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Auer, Thomas. "The electron nuclear spin system in (In,Ga)As quantum dots." Göttingen Sierke, 2008. http://d-nb.info/990846938/04.
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Kettler, Jan [Verfasser]. "Telecom-wavelength nonclassical light from single In(Ga)As quantum dots / Jan Kettler." München : Verlag Dr. Hut, 2017. http://d-nb.info/1128466880/34.
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Hatami, Fariba. "Indium phosphide quantum dots in GaP and in In 0.48 Ga 0.52 P." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2002. http://dx.doi.org/10.18452/14873.
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Im Rahmen dieser Arbeit wurden selbstorganisierte, verspannte InP-Quantenpunkte mittels Gasquellen-Molekularstrahlepitaxie hergestellt und deren strukturelle und optische Eigenschaften untersucht. Die Quantenpunkte wurden sowohl in InGaP-Matrix gitterangepasst auf GaAs-Substrat als auch in GaP-Matrix auf GaP-Substrat realisiert. Die starke Gitterfehlanpassung von 3,8% im InP/InGaP- bzw. 7,7% im InP/GaP-Materialsystem ermöglicht Inselbildung mittels des Stranski-Krastanow-Wachstumsmodus: Ab einer kritischen InP-Schichtdicke findet kein zweidimensionales, sondern ein dreidimensionales Wachstum statt. Die kritische Schichtdicke wurde mit etwa 3 Monolagen für das InP/InGaP- und mit etwa 1,8 Monolagen für das InP/GaP-System bestimmt. Die strukturellen Untersuchungen zeigen, dass InP Quantenpunkte in GaP im Vergleich zu solchen in InGaP größer sind und stärker zum Abbau von Verspannung tendieren. Die in InGaP-Matrix eingebettete InP-Quantenpunkte zeigen sehr ausgeprägte optische Emissionen, die, in Abhängigkeit von den Wachstumsparametern, im Bereich von 1,6 bis 1,75eV liegen. Die Emissionslinie wird der strahlenden Rekombination von in den Quantenpunkten lokalisierten Elektronen und Löchern zugeordnet. Dies wird auch durch das Bänderschema bestätigt, das mit Hilfe der Model-Solid-Theorie modelliert wurde. Darüber hinaus weist die Lebensdauer der Ladungsträger von einigen hundert Pikosekunden darauf hin, dass die InP/InGaP Quantenpunkte vom Typ I sind. Zusätzlich zu den optischen Eigenschaften wurde die Anordnung von dicht gepackten InP-Quantenpunkten in und auf InGaP mittels zweidimensionaler Fourier-Transformation der Daten aus der Atomkraftmikroskopie, Transmissionelektronmikroskopie und diverser Röntgen-Streuexperimente untersucht sowie die planaren und vertikale Ordnungseffekte der Quantenpunkte studiert. Die Untersuchungen zeigen, dass die Ordnung der Quantenpunkte sowohl hinsichtlich ihrer Packungsdichte als auch ihrer Orientierung mit wachsender InP-Bedeckung zunimmt. Darüber hinaus wurde die Verspannungsverteilung in den InP/InGaP-Quantenpunkten mit Hilfe von diffuser Röntgen-Streuung in Verbindung mit kinematischen Simulationen studiert und eine asymmetrische Form der Quantenpunkte festgestellt, die auch Ursache für die gemessene Polarisationsanisotropie der Photolumineszenz sein kann. Die in GaP-Matrix eingebetteten InP-Quantenpunkte wurden im Rahmen dieser Arbeit erstmals erfolgreich auf ihre aktiven optischen Eigenschaften hin untersucht. Sie zeigen eine optische Emission zwischen 1,9 und 2 eV im sichtbaren Bereich. Diese strahlende Rekombination wird ebenfalls dem direkten Übergang zwischen Elektronen- und Löcherzuständen zugeordnet, die in den InP Quantenpunkten lokalisiert sind. Auch Photolumineszenzmessungen unter mechanischem Druck weisen darauf hin, dass es sich in diesem System hauptsächlich um einen direkten räumlichen Übergang handelt. Dieses Ergebnis wird dadurch untermauert, dass die Lebensdauer der Ladungsträger im Bereich von etwa 2 ns liegt, was nicht untypisch für Typ-I-Systeme ist. Die Ergebnisse für zweidimensionale, in GaP eingebettete InP-Schichten zeigen im Gegensatz zu den Quantenpunkten, dass die strahlende Rekombination in InP/GaP Quantentöpfen aufgrund eines indirekten Übergangs (sowohl in Orts- als auch in Impulsraum) zwischen Elektronen- und Löcherzuständen erfolgt. Die optischen Emissionslinien liegen für Quantentöpfe im Bereich von 2,15 bis 2,30eV. Die nachgewiesene sehr lange Lebensdauer der Ladungsträger von etwa 20ns weist weiter darauf hin, dass die Quantentöpfe ein Typ-II-System sind. Nach Modellierung des Bänderschemas für das verspannte InP/GaP-System und Berechnung der Energieniveaus von Löchern und Elektronen darin mit Hilfe der Effektive-Masse-Näherung in Abhängigkeit von der InP-Schichtdicke zeigt sich ferner, dass für InP-Quantentöpfe mit einer Breite kleiner als 3nm die Quantisierungsenergie der Elektronen so groß ist, dass der X-Punkt in GaP energetisch tiefer liegt als der Gamma-Punkt in InP. Dieser Potentialverlauf führt dazu , dass die Elektronen im X-Minimum des GaP lokalisieren, während die Löcher in der InP-Schicht bleiben. Optische Untersuchungen nach thermischer Behandlung der Quantenpunkte führen sowohl im InP/InGaP- als auch im InP/GaP-System zur Verstärkung der Lumineszenz, die bis zu 15 mal internsiver als bei unbehandelten Proben sein kann. Insgesamt zeigt diese Arbeit, dass InP-Quantenpunkte durch ihre optischen Eigenschaften sehr interessant für optoelektronische Anwendungen sind. Die Verwendung von durchsichtigem GaP (mit einer größeren Bandlücke und kleineren Gitterkonstante im Vergleich zu GaAs und InGaP) als Matrix und Substrat hat nicht nur den Vorteil, dass die InP-Quantenpunkte hierbei im sichtbaren Bereich Licht emittieren, sondern man kann in der Praxis auch von einer hochentwickelten GaP-basierten LED-Technologie profitieren. Hauptergebnis dieser Arbeit ist, dass die in indirektes GaP eingebetteten InP-Quantenpunkte aktive optische Eigenschaften zeigen. Sie können daher als aktive Medien zur Realisierung neuartiger effizienter Laser und Leuchtdioden verwendet werden.The growth and structural properties of self-assembled InP quantum dots are presented and discussed, together with their optical properties and associated carrier dynamics. The QDs are grown using gas-source molecular-beam epitaxy in and on the two materials InGaP (lattice matched to GaAs) and GaP. Under the proper growth conditions, formation of InP dots via the Stranski-Krastanow mechanism is observed. The critical InP coverage for 2D-3D transition is found to be 3ML for the InP/ InGaP system and 1.8ML for the InP/GaP system. The structural characterization indicates that the InP/GaP QDs are larger and, consequently, less dense compared to the InP/ InGaP QDs; hence, InP dots on GaP tend to be strain-relaxed. The InP/ InGaP QDs tend to form ordered arrays when InP coverage is increased. Intense photoluminescence from InP quantum dots in both material systems is observed. The PL from InP/GaP QDs peaks between 1.9 and 2 eV and is by about 200 meV higher in energy than the PL line from InP/ InGaP QDs. The optical emission from dots is attributed to direct transitions between the electrons and heavy-holes confined in the InP dots, whereas the photoluminescence from a two-dimensional InP layer embedded in GaP is explained as resulting from the spatially indirect recombination of electrons from the GaP X valleys with holes in InP and their phonon replicas. The type-II band alignment of InP/GaP two-dimensional structures is further confirmed by the carrier lifetime above 19 ns, which is much higher than in type-I systems. The observed carrier lifetimes of 100-500 ps for InP/ InGaPQDs and 2 ns for InP/GaP QDs support our band alignment modeling. Pressure-dependent photoluminescence measurements provide further evidence for a type-I band alignment for InP/GaP QDs at normal pressure, but indicate that they become type-II under hydrostatic pressures of about 1.2 GPa and are consistent with an energy difference between the lowest InP and GaP states of about 31 meV. Exploiting the visible direct-bandgap transition in the GaP system could lead to an increased efficiency of light emission in GaP-based light emitters.
