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Littérature scientifique sur le sujet « Exciton dynamic »

Auteur : Grafiati
Publié le 1 avril 2023

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Articles de revues sur le sujet "Exciton dynamic"

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Tao, Weijian, Qiaohui Zhou et Haiming Zhu. « Dynamic polaronic screening for anomalous exciton spin relaxation in two-dimensional lead halide perovskites ». Science Advances 6, no 47 (novembre 2020) : eabb7132. http://dx.doi.org/10.1126/sciadv.abb7132.

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Two-dimensional lead halide perovskites with confined excitons have shown exciting potentials in optoelectronic applications. It is intriguing but unclear how the soft and polar lattice redefines excitons in layered perovskites. Here, we reveal the intrinsic exciton properties by investigating exciton spin dynamics, which provides a sensitive probe to exciton coulomb interactions. Compared to transition metal dichalcogenides with comparable exciton binding energy, we observe orders of magnitude smaller exciton-exciton interaction and, counterintuitively, longer exciton spin lifetime at higher temperature. The anomalous spin dynamics implies that excitons exist as exciton polarons with substantially weakened inter- and intra-excitonic interactions by dynamic polaronic screening. The combination of strong light matter interaction from reduced dielectric screening and weakened inter-/intra-exciton interaction from dynamic polaronic screening explains their exceptional performance and provides new rules for quantum-confined optoelectronic and spintronic systems.
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Sneyd, Alexander J., Tomoya Fukui, David Paleček, Suryoday Prodhan, Isabella Wagner, Yifan Zhang, Jooyoung Sung et al. « Efficient energy transport in an organic semiconductor mediated by transient exciton delocalization ». Science Advances 7, no 32 (août 2021) : eabh4232. http://dx.doi.org/10.1126/sciadv.abh4232.

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Efficient energy transport is desirable in organic semiconductor (OSC) devices. However, photogenerated excitons in OSC films mostly occupy highly localized states, limiting exciton diffusion coefficients to below ~10−2 cm2/s and diffusion lengths below ~50 nm. We use ultrafast optical microscopy and nonadiabatic molecular dynamics simulations to study well-ordered poly(3-hexylthiophene) nanofiber films prepared using living crystallization-driven self-assembly, and reveal a highly efficient energy transport regime: transient exciton delocalization, where energy exchange with vibrational modes allows excitons to temporarily re-access spatially extended states under equilibrium conditions. We show that this enables exciton diffusion constants up to 1.1 ± 0.1 cm2/s and diffusion lengths of 300 ± 50 nm. Our results reveal the dynamic interplay between localized and delocalized exciton configurations at equilibrium conditions, calling for a re-evaluation of exciton dynamics and suggesting design rules to engineer efficient energy transport in OSC device architectures not based on restrictive bulk heterojunctions.
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Chaouachi, Nizar, et Sihem Jaziri. « Possibility of observation quantum beat coherent exciton states with time-resolved photoemission ». Journal of Applied Physics 131, no 15 (21 avril 2022) : 155704. http://dx.doi.org/10.1063/5.0086440.

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We develop a theoretical study to evaluate the dynamic of the time-resolved photoemission spectrum arising from the dissociation of exciton steady-states 1s, 2s in a monolayer transition metal dichlacogenides. We discuss the dielectric environment effect on the exciton binding energies. Quantum beat signatures in photoemission intensity demonstrate coherent coupling between 1s and 2s excitons. The beating contribution due to excitonic coherence is also discussed. The periodic oscillations arising from coherent superposition states and quantum beats enable exploration of novel coherent phenomena.
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Aslan, Burak, Colin Yule, Yifei Yu, Yan Joe Lee, Tony F. Heinz, Linyou Cao et Mark L. Brongersma. « Excitons in strained and suspended monolayer WSe2 ». 2D Materials 9, no 1 (21 octobre 2021) : 015002. http://dx.doi.org/10.1088/2053-1583/ac2d15.

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Abstract We study suspended membranes of atomically thin WSe2 as hosts of excitons. We perform optical reflectance measurements to probe the exciton physics and obtain the peak energies for the 1 s , 2 s , and 3 s states of the A exciton in suspended WSe2 and consider supported membranes as a reference. We find that elimination of the influence of the dielectric environment enables a strong electron–hole interaction and a concomitant increase in the exciton binding energy in suspended monolayer (1L) WSe2. Based on the experimental results, we calculate the excitonic binding energies by employing the recently developed quantum electrostatic heterostructure model and the commonly employed Rytova–Keldysh potential model. We see that the binding energy of the ground state A exciton increases from about 0.3 eV (on a substrate) to above 0.4 eV (suspended). We also exploit the tunability of the excitons in suspended samples via mechanical strain. By applying external gas pressure of 2.72 atm to a 1L suspended over a circular hole of 8 μm diameter, we strain the WSe2 and obtain a reversible 0.15 eV redshift in the exciton resonance. The linewidth of the A exciton decreases by more than half, from about 50 to 20 meV under 1.5% biaxial strain at room temperature. This line narrowing is due to the suppression of intervalley exciton–phonon scattering. By making use of the observed strain-dependent optical signatures, we infer the two-dimensional (2D) elastic moduli of 1L and 2L WSe2. Our results exemplify the use of suspended 2D materials as novel systems for fundamental studies, as well as for strong and dynamic tuning of their optical properties.
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Uratani, Hiroki. « (Invited) Simulating Dynamic Excitons Via Quantum Molecular Dynamics : A Case Study in Lead Halide Perovskites ». ECS Meeting Abstracts MA2022-01, no 13 (7 juillet 2022) : 904. http://dx.doi.org/10.1149/ma2022-0113904mtgabs.

