Academic literature on the topic 'Facteur g des excitons'
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Journal articles on the topic "Facteur g des excitons"
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Ju, Long, Lei Wang, Ting Cao, Takashi Taniguchi, Kenji Watanabe, Steven G. Louie, Farhan Rana, et al. "Tunable excitons in bilayer graphene." Science 358, no. 6365 (November 16, 2017): 907–10. http://dx.doi.org/10.1126/science.aam9175.
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Excitons, the bound states of an electron and a hole in a solid material, play a key role in the optical properties of insulators and semiconductors. Here, we report the observation of excitons in bilayer graphene (BLG) using photocurrent spectroscopy of high-quality BLG encapsulated in hexagonal boron nitride. We observed two prominent excitonic resonances with narrow line widths that are tunable from the mid-infrared to the terahertz range. These excitons obey optical selection rules distinct from those in conventional semiconductors and feature an electron pseudospin winding number of 2. An external magnetic field induces a large splitting of the valley excitons, corresponding to a g-factor of about 20. These findings open up opportunities to explore exciton physics with pseudospin texture in electrically tunable graphene systems.
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N. R. Senthil Kumar, N. R. Senthil Kumar, A. John Peter A. John Peter, and Chang Woo Lee Chang Woo Lee. "Optical properties of excitons in strained Gax In1-xAs/GaAs quantum dot: ef fect of geometrical conf inement on exciton g-factor." Chinese Optics Letters 11, no. 8 (2013): 082501–82507. http://dx.doi.org/10.3788/col201311.082501.
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Faria Junior, Paulo E., Klaus Zollner, Tomasz Woźniak, Marcin Kurpas, Martin Gmitra, and Jaroslav Fabian. "First-principles insights into the spin-valley physics of strained transition metal dichalcogenides monolayers." New Journal of Physics 24, no. 8 (August 1, 2022): 083004. http://dx.doi.org/10.1088/1367-2630/ac7e21.
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Abstract Transition metal dichalcogenides (TMDCs) are ideal candidates to explore the manifestation of spin-valley physics under external stimuli. In this study, we investigate the influence of strain on the spin and orbital angular momenta, effective g-factors, and Berry curvatures of several monolayer TMDCs (Mo and W based) using a full ab initio approach. At the K-valleys, we find a surprising decrease of the conduction band spin expectation value for compressive strain, consequently increasing the dipole strength of the dark exciton by more than one order of magnitude (for ∼ 1 % – 2 % strain variation). We also predict the behavior of direct excitons g-factors under strain: tensile (compressive) strain increases (decreases) the absolute value of g-factors. Strain variations of ∼1% modify the bright (A and B) excitons g-factors by ∼0.3 (0.2) for W (Mo) based compounds and the dark exciton g-factors by ∼0.5 (0.3) for W (Mo) compounds. Our predictions could be directly visualized in magneto-optical experiments in strained samples at low temperature. Additionally, our calculations strongly suggest that strain effects are one of the possible causes of g-factor fluctuations observed experimentally. By comparing the different TMDC compounds, we reveal the role of spin–orbit coupling (SOC): the stronger the SOC, the more sensitive are the spin-valley features under applied strain. Consequently, monolayer WSe2 is a formidable candidate to explore the role of strain on the spin-valley physics. We complete our analysis by considering the side valleys, Γ and Q points, and by investigating the influence of strain in the Berry curvature. In the broader context of valley- and strain-tronics, our study provides fundamental microscopic insights into the role of strain in the spin-valley physics of TMDCs, which are relevant to interpret experimental data in monolayer TMDCs as well as TMDC-based van der Waals heterostructures.
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Lalitha, D., A. John Peter, and Chang Woo Lee. "Magneto-trions in a GaMnAs/Ga0.6Al0.4As Quantum Dot." International Journal of Nanoscience 14, no. 05n06 (October 2015): 1550023. http://dx.doi.org/10.1142/s0219581x15500234.
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Magneto bound exciton and the charged exciton in a GaMn 0.02 As / Ga 0.6 Al 0.4 As quantum dot are reported with the spatial confinement effect. The numerical calculations are carried out with the inclusion of exchange interaction between the carrier and the magnetic impurities. The binding energies of exciton and the trions and the optical transition energy are obtained as a function of dot radius. Numerical computations are followed using exact diagonalization method. The spin polaronic energy of the exciton and the charged excitons are obtained using a mean field theory in the presence of magnetic field strength. The magnetization of Mn ion impurities as a function of dot radius is investigated. The effective g-factor of conduction (valence) band electron (hole) is obtained in the GaMnAs quantum dot. The magnetic field induced size dependence of effective Landé g-factor is computed. The result shows that (i) the geometrical dependence on sp-d exchange interaction in the GaMn 0.02 As / Ga 0.6 Al 0.4 As quantum dot has great influence with the geometrical confinement, (ii) the monotonic behavior of effective g-factor with the reduction of dot radius is observed, (iii) the Landé factor is more sensitive if the geometrical confinement effect is included and (iv) the value of effective g-factor increases when the spatial confinement is enhanced for all the dot radii. Our results show that the effective Landé g-factor can be manipulated negative to positive values in the GaMn 0.02 As / Ga 0.4 Al 0.6 As quantum dot.
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Corfdir, P., Y. Fontana, B. Van Hattem, E. Russo-Averchi, M. Heiss, A. Fontcuberta i Morral, and R. T. Phillips. "Tuning the g-factor of neutral and charged excitons confined to self-assembled (Al,Ga)As shell quantum dots." Applied Physics Letters 105, no. 22 (December 2014): 223111. http://dx.doi.org/10.1063/1.4903515.
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Song, Fei-Long, Yu-Nuan Wang, Feng Zhang, Shi-Yao Wu, Xin Xie, Jing-Nan Yang, Si-Bai Sun, et al. "The g-factor anisotropy of trapped excitons in CH3NH3PbBr3 perovskite." Acta Physica Sinica 69, no. 16 (2020): 167102. http://dx.doi.org/10.7498/aps.69.20200646.