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Kettler, Jan Ferdinand [Verfasser]. "Telecom-wavelength nonclassical light from single In(Ga)As quantum dots / Jan Kettler." München : Verlag Dr. Hut, 2017. http://d-nb.info/1128466880/34.
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Yu, Kuan-Hung. "Optical Spectroscopy of GaN/Al(Ga)N Quantum Dots Grown by Molecular Beam Epitaxy." Thesis, Department of Physics, Chemistry and Biology, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-19821.
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GaN quantum dots grown by molecular beam epitaxy are examined by micro-photoluminescence. The exciton and biexciton emission are identified successfully by power-dependence measurement. With two different samples, it can be deduced that the linewidth of the peaks is narrower in the thicker deposited layer of GaN. The size of the GaN quantum dots is responsible for the binding energy of biexciton (EbXX); EbXX decreases with increasing size of GaN quantum dots. Under polarization studies, polar plot shows that emission is strongly linear polarized. In particular, the orientation of polarization vector is not related to any specific crystallography orientation. The polarization splitting of fine-structure is not able to resolve due to limited resolution of the system. The emission peaks can be detected up to 80 K. The curves of transition energy with respect to temperature are S-shaped. Strain effect and screening of electric field account for blueshift of transition energy, whereas Varshni equation stands for redshifting. Both blueshifting and redshifting are compensated at temperature ranging from 4 K to 40 K.
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Rolihlahla, Bangile Noel. "Electrochemistry and photophysics of carbon nanodots-decorated nigs(Ni(In, Ga)Se2) quantum dots." university of western cape, 2020. http://hdl.handle.net/11394/7309.
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>Magister Scientiae - MScCurrently, non-renewable sources are mostly used to meet the ever-growing demand for energy. However, these sources are not sustainable. In addition to these energy sources being not sustainable, they are bad for the environment although the energy supply sectors highly depend on them. To address such issues the use of renewable energy sources has been proven to be beneficial for the supply of energy for the global population and its energy needs. Advantageous over non-renewable sources, renewable energy plays a crucial role in minimizing the use of fossil fuel and reduces greenhouse gases. Minimizing use of fossil fuels and greenhouse gases is important, because it helps in the fight against climate change. The use of renewable energy sources can also lead to less air pollution and improved air quality. Although solar energy is the most abundant source of renewable energy that can be converted into electrical energy using various techniques, there are some limitations. Among these techniques are photovoltaic cells which are challenged by low efficiencies and high costs of material fabrication. Hence, current research and innovations are sought towards the reduction of costs and increasing the efficiency of the renewable energy conversion devices.
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Paul, Matthias [Verfasser]. "Fabrication, Characterization, and Integration of In(Ga)As Semiconductor Quantum Dots for Telecommunication Wavelengths / Matthias Paul." München : Verlag Dr. Hut, 2016. http://d-nb.info/1113335726/34.
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Sandall, Ian C. "Characterisation of In(Ga)As quantum dot lasers." Thesis, Cardiff University, 2006. http://orca.cf.ac.uk/56130/.
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Self-assembled InAs quantum dot lasers have been characterised by measuring the modal absorption and gain along with radiative and non-radiative current densities as well as determining threshold current densities as a function of length. The number of dot layers stacked and the GaAs spacer layers used are both shown to influence the dot density and distribution. The peak ground state gain is found to saturate at around a third of the available absorption in intrinsic quantum dot samples (reaching a value of 1.2 0.2 cm"1 per layer). The 'average spontaneous lifetime of a single dot is determined from measurements of the optical cross section (yielding a value of 2.0 0.5 ns). From the lifetime measurements, the number of dots occupied at a given injection has been determined this has shown that gain saturation in quantum dot lasers is due to the incomplete filling of states. The occupancy is shown to increase with the inclusion of p- type modulation doping (from 31% for an intrinsic structure to 43 % and 51 % for doping levels of 15 and 50-p dopants per dot respectively), hence increasing the available ground state gain to 2.2 cm"1 per layer for 50 dopants per dot. In some of the samples studied the use of modulation doping has been shown to lead to an increase in the non-radiative current density. The temperature dependence of the threshold current density in InAs quantum dot lasers is also investigated. It is found that in the p-doped structures the threshold current shows an initial decrease in the threshold current, before increasing at higher temperatures (for example a decrease of lOOAcm" occurs between 180 and 290 K for a 2 mm long cavity with 15-p dopants per dot), this is shown to originate from the temperature dependence of the modal gain in these structures.
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Parnell, Steven Richard. "A study of the optical and structural properties of self-organised In(Ga)As/GaAs quantum dots." Thesis, University of Sheffield, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269285.
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Bommer, Moritz [Verfasser]. "InP/(Al,Ga)InP Quantum Dots on GaAs- and Si-Substrates for Single-Photon Generation at Elevated Temperatures / Moritz Bommer." München : Verlag Dr. Hut, 2013. http://d-nb.info/1042308225/34.
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Hafenbrak, Robert [Verfasser]. "Tuning the exciton fine structure of single (In,Ga)As/GaAs quantum dots to realize a triggered entangled photon source / Robert Hafenbrak." München : Verlag Dr. Hut, 2011. http://d-nb.info/1013526325/34.
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Bommer, Moritz [Verfasser], and Peter [Akademischer Betreuer] Michler. "InP-(Al,Ga)InP quantum dots on GaAs- and Si-substrates for single-photon generation at elevated temperatures / Moritz Bommer. Betreuer: Peter Michler." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2013. http://d-nb.info/1038695120/34.
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Varwig, Steffen [Verfasser], Manfred [Akademischer Betreuer] Bayer, and Metin [Gutachter] Tolan. "Optical electron spin tomography and hole spin coherence studies in (In,Ga)As/GaAs quantum dots / Steffen Varwig. Betreuer: Manfred Bayer. Gutachter: Metin Tolan." Dortmund : Universitätsbibliothek Dortmund, 2014. http://d-nb.info/1100692487/34.
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Varwig, Steffen [Verfasser], Manfred Akademischer Betreuer] Bayer, and Metin [Gutachter] [Tolan. "Optical electron spin tomography and hole spin coherence studies in (In,Ga)As/GaAs quantum dots / Steffen Varwig. Betreuer: Manfred Bayer. Gutachter: Metin Tolan." Dortmund : Universitätsbibliothek Dortmund, 2014. http://nbn-resolving.de/urn:nbn:de:101:1-201605191564.
