Dissertations / Theses: 'InP/ZnS quantum dots'

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Carlini, Lina. "Photosensitization of InP/ZnS quantum dots for photodynamic therapy." Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=106430.

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Photodynamic therapy (PDT) is a treatment that makes use of light and a photosensitizing drug to destroy malignant cells. Current clinically approved drugs suffer from many limitations; the most prevalent of these is due to the absorption coefficient of human tissues in the wavelength regime where these drugs are excitable. Semiconductor quantum dots (QDs) can overcome this drawback since they can be synthesized to become excited at any wavelength. The goal of this thesis is to explore the possibility of using core/shell Indium Phosphide/Zinc Sulfide (InP/ZnS) quantum dots (QDs) for photodynamic therapy applications. Electron paramagnetic resonance (EPR) spectroscopy and colorimetric assays were used to identify the nature of toxic species produced. From these findings, the physical mechanism by which these particles produce toxic species is discussed. It was found that InP/ZnS QDs produced superoxide anions and hydroxyl radicals, the levels of which depended on the ZnS shell thickness. Furthermore, the level of cellular uptake was studied in different cell lines using confocal microscopy. It was found that InP localized in the perinuclear region of all cell lines and that B16 melanoma cells showed the most efficient levels of uptake (2.5 times greater than the uptake from KB cells). Lastly, conjugation of InP QDs to the chemotherapeutic drug doxorubicin (Dox) was studied using flow cytometry and colorimetric assays. It was found that conjugation of Dox to InP led to enhanced levels of cell death; it is proposed that this was due to more efficient drug delivery by the conjugate. In summary, photosensitization processes in InP/ZnS QDs can be exploited for PDT applications; these particles also prove to be promising as a drug delivery agent. Despite this, photophysical processes of these QDs must be further explored to ameliorate their design for PDT.
La thérapie photodynamique (TPD) est un traitement médical qui détruit les cellules cancéreuses en utilisant des photons de lumière, typiquement en forme de laser, afin d'activer des drogues photosensibles. Présentement, les médicaments approuvés pour usage clinique ont d'importantes limitations. Particulièrement, le coefficient d'absorption des tissus humains se retrouve dans la même gamme de longueur d'onde où les médicaments sont excitables; par conséquent, leur efficacité est compromise. Les nanoparticules de matériaux semi-conducteurs, appelées aussi points quantiques (PQs), ont l'habilité de surpasser cette limitation parce qu'ils peuvent être produits pour absorber la lumière à n'importe quelle longueur d'onde. L'objectif de cette thèse est donc d'évaluer la possibilité d'utiliser les PQs pour la TPD. Plus spécifiquement, les PQs composés d'un cœur de phosphure d'indium (InP) avec une coquille du sulfure de zinc (ZnS) ont été examinés. La spectroscopie par résonance paramagnétique électronique (RPE) et les tests colorimétriques ont été utilisés pour identifier la nature des espèces toxiques produites, ainsi que le mécanisme responsable de leur formation. Les résultats ont montré que les particules de InP/ZnS produisent des anions de superoxyde et des radicaux d'hydroxyle; la quantité des radicaux formés dépend de l'épaisseur de la coquille ZnS. En plus, la microscopie confocale a été utilisée pour évaluer l'ingestion intracellulaire des PQs par divers types de cellules. Ces images ont démontré que les PQs se concentrent dans le cytoplasme autour du noyau et que les cellules mélanomes de type B16 sont celles qui absorbent le plus (2.5 fois plus que les cellules KB). Finalement, les PQs ont été conjuguées à un agent chimiothérapeutique (doxorubicin (Dox)) et leur toxicité a été explorée par cytométrie en flux et des tests colorimétriques. La mort cellulaire a augmenté avec l'attachement de PQs, ce qui s'explique par une amélioration de la livraison intracellulaire de Dox. En conclusion, les PQs InP/Zn révèlent être des candidats prometteurs en tant que médicaments et agents de livraison pour la TPD, cependant certains éléments de leur structure restent à être améliorés.

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Panzer, Rene, Chris Guhrenz, Danny Haubold, Rene Hübner, Nikolai Gaponik, Alexander Eychmüller, and Jan J. Weigand. "Tri(pyrazolyl)phosphane als Phosphorpräkursoren für die Synthese von hochemittierenden InP/ZnS Quantenpunkten." Technische Universität Dresden, 2018. https://tud.qucosa.de/id/qucosa%3A31166.

