7 research outputs found
Recommended from our members
Tunable Circular Dichroism by Photoluminescent Moiré Gratings
In nanophotonics, there is a current demand for ultrathin, flexible nanostructures that are simultaneously easily tunable, demonstrate a high contrast, and have a strong response in photoluminescent polarization. In this work, the template-assisted self-assembly of water-dispersed colloidal core–shell quantum dots into 1D light-emitting sub-micrometer gratings on a flexible substrate is demonstrated. Combining such structures with a light-absorbing metallic counterpart by simple stacking at various angles results in a tunable Moiré pattern with strong lateral contrast. Furthermore, a combination with an identical emitter-based grating leads to a chiroptical effect with a remarkably high degree of polarization of 0.72. Such a structure demonstrates direct circular polarized photoluminescence, for the first time, without a need for an additional chiral template as an intermediary. The suggested approach allows for reproducible, large-area manufacturing at reasonable costs and is of potential use for chiroptical sensors, photonic circuit applications, or preventing counterfeit. © 2020 The Authors. Advanced Optical Materials published by Wiley-VCH Gmb
Recommended from our members
Lasing by Template-Assisted Self-Assembled Quantum Dots
Miniaturized laser sources with low threshold power are required for integrated photonic devices. Photostable core/shell nanocrystals are well suited as gain material and their laser properties can be exploited by direct patterning as distributed feedback (DFB) lasers. Here, the 2nd-order DFB resonators tuned to the photoluminescence wavelength of the QDs are used. Soft lithography based on template-assisted colloidal self-assembly enables pattern resolution in the subwavelength range. Combined with the directional Langmuir–Blodgett arrangement, control of the waveguide layer thickness is further achieved. It is shown that a lasing threshold of 5.5 mJ cm−2 is reached by a direct printing method, which can be further reduced by a factor of ten (0.6 mJ cm−2) at an optimal waveguide thickness. Moreover, it is discussed how one can adjust the DFB geometries to any working wavelength. This colloidal approach offers prospects for applications in bioimaging, biomedical sensing, anti-counterfeiting, or displays
Recommended from our members
Understanding Beta-Lactam-Induced Lysis at the Single-Cell Level
Mechanical rupture, or lysis, of the cytoplasmic membrane is a common cell death pathway in bacteria occurring in response to β-lactam antibiotics. A better understanding of the cellular design principles governing the susceptibility and response of individual cells to lysis could indicate methods of potentiating β-lactam antibiotics and clarify relevant aspects of cellular physiology. Here, we take a single-cell approach to bacterial cell lysis to examine three cellular features-turgor pressure, mechanosensitive channels, and cell shape changes-that are expected to modulate lysis. We develop a mechanical model of bacterial cell lysis and experimentally analyze the dynamics of lysis in hundreds of single Escherichia coli cells. We find that turgor pressure is the only factor, of these three cellular features, which robustly modulates lysis. We show that mechanosensitive channels do not modulate lysis due to insufficiently fast solute outflow, and that cell shape changes result in more severe cellular lesions but do not influence the dynamics of lysis. These results inform a single-cell view of bacterial cell lysis and underscore approaches of combatting antibiotic tolerance to β-lactams aimed at targeting cellular turgor
Recommended from our members
Nanoimprint Lithography Facilitated Plasmonic-Photonic Coupling for Enhanced Photoconductivity and Photocatalysis
Imprint lithography has emerged as a reliable, reproducible, and rapid method for patterning colloidal nanostructures. As a promising alternative to top-down lithographic approaches, the fabrication of nanodevices has thus become effective and straightforward. In this study, a fusion of interference lithography (IL) and nanosphere imprint lithography on various target substrates ranging from carbon film on transmission electron microscope grid to inorganic and dopable polymer semiconductor is reported. 1D plasmonic photonic crystals are printed with 75% yield on the centimeter scale using colloidal ink and an IL-produced polydimethylsiloxane stamp. Atomically smooth facet, single-crystalline, and monodisperse colloidal building blocks of gold (Au) nanoparticles are used to print 1D plasmonic grating on top of a titanium dioxide (TiO2) slab waveguide, producing waveguide-plasmon polariton modes with superior 10 nm spectral line-width. Plasmon-induced hot electrons are confirmed via two-terminal current measurements with increased photoresponsivity under guiding conditions. The fabricated hybrid structure with Au/TiO2 heterojunction enhances photocatalytic processes like degradation of methyl orange (MO) dye molecules using the generated hot electrons. This simple colloidal printing technique demonstrated on silicon, glass, Au film, and naphthalenediimide polymer thus marks an important milestone for large-scale implementation in optoelectronic devices. © 2021 The Authors. Advanced Functional Materials published by Wiley-VCH Gmb