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Sharma, Nand Lal [Verfasser]. "Molecular beam epitaxy of tailored (In,Ga)As/GaAs quantum dot heterostructures / Nand Lal Sharma." Paderborn : Universitätsbibliothek, 2017. http://d-nb.info/1145017347/34.
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Hagelin, Alexander. "ZnO nanoparticles : synthesis of Ga-doped ZnO, oxygen gas sensing and quantum chemical investigation." Thesis, Linköpings universitet, Institutionen för fysik, kemi och biologi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-64730.
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Doped ZnO nanoparticles were synthesized by three different methods – electrochemical deposition under oxidizing conditions (EDOC) , combustion method and wet chemical synthesis – for investigating the oxygen gas sensing response. Ga-doped ZnO was mostly synthesized but also In-doped ZnO was made. The samples were analyzed by XRD, SEM, EDX and TEM. Gas response curves are given alongside with Langmuir fitted curves and data for pure ZnO and Ga-doped ZnO. DFT quantum chemical investigation of cluster models ZnO nanoparticles were performed to evaluate defect effects and oxygen and nitrogen dioxide reactions with the ZnO surface. Defects were investigated by DOS and HOMO-LUMO plots , and are oxygen vacancy, zinc vacancy, zinc interstitial and gallium doping by replacing zinc with gallium. Oxygen and nitrogen dioxide reactions were investigated by computing Mulliken charges, bond lengths, DOS spectra and HOMO-LUMO plots.
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Heldmaier, Matthias Michael [Verfasser]. "Optical and electronic properties of single laterally coupled (In,Ga)As/GaAs quantum dot molecules / Matthias Michael Heldmaier." München : Verlag Dr. Hut, 2014. http://d-nb.info/1047995581/34.
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Göhring, HOLGER [Verfasser], Metin [Akademischer Betreuer] Tolan, and Manfred [Gutachter] Bayer. "Structural investigation of the impact of magnetostriction on GaMnAs thin film lattices and the thermal expansion of (In,Ga)As/GaAs quantum dots / Holger Göhring ; Gutachter: Manfred Bayer ; Betreuer: Metin Tolan." Dortmund : Universitätsbibliothek Dortmund, 2017. http://d-nb.info/1136785256/34.
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Akra, Ahiram el. "Croissance de boîtes quantiques In(Ga)As sur substrats de silicium et de SOI pour la réalisation d'émetteurs de lumière." Phd thesis, Ecole Centrale de Lyon, 2012. http://tel.archives-ouvertes.fr/tel-00952829.
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Cette thèse porte sur l'étude de la croissance auto-organisée de boîtes quantiques d'In(Ga)As sur substrat de silicium visant à l'intégration monolithique d'un émetteur de lumière sur silicium à base d'un matériau semiconducteur III-V. Le développement d'un tel système se heurte à deux verrous majeurs : le premier provient d'un très fort désaccord de maille qui rend difficile l'élaboration de boîtes quantiques d'In(Ga)As sur Si présentant de bonnes qualités structurales et optiques, et le second provient de la nature électronique de l'interface entre In(Ga)As et le Si dont il est prédit qu'elle est de type II et donc peu efficace pour l'émission de lumière. L'approche que nous avons proposée consiste à insérer des BQs d'In(Ga)As dans un puits quantique de silicium dans SiO2, fabriqué sur un substrat SOI. Les effets attendus de confinement quantique dans le puits de Si favoriseraient une interface In(Ga)As/Si de type I. D'un point de vue expérimental, nous avons donc étudié l'influence de différents paramètres de croissance (température de croissance, rapport V/III, quantité d'In(Ga)As déposé, teneur en indium des boîtes quantiques ...) sur le mode de croissance et sur les propriétés structurales et optiques des BQs d'In(Ga)As épitaxiées sur substrat de Si(001). Nous avons proposé une interprétation des phénomènes microscopiques qui régissent la formation des boîtes quantiques d'In(Ga)As sur Si en fonction de la teneur en indium. Nous avons aussi montré qu'il est possible de fabriquer des boîtes quantiques d'In0,4Ga0,6As sur Si ne présentant pas de défauts structuraux liés à la relaxation plastique. La luminescence attendue des boîtes quantiques n'a pas pu être obtenue, probablement en raison de deux conditions requises mais antagonistes: la fabrication de boîtes quantiques de très haute qualité structurale (possible uniquement pour de l'In(Ga)As avec une teneur en In inférieure à 50%) et un alignement de bandes à l'interface BQs In(Ga)As/Si de type I (possible théoriquement pour une teneur en In supérieure ou égale à 70%). Ce travail a permis d'enrichir la connaissance et le savoir-faire concernant l'élaboration de boîtes quantiques d'In(Ga)As sur substrat de Si(001) et l'encapsulation de ces boîtes quantiques par du silicium dans un réacteur d'épitaxie par jets moléculaires III-V.
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Pelloux-Gervais, David. "Caractérisation par méthodes nucléaires avancées de boîtes quantiques d'In(Ga)As épitaxiées sur silicium." Phd thesis, INSA de Lyon, 2012. http://tel.archives-ouvertes.fr/tel-00838787.
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L'intégration de semiconducteurs III-V à gap direct sur silicium est un enjeu de taille pour le développement de l'optoélectronique. En effet, si le silicium est aujourd'hui à la base de la microélectronique, la nature indirecte de son gap en fait un très mauvais émetteur de lumière. Parmi les matériaux candidats à l'intégration, l'In(Ga)As présente l'avantage d'un gap direct plus faible que le silicium, favorisant un comportement de puits de potentiel pour les paires électrons-trous. En revanche, le fort désaccord paramétrique entre les deux matériaux fait de la croissance épitaxiale d'In(Ga)As sur silicium un sérieux défi pour le physicien. Cette thèse est focalisée sur l'étude par faisceaux d'ions de boîtes quantiques (BQs) d'In(Ga)As épitaxiées sur silicium et de leur encapsulation ultérieure par du silicium. L'analyse par rétrodiffusion élastique à haute énergie (RBS) a permis de quantifier la composition des îlots d'In(Ga)As et de la couche cap de Si. Des phénomènes d'exo-diffusion d'indium et la présence d'espèces en excès ont été mis en évidence. En pratiquant l'analyse en géométrie de canalisation (RBS-C), nous avons pu caractériser l'épitaxie des BQs sur le substrat ainsi que celle de la couche cap. La deuxième technique utilisée dans ce travail est l'analyse par rétrodiffusion élastique à moyenne énergie (MEIS), qui permet de profiler composition, défauts cristallins, et déformation avec une résolution sub-nanométrique au voisinage de la surface de la cible. Les spectres MEIS en modes aléatoire et canalisé ont permis d'obtenir le profil de composition et de défauts du plan de BQs. Enfin, la déformation du cristal d'In(Ga)As par rapport au monocristal de silicium du substrat a été étudiée grâce à l'effet de blocage du flux d'ions rétrodiffusés qui permet d'observer les ombres des axes et des plans cristallographiques.
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Garrido, Mauricio. "Quantum Optics in Coupled Quantum Dots." Ohio University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1273589966.
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Chiu, Kuei-Lin. "Transport properties of graphene nanodevices - nanoribbons, quantum dots and double quantum dots." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610526.
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Chan, Ka Ho Adrian. "Quantum information processing with semiconductor quantum dots." Thesis, University of Cambridge, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648684.
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Xu, Xiulai. "InAs quantum dots for quantum information processing." Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615012.
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Christ, Henning. "Quantum computation with nuclear spins in quantum dots." München Verl. Dr. Hut, 2008. http://d-nb.info/992162831/04.
