1,721,312 research outputs found
Formation of two-dimensional MoS2 and one-dimensional MoO2 nanowire hybrids
No full textOxidation of two-dimensional (2D) transition metal dichalcogenides have received great interests because it significantly influences their electrical, optical, and catalytic properties. Monoclinic MoO2 nanowires grow along the zigzag direction of 2D MoS2 via thermal annealing at a high temperature with a low oxygen partial pressure. The hybrids of semiconducting 2D MoS2 and metallic 1D MoO2 nanowires have potential to be applied to various devices such as electrical devices, gas sensors, photodetectors, and catalysts
Phase-Engineered WS2 Monolayer Quantum Dots by Rhenium Doping
No full textTransition metal dichalcogenides (TMDs) occur in the thermodynamically stable trigonal prismatic (2H) phase or the metastable octahedral (1T) phase. Phase engineering of TMDs has proven to be a powerful tool for applications in energy storage devices as well as in electrocatalysis. However, the mechanism of the phase transition in TMDs and the synthesis of phase-controlled TMDs remain challenging. Here we report the synthesis of Re-doped WS2 monolayer quantum dots (MQDs) using a simple colloidal chemical process. We find that the incorporation of a small amount of electron-rich Re atoms in WS2 changes the metal-metal distance in the 2H phase initially, which introduces strain in the structure (strained 2H (S2H) phase). Increasing the concentration of Re atoms sequentially transforms the S2H phase into the 1T and 1T′ phases to release the strain. In addition, we performed controlled experiments by doping MoS2 with Re to distinguish between Re and Mo atoms in scanning transmission electron microscopy images and quantified the concentration range of Re atoms in each phase of MoS2, indicating that phase engineering of WS2 or MoS2 is possible by doping with different amounts of Re atoms. We demonstrate that the 1T′ WS2 MQDs with 49 at. % Re show superior catalytic performance (a low Tafel slope of 44 mV/dec, a low overpotential of 158 mV at a current density of 10 mA/cm2, and long-term durability up to 5000 cycles) for the hydrogen evolution reaction. Our findings provide understanding and control of the phase transitions in TMDs, which will allow for the efficient manufacturing and translation of phase-engineered TMDs. © 2023 American Chemical Society.11Nsciescopu
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
In Situ Transmission Electron Microscopy Study for Electrical, Thermal and Mechanical Behaviors of Low Dimensional Materials
Full text linkDepartment of Materials Science and EngineeringTransmission electron microscopy (TEM) is one of microscopy techniques in which a beam of electrons is transmitted through a specimen having thin thickness to form an image and get information. TEM is a major analytical method in the physical, chemical and biological science and is additionally utilized in nanotechnology and semiconductor research. When we carried out TEM analysis, it is important to understand how and why materials change in various parameters. Beginning of understanding is the observation for behaviors of the atoms. In situ TEM can analyze the behavior of atoms and provide information about structure and properties of the materials. Due to the development for in situ TEM holders by many commercial companies, a variety of environments and variables can be controlled into TEM with high vacuum levels and TEM eventually become a very powerful tool for observing reactions at the atomic level.
Discovery of low dimensional materials is contributing to attracting special features in research filed. For example, the surface properties dominate the bulk properties, and quantum size effects are observed due to spatial constraints. Those features have shown extraordinary electronic, optical, thermal, mechanical and chemical properties, which may result in their use in wide range of nanotechnology. However, there is still lacking understanding of these various characteristics, leaving only the potential possibilities. Based on these issues, research on low dimensional materials through TEM would be essential.
In this work, in situ TEM research conducted to investigate the potential possibilities of low dimensional materials such as nanostructures, two-dimensional material through electrical, thermal and mechanical TEM holders. In the case of the electrical holder, leakage current increased in metal-insulator-metal capacitor at nanoscale due to Joule heating and induced crystallization of insulator in the capacitor when the voltage was applied. In the case of heating holder, silicon nanomembrane was used to study for the heteroepitaxial growth of beta silicon carbide due to the crystallization of hydrocarbons as a contamination. Lastly, mechanical holder utilized to study mechanical properties of exfoliated graphene and molybdenum disulfide by uniaxial tensile test in TEM. In addition, we also conducted several simulation studies to understand the behavior of these low dimensional materials in TEM. Ultimately, I will discuss how the results of in situ TEM could contribute.clos
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No full textDepartment of Materials Science and Engineeringclos
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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