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The ultrafast electronic and structural dynamics invoked by photoexcitation, i.e., “dynamic exciton” phenomena, not only are important in the context of practical applications such as solar cells, but also raise many questions from the viewpoint of fundamental science. Experimental measurement, computational simulations, and theoretical interpretation will be the three pillars for deciphering the dynamic exciton phenomena. From the viewpoint of computational simulations, molecular dynamics (MD) techniques combined with quantum chemical calculations, i.e., quantum molecular dynamics (QMD), has been the popular tool to simulate the dynamic exciton phenomena. The quantum chemical calculations, which are typically conducted on the basis of the density-functional theory (DFT), require the large computational resources and time. These have been the limiting factors for the accessible spatial and time scales by the QMD simulations. To extend the coverage of simulations to more complex, large-scale systems, we have developed efficient excited-state QMD methods that can include nonadiabatic effects. Our method combines the density-functional tight binding (DFTB) method, which is an approximate DFT, and the surface hopping method, which is a theoretical framework to incorporate the nonadiabatic effects into the QMD simulations. The method was further improved to be suitable for condensed-phase simulations explicitly including the environment, i.e., solvent, by using a “divide-and-conquer” style quantum chemical calculation technique. These theoretical framework enables us to simulate the coupled electronic–structural dynamics in excited states of systems consisting of 102–103 atoms[1,2,3]. In addition, using the developed method, we conducted the real-time simulations of the ultrafast processes invoked by photoexcitation of lead iodide perovskites, which are known as the key materials for perovskite solar cells. The dissociation of the exciton into the positive and negative charge carriers was observed. Moreover, the hot carrier cooling, where the charge carriers dissipate excess energy via the electron–phonon coupling and relax to the band edges, was also tracked. Finally, the direct evidence of the polaron formation, where the structural deformation is induced by the presence of charge carriers, was observed. These results highlight the importance of the coupling between electronic and structural degrees of freedom. In the talk, recent improvements in the methodology and future perspectives will also be presented[5]. References [1] H. Uratani and H. Nakai, J. Chem. Phys. 152, 224109 (2020). [2] H. Uratani, T. Morioka, T. Yoshikawa, and H. Nakai, J. Chem. Theory Comput. 16, 7299 (2020). [3] H. Uratani, T. Yoshikawa, and H. Nakai, J. Chem. Theory Comput. 17, 1290 (2021). [4] H. Uratani and H. Nakai, J. Phys. Chem. Lett. 11, 4448 (2020). [5] H. Uratani and H. Nakai, J. Chem. Theory Comput. in press. Figure 1
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Zhu, Tong, Jordan M. Snaider, Long Yuan et Libai Huang. « Ultrafast Dynamic Microscopy of Carrier and Exciton Transport ». Annual Review of Physical Chemistry 70, no 1 (14 juin 2019) : 219–44. http://dx.doi.org/10.1146/annurev-physchem-042018-052605.

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We highlight the recent progress in ultrafast dynamic microscopy that combines ultrafast optical spectroscopy with microscopy approaches, focusing on the application transient absorption microscopy (TAM) to directly image energy and charge transport in solar energy harvesting and conversion systems. We discuss the principles, instrumentation, and resolutions of TAM. The simultaneous spatial, temporal, and excited-state-specific resolutions of TAM unraveled exciton and charge transport mechanisms that were previously obscured in conventional ultrafast spectroscopy measurements for systems such as organic solar cells, hybrid perovskite thin films, and molecular aggregates. We also discuss future directions to improve resolutions and to develop other ultrafast imaging contrasts beyond transient absorption.
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Ouyang, Hao, Haitao Chen, Yuxiang Tang, Jun Zhang, Chenxi Zhang, Bin Zhang, Xiang’ai Cheng et Tian Jiang. « All-optical dynamic tuning of local excitonic emission of monolayer MoS2 by integration with Ge2Sb2Te5 ». Nanophotonics 9, no 8 (18 avril 2020) : 2351–59. http://dx.doi.org/10.1515/nanoph-2019-0366.

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AbstractStrong quantum confinement and coulomb interactions induce tightly bound quasiparticles such as excitons and trions in an atomically thin layer of transitional metal dichalcogenides (TMDs), which play a dominant role in determining their intriguing optoelectronic properties. Thus, controlling the excitonic properties is essential for the applications of TMD-based devices. Here, we demonstrate the all-optical tuning of the local excitonic emission from a monolayer MoS2 hybridized with phase-change material Ge2Sb2Te5 (GST) thin film. By applying pulsed laser with different power on the MoS2/GST heterostructure, the peak energies of the excitonic emission of MoS2 can be tuned up to 40 meV, and the exciton/trion intensity ratio can be tuned by at least one order of magnitude. Raman spectra and transient pump-probe measurements show that the tunability originated from the laser-induced phase change of the GST thin film with charge transferring from GST to the monolayer MoS2. The dynamic tuning of the excitonic emission was all done with localized laser pulses and could be scaled readily, which pave a new way of controlling the excitonic emission in TMDs. Our findings could be potentially used as all-optical modulators or switches in future optical networks.
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Chen, Lijia, Lun Cai, Lianbin Niu, Pan Guo et Qunliang Song. « Influence of Temperature on Exciton Dynamic Processes in CuPc/C60 Based Solar Cells ». Micromachines 12, no 11 (22 octobre 2021) : 1295. http://dx.doi.org/10.3390/mi12111295.

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Although the effect of high temperature on the performance of organic solar cells has been widely investigated, it is inevitably influenced by the associated annealing effect (which usually leads to film morphology change and variation in electrical properties), which makes the discussion more sophisticated. In this study, we simplified the issue and investigated the influence of low temperatures (from room temperature to 77 K) on the photocurrent and internal/external quantum efficiency of a CuPc/C60 based solar cell. We found that besides the charge dynamic process (charge transport), one or more of the exciton dynamic processes, such as exciton diffusion and exciton dissociation, also play a significant role in affecting the photocurrent of organic solar cells at different temperatures. Additionally, the results showed that the temperature had negligible influence on the absorption of the CuPc film as well as the exciton generation process, but obviously influenced the other two exciton dynamic processes (exciton diffusion and exciton dissociation).
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AKAI, I., T. KARASAWA et T. KOMATSU. « OPTICAL STARK EFFECTS ON THE STACKING FAULT EXCITONS IN BiI3 ». Journal of Nonlinear Optical Physics & ; Materials 01, no 02 (avril 1992) : 311–37. http://dx.doi.org/10.1142/s0218199192000169.

