Combinaisons de procédés lithographiques ascendants et descendants pour la fabrication de nanostructures sur grandes surfaces pour la photonique

Le but de cette thèse est d'adopter une approche hybride par la combinaison des méthodes de lithographie ascendantes et descendantes pour la fabrication de nanostructures avec des propriétés structurales et optiques d’intérêt. Cette approche multidisciplinaire est un domaine vaste ou les combinaisons prometteuses sont nombreuses mais restent inexplorées jusqu'à présent. Ces travaux vont s’intéresser aussi bien à la chimie des matériaux qu'aux techniques de nanofabrication de salle blanche afin d'apporter des solutions pratiques aux problèmes actuels rencontrés en nanofabrication. Plus précisément, nous nous intéressons à l’étude de certaines techniques de lithographies (en particulier à la nano-impression) et démontrons la possibilité d’améliorer la cadence de fabrication en obtenant des nanostructures sur une échelle de plusieurs centimètres carrés. Les nanostructures fabriquées sont principalement utilisées comme résonateurs de Mie pour leurs propriétés optiques et leur capacité à modifier la lumière incidente. Des démonstrateurs de plusieurs millimètres carrés sont réalisés et montrent des propriétés optiques intéressantes soulignant la viabilité de notre approche.The scope of this thesis is to adopt a hybrid approach through the synergetic combination of bottom-up and top-down lithography methods to fabricate nanostructures with interesting structural and optical properties. This multidisciplinary approach is a vast fruitful field where many combinations are promising but remains unexplored so far. By taking interest in, and bringing together, both materials chemistry and clean-room nanofabrication techniques, this work tries to find practical solutions to tackle some of the current challenges in nanofabrication. In details, we focus on the study of selected lithography techniques (in particular nanoimprint) and demonstrate the possibility to increase the fabrication throughput and obtain nanostructures on a centimeter scale. The nanofabricated structures are then mainly used as Mie resonators for their optical properties and their ability to modify incoming light. Demonstrators of several millimeters are produced and are shown to exhibit interesting optical properties; emphasizing the feasibility of our approach

Full Investigation of Angle Dependence in Dip-Coating Sol-Gel Films

International audienceDip-coating is one of the most convenient methods used in laboratory and industry to deposit a solid layer onto a surface with a controlled thickness from a chemical solution. The present Article investigates the influence of the withdrawal speed on the film thickness and homogeneity with respect to the dipping angle ranging from 90 degrees (conventional vertical configuration) to 1 degrees (quasi-horizontal configuration). Several advantages were found in the latter extreme low-dipping angle conditions that are (i) an available wider range of thickness, (ii) the elimination of the perturbations/effects induced by evaporation, and (iii) the compatibility with large surface and single face deposition at high throughput and using a minimal amount of solution. One shows that experimental data follow the Landau-Levich model, modified by Tallmaclge for angle dependence, only for intermediate regimes of speed. A maximal thickness limited by the physical-chemical characteristics of the initial solution is reached at high speeds while a minimal thickness, corresponding to a single layer of solute interacting with the substrate surface can be obtained at very low speeds

Nano-imprint lithography processing of inorganic-based materials

International audienceWe review past and recent progress in Nano-Imprint Lithography (NIL) methods to (nano-) structure inorganic materials from sol-gel liquid formulations and colloidal suspensions onto a surface. This technique, first inspired by embossing techniques, was developed for soft polymer processing, as final or intermediate materials, but is today fully adapted to hard inorganic materials with high dielectric constant, such as metal oxides, with countless chemical compositions provided by the sol-gel chemistry. Consequently, NIL has become a versatile, high throughput, and highly precise microfabrication method that is mature for lab developments and scaling up. We first describe the state-of-the-art in nanofabrication methods and the plethora of approaches developed in the last decades to imprint metal oxides from inorganic solutions. These are discussed and compared in terms of performances, issues, and ease of implementation. The final part is devoted to relevant applications in domains of interest

NANOIMPRINT LITHOGRAPHY PROCESS AND PATTERNED SUBSTRATE OBTAINABLE THEREFROM

The present invention pertains to the field of nanoimprint lithography (NIL) processes and more specifically to a soft NIL process used for providing a sol-gel patterned layer on a substrate. Specifically, this process comprises a step of adjusting the solvent uptake of the sol- gel film to 10 to 50% vol., preferably between 15 and 40% vol., by varying the relative pressure of the solvent while a soft mould is applied onto the substrate coated with the sol-gel film