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Erdem, Rengin. "Ag2s/2-mpa Quantum Dots." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614384/index.pdf.
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Quantum dots are fluorescent semiconductor nanocrystals that have unique optical properties such as high quantum yield and photostability. These nanoparticles are superior to organic dyes and fluorescent proteins in many aspects and therefore show great potential for both in vivo and in vitro imaging and drug delivery applications. However, cytototoxicity is still one of the major problems associated with their biological applications.
The aim of this study is in vitro characterization and assessment of biological application potential of a novel silver sulfide quantum dot coated with mercaptopropionic acid (2-MPA). In vitro studies reported in this work were conducted on a mouse fibroblast cell line (NIH/3T3) treated with Ag2S/2-MPA quantum dots in 10-600 &mug/mL concentration range for 24 h. Various fluorescence spectroscopy and microscopy methods were used to determine metabolic activity, proliferation rate and apoptotic fraction of QD-treated cells as well as QD internalization efficiency and intracellular localization. Metabolic activity and proliferation rate of the QD treated cells were measured with XTT and CyQUANT®
cell proliferation assays, respectively. Intracellular localization and qualitative uptake studies were conducted using confocal laser scanning microscopy. Apoptosis studies were performed with Annexin V assay. Finally, we also conducted a quantitative uptake assay to determine internalization efficiency of the silver sulfide particles. Correlated metabolic activity and proliferation assay results indicate that Ag2S/2-MPA quantum dots are highly cytocompatible with no significant toxicity up to 600 &mu
g/mL treatment. Optimal cell imaging concentration was determined as 200 &mu
g/mL. Particles displayed a punctuated cytoplasmic distribution indicating to endosomal entrapment. In vitro characterization studies reported in this study indicate that Ag2S/2-MPA quantum dots have great biological application potential due to their excellent spectral and cytocompatibility properties. Near-infrared emission of silver sulfide quantum dots provides a major advantage in imaging since signal interference from the cells (autofluorescence) which is a typical problem in microscopic studies is minimum in this part of the emission spectrum. The results of this study are presented in an article which was accepted by Journal of Materials Chemistry. DOI: 10.1039/C2JM31959D.
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Larsson, Mats. "Spectroscopy of semiconductor quantum dots /." Linköping : Linköpings universitet, 2005. http://www.bibl.liu.se/liupubl/disp/disp2005/tek976s.pdf.
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Foo, Edward. "Ultrafast spectroscopy of quantum dots." Thesis, University of Oxford, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.393775.
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Lee, Steven Frank. "Photodynamics of single quantum dots." Thesis, University of Sussex, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.494932.
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A range of photochemical processes in biologically compatible quantum dots (QDs) at the individual nanocrystal level has been examined. Using objective type total internal reflection fluorescence microscopy we demonstrate the observation of photoluminescence activation (PLA), enhancement (PLE), fluorescence intermittency (Fl), decay and spectral shifting over the photochemical lifetimes of single QDs. The ability to count individual QDs along with their intensities has revealed a measurable nonlinear correlation between the total fluorescence and the QD population that is the result of enhancement and decay in the quantum yield (QY) of individual dots. This allows the differentiation between ensemble photoluminescence enhancement due to the fluorescence activation of a dark, non-emitting fraction of QDs (PLA) and that due to genuine QY modification in individual nanocrystals (PLE).
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Hill, Richard John Allan. "Tunnelling into InAs quantum dots." Thesis, University of Nottingham, 2003. http://eprints.nottingham.ac.uk/10002/.
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This thesis describes an experimental study of the electronic properties of semiconductor heterostructure tunnel devices. InAs self-assembled quantum dots (QDs) are incorporated into the barrier layer of a GaAs/AlAs/GaAs tunnel diode. When a voltage, V, is applied across the device, we observe resonant features in the tunnel current, I, whenever an electron state in one of the qds comes into resonance with an occupied electron state in the emitter. We employ an electron state of a single qd as a spectroscopic probe of a two-dimensional electron system (2DES), from the Fermi energy to the subband edge [1]. For magnetic field B applied parallel to the current, we observe peaks in the I(V) characteristics corresponding to the formation of Landau levels in the 2DES. We obtain quantitative information about the energy dependence of the quasiparticle lifetime, Tqp, of the 2DES. We find that Tqp ~ 2.5 hbar=(Ef - E), in contrast with the expectation for a normal Fermi liquid, but in agreement with predictions for a Fermi liquid state of a disordered 2DES. Close to filling factor nu = 1 we observe directly the exchange enhancement of the g factor. This thesis also describes the design, realisation and measurement of a tunnel diode incorporating InAs QDs and a series of 4 planar electrostatic gates. By applying a bias to the gates, it is possible to selectively inject current into a particular QD. We use magneto-tunnelling spectroscopy to determine the energy levels of the ground and excited state of a single QD, and to map the spatial form of the wave functions of these states [2]. The effect of pressure on the resonant tunnelling of the QDs is also described. [1] P. C. Main et al., Phys. Rev. Lett. 84, 729 (2000) [2] R. J. A. Hill et al., Appl. Phys. Lett. 79, 3275 (2001)
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Tipton, Denver Leonard John. "Electron correlations in quantum dots." Thesis, King's College London (University of London), 2001. https://kclpure.kcl.ac.uk/portal/en/theses/electron-correlations-in-quantum-dots(b6e1a547-fbb8-41f7-9d2b-f235b68b85be).html.
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Tewordt, Matthias Ludwig. "Resonant tunnelling in quantum dots." Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260415.
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Korkusinski, Marek. "Correlations in semiconductor quantum dots." Thesis, University of Ottawa (Canada), 2004. http://hdl.handle.net/10393/29128.
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In this Thesis, I present a theoretical study of correlation effects in strongly interacting electronic and electron-hole systems confined in semiconductor quantum dots. I focus on three systems: N electrons in a two-dimensional parabolic confinement in the absence and in the presence of a magnetic field, an electron-hole pair confined in a vertically coupled double-quantum-dot molecule, and a charged exciton in a quantum-ring confinement in a magnetic field.
To analyse these systems I use the exact diagonalisation technique in the effective-mass approximation. This approach consists of three steps: construction of a basis set of particle configurations, writing the Hamiltonian in this basis in a matrix form, and numerical diagonalisation of this matrix. Each of these steps is described in detail in the text.
Using the exact diagonalisation technique I identify the properties of the systems due to correlations and formulate predictions of how these properties could be observed experimentally. I confront these predictions with results of recent photoluminescence and transport measurements.
First I treat the system of N electrons in a parabolic confinement in the absence of magnetic field and demonstrate how its properties, such as magnetic moments, can be engineered as a function of the system parameters and the size of the Hilbert space.
Next I analyse the evolution of the ground state of this system as a function of the magnetic field. In the phase diagram of the system I identify the spin-singlet nu = 2 phase and discuss how correlations influence its phase boundaries both as a function of the magnetic field and the number of electrons.
I also demonstrate that in higher magnetic fields electronic correlations lead to the appearance of spin-depolarised phases, whose stability regions separate the weakly correlated phases with higher spin. Further on, I consider electron-hole systems. I show that the Coulomb interaction leads to entanglement of the states of an electron and a hole confined in a pair of vertically coupled quantum dots.
Finally I consider the system of two electrons and one hole (a negatively charged exciton) confined in a quantum ring and in the presence of the magnetic field. I show that the energy of a single electron in the ring geometry exhibits the Aharonov-Bohm oscillations as a function of the magnetic field. In the case of the negatively charged exciton these oscillations are nearly absent due to correlations among particles, and as a result the photoluminescence spectra of the charged complex are dominated by the energy of the final-state electron. The Aharonov-Bohm oscillations of the energy of a single electron are thus observed directly in the optical spectra.
