A stimuli-responsive microgel is a three-dimensional polymer network that is able to absorb and expel a solvent (commonly water). These materials are unique in the fact that their sponge-like behavior can be actuated by environmental cues, like temperature, ion concentration, pH, and light. Because of the dynamic properties of these materials they have found applications in drug-delivery systems, micro-assays, selective filtration, artificial muscle, and non-fouling surfaces. The most well-known stimuli-responsive polymer is Poly(N-isopropylacrylamide) or PNIPAAm and it experiences a switchable swelling or deswelling over a critical temperature ( Tc=~32°C). Below the critical temperature, the gel begins mixing with the surrounding solvent and swells; above this temperature, the opposite is true. The unconstrained hydrogel will continue to swell in all directions until equilibrium is established between its propensity for mixing with the surrounding solvent and the elastic restoring forces of the gel matrix. The strength of the elastic restoring forces is dependent on the interconnectedness of the polymer network and is therefore a function of crosslink density. An increase in crosslink density results in a decreased swelling and vice versa. If the hydrogel is mechanically constrained to a surface, it can experience various wrinkling and buckling conformations upon swelling, as the stresses associated with its confinement are relieved. These conformation characteristics are a strong function of geometry (aspect ratio) and extent of swelling (i.e. crosslink density). In order to capitalize on the utility of this material, it is imperative that its volume transition is well characterized and understood. Toward this end, pNIPAAm gels have been created with 1x10-7 to 2x10-³ mol/cm³ crosslink density and characterized. This was done by first examining its bulk, unattached swelling ability and then by evaluating its microscale properties as a surfaceconfined monolithe. The latter was achieved through the use of confocal microscopy and copolymerization with a fluorescent monomer. This method allows for a detail analysis of the deformations experienced (bulk-structural bending and surface undulating) and will ultimately lend itself to the correlation between crosslink density and the onset of mechanical phenomena.

The goal of this study is to design and manufacture a microfluidic device capable of measuring changes in impedance valuesof microfluidic cell cultures. Tocharacterize this, an interdigitated array of electrodes was patterned over glass, where it was then bonded to a series of fluidic networks created in PDMS via soft lithography. The device measured ethanol impedance initially to show that values remain consistent over time. Impedance values of water and 1% wt. saltwater were compared to show that the device is able to detect changes in impedance, with up to a 60% reduction in electrical impedance in saltwater. Cells were introduced into the device, where changes in impedance were seen across multiple frequencies, indicating that the device is capable of detecting the presence of biologic elements within a system. Cell measurements were performed using NIH-3T3 fibroblasts.

The next generation of optoelectronic applications like stimuli-responsive sensors, functional displays or nanophotonic circuits demands a basic understanding of lightmatter interactions on the nanoscale. Top-down fabrication has been employed in the past to demonstrate coherent energy transfer in functional nanostructures, yet these fabrication methods are problematic due to their limited scalability and high costs as well as the high optical losses. This work adapted physical principles like radiation properties of metallic nanoantennas and Bragg diffraction in periodic nanostructures and realized these concepts using bottom-up self-assembly methods based on colloidal chemistry. With this approach, single plasmonic nanoparticles and semiconductor quantum emitters were co-assembled into complex structures. This work took the colloidal concept from plasmonics and introduced quantum dots in order to characterize the radiative and non-radiative decay processes as well as the arising light-matter interactions. Due to electromagnetic coupling between the components, hybridized modes were detected instead of the single particle resonances observed in the isolated case. It was furthermore shown that these colloidal building blocks can be assembled into functional optical grids on a large scale using template-assisted self-assembly. Thus, this work established spectroscopic principles for self-assembled colloidal building blocks that can be integrated in parallelized processes in the future.

Magnetic data storing has been of great interest since 1950 when the first magnetic hard drive was fabricated. A lot has happened since then, but there is still a need for smaller and cheaper devices.  One way to achieve this is by creating nano-sized ferromagnetic areas in a thin film at room temperature, or nano-magnets. In this thesis, the aim is to fabricate and characterize novel amorphous nano-magnets. Using a chromium mask ions can be implanted in a nano-sized pattern in an amorphous iron zirconium thin film. The mask is fabricated by depositing chromium over the iron zirconium and etching the nano-structures into the chromium film.  This requires the parameters for the etching to be optimized. It is discovered the parameters change with the size and shape of the pattern. Magnetization and structural characterization were performed by using the magneto-optical Kerr effect and a magnetic force microscope. The result shows that the nano-magnets become magnetically harder than the reference sample. The study further reveals structural details for further improvements in implanted regions. / <p>Opponent: Stivan Sabir</p>

