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- ItemActive Plasmonic Colloid-to-Film-Coupled Cavities for Tailored Light-Matter Interactions(Washington, DC : Soc., 2019) Goßler, Fabian R.; Steiner, Anja Maria; Stroyuk, Oleksandr; Raevskaya, Alexandra; König, Tobias A.F.For large-scale fabrication of optical circuits, tailored subwavelength structures are required to modulate the refractive index. Here, we introduce a colloid-to-film-coupled nanocavity whose refractive index can be tailored by various materials, shapes, and cavity volumes. With this colloidal nanocavity setup, the refractive index can be adjusted over a wide visible wavelength range. For many nanophotonic applications, specific values for the extinction coefficient are crucial to achieve optical loss and gain. We employed bottom-up self-assembly techniques to sandwich optically active ternary metal-chalcogenides between a metallic mirror and plasmonic colloids. The spectral overlap between the cavity resonance and the broadband emitter makes it possible to study the tunable radiative properties statistically. For flat cavity geometries of silver nanocubes with sub-10 nm metallic gap, we found a fluorescence enhancement factor beyond 1000 for 100 cavities and a 112 meV Rabi splitting. In addition, we used gold spheres to extend the refractive index range. By this easily scalable colloidal nanocavity setup, gain and loss building blocks are now available, thereby leading to new generation of optical devices. Copyright © 2019 American Chemical Society.
- ItemRevealing Fast Proton Transport in Condensed Matter by Means of Density Scaling Concept(Washington, DC : Soc., 2020) Wojnarowska, Zaneta; Musiał, Małgorzata; Cheng, Shinian; Gapinski, Jacek; Patkowski, Adam; Pionteck, Jürgen; Paluch, MarianHerein, we investigate the charge transport and structural dynamics in the supercooled and glassy state of protic ionic material with an efficient interionic Grotthuss mechanism. We found that superprotonic properties of studied acebutolol hydrochloride (ACB-HCl) depend on thermodynamic conditions with the most favorable regions being close to the glass-transition temperature (Tg) and glass-transition pressure (Pg). To quantify the contribution of fast proton hopping to overall charge transport over a broad T–P space, we employed the density scaling concept, one of the most important experimental findings in the field of condensed matter physics. We found that isothermal and isobaric dc-conductivity (σdc) and dynamic light scattering (τα) data of ACB-HCl plotted as a function of (TVγ)−1 satisfy the thermodynamic scaling criterion with the ratio γσ/γα appearing as a new measure of fast charge transport in protic ionic glass-formers in the T–P plane. Such a universal factor becomes an alternative to the well-known Walden rule being limited to ambient pressure conditions.
- ItemPolysulfide driven degradation in lithium–sulfur batteries during cycling – quantitative and high time-resolution operando X-ray absorption study for dissolved polysulfides probed at both electrode sides(London [u.a.] : RSC, 2021) Zech, Claudia; Hönicke, Philipp; Kayser, Yves; Risse, Sebastian; Grätz, Olga; Stamm, Manfred; Beckhoff, BurkhardThe development of operando characterization techniques on realistic batteries is essential for an advanced mechanistic understanding in battery chemistry and, therefore, contributes to their further performance improvement. This manuscript presents operando Near-Edge X-ray Absorption Spectroscopy (NEXAFS) traceable to the SI units (SI is the abbreviation for the International System of Units) during multiple charge–discharge cycles on both electrodes of lithium–sulfur (Li/S) coin cells which enables an absolute quantification of dissolved polysulfides with no need for calibration samples or reference material. We could reveal that during the charging process, polysulfide (PS) movement from the negative to the positive electrode is inhibited. This leads to a steady increase of dissolved polysulfides at the anode side and, therefore, is one of the key points for capacity fading. We quantitatively track the polysulfides dissolved in the electrolyte and correlate for the first time their evolution with the capacity fading of the cell. We analyze the appearance of PS during cell operation at the cathode and anode side to characterize the transport mechanisms of the polysulfide shuttle phenomena and to reveal quantitative information about their evolution at different states of charge and states of health. Our cell design suppresses the contribution of cathodic sulfur, which is mandatory for reference-sample-free quantification in X-ray spectrometry and allows us to use only slightly modified standard coin cell batteries.
