1,720,984 research outputs found
New approach for analyzing the vertical structure of polymer thin films based on surface-enhanced Raman scattering
No full textWe report on a new approach for measuring
the chemical composition of the 20 nanometers at the top or
bottom of a polymer film. This approach is based on a
variation of the surface enhanced Raman scattering effect with
laser illumination through a thin gold layer (∼4 nm). We show
that the introduction of the thin gold layer has little or no
effect on the morphology of the film that is spin coated on top
of it. We demonstrate that this technique has better than 20
nanometer vertical resolution by studying bilayers of polyfluorines with varying thicknesses and by showing the existence of top
and bottom wetting layers in a polymer blend of the same polymers. We also show that the top wetting layer is thinner than the
bottom one. The difference in thicknesses explains how a solar cell with an electron blocking layer at the cathode works
Series of O,N,O-Tridentate Ligands Zinc(II) Complexes with High Solid-State Photoluminescence Quantum Yield
No full textFour neutral complexes were synthesized by reaction of tridentate N-salicylidene-N′-aroylhydrazine ligands with zinc(II) acetate and pyridine as a further ligand. The O,N,O-chelating molecules N-4- [octyloxy(phenoxy)]salicylidene-N′-fluorobenzoylhydrazine (L1), N-4-[octyloxy(phenoxy)]salicylidene-N′-(benzothiazolyl)hydrazine (L 2), N-4-[octyloxy(phenoxy)]salicylidene-N′- cyanobenzoylhydrazine (L3), and N-4-[octyloxy(phenoxy)]salicylidene- N′-nitrobenzoylhydrazine (L4) gave dinuclear O-bridged complexes Zn2Li2Py2n (n = 1 or 2 in a special case). The ligands and complexes were characterized by mass spectrometry and 1H NMR, UV/Vis, photoluminescence (PL), and FTIR spectroscopy. The structures of the complexes were solved by single-crystal X-ray analysis. Nematogenic phase behavior was detected for some ligands by thermogravimetric analysis/differential scanning calorimetry (TGA-DSC) and optical observations. The solution and solid-state photoluminescence spectra were recorded and show that the ligands are roughly nonfluorescent, whereas all of the complexes show noteworthy emission in widely different spectral regions. The photoluminescence maxima of the complexes in the solid state are dependent on the acceptor group, and medium-to-high PL quantum yields were recorded for all of the crystalline complexes. Both periodic and molecular DFT calculations were performed to rationalize the absorbance of these complexes at the "one-particle" level. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Color Tuning and Noteworthy Photoluminescence Quantum Yields in Crystalline Mono/Dinuclear ZnII Complexes
No full textSeries of ZnII complexes with coordinated pyridine and a O,N,O tridentate core are reported. Four species of the general formula ZnLiPy2 were synthesized, where Li is a substituted ((aroylhydrazono)methyl)-3-hydroxyphenyl-4-(octyloxy)benzoate. The structure of the four mononuclear complexes and of dinuclear Zn2L24Py2 was solved by single crystals X-ray analysis. By TGA-DSC analysis and optical observation a nematogenic phase behavior was detected for ligands only and not for complexes. Photoluminescence spectra were recorded both in solution and in solid state Only the complexes showed a noteworthy photoluminescence in the solid state with tunable wavelength by varying the aroyl group. Medium to very high PL quantum yields were recorded on the crystalline complexes obtained in their mononuclear coordination environment. In the case of 4-nitrobenzoyl substituent a dinuclear complex with formula Zn2L24Py2 showed an unprecedent exceptionally high PLQY value. Both periodic and molecular DFT calculations were performed to rationalize the absorbance of these complexes at “one particle” level
Benzodifuroxazinones, a new class of heteroacene molecules for possible applications in organic electronics: Synthesis, electronic properties and crystal structure
No full textA novel class of heteroacene molecules, benzodifuroxazin-4-ones, has been effectively synthesized by means of a thermally activated double cyclization reaction starting from amidic precursors. The new molecules were thermally and optically characterized, revealing an outstanding thermal stability to oxidation and an uncommon enhancement of fluorescent properties in solid state as compared to solution. As shown by single-crystal XRD analysis, the molecules crystallize in a face-to-face (π-stack) arrangement instead of the herringbone structure typical of the most acene derivatives. The electronic properties of both molecules and crystals have been investigated by means of a detailed Density Functional Theory computational analysis: very stable HOMO energies have been calculated and, from the band structure analysis, it is possible to suggest a preferential direction of charge transport along the π-stacking direction. All the reported properties indicate this new class of heteroacene derivatives as interesting candidates for a possible application in organic electronics
Comprehensive study of the influence of different environments on degradation processes in F8BT: Correlating optoelectronic properties with Raman measurements
No full textA new model of organic solar cells reveals open circuit conditions and size dependent power loss induced by the finite conductivity of a transparent contact
No full textGoing 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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