56 results
Search Results
Now showing 1 - 10 of 56
- ItemTiOx/Pt3Ti(111) surface-directed formation of electronically responsive supramolecular assemblies of tungsten oxide clusters(Frankfurt, M. : Beilstein-Institut zur Förderung der Chemischen Wissenschaften, 2021) Moors, Marco; An, Yun; Kuc, Agnieszka; Monakhov, Kirill YuHighly ordered titanium oxide films grown on a Pt3Ti(111) alloy surface were utilized for the controlled immobilization and tip-induced electric field-triggered electronic manipulation of nanoscopic W3O9 clusters. Depending on the operating conditions, two different stable oxide phases, z'-TiO x and w'-TiO x , were produced. These phases show a strong effect on the adsorption characteristics and reactivity of W3O9 clusters, which are formed as a result of thermal evaporation of WO3 powder on the complex TiO x /Pt3Ti(111) surfaces under ultra-high vacuum conditions. The physisorbed tritungsten nano-oxides were found as isolated single units located on the metallic attraction points or as supramolecular self-assemblies with a W3O9-capped hexagonal scaffold of W3O9 units. By applying scanning tunneling microscopy to the W3O9-(W3O9)6 structures, individual units underwent a tip-induced reduction to W3O8. At elevated temperatures, agglomeration and growth of large WO3 islands, which thickness is strongly limited to a maximum of two unit cells, were observed. The findings boost progress toward template-directed nucleation, growth, networking, and charge state manipulation of functional molecular nanostructures on surfaces using operando techniques.
- ItemAnalysis of catalyst surface wetting: The early stage of epitaxial germanium nanowire growth(Frankfurt, M. : Beilstein-Institut zur Förderung der Chemischen Wissenschaften, 2020) Ernst, Owen C.; Lange, Felix; Uebel, David; Teubner, Thomas; Boeck, TorstenThe dewetting process is crucial for several applications in nanotechnology. Even though not all dewetting phenomena are fully understood yet, especially regarding metallic fluids, it is clear that the formation of nanometre-sized particles, droplets, and clusters as well as their movement are strongly linked to their wetting behaviour. For this reason, the thermodynamic stability of thin metal layers (0.1-100 nm) with respect to their free energy is examined here. The decisive factor for the theoretical considerations is the interfacial energy. In order to achieve a better understanding of the interfacial interactions, three different models for estimating the interfacial energy are presented here: (i) fully theoretical, (ii) empirical, and (iii) semi-empirical models. The formation of nanometre-sized gold particles on silicon and silicon oxide substrates is investigated in detail. In addition, the strengths and weaknesses of the three models are elucidated, the different substrates used are compared, and the possibility to further process the obtained particles as nanocatalysts is verified. The importance of a persistent thin communication wetting layer between the particles and its effects on particle size and number is also clarified here. In particular, the intrinsic reduction of the Laplace pressure of the system due to material re-evaporation and Ostwald ripening describes the theoretically predicted and experimentally obtained results. Thus, dewetting phenomena of thin metal layers can be used to manufacture nanostructured devices. From this point of view, the application of gold droplets as catalysts to grow germanium nanowires on different substrates is described. © 2020 Ernst et al.
- ItemAtomic layer deposition for efficient oxygen evolution reaction at Pt/Ir catalyst layers(Frankfurt, M. : Beilstein-Institut zur Förderung der Chemischen Wissenschaften, 2020) Schlicht, Stefanie; Percin, Korcan; Kriescher, Stefanie; Hofer, André; Weidlich, Claudia; Wessling, Matthias; Bachmann, JulienWe provide a direct comparison of two distinct methods of Ti felt surface treatment and Pt/Ir electrocatalyst deposition for the positive electrode of regenerative fuel cells and vanadium-air redox flow batteries. Each method is well documented in the literature, and this paper provides a direct comparison under identical experimental conditions of electrochemical measurements and in identical units. In the first method, based on classical engineering, the bimetallic catalyst is deposited by dip-coating in a precursor solution of the salts followed by their thermal decomposition. In the alternative method, more academic in nature, atomic layer deposition (ALD) is applied to the felts after anodization. ALD allows for a controlled coating with ultralow noble-metal loadings in narrow pores. In acidic electrolyte, the ALD approach yields improved mass activity (557 A·g-1 as compared to 80 A·g-1 at 0.39 V overpotential) on the basis of the noble-metal loading, as well as improved stability. © 2020 Schlicht et al.