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Tri(pyrazolyl)phosphane (5R1,R2) werden als alternative, kostengünstige und geringer toxische Phosphorpräkursoren in der Synthese von InP/ZnS Quantenpunkten (QP) eingesetzt. Ausgehend von diesen Vorläuferverbindungen konnten langzeitstabile (>6 Monate) P(OLA)3 (OLAH = Oleylamin) Stammlösungen synthetisiert werden, aus denen sich die entsprechenden Pyrazole einfach zurückgewinnen lassen. P(OLA)3 fungiert in der Synthese von hochemittierenden InP/ZnS QP sowohl als Phosphorquelle als auch als Reduktionsmittel. Die erhaltenen Kern/Schale-Partikel zeichnen sich durch hohe Photolumineszenz-Quantenausbeuten (PL-QA) von 51–62% in einem spektralen Bereich von 530–620 nm aus. Die Verarbeitung und Anwendung dieser InP/ZnS QP als Farbkonversionsschicht wurde als „proof-of-concept“ in einer weißen Leuchtdiode (LED) demonstriert

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Panzer, Rene, Chris Guhrenz, Danny Haubold, Rene Hübner, Nikolai Gaponik, Alexander Eychmüller, and Jan J. Weigand. "Versatile Tri(pyrazolyl)phosphanes – Application as phosphorus precursors for the synthesis of highly emitting InP/ZnS quantum dots." Technische Universität Dresden, 2018. https://tud.qucosa.de/id/qucosa%3A31156.

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Tri(pyrazolyl)phosphanes (5R1,R2) are utilized as an alternative, cheap and low-toxic phosphorus source for the convenient synthesis of InP/ZnS quantum dots (QDs). From these precursors, remarkably long-term stable stock solutions (>6 months) of P(OLA)3 (OLAH = oleylamine) are generated from which the respective pyrazoles are conveniently recovered. P(OLA)3 acts simultaneously as phosphorus source and reducing agent in the synthesis of highly emitting InP/ZnS core/shell QDs. These QDs are characterized by a spectral range between 530–620 nm and photoluminescence quantum yields (PL QYs) between 51–62%. A proof-of-concept white light-emitting diode (LED) applying the InP/ZnS QDs as color conversion layer was built to demonstrate their applicability and processibility.

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Albahrani, Sayed Mohamed Baqer. "Photoluminescent CdSe/CdS/ZnS quantum dots for temperature and pressure sensing in elastohydrodynamic." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI016/document.

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La température et la pression sont deux paramètres particulièrement importants pour l’optimisation des performances du régime de lubrification élastohydrodynamique (EHL). A ce jour, différentes méthodes expérimentales ont été développées, avec plus ou moins du succès, pour la mesure de ces deux paramètres. Ce travail présente, en continuité de ces approches, des investigations visant à développer une nouvelle technique in situ permettant de mesurer localement ces deux grandeurs dans les contacts élastohydrodynamiques (EHD). Cette technique exploite la sensibilité en photoluminescence (PL) des boîtes quantiques (ou en anglais « quantum dots (QDs)) de CdSe/CdS/ZnS aux variations de température et de pression. A cet égard, des calibrations ont été réalisées afin d’évaluer la sensibilité de ces QDs aux deux paramètres. De plus, la versatilité de ces QDs comme nanosondes a été examinée en testant deux lubrifiants différents : le squalane et un mélange de squalane et de cyclopentane. Des mesures ont été également effectuées sous conditions dynamiques afin d’étudier (i) l’influence de la présence des QDs sur la rhéologie du lubrifiant et (ii) l’influence du taux de cisaillement sur la PL des QDs. Bien que ces différents tests aient prouvé le potentiel des QDs de CdSe/CdS/ZnS, ils ont révélé l’existence d’autres paramètres qui peuvent, tout comme la température et la pression, en modifier la réponse. L’étude a été menée afin d’approfondir la compréhension des mécanismes responsables de tels effets. Plus important encore, une méthodologie a été définie pour minimiser ces effets indésirables, et pour in fine, permettre l’usage de ces QDs en tant que nanosondes fiables
Temperature and pressure are two relevant parameters for the optimization of lubrication performance in the elastohydrodynamic lubrication (EHL) regime. To date, various experimental methods have been developed to measure these two parameters with more or less success. In a continuation of these efforts, some investigations are presented in the current work in view of developing a new in situ technique allowing for local measurements of these two parameters throughout elastohydrodynamic (EHD) contacts. This technique exploits the photoluminescence (PL) sensitivity of CdSe/CdS/ZnS quantum dots (QDs) to changes in temperature and pressure. In this respect, calibrations have been carried out in order to establish the sensitivity of these QDs to the two parameters. Moreover, the versatility of these QDs for sensing applications have been examined by testing two different lubricants, namely squalane and a mixture of squalane and cyclopentane. Some measurements were also conducted under dynamic conditions, in order to study (i) the influence of the QDs presence on the lubricant rheology and (ii) the influence of shear rate on the PL of QDs. Although these different tests demonstrated the potential of CdSe/CdS/ZnS QDs, they revealed the existence of other parameters that affect, in addition to temperature and pressure, their response. A comprehensive study was thus conducted in order to elucidate the mechanisms behind these findings. More importantly, a methodology was defined in order to minimize these undesired influences and, in fine, enable these QDs to be used as reliable nanosensors

