1,721,138 research outputs found
INPLANE RAMAN-SCATTERING OF (001)-SI/GE SUPERLATTICES - THEORY AND EXPERIMENT
No full textUsing a micro-Raman setup, in-plane Raman scattering was performed on short-period (001)-Si/Ge superlattices, and the complete phonon spectrum (longitudinal and transverse, optical and acoustic modes) could be studied. In the relevant wave-vector range, the in-plane dispersion was found to affect the frequencies of folded-acoustic modes, while being negligible for confined optical modes. The comparison with theoretical spectra, calculated by means of first-principles interatomic force constants, shows that the observed deviations of ''unfolded'' confined optical modes from the bulk dispersions can be attributed to interface roughness and is well described by a simple alloy layer model (2-3 intermixed SiGe atomic layers at interfaces)
VIBRATIONAL PROPERTIES OF SI/GE SUPERLATTICES - THEORY AND INPLANE RAMAN-SCATTERING EXPERIMENTS
No full textPhonons in short-period (001)-Si(n)Ge(n) Superlattices (SL's) have been studied both theoretically, by a first priniciples approach including strain and interface intermixing, and experimentally by micro-Raman spectroscopy where in-plane scattering geometries allow the observation of both longitudinal (L) and transverse (T) modes. Experimental data are found to deviate considerably from theoretical predictions for SL's with ideally sharp interfaces, both in frequency of higher-order confined Si-like modes and in the polarization dependence of the SiGe-like ''interface'' peak (lineshape and L-T splitting). Supercell calculations representing interface intermixing within a simple model by 2-3 monolayers of SiGe alloy at the interfaces are found to reproduce these major experimental findings. Measurements of Raman resonance profiles of various SL phonon modes strongly confirm their calculated different spatial localization
INTERFACE MODE IN SI/GE SUPERLATTICES - THEORY AND EXPERIMENTS
No full textThe Raman peak associated with Si-Ge vibrations in short-period Si/Ge (001) superlattices is studied both experimentally and theoretically. On the experimental side, we use a microprobe technique which allows us to investigate the longitudinal (L) and transverse (T) spectra, and find an unexpected behavior of the line shape and L-T spitting of this peak. By means of first-principles calculations, taking into account both strain and interface intermixing, we show that such behavior is consistent with the picture of an intermixed alloy layer at the interfaces, and we are able to identify the character and spatial localization of the individual atomic clusters contributing to the vibrations
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
MICRO-RAMAN SCATTERING IN ULTRATHIN-LAYER SUPERLATTICES - EVIDENCE OF ZONE-CENTER ANISOTROPY OF OPTICAL PHONONS
No full textOptically detected single-electron charging in a quantum dot
No full textBy means of photoluminescence spectroscopy we compare the bias-dependent emissions of single-quantum dots which are embedded in two differently designed photodiode structures. Controlled single-electron charging allows to identify neutral, single- and double-charged excitons in the optical spectra of both samples. At high magnetic fields, one Zeeman component of the single-charged exciton is found to be quenched, which is attributed to the competing effects of tunnelling and spin-flip processes. The strength of the tunnelling coupling between quantum dot and back-contact was found to have a strong influence on the observed spectral features-in particular, the parallel appearance of emission lines resulting from the radiative decay of differently charged quantum dot states is suppressed in case of strong tunnelling interaction. (C) 2002 Elsevier Science B.V. All rights reserved
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