44 research outputs found
“Conformational Self-Recognition as the Origin of Dewetting in Bistable Molecular Surfaces”
No full textInfluence of Sr on the Microstructure of Aluminium–Silicon Alloys
No full textDie Zugabe von Strontium in geringen Mengen von 80–120 ppm Sr ändert die dreidimensionale (3-D) Morphologie der eutektischen Si-Phase in Al–Si Gusslegierungen von groben plattenförmigen zu feinen faserförmigen Netzwerken. Der Übergang von Si-Platten zu Si-Fasern ist allgemein bekannt als sog. chemische Veredelung der eutektischen Mikrostruktur. Um diesen industriell wichtigen, aber bislang unzureichend aufgeklärten Veredelungseffekt zu verstehen, wurden unveredelte und Sr-veredelte Al–Si Gusslegierungen der Zusammensetzungen Al–10 Gew.% Si–0,10 Gew.% Fe (200 ppm Sr) und Al–15 Gew.% Si–0,17 Gew.% Fe (60 ppm Sr) vom Millimeter- bis in den atomaren Bereich untersucht. Der Einfluss des Sr auf die Bildung Fe-reicher Phasen innerhalb der eutektischen Körner wurde mittels Lichtmikroskopie, Rasterelektronen- und Transmissionselektronenmikroskopie umfangreich untersucht. Es wurden fein-verteilte Fe-reiche α-Phasen in den unveredelten Al–Si Legierungen vorgefunden, während zwei Typen Fe-reicher Phasen (α und δ) in den Sr-veredelten Al-Si Legierungen beobachtet wurden. Die 3-D Morphologie der eutektischen Si-Phase und der Fe-reichen Phasen wurde mittels Tomographie mit fokussierten Ionenstrahlen dargestellt. In den Sr-veredelten Al–Si Legierungen wurde beobachtet, dass sich die Fe-reiche α-Phasen als Einschlüsse an den eutektischen Zellgrenzen mit der 3-D Morphologie dünner "Blätter" ausbildet, während die Fe-reiche δ-Phase eine dünne (≤ 250 nm) plättchenförmige 3-D Morphologie aufweist. Die Entwicklung der Morphologie der eutektischen Erstarrungsfront sowie die Verteilung der Fe-reichen Phasen innerhalb der eutektischen Körner werden detailliert beschrieben. Die Verteilung von Sr wurde sowohl mit nm-Auflösung mittels Transmissionselektronenmikroskopie als auch mit atomarer Auflösung mittels tomographischer Atomsonde untersucht. Die kombinierten Untersuchungen zeigen, dass Sr gemeinsam mit Al innerhalb der eutektischen Si-Phase angereichert vorliegt und dabei zwei Typen von Sr–Al–Si Anreicherungen ausbildet. Typ I-Anreicherungen mit stabförmiger 3-D Morphologie liegen in Bereichen hoher Zwillingsdichte an den Entstehungspunkten von koaxialen Zwillingsebenen vor. Diese Typ I-Anreicherungen sind für die hohe Zwillingsdichte in den Si-Fasern verantwortlich. Typ II-Anreicherungen mit annähernd stabförmiger, langgestreckter 3-D Morphologie liegen entlang interner Grenzflächen von zwei leicht unterschiedlich orientierten Si-Fasersegmenten vor. Diese Typ II-Anreicherungen führen zur Verzweigung der Si-Fasern während der eutektischen Erstarrung. In der vorliegenden Arbeit wird gezeigt, wie Sr zwei der in der Literatur bereits vorgeschlagenen Mechanismen ermöglicht, nämlich verstärkte Zwillingsbildung (Impurity Induced Twinning, via Typ I) und gehemmtes Wachstum (Restricted Growth, via Typ II).Addition of strontium as small as 80–120 ppm Sr changes the three-dimensional (3-D) morphology of the eutectic Si phase present in Al–Si casting alloys from coarse plate-like to fine fibrous networks. The transition from Si plates to Si fibres is well known as chemical modification of the eutectic microstructure. In order to understand this industrially important but hitherto insufficiently clarified modification effect, unmodified and Sr-modified Al–Si casting alloys with compositions Al–10 wt.% Si–0.10 wt.% Fe (200 ppm Sr) and Al–15 wt.% Si–0.17 wt.