The self-assembly of magnesium aluminate spinel as a result of dewetting an overlaid thin film of (chiefly) gold was investigated. Thin films of gold were deposited on single-crystalline spinel substrates and were heat-treated to dewet gold film which led to self-assembly of intricate structures consisting of faceted spherical particles atop of frustums. The current work was conducted in continuation of previous studies which reported formation of such intricate structures. The most recent studies had evidently overruled a pure gold self-assembly scenario as was pointed out in preliminary investigations. It was in fact proven that these structures consist of three distinct parts: (i) a single or polycrystalline gold faceted sphere, (ii) quasi-phase interfacial bilayer, and (iii) a crystalline MgAl2O4 necking structure spontaneously risen from spinel substrate. In the current work, samples were produced through different film deposition methods of sputter, thermal evaporation, and e-beam evaporation coating which underwent thermal annealing to induce dewetting of gold film and subsequent self-assembly of intricate structures. Several characterization methods such as electron microscopy, X-ray energy dispersive spectroscopy, electron energy loss spectroscopy, and atom probe tomography were utilized to survey the different features of the intricate structures with focus on chemical analysis of the gold-spinel interface. The results rejected the previous findings about formation of interface complexion at the boundary of gold-spinel. It was found out that gold-spinel interface is in fact an ordinary metal-oxide boundary with sharp atomic distinction and no inter-diffusion or formation of interfacial complexion. It was further discovered that dewetting pure gold thin films does not result in formation of spinel self-assembly and existence of elemental impurities of copper (Cu) in the initial film is vital in development of such structures. Finally, it was concluded that chemical composition of metallic overlayer and the heat treatment parameters most fundamentally influence formation and physical characteristics of those self-assembled structures. / Thesis / Master of Applied Science (MASc)

<p>This thesis describes the experimental results of liquid polymer droplets levelling on thin films of identical polymer liquid. Through varying the thickness of the underlying polymer film relative to the size of the droplet height, we have observed a crossover in the dynamics between droplets spreading on very thin films to droplets levelling on films thicker than the droplet itself. In the thin film regime, the underlying film behaves as a pre-existing precursor film and the droplet spreads according to the well-known Tanner's law where the droplet height, d₀, decreases in time as d₀ ~ t^-1/5. In the opposite regime, when the film thickness is much greater than the initial droplet height, the droplet levels with a much stronger time dependence compared to Tanner's law spreading, d₀ ~ t^-1/2. Not only have we observed the two extreme cases, we have also experimentally observed levelling behaviour of intermediate systems, where the droplet height and film height are on the same order. We have captured experimentally the crossover behaviour of droplets spreading on thin films to droplets levelling on thick films. In addition, we have developed a theoretical model that accurately captures the physics of this crossover using the lubrication approximation for thin film flows. The relevant background information will be presented as well as a detailed description of the sample preparation techniques required to fabricate spherical caps atop thin films of identical material.</p> / Master of Science (MSc)