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A study is made of the optical Stark effects on quasi two-dimensional excitons localized at a stacking fault in layered crystal BiI 3. The dynamic coupling of the driven ground states and driven multiple exciton states by the strong photon field occurs for a wide frequency range of light, from negative to positive detuning. For the positive detuning excitation, an additional nonlinear effect peculiar to condensed matter was also observed. Time-resolved measurements in the sub-nanosecond and picosecond time domains confirmed ultrafast switching between the optical Stark effect and the additional nonlinear effect. From the dependence of the optical Stark shift on the excitation intensity, it is shown that the quasi two-dimensional excition transition has a very large dipole matrix element and third-order nonlinear susceptibility χ(3).
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Tikhomirov, S. A. « Ultrafast dynamics and mechanisms of non-stationary absorption in thin gallium selenide samples ». Proceedings of the National Academy of Sciences of Belarus. Physics and Mathematics Series 57, no 1 (2 avril 2021) : 99–107. http://dx.doi.org/10.29235/1561-2430-2021-57-1-99-107.

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Herein, the dynamics and mechanisms of induced absorption in thin samples of gallium selenide under various excitation conditions are studied using femtosecond kinetic spectroscopy. We have registered several types of induced changes including induced absorption on free charge carriers (“hot” and thermalized electrons), bleaching and absorption due to the population of near-edge trap or exciton states, as well as rapid changes in the absorption of probing radiation in the region of the overlap of the exciting and probing pulses due to two-quantum two-frequency interband transitions. The time ranges of the relaxation processes are estimated. It is shown that when using relatively low-intensity long-wave excitation (790 nm), the resonant excitation of the near-edge states occurs mainly due to two-quantum two-frequency transitions followed by the formation of the dynamic equilibrium between bound and free electrons in the time range up to 5 ps. When electrons are excited deeply into the conduction band with the formation of hot free electrons and their subsequent thermalization to the bottom of the conduction band in the time range up to 1 ps, the population of the near-edge states and the establishment of the dynamic equilibrium between bound and free electrons is realized in the same time range (5 ps) as when they are excited “from below”.
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Thèses sur le sujet "Exciton dynamic"

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Heiber, Michael C. « Dynamic Monte Carlo Modeling of Exciton Dissociation and Geminate Recombination in Organic Solar Cells ». University of Akron / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=akron1353092083.

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Tamai, Yasunari. « Excited State Dynamics in Nanostructured Polymer Systems ». 京都大学 (Kyoto University), 2013. http://hdl.handle.net/2433/174961.

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Visnevski, Dmitri. « Collective dynamics of excitons and exciton-polaritons in nanoscale heterostructures ». Phd thesis, Université Blaise Pascal - Clermont-Ferrand II, 2013. http://tel.archives-ouvertes.fr/tel-00914332.

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In my thesis I will discuss some aspects of collective dynamics of excitons and exciton-polaritons in nanoscale heterostructures. In the first Chapter I will make a brief introduction to the modern semiconductor physics and willdescribe the general elements and notions which will be used further. Other four chapters would be devoted to four works in which I participated, notably, in Chapter 2 I will speak about the coherent interactions between phonons and exciton orexciton-polariton condensates, in Chapter 3 I will discuss the quantum dots lasing and its amplification by an acoustic pulse. Chapter 4 and 5 will be devoted respectively to the polariton multistability and to the condensates of indirect excitons.
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Abbas, Chahine. « Optical spectroscopy of indirect excitons and electron spins in semiconductor nanostructures ». Thesis, Montpellier, 2019. http://www.theses.fr/2019MONTS049.

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Ce travail porte sur l’étude optique de la dynamique de spin de deux systèmes: un gaz d’électrons dans des couches minces de CdTe d’une part et des excitons indirects dans un double puits quantique asymétrique en GaAs d’autre part. Des mesures de photoluminescence résolue en temps et en polarisation, et des mesures de spectroscopie pompe-sonde ont permis la détermination des temps de vie et des temps de relaxation de spin des excitons indirects. Le comportement général de la structure a été décrit, les contraintes techniques ont été mise en évidence et les meilleures conditions expérimentales ont été identifiées. En photoluminescence, nous avons mesuré des temps de vie de l’ordre de la quinzaine de ns et des temps de relaxation de spin de 5 ns dans le meilleur cas. L’utilisation d’un setup de spectroscopie pompe-sonde permettant d’étudier des délais très longs a démontré que des temps plus longs encore peuvent être atteints en séparant d’avantage deux impulsions lasers successives.Pour les électrons dans CdTe nous avons utilisé une autre méthode optique: la spectroscopie de bruit de spin qui s’est récemment imposée comme un outil de choix pour étudier la dynamique de spin dans les semi-conducteurs. Son principe consiste à sonder la dynamique d’un système de spins à travers ses fluctuations spontanées. Pour ce faire, ces fluctuations sont encodées dans le plan de polarisation d’un laser hors résonnant par l’intermédiaire de la rotation Faraday.Alors que les réalisations concrètes de cette technique se limitaient jusqu’à présent aux corrélations temporelles, nous proposons ici la première implémentation permettant d’accéder également aux corrélations spatiales du systèmes de spin. Cet accès à la dynamique spatiale est autorisé par une sélectivité en vecteur d’onde de la lumière diffusée venant de l’échantillon et nous offre l’opportunité de mesurer simultanément le temps de relaxation de spin et le coefficient de diffusion de spin. Ayant ainsi une vision complète de la dynamique de spin dans CdTe, nous avons pu confronter la physique du spin bien connue dans GaAs à nos observations dans CdTe. Contre toutes attentes, il semblerait que nos connaissances de GaAs ne soient pas directement transposables à CdTe
This work provides an optical study of spin dynamics in two different systems: electrons gas in n-doped CdTe thin layers, and indirect excitons in asymmetric GaAs coupled quantum wells. Time and polar resolved photoluminescence and pump-probe spectroscopy allowed the determination of both the lifetime and the relaxation time of indirect excitons.The global behaviour of the dedicated biased sample has been described, major technical constraints have been pointed out and optimal working conditions have been identified. In photoluminescence, we obtained a lifetime of 15 ns and a spin relaxation time of 5 ns. Pump-probe spectroscopy with an exceptional delay range shown that longer characteristic times could be obtained increasing the delay between two laser pulses.An other optical method has been used to study electrons in CdTe thin layers. Spin noise spectroscopy has recently emerged as an ideal tool to study dynamics of spin systems through their spontaneous fluctuations which are encoded in the polarisation state of a laser beam by means of Faraday rotation. Common spin noise setups provide only temporal fluctuations, spatial information being lost averaging the signal on the laser spot. Here, we demonstrate the first implementation of a spin noise setup providing both spatial and temporal spin correlations thanks to a wave vector selectivity of the scattered light. This gave us the opportunity to measure both the spin relaxation time and the spin diffusion coefficient. This complete vision of the spin dynamics in CdTe has been compared to our understanding of spin physics in GaAs. Against all odds, this knowledge seems not to be directly transposable from GaAs to CdTe
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Sajjad, Muhammad Tariq. « Exciton dynamics in carbon nanotubes ». Thesis, University of Surrey, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.576127.

