1,721,028 research outputs found
Croissance de diamant monocristallin épais et élargi de haute qualité dopé au bore : étude et réduction des défauts étendus pour l'optimisation des dispositifs de haute puissance pour une transition énergétique propre
No full textLes travaux de recherche menés dans le cadre de cette thèse ont porté sur la synthèse de films de diamant monocristallin épais, dopés au bore et de haute qualité cristalline en utilisant un procédé de dépôt chimique en phase vapeur assisté par plasma micro-ondes (MPACVD). Le diamant, matériau semi-conducteur à grand gap et reconnu pour ses propriétés exceptionnelles notamment dans le domaine de l'électronique de puissance, permet le développement de composants aux propriétés prometteuses en termes de densité de courant, de tenue en tension et de fonctionnement à température élevée. Par ailleurs, la possibilité de faire croître des films épais fortement dopés au bore a ouvert la voie à la réalisation de composants verticaux tout-diamant. Néanmoins le manque de disponibilité de substrats monocristallins de taille supérieure à 4x4 mm² avec des densités de défauts étendus relativement faibles freine encore son développement. Les objectifs de ce travail étaient de développer des stratégies de croissance permettant de limiter, voire réduire les densités de dislocation et d’augmenter la taille des substrats de diamant. Les résultats obtenus suggèrent que la croissance d'une couche p+ directement sur un substrat HPHT avant le dépôt de la couche active p- permet d'améliorer la qualité cristalline en induisant des niveaux de contrainte qui limitent la propagation des dislocations et conduit à une amélioration globale de la qualité du matériau. Nos travaux ont également permis de réaliser des avancées significatives dans le développement de techniques de croissance latérale conduisant à un élargissement notable de la taille des substrats fortement dopés au bore. Ces conditions de croissance ont pu être utilisées de manière à infléchir la direction de propagation des dislocations comme cela avait déjà été fait dans du diamant intrinsèque et elles ont permis de mettre en évidence l'importance du choix du substrat et aussi le rôle important de l'oxygène en phase gazeuse.The research conducted during this thesis focused on the synthesis of thick, boron-doped monocrystalline diamond films of high crystalline quality using a Microwave Plasma Assisted Chemical Vapor Deposition (MPACVD) process. Diamond, a wide bandgap semiconductor known for its exceptional properties, especially in the field of power electronics, allows for the development of components with promising properties in terms of current density, voltage endurance, and high-temperature operation. Moreover, the ability to grow thick films heavily doped with boron has paved the way for the creation of all-diamond vertical components. However, the limited availability of monocrystalline substrates larger than 4x4 mm² with relatively low extended defect densities still hinders its development. The objectives of this work were to develop growth strategies to limit or even reduce dislocation densities and increase the size of diamond substrates. The results suggest that growing a p+ layer directly on an HPHT substrate before depositing the active p- layer improves the crystalline quality by inducing stress levels that limit dislocation propagation, leading to an overall enhancement in material quality. Our work also achieved significant advancements in the development of lateral growth techniques, resulting in a notable expansion of the size of heavily boron-doped substrates. These growth conditions were used to influence the direction of dislocation propagation, as had already been done in intrinsic diamond, and highlighted the importance of substrate choice and the significant role of oxygen in the gas phase
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
Elaboration de films épais de diamant monocristallin dopé au bore par MPAVCD pour la réalisation de substrats de diamant P +
No full textL objectif principal de ce travail de thèse est la synthèse de films épais (>100 m) de dia-mant monocristallin fortement dopés au bore permettant la fabrication de substrats de diamant et le développement de composants verticaux pour des applications en électronique de puissance. Dans un premier temps, l effet des différents paramètres de croissance a été étudié. Il a ainsi été mis en évidence l existence d une fenêtre de DPMO (caractérisée par le couple pression/puissance) qui permet d assurer un bon compromis entre qualité, vitesse de croissance et efficacité de dopage per-mettant la croissance de films de plusieurs centaines de micromètres. Ensuite, afin d assurer un bon contrôle de la morphologie finale des cristaux, un modèle de croissance géométrique 3D développé au laboratoire, associé à des expériences de croissance dans un plasma H2/CH4/B2H6 a permis de montrer que les conditions déterminées précédemment entrainaient systématiquement l apparition de faces indésirables (110) conduisant à la rupture du cristal. L ajout de faibles quantités d oxygène dans la décharge a permis d interdire la formation de ces faces indésirables et de conserver l intégrité du cristal, condition indispensable pour le développement de substrats permettant la réali-sation de composants électroniques verticaux. Enfin, des substrats CVD à différentes concentration ont été fabriqués et caractérisés par SIMS, FTIR, spectroscopie Raman et diffraction des rayons X haute résolution. Cette étude a ainsi montré l excellente qualité cristalline des films réalisés y com-pris pour les dopages les plus élevés (>1020 cm-3 en bore). Des mesures de résistivité électriques ont par ailleurs montré que les substrats les plus dopés présentent des résistances suffisamment fai-bles pour être utilisés comme substrat pour des composants en électronique de puissance.The main objective of this thesis is the synthesis of thick films (> 100 microns) of monocrystalline diamond heavily doped with boron for the manufacture of diamond substrates and the development of vertical components for applications in power electronics. At first, the effect of different growth parameters was studied. It was thus demonstrated the existence of a window of DPMO (characterized by the pressure torque / power) which ensures a good compromise between quality, speed of growth and doping efficiency per-putting film growth several hundred micrometers. Then, to ensure proper control of the final morphology of the crystals, a 3D geometric model of growth developed in the laboratory, together with growth experiments in a plasma H2/CH4/B2H6 showed that the conditions determined previously resulted systematically the appearance of undesirable side (110) leading to the breakdown of the crystal. The addition of small amounts of oxygen in the discharge allowed to prohibit the formation of these side reactions and to maintain the integrity of the crystal, a prerequisite for the development of substrates for the realization of electronic components vertical. Finally, CVD substrates at various concentrations were fabricated and characterized by SIMS, FTIR, Raman spectroscopy and X-ray diffraction resolution. This study has shown the excellent crystalline quality of the films includ-ing for the highest doping (> 1020 cm-3 boron). Electrical resistivity measurements have also shown that most doped substrates have sufficiently low resistance-able to be used as a substrate for power electronics components.PARIS13-BU Sciences (930792102) / SudocSudocFranceF
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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