Depuis quelques années, nous observons un regain d'intérêt des scientifiques pour les instabilités élastiques observées lors de la déformation sous contrainte de systèmes tels que des multi-couches ou des coques rigides. Le nombre de structures complexes pouvant être générées à partir de ce phénomène initialement étudié par Leonhard Euler a cru de manière exponentielle ces dernières années. En plus de leur intérêt purement académique, ces instabilités sont génératrices de formes tridimensionnelles parfois étonnantes, elles présentent un grand potentiel d'application en tant qu'alternative aux techniques de (photo) lithographie pour la préparation de micro-structures utilisables en optique ou en microfluidique. Dans le cadre de cette thèse, nous nous sommes concentrés sur un des aspects de ces instabilités élastiques: la formation de rides de compression dans des membranes rigides déposées sur des substrats mous (élastomères). Cette étude nous a permis de mieux comprendre le contexte général des instabilités élastiques de membranes d'un point de vue essentiellement expérimental. Deux aspects ont été développés dans ce travail. D'une part, la modification de films de polydiméthylsiloxane (PDMS) par des traitements UV/Ozone et Plasma Kleaner de manière à créer une membrane rigide en surface. D'autre part, la formation de microstructures par la compression ou l'extension de ces films d'élastomères. En jouant sur le traitement en surface (UV ou Plasma) et sur la symétrie de la compression nous avons obtenu un large panel de morphologies contrastées, de la simple « tôle ondulée » micrométrique aux chevrons, structure complexe parfaitement organisée. L'influence des différents paramètres, temps d'irradiation, taux de compression, ... sur la régularité de ces microstructures a été étudiée en détails. D'une manière étonnante, les échantillons traités suffisamment longtemps présentent, en plus des rides microscopiques, une courbure globale permanente. En jouant sur la forme des zones irradiées et la nature de la compression, nous avons créé des surfaces présentant des courbures de Gauss permanente négative (selle de cheval) ou positive (calotte sphérique). Par un choix approprié de la direction de compression, il est même possible d'obtenir des structures tridimensionnelles hélicoïdales. Enfin, nous avons étudié un exemple d'application des micro-structures obtenues par instabilités élastiques, la superhydrophobie. En effet la réalisation de surfaces superhydrophobes fait intervenir non seulement la nature chimique du matériau mais également la morphologie de sa surface. En ajustant les caractéristiques de la microstructuration du PDMS, nous avons pu étudier la transition Wenzel - Cassie indiquant le passage d'une morphologie en gouttes « empalées » vers une morphologie de type « fakir » pour les topographies les plus fortes. Ce travail ouvre de nombreuses perspectives. Du point de vue des applications, de nombreuses propriétés des matériaux peuvent être modulées grâce à une structuration des surfaces à l'échelle micrométrique. D'un point de vue plus fondamental, ce travail expérimental ouvre la voie à des études théoriques dans le domaine de la morphogénèse et de la physique non linéaire. L'apparition des formes et des structures par l'intermédiaire d'instabilités est une des voies vers la complexité.

