Homeotropic orientation of an ion-channel forming mesophase induced by nanotemplate wetting.

Anodic aluminum oxide (AAO) membranes were used as templates to control orientation of an ion-channel forming columnar mesophase obtained by self assembly of a wedge-shaped sulfonate molecule. Inside the AAO structure, the director vector of the mesophase is oriented parallel to the pore axis due to the confinement effect. The molecular arrangement induced by the spatial confinement within the pores is extended over several microns into the remnant film on the AAO surface. The homeotropic alignment of the channels promotes unidimensional ion conduction through the film plane, which is manifested by a considerable increase in conductivity relative to isotropic samples.

Roll-to-roll nanoimprint lithography of high efficiency Fresnel lenses for micro-concentrator photovoltaics.

Roll-to-roll nanoimprint lithography (R2R-NIL) is an enabling technology for the low-cost mass production of high-quality micro- and nano-sized optical elements. Particularly, the fabrication of Fresnel lenses using R2R-NIL is a promising approach to produce optical arrays for micro-concentrator photovoltaic modules. This work investigates the application of a continuous R2R imprinting process based on ultraviolet curing of transparent photopolymer resins (UV-NIL) to fabricate high-efficiency and low-cost Fresnel lenses. The morphological attributes and the related optical performance of the lenses fabricated using roll-to-roll UV-NIL on flexible PET sheets yielded optical efficiency values up to ∼ 69% at a concentration ratio of 178X, whereas a value of ∼ 77% was obtained for the UV-NIL batch processed on a flat rigid substrate. Further improvement of the optical efficiency has been achieved by adding moth-eye inspired antireflective (AR) features on the side opposite to the Fresnel motifs via a double-sided R2R UV-NIL process. The process developed paves the way for cost-effective mass production of high-efficiency Fresnel lenses for micro-concentrator photovoltaics.

Improved thermal stability of antireflective moth-eye topography imprinted on PMMA/TiO2surface nanocomposites.

The thermal stability of antireflective moth-eye topographical features fabricated by nanoimprint lithography on poly (methyl methacrylate) (PMMA) incorporating TiO2nanoparticles is explored. The effect of nanoparticle load on the relaxation dynamics of the moth-eye nanostructure is evaluated via grazing incidence small angle x-ray scattering measurements byin situmonitoring the structural decay of the nanopatterns upon thermal annealing. It is demonstrated that the incorporation of TiO2nanoparticles to the imprinted surface nanocomposite films delays greatly the pattern relaxation which, in turn, enhances the stability of the patterned topography even at temperatures well above the polymer glass transition (Tg). The improved thermal behavior of the antireflective films will significantly enhance their functionality and performance in light-trapping applications where temperatures typically rise, such as solar devices or solar glass panels.

High-resolution thermal imaging with a combination of nano-focus X-ray diffraction and ultra-fast chip calorimetry.

A microelectromechanical-systems-based calorimeter designed for use on a synchrotron nano-focused X-ray beamline is described. This instrument allows quantitative DC and AC calorimetric measurements over a broad range of heating/cooling rates (≤100000 K s(-1)) and temperature modulation frequencies (≤1 kHz). The calorimeter was used for high-resolution thermal imaging of nanogram-sized samples subjected to X-ray-induced heating. For a 46 ng indium particle, the measured temperature rise reaches ∼0.2 K, and is directly correlated to the X-ray absorption. Thermal imaging can be useful for studies of heterogeneous materials exhibiting physical and/or chemical transformations. Moreover, the technique can be extended to three-dimensional thermal nanotomography.

A diacetylene-containing wedge-shaped compound: synthesis, morphology, and photopolymerization.

A novel wedge-shaped compound containing two diacetylene tails, namely, methyl 3,5-bis(trideca-2,4-diyn-1yloxyl)benzoate (DDABM), was synthesized. As shown by UV/Vis spectroscopy this compound can be polymerized under UV irradiation. The crystalline structure of DDABM was investigated by grazing-incidence wide-angle X-ray diffraction on oriented crystalline films deposited on PTFE-rubbed silicon wafer substrates. Furthermore, the spherulites formed in thicker films were analyzed by wide-angle X-ray diffraction. A molecular packing model of DDABM based on the X-ray diffraction data is proposed. The diacetylene units are oriented along a defined lattice direction with a reticular distance of 4.85 Å, which fulfills the requirements for topochemical polymerization. It was observed that UV polymerization does not affect the phase behavior of the compound, but mainly alters its optical properties.

Non-radial growth of helical homopolymer crystals: breaking the paradigm of the polymer spherulite microstructure.

