1,721,147 research outputs found
Nanoimprint lithography: Toward functional photonic crystals
No full textIn this chapter we review the use of nanoimprint lithography and its derivative soft-lithography techniques for the fabrication of functional photonic crystals. Nanoimprint is a viable, scalable, and cost-effective solution for large area patterning. While initially it relied primarily on pattern transfer from a rigid mold to a thermally softened polymer by embossing, in the last two decades the process evolved rapidly, giving rise to new technologies that allow direct imprint of functional materials such as conjugated polymers, metals, biological matter, and metal oxides. These advancements generated increasing interest in the use of nanoimprint lithography for the fabrication of photonic structures for light management in optoelectronic devices. After describing standard nanoimprint lithography and its derivative soft-lithography methods, we briefly discuss nanoimprint capabilities and prospects in photonic applications. In particular we review recent implementations of imprinted photonic structures for light management in organic light emitting diodes, solar cells, solid state lasers and sensors
New materials for metamaterials: perovskites, phase change chalcogenides, and topological insulators
No full textWe introduce a new generation of plasmonic and dielectric materials for metasurfaces and metadevices. These include color-tunable nanostructured hybrid organic-inorganic perovskites, phase-change chalcogenides, and broadband topological insulators
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
Photons as ants: a stigmergic photonic network
No full textStigmergy is the cooperative behaviour of insects mediated by the environment, found for instance in the food searching activities of ants. The ant society communicates indirectly by marking routes with chemicals (pheromones), which attract other ants to tread the same route. Using stigmergy, the entire ant colony is finally able to find the optimal (shortest) path connecting the nest to the food
White light emission in low-dimensional perovskites
No full textLow-dimensional perovskites are rapidly emerging due to their distinctive emission properties, consisting of ultrabroad and highly Stokes shifted luminescence with pure white light chromaticity, which makes them very attractive for solution-processed light-emitting devices and scintillators. To foster the design of new materials and their device applications, it is timely to review the relation between perovskite structural properties and the photophysical phenomena underlying their unique light emission characteristics. From a number of recent studies, it has emerged that broadband emission properties in metal halide frameworks are very common, stemming from the self-localization of small polaron species at specific sites of the inorganic lattice, with a wide energy distribution. This review aims to provide an account of the current understanding of the photophysical processes underpinning luminescence broadening and highly efficient emission in various classes of low-dimensional metal-halide frameworks, and to highlight their potential for solution-processed optoelectronic device applications. The discussion will additionally establish a wider perspective on the role of intrinsic and extrinsic self-trapping, formation of polarons and their effect on charge generation and transport in low-dimensional perovskites
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
First-Principles Study of the Nuclear Dynamics of Doped Conjugated Polymers
No full textInfrared-active vibrational (IRAV) modes are specific optical fingerprints to probe the density, dynamics, and spatial distribution of polarons in ac-electron conjugated polymers. So far, the description of IRAV mode activation and selection rules, resulting from the local breaking of spatial symmetry induced by charge carriers, has been restricted to phenomenological lattice-dynamics models. Overcoming the classical picture, here we combine first-principles calculations with vibrational spectroscopy to study the nuclear dynamics of a model polymer system, poly(3-hexylthiophene) (P3HT). We assign and reproduce quantitatively the transition energies and intensities of vibrational normal modes in the ground and excited electronic states. By comparing the ground, polaronic, and excitonic states of regioregular (RR-) and regiorandom (RRa-) chains, we identify, for the first time, the vibrational fingerprints of neutral singlet excitations in the IRAV spectra of P3HT and highlight structure property correlations. Within this new approach, vibrational spectroscopy provides a comprehensive tool to study not only polaron but also exciton density and dynamics and to better understand the influence of disorder on exciton and charge-carrier localization in functional organic systems
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