Verbesserung der Anwendbarkeit von organischen Leuchtdioden durch integrierte Nanostrukturen

The organic light-emitting diode (OLED) is a promising technology for a variety of applications, such as displays, large-area lighting, integrated sensing, smart packaging, and signage. OLEDs are thin-film devices comprising organic semiconductors, which allow for cost-efficient high-volume manufacturing using solution-based fabrications methods and therefore hold great potential towards disposable and recyclable electronic products. In this thesis, three different approaches to improve the applicability of OLEDs through integrated nanostructures are explored. Nanostructuring the carrier substrate's outside surface provides a way to enhance light extraction as well as customize tactile and visual device perception. Here, a polymer coating containing tetrapodal zinc oxide nanoparticles and color pigments is investigated with respect to surface roughness characteristics and optical properties. Electrical device properties can be altered by integrating nanostructures directly into the OLED semiconductor stack. In this work, periodic nanopatterning of a metal electrode is shown to improve charge injection into the organic semiconductor layer of a single-carrier device through local electric field enhancements. A current increase of up to 300 % is observed, exceeding the planar current injection limit and indicating a local transition to space charge limited operation. Integration of a photonic crystal slab into the waveguide formed by the OLED can also lead to resonant light outcoupling. Here, a fabrication method is presented to create two-dimensional nanogratings with variable grating designs in the commonly used electrode material indium tin oxide. Furthermore, a novel device structure is investigated in which a fluorescent nanopatterned waveguide is placed outside the OLED for directional light emission leading to sharp angle-dependent outcoupling peaks in the emission spectra

Plasmonic Nanostructures for Biosensor Applications

Improving the sensitivity of existing biosensors is an active research topic that cuts across several disciplines, including engineering and biology. Optical biosensors are the one of the most diverse class of biosensors which can be broadly categorized into two types based on the detection scheme: label-based and label-free detection. In label-based detection, the target bio-molecules are labeled with dyes or tags that fluoresce upon excitation, indicating the presence of target molecules. Label-based detection is highly-sensitive, capable of single molecule detection depending on the detector type used. One method of improving the sensitivity of label-based fluorescence detection is by enhancement of the emission of the labels by coupling them with metal nanostructures. This approach is referred as plasmon-enhanced fluorescence (PEF). PEF is achieved by increasing the electric field around the nano metal structures through plasmonics. This increased electric field improves the enhancement from the fluorophores which in turn improves the photon emission from the fluorophores which, in turn, improves the limit of detection. Biosensors taking advantage of the plasmonic properties of metal films and nanostructures have emerged an alternative, low-cost, high sensitivity method for detecting labeled DNA. Localized surface plasmon resonance (LSPR) sensors employing noble metal nanostructures have recently attracted considerable attention as a new class of plasmonic nanosensors.;In this work, the design, fabrication and characterization of plasmonic nanostructures is carried out. Finite difference time domain (FDTD) simulations were performed using software from Lumerical Inc. to design a novel LSPR structure that exhibit resonance overlapping with the absorption and emission wavelengths of quantum dots (QD). Simulations of a composite Au/SiO2 nanopillars on silicon substrate were performed using FDTD software to show peak plasmonic enhancement at QD emission wavelength (560nm). A multi-step fabrication process was developed to create plasmonic nanostructures, and the optical characterization of emission enhancement was performed

Nanopattern formation in UV laser treated a-AlOx and nc-Al/AlOx layers

Hexagonal nanopatterns were fabricated in sputter deposited Al-oxide thin films by means of single UV laser pulses via a layer of self-assembled silica nanospheres. The hexagonal pattern was projected to the surface due to the focussing effect of the silica nanolenses enhancing the local impact of the pulse. As a result of the laser pulse large area ordered structure of nano-pits were formed in RF sputtered amorphous Al-oxide films, while nano-craters were created in DC sputter deposited layers that consist of Al nanocrystals embedded in amorphous matrix. The two different mechanisms governing the nanostructure formation in the a-AlOx and nc-Al/AlOx composite layers were revealed by Atomic Force Microscopy (AFM), cross-sectional Transmission Electron Microscopy (XTEM), spectroscopic ellipsometry and computer simulation

