1,721,036 research outputs found
Optimisation of the optical emission of bilayers of quantum dots
No full textWe discuss a novel approach to the optimisation of quantum dot bilayer structures grown by molecular beam epitaxy. It has been observed that vertically stacked quantum dot structures often exhibit an increase in the average size of the islands with increasing number of quantum dot layers deposited. The understanding of the In segregation induced Stranski-Krastanow transition suggests that this is due to excess of In caused by elemental segregation. In order to limit the non uniformity of the sizes along the stacks we have grown the upper layers with different concentrations of In, showing that the optimum fraction is the one predicted by the kinetic segregation model
Optimisation of the optical emission of bilayers of quantum dots
No full textWe discuss a novel approach to the optimisation of quantum dot bilayer structures grown by molecular beam epitaxy. It has been observed that vertically stacked quantum dot structures often exhibit an increase in the average size of the islands with increasing number of quantum dot layers deposited. The understanding of the In segregation induced Stranski-Krastanow transition suggests that this is due to excess of In caused by elemental segregation. In order to limit the non uniformity of the sizes along the stacks we have grown the upper layers with different concentrations of In, showing that the optimum fraction is the one predicted by the kinetic segregation model
Strain Induced by Ti Salicidation in Sub-quarter-micron CMOS Devices, as Measured by TEM/CBED
No full textThe use of TiSi2 layers as ohmic contacts in complementary MOS (CMOS) devices is expected to introduce large distortions in the underlying silicon which may degrade the device performances. In this work, the TEM technique known as convergent beam electron diffraction (CBED) has been employed to map the strain distributions across (1 1 0) cross-sectional specimens of sub-quarter-micron CMOS structures. Different experimental set-ups in terms of energy filtering, liquid nitrogen cooling and zone axis have been explored and compared to each other by using three differently equipped microscopes. The strain induced on silicon by TiSi2 layers has then been investigated. quantified and compared with that due to the presence of an oxide isolation trench. Also, the effects of depositing a TEN capping layer on TiSi2 have been analysed. Our results show that its presence results in a more tensile strain without altering the strain distribution trend. (C) 2002 Elsevier Science B.V. All rights reserved
AN INVESTIGATION OF THE POROUS SILICON OPTICAL-ABSORPTION POWER-LAW NEAR THE BAND-EDGE
No full textA theoretical investigation of the absorption coefficient of p-type doped porous silicon near the band edge is presented. We assume that the absorption coefficient is constructed by taking an average over a distribution (in terms of band gap) of absorption coefficients of individual crystallites. Exploiting physics fundamental to the crystallite optical absorption process, we derive the relation between the absorption coefficient and the averaged conduction density of states near the band edge for porous silicon. By postulating a specific form for the effective conduction density of states we find excellent agreement with recent optical absorption data for p-type doped porous silicon. We attempt to explain the basis for this postulate phenomenologically by suggesting a certain large-scale behaviour of the particle size distribution. The implication of further experimental verification will be discussed
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
Analysis of Terahertz-Emitting SiGe Quantum Cascade Structures by Transmission Electron Microscopy
No full textTest structures have been grown onto SiGe virtual substrates, with the first being to identify the effect on quantum well morphology of increasing Ge concentration have used a combination of energy dispersive X-ray microanalysis, electron energy-loss imaging and scanning transmission electron microscopy to measure the compositions of the various quantum wells. There is increasing interest in developing optical device structures in the far infrared (THz) region of the electromagnetic spectrum, an area that until had been relatively inaccessible for many science and engineering applications. The significant interest stems from possible applications relating to imaging and sensing in medical-related areas. Transmission electron microscopy and scanning transmission electron microscopy have been used to characterize the microstructure of quantum wells grown over a range of different germanium concentrations. Quantum well structures subsequently grown onto a 20% SiGe virtual substrate with a Ge concentration of 30% were found to be highly uniform and free of morphological distortions
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