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Nitridonickelates: Preparation, Structure and PropertiesMehta, Akash 07 October 2005 (has links) (PDF)
Low valent nickel (less than +1) complexes are rare in nature, however they are regularly encountered in nitridonickelate chemistry. Ternary alkaline earth nitridonickelates exhibit a variety of interesting crystal structures with respect to their covalently bonded nitridonickelate anionic framework. The coordination geometry of low valent nickel in these compounds presents a unique structural feature with nickel being in linear coordination by nitrogen atoms. The nitridonickelate frameworks of compounds investigated in this work are: Ba2[Ni3N2]: The first ternary alkaline earth nitridonickelates with 2D Ni-N anionic network. The formal oxidation state of Ni is +0.67. Ba2(Ba6N)[NiN]6: The structure is made of o1D helical Ni-N anionic chains. Also, the structural stability of this compound´s structure type was found to occur over a wide range of substitution of Ba by Ca and Sr; a max. of 70 percent Ba could be successfully replaced by Sr and Ca atoms retaining the same structure type. The formal oxidation state of Ni is +0.83. Ba[NiN] and the solid solution series Ba[CuxNi1-xN]: The structure is made of 1D zig-zag Ni-N chains. The solid-solution series is isostructural to Ba[NiN] at lower content of Cu while, at higher content it resembles Ba[CoN] structure type, however at very high Cu content it again transforms to Ba[NiN] structure type. The formal oxidation state of Ni is +1.0. Sr2[Ni(CN)N]: The structure consists of N-Ni-(CN) dumbbells. The compound is the first example of cyano-nitridonickelate. The formal oxidation state of Ni is 0. The handling of the ternary alkaline earth nitridonickelates in specific and also of the other nitridometalates in general suffers greatly due to their being air and moisture sensitive. This requires synthetic methods suitable for air and moisture sensitive samples and also the respective instrumental setup for the measurement of their physical properties under inert atmosphere. Up to now no comprehensive investigation of the physical properties of the ternary alkaline earth nitridonickelates has been made. In this work an emphasis was given to systematically investigate the physical properties of the ternary alkaline earth nitridonickelates and to understand their structure specific physical properties. The common features of the investigated ternary alkaline earth nitridonickelates are: 1. the low valency of nickel. 2. the linear coordination of Ni and octahedral coordination of N. During this investigation the low valent character of nickel was experimentally confirmed with the help of X-ray absorption spectroscopy and the interpretation of magnetic susceptibility data where the magnetic moments of the nickel atoms were always consistent with that of a low valent nickel species. The results obtained from the magnetic measurements and electrical conductivity shows that the alkaline earth nitridonickelates order antiferromagnetically at low temperatures and show temperature dependent metallic conductivity whereas the cyano-nitridonickelate Sr2[Ni(CN)N] does not order at low temperature, is paramagnetic, and exhibits semiconducting behaviour. This investigation has provided a better understanding of ternary alkaline earth nitridonickelates with respect to the different structure they exhibit and their associated physical properties. This work motivates to extend the investigations of the physical properties of other nitridometalates. These also exhibit different crystal structures with respect to their nitridometalate anionic framework and thus, structure specific physical properties are also to be expected.
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3D assembly of silica encapsulated semiconductor nanocrystalsRengers, Christin, Voitekhovich, Sergei V., Kittler, Susann, Wolf, André, Adam, Marion, Gaponik, Nikolai, Kaskel, Stefan, Eychmüller, Alexander 15 December 2015 (has links) (PDF)
Non-ordered porous networks, so-called aerogels, can be achieved by the 3D assembly of quantum dots (QDs). These materials are well suited for photonic applications, however a certain quenching of the photoluminescence (PL) intensity is observed in these structures. This PL quenching is mainly attributed to the energy transfer mechanisms that result from the close contact of the nanoparticles in the network. Here, we demonstrate the formation of a novel aerogel material with non-quenching PL behaviour by non-classical, reversible gel formation from tetrazole capped silica encapsulated QDs. Monitoring of the gelation/degelation by optical spectroscopy showed that the optical properties of the nanocrystals could be preserved in the 3D network since no spectral shifts and lifetime shortening, which can be attributed to the coupling between QDs, are observed in the gels as compared to the original colloidal solutions. In comparison with other QD-silica monoliths, QDs in our gels are homogeneously distributed with a distinct and controllable distance. In addition we show that the silica shell is porous and allows metal ions to pass through the shell and interact with the QD core causing detectable changes of the emission properties. We further show the applicability of this gelation method to other QD materials which sets the stage for facile preparation of a variety of mixed gel structures.