- ItemEnhancing sub-bandgap external quantum efficiency by photomultiplication for narrowband organic near-infrared photodetectors([London] : Nature Publishing Group UK, 2021) Kublitski, Jonas; Fischer, Axel; Xing, Shen; Baisinger, Lukasz; Bittrich, Eva; Spoltore, Donato; Benduhn, Johannes; Vandewal, Koen; Leo, KarlDetection of electromagnetic signals for applications such as health, product quality monitoring or astronomy requires highly responsive and wavelength selective devices. Photomultiplication-type organic photodetectors have been shown to achieve high quantum efficiencies mainly in the visible range. Much less research has been focused on realizing near-infrared narrowband devices. Here, we demonstrate fully vacuum-processed narrow- and broadband photomultiplication-type organic photodetectors. Devices are based on enhanced hole injection leading to a maximum external quantum efficiency of almost 2000% at −10 V for the broadband device. The photomultiplicative effect is also observed in the charge-transfer state absorption region. By making use of an optical cavity device architecture, we enhance the charge-transfer response and demonstrate a wavelength tunable narrowband photomultiplication-type organic photodetector with external quantum efficiencies superior to those of pin-devices. The presented concept can further improve the performance of photodetectors based on the absorption of charge-transfer states, which were so far limited by the low external quantum efficiency provided by these devices.
- ItemHeterogeneous freezing on pyroelectric poly(vinylidene fluoride-co-trifluoroethylene) thin films(Chichester [u.a.] : Wiley, 2020) Apelt, Sabine; Höhne, Susanne; Uhlmann, Petra; Bergmann, UteActive deicing of technical surfaces, such as for wind turbines and heat exchangers, currently requires the usage of heat or chemicals. Passive coating strategies that postpone the freezing of covering water would be beneficial in order to save costs and energy. One hypothesis is that pyroelectric active materials can achieve this because of the surface charges generated on these materials when they are subject to a temperature change. High-quality poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) thin films with a high crystallinity, prefererd edge-on orientation, low surface roughness, and comprised of the β-analogous ferroelectric phase were deposited by spin-coating. Freezing experiments with a cooling rate of 1 K min−1 were made on P(VDF-TrFE) coatings in order to separate the effect of different parameters such as the poling direction, film thickness, used solvent, deposition process, underlying substrate, and annealing temperature on the achievable supercooling. The topography and the underlying substrate significantly changed the distribution of freezing temperatures of water droplets in contact with these thin films. In contrast, no significant effect of the thickness, morphology, or pyroelectric effect of the as-prepared domain-state on the freezing temperatures was found.
- ItemPolymer Hydrogels to Guide Organotypic and Organoid Cultures(Weinheim : Wiley-VCH, 2020) Magno, Valentina; Meinhardt, Andrea; Werner, CarstenHuman organotypic and organoid cultures provide increasingly life-like models of tissue/organ development and disease, enable more realistic drug screening, and may ultimately pave the way for new therapies. A broad variety of extracellular matrix-based or inspired materials is instrumental in these approaches. In this review article, the foundations of the related materials design are summarized with an emphasis on the advantages and limitations of decellularized and reconstituted biopolymeric matrices as well as biohybrid and fully synthetic polymer hydrogel systems applied to enable specific organotypic and organoid cultures. Recent progress in the fabrication of defined hydrogel systems offering thoroughly tunable biochemical and biophysical properties is highlighted. Potentialities of hydrogel-based approaches to address the persisting challenges of organoid technologies, namely scalability, connectivity/integration, reproducibility, parallelization, and in situ monitoring are discussed. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
- ItemSelf-Replication of Deeply Buried Doped Silicon Structures, which Remotely Control the Etching Process: A New Method for Forming a Silicon Pattern from the Bottom Up(Weinheim : Wiley-VCH, 2021) Schutzeichel, Christopher; Kiriy, Nataliya; Kiriy, Anton; Voit, BrigitteA typical microstructuring process utilizes photolithographic masks to create arbitrary patterns on silicon substrates in a top-down approach. Herein, a new, bottom-up microstructuring method is reported, which enables the patterning of n-doped silicon substrates to be performed without the need for application of etch-masks or stencils during the etching process. Instead, the structuring process developed herein involves a simple alkaline etching performed under illumination and is remotely controlled by the p-doped micro-sized implants, buried beneath a homogeneous n-doped layer at depths of 0.25 to 1 µm. The microstructuring is realized because the buried implants act upon illumination as micro-sized photovoltaic cells, which generate a flux of electrons and increase the negative surface charge in areas above the implants. The locally increased surface charge causes a local protection of the native silicon oxide layer from alkaline etching, which ultimately leads to the microstructuring of the substrate. In this way, substrates having at their top a thick layer of homogeneously n-doped silicon can be structured, reducing the need for costly, time-consuming photolithography steps. © 2021 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH
