All-optical radiofrequency modulation of Anderson-localized modes

All-optical modulation of light relies on exploiting intrinsic material nonlinearities. However, this optical control is rather challenging due to the weak dependence of the refractive index and absorption coefficients on the concentration of free carriers in standard semiconductors. To overcome this limitation, resonant structures with high spatial and spectral confinement are carefully designed to enhance the stored electromagnetic energy, thereby requiring lower excitation power to achieve significant nonlinear effects. Small mode-volume and high quality (Q)-factor cavities also offer an efficient coherent control of the light field and the targeted optical properties. Here, we report on optical resonances reaching Q - 10^5 induced by disorder on novel photonic/phononic crystal waveguides. At relatively low excitation powers (below 1 mW), these cavities exhibit nonlinear effects leading to periodic (up to - 35 MHz) oscillations of their resonant wavelength. Our system represents a test-bed to study the interplay between structural complexity and material nonlinearities and their impact on localization phenomena and introduces a novel functionality to the toolset of disordered photonics

Real-time optical dimensional metrology via diffractometry for nanofabrication

The ICN2 is funded by the CERCA programme/ Generalitat de Catalunya.Surface patterning technologies represent a worldwide growing industry, creating smart surfaces and micro/nanoscale device. The advent of large-area, high-speed imprinting technologies has created an ever-growing need for rapid and non-destructive dimensional metrology techniques to keep pace with the speed of production. Here we present a new real-time optical scatterometry technique, applicable at the mesoscale when optical inspection produces multiple orders of diffraction. We validate this method by inspecting multiple silicon gratings with a variety of structural parameters. These measurements are cross-referenced with FIB, SEM and scanning stylus profilometry. Finally, we measure thermally imprinted structures as a function of imprinting temperature in order to demonstrate the method suitable for in-line quality control in nanoimprint lithography

Integrated 3D Hydrogel Waveguide Out-Coupler by Step-and-Repeat Thermal Nanoimprint Lithography: A Promising Sensor Device for Water and pH

Hydrogel materials offer many advantages for chemical and biological sensoring due to their response to a small change in their environment with a related change in volume. Several designs have been outlined in the literature in the specific field of hydrogel-based optical sensors, reporting a large number of steps for their fabrication. In this work we present a three-dimensional, hydrogel-based sensor the structure of which is fabricated in a single step using thermal nanoimprint lithography. The sensor is based on a waveguide with a grating readout section. A specific hydrogel formulation, based on a combination of PEGDMA (Poly(Ethylene Glycol DiMethAcrylate)), NIPAAm (N-IsoPropylAcrylAmide), and AA (Acrylic Acid), was developed. This stimulus-responsive hydrogel is sensitive to pH and to water. Moreover, the hydrogel has been modified to be suitable for fabrication by thermal nanoimprint lithography. Once stimulated, the hydrogel-based sensor changes its topography, which is characterised physically by AFM and SEM, and optically using a specific optical set-up

Order quantification of hexagonal periodic arrays fabricated by in situ solvent-assisted nanoimprint lithography of block copolymers

Directed self-assembly of block copolymer polystyrene-b-polyethylene oxide (PS-b-PEO) thin film was achieved by one-pot methodology of solvent vapour assisted nanoimprint lithography (SAIL).Comment: 12 pages, 4 figures, paper accepte

Induced Gravity on RS Branes

It is shown that a localized four-dimensional Einstein term, induced by quantum corrections, modifies significantly the law of gravity in a Randall-Sundrum brane world. In particular, the short-distance behavior of gravity changes from five- to four-dimensional, while, depending on the values of parameters, there can be an intermediate range where gravity behaves as in five dimensions. The spectrum of graviton fluctuations around the brane, their relative importance for the gravitational force, and the relevance of their emission in the bulk for the brane cosmology are analysed. Finally, constraints on parameters are derived from energy loss in astrophysical and particle physics processes.Comment: 20 pages, 1 figure, JHEP.cl

Surface-directed dewetting of a block copolymer for fabricating highly uniform nanostructured microdroplets and concentric nanorings