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Nickel cobalt oxide hollow nanosponges as advanced electrocatalysts for the oxygen evolution reactionEychmüller, Alexander, Zhu, Chengzhou, Wen, Dan, Leubner, Susanne, Oschatz, Martin, Liu, Wei, Holzschuh, Matthias, Simon, Frank, Kaskel, Stefan 17 December 2015 (has links) (PDF)
A class of novel nickel cobalt oxide hollow nanosponges were synthesized through a sodium borohydride reduction strategy. Due to their porous and hollow nanostructures, and synergetic effects between their components, the optimized nickel cobalt oxide nanosponges exhibited excellent catalytic activity towards oxygen evolution reaction.
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Charakterisierung reaktiver Prozesse bei der katodischen VakuumbogenverdampfungKuehn, Michael 17 December 1997 (has links) (PDF)
In der vorliegenden Arbeit werden die waehrend der reaktiven
Vakuumbogenverdampfung ablaufenden Prozesse untersucht und eine modellmaessige
Beschreibung des Gesamtprozesses entwickelt. Das Verfahren wird zur
Herstellung von duennen Schichten zahlreicher chemischer Verbindungen,
insbesondere von Hartstoffschichten auf der Basis der Karbide und Nitride der
Uebergangsmetalle, genutzt. Entsprechend wurden in dieser Arbeit als
Katodenmaterial Titan, Chrom und Zirkonium eingesetzt, als Reaktivgase
Stickstoff und Methan.
Zunaechst werden einige Grundlagen der Vakuumbogenverdampfung dargestellt,
die fuer die Bearbeitung des Themas wesentlich sind. Anschliessend wird der
Aufbau der fuer die Experimente genutzten Beschichtungsapparatur beschrieben.
Im Hauptteil der Arbeit wird zuerst auf experimentellem Wege die
Materialbilanz der Entladung bei Variation des Reaktivgasdruckes analysiert.
Die Generation an Metalldampfplasma wird ueber die Katodenerosionsrate
bestimmt, wobei sich beim Betrieb mit Stickstoff als Reaktivgas signifikante
Unterschiede in der Druckabhaengigkeit der Katodenerosionsrate µ zwischen
Titan bzw. Zirkonium einerseits und Chrom andererseits zeigen. Die Hypothese,
dass hier die Ausbildung einer Verbindungsschicht an der Katodenoberflaeche
den Erosionsprozess beeinflusst, wurde sowohl durch RBS-Messungen als auch
durch Vergleichsexperimente mit einer massiven TiN-Katode bestaetigt. Weitere
Auswirkungen derartiger Oberflaechenbedeckungen auf die Dynamik des
Katodenbrennfleckes wurden durch Videountersuchungen am Beispiel Ti+N_2
nachgewiesen. Die Konsumtion des Reaktivgases waehrend der Entladung wird
anhand der Gasfluss-Druck-Charakteristiken untersucht und das je nach
Katodenmaterial unterschiedliche Gettervermoegen diskutiert. Direkte
Informationen ueber den Stickstoffeinbau in die Schichten in Abhaengigkeit
vom Reaktivgasdruck werden aus RBS-Untersuchungen an entsprechenden
Probenserien gewonnen. Analoge Untersuchungen mit Methan als Reaktivgas
fuehrten zu prinzipiell aehnlichen Resultaten.
Mit den gewonnenen experimentellen Daten als Grundlage wurde ein Modell
entwickelt, das die Materialbilanz der Vakuumbogenverdampfung mathematisch
beschreibt. Hier wurden, ausgehend von einem fuer das reaktive
Magnetronsputtern aufgestellten Modell, die Besonderheiten der stark
lokalisierten Metalldampfgeneration bei der Vakuumbogenverdampfung
beruecksichtigt. Die erreichte Uebereinstimmung der Modellkurven mit den
experimentellen Daten zeigt, dass mit der Modellierung wesentliche
Mechanismen bei der reaktiven Vakuumbogenverdampfung richtig erfasst wurden.
