Search results for "well"
showing 10 items of 2241 documents
Pupils' psychosocial skills in primary education : analysis of their relationship with teaching practices and pupil achievement
2021
The explanation of the differences in success between pupils in primary schools has already mobilized a great deal of research in the field of education. In this thesis, we explore the development of six psychosocial skills (WHO, 1994): cooperation, empathy, self-control, anxiety, self-esteem and internality. Given the prevalence of the effect of teaching practices on the student's educational pathway (Bressoux, 1994, 2001; Hanushek, 2002, 2014), we hypothesized that (1) the interactional profile of primary school teachers was related to the level of development of psychosocial competencies, and (2) the level of development of psychosocial competencies in relation to the teachers' profile h…
Electron spectra in double quantum wells of different shapes
2022
We suggest a method for calculating electronic spectra in ordered and disordered semiconductor structures (superlattices) forming double quantum wells (QW). In our method, we represent the solution of Schr\"odinger equation for QW potential with the help of the solution of the corresponding diffusion equation. This is because the diffusion is the mechanism, which is primarily responsible for amorphization (disordering) of the QW structure, leading to so-called interface mixing. We show that the electron spectrum in such a structure depends on the shape of the quantum well, which, in turn, corresponds to an ordered or disordered structure. Namely, in a disordered substance, QW typically has …
Quantum-well states in ultrathin Ag(111) films deposited onto H-passivated Si(111)-(1x1) surfaces
2002
Ag(111) films were deposited at room temperature onto H-passivated Si(111)-(1x1) substrates, and subsequently annealed at 300 C. An abrupt non-reactive Ag/Si interface is formed, and very uniform non-strained Ag(111) films of 6-12 monolayers have been grown. Angle resolved photoemission spectroscopy has been used to study the valence band electronic properties of these films. Well-defined Ag sp quantum-well states (QWS) have been observed at discrete energies between 0.5-2eV below the Fermi level, and their dispersions have been measured along the GammaK, GammaMM'and GammaL symmetry directions. QWS show a parabolic bidimensional dispersion, with in-plane effective mass of 0.38-0.50mo, along…
Monte Carlo simulation approach for a quantitative characterization of the band edge in InGaN quantum wells
2005
Monte Carlo simulation approach based on exciton hopping through randomly distributed localized states is proposed for quantitative characterization of the band edge of InxGa1–xN/GaN multiple quantum wells with different indium content (x ≈ 0.22–0.27). The band edge dynamics is investigated in the 10–300 K range by analyzing the measured S- and W-shaped temperature behavior of the photoluminescence peak position and linewidth, respectively. The simulation of the W-shaped temperature dependence using double-scaled potential profile model enabled us to estimate the scale of the potential fluctuations due to variation of indium content inside and among In-rich regions formed in InGaN alloy. In…
Tight-binding study of the optical properties of GaN/AlN polar and nonpolar quantum wells
2009
The electronic structure of wurtzite semiconductor superlattices (SLs) and quantum wells (QWs) is calculated by using the empirical tight-binding method. The basis used consists of four orbitals per atom (sp3 model), and the calculations include the spin-orbit coupling as well as the strain and electric polarization effects. We focus our study on GaN/AlN QWs wells grown both in polar (C) and nonpolar (A) directions. The band structure, wave functions and optical absorption spectrum are obtained and compared for both cases.
Room temperature polariton luminescence from a GaN∕AlGaN quantum well microcavity
2006
The authors report on the demonstration of strong light-matter coupling at room temperature using a crack-free UV microcavity containing GaN/AlGaN quantum wells (QWs). Lattice-matched AlInN/AlGaN distributed Bragg reflectors (DBRs) with a maximum peak reflectivity of 99.5% and SiO2/Si3N4 DBRs were used to form high finesse hybrid microcavities. State-of-the-art GaN/Al0.2Ga0.8N QWs emitting at 3.62 eV with a linewidth of 45 meV at 300 K were inserted in these structures. For a 3 lambda/2 microcavity containing six QWs, the interaction between cavity photons and QW excitons is sufficiently large to reach the strong coupling regime. A polariton luminescence is observed with a vacuum field Rabi…
Exciton mass increase in a GaAs/AlGaAs quantum well in a transverse magnetic field
2017
In this work we have investigated the exciton reflectance spectra of a high quality heterostructure with a GaAs/AlGaAs quantum well in a transverse magnetic field (Voigt geometry). It has been shown that application of the magnetic field leads to a decrease of energy distance between spectral features related to the excitonlike polariton modes. This effect has been treated as the magneto-induced increase of the exciton mass. We have shown that the hydrogenlike and diamagnetic exciton models are insufficient to describe the exciton behavior in the intermediate magnetic fields studied. Considering the symmetry of the problem, we have developed a phenomenological model which adequately describ…
Resonant Rayleigh scattering by confined two-dimensional excitonic states
1997
A systematic study of resonant Rayleigh scattering in semiconductor single quantum wells has been carried out. The dependence of the scattering efficiency on the well width and the temperature has been investigated. The behaviour observed in the resonant Rayleigh spectra can be explained in terms of the confinement of the excitonic states in the plane of the well due to fluctuations in the well width. A microscopic theoretical model for the elastic scattering of light by weakly confined two-dimensional excitonic states has been developed. The Rayleigh scattering efficiency has been calculated to the lowest-order of perturbation theory and the results found to be in good agreement with the e…
Two-phonon magneto-Raman scattering in quantum wells: Fröhlich interaction
1996
We have developed a theoretical model of two-phonon resonant magneto-Raman scattering in a semiconductor quantum well (QW). Frohlich electron-phonon interaction has been considered and the corresponding selection rules are derived for Faraday geometry and backscattering configuration. The resonant profiles are analyzed as a function of magnetic field and laser energy. To simplify the discussion a three-band model with parabolic masses has been used as a first approach, studying later the role of heavy-hole light-hole admixture in the scattering process. It is shown that, due to mixing effects, Frohlich interaction contributes to the two-phonon Raman spectra in the parallel (z(σ ± , σ ± ) z)…
Congenital mitral regurgitation caused by a perforation in the anterior leaflet: Perioperative evaluation by color-coded Doppler echocardiography
1990
Color-coded two-dimensional (2D) echocardiography confirmed the presence of severe congenital mitral regurgitation in an 8-month-old infant. Intraoperative inspection revealed an isolated perforation in the anterior leaflet.