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1.
2.
Summary The normal incidence reflectivity spectrum of excitons in GaAs/Ga1−x
Al
x
As multiple quantum wells is calculated within the local response approximation. It is shown that the reflectivity lineshape
strongly depends on the sample geometry. Using realistic parameters of a multiple quantum well structure, we obtain an excellent
fit of the experimental reflectivity curve, thus giving exciton energies, oscillator strengths and exciton broadening parameters.
Riassunto Lo spettro di riflettività ad incidenza normale degli eccitoni nei pozzi quantistici multipli di GaAs/Ga1−x Al x As è calcolato nell’ambito dell’approssimazione locale. Si mostra con la forma della linea di riflettività dipende in gran misura dalla forma geometrica del campione. Usando parametri realistici di una struttura a pozzi quantistici multipli, si ottiene un’ottima approssimazione della curva di riflettività sperimentale, che fornisce così energie eccitoniche, forze dell’oscillatore e parameri di ampliamento eccitonico.
Резюме В рамках приближения линейного отклика вычисляется спекрт отражательной способности экситонов при нормальном падении для множественных квантовых ям в GaAs/Ga1−x Al x As. Показывается, что форма линии отражательной способности сильно зависит от геометрии образца. Используя реалистические параметры структуры множественных квантовых ям, мы получаем хорошее соответствие с экспериментальной кривой для отражательной способности. Получаются энергии экситонов, силы осцилляторов и парам⪟тры экситонного уширения.相似文献
3.
G. Scamarcio L. Tapfer W. König K. Ploog A. Cingolani 《Applied Physics A: Materials Science & Processing》1990,51(3):252-254
Far infrared reflectivity measurements are performed on a series of GaAs/AlAs multiple quantum well (MQW) heterostructures with systematically varied thicknesses of the constituent layers. In addition to the artificial anisotropy we observe two distinct bulk-like Reststrahlen regions. The widths of the GaAs-like and the AlAs-like Reststrahlen bands strongly depend on the relative thicknesses of the constituent layers of the MQW heterostructures, in excellent agreement with the predictions of the effective-medium theory.Prof. Aldo Cingolani passed away just before the publication of this article. We would like to dedicate this paper to his memory 相似文献
4.
Friedel-Crafts reaction of benzylic or tertiary nitro compounds with benzene gave normal alkylation products. Similarly, 2-nitropropane (2-NP) gave cumene (1) which underwent further transformation affording a mixture whose behaviour with time was investigated : results were consistent with oxidative formation of the cumyl carbonium ion (7'). 相似文献
5.
Tedesco E Della F Favaretto L Barbarella G Albesa-Jové D Pisignano D Gigli G Cingolani R Harris KD 《Journal of the American Chemical Society》2003,125(40):12277-12283
The "rigid-core" material 3,5-dimethyl-2,3'-bis(3-methylthiophene)-dithieno[3,2-b:',3'-d]thiophene-4,4-dioxide (DTTOMe4) has the highest photoluminescence ever reported for thiophene-based molecules in the solid state. We report the structure of this material, determined directly from powder X-ray diffraction data using the Genetic Algorithm method for structure solution, followed by Rietveld refinement, and the structural properties are discussed in relation to the structures of the corresponding subsystems DTTO and DTTOMe. While the crystal structures of the latter compounds contain cofacial dimers, the crystal structure of DTTOMe4 comprises layers of molecules aligned in an antiparallel fashion. Intermediate neglect of differential overlap with single configuration interaction (INDO/SCI) calculations on the intermolecular interactions in the three crystal structures show that the different solid-state photoluminescence efficiencies of DTTOMe4, DTTOMe, and DTTO cannot be correlated with the different types of dipole-dipole alignment in the solid state. Instead, photoluminescence efficiencies correlate well with the rate of formation of nonradiatively decaying charge-transfer pairs upon photoexcitation. Because of larger intermolecular distances in DTTOMe4, the photoluminescence is less effectively quenched by charge-transfer processes than in DTTOMe and DTTO. 相似文献
6.
Raganato MF Vitale V Della Sala F Anni M Cingolani R Gigli G Favaretto L Barbarella G Weimer M Görling A 《The Journal of chemical physics》2004,121(8):3784-3791
Modifications of the optical properties of dimethyl-dithienothiophenes due to the oxygen functionalization of the central sulfur atom are investigated. We have measured the absorption, photoluminescence (PL) and PL excitation spectra, the PL quantum efficiencies, and the PL decay times. These experimental results are interpreted and compared with first-principles time-dependent density-functional theory calculations, which predict, for the considered systems, excitation and emission energies with an accuracy of 0.1 eV. It is found that the oxygenation strongly changes optical and photophysical properties. These effects are related to the modifications of the energetically lowest-unoccupied molecular orbital and the energetically second highest occupied one, which change the relative position of the two lowest singlet and triplet excited states. 相似文献
7.
Nontrivial Solutions for p-Laplace Equations with Right-Hand Side Having p-Linear Growth at Infinity
Silvia Cingolani 《偏微分方程通讯》2013,38(8):1191-1203
ABSTRACT The existence of a nontrivial solution for quasi-linear elliptic equations involving the p-Laplace operator and a nonlinearity with p-linear growth at infinity is proved. Techniques of Morse theory are employed. 相似文献
8.
I.M. Catalano A. Cingolani M. Ferrara M. Lugarà A. Minafra 《Solid State Communications》1978,25(5):349-351
Stimulated emission at 3.435 eV in GaN at 80 K is reported. This emission is attributed to a cooperative excitonic process and is observed only in undoped samples. One and two photon optical pumping has been used and optical gain of about 103 cm-1 has been measured. 相似文献
9.
D. Giardin R. Ballini G. M. Cingolani C. Melchiorre B. R. Pietroni 《Tetrahedron》1980,36(24):3565-3569
meso and dl diastereomeric pairs of cyclic compounds with geminal probe groups in suitable position were analysed by PMR: anisochronism of diastereotopic probe protons was used for assignment of configuration; moreover, analysis of ring proton signals gave information on conformational features. 相似文献
10.
The electro-optic coefficient of CdS0.75 Se0.25 is measured at the frequency of the He-Ne laser light and the application of this crystal in light modulators is discussed. The figure of merit is found to be |3orc| = 7 × 10-9 cm/V at room temperature. The voltage required to achieve one half wave retardation is 9 kV. 相似文献