Many lithographic methods to pattern surfaces both by a mechanical manipulation of the surface or by printing functionalities in the form of particles or molecules have been developed and used in research. Examples for contact-lithographic methods are soft lithography and polymer-pen lithography. One of the main drawbacks of the these methods is the lateral dimension of the obtained pattern. Due to limitations of stamps, materials and the methods themselves, feature sizes of arrays consisting of discrete spots in the sub-micrometer range remain challenging. Another factor in the state-of-the-art contact-lithographic methods is the ex situ adsorption of ink prior to the stamping procedure and thus, an uninterrupted flow of ink cannot be guaranteed. As the variety of imaginable inks is wide and the appropriate solvent often appears to be of organic nature, state-of-the-art contact-lithographic methods are unable to print these inks. The elastomeric polymer stamps used within contact-lithographic methods swell or dissolve in contact with organic solvents. Often, contact-lithographic methods require expensive equipment or defined conditions, e.g. high vacuum or a solvent-enriched humidity, and cannot be carried out in a simple and efficient way under ambient conditions. In this work, a new approach to generate patterned structures with feature sizes in the sub-micrometer range and spot-to-spot distances in the one-micron range is presented. Stamps with an integrated, continuous pore system generate the patterns while the ink is supplied through the capillaries of the stamp. The method of capillary nanostamping provides a simple and low-cost stamping procedure by the synthesis of spongy mesoporous silica stamps. Due to a continuous pore system within the stamp, the ink can be supplied continuously and even without a refilling system, the stamp itself serves as ink reservoir. This provides a continuous or intermittently ink supply for a stamping process with several stamping cycles without the need to refill the stamp. A new stamp or re-inking after one stamping cycle is not necessary. The stamping process is carried out manually by hand under ambient conditions. Due to the silica network, the stamps can be infiltrated with organic solvents. The development of spongy mesoporous silica stamps for capillary nanostamping is presented in this work by demonstrating the progress from pure silica stamps in a typical well-known sol-gel synthesis to spongy and flexible silica stamps with a reduced network bonding and hydrophobic internal residues. For the proof of concept of capillary nanostamping with spongy mesoporous silica stamps, several different inks are stamped. All inks are chosen with respect to a potential application and consist of a volatile organic solvent to proof the stability of the stamps against these solvents, and a non-volatile component, which remains on the substrate surface after precipitation and drying of the solvent. As ink, a dispersion of C60 fullerenes in toluene is stamped onto perfluorinated glass slides. A solution of 1-dodecanethiol in ethanol is stamped onto a gold-coated glass with the outcome of a heterogeneous surface. As a model for nanoparticles, nanodiamonds dispersed in isopropanol are stamped and subsequently functionalized with a fluorescent dye in a click-reaction. A polymer and two different block copolymers dissolved in toluene/chloroform are stamped onto differently functionalized substrate surfaces to analyze the dependency of the nature of the substrate on the stamping results. In a final experiment, a solution of 17α-ethinylestradiol in acetonitrile is stamped as a model for an active pharmaceutical ingredient and subsequently detached from the substrate surface to obtain a defined nanodispersion.

The goals of this research project were the design and construction of a carbon nanotube (CNT) reactor based on the plasma enhanced chemical vapor deposition (PECVD) principle and the development of a method for directed assembly of CNTs by catalyst patterning. PECVD was selected as the growth method due to the requirement of a catalyst for the growth process, thereby facilitating directed assembly and controlled diameter CNT growth at well-defined locations. The reactor was built in accord with horizontal flow design using standard ultra high vacuum components. The controllable parameters of the reactor include sample temperature, DC plasma intensity, chamber pressure, gas flow ratios, and total gas flow. The most favorable parameters for growing CNTs of well defined length, diameter, and separation were obtained by initially using parameter values obtained from literature, then optimized by changing a parameter and noting the effect on CNT growth. Catalyst patterns for the directed assembly of CNTs were prepared by electron-beam lithography (EBL). Experiments were performed that demonstrated the feasibility of using lithographic methods to achieve directed assembly of carbon nanotubes for the manufacture of CNT devices. Experiments focusing on growth interruption and regrowth of CNTs were conducted to investigate methods of introducing tailored branching points into carbon nanotubes during the growth process. These experiments clearly demonstrate that growth interruption increases the occurrence of CNT branching. An analysis of the relationships between CNT diameter, branching points, and the number of growth steps was conducted.