Through a combination of nanoimprint lithography and block copolymer self-assembly, a highly regular dewetting process of a symmetric diblock copolymer occurs whereby the hierarchal formation of microdroplets and concentric nanorings emerges. The process is driven by the unique chemical properties and geometrical layout of the underlying patterned silsesquioxane micrometer-sized templates. Given the presence of nonpreferential substrate−polymer interactions, directed dewetting was utilized to produce uniform arrays of microsized droplets of microphase separated polystyrene-block-poly(methyl methylacrylate) (PS-b-PMMA), following thermal annealing at 180 °C. Microdroplets with diameters greater than 400 nm exhibited a hexagonal close-packed arrangement of nanodots on the surface with polydomain ordering. At the droplet periphery, the polydomain ordering was severely disrupted because of a higher in-plane radius of curvature. By reducing the droplet size, the in-plane radius of curvature of the microdroplet becomes significant and the PMMA cylinders adopt parallel structures in this confined geometry. Continuous scaling of the droplet results in the generation of isolated, freestanding, self-aligned, and self-supported oblique nanorings (long axis ∼250−350 nm), which form as interstitial droplets between the larger microdroplets. Optical and magnetic-based nanostructures may benefit from such hierarchal organization and self-supporting/aligned nanoring templates by combining more than one lithography technique with different resolution capabilities

Introducing surface functionality on thermoformed polymeric films

Altres ajuts: this work has been performed within the PLASTFUN project (Planta Pilot de Peces Plàstiques amb Superficies Funcionals Avançades), within the Industries of the Future community (IDF) RIS3CAT, supported by the European Regional Development Fund (ERDF) as part of the operative frame FEDER of Catalonia 2014-2020 EC [COMRDI 16-1-0018], included in the 7th Framework Program. AF, NK and CMST acknowledge support from the CERCA Programme of the Generalitat de Catalunya.We present a fabrication process for the production of 3-dimensional micro-structured polymeric films. The microstructures are fabricated in a single step using thermal nanoimprint lithography as patterning technique. The micro-structured polymer films are then transformed into a 3D shape by means of a plug-assisted thermoforming process, while keeping the functionality of the micro-patterned areas. The preserved functionality is characterized by water contact angle measurements, while the deformation of the micro-structured topographies due to the thermoforming process is analyzed using confocal microscopy and Digital Image Correlation (DIC) techniques. This combined fabrication process represents a promising solution to complement in-mold decoration approaches, enabling the production of new functional surfaces. As the microstructures are fabricated by means of a mechanical modification of the surface, without the need of chemical treatments or coatings, the presented technique represents a promising, simple and green solution, suitable for the industrial fabrication of 3D nonplanar shaped functional surfaces

Fabrication and replication of re-entrant structures by nanoimprint lithography methods

In this work, the authors present and demonstrate a simple method to fabricate and mass replicate re-entrant structures. The method consists of the direct imprinting of polymer mushroomlike microstructures produced by a combination of photolithography and nickel up-plating process. In particular, they have studied the conditions to generate highly robust mushroomlike topographies and their topographical impact on the replication process. They discuss all the imprinting conditions suitable to replicate such topographies using both ultraviolet light assisted nanoimprint lithography (UV-NIL) and thermal NIL methods in two polymer films, poly(methyl methacrylate) and polypropylene, and a hybrid (organic-inorganic) UV light curable photoresist, namely, Ormocomp. Re-entrant topographies have been widely studied for liquid/oil repelling and dry adhesive properties, whereas in their experiments, they have proved evidence for their amphiphobic potential

In-line metrology for roll-to-roll UV assisted nanoimprint lithography using diffractometry

En publicar-se l'article, l'autor Martin Kreuzer treballa a: ALBA Laboratori de Llum de SincrotróWe describe and discuss the optical design of a diffractometer to carry out in-line quality control during roll-to-roll nanoimprinting. The tool measures diffractograms in reflection geometry, through an aspheric lens to gain fast, non-invasive information of any changes to the critical dimensions of target grating structures. A stepwise tapered linear grating with constant period was fabricated in order to detect the variation in grating linewidth through diffractometry. The minimum feature change detected was ∼40 nm to a precision of 10 nm. The diffractometer was then integrated with a roll-to-roll UV assisted nanoimprint lithography machine to gain dynamic measurements in situ