1,720,962 research outputs found
High quality epitaxial graphene by hydrogen-etching of 3C-SiC(111) thin-film on Si(111)
No full textEtching with atomic hydrogen, as a preparation step before the high-temperature growth process of graphene onto a thin 3C-SiC film grown on Si(111), greatly improves the structural quality of topmost graphene layers. Pit formation and island coalescence, which are typical of graphene growth by SiC graphitization, are quenched and accompanied by widening of the graphene domain sizes to hundreds of nanometers, and by a significant reduction in surface roughness down to a single substrate bilayer. The surface reconstructions expected for graphene and the underlying layer are shown with atomic resolution by scanning tunnelling microscopy. Spectroscopic features typical of graphene are measured by core-level photoemission and Raman spectroscop
Graphene-mediated interaction between FePc and intercalated cobalt layers
Full text linkThe interaction strength of FePc molecules adsorbed on graphene-Co, obtained by intercalation of Co layer(s) under graphene (Gr) grown on Ir(111), has been investigated by core level photoemission and X-ray absorption spectroscopy. Upon intercalation of a single layer of Co beneath Gr, the Co atoms are pseudomorphic with the Ir(111) lattice, inducing a rippled Gr layer with valley and hill regions. FePc molecules, adsorbed on Gr/1 ML Co, are trapped in the valley regions and the Fe metallic centers strongly interact with the Gr/Co system. The intercalation of further Co layers leads to a relaxation of the Co lattice up to the formation of a commensurate (1 × 1) Gr/Co system. The Fe centers of the molecules adsorbed on the flat commensurate Gr/Co are found to be less interacting. We have determined that, even though the organic macrocycles of the FePc molecules, flat lying on the Gr/Co system, are completely decoupled by the presence of the Gr intralayer, the Fe–Co interaction is mediated by the graphene spacer and dependent on Gr corrugation
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
Meta-analysis: the molecular organization of non-fullerene acceptors
No full textThe rapid development of Non-Fullerene Acceptors (NFAs) for organic solar cells has recently pushed the Power Conversion Efficiencies (PCE) over the 15% threshold, surpassing fullerene-based state-of-the-art devices. However, for the commercialization of large-scale photovoltaic modules, thick active layers films (150–300 nm) with high PCE and fill factors are required. The realization of materials with higher charge mobilities is fundamental for the roll-to-roll printing industry, and therefore understanding the factors that limit charge transport properties of NFAs becomes crucial for commercialization. The study of the molecular packing and arrangement of NFAs in the solid-state provides direct insight to the propensity of the pristine materials to crystallize and contribute efficiently to the charge transport. In this work we combine experimental techniques and molecular modelling, with the aim of analyzing the way in which NFAs interact in the solid-state and the key components of their structures for building efficient percolation pathways for charge transport. To this end, several new molecules were synthesized and crystallized by solvent vapour diffusion, which were then characterized by single crystal X-Ray Diffraction (XRD). These structures were further compared to a wide selection of literature materials. Density Functional Theory (DFT) calculations were also carried out to examine the electronic transport of these materials with respect to their molecular packing motifs
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
Superexchange pathways stabilize the magnetic coupling of MnPc with Co in a spin interface mediated by graphene
Full text linkWe investigate the magnetic response of a spin interface constituted by MnPc molecules adsorbed on graphene/Co and its robustness against thermal fluctuations by x-ray magnetic circular dichroism. Element-selective hysteresis loops reveal a remarkable antiferromagnetic coupling between MnPc and Co that is strong both in perpendicular and in-plane magnetic orientations, thanks to the magnetic anisotropy properties and electronic configuration of MnPc. The magnetic interaction between MnPc and Co is mediated by the molecular states and the graphene π orbitals in a superexchange mechanism that allows a strong exchange coupling while the molecular orbitals symmetries are preserved by the graphene decoupling layer. Our results show that the strength and stability of the magnetic coupling between MnPc molecules and Co layer(s), intercalated at the graphene/Ir(111) interface, is further optimized by the open
3d shell of the central Mn ion. The magnetic properties are compared with analogous molecular spin interfaces with high thermal stability, paradigmatic examples to exploit in surface-supported molecular spin electronics
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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