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Layered α-TiCl₃: Microsheets on YSZ Substrates for Ethylene Polymerization with Enhanced Activity
(2019)
The transition metal halide α-titanium(III) chloride (α-TiCl₃) is a layered two-dimensional compound and a well-established Ziegler–Natta catalyst for the polymerization of ethylene. A new synthesis technique is used to obtain thin sheets of α-TiCl₃ that show exceptional physical properties in contrast to their bulk counterparts, due to an enlarged surface-to-volume ratio. Chemical vapor transport (CVT) of α-titanium(III) chloride directly on substrates results in microsheets that exhibit an improved catalytic effect. For rational planning of synthesis conditions, thermodynamic simulations of occurring gas-phase equilibria were performed. Based on these calculation results, crystal growth was achieved by adding GaCl₃via pure short term CVT in a temperature gradient of 700–600 K on yttrium-stabilized zirconia (YSZ) substrates. Phase pure, as-grown, single crystal sheets with high crystallinity and a thickness of around 4 μm were obtained. These thin sheets of α-TiCl₃ on YSZ substrates were implemented as catalysts for the ethylene polymerization reaction. A significant improvement of catalytic activity of 16% was achieved, probably due to an increased surface-to-volume ratio. As a highlight, the as-grown microsheets were exfoliated subsequently to a thickness lower than 200 nm and an even higher catalytic activity of up to 24% was confirmed experimentally due to delamination effects. This is the first time that an improved catalytic effect of α-TiCl₃ is observed as a result of downscaling from bulk to microsheets by CVT.
2D layered honeycomb magnet α-ruthenium(III) chloride (α-RuCl3) is a promising candidate to realize a Kitaev spin model. As alteration of physical properties on the nanoscale is additionally intended, new synthesis approaches to obtain phase pure α-RuCl3 nanocrystals have been audited. Thermodynamic simulations of occurring gas phase equilibria were performed and optimization of synthesis conditions was achieved based on calculation results. Crystal growth succeeded via chemical vapor transport (CVT) in a temperature gradient of 973 K to 773 K on YSZ substrates. Single crystal sheets of high crystallinity with heights ≤ 30 nm were obtained via pure CVT. The crystal properties were characterized by means of optical and electron microscopy, AFM, SAED, micro-Raman and XPS proving their composition, morphology, crystallinity and phase-purity. A highlight of our study is the successful individualization of nanocrystals and the delamination of nanosheets on YSZ substrates down to the monolayer limit (≤ 1 nm) which was realized by means of substrate exfoliation and ultrasonication in a very reproducible way.
Alpha-molybdenum(III) chloride (MoCl₃) belongs to layered van-der-Waals materials, which are in focus to exhibit interesting properties due to their weak chemical and magnetic interactions. Especially the structure of alpha-MoCl₃ has been discussed in terms of symmetry breaking dimerization of Mo atoms at room temperature, which might led to exotic ground states. By exploiting the 2D materials characteristics, an investigation of physical properties on the nanoscale is intended. We herein demonstrate the probably first approach to synthesize phase pure, as-grown alpha-MoCl₃ few-layer nanosheets by means of a pure short time chemical vapor transport (CVT) process. Vapor growth benefits from a one-step deposition of high crystalline alpha-MoCl₃ nanosheets without stacking faults on a substrate. Thus, mostly applied subsequent delamination, associated with the introduction of structural defects, becomes redundant. According to the CVT process thermodynamic simulations of gas phase equilibria have been performed and the synthesis conditions could be optimized based on the calculation results. By CVT the as-grown nanolayers are deposited on sapphire (Al₂O₃) substrates by applying a temperature gradient of 70 K from 743 K to 673 K. Single crystalline sheets with thicknesses ≤75 nm down to five layer (3 nm) could be obtained by using a pure CVT process. According to the deposited nanostructures we approve the desired composition, morphology, phase purity and high crystallinity by using several microscopy and spectroscopy techniques. Furthermore, we show micro-RAMAN measurements which hint at a slight increase in phonon energies for nanosheets in comparison to the corresponding bulk phase.