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Lacroix, Y., C. A. Tran, S. P. Watkins, and M. L. W. Thewalt. "Optical identification of the exciton–polariton in epitaxial InAs." Canadian Journal of Physics 74, S1 (December 1, 1996): 212–15. http://dx.doi.org/10.1139/p96-861.
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We report optical identification of the exciton–polariton in epitaxial InAs by combined photoluminescence, reflectance, and transmittance spectroscopy. The photoluminescence of these samples showed identifiable spectral lines a thousand times narrower than previously published results from other groups. The measurements were made at 1.4 K and at magnetic fields up to 7 T. Contrary to what is observed in other III–V semiconductors such as GaAs or InP, the free exciton (polariton) is nearly invisible in the photoluminescence spectrum without the application of a magnetic field. We believe that the relatively large residual donor concentration coupled with the large spatial extent of the exciton wave function in this material inhibit the existence of unbound excitonic recombination. Reflectance and transmittance spectroscopy provide very strong evidence that our identification is correct, and the magnetic field dependence yielded values of the electron effective mass and g-factor of (0.026 + 0.002)m0 and −15.3 ± 0.2, respectively, based on this assignment.
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Kono, Junichiro. "(Invited, Digital Presentation) Macroscopically Aligned Carbon Nanotubes for Photonics, Electronics, and Thermoelectrics." ECS Meeting Abstracts MA2022-01, no. 10 (July 7, 2022): 775. http://dx.doi.org/10.1149/ma2022-0110775mtgabs.
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The remarkable flexibility, stable chemical structure, and extraordinary thermal, electrical, and optical properties of carbon nanotubes (CNTs) are promising for a variety of applications in flexible and/or high-temperature electronics, optoelectronics, and thermoelectrics, including wearables, refractory photonics, and waste heat harvesting [1]. However, the long-standing goal in the preparation of CNT ensembles is how to maintain the extraordinary properties of individual CNTs on a macroscopic scale. The polydispersity and randomness remain two main challenges. Here, we will discuss different methods for creating macroscopically aligned CNTs, including spontaneous formation of wafer-scale aligned CNT films via controlled vacuum filtration [2-4] and production of ultrahigh-conductivity CNT fibers and films through solution spinning and coating [5,6]. We will then describe the optical [2,7-11], dc and ac electrical [2,12-17], thermal [18], and thermoelectric [19-21] properties of these materials. These results are promising for device applications in various fields such as flexible CNT broadband detectors [22-26], spectrally selective thermal emitters [11], and thermoelectric devices [20,21]. W. Gao et al., “Macroscopically Aligned Carbon Nanotubes for Flexible and High-Temperature Electronics, Optoelectronics, and Thermoelectrics,” Journal of Physics D: Applied Physics 53, 063001 (2020). X. He et al., “Wafer-Scale Monodomain Films of Spontaneously Aligned Single-Walled Carbon Nanotubes,” Nature Nanotechnology 11, 633 (2016). W. Gao and J. Kono, “Science and Applications of Wafer-Scale Crystalline Carbon Nanotube Films Prepared through Controlled Vacuum Filtration,” Royal Society Open Science 6, 181605 (2019). N. Komatsu et al., “Groove-Assisted Global Spontaneous Alignment of Carbon Nanotubes in Vacuum Filtration,” Nano Letters 20, 2332 (2020). N. Behabtu et al., “Strong, Light, Multifunctional Fibers of Carbon Nanotubes with Ultrahigh Conductivity,” Science 339, 182 (2013). L. W. Taylor et al., “Improved Properties, Increased Production, and the Path to Broad Adoption of Carbon Nanotube Fibers,” Carbon 171, 689 (2021). K. Yanagi et al., “Intersubband Plasmons in the Quantum Limit in Gated and Aligned Carbon Nanotubes,” Nature Communications 9, 1121 (2018). W. Gao et al., “Continuous Transition between Weak and Ultrastrong Coupling through Exceptional Points in Carbon Nanotube Microcavity Exciton–Polaritons,” Nature Photonics 12, 362 (2018). M. E. Green et al., “Bright and Ultrafast Photoelectron Emission from Aligned Single-Wall Carbon Nanotubes through Multiphoton Exciton Resonance,” Nano Letters 19, 158 (2019). F. Katsutani et al., “Direct Observation of Cross-Polarized Excitons in Aligned Single-Chirality Single-Wall Carbon Nanotubes,” Physical Review B 99, 035426 (2019). W. Gao et al., “Macroscopically Aligned Carbon Nanotubes as a Refractory Platform for Hyperbolic Thermal Emitters,” ACS Photonics 6, 1602 (2019). X. Wang et al., “High-Ampacity Power Cables of Tightly-Packed and Aligned Carbon Nanotubes,” Advanced Functional Materials 24, 3241 (2014). A. Zubair et al., “Carbon Nanotube Fiber Terahertz Polarizer,” Applied Physics Letters 108, 141107 (2016). D. Tristant et al., “Enlightening the Ultrahigh Electrical Conductivities of Doped Double-Wall Carbon Nanotube Fibers by Raman Spectroscopy and First-Principles Calculations,” Nanoscale 18, 19668 (2016). N. Komatsu et al., “Modulation-Doped Multiple Quantum Wells of Aligned Single-Wall Carbon Nanotubes,” Advanced Functional Materials 27, 1606022 (2017). F. R. G. Bagsican et al., “Terahertz Excitonics in Carbon Nanotubes: Exciton Autoionization and Multiplication,” Nano Letters 20, 3098 (2020). A. Baydin et al., “Giant Terahertz Polarization Rotation in Ultrathin Films of Aligned Carbon Nanotubes,” Optica 8, 760 (2021). S. Yamaguchi et al., “One-Directional Thermal Transport in Densely Aligned Single-Wall Carbon Nanotube Films,” Applied Physics Letters 115, 223104 (2019). K. Fukuhara et al., “Isotropic Seebeck Coefficient of Aligned Single-Wall Carbon Nanotube Films,” Applied Physics Letters 113, 243105 (2018). Y. Ichinose et al., “Solving the Thermoelectric Trade-Off Problem with Metallic Carbon Nanotubes,” Nano Letters 19, 7370 (2019). N. Komatsu et al., “Macroscopic Weavable Fibers of Carbon Nanotubes with Giant Thermoelectric Power Factor,” Nature Communications 12, 4931 (2021). S. Nanot et al., “Broadband, Polarization-Sensitive Photodetector Based on Optically-Thick Films of Macroscopically Long, Dense, and Aligned Carbon Nanotubes,” Scientific Reports 3, 1335 (2013). X. He et al., “Photothermoelectric p-n Junction Photodetector with Intrinsic Broadband Polarimetry Based on Macroscopic Carbon Nanotube Films,” ACS Nano 7, 7271 (2013). X. He et al., “Carbon Nanotube Terahertz Detector,” Nano Letters 14, 3953 (2014). X. He, F. Léonard, and J. Kono, “Uncooled Carbon Nanotube Photodetectors,” Advanced Optical Materials 3, 989 (2015). A. Zubair et al., “Carbon Nanotube Woven Textile Photodetector,” Physical Review Materials 2, 015201 (2018).