Anisotropic and non-linear optical properties of self-assembled colloidal metasurfaces
Photonic metasurfaces obtain their unique optical properties from the periodic arrangement of sub-wavelength building blocks and can manipulate light in ways that differ significantly from bulk materials. Until recently, metasurfaces have been fabricated using top-down methods on a limited surface area. With the development of directed self-assembly methods and utilization of nanoscale colloids, metasurfaces can be fabricated on a larger scale and with reasonable efforts. In particular, soft nanoimprint lithography, based on the controlled drying of the colloidal solution within a structured template, allows for the precise placement of versatile colloidal building blocks on a substrate of choice. In this dissertation, the material and optical properties of self-assembled plasmonic and photoluminescent nanoparticles are systematically studied in terms of their short- and long-range interactions. It is shown that 1D plasmonic lattices exploit the intrinsic anisotropy and substrate-dependent collective resonant coupling. Likewise, semiconductor nanoparticles organized into linear gratings, result in light-emitting metasurfaces, featuring geometry-dependent amplification of the photoluminescence that can be further promoted to a non-linear amplification regime. Moreover, on flexible substrates, these self-assembled light-emitting metasurfaces can be stacked and twisted, inducing remarkably strong chiral effects and subsequently used for directional light sources, nanolasers, sensing, and labeling applications. Supported by theoretical modeling, this work provides a novel approach to realize anisotropic and non-linear optical properties on centimeter-scaled surface area using soft-lithography and directed self-assembly methods. It bridges the gap between nanoscale colloids and optoelectronics while advancing the integration of metasurfaces into functional devices.Photonische Metaoberflächen erhalten ihre einzigartigen optischen Eigenschaften durch die periodische Anordnung von Bauelementen im Sub-Wellenlängenbereich und können Licht auf eine Weise manipulieren, die sich deutlich von Ausgangsmaterialien unterscheidet. Bis vor kurzem wurden Metaoberflächen mit Top-Down-Methoden auf einer begrenzten Oberfläche hergestellt. Mit der Entwicklung von Methoden der gerichteten Selbstorganisation und der Nutzung von Kolloiden im Nanomaßstab können Metaoberflächen in größerem Maßstab und mit angemessenem Aufwand hergestellt werden. Insbesondere die Soft-Nanoimprint-Lithographie, die auf der kontrollierten Trocknung der kolloidalen Lösung innerhalb einer strukturierten Template basiert, ermöglicht die präzise Platzierung vielseitiger kolloidaler Bauelemente auf einem Substrat der Wahl. In dieser Dissertation werden die materiellen und optischen Eigenschaften selbstorganisierter plasmonischer und photolumineszenter Nanopartikel im Hinblick auf ihre Kurz- und Langstreckenwechselwirkungen systematisch untersucht. Es wird gezeigt, dass plasmonische 1D-Gitter die intrinsische Anisotropie und die substratabhängige kollektive Resonanzkopplung ausnutzen. Ebenso führen Halbleiter-Nanopartikel, die in linearen Gittern organisiert sind, zu lichtemittierenden Metaoberflächen, welche eine geometrieabhängige Verstärkung der Photolumineszenz aufweisen, die bis zu einem nichtlinearen Verstärkungsregime weitergeführt werden kann. Außerdem können diese selbstorganisierten, lichtemittierenden Metaoberflächen auf flexiblen Substraten gestapelt und verdreht werden, was zu bemerkenswert starken chiralen Effekten führt und anschließend für gerichtete Lichtquellen, Nanolaser, Sensor- und Beschriftungsanwendungen genutzt werden kann. Unterstützt durch theoretische Modellierung bietet diese Arbeit einen neuartigen Ansatz zur Realisierung anisotroper und nichtlinearer optischer Eigenschaften auf zentimetergroßen Oberflächen unter Verwendung von Softlithographie und Methoden der gerichteten Selbstmontage. Sie überbrückt die Lücke zwischen Kolloiden im Nanomaßstab und der Optoelektronik und treibt gleichzeitig die Integration von Metaoberflächen in funktionale Geräte voran
Recommended from our members
Complex Metal Nanostructures with Programmable Shapes from Simple DNA Building Blocks
Advances in DNA nanotechnology allow the design and fabrication of highly complex DNA structures, uisng specific programmable interactions between smaller nucleic acid building blocks. To convey this concept to the fabrication of metallic nanoparticles, an assembly platform is developed based on a few basic DNA structures that can serve as molds. Programming specific interactions between these elements allows the assembly of mold superstructures with a range of different geometries. Subsequent seeded growth of gold within the mold cavities enables the synthesis of complex metal structures including tightly DNA-caged particles, rolling-pin- and dumbbell-shaped particles, as well as T-shaped and loop particles with high continuity. The method further supports the formation of higher-order assemblies of the obtained metal geometries. Based on electrical and optical characterizations, it is expected that the developed platform is a valuable tool for a self-assembly-based fabrication of nanoelectronic and nanooptic devices. © 2021 The Authors. Advanced Materials published by Wiley-VCH Gmb