Radial symmetry is essential for the conventional view of the polymer spherulite microstructure. Typically it is assumed that, in the course of the spherulite morphogenesis, the lamellar crystals grow radially. Using submicron X-ray diffraction, it is shown that in banded spherulites of poly(propylene adipate) the crystals have the shape of a helix with flat-on crystals winding around a virtual cylinder of about 6 µm in diameter. The helix angle of 30° implies that the crystal growth direction is tilted away from the spherulite radius by this angle. The implications of the helical crystal shape contradict the paradigm of the spherulitic microstructure. The radial growth rate of such spherulites does not correspond to the crystal growth rate, but to the propagation rate of the virtual cylinder the ribbons wind around.

High-Performance Implantable Sensors based on Anisotropic Magnetoresistive La0.67Sr0.33MnO3 for Biomedical Applications.

We present the design, fabrication, and characterization of an implantable neural interface based on anisotropic magnetoresistive (AMR) magnetic-field sensors that combine reduced size and high performance at body temperature. The sensors are based on La0.67Sr0.33MnO3 (LSMO) as a ferromagnetic material, whose epitaxial growth has been suitably engineered to get uniaxial anisotropy and large AMR output together with low noise even at low frequencies. The performance of LSMO sensors of different film thickness and at different temperatures close to 37 °C has to be explored to find an optimum sensitivity of ∼400%/T (with typical detectivity values of 2 nT·Hz-1/2 at a frequency of 1 Hz and 0.3 nT·Hz-1/2 at 1 kHz), fitted for the detection of low magnetic signals coming from neural activity. Biocompatibility tests of devices consisting of submillimeter-size LSMO sensors coated by a thin poly(dimethyl siloxane) polymeric layer, both in vitro and in vivo, support their high suitability as implantable detectors of low-frequency biological magnetic signals emerging from heterogeneous electrically active tissues.

Correlation lengths, porosity and water adsorption in TiO2 thin films prepared by glancing angle deposition.

This paper reports a thorough microstructural characterization of glancing angle deposited (GLAD) TiO(2) thin films. Atomic force microscopy (afm), grazing-incidence small-angle x-ray scattering (GISAXS) and water adsorption isotherms have been used to determine the evolution of porosity and the existence of some correlation distances between the nanocolumns constituting the basic elements of the film's nanostructure. It is found that the deposition angle and, to a lesser extent, the film thickness are the most important parameters controlling properties of the thin film. The importance of porosity and some critical dimensions encountered in the investigated GLAD thin films is highlighted in relation to the analysis of their optical properties when utilized as antireflective coatings or as hosts and templates for the development of new composite materials.

Assessment and formation mechanism of laser-induced periodic surface structures on polymer spin-coated films in real and reciprocal space.

In this work we evaluate the potential of grazing incidence X-ray scattering techniques in the investigation of laser-induced periodic surface structures (LIPSSs) in a series of strongly absorbing model spin-coated polymer films which are amorphous, such as poly(ethylene terephthalate), poly(trimethylene terephthalate), and poly(carbonate bisphenol A), and in a weaker absorbing polymer, such as semicrystalline poly(vinylidene fluoride), over a narrow range of fluences. Irradiation was performed with pulses of 6 ns at 266 nm, and LIPSSs with period lengths similar to the laser wavelength and parallel to the laser polarization direction are formed by devitrification of the film surface at temperatures above the characteristic glass transition temperature of the polymers. No crystallization of the surface is induced by laser irradiation, and crystallinity of the material prevents LIPSS formation. The structural information obtained by both atomic force microscopy and grazing incidence small-angle X-ray scattering (GISAXS) correlates satisfactorily. Comparison of experimental and simulated GISAXS patterns suggests that LIPSSs can be well described considering a quasi-one-dimensional paracrystalline lattice and that irradiation parameters have an influence on the order of such a lattice.

Confinement-induced one-dimensional ferroelectric polymer arrays.

This work demonstrates the use of wetting nanoporous alumina template with polymer solution to produce arrays of isolated poly(vinylidene fluoride) (PVDF) ferroelectric gamma-type nanorods supported within a nonpolar alpha-structure film. The method is based upon a crystal phase transition which occurs due to PVDF confinement within alumina nanoporous. The system was studied using scanning X-ray microdiffraction (micro-XRD) that allows the solid-solid phase transition from the alpha-nonpolar crystal form (bulk) to the gamma polar ferroelectric form (nanorod array) to be spatially resolved, as well as providing crystallinity and orientation information. The results reveal that the interaction between polymer chains and the porous membrane's walls imposes a flat-on lamella growth along the nanorrods long axis, while improving crystal orientation.

Assessing Fast Structure Formation Processes in Isotactic Polypropylene with a Combination of Nanofocus X-ray Diffraction and In Situ Nanocalorimetry.