Synthesis of micro- and nanosheets of CrCl3–RuCl3 solid solution by chemical vapour transport
(2022)
Solid solutions of 2D transition metal trihalides are rapidly growing in interest for the search for new 2D materials with novel properties at nanoscale dimensions. In this regard, we present a synthesis method for the Cr1−xRuxCl3 solid solution and describe the behaviour of the unit cell parameters over the whole composition range, which in general follows Vegard's law in the range of a = 5.958(6)CrCl3 … 5.9731(5)RuCl3 Å, b = 10.3328(20)CrCl3 … 10.34606(21)RuCl3 Å, c = 6.110(5)CrCl3 … 6.0385(5)RuCl3 Å and β = 108.522(15)CrCl3 … 108.8314(14)RuCl3 °. The synthesized solid solution powder was subsequently used to deposit micro- and nanosheets directly on a substrate by applying chemical vapour transport in a temperature gradient of 575 °C → 525 °C for 2 h and 650 °C → 600 °C for 0.5 h as a bottom-up approach without the need for an external transport agent. The observed chromium chloride enrichment of the deposited crystals is predicted by thermodynamic simulation. The results allow for a nanostructure synthesis of this solid solution with a predictable composition down to about 30 nm in height and lateral size of several μm. When applying a quick consecutive delamination step, it is possible to obtain few- and monolayer structures, which could be used for further studies of downscaling effects for the CrCl3–RuCl3 solid solution. X-ray photoelectron spectroscopy, transmission electron microscopy and Raman spectroscopy were used to confirm the purity and quality of the synthesized crystals.
The experimental observation of intrinsic ferromagnetism in single layered chromium trihalides CrX₃ (X = Cl, Br, I) has gained outstanding attention recently due to their possible implementation in spintronic devices. However, the reproducible preparation of highly crystalline chromium(III) halide nanolayers without stacking faults is still an experimental challenge. As chromium trihalides consist of adjacent layers with weak interlayer coupling, the preparation of ultrathin CrX₃ nanosheets directly on substrates via vapor transport proves as an advantageous synthesis technique. It is demonstrated that vapor growth of ultrathin highly crystalline CrX₃ micro‐ and nanosheets succeeds directly on yttrium stabilized zirconia substrates in a one‐step process via chemical vapor transport (CVT) in temperature gradients of 100 K (600°C → 500°C for CrCl₃ and 650°C → 550°C for CrBr₃ or CrI₃) without a need for subsequent delamination. Due to simulation results, optimization of synthesis conditions is realized and phase pure CrX₃ nanosheets with thicknesses ≤25 nm are obtained via short term CVT. The nanosheets morphology, crystallinity, and phase purity are analyzed by several techniques, including microscopy, diffraction, and spectroscopy. Furthermore, a potential subsequent delamination technique is demonstrated to give fast access to CrX₃ monolayers using the example of CrCl₃ .
Simulation fluidgedämpfter Strukturschwingungen mittels partitionierter Fluid-Struktur-Kopplung
(2005)
The study of hypersurfaces in a torus leads to the beautiful zoo of amoebas and their contours, whose possible configurations are seen from combinatorial data. There is a deep connection to the logarithmic Gauss map and its critical points. The theory has a lot of applications in many directions.
In this report we recall basic notions and results from the theory of amoebas, show some connection to algebraic singularity theory and discuss some consequences from the well known classification of singularities to this subject. Moreover, we have tried to compute some examples using the computer algebra system SINGULAR and discuss different possibilities and their effectivity to compute the critical points. Here we meet an essential obstacle: Relevant examples need real or even rational solutions, which are found only by chance. We have tried to unify different views to that subject.
