1,720,974 research outputs found
Physical confinement versus adsorption driven reconstruction: The case of sulfate anion interaction with vicinal Cu(111) surfaces
No full textNano-electrochemistry, i.e., the research of the properties of nano-(structured) electrodes and their influence on
electrochemical processes when immersed inside an electrolyte, represents a hot topic in view of applications in
nano-electronics, electro-catalysis and energy storage devices. The role of physical confinement in the electrochemical fabrication and performances of the respective systems have been recently addressed in the context of
metal-organic networks on surfaces, but rarely of nano-structured bare metal surfaces, for instance, regularly
stepped (vicinal) surfaces. In this work we investigate the interplay between physical confinement and adsorbate
induced restructuring by the electrochemical adsorption of sulfate anions on the flat and two distinctly different
vicinal Cu(111) surfaces. Sulfate adsorption on the flat Cu(111) surface is known to create a long-range ordered
Moir ́e-superstructure with lattice parameters in the 2–4 nm range due to an expansion of the topmost layer of
copper atoms with respect to the underlying crystal planes. This restructuring is also observed on a vicinal Cu
(111) surface whose original terrace width is considerably smaller than the lattice vectors of the sulfate induced
Moir ́e-structure. The results clearly indicate not only that the Moir ́e formation lifts the physical confinement
imposed by the initial terrace width, but also shine more light on the Moir ́e formation process itself. Such
adsorbate induced restructuring, of course, depends on the respective adsorbate – electrode combination, but
must, in principle, always be taken into account in order to understand electrochemical processes at nanostructured (and nano-sized) electrode surfaces
A combined EC-STM and EC-AFM investigation of the sulfate adsorption on a Cu(111) electrode surface up to the anodic corrosion potential
No full textNowadays, sulfate adsorption on single Cu(111) crystals, when immersed in diluted sulfuric acid solution, can be considered a benchmark to test the so-called electrochemical scanning tunneling microscopy (EC-STM), because the formation of a well ordered sulfate superstructure and a characteristic Moiré pattern can be detected by STM on different length scales. Clearly, EC-STM shows more difficulties in the image acquisition when the applied potential is close to or within the anodic corrosion regime, i.e., when copper undergoes a dissolution process that releases copper ions (Cu2+) into solution, because both the developed high faradaic current flowing through the sample and a significant disintegration of the electrode surface may cause severe instability during the STM scan. Here, we successfully combine the EC-STM with the EC-atomic force microscopy (EC-AFM) to extend the surface characterization towards the corrosion regime. In addition, the Cu(111) surface morphology has never been explored with EC-AFM after the copper re-deposition occurring in the reverse potential scan at EC-potentials lower than the anodic corrosion one. Consequently, our combined investigation, performed on different length scales, highlights the effects of the redox processes in the whole EC potential interval that can be explored during the cyclic voltammetry (CV)
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
Optical Anisotropy of Porphyrin Nanocrystals Modified by the Electrochemical Dissolution
Full text linkReflectance anisotropy spectroscopy (RAS) coupled to an electrochemical cell represents a powerful tool to correlate changes in the surface optical anisotropy to changes in the electrochemical currents related to electrochemical reactions. The high sensitivity of RAS in the range of the absorption bands of organic systems, such as porphyrins, allows us to directly correlate the variations of the optical anisotropy signal to modifications in the solid-state aggregation of the porphyrin molecules. By combining in situ RAS to electrochemical techniques, we studied the case of vacuum-deposited porphyrin nanocrystals, which have been recently observed dissolving through electrochemical oxidation in diluted sulfuric acid. Specifically, we could identify the first stages of the morphological modifications of the nanocrystals, which we could attribute to the single-electron transfers involved in the oxidation reaction; in this sense, the simultaneous variation of the optical anisotropy with the electron transfer acts as a precursor of the dissolution process of porphyrin nanocrystals
Probing the correlation between morphology and optical anisotropy in ZnTPP films grown at different temperatures
Full text linkFilms of tetraphenylporphyrins (TPP) have been recently investigated for their ability in protecting graphite electrode surfaces from degradation. The effectiveness of the protection depends on both the molecule–substrate and molecule–molecule interactions, which determine the type of film growth and its morphology. For instance, meso-tetraphenyl porphyrin-Zn(II) (ZnTPP) arranges differently depending on the substrate, conditions used for deposition and post-growth treatments. Since many parameters influence film morphology and strategies to reach an efficient protective coverage, here we investigate the role of the substrate temperature in determining morphological variations in thick ZnTPP films. ZnTPP molecules were sublimated by an organic molecular beam epitaxy (OMBE) system on a highly oriented pyrolytic graphite (HOPG) substrate, controlled in temperature by a variable temperature cryostat. The film morphology was characterized by atomic force microscopy (AFM), whereas the type of growth by reflectance anisotropy spectroscopy (RAS), which is highly sensitive to the orientation and type of arrangement of molecules on the substrate; changes in the film valence electronic structure were monitored in situ by UV photoemission spectroscopy (UPS). The comparison between AFM and RAS investigations clearly correlates a ZnTPP film morphology to the characteristic optical signal, both influenced by temperature conditions and diffusivity of molecules on the substrate
- …
