1,721,142 research outputs found
Identification of van Hove singularities in the GaN dielectric function: a comparison of the cubic and hexagonal phase
No full textWe present a detailed analysis of interband transition structures in the dielectric function of GaN. The dielectric function of the stable wurtzite and the metastable zinc blende phase were determined by means of synchrotron spectroscopic ellipsometry in the spectral range between 3 eV and 20 eV where the most significant structures of the dielectric function are located. In the hexagonal case, both the ordinary and extraordinary dielectric tensor component was measured on GaN films with M-plane/[1 (1) over bar 00] orientation. In a comparative discussion of the two hexagonal tensor components and the zinc blende dielectric function, all prominent absorption structures were assigned to specific interband transitions at high symmetry points in the Brillouin zone. The assignment considers the individual dipole transition probabilities depending on the crystal symmetry and the geometry of the measurement. Furthermore, a detailed theoretical band-to-band analysis of dielectric function features, published by Lambrecht et al. [1], was considered. In conclusion, we suggest a new labeling of absorption structures as used in classical III-V materials like GaAs, which reflects the origin of transition structures from specific points in the respective Brillouin zones. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei
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
Vibrational Raman scattering from surfaces of III-V semiconductors: Microscopic and macroscopic surface modes
No full textWith ongoing instrumental improvements Raman spectroscopy (RS) is advancing into the study of surface vibrational modes of semiconductors. On compound semiconductors, like the IIIV's, two distinct types of surface modes occur, microscopic modes being vibrations confined to the surface and macroscopic modes penetrating much deeper into the bulk, dependent on the electromagnetic boundary conditions. Both mode types depend on surface properties, the microscopic ones on the atomic scale, and the macroscopic ones on the scale of the surface polariton wavelength. While the former one delivers surface atomic structure information, the latter one may be useful for instance to study the morphology of surfaces, such as the shape of semiconductor nanowires. We discuss Raman spectra obtained on the atomically well-defined III-V(110) model surfaces and recent results obtained on isolated III-V nanowires. The comparison of both gives insight in the capabilities of Raman scattering from surface phonons: The contributions of surface phonons, surface resonances, and macroscopic modes (Fuchs-Kliewer modes, surface phonon polaritons) to the Raman spectra become evident
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
Ge growth on GaAs(001) surfaces studied by reflectance anisotropy spectroscopy
No full textSurface modifications induced by germanium deposition onto clean GaAs(001) substrates have been monitored by reflectance anisotropy spectroscopy (RAS) and low energy electron diffraction (LEED). The clean GaAs(001) surfaces onto which Ge has been evaporated were c(4 x 4), (2 x 4), and (4 x 1) reconstructed. Regardless of the initial surface reconstruction, after deposition of 0.5 monolayers of Ge and further annealing at 850 K, we have always observed a (1 x 2) LEED pattern and the same characteristic RAS spectrum. On the contrary, overlayer structures obtained at intermediate stages between the clean surface and this (1 x 2) phase depend upon the initial surface reconstruction. Modifying the (1 x 2) reconstructed surface by deposition of additional monolayers of Ge or exposure to atmosphere, we have separated the surface, interface, and bulk contributions to the RAS spectra. Finally, monitoring the characteristic linear-electro-optical feature appearing at E1 and E1 + Δ1 bulk critical points, we discuss how its change in amplitude and sign could be connected to a variation of the substrate doping induced by annealing
Optical resonances of indium islands on GaAs(001) observed by reflectance anisotropy spectroscopy
No full textThe optical properties of indium islands on GaAs(001) surfaces have been studied by reflectance anisotropy spectroscopy as a function of metal coverage. A large optical anisotropy is observed, which shows an oscillatory behavior and scales with the island size: mean island sizes determined by scanning electron microscope correspond to the wavelengths where extremes in the optical anisotropy arise. We explain this behavior by surface plasmon resonances of the island structure which induce a huge optical anisotropy related to the anisotropic shape and distribution of the In islands. Model calculations of the reflectance anisotropy spectroscopy signal based on a layer system where the island film is represented by an effective medium consisting of ellipsoidal metal particles in a vacuum matrix reproduce the main oscillation and support our conclusion
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