 / Chapter 4.4 --- Determination of bounded water content of PEDOT:PSS at different RH by FTIR --- p.108 / Chapter 4.4.1 --- Experimental --- p.109 / Chapter 4.4.2 --- Results and discussion --- p.112 / Chapter 4.5 --- Conclusions --- p.118 / Chapter Chapter 5 --- Conclusions --- p.120 / References --- p.122

Lau Wing Fai. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (leaves 101-105). / Abstracts in English and Chinese. / Abstract --- p.i / Abstract (Chinese version) --- p.iii / Acknowledgement --- p.iv / Content --- p.v / List of figure caption --- p.vii / List of table caption --- p.xi / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Nomenclature --- p.1 / Chapter 1.2 --- Comparison of diamond and DLC --- p.2 / Chapter 1.3 --- Comparison of the amorphous hydrogenated and hydrogen free amorphous carbon --- p.4 / Chapter 1.4 --- Application of DLC --- p.7 / Chapter 1.5 --- ta-C growth mechanism --- p.9 / Chapter 1.6 --- Recent activities on ta-C films --- p.11 / Chapter 1.7 --- Goal of this project and organization of this thesis --- p.11 / Chapter Chapter 2 --- Deposition of ta-C films / Chapter 2.1 --- Ta-C film deposition systems --- p.12 / Chapter 2.1.1 --- Direct ion beam deposition --- p.13 / Chapter 2.1.2 --- Laser ablation --- p.14 / Chapter 2.1.3 --- Mass selected ion beam deposition (MSIBD) --- p.15 / Chapter 2.1.4 --- Arc discharge and filtered arc discharge (FAD) methods --- p.16 / Chapter 2.2 --- The pulsed filtered vacuum arc deposition system --- p.18 / Chapter 2.2.1 --- Working principle --- p.18 / Chapter 2.2.2 --- Film thickness control --- p.20 / Chapter 2.3 --- System modification --- p.22 / Chapter 2.3.1 --- Cathode erosion improvement --- p.22 / Chapter 2.3.2 --- Enhancement of stabilization of the cathodic arc --- p.23 / Chapter 2.4 --- Sample preparation --- p.24 / Chapter 2.4.1 --- Film deposition --- p.24 / Chapter 2.4.2 --- Thermal treatments --- p.24 / Chapter Chapter 3 --- Characterization methods / Chapter 3.1 --- Raman spectroscopy --- p.25 / Chapter 3.2 --- IR Photoelasticity (PE) --- p.27 / Chapter 3.2.1 --- Basic principle --- p.27 / Chapter 3.2.2 --- Senarmont method --- p.30 / Chapter 3.3 --- Ellipsometry --- p.33 / Chapter 3.3.1 --- Principle of ellipsometry --- p.33 / Chapter 3.3.2 --- Mathematical representation --- p.37 / Chapter 3.3.2a --- Bulk layer --- p.37 / Chapter 3.3.2b --- Single layer structure --- p.38 / Chapter 3.3.3 --- Spetroscopioc rotating analyzer ellipsometer --- p.39 / Chapter 3.3.4 --- Analysis method --- p.42 / Chapter 3.3.5 --- Forouhi and Bloomer (F.B.) model --- p.43 / Chapter 3.4 --- Tribology --- p.44 / Chapter 3.4.1 --- The definition of friction --- p.44 / Chapter 3.4.2 --- Tribometer --- p.46 / Chapter Chapter 4 --- Results / Chapter 4.1 --- As-deposited samples --- p.47 / Chapter 4.1.1 --- Sp3 fraction --- p.47 / Chapter 4.1.2 --- Stress --- p.52 / Chapter 4.1.3 --- Optical properties --- p.57 / Chapter 4.1.3.1 --- Optical model for ta-C film --- p.57 / Chapter 4.1.3.2 --- Figure of merit --- p.59 / Chapter 4.1.3.3 --- Result and discussion --- p.59 / Chapter 4.1.4 --- Mechanical properties --- p.70 / Chapter 4.1.4.1 --- Hardness --- p.70 / Chapter 4.1.4.2 --- Friction --- p.76 / Chapter 4.2 --- Annealed samples --- p.81 / Chapter 4.2.1 --- Thermal stability of the ta-C film --- p.81 / Chapter 4.2.2 --- Stress relaxation --- p.85 / Chapter 4.2.3 --- Stress and G peak shift --- p.92 / Chapter Chapter 5 --- Future work / Chapter 5.1 --- Film roughness and thickness profile improvement --- p.95 / Chapter 5.2 --- Pulsed substrate bias --- p.97 / Chapter 5.3 --- Field emission and doping possibility --- p.97 / Chapter Chapter 6 --- Conclusion --- p.98 / Reference --- p.101 / Conference / publications --- p.105

Melting and solidification constitute the fundamental pathways through which a thin-film material is processed in many beam-induced crystallization methods. In this thesis, we investigate and leverage a specific beam-induced, melt-mediated crystallization approach, referred to as Mixed-Phase Solidification (MPS), to examine and scrutinize how a polycrystalline Si film undergoes the process of melting and solidification. On the one hand, we develop a more general understanding as to how such transformations can transpire in polycrystalline films. On the other hand, by investigating how the microstructure evolution is affected by the thermodynamic properties of the system, we experimentally reveal, by examining the solidified microstructure, fundamental information about such properties (i.e., the anisotropy in interfacial free energy). Specifically, the thesis consists of two primary parts: (1) conducting a thorough and extensive investigation of the MPS process itself, which includes a detailed characterization and analysis