Ce travail de thèse est consacré à l’étude expérimentale des mécanismes de démouillage de films solides d’épaisseur nanométrique conduisant à la transformation d’un film mince en une assemblée d’îlots tridimensionnels. L’utilisation de la microscopie à électrons lents (LEEM) nous a permis d’étudier la morphologie et la cinétique in situ et en temps réel du démouillage de films de Si/SiO2 (SOI) et de Ge/SiO2 (GOI) obtenus par collage moléculaire (procédé Smart Cut™). Ces mesures expérimentales ont été complétées par des analyses par diffusion centrale des rayons X en incidence rasante (GISAXS) et des observations ex situ par microscopie à force atomique (AFM). Les mécanismes de démouillage de SOI et GOI sont thermodynamiquement pilotés par la capillarité et cinétiquement contrôlés par la diffusion de surface. L’étude complémentaire du démouillage à partir de fronts cristallographiquement orientés obtenus par lithographie nous a permis d’analyser le rôle central du facettage, de l’anisotropie cristalline et des processus de formation du bourrelet de démouillage. En particulier, le rôle de la nucléation 2D sur la cinétique d’épaississement (couche par couche) du bourrelet a pu être mis en évidence. Les résultats expérimentaux ont pu être confrontés à des modèles analytiques et des simulations de type Monte Carlo cinétique. Nous en avons déduit les valeurs des paramètres physiques pertinents et avons attribué les différences de morphologies entre SOI et GOI à la présence de facettes spécifiques. / This work is devoted to the experimental study of the dewetting mechanisms of ultrathin solid films by which a metastable film transforms into an assembly of tridimensional crystallites. Using low energy Electron Microscopy (LEEM) we analyse, in situ and in real time, the morphology and the kinetics of the dewetting of Si/SiO2 (SOI) and Ge/SiO2 (GOI) systems obtained by molecular bonding (Smart Cut™ process). Further information has been obtained by Grazing Incidence Small Angle X–ray Scattering (GISAXS) and Atomic Force Microscopy (AFM) measurements. We show that the dewetting is driven by surface free energy minimization and mediated by surface diffusion. A complementary study of artificial well-oriented dewetting fronts obtained by lithography enables us to analyze the important role played by facets, the crystal anisotropy and the rim thickening mechanism. We show that the rim thickening proceeds in a layer-by-layer mode and is limited by 2D nucleation. Thanks to analytical models and Kinetics Monte Carlo simulations, numerical values of the pertinent physical parameters involved in the dewetting process are obtained and the morphological differences between SOI and GOI are attributed to the presence of specific facets.

In der vorliegenden Arbeit wird das Entstehen von Singularitäten an Oberflächen von dünnen Flüssigkeitsfilmen studiert. Unter einer Singularität versteht man hier das plötzliche Aufreißen einer Flüssigkeitsoberfläche an einer Stelle. Nach einer Diskussion physikalischer Phänomene, wird ein 2D Modell zur Beschreibung von Flüssigkeitsfilmen hergeleitet. Dieses Modell beinhaltet u.a. Oberflächenspannung, van der Waals''sche Kräfte und eine Navier-slip Randbedingung (Schlupf-Randbedingung) zwischen Substrat und Flüssigkeit, d.h. die Flüssigkeite haftet nicht an der Grenzfläche zum Substrat. Dieses Phänomen wird vor allen Dingen im Nano- und Mikrometerbereich beobachtet. Dieses Modell wird vereinfacht und man erhält die sogenannte "strong-slip" Gleichung. In dieser Dissertation werden verschiedene Ansätze verfolgt, um die Singularität der Flüssigkeitsoberfläche zu beschreiben. Der Entstehungsprozess der Singularität wird durch die lineare Stabilitätsuntersuchung beschrieben. Da die Linearisierung schnell ihre Gültigkeit verliert, wird das nichtlineare Verhalten der Singularität mit einem numerischen Verfahren beschrieben. Das dazu hier konstruierte Finite-Differenzen-Schema besitzt eine hohe räumliche und zeitliche Genauigkeit. Dadurch können verschiedene Regime, in denen die Singularität eine selbstähnliche Dynamik besitzt, untersucht und beschrieben werden. Im zweiten Teil der Arbeit werden die Gleichungen weiter vereinfacht. Dadurch können qualitative Eigenschaften der Singularitätsentstehung bewiesen werden. Weiterhin kann so eine Verbindung zu Modellen der Ostwald-Reifung hergestellt werden und man gelangt zu ähnlichen mathematischen Aussagen wie für selbstähnliche Vergröberungsprozesse. Insbesondere wird in der Arbeit gezeigt, dass die Singularität nach endlicher Zeit auftritt. Für das vereinfachte Problem werden hinreichende und notwendige Bedingungen für selbstähnliches Verhalten angegeben. / In this thesis we study the formation of surface singularites of thin liquid films, i.e., rupture of thin liquid films. First, important physical phenomena are discussed and a two-dimensional model for thin-film rupture is derived . That model contains surface tension, van der Waals forces between a liquid and a underlying substrate, and a Navier-slip condition. Using the thin-film hypothesis, this model is simplified and one obtains the so-called strong-slip equation. The phenomenon slip, where the velocity of the liquid is non-zero at a fluid-solid interface, is particularly important at microscopic length scales. In this text we study interfacial singularities with various approaches. The creation of a singularity is described by a linear stability analysis. The non-linear behavior is investigated by a numerical analysis. A finite-difference scheme is used to study the non-linear self-similar dynamics of the singularity. In the second part of this thesis the equations are further simplified. This allows to study qualitative properties of the singularity formation. Furthermore, we can establish a correspondence to models for Ostwald rippending and obtain similar mathematical statements as they are known for self-similar coarsening processes. In particular it is shown that rupture happens after a finite time. In addition, necessary and sufficient condition for self-similar rupture are proven.

