Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 147 for “"Excitonic"”.
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Temperature dependent excitonic effects in silicon
… of bandgap energy can be obtained by adding the excitonic binding energy and the corresponding phonon energy to the optically measured threshold. Observing excitonic effects in the absorption process is an effective means of understanding the phonon and exciton behaviour and the material’s …
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Collective Phenomena in Excitonic Quantum Matter
… leads to the macroscopic condensation of “excitonic insulators” in small-bandgap materials, with quantum coherence and possible super-transport persisting up to room temperature. Alternatively, in large-bandgap semiconductors, the Bose-Einstein condensation of optically active metastable …
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Excitonic spin engineering in optoelectronic devices
Despite decades of research, solar cell efficiencies struggle to get higher than 25%. This is due to two fundamental losses in the device: thermalization of high energy photons and transmission of low energy photons. In this work, we demonstrate efforts to improve both these losses, which, when …
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Excitonic phases in stressed, ultra-pure silicon
Restriction data tranferred 2014-07-01T11:32:22-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: Thesis
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Excitonic optical nonlinearities in semiconductors and semiconductor microstructures.
This dissertation describes the study of excitonic optical nonlinearities in semiconductors and semiconductor microstructures. The main emphasis is placed on the evolution of optical nonlinearities as one goes from bulk to quantum-confined structures. Included are experimental studies of …
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Growth and Characterisation of ZnO Nanostructures: Excitonic Properties and Morphology
The growth mechanism of aligned ZnO nanostructures, grown by the vapour phase transport (VPT) growth method, specifically with nanorod and nanowall morphologies has been studied. The thesis begins with an introductory chapter on ZnO nanostructures and related topics, and the second chapter …
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Application of quantum Monte Carlo methods to excitonic and electronic systems
The work in this thesis is concerned with the application and development of quantum Monte Carlo (QMC) methods. We begin by proposing a technique to maximise the efficiency of the extrapolation of DMC results to zero time step, finding that a relative time step ratio of 1:4 is optimal. We discuss …
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A method for the calculation of excitonic effects in certain metals
Due to the long-range screening behavior of electrons in metals, interactions between excited electrons and their corresponding holes are few and are generally ignored. In this thesis, we attempt to include this electron-hole interaction into the calculation by randomly choosing a finite number of …
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Ultrafast photoinduced dynamics of low-dimensional excitonic materials at room temperature
… We next turn our attention to the quasi-1D excitonic insulator candidate Ta₂NiSe₅. At 328 K, this material is proposed to undergo a spontaneous symmetry breaking, leading to the Bose-Einstein condensation of excitons in the ground state. Yet, experiment and theory continue to wrestle over …
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Excitonic spin engineering for solar cells and organic light-emitting diodes
… devices. In this thesis, we explore excitonic concepts for improving both organic-light emitting diodes (OLEDs) and silicon solar cells. OLEDs are already commercially successful. However they still suffer from several major drawbacks. Multiexcited-state phenomena are believed to be …
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Luminescence Studies of the Excitonic System in Germanium: Phase Properties and Transport
… presents the results of three studies of the excitonic system in Ge. These studies employ near-infrared spectroscopy and imaging techniques to examine the phase and transport properties of the low temperature exciton-plasma system.
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Luminescence studies of the excitonic system in germanium: Phase properties and transport
… presents the results of three studies of the excitonic system in Ge. These studies employ near-infrared spectroscopy and imaging techniques to examine the phase and transport properties of the low temperature exciton-plasma system. The first study, presented in Chapter II, examines the …
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The electronic, optical and excitonic effects of high hydrostatic pressure on semiconductors
This thesis describes the results from high pressure experiments on semiconductors, and some theoretical background for those experiments. The primary goal is to better understand the properties of these useful materials through studies of the effect of hydrostatic pressure.
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A study of the molecular behavior in the vibronic and excitonic properties of silicon nanoparticles
The molecular behavior of silicon nanoparticles, produced via electrochemical etching of a bulk precursor, is studied. The smallest particle, 1 nrn in diameter, is amenable to first principles modeling due to the manageable number of atoms in the structure. The ability to produce these particles in …
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Properties of Type-II ZnTe/ZnSe Submonolayer Quantum Dots Studied via Excitonic Aharonov-Bohm Effect and Polarized Optical Spectroscopy
… I use magneto-photoluminescence, including excitonic Aharonov-Bohm (AB) effect and polarized optical spectroscopy as the primary tools in this work.</p> <p>I present previous studies as well as the background of optical and magneto-optical processes in semiconductor nanostructures and …
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Exciton Dynamics and Anisotropy in 2D Metal Organochalcogenolate Semiconductors
… (MOCs). Since its blue-emitting excitonic properties were discovered in 2018, AgSePh has attracted attention from the scientific community. From a fundamental science perspective, AgSePh provides an excellent platform for exploring many-body interactions among quasiparticles (such …
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Coherence in nanostructured excitons
… to chemical energy. Recently, studies found that excitonic interactions play a significant role in controlling antennas' light harvesting abilities, and that coherence may greatly affect energy transport efficiencies. While these studies have propelled our understanding of excitons in these …
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Optical studies of DNA-wrapped carbon nanotubes
… In light of the recent developments in the excitonic theory of D systems in general and of 1D carbon nanotubes in particular, the observed phonon-assisted processes are interpreted and examined in terms of excitonic states. An intense up-shifted phonon-assisted transition observed in PL …
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I. Excitonic phase diagram in Si: evidence for two condensed phases ; II. Motion of photoexcited carriers in GaAs/Alx̳Ga1̳-̳x̳As multiple quantum wells : anomalous confinement at high densities
… Two major topics are addressed: I. Excitonic Phase Diagram in Si: Evidence for Two Condensed Phases At low temperatures and sufficient densities, free excitons in Si and Ge undergo a simultaneous gas-liquid and insulator-metal transition into droplets of electron-hole liquid. Some …
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