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.

The work presented in this dissertation is motivated by the need for deeper understanding of phase transformations involving interfaces and defects, to advance the science of materials processing and to address the challenges in current and emerging technology. We take on several independent approaches to the problem, including theory, experiment, and simulation, which allows us to formulate and validate a coherent and comprehensive picture of phase transformation mechanisms. Our model involves recompiling the traditional components of Gibbsian thermodynamics and Classical Nucleation Theory (CNT), to conformably capture the other two classes of phase transformation phenomena, namely phase coexistence (CE) and free growth (FG), and their impact on the nonlinear kinetic phase evolution pathway. Our work is timely in filling the insufficient coverage of these mechanisms in materials science literature, because they can become especially significant in small and confined material systems, which are becoming progressively more technologically relevant. A particular application that motivated our study is the analysis of microstructure evolution during fabrication of high-uniformity polycrystalline Si (poly-Si) thin films used in backplanes for advanced displays. Nanomaterials, such as transistors with <10 nm features, are also becoming more ubiquitous, and the science of their synthesis and stability can benefit from our work as well. The experimental data available so far on phase transitions involving interfaces is limited due to the difficulty of distinguishing such localized, transient, and minute quantities of different phases of matter, as well as it is ridden by complications pertaining to each individual material system, all of which obstruct the analysis of physical behavior in terms of a concise and general theoretical description. In the work presented here we aim to bridge this gap between the material processing methods and theory by performing experiments and simulations, specifically designed to avoid excessive complicating factors and facilitate a clear conceptual connection. We explain the observations in the context of a simple phenomenological picture, which we developed from the classical fundamental principles, generalizing them to capture nontrivial phase evolution behaviors. Specifically, we perform (1) a designed laser irradiation experiment, (2) thermodynamic and kinetic analyses, (3) and molecular dynamics (MD) simulation, to capture the interface-involving melting and solidification mechanisms, and quantify their impact on phase initiation and evolution. In materials processing, only nucleation and growth is typically considered as the governing mechanism of phase initiation and evolution. According to our broader analysis, which is based on the classical principles of Gibbsian thermodynamics, we additionally identify and describe phase coexistence (CE) and free growth (FG) as equally relevant, and possibly dominant, modes of phase transformation behavior encountered in real material systems. These mechanisms are distinct from nucleation, which requires sub-critical clusters to overcome a substantial thermodynamic barrier. CE represents a state where finite quantities of a new phase can spontaneously appear and exist in stable or metastable equilibrium within the parent phase matrix, as encountered for instance in the case of curvature-induced premelting. In contrast, FG is characterized by a critical temperature condition to eliminate the energy barrier for phase transformation, and can be mathematically classified as neither nucleation nor CE. By focusing on CE and FG in this dissertation, we thus capture two out of three mathematically and thermodynamically identifiable initiation modes of phase transformation in condensed systems. To study how CE and FG can be manifested in systems of our interest, we employ a thermodynamic analysis of phase initiation and evolution that has been recently developed and refined in our group. There, we first recognize the significance of the Gibbs-Thomson Variation (GTV), which determines the thermodynamic driving force per area at a point on the inter-phase interface, based on local interface curvature and temperature. GTV applies everywhere on the inter-phase boundary and identifies the thermodynamically favored interface evolution pathway. When the interface is under morphological equilibrium, as implicitly assumed in Classical Nucleation Theory (CNT) descriptions, GTV can be translated into a global Gibbs-Thomson Function (GTF), which enables us to readily capture the thermodynamic landscape of phase transformation in complex confined systems by simply tracking the morphological-equilibrium curvature evolution function κ^ME (V) of the interface. When we approach the problem using different methods, we obtain results consistent with our theoretical description, and gain further insight into CE and FG phenomena in systems of our interest. Our experiment involving partial melting of planarized poly-Si thin films indicates that the influence of CE and FG on the melting behavior cannot be dismissed. Applying our thermodynamic analysis to a cuboid grain model, which by design is close to our experimental system, we confirm that CE and FG can indeed be expected or even dominant over a range of realistic material configurations. We pay particular attention to the scenarios where the evolving liquid phase cluster encounters abrupt changes of morphological or chemical boundary conditions, such as connecting with new catalyzing interfaces or other clusters. As a result of such a touch event, sudden and discontinuous change of the solid-liquid interface shape can take place, which we call a transmorphic transition, potentially having a critical impact on the subsequent phase transformation pathway of the entire system. We further employ discrete cluster kinetics simulation to illustrate a striking example of FG as a phase initiation and evolution mechanism, in which transmorphic transitions are enabled purely by thermal fluctuations, in absence of a thermodynamic driving force. As a completely independent, and therefore meaningful, approach, we also perform molecular dynamics (MD) simulations. This method a priori assumes nothing about the solid-liquid interface curvature, and yet the emergent behavior from thermal fluctuations of individual atoms shows a behavior qualitatively remarkably consistent with our theoretical picture under CE and FG conditions. In the previous treatments in literature nucleation, CE, and FG have not been as systematically defined and categorized as the only three mechanisms of phase initiation and evolution in condensed and confined systems, and the role of thermal fluctuations in CE and FG has not been studied to the degree presented here. Our work thus has broad implications for the science of phase transformations, as well as applications of contemporary technological relevance, such as melt-mediated synthesis and processing of polycrystalline thin films and nanomaterials.