A combination of in situ nanocalorimetry with simultaneous nanofocus 2D Wide-Angle X-ray Scattering (WAXS) was used to study polymorphic behaviour and structure formation in a single micro-drop of isotactic polypropylene (iPP) with defined thermal history. We were able to generate, detect, and characterize a number of different iPP morphologies using our custom-built ultrafast chip-based nanocalorimetry instrument designed for use with the European Synchrotron Radiation Facility (ESRF) high intensity nanofocus X-ray beamline facility. The detected iPP morphologies included monoclinic alpha-phase crystals, mesophase, and mixed morphologies with different mesophase/crystalline compositional ratios. Monoclinic crystals formed from the mesophase became unstable at heating rates above 40 K s-1 and showed melting temperatures as low as ~30 K below those measured for iPP crystals formed by slow cooling. We also studied the real-time melt crystallization of nanogram-sized iPP samples. Our analysis revealed a mesophase nucleation time of around 1 s and the co-existence of mesophase and growing disordered crystals at high supercooling ≤328 K. The further increase of the iPP crystallization temperature to 338 K changed nucleation from homogeneous to heterogeneous. No mesophase was detected above 348 K. Low supercooling (≥378 K) led to the continuous growth of the alpha-phase crystals. In conclusion, we have, for the first time, measured the mesophase nucleation time of supercooled iPP melted under isothermal crystallization conditions using a dedicated experimental setup designed to allow simultaneous ultrafast chip-based nanocalorimetry and nanofocus X-ray diffraction analyses. We also provided experimental evidence that upon heating, the mesophase converts directly into thermodynamically stable monoclinic alpha-phase crystals via perfection and reorganization and not via partial melting. The complex phase behaviour of iPP and its dependence on both crystallization temperature and time is presented here using a time-temperature-transformation (TTT) diagram.

Bioinspired antireflective flexible films with optimized mechanical resistance fabricated by roll to roll thermal nanoimprint.

This work describes the fabrication process of moth eye antireflective poly (methyl methacrylate) transparent films via roll to roll thermal nanoimprint lithography. The process parameters are investigated and adjusted in order to obtain from a single moth-eye structured mold, a range of antireflective topographies that gradually vary their geometry from protruding to intruding nanocones. A correlation between the process parameters with the optical and mechanical properties of the films is established to illustrate the influence of the processing parameters and serve as guideline to produce antireflective flexible films with balanced properties and optimized performance adequate to the application environment. A finite element model is described predicting the mechanical behavior of the moth-eye PMMA imprinted nanostructures.

Structure of glancing incidence deposited TiO(2) thin films as revealed by grazing incidence small-angle X-ray scattering.

For the first time, grazing incidence small-angle X-ray scattering (GISAXS) analysis is used to characterize the morphology of TiO(2) thin films grown by glancing angle physical vapor deposition (GLAD). According to cross-section scanning electron microscopy (SEM) images, the films consist of near isotilted TiO(2) columns of different length and width depending on film thickness. The obtained GISAXS patterns show a characteristic asymmetry with respect to the incidence plane, which is associated with the tilted geometry of the TiO(2) columns. The patterns also show the existence of two populations of columns in these GLAD-TiO(2) films. The population of the thinnest columns appears related to the first grown layer and is common for all the films investigated, while the second population of columns grows with the thickness of the films and has been related to wider columns formed by shadowing at the expense of the initially formed columns.

Vertical datum transformation grids for Mexico.

Mexico has used two vertical datums-the U.S. National Geodetic Vertical Datum of 1929 (NGVD29) and the North American Vertical Datum of 1988 (NAVD88). Because Mexico started using the NAVD88 as its vertical datum in 2015, most of Mexico's data is referenced to the NGVD29 and recent high resolution data are referenced to the NAVD88. Compounding this situation, satellite-derived Digital Elevation Models (DEMs) are referenced to the Earth Gravimetric Model 96 (EGM96), and no tools are currently available in Mexico to transform elevation data between the aforementioned vertical datums. To overcome this problem, this work presents the development of two surfaces to transform orthometric heights between the NGVD29 and NAVD88 or between the NGVD29 and EGM96 in Mexico. These surfaces can be used by any interested user to transform orthometric heights referenced to the aforementioned datums.

Engineered protein-based functional nanopatterned materials for bio-optical devices.

The development of new active biocompatible materials and devices is a current need for their implementation in multiple fields, including the fabrication of implantable devices for biomedical applications and sustainable devices for bio-optics and bio-optoelectronics. This paper describes a simple strategy to use designed proteins to develop protein-based functional materials. Using simple proteins as self-assembling building blocks as a platform for the fabrication of new optically active materials takes previous work one step further towards the design of materials with defined structures and functions using naturally occurring protein materials, such as silk. The proposed fabrication strategy generates thin and flexible nanopatterned protein films by letting the engineered protein elements self-assemble over the surface of an elastomeric stamp with nanoscale features. These nanopatterned protein films are easily transferred onto 3D objects (flat and curved) by moisture-induced adhesion. Additionally, flexible nanopatterned protein films are prepared by incorporating a thin polymeric layer as a back support. Finally, taking advantage of the tunability of the selected protein scaffold, the flexible protein-based surfaces are endowed with optical functions, achieving efficient lasing features. As such, this work enables the simple and cost-effective production of flexible and nanostructured, protein-based, optically active biomaterials and devices over large areas toward emerging applications.

