1,720,957 research outputs found
Integrated Devices for Photoelectrochemical Water Splitting Using Adapted Silicon Based Multi-Junction Solar Cells Protected by ALD TiO2 Coatings
No full textIn this study, we present different silicon based integrated devices for photoelectrochemical water splitting, which provide enough photovoltage to drive the reaction without an external bias. Thin films of titanium dioxide, prepared by atomic layer deposition (ALD), are applied as a surface passivation and corrosion protection. The interfaces between the multi-junction cells and the protective coating were optimized individually by etching techniques and finding optimal parameters for the ALD process. The energy band alignment of the systems was studied by X-ray photoelectron spectroscopy (XPS). Electrochemically deposited platinum particles were used to reduce the HER overpotential. The prepared systems were tested in a three-electrode arrangement under AM 1.5 illumination in 0.1 M KOH. In final tests the efficiency and stability of the prepared devices were tested in a two-electrode arrangement in dependence of the pH value with a ruthenium-iridium oxide counter electrode. For the tandem-junction device solar to hydrogen efficiencies (STH) up to 1.8% were reached, and the triple-junction device showed a maximum efficiency of 4.4%
Stability and Degradation Mechanism of Si-based Photocathodes for Water Splitting with Ultrathin TiO2 Protection Layer
No full textUsing transmission and scanning electron microscopy, we study mechanisms which determine the stability of Silicon photocathodes for solar driven water splitting. Such tandem or triple devices can show a promising stability as photocathodes if the semiconductor surface is protected by an ultrathin TiO2 protection layer. Using atomic layer deposition (ALD) with Cl-precursors, 4–7 nm thick TiO2 layers can be grown with high structural perfection. The layer can be electrochemically covered by Pt nanoparticels serving as electro-catalysts. However, Cl-remnants which are typically present in such layers due to incomplete oxidation, are the origin of an electrochemical degradation process. After 1 h AM1.5G illumination in alkaline media, circular shaped corrosion craters appear in the topmost Si layer, although the TiO2 layer is intact in most parts of the crater. The crater development is stopped at local inhomogenities with a higher Pt coverage. The observations suggests that reduced Titanium species due to Cl−/O2− substitution are nucleation sites of the initial corrosion steps due to enhanced solubility of reduced Ti in the electrolyte. This process is followed by electrochemical dissolution of Si, after direct contact between the electrolyte and the top Si layer surface. To increase the stability of TiO2 protected photocathodes, formation of reduced Ti species must be avoided
Photoelektrochemische Wasserspaltung mittels adaptierter siliziumbasierter Halbleiter-Mehrfachstapelstrukturen
Full text linkDas Thema dieser Arbeit ist die photoelektrochemische Wasserspaltung mittels adaptierter siliziumbasierter Halbleiter-Mehrfachstapelstrukturen. Diese wurden mit oxidischen Oberflächenpassivierungsschichten (TiO2, Ta2O5) und einem angekoppelten Elektrokatalysator (Pt) ausgestattet, mit dem Ziel, diese als integrierte Photokathoden zur direkten, solargetriebenen Energieumwandlung einzusetzen. Es wurde ein direkter Zusammenhang zwischen der elektronischen Struktur, die mittels Photoelektronenspektroskopie ermittelt wurde, und der photoelektrochemischen Charakteristik hergestellt. Damit konnte gezeigt werden, dass Grenzflächeneffekte einen großen Einfluss auf die Gesamtperformance eines integrierten Systems zur lichtgetriebenen Wasserspaltung ausüben. Die Abhängigkeit der Gesamtcharakteristik von den einzelnen Komponenten (Photoabsorber, Passivierungsschicht, Elektrokatalysator) wurde mit Hilfe von geeigneten Modellsystemen bestimmt. Die Untersuchungen erfolgten mit spektroskopischen, (photo)-elektrochemischen, elektrischen, optischen und mikroskopischen Methoden. Die präparierten Photokathoden wurden unter realen Prozessbedingungen mit einer geeigneten Sauerstoffanode (RuO2-IrO2) betrieben. Den höchsten STH-Wirkungsgrad von 4,4 % erreichte das a-Si:H/a-Si:H/μc-Si:H/TiO2/Pt-Triplezellensystem unter AM1.5-Beleuchtung in 1 M H2SO4. Zusätzlich wurden alternative PV-EC-Systeme untersucht, die sich durch eine Abkopplung der Photovoltaik-Einheit von der Elektrolyse-Einheit kennzeichnen. In diesem Zusammenhang erfolgte eine Substitution des Edelmetallkatalysators durch einen kostengünstigen, auf der Erde häufiger vorkommenden Elektrokatalysator (NiOx)
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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
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