L'impression par transfert, une technique utilisée pour transférer divers matériaux tels que des molécules d'ADN, de la résine photosensible ou des nanofils semi-conducteurs, s'est dernièrement révélée utile pour la réalisation de structures de silicium statiques sous le nom de micro-maçonnerie. L'étude présentée ici explore le potentiel de la technique de micro-maçonnerie pour la fabrication de résonateurs MEMS. Dans ce but, des microplaques de silicium ont été transférées sur des couches d'oxyde avec cavités intégrées à l'aide de timbres de polymère afin de créer des structures de type plaques suspendues. Le comportement dynamique de ces structures passives a été étudié sous pression atmosphérique et sous vide en utilisant une excitation externe par pastille piézo-électrique mais aussi le bruit thermomécanique. Par la suite, des résonateurs MEMS actifs, à actionnement électrostatique et détection capacitive intégrés, ont été fabriqués en utilisant des étapes supplémentaires de fabrication après impression. Ces dispositifs ont été caractérisés sous pression atmosphérique. Les facteurs de qualité intrinsèques des dispositifs fabriqués ont été évalués à 3000, ce qui est suffisant pour les applications de mesure à pression atmosphérique et en milieu liquide. Nous avons démontré que, puisque l'adhérence entre la plaque et l'oxyde est suffisamment forte pour empêcher une diaphonie mécanique entre les différentes cavités d'une même base, plusieurs résonateurs peuvent être facilement réalisés en une seule étape d'impression. Ce travail de thèse montre que la micro-maçonnerie est une technique simple et efficace pour la réalisation de résonateurs MEMS actifs de type plaque à cavité scellée. / Lately, transfer printing, a technique that is used to transfer diverse materials such as DNA molecules, photoresist, or semiconductor nanowires, has been proven useful for the fabrication of various static silicon structures under the name micro-masonry. The present study explores the suitability of the micro-masonry technique to fabricate MEMS resonators. To this aim, silicon microplates were transfer-printed by microtip polymer stamps onto dedicated oxide bases with integrated cavities in order to create suspended plate structures. The dynamic behavior of fabricated passive structures was studied under atmospheric pressure and vacuum using both external piezo-actuation and thermomechanical noise. Then, active MEMS resonators with integrated electrostatic actuation and capacitive sensing were fabricated using additional post-processing steps. These devices were fully characterized under atmospheric pressure. The intrinsic Q factor of fabricated devices is in the range of 3000, which is sufficient for practical sensing applications in atmospheric pressure and liquid. We have demonstrated that since the bonding between the plate and the device is rigid enough to prevent mechanical crosstalk between different cavities in the same base, multiple resonators can be conveniently realized in a single printing step. This thesis work shows that micro-masonry is a powerful technique for the simple fabrication of sealed MEMS plate resonators.

Les filtres CRIGFs sont une nouvelle génération de filtres optiques réflectifs nanostructurés qui présentent un très fort intérêt pour de nombreuses applications. Cependant, leur fabrication est relativement complexe : il s'agit de composants structurés à des échelles petites devant la longueur d'onde d'utilisation, mais de surface totale relativement grande. Ils sont usuellement fabriqués en utilisant des procédés de lithographie de type lithographie électronique, qui présente une résolution suffisante mais qui est séquentielle et donc lente pour de telles surfaces de composant. En outre, les CRIGFs sont souvent réalisés sur des substrats isolants, ce qui complexifie encore plus l'utilisation de cette lithographie. Lors de cette thèse, un procédé de fabrication des CRIGFs a été développé à partir de la lithographie par nanoimpression via moule souple (SNIL). Cette technologie collective et à haut rendement contourne les inconvénients et garde les avantages de la traditionnelle lithographie électronique. Elle permet de fabriquer des motifs nanométriques par simple pressage d'un moule souple sur une couche de résine de polymères sous insolation d'ultraviolets. Après avoir stabilisé le procédé et établi les limites de la technologie, de nombreux filtres CRIGFs ont ainsi été créés. Ils présentent des résultats optiques équivalents dans le proche infrarouge (NIR) à ceux fabriqués par lithographie électronique. Dans un deuxième temps, le caractère générique du procédé mis en place a été démontré de plusieurs façons. Premièrement, nous avons montré qu'il était possible à l'aide de celui-ci de dépasser les compromis usuels de conception en structurant directement le guide d'onde, qui sera ensuite ré-encapsulé. Deuxièmement, nous avons montré que ce même procédé pouvait être directement transféré pour réaliser des filtres CRIGF dans la gamme du moyen infrarouge, bien que les filtres soient alors réalisés sur un matériau cristallin III-V et présentent des dimensions micrométriques plutôt que nanométriques. Enfin, nous avons démontré la grande souplesse et stabilité du procédé en l'utilisant pour explorer différentes géométries potentiellement intéressantes de cette nouvelle famille de filtres optiques nanostructurés. Nous avons notamment étudié des CRIGFs comportant un gradient de période qui ont permis pour la première fois d'obtenir un filtre CRIGF accordable. Pour finir, nous nous sommes attachés à étudier le potentiel de réalisation de filtres CRIGFs plus complexes et présentant plusieurs niveaux de corrugation. / Cavity resonator integrated grating filters (CRIGFs) are a new generation of nanostructured reflective filters. They present a strong interest for many applications. However, their manufacturing is relatively complex: CRIGFs are components structured at small scales compared to the wavelength of interest but on a relatively large area. They are usually made by electron beam lithography technique which presents a sufficient resolution but does not allow parallel patterning and is thereby time consuming for large area components. Furthermore, CRIGFs are often fabricated on insulating wafers which make the e-beam lithography process more complicated. In this PhD, a CRIGF process manufacturing has been implemented through soft mold nanoimprint lithography (SNIL). This high throughput collective technology keeps the benefits of the traditional electron beam lithography while overcoming its limits. Nano-scale patterns can be made by a simple stamping under UV exposure of a soft mold on a polymer resist layer. After stabilizing the process and assessing the technique limits, plenty of CRIGFs have been manufactured. They exhibit optical performances in the near- infrared range equivalent to those manufactured by e-beam lithography. Secondly, it has been demonstrated that the implemented process is generic. We have shown the possibility to overcome the usual design trade-offs by structuring directly the waveguide, before embedding. Moreover, this same process has been shown to be applied in a straightforward way to fabricate CRIGFS in the mid-infrared range using a III-V crystalline material and micrometric sized patterns. Finally, we have demonstrated the great flexibility and sustainability of the process by testing different potential geometries of CRIGFs. Notably, we have designed a CRIGF with a period gradient leading to the first tunable CRIGF ever demonstrated. Lastly, we have evaluated the potential manufacturing of complex CRIGFs with several corrugation levels.

