1,720,998 research outputs found
Structural and morphological modifications of thermally reduced cerium oxide ultrathin epitaxial films on Pt(111)
No full textThe modifications of the stoichiometry, morphology and surface structure of cerium oxide ultrathin films
induced by thermal treatments under vacuum and oxygen partial pressure were studied using in situ X-ray
photoemission spectroscopy, scanning tunnelling microscopy and low energy electron diffraction. The
effect of the film nominal thickness, heating temperature and heating time on the degree of reduction of
the film was investigated. The reduction is more relevant on the film surface, where different ordered
surface structures were observed at different degrees of reduction for very thin films. The obtained results
are discussed taking into account the dimensionality of the oxide and the effects of the proximity of the Pt
substrate. After reduction it was always possible to re-oxidize the films back to their original oxidation
state by thermal treatment under oxygen-rich conditions
Plasmonic properties and stability of Au and Cu nanoparticles embedded in cerium oxide
Full text linkWith the aim of sensitizing cerium oxide—a very important catalytic material—to visible light, its coupling with Au and Cu nanoparticles is investigated. The samples are grown by physical synthesis by embedding a layer of nanoparticles between two cerium oxide films. The films are controlled in composition by in-situ x-ray photoemission spectroscopy and in morphology by ex-situ scanning electron microscopy. The optical properties as a function of the oxide thickness, investigated by spectrophotometry in the UV-Vis range, are interpreted based on the results of the morphological characterization and of simulations based on the Maxwell Garnett model. The stability of chemical and optical properties after air exposure is also investigated. The results, indicating that stable materials with tuneable optical properties can be obtained, are important in view of the potential application of the investigated systems in photocatalysis
Mapping the local stoichiometry in Cu nanoparticles during controlled oxidation by STEM-EELS spectral imaging
Full text linkCopper nanoparticles (NPs) can be coupled with cuprous oxide, combining photoelectrocatalytic properties with a broad-range optical absorption. In the present study, we aimed to correlate changes in morphology, electronic structure and plasmonic properties of Cu NPs at different stages of oxidation. We demonstrated the ability to monitor the oxidation of NPs at the nanometric level using STEM-EELS spectral maps, which were analyzed with machine learning algorithms. The oxidation process was explored by exposing Cu NPs to air plasma, revealing systematic changes in their morphology and composition. Initial plasma exposure created a Cu2O shell, while prolonged exposure resulted in hollow structures with a CuO shell. This study identified procedures to obtain a material with Cu2O surface stoichiometry and absorption extended into the near-infrared range. Moreover, this study introduced a novel application of machine learning clustering techniques to analyze the morphological and chemical evolution of a nanostructured sample
Morphology, Stoichiometry, and Interface Structure of CeO2 Ultrathin Films on Pt(111)
No full textStudies of model systems based on cerium oxide are important to improve current understanding of the properties of ceria-based materials, which find wide application based on the ability of cerium oxide to store, release, and transport oxygen. We report a study of CeO2 ultrathin films grown on the Pt(111) surface by reactive deposition of Ce using molecular or atomic oxygen as the oxidizing gas. High-temperature treatments in O-2 allowed us to obtain epitaxial structures with a very good quality in terms of morphology, stoichiometry, and structure. The cerium oxide films have a very flat morphology with terraces several tens of nanometers wide. The stoichiometry of the films is mainly CeO2, and the concentration of Ce3+ ions in the film can be reversibly increased by temperature treatments. We propose that the Pt substrate oxidation has a determinant role for the epitaxial stabilization of ceria films
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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