1,721,055 research outputs found
Impact of the crystallographic structure of epitaxially grown strained sodium-bismuth-titanate thin films on local piezo- and ferroelectric properties
No full textInfluence of growth parameters on the residual strain in 3C-SiC epitaxial layers on (001) silicon
No full text3C-SiC epitaxial layers were grown on on-axis Si (001) substrates by low-pressure hot-wall chemical vapour deposition. Depending on the growth parameters, the residual strain in the 3C-SiC layer was seen to be tensile or compressive. In this work, the influence of parameters, such as growth temperature and C/Si ratio in the vapour phase, on residual strain and macroscopic layer bow is investigated. We found that the wafer bow changes from convex, at a deposition temperature of 1270 degrees C, to concave at 1370 degrees C. High resolution x-ray diffraction data indicate that the crystalline perfection of the layers is lower for decreasing deposition temperature and increasing compressive strain. No remarkable influence of the C/Si ratio in the gaseous atmosphere on the FWHM of the rocking curve was observed
Polarity- and orientation-related defect distribution in 4H-SiC single crystals
No full textIn order to further improve the crystal quality, the influence of polarity and off-orientation on crystallographic perfection of 4H-SiC single crystals was investigated. Micropipe density (MPD), stacking fault density (SFD) and dislocation density (DD) were determined for 2" single crystals grown in (0001) direction 0-7 degrees off towards (1120) and for crystals tip to 1" in diameter grown in (1150) (a) and (1100) (m) directions and using repeated a-face growth (RAF). KOH etching, optical microscopy and X-ray topography were used for the characterization. It is shown that the MPD and DD decrease with increasing off-orientation for the growth in polar directions, respectively, on C- and Si-terminated seeds. A similar behaviour was found for the SFD and DD in non-polar directions with off-orientation towards c-direction. The non-polar crystals were free of micropipes. Nevertheless, while the DD could be reduced up to three orders of magnitude for the growth along non-polar directions, compared with that in c-direction, the SFD continuously increased. RAF is suitable to completely eliminate the micropipes and to reduce slightly the SFD. However, during the final growth step in polar c-direction MPs as well as SFs tend to form again, with a concentration that is comparable with the standard c-plane growth. The results will be discussed in terms of growth mechanism and kinetic aspects. (c) 2006 Elsevier B.V. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
Boron as an anti-surfactant in sublimation growth of AlN single crystals
No full textWe study the influence of B evaporating from BN crucible walls on the nucleation and growth of AlN by a physical vapor transport. An experimental analysis by means of electron microscopy and optical spectroscopy shows that B incorporation and surface segregation depends on the orientation of the respective surface facet. Surface segregation is found to be predominant on {11-20} facets. This leads to the formation of wurtzite BN nuclei on these facets which extend over the whole surface and may form closed layers. Both boron surface segregation and growth of BN nuclei influence Al and N adsorption and surface diffusion, and in consequence reduce the growth rate. The differences in surface segregation of B on different facets can be understood in terms of incorporation kinetics of boron adatoms into the AlN crystal. B thus acts as a facet selective antisurfactant. (c) 2006 American Institute of Physics
- …