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Yang, Kaiyu, and 楊開宇. "Quantum information processing with quantum dots and Josephson junctions." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2003. http://hub.hku.hk/bib/B29285835.
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Goldmann, Eyal. "Studies of quantum dots in the quantum hall regime /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC IP addresses, 1999. http://wwwlib.umi.com/cr/ucsd/fullcit?p9945779.
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Curtin, Oliver James. "Quantum criticality and emergent symmetry in coupled quantum dots." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/42499.
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We consider strongly correlated regimes which emerge at low temperature in coupled quantum dot (or magnetic impurity) systems. In strongly correlated systems a single particle description fails to explain the observed behaviour, so we resort to many body methods. We describe our system using a 2-impurity Anderson model and develop a numerical renormalisation group procedure which provides non-perturbative insight into the low energy behaviour, through calculation of dynamic quantities. We combine this approach with renormalised perturbation theory, thus acquiring a picture of how the Hamiltonian and interactions change at low energies. These approaches are first used to study the emergence of a Kondo effect with an SU(4) symmetry in capacitively-coupled double quantum dot systems. We classify the 'types' of SU(4) symmetry which can emerge and show how an experimentalist might achieve such emergence through tuning their system. We provide a way of distinguishing between the SU(2) and SU(4) Kondo regimes by considering the conductance. We also study a quantum critical point which occurs in the Heisenberg coupled quantum dot/impurity model. There is an anomalous entropy contributed by the impurities in this regime which is indicative of an uncoupled Majorana Fermion. We calculate dynamic quantities in regimes with different symmetries and establish correspondence with the 2-channel Kondo model. We formulate possible pictures of the underlying mechanisms of the critical point and construct a Majorana fermion model for the case with particle-hole symmetry, which explains the non-Fermi liquid energy levels and degeneracies obtained. We conjecture that a Majorana zero mode is present, and that this is responsible for the anomalous entropy.
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Pegahan, Saeed. "QUANTUM ERROR CORRECTION AND LEAKAGE ELIMINATION FOR QUANTUM DOTS." OpenSIUC, 2015. https://opensiuc.lib.siu.edu/theses/1753.
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The development of a quantum computer presents one of the greatest challenges in science and engineering to date. The promise of more ecient computing based on entangled quantum states and the superposition principle has led to a worldwide explosion of interest in the elds of quantum information and computation. Decoherence is one of the main problems that gives rise to dierent errors in the quantum system. However, the discovery of quantum error correction and the establishment of the accuracy threshold theorem provide us comprehensive tools to build a quantum computer. This thesis contributes to this eort by investigating a particular class of quantum error correcting codes, called Decoherence free subsystems. The passive approach to error correction taken by these encodings provides an ecient means of protection for symmetrically coupled system-bath interactions. Here I will present methods for determining the subsystem-preserving evolutions for noiseless subsystem encodings and more importantly implementing a Universal quantum computing over three-quantum dots.
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Siegert, Jörg. "Carrier dynamics in semiconductor quantum dots." Doctoral thesis, KTH, Mikroelektronik och tillämpad fysik, MAP, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4019.
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This thesis presents results of time-resolved photoluminescence experiments conducted on several different self-assembled InGaAs/GaAs and InAs/GaAs semiconductor quantum dot (QD) structures. Depending on the application in mind, different structural, electronic or optical properties have a different weight of importance. Fast carrier capture and relaxation is critical for QD based lasers, for example. In this thesis, the influence of surplus carriers, introduced through modulation-doping, is studied. It is shown that carrier capture is essentially unaffected whereas the intradot relaxation mechanisms, at least at low carrier concentrations, are fundamentally different. The phonon mediated cascade relaxation found in the undoped reference sample is replaced by efficient scattering with the built-in carriers in the case of the doped structures. Moreover, spin relaxation also depends on presence of extra carriers. During energy relaxation via carrier-carrier scattering, the spin polarization is preserved whereas in the undoped sample the strong interaction of relaxing carriers with LO phonons causes spin relaxation. The decay of the ground state spin polarization proceeds at the same rate for doped and undoped structures and is shown to be caused by acoustic phonons, even up to 300 K. While optimizing QD growth for specific applications, it is imperative to evaluate the influence of nonradiative recombination, which is most often detrimental. While misfit dislocations, deliberately introduced in the substrate, lead to the formation of laterally ordered, uniform dots, these samples are found to suffer from strong nonradiative recombination. Structures with different barrier thicknesses and numerical simulations indicate defects in the vicinity of the QDs as main origin of fast carrier trapping. On the other hand, it is shown that direct dot doping, compared to barrier doping or undoped structures, causes only minor degradation of the optical properties. Directly doped dots even exhibit a significantly weaker photoluminescence quenching with temperature, making them prospective for devices operating at room temperature. Finally, the superior proton radiation hardness of QD structures compared to quantum wells is demonstrated, which is due to the three-dimensional confinement. The increase of photoluminescence intensity at low to moderate doses is interpreted as an enhanced carrier transfer into the dots via the defects introduced into the material by the protons.QC 20100920
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Larsson, Arvid. "Optical spectroscopy of InGaAs quantum dots." Doctoral thesis, Linköpings universitet, Halvledarmaterial, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-64707.