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SCHMIDT, T., L. WORSCHECH, M. SCHEIBNER, T. SLOBODSKYY, L. W. MOLENKAMP, and A. FORCHEL. "SPIN POLARIZATION IN SEMIMAGNETIC CdMnSe/ZnSe QUANTUM DOTS WITH ZERO EXCITON g FACTOR." International Journal of Modern Physics B 21, no. 08n09 (April 10, 2007): 1626–31. http://dx.doi.org/10.1142/s0217979207043324.
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We have investigated the degree of circular polarization (ρ) in the emission of semimagnetic CdMnSe/ZnSe quantum dots (QDs) with Mn contents of nominally 0, 1 and 2 %. Circularly polarized excitation was used to control the polarization of the excited carriers. The g factors were determined from the dependence of ρ on the magnetic field strength. We demonstrate that in QDs with 1 % Mn the exciton g factor is vanishingly small. We also present measurements on the excitation power dependent changes of the polarization. A direct heating mechanism is identified as origin of the drastic enhancement of the g factor by ramping up the excitation power. For high laser powers the exciton g factor increases by a factor of 30. In addition, by comparing the luminescence polarization of QDs with 2 % Mn and without Mn a sign reversal of the g factor was observed.
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Denis, Pascale L., Alina N. Stamate, and Michel Cossette. "L’effet de retest du facteur g en sélection du personnel." Humain et Organisation 7, no. 1 (June 22, 2022): 1–16. http://dx.doi.org/10.7202/1089953ar.
Full textDissertations / Theses on the topic "Facteur g des excitons"
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Wang, Shuli. "Étude des propriétés électroniques des perovskites bidimensionnelles à halogénure métallique par spectroscopie magnéto-optique." Electronic Thesis or Diss., Toulouse, INSA, 2023. http://www.theses.fr/2023ISAT0004.
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Ces dernières années, les matériaux pérovskites bidimensionnels (2D) ont attiré une attention considérable en raison de leurs propriétés électroniques et optiques uniques et excellentes, qui en font un semi-conducteur extrêmement prometteur pour les applications d'émission de lumière et d'affichage. En outre, la pérovskite non magnétique peut devenir un semi-conducteur magnétique en incorporant des impuretés magnétiques dans les réseaux de la pérovskite hôte pour introduire des propriétés magnétiques. La coexistence d'excellentes propriétés optoélectroniques et magnétiques fait de la pérovskite 2D semi-magnétique un matériau très prometteur pour les dispositifs semi-conducteurs opto-spintronique pour le traitement de l'information et les communications.Dans cette thèse, nous explorons les propriétés électroniques et optiques des pérovskites 2D via la spectroscopie magnéto-optique. Nous commençons par effectuer des mesures de magnéto-photoluminescence (PL) et de magnéto-transmission sur des nanoplaquettes à base de CsPbBr3 avec une épaisseur différente de la dalle de plomb-halogénure, allant de 2 à 4 couches de plan octaédrique de plomb-halogénure. En appliquant des champs magnétiques dans le plan jusqu'à 65 T, l'état excitonique sombre optiquement inactif est éclairci. Cette approche nous permet d'observer directement une amélioration de l'émission PL du côté basse énergie du spectre PL, ce qui indique que l'état excitonique sombre optiquement inactif est l'état le plus bas dans ces nanoplaquettes. De plus, en combinant nos résultats de magnéto-PL et de magnéto-transmission avec les prédictions théoriques de la division de la structure fine de l'exciton, nous déterminons avec précision la division d'énergie entre les excitons sombres et brillants. Nous démontrons qu'en effet, la division des excitons sombres et brillants augmente avec la diminution des couches du plan octaédrique du plomb-halogénure. Nous démontrons également que l'émission efficace de ces nanoplatelles est due à un effet de goulot d'étranglement phononique, qui réduit considérablement la relaxation des excitons photoexcités vers l'état sombre optiquement inactif.Enfin, nous étudions les propriétés électroniques de la perovskite 2D (PEA)2PbI4 dopée au Mn par spectroscopie de magnéto-transmission pour différentes fractions molaires de Mn. Nous constatons que le facteur g de Lande des excitons peut être contrôlé par la concentration de Mn incorporé. Avec l'augmentation de la concentration x de Mn de 0 à 2%, le facteur g augmente, ce que nous attribuons à l'interaction d'échange sp-d entre les excitons de bord de bande et les spins hébergés dans les ions Mn. Si la concentration en Mn est encore augmentée, jusqu'à 5%, le facteur g des excitons diminue. Cette contre-tendance anormale est attribuée aux interactions Mn-Mn, qui résultent en un couplage anti-ferromagnétique efficaceAbstract: In recent years, two-dimensional (2D) perovskite materials have attracted considerable attention duo to their unique and excellent electronic and optical properties, which make them an extremely promising semiconductor for light-emitting and display applications. Furthermore, the nonmagnetic perovskite can be semi magnetic semiconductor by incorporating magnetic impurities into lattices of the host perovskite to introduce magnetic properties. The coexistence of both excellent optoelectronic and magnetic properties, makes semi magnetic 2D perovskite to be a considerably promising material for opto-spintronic semiconductor devices for information processing and communications.In this thesis, we explore the electronic and optical properties of 2D perovskites via magneto-optical spectroscopy. We start from performing magneto-photoluminescence (PL) and magneto-transmission measurements on CsPbBr3-based nanoplatelets with a different thickness of the lead-halide slab, ranging from 2 to 4 layers of lead-halide octahedral plane. By applying in-plane magnetic fields up to 65 T, the optically inactive dark excitonic state is brightened. This approach allows us to directly observe an improvement of the PL emission on the low-energy side of the PL spectrum, which