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- ItemLarge-area wet-chemical deposition of nanoporous tungstic silica coatings(London [u.a.] : RSC, 2015) Nielsen, K.H.; Wondraczek, K.; Schubert, U.S.; Wondraczek, L.We report on a facile procedure for synthesis of nanoporous coatings of tungstic silica through wet-chemical deposition and post-treatment of tungsten-doped potassium silicate solutions. The process relies on an aqueous washing and ion exchange step where dispersed potassium salt deposits are removed from a 150 nm silicate gel layer. Through an adjustment of the pH value of the washing agent within the solubility regime of a tungstic salt precursor, the tungsten content of the remaining nanostructured coating can be controlled. We propose this route as a universal approach for the deposition of large-area coatings of nanoporous silica with the potential for incorporating a broad variety of other dopant species. As for the present case, we observe, on the one hand, antireflective properties which enable the reduction of reflection losses from float glass by up to 3.7 percent points. On the other hand, the incorporation of nanoscale tungstic precipitates provides a lever for tailoring the coating hydrophilicity and, eventually, also surface acidity. This may provide a future route for combining optical performance with anti-fouling functionality.
- Item1D p–n Junction Electronic and Optoelectronic Devices from Transition Metal Dichalcogenide Lateral Heterostructures Grown by One-Pot Chemical Vapor Deposition Synthesis(Weinheim : Wiley-VCH, 2021) Najafidehaghani, Emad; Gan, Ziyang; George, Antony; Lehnert, Tibor; Ngo, Gia Quyet; Neumann, Christof; Bucher, Tobias; Staude, Isabelle; Kaiser, David; Vogl, Tobias; Hübner, Uwe; Kaiser, Ute; Eilenberger, Falk; Turchanin, AndreyLateral heterostructures of dissimilar monolayer transition metal dichalcogenides provide great opportunities to build 1D in-plane p–n junctions for sub-nanometer thin low-power electronic, optoelectronic, optical, and sensing devices. Electronic and optoelectronic applications of such p–n junction devices fabricated using a scalable one-pot chemical vapor deposition process yielding MoSe2-WSe2 lateral heterostructures are reported here. The growth of the monolayer lateral heterostructures is achieved by in situ controlling the partial pressures of the oxide precursors by a two-step heating protocol. The grown lateral heterostructures are characterized structurally and optically using optical microscopy, Raman spectroscopy/microscopy, and photoluminescence spectroscopy/microscopy. High-resolution transmission electron microscopy further confirms the high-quality 1D boundary between MoSe2 and WSe2 in the lateral heterostructure. p–n junction devices are fabricated from these lateral heterostructures and their applicability as rectifiers, solar cells, self-powered photovoltaic photodetectors, ambipolar transistors, and electroluminescent light emitters are demonstrated. © 2021 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH
- ItemPhotodoping and Fast Charge Extraction in Ionic Carbon Nitride Photoanodes(Weinheim : Wiley-VCH, 2021) Adler, Christiane; Selim, Shababa; Krivtsov, Igor; Li, Chunyu; Mitoraj, Dariusz; Dietzek, Benjamin; Durrant, James R.; Beranek, RadimIonic carbon nitrides based on poly(heptazine imides) (PHI) represent a vigorously studied class of materials with possible applications in photocatalysis and energy storage. Herein, for the first time, the photogenerated charge dynamics in highly stable and binder-free PHI photoanodes using in operando transient photocurrents and spectroelectrochemical photoinduced absorption measurements is studied. It is discovered that light-induced accumulation of long-lived trapped electrons within the PHI film leads to effective photodoping of the PHI film, resulting in a significant improvement of photocurrent response due to more efficient electron transport. While photodoping is previously reported for various semiconductors, it has not been shown before for carbon nitride materials. Furthermore, it is found that the extraction kinetics of untrapped electrons are remarkably fast in these PHI photoanodes, with electron extraction times (ms) comparable to those measured for commonly employed metal oxide semiconductors. These results shed light on the excellent performance of PHI photoanodes in alcohol photoreforming, including very negative photocurrent onset, outstanding fill factor, and the possibility to operate under zero-bias conditions. More generally, the here reported photodoping effect and fast electron extraction in PHI photoanodes establish a strong rationale for the use of PHI films in various applications, such as bias-free photoelectrochemistry or photobatteries. © 2021 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH
- ItemMerging Top-Down and Bottom-Up Approaches to Fabricate Artificial Photonic Nanomaterials with a Deterministic Electric and Magnetic Response(Weinheim : Wiley-VCH Verlag, 2020) Dietrich K.; Zilk M.; Steglich M.; Siefke T.; Hübner U.; Pertsch T.; Rockstuhl C.; Tünnermann A.; Kley E.-B.Artificial photonic nanomaterials made from densely packed scatterers are frequently realized either by top-down or bottom-up techniques. While top-down techniques offer unprecedented control over achievable geometries for the scatterers, by trend they suffer from being limited to planar and periodic structures. In contrast, materials fabricated with bottom-up techniques do not suffer from such disadvantages but, unfortunately, they offer only little control on achievable geometries for the scatterers. To overcome these limitations, a nanofabrication strategy is introduced that merges both approaches. A large number of scatterers are fabricated with a tailored optical response by fast character projection electron-beam lithography and are embedded into a membrane. By peeling-off this membrane from the substrate, scrambling, and densifying it, a bulk material comprising densely packed and randomly arranged scatterers is obtained. The fabrication of an isotropic material from these scatterers with a strong electric and magnetic response is demonstrated. The approach of this study unlocks novel opportunities to fabricate nanomaterials with a complex optical response in the bulk but also on top of arbitrarily shaped surfaces. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim