1,720,988 research outputs found
Optical nonlinearity goes ultrafast in 2D semiconductor-based nanocavities
Full text linkHybrid systems of silver nanodisks strongly coupled to monolayer tungsten-disulfide (WS(2)) show giant room-temperature nonlinearity due to their deeply sub-wavelength localized nature, resulting in ultrafast modifications of nonlinear absorption in a solid-state system
High efficiency ITO-free flexible white organic light-emitting diodes based on multi-cavity technology
No full textThe technology of white organic light-emitting diodes (WOLEDs) is attracting growing interest due to their potential application in indoor lighting. Nevertheless the simultaneous achievement of high luminous efficacy (LE), high color rendering index (CRI), very low manufacturing costs and compatibility with flexible thin substrates is still a great challenge. Indeed, very high efficiency devices show usually low values of CRI, not suitable for lighting applications, and use expensive indium tin oxide (ITO) electrodes which are not compatible with low cost and/or flexible products. Here we show a novel low cost ITO-free WOLED structure based on a multi-cavity architecture with increased photonic mode density and still broad white emission spectrum, which allows for simultaneous optimization of all device characteristics. Without using out-coupling optics or high refractive index substrates, CRI of 85 and LE as high as 33 lm W-1 and 14 lm W-1 have been demonstrated on ITO-free glass and flexible substrates, respectively. (C) 2013 Elsevier Ltd. All rights reserved
Ultrafast Dynamics of 2D Materials and their Heterostructures
No full textThe extreme confinement and reduced screening in monolayer Transition Metal Dichalcogenides (TMDs) leads to the appearance of tightly bound excitons which can also couple to free charges, forming trions, owing to strong Coulomb interactions. Low temperatures and encapsulation in hexagonal Boron Nitride (hBN) can narrow the excitonic linewidth, approaching the regime of homogeneous broadening, mostly dominated by the radiative decay. Ultrafast spectroscopy is a powerful tool to study exciton formation and relaxation dynamics in TMD monolayers. However, high-quality hBN-encapsulated structures have usually lateral sizes of the order of a few microns, calling for the combination of high spatial and temporal resolution in pump-probe experiments. Here we use a custom broadband pump-probe optical microscope to measure the ultrafast dynamics of excitons and their complexes in high-quality hBN-encapsulated monolayer and bilayer of MoS2 at 8K. In monolayers, neutral excitons with a narrow linewidth of 7.5 meV, approaching the homogeneous limit, show very fast recombination time of ∼ 130 fs measured in pump-probe. Moreover, we observe markedly different dynamics of the trions and biexcitons over the neutral ones. Finally, we investigate the static and dynamic nonlinear behavior of intra and interlayer excitons in bilayers, showing very peculiar and unprecedented inter-species scattering effects, linked to the charge tunneling between the layers
High quality factor microcavity OLED employing metal-free electrically active Bragg mirrors
No full textA Fabry-Perot microcavity with a high quality Q-factor is an excellent tool to finely tune and narrow the emission spectrum of embedded organic dyes, leading also to a modification of the radiative emission rate (Purcell effect). For a real application of these properties in light emitting diodes and lasers, high Q-factors should be also provided in electrically-driven organic microcavities, that is still a challenge when organic materials are employed. Metallic contacts can be safely deposited onto organic layers, although they result in strong absorption losses. In this work, we successfully integrated an Organic LED architecture within specifically tailored metal-free electrically active Bragg mirrors, finely optimized to achieve simultaneously high reflectivity and good electrical properties. The resulting electroluminescent microcavity showed a Q-factor of more than 200 (emission linewidth of 2.7 nm at a peak wavelength of 555 nm) and a clear proof of the occurrence of Purcell effect leading to a decrease of exciton radiative lifetime by a factor above 6. Finally, we analysed the parameters that still limit the Q-factor of our architecture, paving the way for future improvements. The proposed approach can be exploited for the fabrication of novel monochromatic organic light sources for telecommunications or biological sensing and it represents an important step towards the realization of electrically driven organic lasers
A colour tunable microcavity by weak-to-strong coupling regime transition through a light-switchable material
No full textAn organic based microcavity showing fully reversible colour tunability has been achieved for the first time. The emission output changes according to the modulation from pure photonic to polaritonic resonant modes through UV irradiation of the light-switchable matrix
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
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