indicates that the optically inactive dark excitonic state is the lowest-lying state in these nanoplatelets. Additionally, combining our magneto-PL and magneto-transmission results with theoretical predictions of the exciton fine structure splitting, we accurately determine the energy splitting between the dark and bright excitons. We demonstrate that indeed the dark-bright exciton splitting increases with decreasing layers of lead-halide octahedral plane. We also demonstrate that the efficient emission from these nanoplateltes is due to a phonon bottleneck effect, which significantly reduces the relaxation of the photo excited excitons to the optically inactive dark state.Finally, we investigate the electronic properties of Mn-doped 2D (PEA)2PbI4 perovskite via magneto-transmission spectroscopy for various Mn molar fractions. We find that the exciton Lande g-factor can be controlled by the incorporated Mn concentration. With increasing Mn concentration x from 0 to 2%, the g-factor increases, which we attribute to the sp-d exchange interaction between band-edge excitons and spins hosted in Mn ions. If the Mn concentration is increased further, up to 5%, the exciton g-factor decreases. This anomalous counter-trend is attributed to the Mn-Mn interactions, which result in an effective anti-ferromagnetic coupling
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Godoy, Marcio Peron Franco de. "Propriedades de pontos quânticos de InP/GaAs." [s.n.], 2006. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277715.
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Orientador: Fernando IikawaTese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
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Resumo: Neste trabalho estudamos as propriedade estruturais e ópticas de pontos quânticos auto-organizados de InP crescidos sobre o substrato de GaAs. Esta estrutura apresenta o alinhamento de bandas tipo-II na interface, confinando o elétron no ponto quântico, enquanto o buraco mantém-se na barreira, próximo à interface devido à interação coulombiana atrativa. As amostras foram crescidas por epitaxia de feixe químico (CBE) no modo Stranskii-Krastanov. Os pontos quânticos apresentam raio médio de 25 nm e grande dispersão de altura (1-5 nm) e ocorre a relaxação parcial do parâmetro de rede, chegando a 2 %, em pontos quânticos superficiais. Do ponto de vista de propriedades ópticas, a fotoluminescência de pontos quânticos superficiais exibe uma eficiente emissão óptica, devido a baixa velocidade de recombinação dos estados superficiais do InP, e reflete a densidade e distribuição bimodal de tamanhos. Além disso, sua emissão óptica em função da intensidade de excitação exibe comportamento diverso em comparação com pontos quânticos cobertos com uma camada de GaAs. Em pontos quânticos cobertos, determinamos a energia de ativação térmica, que varia de 6 a 8 meV, e é associada à energia de ligação do éxciton ou energia de ionização do buraco. O decaimento temporal da luminescência de pontos quânticos é de 1,2 ns, um tempo relativamente curto para um ponto quântico tipo-II. A análise das propriedades magneto-ópticas em pontos quânticos individuais, inédita em QDs tipo-II, permitiu verificar que o fator-g do éxciton é praticamente constante, independentemente do tamanho dos QDs, devido ao fato dos buracos estarem levemente ligados. Por fim, mostramos a versatilidade do sistema acoplando-o a um poço quântico de InGaAs. Este acoplamento introduz mudanças na superposição das funções de onda do par elétron-buraco que permitem a manipulação do tempo de decaimento da luminescência e da energia de ligação excitônica
Abstract: We have investigated structural and optical properties of InP self-assembled quantum dots grown on GaAs substrate. This system presents a type-II band lineup where only electrons are confined in the InP quantum dots. The InP/GaAs quantum dots were grown by chemical beam epitaxy in the Stranskii-Krastanov mode. Our quantum dots present a mean radius of 25 nm and large height dispersion, 1-5 nm, and a partial relieve of the strain up to 2 % is observed. The photoluminescence spectra of surface quantum dots show an efficient optical emission, which is attributed to the low surface recombination velocity in InP. We observed a bimodal dispersion of the dots size distribution, giving rise to two distinct emission bands. A remarkable result is the relatively large blue shift of the emission band from uncapped samples as compared to those for capped dots. In capped quantum dots, we obtained the thermal activation energy, from 6 to 8 meV, which is associated to the exciton binding energy or hole ionization energy. The observed luminescence decay time is about 1.2 ns, relatively short decay time for type II system. We investigated magneto-optical properties using single-dot spectroscopy. The values of the exciton g factor obtained for a large number of single InP/GaAs dots are mainly constant independent of the emission energy and, therefore, of the quantum dot size. The result is attributed to the weak confinement of the holes in InP/GaAs QDs. We have also investigated structures where InP quantum dots are coupled to a InGaAs quantum well. This system permits the manipulation of the wave function overlap between electron-hole in order to control the optical emission decay time and exciton binding energy
Doutorado
Física
Doutor em Ciências
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Raskin, Maxim. "Ultraschnelle Ladungsträger- und Spindynamik in II-VI und III-V Halbleitern mit weiter Bandlücke." Doctoral thesis, Universitätsbibliothek Chemnitz, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-125227.
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Die vorliegende Arbeit beschäftigt sich mit der Herstellung und Charakterisierung von verdünnten magnetischen II-VI und III-V Halbleiter-Dünnschichten. Diese Systeme bieten vereinfachte optische kohärente Kontrolle von Spin-basierten Prozessen und eignen sich hervorragend für den Einsatz in zukünftigen opto-magnetischen Anwendungen.