- ItemThe patterning toolbox FIB-o-mat: Exploiting the full potential of focused helium ions for nanofabrication(Frankfurt, M. : Beilstein-Institut zur Förderung der Chemischen Wissenschaften, 2021) Deinhart, Victor; Kern, Lisa-Marie; Kirchhof, Jan N.; Juergensen, Sabrina; Sturm, Joris; Krauss, Enno; Feichtner, Thorsten; Kovalchuk, Sviatoslav; Schneider, Michael; Engel, Dieter; Pfau, Bastian; Hecht, Bert; Bolotin, Kirill I.; Reich, Stephanie; Höflich, KatjaFocused beams of helium ions are a powerful tool for high-fidelity machining with spatial precision below 5 nm. Achieving such a high patterning precision over large areas and for different materials in a reproducible manner, however, is not trivial. Here, we introduce the Python toolbox FIB-o-mat for automated pattern creation and optimization, providing full flexibility to accomplish demanding patterning tasks. FIB-o-mat offers high-level pattern creation, enabling high-fidelity large-area patterning and systematic variations in geometry and raster settings. It also offers low-level beam path creation, providing full control over the beam movement and including sophisticated optimization tools. Three applications showcasing the potential of He ion beam nanofabrication for two-dimensional material systems and devices using FIB-o-mat are presented.
- ItemBuilding Hierarchical Martensite(Weinheim : Wiley-VCH, 2020) Schwabe, Stefan; Niemann, Robert; Backen, Anja; Wolf, Daniel; Damm, Christine; Walter, Tina; Seiner, Hanuš; Heczko, Oleg; Nielsch, Kornelius; Fähler, SebastianMartensitic materials show a complex, hierarchical microstructure containing structural domains separated by various types of twin boundaries. Several concepts exist to describe this microstructure on each length scale, however, there is no comprehensive approach bridging the whole range from the nano- up to the macroscopic scale. Here, it is described for a Ni-Mn-based Heusler alloy how this hierarchical microstructure is built from scratch with just one key parameter: the tetragonal distortion of the basic building block at the atomic level. Based on this initial block, five successive levels of nested building blocks are introduced. At each level, a larger building block is formed by twinning the preceding one to minimize the relevant energy contributions locally. This naturally explains the coexistence of different types of twin boundaries. The scale-bridging approach of nested building blocks is compared with experiments in real and reciprocal space. The approach of nested building blocks is versatile as it can be applied to the broad class of functional materials exhibiting diffusionless transformations. © 2020 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH
- ItemCell-Instructive Multiphasic Gel-in-Gel Materials(Weinheim : Wiley-VCH, 2020) Kühn, Sebastian; Sievers, Jana; Stoppa, Aukha; Träber, Nicole; Zimmermann, Ralf; Welzel, Petra B.; Werner, CarstenDeveloping tissue is typically soft, highly hydrated, dynamic, and increasingly heterogeneous matter. Recapitulating such characteristics in engineered cell-instructive materials holds the promise of maximizing the options to direct tissue formation. Accordingly, progress in the design of multiphasic hydrogel materials is expected to expand the therapeutic capabilities of tissue engineering approaches and the relevance of human 3D in vitro tissue and disease models. Recently pioneered methodologies allow for the creation of multiphasic hydrogel systems suitable to template and guide the dynamic formation of tissue- and organ-specific structures across scales, in vitro and in vivo. The related approaches include the assembly of distinct gel phases, the embedding of gels in other gel materials and the patterning of preformed gel materials. Herein, the capabilities and limitations of the respective methods are summarized and discussed and their potential is highlighted with some selected examples of the recent literature. As the modularity of the related methodologies facilitates combinatorial and individualized solutions, it is envisioned that multiphasic gel-in-gel materials will become a versatile morphogenetic toolbox expanding the scope and the power of bioengineering technologies. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
- ItemRobust Single Molecule Magnet Monolayers on Graphene and Graphite with Magnetic Hysteresis up to 28 K(Weinheim : Wiley-VCH, 2021) Spree, Lukas; Liu, Fupin; Neu, Volker; Rosenkranz, Marco; Velkos, Georgios; Wang, Yaofeng; Schiemenz, Sandra; Dreiser, Jan; Gargiani, Pierluigi; Valvidares, Manuel; Chen, Chia-Hsiang; Büchner, Bernd; Avdoshenko, Stanislav M.; Popov, Alexey A.The chemical functionalization of fullerene single molecule magnet Tb2@C80(CH2Ph) enables the facile preparation of robust monolayers on graphene and highly oriented pyrolytic graphite from solution without impairing their magnetic properties. Monolayers of endohedral fullerene functionalized with pyrene exhibit magnetic bistability up to a temperature of 28 K. The use of pyrene terminated linker molecules opens the way to devise integration of spin carrying units encapsulated by fullerene cages on graphitic substrates, be it single-molecule magnets or qubit candidates. © 2021 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH
