1,720,973 research outputs found
Phosphorus Chains and Pentamers: The Precursors of Blue Phosphorene on the Ag(111) Substrate
No full textPhosphorus (P) has many isomers of very similar stabilities
that
makes the controllable synthesis of each isomer difficult. Although
numerous experiments have been devoted to the synthesis of blue phosphorene
(BLP), there is still limited success. Here, we present a systematic
theoretical study of the phosphorus isomers on the Ag(111) surface.
We found that one-dimensional armchair chains have high stability
at a low P concentration, and five-membered rings of phosphorus or
phosphorus pentamers are the most stable structures at medium P concentration.
We also identified a few patterns of phosphorus pentamers on the Ag(111)
surface, one of which agrees well with experimental observation. Finding
that BLP is highly stable at high P coverage, we predict the transformation
from phosphorus chains through pentamers to BLP on the Ag(111) surface.
Our theoretical study provides a guideline for the experimental synthesis
of BLP on the Ag(111) surface
Negative thermal expansion behaviour of graphdiyne
No full textNegative thermal expansion (NTE) is an effect of a material contracting upon heating, and NTE materials are useful for the preparation of zero thermal expansion (ZTE) composite materials for applications in energy conversion and electronic devices. In this work, the NTE behaviour of graphdiyne (GDY) was observed and studied by temperature-dependent Raman spectroscopy. The characteristic Y mode in Raman spectra of GDY film exhibit blueshift with increasing temperature, in contrast to the redshift of positive thermal ex-pansion materials. Our theoretical calculations show that the dimension of GDY decreases when the temperature is elevated, and the blueshift of the Y mode is due to the contraction of GDY. The thermal expansion coefficient (TEC) of GDY in the temperature range of 180-420 K was found to be negative, - 7.18 x 10(-6) K-1 at room temperature. Our results provide a measure of the thermal property of GDY and indicate promising applications of GDY in NTE composite materials. (C) 2022 Elsevier Ltd. All rights reserved
2D fin field-effect transistors integrated with epitaxial high-k gate oxide
No full textPrecise integration of two-dimensional (2D) semiconductors and high-dielectric-constant (k) gate oxides into three-dimensional (3D) vertical-architecture arrays holds promise for developing ultrascaled transistors1–5, but has proved challenging. Here we report the epitaxial synthesis of vertically aligned arrays of 2D fin-oxide heterostructures, a new class of 3D architecture in which high-mobility 2D semiconductor fin Bi2O2Se and single-crystal high-k gate oxide Bi2SeO5 are epitaxially integrated. These 2D fin-oxide epitaxial heterostructures have atomically flat interfaces and ultrathin fin thickness down to one unit cell (1.2 nm), achieving wafer-scale, site-specific and high-density growth of mono-oriented arrays. The as-fabricated 2D fin field-effect transistors (FinFETs) based on Bi2O2Se/Bi2SeO5 epitaxial heterostructures exhibit high electron mobility (μ) up to 270 cm2 V−1 s−1, ultralow off-state current (IOFF) down to about 1 pA μm−1, high on/off current ratios (ION/IOFF) up to 108 and high on-state current (ION) up to 830 μA μm−1 at 400-nm channel length, which meet the low-power specifications projected by the International Roadmap for Devices and Systems (IRDS)6. The 2D fin-oxide epitaxial heterostructures open up new avenues for the further extension of Moore’s law. © 2023, The Author(s), under exclusive licence to Springer Nature Limited.11Nsciescopu
Stabilities of Isomers of Phosphorus on Transition Metal Substrates
No full text© 2021 American Chemical Society.Great efforts have been dedicated to synthesizing phosphorene on transition metal surfaces, but there has been limited success until now. The strong interaction between phosphorus and the substrate may lead to many possible highly stable isomers of phosphorus, making the synthesis of phosphorene difficult. Here, we studied whether functionalizing transition metal surfaces by different phosphorous isomers can assist the epitaxial growth of blue phosphorene. Using density functional theory, we systematically explored five families of phosphorous isomers, blue phosphorene, modified blue phosphorene, surface phosphide, metal-phosphorus hybrid, and blue phosphorene on surface phosphide, on six different transition metal surfaces, Ag(111), Au(111), Cu(111), Co(0001), Ni(111), and Pt(111). It is found that blue phosphorene can be formed on less active transition metal surfaces, such as Ag(111) and Au(111), if the flux of phosphorus is sufficiently high. On more active transition metal surfaces, surface phosphides tend to form first and blue phosphorene may be formed on top of the surface phosphide. This study highlights the structural diversity of the transition metal surfaces in an active environment and provides guidance for the synthesis of phosphorene on transition metal surfaces.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
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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