This work is devoted to the equation <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Cint_%7BS%7D%0A%5Cfrac%7Bu(y)%20%5C,%20dS(y)%7D%7B%7Cx-y%7C%5E%7BN-1%7D%7D%20=%20f(x)%20%5Ctext%7B,%7D%20%5Cqquad%20%5Cqquad%20x%20%5Cin%20S%20%5Ctext%7B,%7D%0A%5Cqquad%20%5Cqquad%20%5Cqquad%20%5Cqquad%20%5Cqquad%20%5Cqquad%20%5Cqquad%20(1)%0A" /> where S is the graph of a Lipschitz function φ on RN with small Lipschitz constant, and dS is the Euclidian surface measure. The integral in the left-hand side is referred to as a simple layer potential and f is a given function. The main objective is to find a solution u to this equation along with estimates for solutions near points on S. Our analysis is carried out in local Lp-spaces and local Sobolev spaces, and the estimates are given in terms of seminorms. In Paper 1, we consider the case when S is a hyperplane. This gives rise to the classical Riesz potential operator of order one, and we prove uniqueness of solutions in the largest class of functions for which the potential in (1) is defined as an absolutely convergent integral. We also prove an existence result and derive an asymptotic formula for solutions near a point on the surface. Our analysis allows us to obtain optimal results concerning the class of right-hand sides for which a solution to (1) exists. We also apply our results to weighted Lp- and Sobolev spaces, showing that for certain weights, the operator in question is an isomorphism between these spaces. In Paper 2, we present a fixed point theorem for a locally convex space <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Cmathscr%7BX%7D" />, where the topology is given by a family <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5C%7Bp(%20%5C,%20%5Ccdot%20%5C,%20;%20%5Calpha%20)%5C%7D_%7B%5Calpha%20%5Cin%20%5COmega%7D" /> of seminorms. We study the existence and uniqueness of fixed points for a mapping<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Cmathscr%7BK%7D%20%5C,%20:%20%5C;%20%5Cmathscr%7BD_K%7D%20%5Crightarrow%20%5Cmathscr%7BD_K%7D" /> defined on a set <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Cmathscr%7BD_K%7D%20%5Csubset%20%5Cmathscr%7BX%7D" />. It is assumed that there exists a linear and positive operator K, acting on functions defined on the index set Ω, such that for every <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?u,v%20%5Cin%20%5Cmathscr%7BD_K%7D" />,   <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?p(%5Cmathscr%7BK%7D(u)%20-%20%5Cmathscr%7BK%7D(v)%20%5C,%20;%20%5C,%20%5Calpha%20)%20%0A%5Cleq%20K(p(u-v%20%5C,%20;%20%5C,%20%5Ccdot%20%5C,%20))%20(%5Calpha)%20%5Ctext%7B,%7D%20%5Cqquad%20%5Cqquad%20%5Calpha%20%5Cin%20%5COmega%0A%5Ctext%7B.%7D%0A" /> Under some additional assumptions, one of which is the existence of a fixed point for the operator K + p(<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Cmathscr%7BK%7D(0)" /> ; · ), we prove that there exists a fixed point of <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Cmathscr%7BK%7D" />. For a class of elements satisfying Kn (p(u ; · ))(α) → 0 as n → ∞, we show that fixed points are unique. This class includes, in particular, the solution we construct in the paper. We give several applications, proving existence and uniqueness of solutions for two types of first and second order nonlinear differential equations in Banach spaces. We also consider pseudodifferential equations with nonlinear terms. In Paper 3, we treat equation (1) in the case when S is a general Lipschitz surface and 1 &lt; p &lt; ∞. Our results are presented in terms of Λ(r), which is the Lipschitz constant of φ on the ball centered at the origin with radius 2r. Estimates of solutions to (1) are provided, which can be used to obtain knowledge about behaviour near a point on S in terms of seminorms. We also show that solutions to (1) are unique if they are subject to certain growth conditions. Examples are given when specific assumptions are placed on Λ. The main tool used for both existence and uniqueness is the fixed point theorem from Paper 2. In Paper 4, we collect some properties and estimates of Riesz potential operators, and also for the operator that was used in Paper 1 and Paper 3 to invert the Riesz potential of order one on RN, for the case when the density function is either radial or has mean value zero on spheres. It turns out that these properties define invariant subspaces of the respective domains of the operators in question.