of the microstructure evolution of the film as it undergoes MPS cycles, along with additional development and refinement of a previously proposed thermodynamic model to describe the MPS melting-and-solidification process; and (2) performing MPS-based experiments that were systematically designed to reveal more information on the anisotropic nature of Si-SiO₂ interfacial energy (i.e., σ_{Si-SiO₂}). MPS is a recently developed radiative-beam-based crystallization technique capable of generating Si films with a combination of several sought-after microstructural characteristics. It was conceived, developed, and characterized within our laser crystallization laboratory at Columbia University. A preliminary thermodynamic model was also previously proposed to describe the overall melting and solidification behavior of a polycrystalline Si film during an MPS cycle, wherein the grain-orientation-dependent solid-liquid interface velocity is identified as being the key parameter responsible for inducing the observed microstructure evolution. The present thesis builds on the abovementioned body of work on MPS. To this end, we note that the limited scope of previous investigations motivates us to perform more thorough characterization and analysis of the experimental results. Also, we endeavor to provide more involved explanations and expressions to account for the observed microstructure evolution in terms of the proposed thermodynamic model. To accomplish these tasks forms the motivation for the first portion of this thesis. In this section we further develop the thermodynamic model by refining the expression for the solid-liquid interface velocities. In addition, we develop an expression for the grain-boundary-location-displacement distance in an MPS cycle. This is a key fundamental quantity that effectively captures the essence of the microstructure evolution resulting from MPS processing. Experimentally, we conduct a thorough investigation of the MPS process by focusing on examining the details of the microstructure evolution of {100}-surface-oriented grains. Firstly, we examine and analyze the gradual evolution in the microstructure of polycrystalline Si films being exposed to multiple MPS cycles. A Johnson-Mehl-Avrami-Kolmogorov-type (JMAK-type) analysis is proposed and developed to describe the microstructure transformation. Secondly, we investigate the behavior of grains with surface orientations close to the <100> pole. Orientation-dependent (in terms of their extent of deviation from the <100> pole) microstructure evolution is revealed. This observation indicates that the microstructure of the film continues to evolve to form an even tighter distribution of grains around the <100> pole as the MPS process proceeds. During MPS melting-and-solidification cycles, a unique near-equilibrium environment is created and stabilized by radiative beam heating. Therefore, the microstructure of the resulting films is expected to be explicitly and dominantly affected by various thermodynamic properties of the system. Specifically, we identify the orientation-dependent value of the Si-SiO₂ interfacial energy as a key factor. This being the case, the MPS method actually provides us with an ideal platform to experimentally study the Si-SiO₂ interfacial energy. In the second part of this thesis, we perform MPS-based experiments to systematically investigate the orientation-dependent Si-SiO₂ interfacial energy. Two complementary approaches are designed and conducted, both of which are built on examining the texture evolution of different surface orientations resulting from MPS melting-and-solidification cycles. The first approach, “Large-Area Statistical Analysis”, statistically examines the overall microstructure evolution of non-{100}-surface-oriented grains. By interpreting the changes in the surface-orientation distribution of the grains in terms of the thermodynamic model, we identify the orientation-dependent hierarchical order of Si-SiO₂ interfacial energies. The second approach, “Same-Area Local Analysis”, keeps track of the same set of grains that undergo several MPS cycles. An equivalent set of information on the Si-SiO₂ interfacial energy is extracted. Both methods reveal, in a consistent manner, an essentially identical Si-SiO₂ interfacial energy hierarchical order for a selected group of orientations. Also, the “Same-Area Local Analysis” provides some additional information that cannot otherwise be obtained (such as information about the evolution of two adjacent grains of specific orientations). Using such information and based on the grain-boundary-location-displacement distance derived using the thermodynamic model, we further deduce and evaluate the magnitude of Δσ_{Si-SiO₂} for certain orientation pairs.

