1,720,980 research outputs found
Atom-by-atom identification of catalytic active sites in operando conditions by quantitative noise detection
No full textElectrochemical scanning tunneling microscopy (EC-STM) allows direct observation of surfacechanges at theatomic scale in thepresenceofan electrolyte at different electrochemical potentials. Recently, it has been demonstrated that the noise in the tunneling current of EC-STM allows identifying electrocatalytically active sites under reaction condi- tions. However, this method has never been applied to atom-by-atom investigations and could not provide a quantitative evaluation of the catalytic activity. Using the hydrogen evolution reaction as case study, we demonstrate that the quantitative analysis of the noise in the tunneling current allows quantifying the local onset potential and pro- vides informationaboutthemicroscopicmechanismofelectrochemical reactions on subnanometric electrocatalytic sites, such as chemically heterogeneous flat interfaces, nanoparticles, andeven single-atom de- fects. This unique method allows surpassing the current limits of not only the state-of-the-art EC-STM but also other operando and micro- scopy techniques
Potential Driven Non-Reactive Phase Transitions of Ordered Porphyrin Molecules on Iodine-Modified Au(100): An Electrochemical Scanning Tunneling Microscopy (EC-STM) Study
Full text linkThe modelling of long-range ordered nanostructures is still a major issue for the scientific community. In this work, the self-assembly of redox-active tetra(N-methyl-4-pyridyl)-porphyrin cations (H2TMPyP) on an iodine-modified Au(100) electrode surface has been studied by means of Cyclic Voltammetry (CV) and in-situ Electrochemical Scanning Tunneling Microscopy (EC-STM) with submolecular resolution. While the CV measurements enable conclusions about the charge state of the organic species, in particular, the potentio-dynamic in situ STM results provide new insights into the self-assembly phenomena at the solid-liquid interface. In this work, we concentrate on the regime of positive electrode potentials in which the adsorbed molecules are not reduced yet. In this potential regime, the spontaneous adsorption of the H2TMPyP molecules on the anion precovered surface yields the formation of up to five different potential-dependent long-range ordered porphyrin phases. Potentio-dynamic STM measurements, as a function of the applied electrode potential, show that the existing ordered phases are the result of a combination of van der Waals and electrostatic interactions
Enhancing the Oxygen Electroreduction Activity through Electron Tunnelling: CoOx Ultrathin Films on Pd(100)
No full textInterfacial chemistry and electroactivity of black phosphorus decorated with transition metals
No full textBlack phosphorus (BP) exhibits a significant chemical reactivity toward transition metals, which is strongly dependent on its electronic and morphological features. Using as a case study metal Co atoms deposited by physical vapor deposition on chemically exfoliated BP thin films, we document that environmentally oxidized BP edges react immediately with the formation of Co(II)–POx species, but later also the basal plane strongly reacts, already at room temperature, to form an interfacial phosphide. Atomically resolved scanning tunneling microscopy data reveal the formation of a Co2P(112) layer, upon which the further growth of metal Co nanoparticles takes place. X-ray photoemission spectroscopy data show similar interfacial reactions also for atomic W, suggesting a quite general behavior. The electrochemical and photoelectrocatalytic properties of the resulting metal–BP nanohybrids are investigated by linear sweep voltammetry and electrochemical impedance spectroscopy. The Co–BP nanohybrid shows a marked stability in acid media and a significant increase of the electrocatalytic activity for the hydrogen evolution reaction with respect to bare BP, due to the formation of a very stable phosphide phase, and even an interesting photoactivity connected to the formation of p–n junction between BP and Co2P. On the other hand, the W–BP nanohybrid exhibits a modest performance in the electrocatalytic production of hydrogen because of the formation of less active oxide phases as a consequence of environmental oxidation
Strain Induced Phase Transition of WS2 by Local Dewetting of Au/Mica Film upon Annealing
Full text linkHere, we present a proof-of-concept experiment where phase engineering at the nanoscale of 2D transition metal dichalcogenides (TMDC) flakes (from semiconducting 2H phase to metallic 1T phase) can be achieved by thermal annealing of a TMDC/Au/mica system. The local dewetting of Au particles and resulting tensile strain produced on the TMDC flakes, strongly bound to the Au surface through effective S-Au bonds, can induce a local structural phase transition. An important role is also played by the defects induced by the thermal annealing: when vacancies are present, the threshold strain needed to trigger the phase transition is significantly reduced. Scanning photoelectron microscopy (SPEM) was revealed to be the perfect tool to monitor the described phenomena
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
- …