Moth-eye mimetic cytocompatible bactericidal nanotopography: a convergent design.

The rapid emergence of antibiotic resistant bacteria has prompted the need for radically different approaches to combat bacterial infections. Among these, bioinspired surface topographies have emerged as an effective sustainable strategy to deter bacterial infection. This study demonstrates the bactericidal activity and cytocompatibility of the moth-eye mimetic topography produced by thermal polymer nanoimprinting. The moth-eye topography was found to have bactericidal capabilities against Gram negative and Gram positive bacteria. Electron microscopy imaging revealed the bactericidal effect caused by mechanical rupture of the bacteria wall inflicted by the topography on the adhered cells. The cytocompatibility of the surfaces was evidenced by assessing the proliferation and morphology of keratinocytes cultured on the nanotopography. The technology meets important needs in medical implant technology for materials that not only have good biocompatibility but also antibacterial properties for reducing the risk of infections and related health complications.

Nano-engineering safer-by-design nanoparticle based moth-eye mimetic bactericidal and cytocompatible polymer surfaces.

Nanotechnology provides a new design paradigm for alternative antibacterial strategies in the fight against drug-resistant bacteria. In this paper, the enhanced bactericidal action of moth-eye nanocomposite surfaces with a collaborative nanoparticle functional and topography structural mode of action is reported. The moth-eye nanocomposite surfaces are fabricated in combined processing steps of nanoparticle coating and surface nanoimprinting enabling the production of safer-by-design nanoparticle based antibacterial materials whereby the nanoparticle load is minimized whilst bactericidal efficiency is improved. The broad antibacterial activity of the nanocomposite moth-eye topographies is demonstrated against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli and Pseudomonas aeruginosa as model bacteria. The antibacterial performance of the moth-eye nanocomposite topographies is notably improved over that of the neat moth-eye surfaces with bacteria inhibition efficiencies up to 90%. Concurrently, the moth-eye nanocomposite topographies show a non-cytotoxic behaviour allowing for the normal attachment and proliferation of human keratinocytes.

Single-imprint moth-eye anti-reflective and self-cleaning film with enhanced resistance.

Antireflective transparent materials are essential for a myriad of applications to allow for clear vision and efficient light transmission. Despite the advances, efficient and low cost solutions to clean antireflective surfaces have remained elusive. Here, we present a practical approach that enables the production of antireflective polymer surfaces based on moth-eye inspired features incorporating photoinduced self-cleaning properties and enhanced mechanical resistance. The methodology involves the fabrication of sub-wavelength moth-eye nanofeatures onto transparent surface composite films in a combined processing step of nanoparticle coating and surface nanoimprinting. The resulting surfaces reduced the optical reflection losses from values of 9% of typical PMMA plastic films to an optimum value of 0.6% in the case of double-sided moth-eye nanoimprinted films. The composite moth-eye topography also showed an improved stiffness and scratch resistance. This technology represents a significant advancement not limited by scale, for the development of antireflective films for low cost application products.

Multifunctional Nano-engineered Polymer Surfaces with Enhanced Mechanical Resistance and Superhydrophobicity.

This paper presents a multifunctional polymer surface that provides superhydrophobicity and self-cleaning functions together with an enhancement in mechanical and electrical performance. These functionalities are produced by nanoimprinting high aspect ratio pillar arrays on polymeric matrix incorporating functional reinforcing elements. Two distinct matrix-filler systems are investigated specifically, Carbon Nanotube reinforced Polystyrene (CNT-PS) and Reduced Graphene Oxide reinforced Polyvinylidene Difluoride (RGO-PVDF). Mechanical characterization of the topographies by quantitative nanoindentation and nanoscratch tests are performed to evidence a considerable increase in stiffness, Young's modulus and critical failure load with respect to the pristine polymers. The improvement on the mechanical properties is rationalized in terms of effective dispersion and penetration of the fillers into the imprinted structures as determined by confocal Raman and SEM studies. In addition, an increase in the degree of crystallization for the PVDF-RGO imprinted nanocomposite possibly accounts for the larger enhancement observed. Improvement of the mechanical ruggedness of functional textured surfaces with appropriate fillers will enable the implementation of multifunctional nanotextured materials in real applications.