% Fe (60 ppm Sr) were investigated in the range from micrometric to atomic scale. The influence of Sr on the formation of Fe-rich phases within eutectic grains was extensively studied by optical microscopy, scanning electron and transmission electron microscopy. Finely distributed Fe-rich α-phases were observed in the unmodified alloys, whereas two types of Fe-rich phases (α and δ) were found in the Sr-modified Al–Si alloys the existence of. The 3-D morphology of the eutectic Si phase and the Fe-rich phases was visualised by focused ion beam tomography. The Fe-rich α-phase was found to form as 3-D "sheet"-like inclusions at eutectic cell boundaries, whereas the Fe-rich δ-phase solidifies as thin (≤ 250 nm) platelets. The evolution of the morphology of the eutectic solidification front and the distribution of Fe-rich phases within the eutectic grains are described in detail. The distribution of Sr was studied both with nanometric resolution by transmission electron microscopy and with atomic resolution by atom probe tomography. The combined investigations indicate that Sr co-segregates with Al within the eutectic Si phase and forms two types of Sr–Al–Si co-segregations. Type I co-segregations with a rod-like 3-D morphology are located in regions of high twin density at the origin of co-axial twin planes. They are responsible for the high twin density in Si fibres. Type II co-segregations with a more extended rod-like 3-D morphology are located at internal boundaries between two slightly differently oriented Si fibre sections. They control the branching of the eutectic Si fibres during eutectic solidification. The present work shows how Sr enables both kinds of mechanisms previously postulated in the literature, namely "Impurity Induced Twinning" (via type I) and "Restricted Growth" (via type II)
Ionized Jet Deposition of MoS2 on Gas Diffusion Layer Electrodes for Next Generation Alkaline Electrolyzers
No full textThis study focuses on optimizing MoS2 catalysts for the hydrogen evolution reaction (HER) in anion exchange membrane (AEM) electrolyzers. A scalable Ionized Jet Deposition (IJD) technique is employed to deposit MoS2 onto various carbon supports, exploring the relationship between substrate properties and catalytic performance. The results demonstrate that substrate choice plays a pivotal role in enhancing HER activity and durability. MoS2 deposited on Freudenberg carbon support exhibited the best catalytic activity, achieving a current density of 10 mA mu g(-)(1)Mo at -0.48 V versus RHE in an alkaline environment, even with a low catalyst loading (12-49 mu g cm(-)(2)). Conversely, sulfur-doped carbon supports showed lower HER activity but superior stability, with a minimal voltage degradation of just 0.025 V after 6 h of testing at 10 mA cm(-)(2). To further understand these results, bubble evolution studies, and contact angle measurements are conducted. Stable electrodes demonstrated small contact angles and enhanced bubble release from the surface, indicating the importance of hydrophilicity in improving performance and durability. This work highlights the synergy between scalable synthesis techniques and substrate optimization, offering a promising path for advancing cost-efficient, durable electrocatalysts in large-scale AEM electrolyzers for green hydrogen production
Correction: Functionalization of SiC/SiOX nanowires with a porphyrin derivative: A hybrid nanosystem for X-ray induced singlet oxygen generation (Molecular Systems Design and Engineering (2017) DOI: 10.1039/c7me00005g)
No full textThe authors regret an error in the name of the 5th author which was incorrectly shown as R. Rossi instead of F. Rossi. The corrected list of authors and affiliations for this paper is shown here. The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers
Wirksamkeit einer gamification-basierten Smartphone-Applikation zur Gewichtsreduzierung bei Kindern und Jugendlichen mit Übergewicht und Adipositas- Studienprotokoll für eine randomisierte kontrollierte Studie
No full textDie Evaluation des Risiko-Ertrags-Profils von Aktienpositionen mit Optionen auf der Grundlage des Shortfall-Ansatzes
No full textAvailable from Bibliothek des Instituts fuer Weltwirtschaft, ZBW, D-21400 Kiel C 208276 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman