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ABSTRACT The confinement of excited charges in carbon nanotubes has significant effect on their optical and electronic properties. The absorption of light generates strongly correlated electron-hole pairs (excitons) in carbon nanotubes. We present a study of the decay of these photogenerated excitons in solutions of semiconducting SWNTs using the degenerate pump probe technique. Under specific experimental conditions, the exciton-exciton reactions on carbon nanotubes were found to correspond to an ideal ID coalescence-diffusion system with distinct regions of reaction-limited and diffusion-limited behaviours. We provided the first experimental evidence for such a system of 'universal behaviour' at longer times which exhibits a power law decay whose exponent and amplitude are independent of the initial population - one of the key characteristics of this reaction-diffusion system. We also show for the first time that exciton-exciton interactions are long-range, and further that the transition between reaction-limited and diffusion-limited regimes is much more abrupt than is predicted by existing theories. A modified theory incorporating a finite reaction length provided an excellent fit to the experimental data for a reaction length of -7 nm. We determined the reaction rate constant of k; = (3.76 ± 0.04) nmfps and the diffusion coefficient of D = (8.1 ± 0.4) nm2/ps from fitting of the asymptotic regimes with rate equations. We also provided the first experimental evidence of sub-diffusive transport of excitons in quasi ID SWNTs through studies of exciton annihilation dynamics in HiPco and CoMoCat SWNTs, where we observed that excitons in HiPco SWNTS exhibit normal diffusive transport where decay follows a Clal power law with decay exponent (a :::::: 0.5), whereas excitons in CoMoCat SWNTs decay more slowly with decay exponent (a :::::: 0.3) as result of sub-diffusive transport. We correlate this slow decay to a higher defect concentration in CoMoCat SWNTs as compared to HiPco measured using Raman spectroscopy and X-ray photoelectron spectroscopy. The experimental results were also compared to results from a Monte Carlo simulation of ID diffusion in a fluctuating potential landscape which shows good agreement with experiment and underlines the necessity to consider spatial aspects (separation of defects and interaction range) in theoretical approaches to the dynamics. The study of excitonic decay in single walled carbon nanotubes is very important in terms of understanding of fundamental photophysics of ID system and their possible application in electronics and photonic devices especially in light emitting devices and non-linear optics. 2
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Bouet, Louis. « Valley dynamics and excitonic properties in monolayer transition metal dichalcogenides ». Thesis, Toulouse, INSA, 2015. http://www.theses.fr/2015ISAT0033/document.

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La possibilité de créer des monocouches de dichalcogenures à métaux de transition (MoS2, WSe2,MoSe2 pour ceux étudiés dans ce manuscrit) a été démontrée récemment (2005) et a ouvert la voie à l’étude de ces matériaux sous leur forme 2D. Il apparaît depuis que les propriétés de ces semi-conducteurs sous leur forme monocouche offrent des perspectives intéressantes à la fois du point de vue de la physique fondamentale et des potentielles applications qui peuvent en découler ; en plus de bénéficier d’un fort couplage avec la lumière, l’existence d’un gap important (situé dans le visible, 1.7-1.8 eV) permet entre autres de réaliser des transistors d’épaisseur mono-atomique. Par ailleurs, la physique de ces matériaux est prometteuse pour les applications dans le domaine de l’optoélectronique. En effet, lorsque le matériau est affiné jusqu’à la monocouche atomique, son gap optique devient direct et la brisure de symétrie d’inversion associée au fort couplage spin-orbite provoque l’apparition de règles de sélection optique originales qui relient directement la polarisation de la lumière émise ou absorbée à une des deux vallées non-équivalentes de l’espace réciproque. Cela ouvre la possibilité d’explorer une nouvelle physique, basée sur l’indice de vallée et intitulée en conséquence vallée-tronique, avec comme perspectives futures la manipulation de l’indice de vallée et l’exploitation d’effetsliés à cette relation originale entre propriétés optiques et électroniques (effet vallée-Hall par exemple). Cemanuscrit de thèse regroupe une série d’expériences réalisées dans le but de comprendre et caractériser les propriétés optoélectroniques de ces matériaux. Un premier chapitre introductif présente le contexte scientifique de ces travaux de recherche et démontre l’origine des propriétés électroniques et optiques de ces matériaux via un modèle théorique simple. Le second chapitre présente en détails les échantillons étudiés ainsi que le dispositif expérimental utilisé lors des mesures. Enfin les chapitres 3 à 6 détaillent les expériences menées et les résultats obtenus ; le lecteur y trouvera des mesures de photoluminescence apportant la démonstration expérimentale des règles de sélection optique, l’identification des différents raies spectrales d’émission pour les différentstypes d’échantillons mentionnés plus haut ainsi que des mesures de photoluminescence résolues en temps permettant d’extraire la dynamique des propriétés des porteurs photo-générés. Une part importante de ce manuscrit est consacrée à l’étude expérimentale des propriétés excitoniques de ces matériaux dont la structure de bande électronique est finalement sondée via des études de magnéto-spectroscopie
The possibility of isolating transition metal dichalcogenide monolayers by simple experimental means has been demonstrated in 2005, by the same technique used for graphene. This has sparked extremely diverse and active research by material scientists, physicists and chemists on these perfectly two-dimensional (2D) materials. Their physical properties inmonolayer formare appealing both fromthe point of view of fundamental science and for potential applications. Transition metal dichalcogenidemonolayers such asMoS2 have a direct optical bandgap in the visible and show strong absorption of the order of 10% per monolayer. For transistors based on single atomic layers, the presence of a gap allows to obtain high on/off ratios.In addition to potential applications in electronics and opto-electronics these 2D materials allow manipulating a new degree of freedom of electrons, in addition to the spin and the charge : Inversion symmetry breaking in addition to the strong spin-orbit coupling result in very original optical selection rules. The direct bandgap is situated at two non-equivalent valleys in k-space, K+ and K−. Using a specific laser polarization, carriers can be initialized either in the K+ or K− valley, allowing manipulating the valley index of the electronic states. This opens up an emerging research field termed "valleytronics". The present manuscript contains a set of experiments allowing understanding and characterizing the optoelectronic properties of these new materials. The first chapter is dedicated to the presentation of the scientific context. The original optical and electronic properties of monolayer transition metal dichalcogenides are demonstrated using a simple theoreticalmodel. The second chapter presents details of the samples and the experimental setup. Chapters 3 to 6 present details of the experiments carried out and the results obtained. We verify experimentally the optical selection rules. We identify the different emission peaks in the monolayer materials MoS2, WSe2 and MoSe2. In time resolved photoluminescence measurements we study the dynamics of photo-generated carriersand their polarization. An important part of this study is dedicated to experimental investigations of the properties of excitons, Coulomb bound electron-hole pairs. In the final experimental chapter, magneto-Photoluminescence allows us to probe the electronic band structure and to lift the valley degeneracy
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Brüggemann, Ben. « Theory of ultrafast exciton dynamics in photosynthetic antenna systems ». Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2004. http://dx.doi.org/10.18452/15037.

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Die Multiexzitonen-Theorie des Anregungsenergie-Transfers in Farbstoff-Protein-Komplexen und biologischen Antennensystemen wird um den Prozess der Exziton-Exziton-Vernichtung erweitert. Um eine mikroskopische Beschreibung zu erzielen, wird eine Herangehensweise benutzt, die auf der Internen Konversion der Anregungsenergie innerhalb der Farbstoffmoleküle basiert. Diese Interne Konversion führt zu nicht strahlenden Übergängen von höheren zu niedrigeren Exziton-Mannigfaltigkeiten. Neben der Einbeziehung der Exziton-Exziton-Vernichtung beinhaltet die hier verwendete Multiexziton-Dichtematrixtheorie auch die Kopplung zu niedrig-energetischen Schwingungs-Freiheitsgraden und dem elektrischen Feld. Für den Übergang von der Zwei- zu der Einexzitonen -Mannigfaltigkeit werden exakte und genäherte Ausdrücke hergeleitet. Die erste Anwendung der erweiterten Multiexziton-Dichtematrixtheorie ist die Berechnung von ultra-schnellen differentiellen Absoptionsspektren. Um den Prozess der Exziton-Exziton-Vernichtung in intensitätsabhängigen differenziellen Absorptionsspektren näher zu untersuchen, wird diese Herangehensweise auf den B850 Ring des LH2 von rhodobacter sphaeroides angewendet. Die Bedeutung der Exziton-Exziton-Vernichtung und der Einfluss von statischer Unordnung werden detailiert diskutiert. Die Simulationen der differentiellen Absorptionsspektren mit statischer Unordnung und Orientierungsmittelung zeigen gute Übereinstimmung mit experimentellen Beobachtngen. Durch die Veröffentlichung der Strukturdaten des Photosystem I (PS1) von Synechococcus elongatus wurde es zum ersten Mal möglich, ein Exziton-Modell für die 96 Chorophyllmoleküle einzuführen, die in die Proteinmatrix dieses Antennensystems eingebettet sind. Das Ziel dabei ist, sowohl die linearen Spektren in einem weiten Temperaturbereich, als auch die zeitaufgelöste Fluoreszenz zu reproduzieren. Die Kopplungen und die Dipolmomente der Chlorophyllmoleküle wurden den Strukturdaten entnommen. Da die Energien der einzelnen Farbstoffe stark von deren unmittelbarer Umgebung abhängt, werden diese bestimmt, indem simulierte Absorption, Lineardichroismus und Zirkulardichroismus bei niedrigen Temperaturen den experimentellen Spektren angepasst werden. Nachdem einige Chlorophyllmoleküle den Zuständen mit den niedrigsten Energien zugeordnet wurden, werden die Energien mit Hilfe eines evolutionären Algorithmus angepasst. Die Qualität des PS1 Modells wird durch die Berechnung der zeitabhängigen Fluoreszenz untermauert (mit zusätzlicher inhomogener Linienbreite), die Simulationen stimmen gut mit aktuellen experimentellen Resultaten überein. Die oben erwähnten Exziton-Modelle beschreiben die jeweiligen Experimente erfolgreich. Der nächste Schritt ist, diese Modelle zu nutzen, um einen neuen Typ von Experiment vorzuschlagen, das Exciton-Steuerungs-Experiment. Auf dem Exciton-Modell des FMO Komplexes von Prosthecochloris aestuarii und dem oben erwähnten PS1 Modell von Synechococcus elongatus aufbauend wird die Bildung von exzitonischen Wellenpaketen durch Laser-Anregung studiert. Diese stellen eine kohärente Überlagerung exzitonischer Zustände dar, ähnlich der bei Schwingungs-Wellenpaketen. Um die spezielle Form des Femtosekunden-Laserpulses zu bestimmen, der zu einer räumlichen Lokalisierung der Anregungsenergie führt, wird die Theorie der optimalen Steuerung verwendet. Die Möglichkeit, solch einen lokalisierten Zielzustand zu erreichen, wird aufgezeigt, auch unter dem Einfluss von energetischer Unordnung und Exziton-Exziton Vernichtung. Ferner wird gezeigt, dass die Effizienz der Lokalisierung und die Länge des optimalen Pulses stark von der Temperatur abhängen.
The multi-exciton description of excitation energy transfer in chromophore complexes and biological light harvesting antenna systems is extended to include the exciton-exciton annihilation processes. To achieve a complete microscopic description the approach is based on intra--chromophore internal conversion processes which leads to non-radiative transitions from higher to lower lying exciton manifolds. Besides an inclusion of exciton-exciton annihilation the used multi-exciton density matrix theory also accounts for a coupling to low-frequency vibrational modes and the radiation field. Concentrating on transitions from the two- to the single-exciton manifold exact and approximate expressions for the annihilation rate are derived. A first application of the introduced extended multi-exciton density matrix theory is given by the computation of ultrafast transient absorption spectra. To elucidate the process of exciton-exciton annihilation in intensity dependent transient absorption data the approach is applied to the B850 ring of the LH2 found in rhodobacter sphaeroides. The signatures of exciton-exciton annihilation as well as the influence of static disorder are discussed in detail. The simulations of transient absorption including static disorder and orientational averaging are in good agreement with experimental data. The recently published structure of the Photosystem I (PS1) of Synechococcus elongatus made it for the first time possible to introduce an excitonic model for the 96 chlorophylls embedded in the protein matrix of that core-antenna system, as presented in this work. The challenge has been to reproduce linear frequency domain spectra in a wide temperature range as well as the time resolved fluorescence. The couplings and the dipole-moments of the chlorophylls are extracted from the x-ray crystal structure. Since the position of the energetic levels of the chlorophylls depend on the respective surrounding their determination is achieved by fitting low temperature absorption, linear dichroism and circular dichroism at the same time. After assigning some chromophores to the red-most states, an evolutionary algorithm is used to get the best fit. The quality of the resulting PS1 model (additionally accounting for inhomogeneous line broadening) is confirmed in calculating time dependent fluorescence spectra which show a good agreement with recent experimental results. The outlined method is also applicable to other photosynthetic antenna systems. The above described exciton models successfully explain the respective measurements. In a second step, they will be used to propose a new type of experiment, the exciton control experiment. Based on an exciton model for the FMO complex of Prosthecochloris aestuarii and the proposed PS1 model of Synechococcus elongatus one studies the laser pulse formation of excitonic wavepackets, i.e. a coherent superposition of excitonic states similar to vibrational wavepackets. Optimal Control theory is used to calculate the shape of femtosecond laser pulses that leads to a spatial localization of excitation energy. The possibility to populate such a localized target state is demonstrated, even in the presence of disorder or exciton-exciton annihilation, and it is shown that the efficiency of localization as well as the length the most suited pulses strongly depend on temperature.
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Nelson, Delene J. « Exciton operators, communication relations and dynamics ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ33420.pdf.

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Lagoudakis, Pavlos G. « Exciton polariton dynamics in semiconductor microcavities ». Thesis, University of Southampton, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.274583.

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Grevatt, Treena. « Exciton spin dynamics in quantum wells ». Thesis, University of Southampton, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.242274.

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Livres sur le sujet "Exciton dynamic"

1

Bergin, Randy M., et Randy M. Bergin. Exciton quasiparticles : Theory, dynamics, and applications. Hauppauge, N.Y : Nova Science Publishers, 2010.

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Monahan, Nicholas R. Ultrafast Exciton Dynamics at Molecular Surfaces. [New York, N.Y.?] : [publisher not identified], 2015.

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Bergin, Randy M. Exciton quasiparticles : Theory, dynamics, and applications. Hauppauge, N.Y : Nova Science Publishers, 2010.

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Bohn, Bernhard Johann. Exciton Dynamics in Lead Halide Perovskite Nanocrystals. Cham : Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-70940-2.

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Schröter, Marco. Dissipative Exciton Dynamics in Light-Harvesting Complexes. Wiesbaden : Springer Fachmedien Wiesbaden, 2015. http://dx.doi.org/10.1007/978-3-658-09282-5.

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Baldassare, Di Bartolo, North Atlantic Treaty Organization. Scientific Affairs Division. et NATO Advanced Research Study Institute and International School of Atomic and Molecular Spectroscopy Workshop on Spectroscopy and Dynamics of Collective Excitation in Solids (1995 : Erice, Italy), dir. Spectroscopy and dynamics of collective excitations in solids. New York : Plenum Press, 1997.

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K, Kuchitsu, dir. Dynamics of excited molecules. Amsterdam : Elsevier, 1994.

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H, Sockel, dir. Wind-excited vibrations of structures. New York : Springer-Verlag, 1994.

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1947-, Whitehead J. C., et Royal Society of Chemistry (Great Britain). Faraday Division., dir. Dynamics of electronically excited states in gaseous, cluster and condensed media. London : Faraday Division, Royal Society of Chemistry, 1998.

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Mezey, Paul G. Potential energy hypersurfaces. Amsterdam : Elsevier, 1987.

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Chapitres de livres sur le sujet "Exciton dynamic"

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Singh, Jai. « Exciton Dynamics ». Dans Excitation Energy Transfer Processes in Condensed Matter, 151–202. Boston, MA : Springer US, 1994. http://dx.doi.org/10.1007/978-1-4899-0996-1_5.

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Shah, Jagdeep. « Exciton Dynamics ». Dans Ultrafast Spectroscopy of Semiconductors and Semiconductor Nanostructures, 225–61. Berlin, Heidelberg : Springer Berlin Heidelberg, 1999. http://dx.doi.org/10.1007/978-3-662-03770-6_6.

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Shah, Jagdeep. « Exciton Dynamics ». Dans Ultrafast Spectroscopy of Semiconductors and Semiconductor Nanostructures, 225–61. Berlin, Heidelberg : Springer Berlin Heidelberg, 1996. http://dx.doi.org/10.1007/978-3-662-03299-2_6.

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Laussy, Fabrice P. « Quantum Dynamics of Polariton Condensates ». Dans Exciton Polaritons in Microcavities, 1–42. Berlin, Heidelberg : Springer Berlin Heidelberg, 2012. http://dx.doi.org/10.1007/978-3-642-24186-4_1.

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Satarić, M., Z. Ivić et R. Žakula. « The Temperature Dependence of Exciton-Phonon Coupling in the Context of Davydov’s Model ; The Dynamic Damping of Soliton ». Dans Davydov’s Soliton Revisited, 295–308. Boston, MA : Springer US, 1990. http://dx.doi.org/10.1007/978-1-4757-9948-4_22.

