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Die Untersuchung der optischen und Photokatalytischen Eigenschaften von TiO2-Nanoröhren und ihrer Anwendungen
Get PDFOver the last decades, titanium dioxide (TiO2) nanostructures in different arrangements, and particularly layers of vertically aligned TiO2 nanotubes (NTs), have received enormous attention for various energy conversion / storage applications owing to TiO2’s promising (photo)-electrochemical and photocatalytic properties, outstanding electrochemical stability, non-toxicity, low cost and extensive availability. Particularly, one-dimensional (1D) TiO2 nanostructures can provide unique benefits such as large specific surface area, orthogonal charge separation, a direct pathway for electron percolation and quantum confinement. Such highly ordered arrays of TiO2 NTs can be directly grown on a Ti metal piece, e.g. a Ti foil, by means of electrochemical anodization, and their morphology (nanotube thickness, inner / outer wall diameter, inter-tube distance among others) can be readily tuned by changing simple anodization parameters (applied voltage, time, temperature, water content, etc.).
The present thesis focusses on the fabrication of anodic titania nanotubes layers, membranes, and electrodes for application in photocatalysis, solar cells and batteries. The work particularly investigates morphological, optical and charge transport properties of such NT structures and their effects on light conversion and energy storage properties.
In a first section, we discuss the effect of the top surface morphology of TiO2 NTs for the photocatalytic H2 evolution reaction, in relation, for instance, with the light penetration depth into the semiconductor nanostructures. We follow up by describing various optical properties (such as light absorption and reflectance) of self-standing membranes produced by detaching anodic TiO2 nanotube layers from Ti followed by their direct transfer onto adequate transparent substrates. This approach allowed investigation in a transmission geometry, which provides significantly more reliable data than common reflectance measurements of NT layers on metallic Ti foils. Light transmission and reflectance measurements were carried out as a function of the membranes’ thickness and crystalline form. A series of wavelength-dependent light attenuation coefficients could thereby be extrapolated and examined in relation to photocurrent data. We also investigated a feature specific to anodic NT, namely their intrinsic carbon contamination content, and its effect on the optical and photo-electrochemical properties.
Furthermore, such nanotube membranes were studied in view of their photocatalytic H2 evolution ability after modification with co-catalytic Pt nanoparticles. We investigated the H2 evolution in relation to membrane thickness, light absorbance, and electron diffusion length in the nanotubes. In particular, we focused on understanding how the photocatalytic enhancement ascribed to Pt modification varies with the membrane thickness, and therefore with factors such as photon harvesting, electron diffusion length and electron trapping/transfer to reactants.
We followed up by exploring solar energy conversion properties of TiO2 nanotubes in the context of solar cells. Specifically, we studied the use of Li+ inserted TiO2 nanotube arrays as photo-anode scaffolds in dye-sensitized solar cells (DSSCs). We achieved Li+ insertion into TiO2 NTs by an electrochemical (cathodic) treatment in Li ion based electrolytes, and observed that such lithiated photo-anodes, upon further TiO2 nanoparticle decoration to increase the surface area, can in DSSCs yield power conversion efficiencies of up to 7.0 %, this is in contrast to efficiencies of ~4.8 % for untreated NTs. We ascribe this result to the enhanced charge transfer properties obtained with lithiation, that is, to the improved electron transport and conductivity of Li-TiO2 NTs.
Finally, such increased conductivity achieved by Li ion insertions was also investigated in terms of energy storage application, thereby fabricating efficient and stable electrodes for batteries. We outline in this context how Li+ pre‐insertion in TiO2 NTs can condition the solid electrolyte interphase (SEI) for Na+ replacement - this was found not only to lead to an enhanced electronic conductivity in the NTs, but also to expand the anatase lattice for facilitated subsequent Na+ cycling, allowing for a strongly improved performance of sodium battery systems based on an exceptional Na+ cycling stability and an excellent rate capability.In den letzten Jahrzehnten haben Titandioxid-(TiO2) Nanostrukturen in unterschiedlichen Anordnungen und insbesondere Schichten vertikal ausgerichteter TiO2-Nanoröhren (NTs) enorme Aufmerksamkeit für verschiedene Anwendungen zur Energieumwandlung bzw. -speicherung erhalten. Dies ist in den vielversprechenden (photo-)elektrochemischen und photokatalytischen Eigenschaften, der hervorragenden elektrochemischen Stabilität, Ungiftigkeit, der geringen Kosten und großen Verfügbarkeit von TiO2 begründet. Insbesondere eindimensionale (1D) TiO2-Nanostrukturen können einzigartige Vorteile bieten, wie eine große spezifische Oberfläche, orthogonale Ladungstrennung, gerichteten Elektronenfluss und Quanten-Confinement. Solche hochgeordneten Anordnungen von TiO2 NTs können direkt auf einem Ti-Metallstück, z.B. einer Ti-Folie, durch elektrochemische Anodisierung aufgewachsen werden. Ihre Morphologie (Nanoröhrendicke, Innen- / Außenwanddurchmesser, Abstand zwischen den Röhren, uvm.) kann unkompliziert durch das Ändern simpler Anodisierungsparameter (angelegte Spannung, Zeit, Temperatur, Wassergehalt, usw.) angepasst werden.