Engineering patterned and dynamic surfaces for the spatio-temporal control of cell behaviour

Stem cell shape and mechanical properties in vitro can be directed by geometrically defined micropatterned adhesion substrates. However conventional methods are limited by the fixed micropattern design, which cannot recapitulate the dynamic changes of the natural cell microenvironment. Recent advancements in microfabrication technologies in combination with the use of light-responsive materials, allow to manipulate the shape of living cells in real-time in a non-invasive Spatio-temporal controlled way to introduce additional geometrically defined adhesion sites and to study relative cell behaviour. Here, the confocal laser technique is exploited for dynamically evaluate the variation over time of the tensional and morphological cell state. This method allows the precise control of specific actin structures that regulate cell architecture. Actin filament bundles, initially randomly organized in circular-shaped cells, are induced to align and distribute to form a rectangular-shaped cell in response to specific dynamic changes in the cell adhesion pattern. The changes in morphology also reflect dramatic changes in FAs distribution, cell mechanics, nuclear morphology, and chromatin conformation. The reported strategy is convenient to explore the cell-substrate interface and the mechanisms through which cell geometry regulates cell signalling in a facile and cost-effective manner and it open new routes to understand how the field of dynamic platforms should potentially contribute to unveil complex biological events such as the modulation of cell shape

Highly efficient sequestration of aqueous lead on nanostructured calcite substrates

Following defocused ion beam sputtering, large area highly corrugated and faceted nanoripples are formed on calcite (10.4) faces in a self-organized fashion. High resolution atomic force microscopy (AFM) imaging reveals that calcite ripples are defined by facets with highly kinked (11.0) and (21.12) terminations. In situ AFM imaging during the exposure of such modified calcite surfaces to PbCl2 aqueous solution reveals that the nanostructured calcite surface promotes the uptake of Pb. In addition, we observed the progressive smoothing of the highly reactive calcite facet terminations and the formation of Pb-bearing precipitates elongated in registry with the underlying nanopattern. By SEM–EDS analysis we quantified a remarkable 500% increase of the Pb uptake rate, up to 0.5 atomic weight % per hour, on the nanorippled calcite in comparison to its freshly cleaved (10.4) surfaces. These results suggest that nanostructurated calcite surfaces can be used for developing future systems for lead sequestration from polluted waters.Universidad Técnica de AmbatoJuan de la Cierva-Formación postdoctoral contract (ref. FJC2018–035820- I)Spanish Ministry of ScienceMinistero dell’Università e della Ricerca (MUR)National Recovery and Resilience Plan (NRRP)Mission 4 Component 2 Investment 1.3 - Call for tender No. 1561 of 11.10.2022The European Union – NextGenerationEU • Award Number: Project code PE0000021Concession Decree No. 1561 of 11.10.2022 adopted by Ministero dell’Università e della Ricerca (MUR)CUP D33C22001300002 Project title “Network 4 Energy Sustainable Transition – NEST”. FBdM acknowledges support by UNIGE in the framework of BIPE2020 program and technical suppor

Solution-Processed Epitaxial Growth of Arbitrary Surface Nanopatterns on Hybrid Perovskite Monocrystalline Thin Films.

Semiconductor surface patterning at the nanometer scale is crucial for high-performance optical, electronic, and photovoltaic devices. To date, surface nanostructures on organic-inorganic single-crystal perovskites have been achieved mainly through destructive methods such as electron-beam lithography and focused ion beam milling. Here, we present a solution-based epitaxial growth method for creating nanopatterns on the surface of perovskite monocrystalline thin films. We show that high-quality monocrystalline arbitrary nanopatterns can form in solution with a low-cost simple setup. We also demonstrate controllable photoluminescence from nanopatterned perovskite surfaces by adjusting the nanopattern parameters. A seven-fold enhancement in photoluminescence intensity and a three-time reduction of the surface radiative recombination lifetime are observed at room temperature for nanopatterned MAPbBr3 monocrystalline thin films. Our findings are promising for the cost-effective fabrication of monocrystalline perovskite on-chip electronic and photonic circuits down to the nanometer scale with finely tunable optoelectronic properties