- ItemTuning the Local Availability of VEGF within Glycosaminoglycan-Based Hydrogels to Modulate Vascular Endothelial Cell Morphogenesis(Weinheim : Wiley-VCH, 2020) Limasale, Yanuar Dwi Putra; Atallah, Passant; Werner, Carsten; Freudenberg, Uwe; Zimmermann, RalfIncorporation of sulfated glycosaminoglycans (GAGs) into cell-instructive polymer networks is shown to be instrumental in controlling the diffusivity and activity of growth factors. However, a subtle balance between local retention and release of the factors is needed to effectively direct cell fate decisions. To quantitatively unravel material characteristics governing these key features, the GAG content and the GAG sulfation pattern of star-shaped poly(ethylene glycol) (starPEG)–GAG hydrogels are herein tuned to control the local availability and bioactivity of GAG-affine vascular endothelial growth factor (VEGF165). Hydrogels containing varying concentrations of heparin or heparin derivatives with different sulfation pattern are prepared and thoroughly characterized for swelling, mechanical properties, and growth factor transport. Mathematical models are developed to predict the local concentration and spatial distribution of free and bound VEGF165 within the gel matrices. The results of simulation and experimental studies concordantly reveal how the GAG concentration and sulfation pattern determine the local availability of VEGF165 within the cell-instructive hydrogels and how the factor—in interplay with cell-instructive gel properties—determines the formation and spatial organization of capillary networks of embedded human vascular endothelial cells. Taken together, this study exemplifies how mathematical modeling and rational hydrogel design can be combined to pave the way for precision tissue engineering. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
- ItemEffects of PNDIT2 end groups on aggregation, thin film structure, alignment and electron transport in field-effect transistors(London [u.a.] : RSC, 2016) Matsidik, Rukiya; Luzio, Alessandro; Hameury, Sophie; Komber, Hartmut; McNeill, Christopher R.; Caironi, Mario; Sommer, MichaelTo develop greener protocols toward the sustainable production of conjugated polymers, we combine the advantages of atom-economic direct arylation polycondensation (DAP) with those of the green solvent 2-methyltetrahydrofuran (MeTHF). The n-type copolymer PNDIT2 is synthesized from unsubstituted bithiophene (T2) and 2,6-dibromonapthalene diimide (NDIBr2) under simple DAP conditions in MeTHF. Extensive optimization is required to suppress nucleophilic substitution of NDIBr end groups, which severely limits molar mass. Different carboxylic acids, bases, palladium precursors and ligands are successfully screened to enable quantitative yield and satisfyingly high molar masses up to Mn,SEC ∼ 20 kDa. In contrast to PNDIT2 made via DAP in toluene with tolyl-chain termini, nucleophilic substitution of NDIBr chain ends in MeTHF finally leads to NDI-OH termination. The influence of different chain termini on the optical, thermal, structural and electronic properties of PNDIT2 is investigated. For samples with identical molecular weight, OH-termination leads to slightly reduced aggregation in solution and bulk crystallinity, a decreased degree of alignment in directionally deposited films, and a consequently reduced, but not compromised, electron mobility with promising values still close to 0.9 cm2 V−1 s−1.
- ItemOn the anomalous optical conductivity dispersion of electrically conducting polymers: Ultra-wide spectral range ellipsometry combined with a Drude-Lorentz model(London [u.a.] : RSC, 2019) Chen, Shangzhi; Kühne, Philipp; Stanishev, Vallery; Knight, Sean; Brooke, Robert; Petsagkourakis, Ioannis; Crispin, Xavier; Schubert, Mathias; Darakchieva, Vanya; Jonsson, Magnus P.Electrically conducting polymers (ECPs) are becoming increasingly important in areas such as optoelectronics, biomedical devices, and energy systems. Still, their detailed charge transport properties produce an anomalous optical conductivity dispersion that is not yet fully understood in terms of physical model equations for the broad range optical response. Several modifications to the classical Drude model have been proposed to account for a strong non-Drude behavior from terahertz (THz) to infrared (IR) ranges, typically by implementing negative amplitude oscillator functions to the model dielectric function that effectively reduce the conductivity in those ranges. Here we present an alternative description that modifies the Drude model via addition of positive-amplitude Lorentz oscillator functions. We evaluate this so-called Drude-Lorentz (DL) model based on the first ultra-wide spectral range ellipsometry study of ECPs, spanning over four orders of magnitude: from 0.41 meV in the THz range to 5.90 eV in the ultraviolet range, using thin films of poly(3,4-ethylenedioxythiophene):tosylate (PEDOT:Tos) as a model system. The model could accurately fit the experimental data in the whole ultrawide spectral range and provide the complex anisotropic optical conductivity of the material. Examining the resonance frequencies and widths of the Lorentz oscillators reveals that both spectrally narrow vibrational resonances and broader resonances due to localization processes contribute significantly to the deviation from the Drude optical conductivity dispersion. As verified by independent electrical measurements, the DL model accurately determines the electrical properties of the thin film, including DC conductivity, charge density, and (anisotropic) mobility. The ellipsometric method combined with the DL model may thereby become an effective and reliable tool in determining both optical and electrical properties of ECPs, indicating its future potential as a contact-free alternative to traditional electrical characterization. © The Royal Society of Chemistry 2019.