ZnO-, ZnXO-, GaN- und GaXN-Proben (X = Mangan, Cobalt) sind mit Hilfe der naßchemischen Sol-Gel Synthese hergestellt worden. Sie werden mit Hilfe der Photolumineszenzspektroskopie untersucht. Die spektrale Position der elektronischen Niveaus in der Nähe der Bandkante dieser Materialien wird bestimmt, um in weiteren Experimenten die freien und gebundenen Exzitonen einzeln abzufragen. Mit der Methode der zeitaufgelösten differentiellen Transmissionsspektroskopie (TRDT) werden die Lebensdauern dieser Ladungsträger bestimmt und mit ultraschnellen Prozessen der optischen Anregung und Relaxation in Verbindung gebracht. Die Methode der zeitaufgelösten Faraday-Rotation-Spektroskopie (TRFR) wird angewandt, um die kohärente Spindynamik des optisch angeregten Teilchenensembles zu beschreiben. Die Kohärenz unterliegt den Störeinflüssen verschiedener Streumechanismen, die in der vorliegenden Arbeit identifiziert und quantitativ beschrieben werden. Bei einigen untersuchten Materialsystemen (ZnCoO, ZnMnO und GaMnN) wird die jeweilige spezifische Elektron-Ion Austauschenergie N0α bestimmt, welche die Kopplungsstärke der elektronischen Spins zu denen der Dotierionen beschreibt.
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Bouvet, Samuel. "Lipides et trafic : rôles de GBF1, facteur d’échange de la petite protéine G Arf1." Thesis, Paris 11, 2013. http://www.theses.fr/2013PA112172/document.
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La cellule eucaryote compartimentalise ses tâches au sein d’organelles communiquant les unes avec les autres au moyen de vésicules de transport. Le trafic vésiculaire est contrôlé par des petites protéines G de la superfamille Ras, activées par un changement de nucléotide guanidique catalysé par un facteur d’échange (GEF). En particulier, au niveau du cis-Golgi la petite protéine G Arf1 est activée par GBF1, permettant le transport rétrograde des vésicules COPI vers le réticulum endoplasmique. Récemment, GBF1 a été impliqué dans d’autres fonctions, notamment dans le cycle réplicatif de certains virus ou dans le métabolisme des gouttelettes lipidiques.Les gouttelettes lipidiques sont les organelles ubiquitaires du stockage des lipides et ont un rôle majeur dans l’homéostasie des lipides à l’échelle de la cellule. Le trafic intracellulaire des ces organelles dynamiques serait contrôlé par des petites protéines G. Notre équipe à montré dans une précédente étude que GBF1 est localisé sur les gouttelettes lipidiques et est impliqué dans le recrutement de PLIN2 et de la lipase ATGL sur les gouttelettes lipidiques. Cette thèse montre, par des études de biologie cellulaire et de microscopie, que GBF1 possède un domaine de fixation aux phospholipides via une hélice amphipatique. Cette hélice est nécessaire et suffisante pour l’association aux gouttelettes lipidiques in cellulo. La régulation de la localisation de GBF1 repose sur l’interaction avec Rab1B (cascade entre Rab1 et Arf1 dans la voie sécrétoire précoce) ainsi que sur les interactions intramoléculaires entre les différents domaines de GBF1The eukaryotic cell physically separates its functions within several membrane-bound organelles, which communicate using vesicles. Vesicular trafficking is under the control of small GTPases that exist as an inactive GDP-bound form and an active GTP-bound form. The switch between GDP and GTP is catalyzed by a guanine nucleotide exchange factor (GEF). On cis-Golgi membranes, Arf1, activated by the large GEF GBF1, recruits the COPI coat. COPI coated vesicles ensure the retrograde transport from the Golgi to the ER. Recently, GBF1 has been implicated in other pathways, such as the life cycle of various viruses and lipid droplet metabolism.Lipid droplets (LD), the major lipid storage organelle, play a major role in lipid homeostasis within the cell. LDs are connected to membrane trafficking and are therefore under the control of GTPases. In previous studies, our team showed that GBF1 localizes around LDs and that it is required for protein loading onto the LD surface. Here, data support the idea that GBF1 localizes to the LD surface. Using cell biology tools and microscopy, we identified, within GBF1, a lipid binding domain. In this domain, a single amphipathic helix is necessary and sufficient for LD targeting in cells. The regulation of GBF1 localization relies on interaction with Rab1 (data support a Rab1-Arf1 cascade between the ER and the Golgi) and on intramolecular interactions between GBF1 domains
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Paleotti, Olivia. "Rôle de la petite protéine G Arf6 et de son facteur d'échange Efa6 dans l'endocytose dépendante de la clathrine." Nice, 2006. http://www.theses.fr/2006NICE4027.
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Les petites protéines G de la famille Arf sont des protéines impliquées dans les processus de transport vésiculaire et de réorganisation du cytosquelette d'actine. Les Arfs oscillent entre une forme dite " inactive ", liée au GDP et une forme dite " active ", liée au GTP. L'activation est catalysée par les facteurs d'échange (les Arf-GEFs) et l'inactivation par des protéines GAPs (GTPase Activating Protein). Dans le laboratoire, nous nous intéressons aux différentes fonctions cellulaires de l'isoforme Arf6 et de son facteur d'échange spécifique Efa6. Au cours de ma thèse, je me suis plus particulièrement intéressée au rôle d'Arf6 dans l'endocytose dépendante de la clathrine. Les récepteurs couplés aux protéines G (RCPGs), une fois activés par leur ligand, sont désensibilisés par liaison à la β-arrestine puis internalisés par la machinerie d'endocytose. Au cours de ma thèse, j'ai cherché à définir le site d'interaction d'Arf6 sur la β-arrestine. Dans mon étude, je montre également que la β-arrestine interagit avec le facteur d'échange, Efa6. Par ailleurs, intrigués par le rôle d'Arf1 au niveau du Golgi, nous nous sommes intéressés à un rôle similaire d'Arf6 à la membrane plasmique. En effet, Arf1 recrute à la membrane golgienne les complexes adaptateurs à la clathrine AP-1, AP-3 et AP-4, pour former des vésicules recouvertes de clathrine impliquées dans le transport entre le réseau trans-Golgien et les endosomes. Le complexe AP-2, étant à l'inverse des autres APs localisé à la membrane plasmique, nous avons démontré biochimiquement une interaction entre Arf6 et le complexe AP-2. Nous avons établi que cette interaction était dépendante du GTP et spécifique de l'isoforme Arf6Arfs small G proteins are implicate in vesicular transport and actin reorganisation. They exist in two forms: an inactive form, bound to the GDP and an active form, bound to the GTP. Exchange factors activate Arfs and GAPs (GTPase Activating Protein) inactivate them. We worked on Arf6 and on its exchange factor Efa6 in cellular functions. During my PhD, I studied Arf6 in clathrin-dependant endocytosis. G protein-coupled receptors (GPCRs) are desensibilized by β-arrestins that link GPCRs to the endocytic machinery. We showed that Arf6 and Efa6 could both interact with β-arrestins. Moreover, Arf1 recruits the adaptator proteins (AP-1, 3 and 4) at the golgi membrane to form endocytic vesicles. We showed that Arf6 could recruit AP-2 complex at the plasma membrane in a GTP-dependent manner
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BERAUD, DUFOUR SOPHIE. "Mecanisme d'activation de la protein g, arf1 : role coordonne des membranes lipidiques et du facteur d'echange, arno." Nice, 1999. http://www.theses.fr/1999NICE5305.