Carbon nanotube columns for flow systems:influence of synthesis parameters

Flow reactors are expected to play an increasingly important role in the production of chemicals. A simple carbon-based scaffold to easily develop flow systems is here detailed. Using a chemical vapour deposition technique, the controlled in situ growth of vertically aligned (VA) multi-wall carbon nanotubes (MWCNTs) into quartz columns with 2 mm inner diameter is achieved. Several of the described MWCNT columns (CNCs) can be produced at a time. The influence of synthesis parameters on the formation of these VA-MWCNT scaffolds is reported and discussed (e.g. injection time of the precursor, carrier gas flow rate, inner diameter and length of the quartz column, position in the furnace during synthesis). Raman spectroscopy, optical microscopy, scanning and transmission electron microscopy are used to assess the coverage of the inner channel of the quartz column with VA-MWCNTs and their overall quality. The length of the CNCs together with the carrier gas flow rate are found to be key parameters to control the MWCNT length profile within the CNCs. Fluoresceinamine molecules and platinum nanoparticles are successfully immobilised within these MWCNT scaffolds. The benefits of the CNCs for flow system design are summarised as the controlled filling with MWCNTs makes the detailed CNCs versatile scaffolds for flow catalysis and filtration

Multi-functional metasurfaces based on direct nano-imprint of Titania sol gels coatings

International audienceDielectric Mie resonators are taking momentum in the last years thanks to their peculiar properties in light management at visible and near-infrared frequencies. However, their full exploitation demands for cheap materials and versatile fabrication methods, extendible over large surfaces and potentially C-MOS compatible. Here, a sol-gel deposition and nano-imprint lithography method is used to obtain Titania-based Mie resonators over large areas (several mm 2), showing that this platform can potentially be exploited for light management with different devices. First, it is demonstrated their use for structural colours and efficient band pass filters covering the visible spectrum. Then, exploiting sharp Fano resonances in reflection, their potential for refractive index sensing is addressed obtaining a figure of merit of ~20. Finally, when placing the resonators on porous silica, a large and reversible colour tuning can be produced as a result of water adsorption within the substrate porosity. These results open the path to Titania sub-micrometric structures for applications as a multi-functional metamaterial for smart windows, displays and all-optical sensing

Environment-controlled sol-gel soft-NIL processing for optimized titania, alumina, silica and yttria-zirconia imprinting at sub-micron dimensions

International audienceMetal oxide (MOX) surface nanopatterns can be prepared using Soft-Nano-Imprint-Lithography (soft-NIL) combined with sol–gel deposition processing. Even if sol–gel layers remain gel-like straight after deposition, their accurate replication from a mould remains difficult as a result of the fast evaporation-induced stiffening that prevents efficient mass transfer underneath the soft mould. The present work reports a detailed investigation of the role of the xerogel layer conditioning (temperature and relative humidity) prior to imprinting and its influence on the quality of the replication. This study is performed on four different systems namely titania, alumina, silica and yttria-stabilised zirconia. We demonstrate that the quality of the replica can be considerably improved without the use of sacrificial stabilising organic agents, but by simply applying an optimal aging at controlled temperature and relative humidity specific to each different reported MOX. In each case this condition corresponds to swelling the initial xerogels of around 30%vol by water absorption from humidity. We show that this degree of swelling represents the best compromise for sufficiently increasing the xerogel fluidity while limiting the shrinkage upon final thermal curing

Large scale self-organisation of 2D hexagonal Ge and Au nanodots on patterned TiO 2

International audienceWe report a new strategy for the ordering of 2D arrays of Ge and Au nanodots on a silicon wafer using a patterned titanium oxide layer. In a rst step, a TiO 2 layer is prepared by block-copolymer-micelles-assisted sol-gel deposition on a full Si wafer, followed by a thermal annealing. The process leads to hexagonally positioned perforations of homogeneous size and spacing. In a second step, these TiO 2 Inorganic NanoPatterns (INPs) are used as templates for the organization of Ge and Au nanodots. Germanium adatoms deposited by Molecular Beam Epitaxy on INPs, diuse and self-assemble into nanodots, located within the INPs pores. They form homogeneous sub-20 nm Ge nanodots in epitaxy on the silicon substrate and regularly distributed with one dot per perforation. The same approach is used for the formation of Au nanodots. In this case, a gentle mechanical polishing is requiered to suppress the dots seating at 1 the top of the TiO 2 network. The process developed in this study paves the way to the large scale self-organisation of quantum dots that are highly interesting for various applications, such as opto-electronics, and microelectronics

Scalable Disordered Hyperuniform Architectures via Nanoimprint Lithography of Metal Oxides

International audienceFabrication and scaling of disordered hyperuniform materials remain hampered by the difficulties in controlling the spontaneous phenomena leading to this novel kind of exotic arrangement of objects. Here, we demonstrate a hybrid top-down/ bottom-up approach based on sol−gel dip-coating and nanoimprint lithography for the faithful reproduction of disordered hyperuniform metasurfaces in metal oxides. Nano-to microstructures made of silica and titania can be directly printed over several cm 2 on glass and on silicon substrates. First, we describe the polymer mold fabrication starting from a hard master obtained via spontaneous solid-state dewetting of SiGe and Ge thin layers on SiO 2. Then, we assess the effective disordered hyperuniform character of master and replica and the role of the thickness of the sol− gel layer on the metal oxide replicas and on the presence of a residual layer underneath. Finally, as a potential application, we show the antireflective character of titania structures on silicon. Our results are relevant for the realistic implementation over large scales of disordered hyperuniform nano-and microarchitectures made of metal oxides, thus opening their exploitation in the framework of wet chemical assembly