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The work presented in this thesis deals with optical studies of semiconductor quantum dots (QDs) in the InGaAs material system. It is shown that for self-assembled InAs QDs, the interaction with the surrounding GaAs barrier and the InAs wetting layer (WL) in particular, has a very large impact on their optical properties. The ability to control the charge state of individual QDs is demonstrated and attributed to a modulation in the carrier transport dynamics in the WL. After photo-excitation of carriers (electrons and holes) in the barrier, they will migrate in the sample and with a certain probability become captured into a QD. During this migration, the carriers can be affected by exerting them to an external magnetic field or by altering the temperature. An external magnetic field applied perpendicular to the carrier transport direction will lead to a decrease in the carrier drift velocity since their trajectories are bent, and at sufficiently high field strength become circular. In turn, this decreases the probability for the carriers to reach the QD since the probability for the carriers to get trapped in WL localizing potentials increases. An elevated temperature leads to an increased escape rate out of these potentials and again increases the flow of carriers towards the QD. These effects have significantly different strengths for electrons and holes due to the large difference in their respective masses and therefore it constitutes a way to control the supply of charges to the QD. Another effect of the different capture probabilities for electrons and holes into a QD that is explored is the ability to achieve spin polarization of the neutral exciton (X0). It has been concluded frequently in the literature that X0 cannot maintain its spin without application of an external magnetic field, due to the anisotropic electron – hole exchange interaction (AEI). In our studies, we show that at certain excitation conditions, the AEI can be by-passed since an electron is captured faster than a hole into a QD. The result is that the electron will populate the QD solely for a certain time window, before the hole is captured. During this time window and at polarized excitation, which creates spin polarized carriers, the electron can polarize the QD nuclei. In this way, a nuclear magnetic field is built up with a magnitude as high as ~ 1.5 T. This field will stabilize the X0 spin in a similar manner as an external magnetic field would. The build-up time for this nuclear field was determined to be ~ 10 ms and the polarization degree achieved for X0 is ~ 60 %. In contrast to the case of X0, the AEI is naturally cancelled for the negatively charged exciton (X-) and the positively charged exciton (X+) complexes. This is due to the fact that the electron (hole) spin is paired off in case of X- (X+). Accordingly, an even higher polarization degree (~ 73 %) is measured for the positively charged exciton. In a different study, pyramidal QD structures were employed. In contrast to fabrication of self-assembled QDs, the position of QDs can be controlled in these samples as they are grown in inverted pyramids that are etched into a substrate. After sample processing, the result is free-standing AlGaAs pyramids with InGaAs QDs inside. Due to the pyramidal shape of these structures, the light extraction is considerably enhanced which opens up possibilities to study processes un-resolvable in self-assembled QDs. This has allowed studies of Auger-like shake-up processes of holes in single QDs. Normally, after radiative recombination of X+, the QD is populated with a ground state hole. However, at recombination, a fraction of the energy can be transferred to the hole so that it afterwards occupies an excited state instead. This process is detected experimentally as a red-shifted luminescence satellite peak with an intensity on the order of ~ 1/1000 of the main X+ peak intensity. The identification of the satellite peak is based on its intensity correlation with the X+ peak, photoluminescence excitation measurements and on magnetic field measurements.Arbetet som presenteras i denna avhandling rör studier av kvantprickars optiska egenskaper. En kvantprick är en halvledarkristall som endast är några tiotals nanometer stor. Den ligger oftast inbäddad inuti en större kristall av ett annat halvledarmaterial och pga. den begränsade storleken får en kvantprick mycket speciella egenskaper. Bland annat så kommer elektronerna i en kvantprick endast att kunna anta vissa diskreta energinivåer liknande situationen för elektronerna i en atom. Följaktligen kallas kvantprickar ofta för artificiella atomer. För halvledarmaterial gäller det generellt att det inte endast är fria elektroner i ledningsbandet, som kan leda ström utan även tomma elektrontillstånd i valensbandet, vilka uppträder som positivt laddade partiklar, kan leda ström. Dessa kallas kort och gott för hål. I en kvantprick har hålen såsom elektronerna helt diskreta energinivåer. Precis som är fallet i en atom, så kommer elektroniska övergångar mellan olika energinivåer i en kvantprick att resultera i att ljus emitteras. Energin (dvs. våglängden alt. färgen) för detta ljus bestäms av hur energinivåerna i kvantpricken ligger, för elektronerna och hålen, och genom att analysera ljuset kan man således studera kvantprickens egenskaper. Studierna i den här avhandlingen visar att växelverkan mellan en kvantprick och den omgivande kristallen, som den ligger inbäddad i, har stor inverkan på kvantprickens optiska egenskaper. T.ex. visas att man kan kontrollera antalet elektroner, som kommer att finnas i kvantpricken genom att modifiera hur elektronerna kan röra sig i omgivningen. Dessa rörelser modifieras här genom att variera temperaturen och genom att lägga på ett magnetiskt fält. Ett magnetiskt fält, vinkelrätt mot en elektrons rörelse, kommer att böja av dess bana och dess chans att nå fram till kvantpricken kan således minskas. Elektronen kan då istället fastna i andra potentialgropar i kvantprickens närhet. Genom att öka temperaturen, vilket ger elektronerna större energi, kan deras chans att nå fram till kvantpricken å andra sidan öka. En annan effekt, som studerats, är möjligheten att kontrollera spinnet hos elektronerna i en kvantprick. Även i dessa studier visar det sig att växelverkan med omgivningen spelar stor roll och kan användas till att kontrollera elektronens spin. Mekanismen som föreslås är att om elektronerna hinner före hålen till kvantpricken, så hinner de överföra sitt spin till atomkärnorna i kvantpricken. På detta sätt kan man få atomkärnornas spin polariserat, vilket resulterar i ett inbyggt magnetfält, i storleksordningen 1.5 Tesla, som i sin tur hjälper till att upprätthålla en hög grad av spinpolarisering även hos elektronerna. För att få elektronerna att hinna först, måste deras rörelser i omgivningen kontrolleras. I en ytterligare studie undersöktes den process där en elektronisk övergång i kvantpricken inte enbart resulterar i emission av ljus, utan även i att en annan partikel tar över en del av energin och blir exciterad. Dessa processer avspeglas i att en del av det ljus som emitteras har lägre energi. Detta ljus är också mycket svagt, ca 1000 ggr lägre intensitet, och möjligheten att kunna mäta detta är helt beroende på hur ljusstarka kvantprickarna är. De prover som använts i denna studie består av pyramidstrukturer, ca 7.5 mikrometer stora, med kvantprickar inuti. Denna geometri ger ca 1000 ggr bättre ljusutbyte jämfört med traditionella strukturer, vilket möjliggjort studien.
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Jain, Manasi Pancholy. "Quantum dots: from cytotoxicity to metalloestrogenicity." Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=110346.
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The fields of Nanomedicine is rapidly expanding. Already numerous nanoparticles have entered clinical trials. However, certain nanostructures, though, therapeutically and diagnostically promising, can induce toxicity both in vitro and in vivo; cadmium telluride quantum dots fall into this category. Quantum dots (QDs) are highly fluorescent, semi-conducting nanocrystals, that consist of a metallic core. Compared to traditional fluorophores, QDs have superior optical qualities, including resistance to photobleaching, broad spectrum excitation and narrow emission. Cadmium telluride (CdTe) QDs were the first to be synthesized without organic solvents, and thus, considered suitable for biological application. However, early studies demonstrated that QDs induced cytotoxicity and oxidative stress. Although, this QD-toxicity was ascribed to cadmium (Cd) liberation from the QD-core, no empirical evidence was shown. Due to the attractiveness of QDs for biological applications, it was necessary that the mechanisms involved in QD-toxicity be understood so they may be prevented. Preliminary studies from our laboratory indicated that the antioxidant, N-acetlycysteine could prevent QD-toxicity. We, thus, hypothesized that QD-toxicity was not exclusively due to cadmium leaching from the QD. To evaluate this, an assay measuring free Cd was adapted for cellular use, to measure Cd present in both the cellular media and intracellularly. The cytotoxicity of various QDs was evaluated and correlated with the intracellular Cd. Results from this study showed no correlation between QD-toxicity and Cd release from QDs. We next questioned whether QD-toxicity could be explained as the sum of parts of the toxicity associated with core constituting metals, and whether the complexity of the model system used influences the cytotoxicity observed. We employed three model systems of the peripheral nervous system (an immortalized cell line, heterogeneous primary