Tuning the Work Function of Graphene-on-Quartz with a High Weight Molecular Acceptor
No full textUltraviolet and X-ray photoelectron spectroscopies in combi- nation with density functional theory (DFT) calculations were used to study the change in the work function (Φ) of graphene, supported by quartz, as induced by adsorption of hexaazatriphenylene−hexacarbonitrile (HATCN). Near edge X-ray absorption fine structure spectroscopy (NEXAFS) and DFT modeling show that a molecular-density-dependent reorientation of HATCN from a planar to a vertically inclined adsorption geometry occurs upon increasing surface coverage. This, in conjunction with the orientation- dependent magnitude of the interface dipole, allows one to explain the evolution of graphene Φ from 4.5 eV up to 5.7 eV, rendering the molecularly modified graphene-on-quartz a highly suitable hole injection electrode
Tuning the Electronic Structure of Graphene by Molecular Dopants: Impact of the Substrate
No full textA combination of ultraviolet and X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and first principle calculations was used to study the electronic structure at the interface between the strong molecular acceptor 1,3,4,5,7,8-hexafluorotetracyano-naphthoquinodimethane (F6TCNNQ) and a graphene layer supported on either a quartz or a copper substrate. We find evidence for fundamentally different charge redistribution mechanisms in the two ternary systems, as a consequence of the insulating versus metallic character of the substrates. While electron transfer occurs exclusively from graphene to F6TCNNQ on the quartz support (p-doping of graphene), the Cu substrate electron reservoir induces an additional electron density flow to graphene decorated with the acceptor monolayer. Remarkably, graphene on Cu is n-doped and remains n-doped upon F6TCNNQ deposition. On both substrates, the work function of graphene increases substantially with a F6TCNNQ monolayer atop, the effect being more pronounced (∼1.3 eV) on Cu compared to quartz (∼1.0 eV) because of the larger electrostatic potential drop associated with the long-distance graphene-mediated Cu-F6TCNNQ electron transfer. We thus provide a means to realize high work function surfaces for both p- and n-type doped graphene
Distribution of Fe rich phases in eutectic grains of Sr modified Al 10 wt. Si 0.1 wt. Fe casting alloy
No full textThe addition of Sr to Al Si based alloys is known to modify the morphology of the eutectic Si phase and to influence the nucleation of eutectic grains. Understanding the distribution and the morphology of small constituent phases in eutectic grains such as Fe rich intermetallic phases can further yield an insight into the cellular substructure of eutectic grains formed during solidification. The addition of 200 ppm Sr to an Al 10Si 0.1Fe alloy and its influence on the formation of Fe rich phases was comprehensively studied by several microscopy techniques. Optical microscopy combined with scanning electron microscopy revealed the existence of two types of Fe rich phases at cell boundaries of eutectic grains. The Fe rich phases were identified as a Al14Fe3Si2 and d Al4FeSi2 by transmission electron microscopy. Both Fe rich phases are located at distinct regions in the eutectic grain, namely in the transition region region 2 aphase and the outer region region 3 d phase of the eutectic grain. The three dimensional morphology of the eutectic Si phase and the Fe rich phases at the eutectic cell boundaries was investigated by focused ion beam tomography. The Fe rich a phase was found to form concentrated networks with the 3D morphology of sheets , whereas the Fe rich d phases exist as thin platelets. The distribution of Fe rich phases in the cellular substructure of eutectic grains are described on the basis of the evolution of the eutectic solidification front by a qualitative solidification mode
