1,720,980 research outputs found
Synthesis and Characterization of Halide Perovskites and Lower-Dimensional Metal Halide Based Materials
No full textThe goal of this doctoral thesis is to synthesize metal halide octahedra based materials of varying dimensionality and explore their intrinsic structure-property relationships while attempting to apply them in prototype devices.
In Chapter 2 we found using our solvent acidolysis crystallization (SAC) method, 44% of methylammonium can be replaced with a larger organic cation (dimethylammonium) without breaking the 3-dimensional (3D) perovskite structure. We then employed different temperature-dependent studies to explore the implications of such a mixed organic cation composition on the structure and on the optoelectronic properties as well as on photodetector performance.
In Chapter 3 we used the SAC process to fabricate lead-free 2D methylammonium copper halide materials. Here we found that tuning the halide compositions not only modulated the bulk phase and optical properties but also the finer structural effects such as vacancy positions and thermal disorder parameters. We connected these local atomic scale observations to the efficacy of ionic migration in these materials that also modulates their performance in resistive switching memory devices.
In Chapter 4 we explored the structural versatility of Cs-Pb-Br based compounds by studying the connection between the nature and size of the solvated species and the precipitated 0D Cs4PbBr6 and 3D CsPbBr3 powders. Identifying the spectroscopic signatures of the species helped us select the appropriate solvents to obtain 3D-free Cs4PbBr6 that we studied for the first time using 133Cs and 207Pb solid-state nuclear magnetic resonance. We hypothesized on the possible origins of the green emission in these 0D compounds and also studied their suitability for radioluminescence applications
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
Synthesis and characterization of mixed-metal hybrid perovskites
No full textMetal halide perovskites have attracted a lot of attention over the last decade as a potential low cost alternative to traditional silicon based photovoltaics. Solar cells based on these materials have already achieved power conversion efficiency (PCE) of 22%. However, these high performing compositions are lead containing which is regarded as a potential risk for humans as well as the environment. A lot of research effort has been put into completely replacing lead with other group-14 elements such as tin and germanium, due to their similar sizes and electronic configuration. These kinds of perovskites have shown promising optoelectronic properties but are highly unstable due to the easy oxidation of tin and germanium.In this thesis an alternative approach of mixing lead with other smaller divalent metal cations is explored. MAPbI3 is synthesized using lead acetate due to the facile removal of byproducts and its tolerance for mixing with other metal salts. The alternate metal salts were selected on the basis of their solubility in commonly used solvents and the suitability of the crystal structure of the precursor compound for perovskite structure formation. We found manganese to be a suitable substituent of lead and the upper limit for these mixed metal perovskites after geometrical calculations as well as experimental verification is found to be around 30%. Though the mixed metal compositions maintain the tetragonal crystal structure of lead based perovskites, a secondary crystalline phase is observed with increased lead substitution. Efforts are made to identify its composition and to remove it by optimizing the thermal treatment as well as the ratio between the other precursors. The optimized recipe for 30% lead substituted showed phase purity as well as good optical and electronic properties. Detailed compositional analysis revealed that, unlike MAPbI3 synthesized using chloride based precursors, in these mixed metal compositions chlorine is also incorporated in the films containing manganese especially near the substrate interface. This suggests that the smaller metal cation has an affinity for the smaller halide anion and that it plays a key role in the initiation of nucleation in such mixed metal (Pb:Mn) compositions. Finally, solar cells were made as a proof of concept incorporating these mixed metal perovskites and devices with up to 1.45% PCE were obtained
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
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