1,720,964 research outputs found
Excitons in CsPbX3 (X = Cl, Br, I) ternary nanocrystallites in thin films matrices
No full textTernary nanophases based on Cs-Pb-X (X = Br. Cl, I) composition, were evidenced in polycrystalline thin films grown by physical vapour deposition. Optical properties of these nanostructures were determined by absorption, emission and decay kinetics measurements. Nanocrystals of CsPbX3 type were found to be in agreement with reported band-structure calculations (X = Cl, Br). they show optical features of a wide band-gap semiconductor with direct band-to-band transitions. Ternary bromide and chloride phases show., at 10K, a pronounced fast free Wannier exciton emission (leading decay time < I ns) peaking round 537 and 420 nm, respectively, with very small Stokes-shift. On the contrary, the nanophase of CsPbI3 is characterised by the auto-localised exciton emission around 535nm, longer decay times in ts time scale and a pronounced Stokes-shift. In all the cases, the optical features are closely similar to the ones of the bulk ternary crystals. which were reported earlier. (C) 2001 Elsevier Science B.V. All rights reserved
OPTICAL-TUNNELING TIME MEASURES - A MICROWAVE MODEL
No full textThe results of a relatively simple experiment in the microwave range, where a step narrowing in the waveguide simulates a quantum mechanical rectangular potential barrier, are reported. This work represents a contribution toward the understanding of a complicated problem mainly to facilitate the performing of a microwave experiment which magnifies the time scale up to nanoseconds. The measurements are compared with theoretical predictions as deduced from the proposed models of quantum tunnelin
Luminescence of ternary nanoaggregates in CsI-PbI2 thin films
No full textThin films of about 400 nm thickness were grown by vacuum co-evaporation of powders of CsI and PbI2 compounds from two independent molybdenum crucibles on quartz and glass substrates. The absorption, luminescence and decay kinetics characteristics of thin films were measured in the temperature range 4-300 K. At 4.3 K the CsPbI3 aggregates show an emission peak around 535 nm and a smooth excitation spectrum with sharp excitonic peak around 406 nm. The Cs4PbI6 aggregates emission is centered around 430 nm with two characteristic excitation peaks around 365 and 290 nm. The Cs-4 PbI6 phase shows well-expressed two-component decay kinetics similar to that of Cs-4 PbX6 (X = Cl,Br) and KI: Pb bulk materials. X-ray diffraction spectroscopy confirmed the formation of CsPbI3 and Cs-4 PbCI6 nanoaggregates in the thin him samples. (C) 2000 Elsevier Science B.V. All rights reserved
Optical and structural properties of ternary nanoaggregates in CsI-PbI2 co-evaporated thin films
No full textThin films were grown by vacuum co-evaporation of CsI and PbI2 compounds from two independent crucibles. X-ray diffraction spectroscopy revealed formation of CsPbI3 and Cs4PbI6 nanoaggregates in the thin film samples and gave an estimate of their volume percentage as well. It provided also the grain size estimates, which were compared with direct observation of a thin film surface by atomic force microscopy. The absorption, luminescence and decay kinetics characteristics of thin films grown were measured. The optical characteristics of the mentioned ternary nanoaggregates were determined and compared with those of CsPbX3 and Cs4PbX6 (X = Cl, Br) bulk structures
Observation of Zenneck-type waves in microwave propagation experiments
No full textThe debated question of the superluminal speed of information remains open to different interpretations in spite of recent, apparently conclusive, contributions. A different point of view is here considered, which is based on experimental results of microwave propagation experiments, in far-field conditions. They support the hypothesis of the existence of fast waves of the Zenneck type. (c) 2006 American Institute of Physics
Free and localised exciton of ternary nanocrystals in CsX-PbX2 thin films (X = Cl, Br, I)
No full textThe creation of Pb2+ -based ternary nanophases was evidenced in co-evaporated CsX-PbX2 (X=Cl, Br, I) thin films using X-ray diffraction spectroscopy (XRD). The optical properties of CsPbX3 and Cs4PbX6 nanostructures were determined. CsPbX3 (X = Cl,Br) are wide gap semiconductors with direct band transitions and a pronounced Wannier free exciton emission showing subnanosecond decay times and very small Stokes-shift. On the contrary, it is supposed that, in CsPbI3, the auto-localization of the exciton state results in a broad and much slower emission with large Stokes shift. Cs4PbX6 is characterized by the auto-localized exciton emission in the near UV/violet spectral region and two component decay kinetics closely similar to that of Pb2+ emission centers in KX:Pb2+ (X = Cl, Br, I)
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
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
- …
