1,720,957 research outputs found
Gallium phase change as a mechanism for resonance tuning in photonic nanostructures
No full textThis thesis covers contributions to the field of electromagnetic metamaterials, a broad, dynamic area that has produced a considerable array of new phenomena and is now looking to the prospect of tuning and switching the characteristics of novel materials and surfaces, using many means including thermal and electromagnetic excitation, in order to extend their usefulness and to enable their application in practical devices. In particular, this work develops materials that allow electromagnetic and thermal control of material optical properties and methods that facilitate the use of metasurface physics on macroscopic scales.The reversible photoconductivity effect produced by phase coexistence in an elemental metal has been enhanced in a metamaterial for the first time. A gap plasmon absorber type metasurface was developed to enhance the photoconductivity of a gallium metal interface under near infrared illumination, achieving an order of magnitude increase in the strength of the phenomenon in a pump-probe experiment. The enhanced nonlinearity displayed at the pump wavelength of 1310nm corresponds to an effective nonlinear dielectric susceptibility x(3) of greater than 1 × 10−8 m3 V−2.Competing descriptions of the mechanism behind the reversible photoconductivity effect in elemental gallium, including an analytic model based on heat transfer, a non-thermal model of light-induced excitation, full finite element simulation and a novel cellular automaton method have been implemented and compared. These models have been adapted and applied to the metasurface-enhanced interface for the enhancement of the effect. It was found that an exclusively thermodynamic theoretical treatment of laser heating is insufficient to explain the magnitude of the observed excitation and hence an additional possibly non-thermal photoexcited mechanism must contribute.Processing methods were developed for the testing of nano-imprint metamaterial manufacturing with liquid metals under controlled environmental conditions, using a custom-built pressure controlled processing chamber. Using this methodology a feasibility study of the production of a nanoimprinted liquid metal photonic structure was conducted, successfully demonstrating the infiltration of nanoscale gratings of period 600nm with liquid gallium and optical switching of the resulting composite interface.The templated deposition of ordered arrays of gallium nanoparticles on structured substrates has been demonstrated for the first time. Bulk gallium was thermally evaporated onto substrates structured with gratings and checkerboard-type patterns of period 200 to 1600nm. Fourier and image analysis of the produced ordering shows a pronounced tendency for the nanoparticle growth to align with the substrate patterns in both positional frequency and diameter. Such ordered arrays of metallic particles could form an active medium as a component of a plasmonic metamaterial
Templated assembly of metal nanoparticle films on polymer substrates
No full textWe report on directed self-assembly of ordered, vapor-deposited gallium nanoparticles on surface-relief-structured polymer substrates. Grating templates impose periodic order in one dimension, most effectively when the grating half-period is of order the mean unperturbed center-to-center particle spacing for a given mass-thickness of Ga. Self-organized order also emerges in the perpendicular direction as a consequence of the liquid-phase particles’ nucleation, growth and coalescence on the ridges of the grating pattern in relative isolation from the adjacent slots, and vice versa
Ga particle templated assembly dataset
No full textSEM image set for:
Waters, Robin et al (2016) Templated assembly of metal nanoparticle films on polymer substrates. Applied Physics Letters.</span
Cellular automata dynamics of nonlinear optical processes in a phase-change material
No full textChanges in the arrangement of atoms in matter, known as structural phase transitions or phase changes, offer a remarkable range of opportunities in photonics. They are exploited in optical data storage and laser-based manufacturing, and have been explored as underpinning mechanisms for controlling laser dynamics, optical and plasmonic modulation, and low-energy switching in single nanoparticle devices and metamaterials. Comprehensive modeling of phase-change processes in photonics is, however, extremely challenging as it involves a number of entangled processes including atomic/molecular structural change, domain and crystallization dynamics, change of optical properties in inhomogeneous composite media, and the transport and dissipation of heat and light, which happen on time and length scales spanning several orders of magnitude. Here, for the first time, we show that the description of such complex nonlinear optical processes in phase-change materials can be reduced to a cellular automata model. Using the important example of a polymorphic gallium film, we show that a cellular model based on only a few independent and physically-interpretable parameters can reproduce the experimentally measured behaviors of gallium all-optical switches over a wide range of optical excitation regimes. The cellular automata methodology has considerable heuristic value for the study of complex nonlinear optical processes without the need to understand details of atomic dynamics, band structure, and energy conservation at the nanoscale.</p
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
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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