Combinatorial techniques have changed the paradigm of materials research by allowing a faster data acquisition in complex problems with multidimensional parameter space. The focus of this thesis is to demonstrate biomaterials design and characterization via preparation of two dimensional combinatorial libraries with chemically-distinct structured patterns. These are prepared from blends of biodegradable polymers using thickness and temperature gradient techniques. The desired pattern in the library is chemically-distinct cell adhesive versus non-adhesive micro domains that improve library performance compared to previous implementations that had modest chemical differences. Improving adhesive contrast should minimize the competing effects of chemistry versus physical structure. To accomplish this, a method of blending and crosslinking cell adhesive poly(季aprolactone) (PCL) with cell non-adhesive poly(ethylene glycol) (PEG) was developed. We examine the interaction between MC3T3-E1 osteoblast cells and PCL-PEG libraries of thousands of distinct chemistries, microstructures, and roughnesses. These results show that cells grown on such patterned biomaterial are sensitive to the physical distribution and phases of the PCL and PEG domains. We conclude that the cells adhered and spread on PCL regions mixed with PEG-crosslinked non-crystalline phases. Tentatively, we attribute this behavior to enhanced physical, as well as chemical, contrast between crystalline PCL and non-crystalline PEG.

Silver (Ag) is an ideal low-loss platform for plasmonic applications, but from a materials standpoint it presents challenges. Development of plasmonic devices based on Ag thin film has been hindered both by the dificulty of fabricating such film and by its fragility out of vacuum. Silver is non-wetting on semiconducting and insulating substrates, but on certain semiconductors and insulators can adopt a metastable atomically at epitaxial film morphology if it is deposited using the "two-step" growth method. This method consists of deposition at low temperature and annealing to room temperature. However, epitaxial Ag is metastable, and dewets out of vacuum. The mechanisms of dewetting in this system remain little understood. The fragility of Ag film presents a particular problem for the engineering of plasmonic devices, which are predicted to have important industrial applications if robust low-loss platforms can be developed. This dissertation presents two sets of experiments. In the first set, scanning probe techniques and low energy electron microscopy have been used to characterize Ag(111) growth and dewetting on two orientations of silicon (Si), Si(111) and Si(100). These studies reveal that multiple mechanisms contribute to Ag film dewetting. Film stability is observed to increase with thickness, and thickness to play a decisive role in determining dewetting processes. A method has been developed to cap Ag film with germanium (Ge) to stabilize it against dewetting. The second set of experiments consists of optical studies that focus on the plasmonic properties of epitaxial Ag film. Because of the problems posed until now by epitaxial Ag growth and stabilization, research and development in the area of plasmonics has been limited to devices based on rough, thermally evaporated Ag film, which is robust and simple to produce. However, plasmonic damping in such film is higher than in epitaxial film. The optical studies presented here establish that Ag film can now be stabilized sufficiently to allow optical probing and device applications out of vacuum. Furthermore, they demonstrate the superiority of epitaxial Ag film relative to thermally evaporated film as a low-loss platform for plasmonic devices spanning the visible and infrared regimes. / text