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Arf1 est une petite proteine g impliquee dans le transport vesiculaire. Comme toutes les proteines g, elle existe sous 2 etats conformationnels differents : un etat inactif lie au gdp et un etat actif lie au gtp. Nous avons confirme qu'arf1 g d p interagit faiblement avec les membranes via des interactions electrostatiques et l'insertion de son myristate dans la bicouche lipidique. Nous avons montre qu'arf1 g t p est fortement lie aux membranes grace a l'insertion de son myristate et de residus de l'helice n-terminale, suite a la bascule de celle-ci. L'echange gdp-gtp d'arf1 est fortement active par le domaine sec7 du facteur d'echange nucleotidique arno. Arno possede egalement un domaine coiled-coil et un domaine ph, responsable de son recrutement a la membrane. L'interaction entre ces deux proteines a ete etudiee en solution en utilisant le domaine sec7 d'arno et une proteine arf1 tronquee de son helice, arf117. La resolution de la structure et des etudes de mutagenese nous ont permis de montrer que la gorge hydrophobe d'arno-sec7 est le siege de l'interaction avec arf1. Nous avons decouvert, grace a des mesures d'activite et des experiences de gel filtration, les sites d'interaction d'arf1 avec arno-sec7 : l'insertion de la region switch i d'arf1 dans la gorge hydrophobe du domaine sec7 et la formation d'une paire ionique entre la lysine 73 de la region switch ii d'arf1 et l'aspartate 183 de la gorge du domaine sec7. Nous avons egalement montre que le glutamate 156 du domaine sec7 est essentiel a la catalyse de l'echange nucleotidique car il vient destabiliser le magnesium et le phosphate du nucleotide. Nous avons donc appele ce residu le glutamic finger. Puis nous avons suivi la bascule de l'helice n-terminale suite a l'interaction d'arf1 avec arno-sec7 ce qui nous a permis de degager un modele dans lequel l'helice d'arf1 a bascule avant l'interaction avec arno-sec7 et ou arno-sec7 vient empecher la rebascule de l'helice.
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Jguirim, Naira. "Micro-fabrication additive des filtres à fort facteur de qualité pour des applications en bande W/G." Thesis, Limoges, 2021. http://www.theses.fr/2021LIMO0031.
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Dans le cadre de ce travail, des filtres passe-bande hyperfréquences ont été développées pour répondre à des spécifications proposées en bandes W et G. Nous avons utilisé la technologie de micro-fabrication additive permettant d’avoir des cavités métalliques à air avec un fort facteur de qualitéAs part of this work, millimeter band-pass filters were developed to meet the given specifications in W and G bands. We used additive micro-fabrication technology which allowed us to fabricate filters based on metallic cavities with an air-filled 3D architecture and a strong quality factor
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Karlin, Lionel Azoulay Elie. "Détérioration respiratoire en sortie d'aplasie sous facteur de croissance hématopoïétique (G-CSF) à propos de 20 cas /." Créteil : Université Paris-Val-de-Marne, 2004. http://doxa.scd.univ-paris12.fr:80/theses//th0222006.pdf.
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Yatime, Laure. "Rôle du facteur d'initiation e/aIF2 dans le démarrage de la traduction chez les Eucaryotes et chez les archées." Phd thesis, Ecole Polytechnique X, 2005. http://pastel.archives-ouvertes.fr/pastel-00001539.
