1,721,006 research outputs found
Sensitive Piezoresistive sensors made of Graphene-based 3D ordered porous structures for wearable electronics
No full textRecent years have shown significant progress in developing stretchable electrodes, which remain the fundamental building block in flexible and wearable electronic devices. The excellent properties of graphene have made it the best candidate for the next generation of flexible electronics applications. Wearable sensors require several properties such as high flexibility, stretchability, lightweight, and inexpensive fabrication, and they have to be suitable for integration with electrical components. One solution is the combination of nanostructures that act as sensors and polymers that guarantee the flexibility of the device. Different methods have been proposed in the literature to achieve these essential properties. However, all techniques develop a flexible sensor that is completely enclosed by the polymer, which reduces the effect of external stimuli, limiting the graphene sensitivity. In order to improve the sensitivity of the piezoresistive system, here we present a device in which the 3D polymer skeleton is covered by graphene layers grown by the CVD method.
We investigated the electrical and mechanical properties of the graphene/polymer 3D structures by measuring their electrical resistance variation as a function of compressive and tensile strain. In this presentation, the optimised methodology to produce these materials will be presented and the results obtained discussed.
The realization of a piezoelectric sensor with an exposed graphene surface would be exploitable for several applications, such as biosensing, where the device will also be sensitive to external analytes
Real-time Structural and Electrical Investigation of PDI8-CN2 based OFET
No full textSemiconductor thin-film devices based on organic molecules are of great interest for the development of high performance organic field effect transistors (OFETs) and organic light emitting diodes (OLEDs), as well as to underscore fundamental charge transport effects in molecular solids. Among the n-type organic molecules, perylene derivatives are very promising. In particular PDI-8CN2, N,N’-bis(n-octyl)-dicyanoperylene-3,4:9,10-bis (dicarb-oximide), has been reported to allow the fabrication of OFETs with excellent electrical performance (high-mobility: 0.16-0.6 cm2 V-1s-1) and remarkably high stability in air. In these systems, the charge mobility depends on the overlap between π-π orbitals of vicinal molecules, which is mainly influenced by the structure and morphology of the first layers of organic film at the interface with the dielectric. Since the structure of these first layers may significantly differ from that of the bulk, the determination of the molecular orientation and packing of organic molecules at the substrate interface is a crucial input for modelling the electronic band structure and the associated charge-transport properties. For this reason we have performed Grazing Incidence X-ray Diffraction (GIXD) and X-Ray Reflectivity (XRR) measurements, in situ and real time during the UHV deposition of PDI-8CN2. Moreover, in situ and real time electrical measurements were performed on FET structures during the semiconductor deposition. Thanks to these time resolved measurements we could describe i) the thin-film growth dynamics, ii) the molecular packing and microstructure of the organic thin film, iii) the influence of the substrate temperature and the deposition flux, and iv) the relation between the charge transport properties and the growth mechanism of the thin film
Tuneable Permeability to H2, CO2, He, and Ar in Graphene Oxide−PDDA Self-Assembled Multilayers, Yielding Good Selectivity at High Flux
Full text linkToday, the most effective and suitable method to obtain molecular H2 is the
extraction from mixtures where it is present, using gas-sieving membranes.
To this aim, the preparation and characterization of layered nano-composites
are described, made of alternated layers of positively charged Poly(Diallyl
Dimethyl Ammonium chloride) (PDDA) and negatively charged graphene
oxide (GO) nanosheets with high and tunable selectivity for H2 purification.
The composites are assembled exploiting electrostatic interactions and the
layer-by-layer technique; this study correlates permeance tests with changes
in chemical composition and structure of the material using X-rays
Photoelectron Spectroscopy, X-rays diffraction water contact angle, and
surface zeta-potential measurements. Thanks to its layered nature, the
GO-PDDA composite shows an excellent selectivity, allowing faster
permeation of H2 as compared to CO2 and Argon. By transforming the GO to
reduced GO, the porosity of the nanosheets can be further increased, in this
way increasing the permeance of the material and its selectivity at the same
time, thus allowing to overcome the Robeson limit, the technological upper
boundary to the performance of actual membranes
Sensitive Piezoresistive sensors made of Graphene-based 3D ordered porous structures for wearable electronics
No full textRecent years have shown significant progress in the development of stretchable electrodes, which remain the fundamental building block in flexible and wearable electronic devices. The excellent properties of graphene have made it the best candidate for the next generation of flexible electronics applications. Wearable sensors require several properties such as high flexibility, stretchability, lightweight, and inexpensive fabrication, and they must be suitable for integration with electrical components. One solution is the combination of nanostructures that act as sensors and polymers that guarantee the flexibility of the device. Different methods have been proposed in the literature to achieve these essential properties. However, all techniques develop a flexible sensor that is completely enclosed by the polymer, which reduces the effect of external stimuli, limiting the sensitivity of graphene. In order to improve the sensitivity of the piezoresistive system, we present a device in which the 3D polymer skeleton is covered by graphene layers grown by the CVD method, as shown in Figure 1a.
We investigated the electrical and mechanical properties of the graphene/polymer 3D structures by measuring their electrical resistance variation as a function of compressive and tensile strain. In this presentation, we will present the optimized methodology to produce these materials and discuss the results obtained.
Moreover, the realization of a piezoelectric sensor with an exposed graphene surface would be useful for several applications, such as biosensing, where the device would also be sensitive to external analytes
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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