Aus den Ergebnissen folgt, dass die Erzeugung von reaktionsfaehigen
Stickstoffspezies an die Katodenerosion gekoppelt ist: erstens ueber die
Erosion nitridbedeckter Oberflaechenbereiche und zweitens ueber die
Wechselwirkung des Metalldampfplasmas mit dem Reaktivgas.
Diese Wechselwirkungsprozesse werden durch Untersuchungen mit elektrischen
Sondenmessungen sowie mittels optischer Emissionsspektroskopie (OES) naeher
charakterisiert. Als wesentliches Ergebnis zeigt sich dabei, dass trotz der
Unterschiede hinsichtlich des Verhaltens an der Katode bei Ti- bzw.
Cr-Entladungen in Stickstoff Anregungs- und Ionisationsgrad des Reaktivgases
praktisch gleich sind. Im Zusammenhang damit wird die Rolle von
Ladungstransfer- und Anregungsprozessen infolge von Stoessen schneller
Ionen mit Molekuelen und Neutralatomen diskutiert.
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Insight into Bio-metal Interface Formation in vacuo: Interplay of S-layer Protein with Copper and IronMakarova, Anna A., Grachova, Elena V., Neudachina, Vera S., Yashina, Lada V., Blüher, Anja, Molodtsov, Serguei L., Mertig, Michael, Ehrlich, Hermann, Adamchuk, Vera K., Laubschat, Clemens, Vyalikh, Denis V. 22 July 2015 (has links) (PDF)
The mechanisms of interaction between inorganic matter and biomolecules, as well as properties of resulting hybrids, are receiving growing interest due to the rapidly developing field of bionanotechnology. The majority of potential applications for metal-biohybrid structures require stability of these systems under vacuum conditions, where their chemistry is elusive, and may differ dramatically from the interaction between biomolecules and metal ions in vivo. Here we report for the first time a photoemission and X-ray absorption study of the formation of a hybrid metal-protein system, tracing step-by-step the chemical interactions between the protein and metals (Cu and Fe) in vacuo. Our experiments reveal stabilization of the enol form of peptide bonds as the result of protein-metal interactions for both metals. The resulting complex with copper appears to be rather stable. In contrast, the system with iron decomposes to form inorganic species like oxide, carbide, nitride, and cyanide.
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Dephasing and phase-coherence in disordered mesoscopic conductorsVölker, Axel 08 July 1996 (has links)
No description available.
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Einsatz spektroskopischer Verfahren für die Eigenschaftsbestimmung von Polyethylenterephthalat-Multifilamenten /Linnemann, Bernhard. January 2008 (has links)
Techn. Hochsch., Diss.--Aachen, 2007.
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Einsatz spektroskopischer Verfahren für die Eigenschaftsbestimmung von Polyethylenterephthalat-MultifilamentenLinnemann, Bernhard January 2007 (has links)
Zugl.: Aachen, Techn. Hochsch., Diss., 2007
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Characterization of the physical properties of the Rosetta target comet 67P/Churyumov-GerasimenkoTubiana, Cecilia January 2008 (has links)
Zugl.: Braunschweig, Techn. Univ., Diss., 2008
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Insight into Bio-metal Interface Formation in vacuo: Interplay of S-layer Protein with Copper and IronMakarova, Anna A., Grachova, Elena V., Neudachina, Vera S., Yashina, Lada V., Blüher, Anja, Molodtsov, Serguei L., Mertig, Michael, Ehrlich, Hermann, Adamchuk, Vera K., Laubschat, Clemens, Vyalikh, Denis V. 22 July 2015 (has links)
The mechanisms of interaction between inorganic matter and biomolecules, as well as properties of resulting hybrids, are receiving growing interest due to the rapidly developing field of bionanotechnology. The majority of potential applications for metal-biohybrid structures require stability of these systems under vacuum conditions, where their chemistry is elusive, and may differ dramatically from the interaction between biomolecules and metal ions in vivo. Here we report for the first time a photoemission and X-ray absorption study of the formation of a hybrid metal-protein system, tracing step-by-step the chemical interactions between the protein and metals (Cu and Fe) in vacuo. Our experiments reveal stabilization of the enol form of peptide bonds as the result of protein-metal interactions for both metals. The resulting complex with copper appears to be rather stable. In contrast, the system with iron decomposes to form inorganic species like oxide, carbide, nitride, and cyanide.
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