Browsing by Author "Karg, Matthias"
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- ItemMechanotunable Plasmonic Properties of Colloidal Assemblies(Weinheim : Wiley-VCH, 2020) Brasse, Yannic; Gupta, Vaibhav; Schollbach, H.C. Tomohiro; Karg, Matthias; König, Tobias A.F.; Fery, AndreasNoble metal nanoparticles can absorb incident light very efficiently due to their ability to support localized surface plasmon resonances (LSPRs), collective oscillations of the free electron cloud. LSPRs lead to strong, nanoscale confinement of electromagnetic energy which facilitates applications in many fields including sensing, photonics, or catalysis. In these applications, damping of the LSPR caused by inter- and intraband transitions is a limiting factor due to the associated energy losses and line broadening. The losses and broad linewidth can be mitigated by arranging the particles into periodic lattices. Recent advances in particle synthesis, (self-)assembly, and fabrication techniques allow for the realization of collective coupling effects building on various particle sizes, geometries, and compositions. Beyond assemblies on static substrates, by assembling or printing on mechanically deformable surfaces a modulation of the lattice periodicity is possible. This enables significant alteration and tuning of the optical properties. This progress report focuses on this novel approach for tunable spectroscopic properties with a particular focus on low-cost and large-area fabrication techniques for functional plasmonic lattices. The report concludes with a discussion of the perspectives for expanding the mechanotunable colloidal concept to responsive structures and flexible devices. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
- ItemMulti-shell hollow nanogels with responsive shell permeability([London] : Macmillan Publishers Limited, part of Springer Nature, 2016) Schmid, Andreas J.; Dubbert, Janine; Rudov, Andrey A.; Pedersen, Jan Skov; Lindner, Peter; Karg, Matthias; Potemkin, Igor I.; Richtering, WalterWe report on hollow shell-shell nanogels with two polymer shells that have different volume phase transition temperatures. By means of small angle neutron scattering (SANS) employing contrast variation and molecular dynamics (MD) simulations we show that hollow shell-shell nanocontainers are ideal systems for controlled drug delivery: The temperature responsive swelling of the inner shell controls the uptake and release, while the thermoresponsive swelling of the outer shell controls the size of the void and the colloidal stability. At temperatures between 32 °C < T < 42 °C, the hollow nanocontainers provide a significant void, which is even larger than the initial core size of the template and they possess a high colloidal stability due to the steric stabilization of the swollen outer shell. Computer simulations showed, that temperature induced switching of the permeability of the inner shell allows for the encapsulation in and release of molecules from the cavity.
- ItemPlasmonic nanomeshes: Their ambivalent role as transparent electrodes in organic solar cells(London : Nature Publishing Group, 2017) Stelling, Christian; Singh, Chetan R.; Karg, Matthias; König, Tobias A.F.; Thelakkat, Mukundan; Retsch, MarkusIn this contribution, the optical losses and gains attributed to periodic nanohole array electrodes in polymer solar cells are systematically studied. For this, thin gold nanomeshes with hexagonally ordered holes and periodicities (P) ranging from 202 nm to 2560 nm are prepared by colloidal lithography. In combination with two different active layer materials (P3HT:PC 61 BM and PTB7:PC 71 BM), the optical properties are correlated with the power conversion efficiency (PCE) of the solar cells. A cavity mode is identified at the absorption edge of the active layer material. The resonance wavelength of this cavity mode is hardly defined by the nanomesh periodicity but rather by the absorption of the photoactive layer. This constitutes a fundamental dilemma when using nanomeshes as ITO replacement. The highest plasmonic enhancement requires small periodicities. This is accompanied by an overall low transmittance and high parasitic absorption losses. Consequently, larger periodicities with a less efficient cavity mode, yet lower absorptive losses were found to yield the highest PCE. Nevertheless, ITO-free solar cells reaching ∼77% PCE compared to ITO reference devices are fabricated. Concomitantly, the benefits and drawbacks of this transparent nanomesh electrode are identified, which is of high relevance for future ITO replacement strategies.