1,721,239 research outputs found
Transport Properties of Doped Wide Band Gap Layered Oxychalcogenide Semiconductors Sr<sub>2</sub>GaO<sub>3</sub>CuCh, Sr<sub>2</sub>ScO<sub>3</sub>CuCh, and Sr<sub>2</sub>InO<sub>3</sub>CuCh (Ch = S or Se)
No full textThe structural, electrical, and optical properties of a series of six layered oxychalcogenides with the general formula Sr2MO3CuCh, where M = Ga, Sc, or In and Ch = S or Se, have been investigated. From this set, we report the structure and properties of Sr2GaO3CuSe for the first time, as well as the full structural details of Sr2ScO3CuSe, which have not previously been available. A systematic study of the suitability of all of the Sr2MO3CuCh phases as p-type conductors has been carried out, after doping with both sodium and potassium to a nominal composition of A0.05Sr1.95MO3CuCh, (A = Na or K), to increase the hole carrier concentration. Density functional theory calculations were used to determine the electronic band structure and predict the transport properties, while optical properties were determined using UV–vis spectroscopy, and structures were confirmed using Rietveld refinement against powder X-ray diffraction data. Room-temperature conductivity measurements were carried out on both pristine samples and doped samples, 18 compositions in total, using four-point probe measurements. We found that the most conductive sample was K0.05Sr1.95GaO3CuSe, with a measured conductivity of 0.46 S cm–1, collected from a sintered pellet. We have also been able to identify a relationship between the conductivity and the geometry of the copper chalcogenide layer within the Sr2MO3CuCh series of compounds. As this geometry can be controlled through the material composition, the identification of this structure–property relationship highlights a route to the selection and identification of materials with even higher conductivities
The adsorption of Cu on the CeO2(110) surface
No full textWe report a detailed density functional theory (DFT) study in conjunction with X-ray absorption fine structure (XAFS) experiments on the geometrical and local electronic properties of Cu adatoms and Cu(II) ions in presence of water molecules and of CuO nanoclusters on the CeO2(110) surface. Our study of (CuO)n(=1, 2 & 4) clusters on CeO2(110) shows that based on the Cu–O environment, the geometrical properties of these clusters may vary and their presence may lead to relatively higher localization of charges on the exposed surfaces. We find that in presence of an optimum concentration of water molecules, Cu has a square pyramidal geometry, which agrees well with our experimental findings; we also find that Cu(II) facilitates water adsorption on the CeO2(110) surface. We further show that at a critical concentration of water molecules is required for the hydrolysis of water on Cu(OH)2/CeO2(110) and on pristine CeO2(110) surfaces
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
No full text“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
Photocatalytic, structural and optical properties of mixed anion solid solutions Ba3Sc2-xInxO5Cu2S2 and Ba3In2O5Cu2S2-ySey
No full textNine members of two contiguous solid solutions, Ba3Sc2−xInxO5Cu2S2 and Ba3In2O5Cu2S2−ySey (x, y = 0, 0.5, 1, 1.5 and 2), were synthesised at temperatures between 800 °C and 900 °C by stoichiometric combination of binary precursors. Their structures were determined by Rietveld refinement of X-ray powder diffraction data and found to adopt the SmNi3Ge3 structure with I4/mmm symmetry. Approximate Vegard law relationships were found within each solution between the lattice parameters and composition, with an observed cell volume of 466.4 Å3 for Ba3Sc2O5Cu2S2 increasing to 481.0 Å3 for Ba3In2O5Cu2S2 and finally to 499.0 Å3 for Ba3In2O5Cu2Se2. In the first solid solution, this volume increase is driven by the replacement of scandium by the larger indium ion, generating increased strain in the copper chalcogenide layer. In the second solution the substitution into the structure of the larger selenium drives further volume expansion, while relieving the strain in the copper chalcogenide layer. Band gaps were estimated from reflectance spectroscopy and these were determined to be 3.3 eV, 1.8 eV, and 1.3 eV for the three end members Ba3Sc2O5Cu2S2, Ba3In2O5Cu2S2, and Ba3Sc2In2O5Cu2Se2, respectively. For the intermediate compositions a linear relationship between band gap size and composition was observed, driven in the first solution by the introduction of the more electronegative indium lowering the conduction band minimum and in the second solution by the substitution of the electropositive selenium raising the valance band maximum. Photocatalytic activity was observed in all samples under solar simulated light, based on a dye degradation test, with the exception of Ba3In2O5Cu2Se1.5S0.5. The most active sample was found to be Ba3Sc2O5Cu2S2, the material with the largest band gap
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe 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
Computationally driven discovery of layered quinary oxychalcogenides: Potential p-type transparent conductors?
No full textSummary: n-type transparent conductors (TCs) are key materials in the modern optoelectronics industry. Despite years of research, the development of a high-performance p-type TC has lagged far behind that of its n-type counterparts, delaying the advent of “transparent electronics”-based p-n junctions. Here, we propose the layered oxysulfide [Cu 2S 2][Sr 3Sc 2O 5] as a structural motif for discovering p-type TCs. We have used density functional theory to screen 24 compositions based on this motif in terms of their thermodynamic and dynamic stability and their electronic structure, thus predicting two p-type TCs and eight other stable systems with semiconductor properties. Following our predictions, we have successfully synthesized our best candidate p-type TC, [Cu 2S 2][Ba 3Sc 2O 5], which displays structural and optical properties that validate our computational models. It is expected that the design principles emanating from this analysis will move the field closer to the realization of a high figure-of-merit p-type TC.Progress and Potential: This work has predicted and experimentally realized the p-type transparent conductor [Cu 2S 2][Ba 3Sc 2O 5], and at the same time has developed design principles for layered oxychalcogenide materials of this structure type. The layered oxychalcogenide materials offer a large configurational space of potentially stable compounds with tunable functional properties for a wide range of applications. The longer-term ambitions of the research are to use the combined methods of density functional theory and experiments to search for and understand further layered oxychalcogenide structure types and configurations for different semiconductor applications. This research has the potential to affect the types of electronic devices by bringing us closer to the realism of transparent electronics. The research presented will also further the development of applications for which transparent conductors are essential, such as solar cells. Abstract: The realization of transparent electronics is hindered by the lack of a suitable high-mobility p-type transparent conductor (TC). This work used ab initio simulations to search for a p-type TC based on the layered oxychalcogenide [Cu 2S 2][A 3M 2O 5] structure. The main result of this study was the discovery of the optimum p-type oxychalcogenide TC, [Cu 2S 2][Ba 3Sc 2O 5], predicted to have a higher optical band gap, better hole mobility, and greater stability than its parent compound [Cu 2S 2][Ba 3Sc 2O 5]; this was verified experimentally. </p
Dispelling the Myths Behind First-author Citation Counts
No full textWe 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
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