cultures and a three dimensional tissue model) and evaluated the toxicity of Cd, Te and QDs in each. Our findings showed that QDs are not a sum of parts and QD-toxicity is better ascribed to the induction of oxidative stress which is prevented by application of the multi-modal antioxidant, lipoic acid. Further, the model systems did not depict QD-toxicity comparably, stressing the need for standardization in nanotoxicological studies. Finally, it had been shown that Cd association with the estrogen receptor (ER) in ER expressing cells can activate estrogenic signalling. As such, Cd is considered a metalloestrogen. Given that QDs liberate Cd that can be detected in the cell, we investigated whether in ER expressing cells, QDs may act as metalloestrogens and induce estrogenic signalling. Results in vitro showed that QDs exert potent estrogenic signalling, comparable with estradiol, including cell proliferation, AKT phosphorylation, ERK phosphorylation and nuclear ER activation. These effects could be attenuated via pretreatment with the specific ER antagonist, ICI 182780, affirming that QD-induced estrogenic activity was mediated via the ER. To determine whether the estrogenic activity of QDs could also be demonstrated in vivo, ovariectomized mice were treated with QDs for two weeks, prior to being sacrificed. Subsequently, the wet weights of the mice uteruses were measured. In mice treated with QDs and estradiol a comparable 2.5 fold increase in uterine wet weight was observed. Taken together, these results indicate that CdTe QDs are both cytotoxic and endocrine disrupting, metalloestrogens. Though these nanocrystals may have valuable applications in biology the implications of QD-use are dangerous to plants, animals, humans and the environment. Therefore, it is imperative that Cd-free QDs be developed that retain the attractive qualities of QDs while preventing the detrimental side effects. Further, standardized testing of nanoparticles is imperative for the safe use of these novel tools.La nanotechnologie et la nanomédecine sont des domaines en pleine expansion. Certaines nanoparticules sont déjà entrées dans des essais cliniques et sont deja utilisées par les patients. Par contre, certaines nanostructures, bien qu'elles soient prometteuses à des fins cliniques ou diagnostiques, sont capables d'induire de la cytotoxicité in vitro et in vivo; les boîtes quantiques de cadmium telluride (CdTe) constituent un exemple.Les boîtes quantiques (BQ) sont des nanocrystaux semi-conducteurs fluorescents qui contiennent un noyau métallique entouré d'une couche organique. Les BQ ont des propriétés optiques supérieures aux autres fluorophores traditionnelles. Par exemple, ils sont plus résistants au photoblanchiment et sont caractérisés par un spectre d'excitation large et d'émission étroit. Les BQ CdTe, les premiers à être synthétisés sans l'utilisation de solvant organique, ont été prometteurs dans certaines applications biologiques. Cependant, les premières études ont démontré que ces BQ induisent de la cytotoxicité et produisent du stress oxydatif. Le cadmium (Cd) libéré pourrait être à la base de ces effets toxiques, mais cela n'a pas encore été prouvé. Les études préliminaires au sein de notre laboratoire démontrent que le pré-traitement avec un antioxydant, N-acétyl-cystéine, était capable de diminuer le niveau de toxicité associée au BQ. On a avancé l'hypothèse que cette toxicité n'était pas exclusivement liée au Cd qui est libéré des BQ. Nous avons effectué des expériences fluorométriques où nous mesurions les niveaux de Cd libres dans la cellule et dans le milieu extracellulaire. Ces expériences indiquent qu'il n'existe aucune corrélation entre la toxicité associée au BQ et le Cd libéré. Par après, nous nous sommes demandé si les constituants métalliques du noyau des BQ et les modèles dans lesquels les BQ avaient été évalués, étaient impliqués dans la toxicité associée au BQ. Nous avons évalué la toxicité du Cd, tellurium et BQ dans trois modèles du système nerveux périphérique (lignée de cellule immortalisée, cultures primaires hétérogènes et modèle de tissue tridimensionnel). Les résultats démontrent que la toxicité des BQ est principalement attribuée à l'induction du stress oxydatif, qui peut être prévenu en appliquant un antioxydant multimodal, l'acide lipoique.Dans les cellules, Cd peut s'associer avec les récepteurs d'œstrogènes (RE) et activer les voies de signalisation reliées à ce récepteur. Par conséquent, Cd est considéré comme étant un métallo-œstrogène. Nous avons montré que les BQ libèrent du Cd et que celui-ci est internalisé et retenu dans les cellules. Les effets induits par les BQ dépendaient du modèle biologique utilisé. Les études in vitro montrent que les BQ exercent une forte signalisation oestrogénique comparable à celle de estradiol et induisent la prolifération cellulaire, la phosphorylation d'AKT et d'ERK et l'activation du RE nucléaire. Ces effets étaient atténués par un pré-traitement avec un inhibiteur du RE, ICI 182780. Ces résultats affirment, donc, que les BQ exercent leurs activités oestrogéniques via les RE. Dans nos études in vivo nous avons utilisé des souris ovariectomisées qui avaient été traitées avec des BQ ou du estradiol pendant deux semaines, et par ensuite sacrifiées. Les traitements ont fait augmenter de 2.5 fois le poids de l'utérus des souris. Dans l'ensemble, ces résultats montrent que les BQ CdTe exercent à la fois des effets cytotoxiques et métallo-eostrogéniques. Malgré leurs potentiels d'application en imagerie ou dans les procédures diagnostiques, il est clair que les BQ peuvent nuire aux plantes, aux animaux, aux humains et à l'ensemble de l'environnement. Il y a un besoin urgent de développer des BQ sans cadmium qui possèdent des qualités attrayantes de BQ mais qui sont dépourvus d'effets secondaires détrimentaux. Cet objectif pourra être atteint à l'aide d'essais plus élaborés et sophistiqués pour déceler les risques des nanoparticules.
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Siegert, Jörg. "Carrier dynamics in semiconductor quantum dots /." Stockholm, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4019.
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Hull, Peter J. "Synthesis and characterisation of quantum dots." Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318760.
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Mulrooney, Ray. "Analyte sensing with luminescent quantum dots." Thesis, Robert Gordon University, 2009. http://hdl.handle.net/10059/452.
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Semiconducting nanocrystals otherwise known as Quantum Dots (QDs) have attracted considerable attention over the last number of years due to their unique optical properties and potential applications. Their narrow size-tunable emission spectra, broad absorption spectra, resistance to photobleaching and long fluorescent lifetimes make them ideal for sensing ions and small molecules. This thesis explores the potential of QDs to function as the emissive unit in fluorescent probes. Primarily, the focus of the work is to develop QD-based sensors that operate through an electron transfer mechanism. Chapter 3 discusses the synthesis and characterisation of CdSe and CdSe/ZnS QDs. Three different sized QDs were prepared each with distinct emission wavelengths. The sizes of these nanoparticles were determined by three methods, transmission electron microscopy (TEM), dynamic light scattering (DLS) and by a UV-vis method. Surface functionalisation of these synthesised QDs (chapter 4) with mercaptosuccinic acid rendered them water soluble and were shown to display selectivity for Cu2+ over a number of biologically relevant metal ions. The negatively charged surface of the QDs and the position of copper in the Irving-William series were believed to be responsible for this interaction. Positively charged CdSe/ZnS QDs were also prepared and were shown to detect ATP and to a much lesser extent GTP over the other nucleotides screened. The greater net negative charge of the ATP and GTP when compared to their mono and diphosphate analogues was the likely cause of this discrimination. In chapter 5 the relatively unexplored field of anion sensing with QDs was examined using charge neutral urea and thiourea receptors. Based on a design by Gunnlaugsson et al, a CdSe/ZnS QD with a thiourea receptor anchored to its surface displayed similar PET-mediated fluorescence quenching as an organic dye sensor containing the same receptor. A ferrocenyl urea receptor was also anchored to a QD surface and shown to “switch off” the QD’s fluorescence emission. On addition of fluoride ions the emission was restored, most likely due to a modulation of the ferrocene’s redox activity. In chapter 6 the assembly of Schiff base receptors on the surface of preformed CdSe/ZnS QDs were shown to arrange in such a way to enable the simultaneous detection of Cu2+ and Fe3+. The intriguing aspect of this study was that the receptors themselves displayed no selectivity for any metal ion until they were assembled on the QDs. Recognition was also confirmed by a distinct colour change visible to the naked eye.
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Dowley, David Gordon. "Modelling optical emission in quantum dots." Thesis, University of Leeds, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.522934.
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Smith, Christopher Roy. "Quantum dots for antibody based sensors." Thesis, Imperial College London, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.528301.
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Bylsma, Jason Michael. "Multidimensional Spectroscopy of Semiconductor Quantum Dots." Scholar Commons, 2012. http://scholarcommons.usf.edu/etd/4001.
