1,721,015 research outputs found
Two Dimensional Perovskites/Transition Metal Dichalcogenides Heterostructures: Puzzles and Challenges
No full textTwo-dimensional (2D) layered materials have been in the spotlight of scientists’ interest for more than a decade. The inherently weak interaction between the layers in 2D crystals allows stacking different materials and building heterostructures with novel functional properties. Here, we review the most recent advances on heterostructures composed of transition metal dichalcogenides and 2D perovskites. We show that combining these materials yields a rich and unique platform for the investigation of energy and charge transfer mechanisms, as well as band alignment engineering. We summarize the current understanding of the fascinating photophysics of these heterostructures, emphasizing the open questions related to their fundamental properties. We conclude by highlighting how this platform offers an unprecedented number of tuning knobs to control their optoelectronic properties and some potentially interesting directions to explore in the near future
Perspective on the physics of two-dimensional perovskites in high magnetic field
Full text linkTwo-dimensional (2D) metal halide perovskites consist of atomically thin layers composed of low bandgap metal-halide slabs, surrounded by high bandgap organic ligands, which behave as barriers. In this Perspective, we highlight how the use of large magnetic fields has been an extremely insightful tool to unravel some of the fundamental electronic properties of 2D perovskites. We focus on the combination of magnetoabsorption measurements and theoretical modeling to extract the carrier effective mass, on the use of magnetic field to clarify the fine structure of the exciton manifold, and on how magnetic fields can be helpful to correctly assign side peaks in the complex absorption or photoluminescence spectra displayed by 2D perovskites. We finally point out some challenges which might be successfully addressed by magneto-optical experimental techniques
Moire Intralayer Excitons in a MoSe2/MoS2 Heterostructure
No full textSpatially periodic structures with a long-range period, referred to as a moire pattern, can be obtained in van der Waals bilayers in the presence of a small stacking angle or of lattice mismatch between the monolayers. Theoretical predictions suggest that the resulting spatially periodic variation of the band structure modifies the optical properties of both intra- and interlayer excitons of transition metal dichalcogenide heterostructures. Here, we report on the impact of the moire pattern formed in a MoSe2/MoS2 heterobilayer encapsulated in hexagonal boron nitride. The periodic in-plane potential results in a splitting of the MoSe2 exciton and trion in emission and (for the exciton) absorption spectra. The observed energy difference between the split peaks is fully consistent with theoretical predictions
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
Magnetoexcitons in large area CVD-grown monolayer MoS2 and MoSe2 on sapphire
Full text linkMagnetotransmission spectroscopy was employed to study the valley Zeeman effect in large area monolayer MoS2 and MoSe2. The extracted values of the valley g factors for both A and B excitons were found to be similar with g(v) similar or equal to -4.5. The samples are expected to be strained due to the CVD growth on sapphire at high temperature (700 degrees C). However, the estimated strain, which is maximum at low temperature, is only similar or equal to 0.2%. Theoretical considerations suggest that the strain is too small to significantly influence the electronic properties. This is confirmed by the measured value of the valley g factor, and the measured temperature dependence of the band gap, which are almost identical for CVD and mechanically exfoliated MoS2.LANE
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
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