A constrained thin film desorption scheme has been experimentally tested to determine the desorption rates for water from an aqueous lithium bromide mixture through a confining membrane. Variable conditions include the inlet concentration, pressure differential across the membrane, and channel height. Desorption takes place in a channel created between two parallel plates with one of the walls being both heated and porous. A hydrophobic porous membrane creates a liquid-vapor interface and allows for vapor removal from the channel. Inlet concentrations of 32 wt%, 40 wt%, and 50 wt% lithium bromide were tested at an inlet sub-atmospheric pressure of 33.5 kPa. Pressure differentials across the membrane of 6 kPa and 12 kPa were imposed along with two channel heights of 170 μm and 745 μm. All cases were run at an inlet mass flow rate of 3.2 g/min, corresponding to Reynolds numbers of approximately 2.5 to 4.5. The membrane surface area for desorption was 16.8 cm². A maximum desorption rate (vapor mass flow rate) of 0.51 g/min was achieved, for the 32 wt%, 12 kPa pressure differential, and 170 μm channel. Increasing the pressure differential across the channel allowed for higher desorption rates at a fixed wall superheat, and delayed the transition to boiling. As the inlet concentration increased the desorber's performance decreased as more energy was required to produce a fixed desorption rate. Results are also presented for the variation in the heat transfer coefficient with the wall superheat temperature. The increase in the channel height had a negative influence on the heat transfer coefficient, requiring larger superheat values to produce a fixed desorption rate. / Graduation date: 2005 / Best scan available for tables and computer code in the appendices. The original is faded.

This thesis examines melting in superheated silicon films in contact with SiO₂ under pulsed laser irradiation. An excimer-laser pulse was employed to induce heating of the film by irradiating the film through the transparent fused-quartz substrate such that most of the beam energy was deposited near the bottom Si-SiO₂ interface. Melting dynamics were probed via in situ transient reflectance measurements. The temperature profile was estimated computationally by incorporating temperature- and phase-dependent physical parameters and the time-dependent intensity profile of the incident excimer-laser beam obtained from the experiments. The results indicate that a significant degree of superheating occurred in the subsurface region of the film. Surface-initiated melting was observed in spite of the internal heating scheme, which resulted in the film being substantially hotter at and near the bottom Si-SiO₂ interface. By considering that the surface melts at the equilibrium melting point, the solid-phase-only heat-flow analysis estimates that the bottom Si-SiO₂ interface can be superheated by at least 220K during excimer-laser irradiation. It was found that at higher laser fluences (i.e., at higher temperatures), melting can be triggered internally. At heating rates of 10¹⁰ K/s, melting was observed to initiate at or near the (100)-oriented Si-SiO₂ interface at temperatures estimated to be over 300K above the equilibrium melting point. Based on theoretical considerations, it was deduced that melting in the superheated solid initiated via a nucleation and growth process. Nucleation rates were estimated from the experimental data using Johnson-Mehl-Avrami-Kolmogorov (JMAK) analysis. Interpretation of the results using classical nucleation theory suggests that nucleation of the liquid phase occurred via the heterogeneous mechanism along the Si-SiO₂ interface.