Graduation date: 1991

La progresiva miniaturización de los materiales a la escala nanométrica ha abierto en la última década nuevas expectativas en el campo de la Ciencia de Materiales. Dichos materiales nanométricos presentan propiedades únicas, difiriendo a menudo de las propiedades del propio material a la macroescala, las cuales abren un amplio abanico de nuevas fenomenologías, y en consecuencia, de aplicaciones tecnológicas. De especial interés han sido los nanomateriales magnéticos, incluyendo las nanopartículas magnéticas o sistemas moleculares, dado que emergen como sistemas clave en el desarrollo de nuevas tecnologías de interés tales como sistemas de almacenamiento de memoria, computación cuántica o dispositivos de espintrónica. El desarrollo de aplicaciones reales en base al uso de dichos nanomateriales requiere primero la búsqueda de nuevas estrategias de estructuración que permitan organizar dichos sistemas magnéticos en superficies, a la vez que estudiar cómo es su comportamiento en la transición de la macroescala a la micro- o nanoescala. En este sentido es de interés estudiar cómo sus propiedades magnéticas pueden verse afectadas por efectos de la estructuración o de la propia superficie. En este contexto, de cara a estudiar las propiedades magnéticas de estos sistemas, una de las aproximaciones que está atrayendo mayor interés es el uso de dispositivos superconductores de interferencia cuántica (SQUIDs) y sensores Hall. Estos sensores han experimentado una gran revolución al ser miniaturizados, lo que ha permitido aumentar notablemente su sensibilidad hasta la detección de la magnetización de una sola nanopartícula o molécula. En este continuo avance, una de las principales limitaciones es la necesidad de desarrollar nuevas estrategias de integración que permitan depositar los sistemas magnéticos de un modo controlado en las zonas de máxima sensibilidad de estos sensores miniaturizados. En este contexto, la presente Tesis doctoral ha sido dedicada al desarrollo de nuevas estrategias de integración de cara a mejorar el control en la integración de sistemas magnéticos. Las estrategias propuestas han permitido por primera vez realizar este proceso sin la necesidad de modificar previamente ni el material magnético ni la superficie del sensor, consiguiendo depositar en zonas definidas del sensor con control (sub)micrométrico. En concreto, se ha demostrado la viabilidad y la universalidad de la técnica de deposición directa por litografía de AFM (conocida como Dip-pen Nanolithography, DPN) para la integración de nanomateriales magnéticos, abarcando un amplio rango de materiales desde nanopartículas hasta sistemas moleculares con comportamiento de imán unimolecular, en una gran variedad de sensores con diferentes dimensiones y requisitos. / The reduction of magnetic materials to the nanometric scale has opened in the last decades new perspectives in Material Science. Nanosized materials exhibit unique properties, which can considerably differ from the properties of the corresponding bulk materials, opening a wide range of new phenomenologies and therefore of technological applications. Two of the most prospective nanomaterials over the last years have been magnetic nanoparticles and molecular materials. Such nanostructured materials have attracted much interest not only from a fundamental point of view but also because their potential use in high-density information storage devices, quantum computing applications and in spintronics. However, before these applications become a reality, there is a fundamental issue that needs to be addressed, namely, the development of strategies to evolve from bulk materials to single entities suitable to be grafted on surfaces, sensors or other systems able to act as a device. The challenge is the definition of experimental strategies to properly assemble and integrate these molecular materials into functional devices without compromising their properties. In this context, there is an interest in understanding how the structuration procedure or even the surface can modify the behavior of such nanomaterials once deposited. Nevertheless, to answer these questions one of the approximations that is attracting more attention and probably more results is that of typical magnetic characterization techniques for bulk crystalline samples such as superconducting quantum interference devices (SQUID) or Hall magnetometer sensors. These systems have been miniaturized to increase their sensitivity down to a single magnetic or NP moment, involving the need for the development of specific deposition and structuration techniques to integrate the magnetic materials into the sensors with the required control on positioning and quantity of material. In this context, the present Thesis has been devoted to the development of novel structuration strategies to improve the control on the integration of magnetic nanosystems. The proposed strategies have allowed for first time to perform this process without the need of pre-modifying either the magnetic nanomaterial or the surface of the sensor, while depositing on specific areas of the sensor with (sub)micrometric precision. In particular, we have demonstrated the viability and generality of direct-write atomic force microscopy (AFM) lithography (also known as Dip-pen Nanolithography, DPN) to overcome most of the challenges that implies such integration. For this, different experimental approaches have been explored for the integration of magnetic nanomaterials intended to be as much representative as possible, ranging from magnetic nanoparticles to molecular systems exhibiting single molecule magnet (SMM) behavior, on a wide variety of sensors displaying different dimensions and requirements.

In this thesis, the spectral behavior of the fundamental and sum-frequency waves, generated from the surface of a thin metal film in the Kretschmann configuration, is theoretically studied with coherent ultrashort pulses. As a first exploration of considering spectral response in nonlinear plasmonics, it is shown that the spectra of reflected sum-frequency waves exhibit pronounced shifts for the incident fundamental waves close to the plasmon coupling angle, whereas meanwhile those of reflected fundamental waves display energy holes. We also demonstrate that the scale of discovered plasmon-enhanced spectral changes is strongly influenced by the magnitude of the incidentce angle and the source pulse duration, and at a certain angle a spectral switch is observed. The appearance of large sum-frequency wave shifts can serve as an unambiguous plasmon signatur in nonlinear surface spectroscopy. Also, the discovered spectral switch can trigger extremely surface-sensitive nonlinear plasmonic sensors.

De nouveaux arylthiophènes, soit le 4-(thièn-3-yl)benzènethiol (3TPT) et le 4-(thièn-3-yl)benzylthiol (3TBT) ont été synthétisés, électrodéposés et électropolymérisés sur un substrat d'or. L'objectif de ce projet était de former des monocouches organiques conjuguées dont la conductivité serait modulée par un évènement de reconnaissance moléculaire (par l'utilisation de bioconjugués) ou atomique (tel que la complexation de métaux divalents avec des groupements carboxylates). Des arylthiols, soit le thiophénol (TP), le diphénylthiol (DPT) et le p-dithiophénol (p-DTP) ont été utilisés comme composés modèles afin de mettre au point une méthode de déposition électrochimique efficace générant des monocouches complètes et organisées. Le p-DTP a été utilisé comme modèle dans le transport électronique à cause de la délocalisation des électrons-π dans le système aromatique et aussi de par sa possibilité de former des fils moléculaires. L'électrodéposition oxydative de ces arylthiols et arylthiophènethiols génère un taux de recouvrement élevé et reproductible comparativement à l'adsorption spontanée. Des études XPS ont suggérées que l'adsorption des arylthiophènethiols se fait par le soufre lié au noyau benzène tandis que le soufre du thiophène demeure libre. Dans le cas du p-DTP où il y a présence de deux soufres aromatiques, les études XPS indiquent que seulement un des deux soufres est lié à la surface. L'ajout d'une fonction méthylène d'espacement entre le noyau aromatique et la fonction d'ancrage thiol augmente la libre rotation des molécules et génère des taux de recouvrement plus élevés. Les monocouches électrodéposées de p-DTP se polymérisent linéairement de manière à former des fils moléculaires d'environ six unités. Les monocouches de 3TPT et de 3TBT ont été polymérisées oxydativement et efficacement par les carbones en alpha du soufre du thiophène. Dans ce type de polymère de surface, les électrons peuvent voyager autant perpendiculairement et parallèlement à la surface conductrice grâce au système totalement conjugué. Une copolymérisation mixte a aussi été faite, c'est-à-dire entre les unités adsorbées et un thiophène fonctionnalisé en solution, soit le 3-acétonitrilethiophène (3ACNT). Les résultats XPS indique que ce type de copolymérisation de surface forme des fils moléculaires ce qui contraste avec ce qui a été observé pour polymérisation entre les adsorbats. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : Nanotechnologies, Chimie interfaciale, Électropolymérisation, Spectroscopie, Thiophènes, Monocouches organiques conductrices.