Die vorliegende Arbeit fokussiert auf die Herstellung von Schichten, Membranen und Elektroden aus anodischen Titandioxid-Nanoröhren zur Anwendung in der Photokatalyse, in Solarzellen und Batterien. Die Arbeit untersucht insbesondere morphologische, optische und Ladungstransporteigenschaften solcher NT-Strukturen und deren Auswirkungen auf die Lichtumwandlung und die Energiespeichereigenschaften.
In einem ersten Abschnitt diskutieren wir den Effekt der Morphologie der äußersten Oberfläche von TiO2-NTs auf die photokatalytische H2-Entwicklung, beispielsweise in Bezug auf die Lichteintrittstiefe in die Halbleiternanostrukturen. Anschließend werden verschiedene optische Eigenschaften (wie Lichtabsorption und Reflexionsvermögen) von freistehenden Membranen beschrieben, die durch Ablösen anodischer TiO2-Nanoröhrenschichten von Ti und anschließende direkte Übertragung auf geeignete transparente Substrate hergestellt werden. Dieser Ansatz ermöglichte die Untersuchung in Transmissionsgeometrie, was wesentlich zuverlässigere Daten liefert als gebräuchliche Reflexionsmessungen von NT-Schichten auf metallischen Ti-Folien. Lichtdurchlässigkeits- und Reflexionsmessungen wurden in Abhängigkeit von der Membrandicke und der Kristallinität durchgeführt. Eine Reihe von wellenlängenabhängigen Lichtschwächungskoeffizienten könnte dadurch extrapoliert und in Bezug auf Photostromdaten untersucht werden. Wir untersuchten ebenfalls ein Merkmal, welches für anodisches NT spezifisch ist, ihren intrinsischen durch Kontamination verursachten Kohlenstoffgehalt und seine Wirkung auf die optischen und (photo-)elektrochemischen Eigenschaften des Materials.
Darüber hinaus wurden die Nanoröhrenmembranen nach Modifikation mit co-katalytischen Pt-Nanopartikeln im Hinblick auf ihre Fähigkeit, photokatalytisch H2 zu erzeugen, geprüft. Wir untersuchten die H2-Entwicklung in Bezug auf Membrandicke, Lichtabsorption und Elektronendiffusionslänge in den Nanoröhren. Insbesondere konzentrierten wir darauf aufzuklären, wie die mit der Pt-Modifikation einhergehende photokatalytische Verbesserung mit der Membrandicke – und damit mit Faktoren wie Photonenertrag, Elektronendiffusionslänge und Einfang bzw. Transfer von Elektronen auf Reaktanten – variiert. Weiterhin haben wir die Eigenschaften der Umwandlung von Solarenergie durch TiO2-Nanoröhren im Kontext von Solarzellen analysiert. Insbesondere untersuchten wir die Verwendung von mit Li+ versetzten TiO2-Nanoröhren-Schichten als Photoanoden in farbstoffsensibilisierten Solarzellen (DSSCs). Wir erreichten de Einbau von Li+ in TiO2-NTs durch eine elektrochemische (kathodische) Behandlung in Elektrolyten auf Li-Ionen-Basis und beobachteten, dass solche lithiierten Photoanoden – bei weiterer Dekoration mit TiO2-Nanopartikeln zur Vergrößerung der Oberfläche – in DSSCs Effizienzen von bis zu 7.0% bei der Energieumwandlung erzielen können. Dem gegenüber stehen Wirkungsgrade von lediglich ~ 4.8% für unbehandelte NTs. Wir führen dieses Ergebnis auf die verbesserten Eigenschaften im Ladungstransfer zurück, welche durch Lithiierung erhalten werden, d.h. auf den verbesserten Elektronentransport und die verbesserte Leitfähigkeit von Li-TiO2-NTs.
Schließlich wurde eine solche, durch Einbau von Li-Ionen erzielte, erhöhte Leitfähigkeit auch für Anwendungen zur Energiespeicherung untersucht, d.h. zur Herstellung effizienter und stabiler Elektroden für Batterien. Wir skizzieren in diesem Zusammenhang, wie die Li+ -Vorinsertion in TiO2-NTs die Festkörperelektrolyt-Phasengrenzfläche (SEI) für den Na+ -Austausch konditionieren kann - dies führte nicht nur zu einer verbesserten elektronischen Leitfähigkeit in den NTs, sondern auch zu einer Ausdehnung des Anatasgitters, was wiederum zu einer Erleichterung in anschließenden Na+ -Ladezyklen führte und eine stark verbesserte Leistung von Natriumbatteriesystemen auf der Grundlage einer außergewöhnlich hohen Na+ -Ladezyklusstabilität und einer hervorragenden Ladungs- und Entladungsrate ermöglichte
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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