1,721,015 research outputs found
Structural and piezoelectric properties of DC-sputtered AlN films deposited on different Si-based substrates
No full textWe study the DC magnetron sputtering deposition of AlN on different substrates: (100) resistive Si, Si3N4 on Si and SiO2 on Si. The growth conditions of such films have been analysed to obtain the best structural and piezoelectric properties on each substrate. We show that, while AlN follows a columnar growth from the early stage of deposition on Si, the non—crystalline nature of Si3N4 and SiO2 induces an amorphous early growth stage on such substrates. Despite this structural difference, high performances have been obtained by AlN delay lines realised on both Si3N4/Si and pure resistive Si, providing further flexibility in the development of Si-based technological applications
Optical properties of InGaAs QDs grown in a GaAs matrix by MOCVD, emitting at 1300 nm at room temperature
No full textPhotomodulated reflectance studies of quantum dot in MCLED structures: monitoring cavity-ground state exciton resonance
No full textSelf-assembled quantum dots emitting around 1.3 μm and embedded in a microcavity structure are analysed by photo-reflectance (PR) measurements performed at different temperatures. The temperature dependence of the PR spectra line-shape and amplitude allows us to determine the tuning condition of the quantum dot ground state transition with the cavity mode. We found that in our structure the perfect tuning is obtained around 250 K
First electrically injected QD-MCLED emitting at 1.3 μm, grown by metalorganic chemical vapor deposition
No full textGoing 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
1.31 mu m InGaAs quantum dot light-emitting diodes grown directly in a GaAs matrix by metalorganic chemical-vapor deposition
No full textOptical properties of 1.31 μm InGaAs quantum dot light emitting diodes (QD LED) grown in GaAs matrix by using metalorganic chemical vapor deposition (MOCVD) was investigated. It was found that the external quantum efficiency of the device was 0.03% despite of the low dot density. It was observed that the full width at half maximum of the device was as narrow as 24meV for the room temperature ground state transition at 1.31 μm. The results show that the quantum efficiency per dot is 30% higher than the other state of the art InGaAs/InGaAs QD LED
Fabrication of GaN/AlGaN 1D photonic crystals designed for nonlinear optical applications
No full textIn this paper we present a reliable process to fabricate GaN/AlGaN one dimensional photonic crystal (1D-PhC) microcavities with nonlinear optical properties. We used a heterostructure with a GaN layer embedded between two AlGaN/GaN Distributed Bragg Reflectors on sapphire substrate, designed to generate a λ= 800 nm frequency downconverted signal (χ(2) effect) from an incident pump signal at λ= 400 nm. The heterostructure was epitaxially grown by metal organic chemical vapour deposition (MOCVD) and integrates a properly designed 1D-PhC grating, which amplifies the signal by exploiting the double effect of cavity resonance and non linear GaN enhancement. The integrated 1D-PhC microcavity was fabricate combing a high resolution e-beam writing with a deep etching technique. For the pattern transfer we used ~ 170 nm layer Cr metal etch mask obtained by means of high quality lift-off technique based on the use of bi-layer resist (PMMA/MMA). At the same time, plasma conditions have been optimized in order to achieve deeply etched structures (depth over 1 micron) with a good verticality of the sidewalls (very close to 90°). Gratings with well controlled sizes (periods of 150 nm, 230 nm and 400 nm respectively) were achieved after the pattern is transferred to the GaN/AlGaN heterostructure. © 2010 Copyright SPIE - The International Society for Optical Engineering
Improved performances of 1.3 mu m InGaAs QD structures grown at high temperature by metal organic chemical vapour deposition
No full textWe present InGaAs quantum dots (QDs) grown by metal organic chemical vapour deposition in which, by increasing the growth temperature (from 550 up to 610 °C), a high emission efficiency beyond 1.3 μm and narrow linewidth (down to 22 meV at room temperature) can be preserved, with a relevant decrease of defect density. The possibility to grow QDs at higher temperature, close to the cladding growth temperature, allows a strong reduction of the annealing effect when the QDs are inserted in device structures. The spectral blue shift, consequence of this effect, is reduced of 90% in QDs grown at 590 °C, with respect to those grown at 550 °C, thus providing electroluminescence emission near 1.3 μm
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
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