- ItemPerovskite Origami for Programmable Microtube Lasing(Weinheim : Wiley-VCH, 2021) Dong, Haiyun; Saggau, Christian Niclaas; Zhu, Minshen; Liang, Jie; Duan, Shengkai; Wang, Xiaoyu; Tang, Hongmei; Yin, Yin; Wang, Xiaoxia; Wang, Jiawei; Zhang, Chunhuan; Zhao, Yong Sheng; Ma, Libo; Schmidt, Oliver G.Metal halide perovskites are promising materials for optoelectronic and photonic applications ranging from photovoltaics to laser devices. However, current perovskite devices are constrained to simple low-dimensional structures suffering from limited design freedom and holding up performance improvement and functionality upgrades. Here, a micro-origami technique is developed to program 3D perovskite microarchitectures toward a new type of microcavity laser. The design flexibility in 3D supports not only outstanding laser performance such as low threshold, tunable output, and high stability but also yields new functionalities like 3D confined mode lasing and directional emission in, for example, laser “array-in-array” systems. The results represent a significant step forward toward programmable microarchitectures that take perovskite optoelectronics and photonics into the 3D era. © 2021 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH.
- ItemSemitransparent Perovskite Solar Cells with an Evaporated Ultra-Thin Perovskite Absorber(Weinheim : Wiley-VCH, 2023) Zhang, Zongbao; Ji, Ran; Jia, Xiangkun; Wang, Shu‐Jen; Deconinck, Marielle; Siliavka, Elena; Vaynzof, YanaMetal halide perovskites are of great interest for application in semitransparent solar cells due to their tunable bandgap and high performance. However, fabricating high-efficiency perovskite semitransparent devices with high average visible transmittance (AVT) is challenging because of their high absorption coefficient. Here, a co-evaporation process is adopted to fabricate ultra-thin CsPbI3 perovskite films. The smooth surface and orientated crystal growth of the evaporated perovskite films make it possible to achieve 10 nm thin films with compact and continuous morphology without pinholes. When integrated into a p-i-n device structure of glass/ITO/PTAA/perovskite/PCBM/BCP/Al/Ag with an optimized transparent electrode, these ultra-thin layers result in an impressive open-circuit voltage (VOC) of 1.08 V and a fill factor (FF) of 80%. Consequently, a power conversion efficiency (PCE) of 3.6% with an AVT above 50% is demonstrated, which is the first report for a perovskite device of a 10 nm active layer thickness with high VOC, FF and AVT. These findings demonstrate that deposition by thermal evaporation makes it possible to form compact ultra-thin perovskite films, which are of great interest for future smart windows, light-emitting diodes, and tandem device applications.
- ItemTuning the Volume Phase Transition Temperature of Microgels by Light(Weinheim : Wiley-VCH, 2021) Jelken, Joachim; Jung, Se-Hyeong; Lomadze, Nino; Gordievskaya, Yulia D.; Kramarenko, Elena Yu.; Pich, Andrij; Santer, SvetlanaTemperature-responsive microgels find widespread applications as soft materials for designing actuators in microfluidic systems, as carriers for drug delivery or catalysts, as functional coatings, and as adaptable sensors. The key property is their volume phase transition temperature, which allows for thermally induced reversible swelling/deswelling. It is determined by the gel's chemical structure as well as network topology and cannot be varied easily within one system. Here a paradigm change of this notion by facilitating a light-triggered reversible switching of the microgel volume in the range between 32 and 82 °C is suggested. Photo-sensitivity is introduced by photosensitive azobenzene containing surfactant, which forms a complex with microgels consisting of poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAM-AAc) chains when assuming a hydrophobic trans-state, and prefers to leave the gel matrix in its cis-state. Using a similar strategy, it is demonstrated that at a fixed temperature, for example, 37 °C, one can reversibly change the microgel radius by a factor of 3 (7–21 µm) by irradiating either with UV (collapsed state) or green light (swollen state). It is envisaged that the possibility to deploy a swift external means of adapting the swelling behavior of microgels may impact and redefine the latter's application across all fields. © 2021 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH