1,720,987 research outputs found
Nanooptomechanical silicon devices for sensing applications
Full text linkThe interest in the field of plasmonics is growing steadily in the last two decades; from the ability to transmit and receive information at very high speed with greatly reduced losses to the enhancement of very weak signals for chemical and biological analysis, its range of applicability is boundless. The understanding of plasmonic phenomena is also increasing, and with this comes the ability to tune plasmonic properties to the designer’s will. Among other approaches, the use of MicroElectroMechanical Systems (MEMS) for the modulation of plasmonic properties has been recently reported in literature, but no practical application, such as Raman spectroscopy, has been reported beside the field of Tip-Enhanced Raman Spectroscopy, a powerful approach that demonstrated nanometric chemical spatial resolution, but which remains confined the research laboratory benches due to its intrinsic experimental complexity.
In this project, we propose to explore the coupling between mechanical and plasmonic properties of micro and nanosensors in order to realize a mechanical resonator capable of turning on and off a frequency modulated hot spot.
Different strategies have been tried to achieve the desired result: the first version of the optomechanical device was based on a vertical resonator (pillar) put in close proximity with a steady structure, 100 nm apart from each other. The devices are fabricated using electron-beam lithography for the high resolution required for the sub-micron gap and ICP-RIE to obtain an inverted tapered structure of the pillar walls; the evaporation of a gold layer on top of the devices ensures a plasmonic activity of the upper surface during the actuation of the devices. Optical lever techniques and Rayleigh scattering mapping have been used for the mechanical characterization and the onset of an impact oscillation condition is discussed. The Raman scattering intensification due to the formation of a plasmonic hot spot in the contact region has been studied functionalizing the devices with pentacene and an enhancing factor for the Raman signal during actuation can be estimated. However, severe drawbacks have been identified in this configuration, since pillars tilt and bend nanometrically during the motion, causing the hot spots to be randomly localized along the gap and reducing their field enhancement capabilities.
The problems arisen with the first version of the device have been solved through the careful design of a new geometry: the vertical resonator has been changed into a horizontally-oscillating cantilever tuning the width-to-height ratio, and a tip has been added to the design for a well-defined contact point. This new device has been characterized using sample scanning confocal microscopy, both in its mechanical properties and in the surface distribution of the chosen Raman dye, benzotriazole azo (BT-Azo), after the functionalization. Finally, the plasmonic behaviour has been investigated and the signal coming from the hot spot has been successfully isolated using a combination of polarization-dependent excitation light and lock-in deconvolution of the signal at higher harmonics, thus demonstrating the successful realization of a frequency modulated hot spot for Raman spectroscopy applications.
As a side activity, a wire scanner sensor with nanofabricated bridges suspended over a wide window has been fabricated, for the characterization of high-energy electron or light beams. The test of this device has been performed at the BEAR beamline of the Elettra Synchrotron and in the FERMI FEL-1 Free-Electron Laser facility; the performances of this sensor have been proved to be comparable, when not superior, to those of the commercially available devices
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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