1,720,964 research outputs found
Exciton-polaron spectral structures in two-dimensional hybrid lead-halide perovskites
No full textOwing to both electronic and dielectric confinement effects, two-dimensional organic-inorganic hybrid perovskites sustain strongly bound excitons at room temperature. Here, we demonstrate that there are non-negligible contributions to the excitonic correlations that are specific to the lattice structure and its polar fluctuations, both of which are controlled via the chemical nature of the organic countercation. We present a phenomenological yet quantitative framework to simulate excitonic absorption line shapes in single-layer organic-inorganic hybrid perovskites, based on the two-dimensional Wannier formalism. We include four distinct excitonic states separated by 35±5meV, and additional vibronic progressions. Intriguingly, the associated Huang-Rhys factors and the relevant phonon energies show substantial variation with temperature and the nature of the organic cation. This points to the hybrid nature of the line shape, with a form well described by a Wannier formalism, but with signatures of strong coupling to localized vibrations, and polaronic effects perceived through excitonic correlations. Our work highlights the complexity of excitonic properties in this class of nanostructured materials
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
Defect Engineering in 2D Perovskite by Mn(II) Doping for Light-Emitting Applications
No full textLow-dimensional perovskites are considered good candidates for light-emitting applications given their high exciton binding energy. Yet, single-layered two-dimensional (2D) perovskites are strongly limited by trap-assisted recombination and suffer from low luminescence yields, hampering their application in electroluminescence devices. Here, we use synthetic and defect engineering strategies to overcome such issues. We employ metallic doping (Mn2+ and Eu3+) to introduce luminescent impurities in the 2D perovskite NMA2PbX4 (NMA = 1-naphtylmethylammonium). By means of temperature-dependent and time-resolved spectroscopy, we demonstrate efficient energy transfer to Mn2+ centers. This avoids funneling of photo-excited species in inefficient recombination channels, enhancing photoluminescence and giving a quantum yield surpassing 20% in doped films. Eventually, we embody Mn-doped NMA2PbBr4 in a light-emitting diode architecture and show electroluminescence from the Mn2+ 4T1 → 6A1 transition. This proof-of-concept demonstration shows the potential of doping in layered perovskites and prompts the study of a wider range of host-guest structures. Metal halide perovskites have emerged for light-emitting applications, such as light-emitting diodes (LEDs). While intensive research has focused on three-dimensional (3D) perovskites, layered perovskites are also gaining interest for their peculiar light-emitting properties. The higher exciton binding energy of low-dimensional perovskites is considered beneficial to improve the radiative recombination efficiency. However, the luminescence yield of single-layered two-dimensional (2D) perovskites is severely lowered by trap-assisted recombination. By including Mn2+ and Eu3+ in a 2D perovskite, we show that metallic doping can be exploited to enhance and tune its luminescence. Efficient energy transfer from the perovskite to the dopant is achieved, provided that a suitable energy level alignment of the host-guest system is realized. We show that such a mechanism can be exploited to tune the material's electroluminescence in a proof-of-concept LED based on a Mn-doped 2D perovskite. Cortecchia et al. report the use of metallic dopants to overcome the detrimental trap-mediated non-radiative recombination processes, lowering the luminescence yield in two-dimensional perovskites. This results in tuning and enhancement of the perovskite's luminescence properties. In particular, efficient energy transfer and high luminescence yield are obtained with manganese doping. This strategy is shown to be suitable for application in light-emitting diodes
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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