Im vorliegenden Bericht wurden die in Wissenschaft und Praxis diskutierten Instrumente zur finanziellen Beteiligung von Kommunen an EE-Anlagen vertieft analysiert und insbesondere rechtlich geprüft. Dabei kann unterschieden werden zwischen Instrumenten, die an bestehende Abgabenzahlungen an Kommunen anknüpfen (Grundsteuer, Gewerbesteuer, Konzessionsabgabe), und Instrumenten, mit denen eine neue Abgabe zugunsten der Kommune geschaffen wird (Sonderabgabe, Außenbereichsabgabe). Auf der Basis dieser Analyse wurde dann ein eigenes Instrument entwickelt (EEG-integrierter Mechanismus) sowie Ausgestaltungsempfehlungen zur Umsetzung. Neben den Instrumenten zur finanziellen Beteiligung von Kommunen wurde aufgrund der politischen Entwicklungen im Laufe des Forschungsvorhabens zusätzlich das Angebot vergünstigter (Bürger-)Stromtarife als ein Instrument zur Bürgerbeteiligung untersucht und ebenfalls mit Ausgestaltungsvorschlägen empfohlen.
Das vorliegende Papier präsentiert die von den Gutachter/innen erarbeiteten Vorschläge zur finanziellen Beteiligung von Kommunen und BürgerInnen an lokalen Onshore-Windenergieanlagen (WEA). Die beiden empfohlenen kommunalen und Bürgerbeteiligungsinstrumente wurden im Projektverlauf nach mehreren Kriterien ausgewählt. Ein kommunales Beteiligungsinstrument, das über das EEG finanziert wird, behebt die verfassungs- und finanzverfassungsrechtlichen Probleme, die andere vorgeschlagene Steuer- und Abgabeninstrumente mit sich bringen. Eine privatrechtliche Zahlungsvereinbarung wurde daher im Rahmen unserer umfangreichen Bewertung als vorzugswürdig erachtet und wird hier weiter hinsichtlich eines konkreten Umsetzungsvorschlags ausgearbeitet. Als direktes Bürgerbeteiligungsinstrument werden vergünstigte Bürgerstromtarife vorgestellt. Auf Empfehlung des Vermittlungsausschusses des Bundestags und Bundesrats und vor dem Hintergrund der hohen Zustimmungswerte der Bevölkerung zu diesem Instrument, werden vergünstigte Bürgerstromtarife als Bürgerbeteiligungsinstrument zur Implementierung neben einem kommunalen Beteiligungsinstrument empfohlen – direkt verknüpft mit der kommunalen Beteiligung. Beide Vorschläge führen insgesamt zu jährlichen Zahlungen an die betroffenen Kommunen und Bürger/innen im Bereich von 20.000 bis 30.000 Euro pro WEA. Dabei wird dem WEA-Betreiber ermöglicht, alternativ die Zahlungen ausschließlich an die Kommune zu entrichten.
The two-dimensional (2D) chromium trihalides CrCl3, CrBr3, and CrI3 are most famous for their exotic magnetic properties when their crystals get downscaled to nanometer dimensions. One way to tune the properties of such materials and to further increase their potential utility, e.g., in spintronics, is the formation of solid solutions. Here, we present a detailed theoretical and experimental study on the synthesis and nanoplatelet growth of CrBrxCl3–x and CrBrxI3–x solid solutions. Phase pure powder was obtained by tempering the respective parent compounds at 600 and 550 °C, using additional iodine in the case of CrBrxI3–x. The dominant stacking order changes at x = 1.8 for CrBrxCl3–x while remaining similar to CrI3 for the whole CrBrxI3–x series. A consecutive chemical vapor transport from 575 → 525 °C for 2 h (CrBrxCl3–x) or 600 → 550 °C for 3 h with 0.1 mmol additional iodine (CrBrxI3–x) resulted in the deposition of high-quality nanoplatelets on a substrate with only several nanometers in height. The composition can be controlled by the choice of the starting material, since only small shifts in the anion ratio occur during the transport. The deposited CrBrxCl3–x nanoplatelets can then be easily delaminated by ultrasonication in ethanol to reduce the height even further to few-layer dimensions. These nanoplatelets could potentially be used to investigate the property changes (e.g., in terms of magnetic response) for the downscaling of these solid solutions. We further demonstrate the quality of the deposited material by transmission electron microscopy, selected area electron diffraction, and X-ray photoelectron spectroscopy. Raman spectroscopy of the solid solution series reveals a complex evolution of vibrational modes. Photoluminescence measurements on solid solution samples show emission peaks in the near-infrared energy range with the specific energy and intensity being composition and temperature dependent.