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Kulakovskii, Vladimir D., Sergei S. Gavrilov, Sergei G. Tikhodeev et Nikolay A. Gippius. « Polariton Nonlinear Dynamics : Theory and Experiments ». Dans Exciton Polaritons in Microcavities, 43–65. Berlin, Heidelberg : Springer Berlin Heidelberg, 2012. http://dx.doi.org/10.1007/978-3-642-24186-4_2.

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Gutowski, Jürgen, Hans-Georg Breunig et Tobias Voss. « Dynamics of Excitons and Exciton Complexes in Wide-Gap Semiconductors ». Dans Optics of Semiconductors and Their Nanostructures, 133–57. Berlin, Heidelberg : Springer Berlin Heidelberg, 2004. http://dx.doi.org/10.1007/978-3-662-09115-9_6.

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Schröter, Marco. « Dissipative quantum dynamics ». Dans Dissipative Exciton Dynamics in Light-Harvesting Complexes, 5–48. Wiesbaden : Springer Fachmedien Wiesbaden, 2015. http://dx.doi.org/10.1007/978-3-658-09282-5_2.

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Ding, Wenjing. « Dynamic Shimmy of Front Wheel ». Dans Self-Excited Vibration, 167–90. Berlin, Heidelberg : Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-540-69741-1_7.

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Takagahara, T. « Excitonic optical nonlinearity and exciton dynamics in semiconductor quantum dots ». Dans Confined Electrons and Photons, 827–30. Boston, MA : Springer US, 1995. http://dx.doi.org/10.1007/978-1-4615-1963-8_38.

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Actes de conférences sur le sujet "Exciton dynamic"

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Hayat, Alex, Christoph Lange, Lee A. Rozema, Ardavan Darabi, Henry M. van Driel, Aephraim M. Steinberg, Bryan Nelsen, David W. Snoke, Loren N. Pfeiffer et Kenneth W. West. « Exciton-Polariton Dynamic Stark Effect ». Dans Frontiers in Optics. Washington, D.C. : OSA, 2012. http://dx.doi.org/10.1364/fio.2012.ftu5d.3.

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Huang, Libai. « Ultrafast Dynamic Microscopy of Exciton and Charge Transport ». Dans nanoGe Fall Meeting 2021. València : Fundació Scito, 2021. http://dx.doi.org/10.29363/nanoge.nfm.2021.237.

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Yu, Yi, John J. H. Eng, Kunze Lu, Manlin Luo, Bongkwon Son, Pratul Venkatesh, Wen Wei Lee, Yong Hao Tham, Weibo Gao et Donguk Nam. « Dynamic tuning of WSe2 exciton emission via laser annealing ». Dans 2D Photonic Materials and Devices VI, sous la direction de Arka Majumdar, Carlos M. Torres et Hui Deng. SPIE, 2023. http://dx.doi.org/10.1117/12.2649766.

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Weibel, Jason, et David Yaron. « Dynamic dielectric screening and exciton binding energies in conjugated polymers ». Dans Optical Science, Engineering and Instrumentation '97, sous la direction de Z. Valy Vardeny et Lewis J. Rothberg. SPIE, 1997. http://dx.doi.org/10.1117/12.279281.

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Guarneri, Ludovica, Qitong Li, Jung-Hwan Song, Mark L. Brongersma et Jorik van de Groep. « Exciton-Enhanced Light Scattering in Atomically-Thin Metasurfaces ». Dans CLEO : QELS_Fundamental Science. Washington, D.C. : Optica Publishing Group, 2022. http://dx.doi.org/10.1364/cleo_qels.2022.fm4f.3.

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We demonstrate temperature-dependent and dynamic control over light scattering by exciton resonances in atomically-thin optical elements by carving them directly out of monolayer WS2. Using electrostatic ion-liquid gating we dynamically manipulate the material’s exciton resonance.
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Johnson, Anthony M. « Femtosecond Exciton Dynamics of II-VI Semiconductor Multiple Quantum Wells (Invited) ». Dans Inaugural Forum for the Research Center for Optical Physics. Washington, D.C. : Optica Publishing Group, 1993. http://dx.doi.org/10.1364/rcop.1993.tpls2.

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Room temperature excitonic absorption peaks have been difficult to observe in II-VI semiconductors and has been attributed to strong exciton-phonon interactions. The first well-defined room temperature excitonic absorption peaks were measured in CdZnTe/ZnTe multiple quantum wells (MQWs), grown by molecular beam epitaxy on GaAs substrates. We report the first direct measurement of the relative bleaching strength of room temperature excitonic absorption by "cool" free or ionized electron-hole (e-h) pairs and "cold" excitons. In these II-VI MQWs, the exciton binding energy (E b x ≈23meV), the longitudinal-optic (LO) phonon energy (ℏωLO≈25 meV), and the thermal energy (kT ≈ 26 meV) are all comparable and thus the ionized e-h pairs are "cool" (ΔE ≈ 2 meV), in contrast to the "hot" ionized e-h pairs (ΔE ≈ 27 meV) generated in GaAs/AlGaAs MQWs Ebx≈9 meV,ℏωLO≈36 meV. Utilizing 80 fs duration pump pulses to resonantly create a distribution of "cold" excitons followed by a broad band 14 fs probe pulse to measure the induced transmission, we found that the bleaching effect of "cold" neutral excitons on the excitonic absorption was nearly twice as strong as the same density of "cool" uncorrelated e-h pairs, in contrast to theoretical estimates. We have measured a very fast exciton ionization time, τion ≈ 110 fs, which agrees well with the measured homogeneous exciton linewidth broadening, supporting a model of thermal broadening due to the ionization of excitons through LO-phonon scattering. These are the first reported room temperature experiments on femtosecond exciton dynamics in II-VI semiconductor MQWs.
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Burgel, M. V., D. A. Wiersma et K. Duppen. « The Femtosecond Dynamics of Aggregate Excitons in Liquids ». Dans International Conference on Ultrafast Phenomena. Washington, D.C. : Optica Publishing Group, 1994. http://dx.doi.org/10.1364/up.1994.pd.10.

