1,721,089 research outputs found
Nanocrystalline sp(2) and sp(3) carbons: CVD synthesis and Applications
No full textThe design and production of innovative materials based on nanocrystalline sp2- and sp3-coordinated
carbons is presently a focus of the scientific community. We present a review of the nanostructures
obtained in our labs using a series of synthetic routes, which make use of chemical vapor deposition (CVD)
techniques for the selective production of non-planar graphitic nanostructures, nanocrystalline diamonds,
and hybrid two-phase nanostructures
Organized networks of helically wound single-walled C-nanotubes
No full textWe report experimental evidence on the possibility to synthesize organized networks of helically wound single-walled carbon nanotubes (SWNTs). In particular, our experimental approach produces ordered layers constituted by twisted bundles formed by interweaved single-walled nanotubes. Scanning electron microscopy (SEM), scanning tunnelling microscopy (STM) and high resolution transmission electron microscopy (HRTEM) been used to investigate the inner structure of the nanotubes deposits. The results of our studies strongly suggest that aligned arrays of helically wrapped nanotube bundles can be obtained by controlling the spatial dispersion of metallic clusters at the substrate surface. Whereas the spatial distribution of the catalyst govern the packing of the bundles, the dimension of metallic clusters is responsible for the nucleation of single-walled nanotubes from the same location and the consequent wrapping
Structural Investigation of Carbon Nanoplatelets by Graphene Layers self-assembling
No full textLow dimensional carbon based materials are strictly dependent from the intrinsic property of self-assembling. Three simple and fast methods to unzip Single Wall Carbon Nanotubes (SWCNTs) have provided different structural organization of graphite layers,[1] observed by electron microscopy investigations. The graphitic nanoplates were obtained from disruption of SWCNTs by using high-shear mixing and/or treatments in sulfonitric mixtures either at room or high temperatures. Depending on the process procedures, different kinds of re-organization are found to occur, as evidenced by different and complementary electron diffraction and microscopy techniques. To obtain insight into the local nano-structure of self-assembling of the graphitic phases produced from SWCNTs, transmission electron microscopy (TEM) has been used to characterize the morphology arrangement and the crystallinity identifications by Reflection High Energy Electron Diffraction (RHEED).[2] Detailed internal structural investigation has been achieved by selected area electron diffraction (SAED) and with help of its electron diffraction simulation.
Here, we focused our investigation on the structural characterization of self-assembling graphitic layers that it has been and it is a long-standing scientific problem. Unlike crystalline system, where long-range ordering is established by periodic stacking of fundamental building blocks, known as unit cells, rolled open SWCNTs process produces graphitic flakes, having no long-range translational or orientational order, although some degrees of short- and medium-range order do exist. Our structural studies reveal the presence of a deviation from perfect crystal of the graphite aggregations, called turbostratic graphite, because of the presence of rotational and/or translational stacking faults of its hexagonal basal planes. Another interesting outcome of our research is that experimental evidences using electron diffraction technique indicate the existence of an unstable crystallographic phase of graphite with an orthorhombic cell and symmetry Cmma, detected by SAED and RHEED analysis and simulated by using the unit cell parameters reported by previously theoretical studies [3]. The last case study clearly confirms that EDPs are very sensitive to small variations in periodic structure or lattice imperfection and to investigate phase transition phenomena. Moreover, this research also intends to provide the readers with useful informations that to resolve the fundamental problem of how is thick a bi-dimensional structures of also different atomic species, TEM imaging analysis of the flake-edges must be coupled with electron diffraction pattern investigation
Effect of tip geometry on local indentation modulus measurement via atomic force acoustic microscopy technique
No full textAtomic force acoustic microscopy (AFAM) is a dynamical AFM-based technique very promising for nondestructive analysis of local elastic properties of materials. AFAM technique represents a powerful investigation tool in order to retrieve quantitative evaluations of the mechanical parameters, even at nanoscale. The quantitative determination of elastic properties by AFAM technique is strongly influenced by a number of experimental parameters that, at present, are not fully under control. One of such issues is that the quantitative evaluation require the knowledge of the tip geometry effectively contacting the surface during the measurements. We present and discuss an experimental approach able to determine, at first, tip geometry from contact stiffness measurements and, on the basis of the achieved information, to measure sample indentation modulus. The reliability and the accuracy of the technique has been successfully tested on samples (Si, GaAs, and InP) with very well known structural and morphological properties and with indentation modulus widely reported in literature. (c) 2005 American Institute of Physics
Titanium carbide thin-film electrodes: Characterization and evaluation as working electrodes
No full textTitanium carbide (TiC) polycrystalline thin films, obtained by a hybrid chemical vapor deposition/powder flowing technique, were characterized and used to assemble electrodes. The potential window and the electro-chemistry of standard redox couples ([Ru(NH3)(6)](3+), [Fe(CN)(6)](3-)) have been investigated in cyclic voltammetry, demonstrating a behavior similar to glassy carbon electrodes. The quinone (Q)/hydroquinone(H(2)Q) redox couple presented an interesting quasireversible behavior (E-p = 0.07 mV), confirmed also for other quinones.[...
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
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