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The coherent properties of semiconductor nanostructures are inherently difficult to measure and one-dimensional spectroscopies are often unable to separate inhomogeneous and homogeneous linewidths. We have refined and improved a method of performing multidimensional Fourier transform spectroscopy based on four-wave
mixing (FWM) experiments in the box geometry. We have modified our system with broadband beamsplitters in all interferometer arms, high-resolution translation stages and the ability to work in reflection geometry. By improving the phase-stability of our setup and scanning pulse delays with sub-optical cycle precision, we are able to
reproduce 2DFT spectra of GaAs multiple quantum wells. With the FWM signal reflected from the sample surface instead of transmitted through, we show that very low pulse powers can be used to generate coherent 2D signals from colloidal PbS quantum dots. Dephasing times are particularly difficult to measure in small colloidal quantum dots due to environmental broadening effects from the colloidal growth. We show that low-temperature pure excitonic dephasing can be measured via time-integrated measurements as well as from the cross-diagonal linewidths of 2DFT spectra. Ultrafast
sub-picosecond dephasing times are measured at 5 K in 3 nm PbS quantum dots, while excitation-density-dependence is investigated in these dots. By retrieving the global phase with an all-optical method, we are able to retrieve the real-part 2D spectra of PbS quantum dots.
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Chaney, Darren. "Relaxation processes in semiconductor quantum dots." Thesis, University of Leicester, 2004. http://hdl.handle.net/2381/4521.
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In this thesis we investigate the relaxation mechanisms that occur in quantum dots (QDs). First we consider energy relaxation in single particle self-assembled QDs by means of an Auger process. For the first time, relaxation rates are compared for dots of a realistic truncated pyramid shape and for the more elementary dot models considered previously. We find that the fast (pico-second) relaxation necessary for quantum dot based optoelectronics applications is made possible by dot electrons scattering with electrons located in the surrounding bulk material. We show that this relaxation mechanism is dominant by two orders of magnitude over the two-dimensional wetting layer scattering mechanism that has been considered in previous calculations. Exact numerical diagonalisation is used to calculate the two-particle selfassembled QD wave functions. The small size of the QD means that the two electrons in the dot are found to be only weakly interacting. We find the relaxation rate for states of total spin 0 to be larger than the spin I rate by a factor of approximately 2. This is due to the double occupancy of the spin 0 spatial states. We also consider the much slower spin flip relaxation in electrostatic QDs. We include the spin-orbit mixing that results from the bulk inversion asymmetry of the crystal lattice in calculating the exact two-particle states. We find that the spin orbit mixing causes anti-crossings to appear in the energy spectrum and deduce a new conservation rule related to this. We find an oscillation capable of slowing the relaxation time from microseconds to tenths of a second. This oscillation results from the vertical finite well confinement of the QD. It is found to depend on both magnetic field and the QD thickness and is of particular interest for quantum information applications where long-lived excited states are desirable.
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So, Tak Ki. "MBE-grown Fe ferromagnetic quantum dots /." View Abstract or Full-Text, 2003. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202003%20SO.
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Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2003.Includes bibliographical references (leaves 61-62). Also available in electronic version. Access restricted to campus users.
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Schmid, Jörg D. "The Kondo effect in quantum dots." [S.l. : s.n.], 2000. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB8948245.
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APEL, VICTOR MARCELO. "ELECTRONIC CORRELATION IN QUANTUM DOTS SYSTEMS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2004. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=6583@1.
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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICONesta tese investigamos os efeitos das interações elétron- elétron nas propriedades de transporte nanosistemas. Em particular, estudamos sistemas constituídos por dois pontos quânticos conectados a dois contatos, em diferentes topologias. O principal interesse é estudar os efeitos do regime Kondo e da fase eletrônica na condutância. Na configuração onde os dois pontos são inseridos em cada braço de um anel atravessado por um fluxo magnético, denotada por PPL, calculamos as fases das correntes que circulam através de cada braço do anel. Estas fases são determinadas pelo efeito Aharonov-Bohm combinado com a inflência da interação de muitos corpos das cargas nos pontos. Este sistema apresenta ressonância Kondo para um número par de elétrons em concordância com os resultados experimentais1. Outro aspecto interessante da configuração PPL é que, mesmo na ausência de fluxo magnético, pode existir circulação de corrente no anel, dependendo dos parâmetros escolhidos. Consideramos outras duas topologias que envolvem dois pontos quânticos acoplados através de interação de tunelamento. Em uma delas, denotada PAL, os dois pontos estão alinhados com os contatos, e na outra, a configuração PPD, um ponto está inserido nos contatos entanto que o outro interage só com o primeiro. No limite de acoplamento fraco, estas duas configurações apresentam características bem distintas, no só na dependência da condutância com o potencial de porta mas também na correlação de spin dos pontos quânticos. Ambas configurações apresentam ressonância Kondo para um número par de elétrons de diferente natureza. Quando cada ponto está carregado com um elétron, no caso da configuração PAL, os spins dos pontos quânticos estão descorrelacionados enquanto que, na configuração PPD, os spins estão correlacionados ferromagneticamente. No limite do acoplamento forte as propriedades de transporte das dois configurações são similares. Os sistemas discutidos acima são representados por o Hamiltoniano de Anderson de duas impurezas acopladas, o qual é resolvido diagonalizando exatamente um aglomerado que é embebido no resto do sistema. Desta forma obtemos as propriedades de transporte a T = 0. Para estudar a dependência com a temperatura utilizamos o método da equação de movimento (EOM) no limite da repulsão Coulombiana infinita. Aplicamos este método ao caso da topologia PPD, obteniendo resultados para baixas temperaturas consistente com os obtidos com o método do aglomerado.
In this thesis we investigate the effects of the eletron- eletron interaction on the transport properties of nanosystems. In particular, we study systems constituted by two quantum dots conected to leads, in different topologies. Our main interest is to study the effects of the Kondo regime and the electronic phase on the conductance. In the configuration where the two dots are inserted in each arm of a ring threaded by a magnetic flux, denoted by PPL, we calculate the phases of the currents going along each arm of the ring. These phases are determined by the Aharonov-Bohm effect combined with the dots many body charging effects. This system presents the Kondo phenomenon for an even number (two) of electrons in the dots, in agreement with experimental results1. An interesting aspect of PPL configuration is that, even in the absence of magnetic flux there can be a circulating current around the ring, depending on the system parameters. In the two other topologies we consider the two quantum dots coupled through tunneling interaction. In one of them, denoted by PAL, the two dots are aligned with the leads, and in the other, the PPD configuration, one dot is inserted into the leads while the other interacts only with the first. In the weak coupling limit these two configurations present quite different features, not only on the dependence of the conductance on the gate potencials applied to the dots, but also on the dots spin correlation. Both configurations present Kondo resonance for an even number electrons. In the PAL configuration the spins of the charged dots are uncorrelated, while in the PPD configuration they are ferromagnetically correlated. In the strong tunneling coupling limit the transport properties of two interacting dot configurations are very similar. The systems discussed above are represented by an Anderson two- impurity first-neighbor tight-binding Hamiltonian, that is solved by exactly diagonalizing a cluster that is embebed into the rest of the system. In this way we obtain only the properties of the system at T = 0. In order to study temperature dependence phenomena we use the equation of motion method (EOM) in the limit of infinite Coulomb repulsion. We apply it to the dots in the PPD topology. The results for low temperatures are consistent with hose obtained with the cluster method.