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Le facteur hétérotrimérique e/aIF2 joue un rôle central dans le démarrage de la traduction chez les Eucaryotes et chez les Archées. Il conduit l'ARNt initiateur méthionylé jusqu'au ribosome et assure la spécificité de sélection du codon de démarrage sur l'ARNm. La structure cristallographique d'aIF2de l'archée Pyrococcus abyssi, précédemment résolue au laboratoire, a révélé une très forte homologie entre aIF2γ, qui constitue le coeur de l'hétérotrimère, et le facteur d'élongation bactérien EF1A. Cependant, possède des caractéristiques structurales propres qui pourraient être responsables de sa spécificité d'action dans le démarrage de la traduction. Une étape cruciale de ce travail a consisté à développer un test de suivi in vitro de l'association d'aIF2 au Met-ARNti Met. Ce test a permis d'évaluer l'importance des caractéristiques du Met-ARNti Met et la contribution de chacune des sous-unités de l'hétérotrimère dans la formation du complexe aIF2:Met-ARNti Met. Ainsi, il a été montré que le résidu méthionine constitue un déterminant majeur dans la reconnaissance du Met-ARNti Met par aIF2. D'autre part, il apparaît que la sous-unité seule est effectivement capable de lier l'ARNt selon un mode similaire à celui observé pour EF1A mais avec une affinité considérablement réduite par rapport à celle de l'hétérotrimère. Nous avons montré que la présence de la sous-unité αétait nécessaire pour retrouver une affinité optimale vis-à-vis de l'ARNt tandis que la sous-unité βne semble pas jouer de rôle dans cette liaison. L'utilisation d'une stratégie de découpage d'en domaines séparés a montré que c'est le domaine 3 d'aIF2qui lie la sous-unité par l'intermédiaire d'une boucle du domaine 2 de . De plus, le dimère D3semble nécessaire et suffisant pour retrouver une affinité pour l'ARNt comparable à celle du facteur natif. Dans un second temps, des cristaux de la sous-unité entière et d'une forme tronquée correspondant aux domaines 2 et 3 ont été obtenus. Les structures d'D2-3 et d'complet ont été résolues à respectivement 2.26 et 3.37 Å de résolution. L'analyse du modèle structural a révélé une mobilité du domaine 3 d'αpar rapport au bloc rigide formé par les domaines 1 et 2. La comparaison de séquences d'e/aIF2a montré que les zones de conservation d'se situaient principalement dans le domaine 1 et dans le domaine 3 de la protéine, qui possèdent tous les deux des propriétés générales de liaison des ARNs. Le domaine 1 d'αpourrait ainsi interagir avec un autre partenaire de type ARN du démarrage de la traduction, tel que l'ARNm ou l'ARN ribosomal. Finalement, des cristaux d'aIF2de Sulfolobus solfataricus ont été obtenus et la structure de l'hétérodimère a été résolue à 3.0 Å. Cette structure a confirmé les données biochimiques précédemment obtenues : le domaine 3 de la sous-unité interagit avec le domaine 2 de , au niveau de la boucle L1 précédemment caractérisée. L'analyse de cette structure a révélé pour la première fois une conformation des régions Switch de similaire à celle observée au sein du complexe EF1A:GDPNP:ARNt, ce qui permet d'expliquer la GTPdépendance de la fixation du Met-ARNti Met par aIF2. La comparaison de cette structure à celle d'EF1A suggère que seule γpourrait être en contact avec l'ARNt au sein de l'hétérodimère αγ. Le renforcement de l'affinité pour l'ARNt observé en présence d'αnous a conduit à envisager un rôle possible d'αdans l'établissement des conformations observées pour les régions Switch dans la structure d'aIF2γ.
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Gonzalez, Hernandez Felix Guillermo. "Tempos de relaxação e decoerência em ensembles de pontos quânticos." [s.n.], 2007. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277852.
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Orientador: Gilberto Medeiros RibeiroTese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
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Resumo: Medidas experimentais foram realizadas para determinar as escalas de tempo de relaxação e decoerência do spin eletrônico como bit quântico. A estrutura dos estados de exciton foi investigada com o objetivo de servir como estados intermediários na manipulação do spin. O sistema utilizado para o estudo de decoerência é um ensemble de pontos quânticos auto-formados semicondutores. Dois temas servem como eixos centrais dos três experimentos desenvolvidos nesta tese: a polarização de spin e o fator g de Landé. No primeiro experimento, ao incluir o efeito do reservatório térmico, foi obtido o grau de polarização do spin (populações dos níveis up e down) para as camadas s e p. O desdobramento dos níveis orbitais em subníveis de spin permitiu obter a magnitude do fator g para estes estados. Mudando a orientação do campo magnético, foram observadas as anisotropias do tensor g e a sua relação com os detalhes do potencial de confinamento. Estas características permitiram inferir o tempo de relaxação T1. A medida da polarização resolvida no tempo foi realizada através de es-pectroscopia óptica de bombeio-prova. Os pulsos de luz e o campo magnético transverso permitem que uma polarização líquida seja inicializada. A rotação de Kerr permitiu observar oscilações desta polarização em torno do campo magnético com freqüência determinada pelo fator g. A perda da coerência de fase do spin resulta no decaimento destas oscilações numa escala de tempo T2. Medidas realizadas num ensemble de spins implicam em que o tempo de decoerência encontra-se limitado pela escala de defasagem T¤2< T2. Uma técnica semelhante à refocalização por spin-eco em experimentos de ressonância magnética nuclear, foi aplicada utilizando pulsos de laser para reverter a defasagem do ensemble. Tanto a possibilidade de medir o sinal de eco como o tempo de decoerência foram medidos como função da temperatura. A estrutura de níveis de exciton e a sua distribuição no ensemble foi estudada também com espectroscopia de bombeio-prova. Foram observados batimentos quânticos entre os níveis de estrutura fina do exciton para sis-temas 0D e 2D limitados pelo tempo de recombinação
Abstract: Experimental measurements were carried out to determine the scales of the relaxation and decoherence time for the electronic spin as quantum bit. The structure of the exciton states was investigated with the objective to serve as intermediate states in the spin manipulation. The system studied for the implementation of the quantum computation is an ensemble of self-assembled semiconductor quantum dots. Two subjects serve as central axes of the three experiments developed in this thesis: the spin polarization and the Landé g-factor. In the first experiment, when including the effect of the thermal reservoir, the degree of spin polarization (populations for the up and down levels) was measured for layers s and p. The splitting of the orbital levels in spin sublevels allowed to get the magnitude of factor g for these states. Changing the orientation of the magnetic field, the g-tensor anisotropies and its relation with the details of the confinement potential had been observed. These characteristics had allowed to infer the relaxation time T1. The time resolved polarization measurement was carried out by optical pump-probe spectroscopy. The pulses of light and the transverse magnetic field allow the initialization of a net polarization. The Kerr rotation allowed to observe oscillations of this polarization around the magnetic field with frequency determined for factor g. The loss of the spin phase coherence results in the decay of these oscillations in a time scale T2. Measurements carried out in an ensemble of spins imply that the decoherence time is limited by the ensemble dephasing time T¤2 < T2. A technique similar to the spin-echo refocalization in nuclear magnetic resonance experiments using laser pulses was applied to reverse the ensemble dephasing. The possibility to measure the echo signal and the decoherence time was measured as a function of the temperature. The structure of exciton levels and its distribution in ensemble were also studied with pump-probe spectroscopy. Quantum beats were observed be-tween the fine structure exciton levels for 0D and 2D systems, yet limited by the recombination time
Doutorado
Física da Matéria Condensada
Doutor em Ciências
Books on the topic "Facteur g des excitons"
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J, Sternberg Robert, and Grigorenko Elena, eds. The general factor of intelligence: How general is it? Mahwah, N.J: L. Erlbaum Associates, 2002.