No description available.

There is a need to discover advanced materials to address the pressing challenges facing humanity, however there are far too many combinations of material composition and processing conditions to explore using conventional experimentation. One powerful approach for accelerating the rate at which materials are explored is by miniaturizing the scale at which experiments take place. Reducing the size of samples has been tremendously productive in biomedicine and drug discovery through standardized formats such as microwell plates, and while these formats may not be the most appropriate for studying polymeric materials, they do highlight the advantages of studying materials in ultra-miniaturized volumes. However, precise and controlled methods for handling diverse samples at the sub-femtoliter-scale have not been demonstrated. In this thesis, we establish that scanning probes can be used as a technique for realizing and interrogating sub-femtoliter scale polymer samples. To do this, we develop and apply methods for patterning materials with control over their size and composition and then use these methods to study material systems of interest. First, we develop a closed-loop method for patterning liquid samples using scanning probes by utilizing tipless cantilevers capable of holding a discrete liquid drop together with an inertial mass sensing scheme to measure the amount of liquid loaded on the probe. Using these innovations, we perform patterning with better than 1% mass accuracy on the pL-scale. While dispensing fluid with tipless cantilevers is successful for patterning pL-scale features and can be considered a candidate for robust nanoscale manipulation of liquids for high-throughput sample preparation, the minimum amount of liquid that can be transferred using this method is limited by number of factors. Thus, in the second section of this thesis, we explore ultrafast cantilevers that feature spherical tips and find them capable of patterning aL-scale features with in situ feedback. The development of methods of interrogating polymers at the pL-scale led us to explore how the mechanical properties of photocurable polymers depend on processing conditions. Specifically, we investigate the degree to which oxygen inhibits photocrosslinking during vat polymerization and how this effect influences the mechanical properties of the final material. We explore this through a series of macroscopic compression studies and AFM-based indentation studies of the cured polymers. Ultimately, the mechanical properties of these systems are compared to pL-scale features patterned using scanning probe lithography and we find that not only does oxygen prevent full crosslinking when it is present during the post-print curing, but the presence of oxygen during printing itself irreversibly softens the material. In addition to developing new methods for realizing ultra-miniaturized samples for study, the novel scanning probe methods in this work have led to new paradigms for rapidly evaluating complex interactions between material systems. In particular, we present a novel method to quantitatively investigate the interaction between the metal-organic frameworks (MOFs) and polymers by attaching a single MOF particle to a cantilever and studying the interaction force between this MOF and model polymer surfaces. Using this approach, we find direct evidence supporting the intercalation of polymer chains into the pores of MOFs. This work lays the foundation for directly characterizing the facet-specific interactions between MOFs and polymers in a high-throughput manner sufficient to fuel a data-driven accelerated material discovery pipeline. Collectively, the focus of this thesis is the development and utilization of novel scanning probe methods to collect data on extremely small systems and advance our understanding of important classes of materials. We expect this thesis to provide the foundation needed to transform scanning probe systems into instruments for performing reliable nanochemistry by combining controlled and quantitative sample preparation at the nanoscale and high-throughput characterization of materials. To conclude, we present an outlook about the necessary technological advancements and promising directions for materials innovations that stem from this work.