1,721,064 research outputs found
Island and wetting-layer intermixing in the Ge/Si(001) system upon capping
No full textIn this paper we present an atomic force microscopy and X-ray photoemission spectroscopy study of the composition and shape evolution of self-assembled Ge/Si(001) islands upon capping with Si. We found that the islands undergo a reverse Straski-Krastanov shape evolution, with a progressive Si-enrichment of both the wetting layer and the islands. We demonstrate that the island shape evolves at constant volume with silicon atom incorporation occurring in the absence of lateral diffusion of Ge and Si atoms from the wetting layer to the islands themselves. (C) 2008 Elsevier Ltd. All rights reserved
SiGe intermixing in Ge/Si(100) islands
No full textWe have applied atomic force microscopy and x-ray photoemission spectroscopy to the study of
SiGe intermixing in Ge/Si~100! self-assembled islands. We have quantified the Ge/Si alloying as a
function of the deposition temperature in the 500–850 °C range. The Si content inside the islands varies from 0% at 550 °C up to 72% at 850 °C. As a consequence of the reduction of the effective mismatch due to the observed SiGe intermixing, the critical base width for island nucleation increases from 25 nm for Tdep,600 °C up to 270 nm for Tdep5850 °C
Spontaneous ordering of self-assembled-Ge island
No full textSelf-assembled quantum dots can be the building blocks of a variety of mesoscopic devices. However, in order to use these structures in large-scale integrated devices, accurate control over their spatial positioning is required. We show here that, by a suitable engineering of the deposition process, it is possible to obtain self-organization resulting in well ordered clusters composed of regularly disposed nano-sized islands. Elastically relaxed Ge islands act as a stressor for a Si layer subsequently deposited (Ge has a 4 % larger lattice cell). This effect results in a modulation of the lattice parameter and strain field in the Si over-layer. In particular the Si lattice in the columnar region on top of the buried islands is tensile strained and will act as preferential nucleation site for the subsequent Ge island growth. We have generated a square array of tensile-strained regions oriented along the [010]-[100] directions on the Si(001) surface exploiting the self-ordering occurring in the growth at 750 degrees C of Ge island multi-layers used as a template. The strain field intensity and shape was modified by changing the thickness of the template Si over-layer: the thicker the overlayer the wider and less intense the strain field in the Si tensile regions. On this template we have grown a Ge island layer at the lower temperature of 600 degrees C. At this growth temperature the islands are much smaller than the lateral extension of the strain field on the Si surface of the template and the nucleation and evolution of several islands inside a single tensile-strained regions is promoted. Upon decreasing the template Si over-layer thickness from 200 to 35 nm the Ge island spatial distribution changes from random to a well-ordered square lattice of multi-island clusters. At intermediate Si over-layer thickness (65 nm), the Ge islands are confined in cluster regions only at the first stage of their evolution (pyramids), while for thinner over-layer (35 nm) islands are assembled in clusters up to the last stage their growth dynamics (relaxed domes). The strong dome-to-dome interaction within a cluster, due to their small mutual separation, has impact also on the dome size by reducing their mean base width of about 35%. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Intermixing-promoted scaling of Ge/Si(100) island sizes
No full textThe shape evolution and the effect of deposition temperature on size and composition of chemical vapor deposition grown Ge/Si(100) islands have been investigated in the deposition temperature range 450-850 degreesC. It is found that the increase of the growth temperature above 600 degreesC entails a strong island enlargement due to an increased Si/Ge intermixing. The crystallographic structure of the islands was investigated by transmission electron microscopy. The analysis of the resulting Moire pattern reveals that the island lattice deformation decreases with increasing island size and that the effective mismatch epsilon between the silicon substrate and the epilayer decreases with increasing deposition temperature. The island nucleation size, the mean size of coherent islands and the critical size for the insertion of misfit dislocations have been found to scale as epsilon(-2), epsilon(-2), and epsilon(-1), respectively. The agreement of our experimental scaling results with the predictions of theoretical calculation performed for homogeneous heterostructures suggests that, although the Si distribution inside the islands is not homogeneous, the island growth is driven by the mean effective strain
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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