1,721,287 research outputs found
X-ray characterization of self-organized periodic body-centered tetragonal lattices of SiGe dots
No full textModern nanotechnology offers new possibilities to create artificial materials such as three-dimensional (3D) ordered island crystals that might be of interest e.g., for optoelectronic applications. We demonstrate that a completely self-organized body-centered tetragonal lattice of SiGe dots can be achieved by reduced pressure chemical vapor deposition (RPCVD). Main subject of this paper is the application of different X-ray diffraction techniques to study the structural properties of a large ensemble of buried SiGe dots with the target to optimize deposition conditions. This includes specular Ï-2Î scans to reveal vertical periodicity and strain state, reciprocal space mapping to determine lateral arrangement and symmetry of dots, and in-plane diffraction to get better inside to the lateral strain distribution close to the surface for further growth simulations. SEM cross-section images of a SiGe/Si superlattice of imperfect lateral periodic structure of SiGe dots
Dataset for Non-Isothermal Phase-Field Simulation of Laser-Written In-Plane SiGe Heterostructures for Photonic Applications
No full textDATASET for Non-Isothermal Phase-Field Simulation of Laser-Written In-Plane SiGe Heterostructures for Photonic Applications in Communications Physics.</span
Misfit dislocation free epitaxial growth of SiGe on compliant nanostructured silicon
No full textThe integration of germanium (Ge) into silicon-based microelectronics technologies is currently attracting increasing interest and research effort. One way to realize this without threading and misfit dislocations is the so-called nanoheteroepitaxy approach. We demonstrate that a modified Si nano-structure approach with nano-pillars or bars separated by TEOS SiO2can be used successfully to deposit SiGe dots and lines free of misfit dislocations. It was found that strain relaxation in the pseudomorphically grown SiGe happens fully elastically. These studies are important for the understanding of the behavior of nano-structured Si for the final goal of Ge integration via SiGe buffer
Direct laser writing of graded-index SiGe waveguides via phase segregation
No full textWe report direct laser writing of graded-index optical waveguides via phase segregation in initially homogenous silicongermanium (SiGe) thin films epitaxially-grown on silicon substrates. We used a continuous wave (CW) laser operating at a wavelength of 532 nm. The laser beam was focused to a 5 μm diameter spot on the surface of SiGe films with a thickness of 575 nm and a Ge concentration of %50. Compositional separation of a SiGe film was induced by melting the surface, and the composition profile was tailored by controlling the scan speed of the laser-induced molten zone in a range of 0.1-200 mm/s. At high scan speeds, scanning the laser beam produces a travelling Ge-rich molten zone, where a build-up of Ge content occurs at the trailing edge because of insufficient diffusion-limited Ge transport. Material characterizations have revealed that the laser-processed SiGe microstripes consist of Ge-rich strip cores (> 70% Ge) surrounded by Si-rich under-claddings (<30% Ge). Scan-speed dependent phase segregation allows for fabrication of graded-index SiGe waveguides with tunable compositional profiles, which were characterized by optical transmission measurements, and modal analysis using simulations. Our method could also be applied to pseudo-binary alloys of ternary semiconductors (AlGaAs), which have equilibrium phase diagrams similar to that of SiGe alloys.</p
Non-isothermal phase-field simulations of laser-written in-plane SiGe heterostructures for photonic applications
Full text linkAdvanced solid-state devices, including lasers and modulators, require semiconductor heterostructures for nanoscale engineering of the electronic bandgap and refractive index. However, existing epitaxial growth methods are limited to fabrication of vertical heterostructures grown layer by layer. Here, we report the use of finite-element-method-based phase-field modelling with thermocapillary convection to investigate laser inscription of in-plane heterostructures within silicon-germanium films. The modelling is supported by experimental work using epitaxially-grown Si
0.5Ge
0.5 layers. The phase-field simulations reveal that various in-plane heterostructures with single or periodic interfaces can be fabricated by controlling phase segregation through modulation of the scan speed, power, and beam position. Optical simulations are used to demonstrate the potential for two devices: graded-index waveguides with Ge-rich (>70%) cores, and waveguide Bragg gratings with nanoscale periods (100–500 nm). Periodic heterostructure formation via sub-millisecond modulation of the laser parameters opens a route for post-growth fabrication of in-plane quantum wells and superlattices in semiconductor alloy films.
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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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