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Cette thèse présente des résultats théoriques et expérimentaux portant sur des écoulements à l'échelle nanoscopique de polymères fondus. L'étude analytique et numérique de l'écoulement d'un film de polymère, préalablement nanostructuré par nanoimpression puis recuit au dessus de sa température de transition vitreuse, a permis de dégager différentes dynamiques de nivellement selon la topographie initiale du film. Certaines ont été appliquées à l'élaboration d'éléments optiques par recuit de nanostructures complexes. Une méthode de mesure de la viscosité Newtonienne et du temps terminal de relaxation d'un polymère déposé en film mince a également pu être développée. Enfin, un travail exploratoire portant sur un procédé de nanoimpression sans épaisseur résiduelle par démouillage est présenté. L'accent a porté sur le calcul précis de la pression de disjonction dans un milieu stratifié en utilisant la théorie moderne de Lifshitz basée sur les propriétés optiques des matériaux en interaction. / This thesis presents a theoretical and experimental work on nanoscale flows of polymer melts. Different leveling dynamics emerge from the analytical and numerical study of the reflow of a polymer film that is first nanoimprinted and then annealed above its glass transition temperature, depending on the initial topography of the film. These concepts were applied to the manufacturing of optical devices from the reflow of complex nanostructures. A method to measure the Newtonian viscosity and the terminal relaxation time of a thin polymer film was also developed. Finally, an exploratory work on a residual-layer-free nanoimprint process based on dewetting is presented. Emphasis was put on the accurate computation of the disjoining pressure in stratified media with the modern Lifshitz theory based on the optical properties of the interacting materials.

Les propriétés des mousses liquides sont majoritairement gouvernées par les caractéristiques de leurs interfaces liquide/gaz. Nous illustrons ces effets à l'échelle locale par différents exemples : – Les réarrangements topologiques, pendant lesquels les bulles changent de voisines, sont les événements élémentaires à l'origine de propriétés rhéologiques et de stabilité des mousses. En réalisant des expériences sur une assemblée de films dans un cadre cubique, nous avons étudié les mécanismes de formation du nouveau film pour différentes solutions de tensioactifs modifiant les propriétés interfaciales. – L'observation de l'éclatement d'un film de savon unique montre que cette dynamique est ralentie à cause de l'élasticité des interfaces, jusqu'à l'apparition de rides ou de fractures pour une compression critique. – Par des mesures force/déplacement, nous avons montré qu'un radeau de particules se comporte comme un granulaire 2D, qui peut se déformer en-dehors du plan de l'interface, et dans lequel la contrainte peut dépendre de la friction à la paroi. De plus, l'ajout de ponts capillaires entre les particules procure au radeau une meilleure résistance à la traction et à la compression. – En injectant de l'air dans une pâte, nous avons créé des bulles stables dans des conditions permettant l'adsorption des tensioactifs à la surface des particules pour les rendre partiellement mouillantes. En utilisant ce mécanisme dans un système cimentaire, des bulles solides sont alors fabriquées / Properties of liquid foams are mainly governed by the features of liquid/gas interfaces. We illustrate this phenomenon at the local scale through different examples : – Topological rearrangements, i.e. switching of neighboring bubbles, are the elementary process of liquid foams stability and dynamics. Experiments are performed in a cubic assembly of films, in order to investigate the mechanism of creation of the new film for different surfactants solutions and therefore different interfacial properties. – Observation of soap film bursting shows that the dynamics is slowed down because of interfacial elasticity, until wrinkles or cracks appear for a critical compression. – Through strength/displacement measurements, we show that a particle raft behaves as a 2D granular material, which can buckle, and whose stress can depend on wall friction. Moreover, the addition of liquid bridges between particles provides higher compressive and tensile strengths to the raft. – Blowing air into a paste allows creating stable bubbles, when surfactants adsorb at particles surface, modifying their wetting properties. We demonstrate that this method can lead to solid bubbles with a cementitious system