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Grigorenko, Elena, and Robert J. Sternberg. General Factor of Intelligence: How General Is It? Taylor & Francis Group, 2002.
Find full textBook chapters on the topic "Facteur g des excitons"
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"Appendice P. Évaluation du facteur de Landé g." In Physique des solides, 957–58. EDP Sciences, 2002. http://dx.doi.org/10.1051/978-2-7598-0178-7.c054.
Full textConference papers on the topic "Facteur g des excitons"
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Senthilkumar, N. R., and A. John Peter. "Effects of gallium alloy content and the geometrical confinement on effective exciton g-factor in a III-V semiconductor quantum dot." In SOLID STATE PHYSICS: PROCEEDINGS OF THE 57TH DAE SOLID STATE PHYSICS SYMPOSIUM 2012. AIP, 2013. http://dx.doi.org/10.1063/1.4791389.
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Ishii, A., T. Uda, and Y. K. Kato. "Room-temperature single photon emission from micron-long air-suspended carbon nanotubes." In JSAP-OSA Joint Symposia. Washington, D.C.: Optica Publishing Group, 2017. http://dx.doi.org/10.1364/jsap.2017.7p_a404_3.
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Carbon nanotubes have great potential for single photon sources as they have stable exciton states even at room temperature and their emission wavelengths cover the telecommunication bands. In recent years, single photon emission from carbon nanotubes has been achieved by creating localized states of excitons [1]. In contrast to such an approach, here we utilize mobile excitons and show that single photons can be generated at room temperature in air-suspended carbon nanotubes with lengths of several microns. We perform photoluminescence microscopy on as-grown air-suspended carbon nanotubes in order to determine their chirality and suspended length. Photon correlation measurements are performed on nanotube emission at room temperature using a Hanbury-Brown-Twiss setup with InGaAs/InP single photon detectors. We observe antibunching with a clear excitation power dependence, where we obtain g(2)(0) value less than 0.5 at low excitation powers (Fig. 1), indicating single photon generation. We show such g(2)(0) data with different chiralities and suspended lengths, and the effects of long exciton diffusion lengths and efficient exciton-exciton annihilation [2] on single photon generation processes are discussed.
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Wittmann, M., M. T. Wick, G. Korn, J. Ringling, and E. Matthias. "Subpicosecond Carrier Relaxation Dynamics and Defect Formation in Wide-Band-Gap Materials." In The European Conference on Lasers and Electro-Optics. Washington, D.C.: Optica Publishing Group, 1998. http://dx.doi.org/10.1364/cleo_europe.1998.cwf57.
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Alkaline-earth fluorides are widely used in optical transmission components in the deep UV as well as for optical coatings because of their wide-band-gap, low refractive indices and hardness. One essential drawback of these materials is the formation of defects (color centers e. g.) during intense irradiation. This limits the lifetime of such optical elements for high power propagation in the UV and reduces the transmission of ultrashort laserpulses nonlinearly. Details of this process, in particular the dynamics during the early stages (formation of self-trappped excitons STE [1]) are therefor of interest.
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Aydın, Kemal Bartu, Levent Aydin, and Fethullah Güneş. "Stochastic Optimization of TiO2-Graphene Nanocomposite by Using Neuro-Regression Approach for Maximum Photocatalytic Degradation Rate." In International Students Science Congress. Izmir International Guest Student Association, 2021. http://dx.doi.org/10.52460/issc.2021.044.
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TiO2 is one of the most common materials for photocatalytic applications due to its stability, affordability, and photoactive efficiency. However, it has some drawbacks, such as limited solar radiation response and quick recombination of excitons. Using graphene could be one of the methods to enhance the photocatalytic properties of TiO2. This study intends to optimize the photocatalytic performance of TiO2/Graphene (TiO2/G) nanocomposite by using neuro-regression analysis. In the analysis, the effect of some hydrothermal synthesis parameters, namely, amount of graphene oxide, ethanol/water ratio, and hydrothermal reaction time on the photocatalytic activity of TiO2/G nanocomposite, have been investigated. The parameters were determined from a literature study focused on overcoming the drawbacks of TiO2 by combining it with graphene oxide. Nelder-Mead, Simulated Annealing, Differential Evolution, and Random Search algorithms are used to obtain the optimum synthesis parameters for maximum photocatalytic activity in the optimization process. The results are indicated that all algorithms give the realizable value for design variables and photodegradation rate.
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Hess, Harald F. "Near-field optical characterization of quantum wells and nanostructures." In Quantum Optoelectronics. Washington, D.C.: Optica Publishing Group, 1995. http://dx.doi.org/10.1364/qo.1995.qwa2.
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A spatial distribution of luminescent centers with sharp (<0.1meV), spectrally distinct emission lines are revealed in a GaAs/AlGaAs quantum wells[1] using low temperature nearfield scanning optical microscopy [2], a technique where a subwavelength source and/or detector of light in close proximity (<40nm) to the sample is used to probe with a resolution beyond the diffraction limit. These centers are the energy eigenstate components that comprise the inhomogeneously broadened line shape observed in standard far-field photoluminescence. Measurements as a function of temperature, magnetic field, and well width establish that these centers arise from excitons localized by quantum well thickness fluctuations. For sufficiently narrow wells, virtually all emission originates from such centers. Quantities such as diffusion (both thermal and tunneling), lateral confinement energies, lifetimes, g-factors from magnetic field induced spin splittings, diamagnetic energy coefficients of the luminescent states can now be measured at a site-by-site individual quantum level rather than averaged over a statistical distribution. This information can be used in turn to provide a direct local picture of the interface fluctuations and how they vary under different MBE growth conditions. Near-field microscopy/spectroscopy provides a means to access energies and homogeneous line widths for the individual eigenstates of these centers, and thus allows the luminescent components to be identified and characterized with the extraordinary detail previously limited to the realm of atomic physics.