The present work utilizes single molecule methods and analysis to investigate soft and hard substrates. First, the effect of charged hard surfaces on charged probes were evaluated, as the soft surfaces were built upon such a structure. Then, selected polymers were selected according to their importance in smart surface technology. The extent of interaction of the selected probes with the array of soft surfaces gives insight to the potential tunability of these surfaces. The three distinct polymers range from ubiquitous usage to advancements in current technology. The studies presented here are needed to characterize, on the nanoscale, the Coulombic interactions of these polymers.

Pressure sensitive adhesive surfaces are often inspired by nature. Miming the toe-surface of gecko, engineered surfaces made of thousands of micro-pillars show promising adhesive properties. This surfaces, covered with cylindrical pillars arranged into a pattern have adhesive properties greatly dependent on the geometrical characteristics. In this thesis, have been studied successively two models of micro-patterned surfaces, one two-dimensional, the other in three-dimensional using a FEM tool. Varying geometry parameters, has been determined optimal geometries to improve adhesive strength on these biomimetic, micropatterned surfaces. This study concludes to the non-adaptability of one-level scale micropatterned surface to large area of adhesion, to the strong advantage from the point of adhesion per contact area for high aspect ratio at each level of the geometry and study the opportunity of hierarchical structures. Some further suggestions of improvements to adhesion properties are discussed in the final chapter.

<p>The field of metamaterials has gained much attention within the scientific community over the past decade. With continuing advances and discoveries leading the way to practical applications, metamaterials have earned the attention of technology based corporations and defense agencies interested in their use for next generation devices. With the fundamental physics developed and well understood, current research efforts are driven by the demand for practical applications, with a famous example being the well-known microwave "invisibility cloak." Gaining exotic electromagnetic properties from their structure as opposed to their</p><p>intrinsic material composition, metamaterials can be engineered to</p><p>achieve tailored responses not available using natural materials. With typical designs incorporating resonant and dispersive elements much smaller than the operating wavelength, a homogenization scheme is possible, which leads to the meaningful interpretation of effective refractive index, and hence electric permittivity and magnetic permeability. The typical metamaterial is composed of arrays of scattering elements embedded in a host matrix. The scattering elements are typically identical, and the electromagnetic properties of the medium can be inferred from the properties of the unit cell. This convenience allows the designer to engineer the effective electromagnetic parameters of the medium by modifying the size, shape, and composition of the unit cell.</p><p>This dissertation summarizes several key projects related to my research efforts in metamaterials. The main focus of this dissertation is to develop practical approaches to frequency tunable and reconfigurable metamaterials. Chapter one serves as a background and introduction to the field of metamaterials. The purpose of chapters two, three and four is to develop different methods to realize tunable metamaterials - a broad class of controllable artificially engineered metamaterials. The second chapter develops an approach to characterizing metamaterials loaded with RF MEMS switches. The third chapter examines the effects of loading</p><p>metamaterial elements with varactor diodes and tunable ferroelectric</p><p>thin film capacitors (BST) for external tuning of the effective medium parameters, and chapter four develops a more advanced method to control the response of metamaterials using a digitally addressable control network. The content of these chapters leads up to an interesting application featured in chapter five - a reconfigurable frequency selective surface utilizing tunable and digitally addressable tunable metamaterials. The sixth and final chapter summarizes the dissertation and offers suggestions for future work in tunable and reconfigurable metamaterials. It is my hope that this dissertation will provide the foundation and motivation for new researchers in the field of metamaterials. I am confident that the reader will gain encouragement from this work with the understanding that very interesting and novel practical devices can be created using metamaterials. May this work be of aid and motivation to their research pursuits.</p> / Dissertation

No description available.