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Room temperature photon echo experiments show that optical dephasing in aggregates of dye molecules in solution is very slow (T2> 100 fs), due to motional narrowing over dynamic perturbations. By pump-probe experiments on multiple-exciton transitions the range of exciton delocalization was determined to be 18 molecules.
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Pagliano, Francesco, Frank van Otten, Tian Xia, Lianhe Li, Edmund Linfield et Andrea Fiore. « Ultrafast Electrical Modulation of the Exciton Energy for the Dynamic Control of Cavity Quantum Electrodynamics ». Dans CLEO : QELS_Fundamental Science. Washington, D.C. : OSA, 2013. http://dx.doi.org/10.1364/cleo_qels.2013.qf1a.4.

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Kuhl, J., A. Honold, L. Schultheis et C. W. Tu. « Enhancement of the Radiative Lifetime of 2D Excitons in a GaAs Quantum Well by Dephasing Collisions ». Dans Quantum Wells for Optics and Opto-Electronics. Washington, D.C. : Optica Publishing Group, 1989. http://dx.doi.org/10.1364/qwoe.1989.mc3.

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The nonlinear optical properties and the ultrafast dynamics of excitons in semiconductors are a major field of present semiconductor research. This interest is explained by the potential applications of excitonic nonlinearities as ultrafast optical switching devices in future optical communication systems. In a recent theoretical paper Hanamura /1/ discussed the advantages of excitons in a quantum well (QW) as a nonliner optical medium combining large 3rd order nonlinear susceptibility χ(3) with a fast response. The strong enhancement of is χ(3) explained as a consequence of both the macroscopic transition dipole moment of the exciton in a QW and the rapid radiative decay of the confined excitons. Hanamura calculated that an exciton in a QW should decay superradiantly through its macroscopic dipole transition moment within a few picoseconds. This superradiant decay requires, however, a coherent polarization of the material and will be strongly reduced if the spatial and temporal coherence of the excited excitons is destroyed by interaction of the excitons with their environment. Such a tight connection between the radiative lifetime τ r and the dephasing T2 has been recently predicted by Feldmann et al. /2/.
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Wegener, M., I. Bar-Joseph, G. Sucha, M. N. Islam, N. Sauer, T. Y. Chang et D. S. Chemla. « Femtosecond dynamics of excitonic absorption in the infrared InGaAs quantum wells ». Dans Quantum Wells for Optics and Opto-Electronics. Washington, D.C. : Optica Publishing Group, 1989. http://dx.doi.org/10.1364/qwoe.1989.mb4.

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Excitons in III-V quantum wells (QW) are strongly coupled to polar longitudinal optical (LO) phonons. The binding energies of the quasi 2D excitons (Eb ≈ 1-10 meV) are smaller than the energies of the LO-phonons (ℏΩLO=30-40meV). Excitons are thus unstable against LO-phonon collisions which can ionize them and release a free electron hole pair with substantial excess energy. It is clear that this process is temperature dependent. At high temperature the collision rate increases and the excitonic life time can be reduced significantly. An experimental investigations of the dynamics of excitonic nonlinearities in GaAs QWs using femtosecond spectroscopic techniques, was able to time resolve the room temperature exciton ionization . An unexpected finding of these experiments was that a population of excitons is more efficient than electron-hole (e-h) plasma in reducing the strength of the exciton resonances. The experimental findings in GaAs QWs were qualitatively explained by a theory2 that accounts only for the effects of the Fermi statistic and completely neglects the long range screening. An extension of this theory was recently presented by Zimmermann3 which uses an elegant technique to performe exact infinite summations over all excitonic states (bound and unbound).
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Rapports d'organisations sur le sujet "Exciton dynamic"

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Kopelman, R. (Nanometer scale exciton spectroscopy and photochemistry : Dynamic imaging of DNA structure-activity relations and radiation signatures). Office of Scientific and Technical Information (OSTI), janvier 1991. http://dx.doi.org/10.2172/6060311.

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Kopelman, R. [Nanometer scale exciton spectroscopy and photochemistry : Dynamic imaging of DNA structure-activity relations and radiation signatures]. Progress report, September 24, 1990--July 24, 1991. Office of Scientific and Technical Information (OSTI), décembre 1991. http://dx.doi.org/10.2172/10107053.

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Kopelman, R. Nanometer scale exciton/photon dynamic spectrochemical imaging for DNA structure-activity relations and radiation signatures. Final progress report, December 24, 1993--December 23, 1996. Office of Scientific and Technical Information (OSTI), juin 1997. http://dx.doi.org/10.2172/486116.

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Jessen, S. W., J. W. Blatchford, Y. Z. Wang, D. D. Gebler et L. B. Lin. Exciton Dynamics in Poly(p-pyridyl Vinylene). Fort Belvoir, VA : Defense Technical Information Center, mars 1996. http://dx.doi.org/10.21236/ada305228.

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Gallagher, T. F. Structure Dynamics of Excited Atoms. Fort Belvoir, VA : Defense Technical Information Center, mars 1988. http://dx.doi.org/10.21236/ada198147.

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Parekh, Jatin C., et Warren C. Gibson. Dynamic Analysis of Quartz Glass Excited Acoustically. Fort Belvoir, VA : Defense Technical Information Center, juin 1992. http://dx.doi.org/10.21236/ada361416.

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Gallagher, Thomas F. Structure and Dynamics of Excited Atoms. Fort Belvoir, VA : Defense Technical Information Center, décembre 2001. http://dx.doi.org/10.21236/ada398434.

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Gallagher, Thomas F. Structure and Dynamics of Excited Atoms. Fort Belvoir, VA : Defense Technical Information Center, janvier 2005. http://dx.doi.org/10.21236/ada435243.

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Gallagher, Thomas F. Structure and Dynamics of Excited Atoms. Fort Belvoir, VA : Defense Technical Information Center, février 1987. http://dx.doi.org/10.21236/ada179887.

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Moore, C. B. The Dynamics of Vibrationally Excited Molecules. Fort Belvoir, VA : Defense Technical Information Center, novembre 1985. http://dx.doi.org/10.21236/ada163764.

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