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Virieux, Heloise. "Nanocristaux luminescents de phosphures d'indium et de zinc : synthèse, enrobage et caractérisation." Thesis, Toulouse, INSA, 2013. http://www.theses.fr/2013ISAT0030/document.

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Ce travail de thèse porte sur la synthèse organo-métallique de nanoparticules (NPs) semi-conductrices colloïdales de phosphures d’indium (InP), de zinc (Zn3P2) et de structures cœur/coquille obtenues par la croissance d’une couche de sulfure de zinc (ZnS) à la surface des NPs. Les objectifs consistent à comprendre et maîtriser la synthèse dans le but de décaler les longueurs d’onde d’absorption et d’émission vers le proche infra-rouge, domaine spectral intéressant pour l’imagerie biomédicale.Le premier chapitre présente l’état de l’art sur les nanocristaux (NCx) d’InP et d’InP/ZnS. Un bref rappel sur les propriétés physico-chimiques des NCx semi-conducteurs est présenté et différentes synthèses sont décrites. Une attention toute particulière a été portée sur la taille des NCx, le décalage de l’émission de fluorescence vers les plus grandes longueurs d’onde et l’optimisation des rendements quantiques. Les potentialités offertes par ces objets soit pour les diodes électroluminescentes (LED) blanches soit pour l’imagerie biomédicale montrent l’intérêt d’utiliser les NCx de type InP/ZnS plutôt que d’autres matériaux à base d’éléments toxiques (Cd, Pb, …).Le deuxième chapitre porte sur une synthèse à partir des carboxylates d’indium connue de la littérature. Le but est alors de caractériser la structure des NPs pour comprendre le déroulement de la synthèse et de l’enrobage. Des mesures par résonance magnétique nucléaire (RMN) en phase solide et spectroscopie photo-électronique par rayons X (XPS) révèlent l’oxydation des NPs d’InP. La couche d’oxyde qui se forme durant la synthèse des NPs d’InP s’épaissit lors de l’enrobage. Cette oxydation provient d’un couplage décarboxylant des acides carboxyliques à haute température en présence des NPs. Elle serait à l’origine de l’inhibition de croissance des objets, ce qui limiterait les gammes de longueurs d’onde atteignables.Le troisième chapitre concerne une nouvelle synthèse à partir d’amidinate d’indium au lieu des carboxylates d’indium. L’intérêt de cette approche est la possibilité d’abaisser considérablement la température de réaction (150°C au lieu de 280°C) et ainsi d’éviter la réaction secondaire de décarboxylation. Un enrobage à basse température (150°C) est aussi mis en place. La synthèse induit également une oxydation de la surface des NPs d’InP. Un nouveau couplage a lieu entre les ligands, l’acide palmitique et l’hexadécylamine, et donne de nouvelles conditions oxydantes. Le jeu sur les ratios des ligands montre qu’en bouleversant le milieu réactionnel, les NPs d’InP ne présentent pas de réponse en luminescence concluante. La synthèse et l’enrobage sont alors réalisés sous atmosphère de dihydrogène (H2) en réacteur Fisher-Porter dans le but de contrer ces conditions oxydantes. La synthèse et l’enrobage donnent des tailles de NPs de l’ordre de 3,4 nm (condition nécessaire pour s’approcher d’une émission dans l'infra-rouge) et un rendement quantique de 18-20 %, résultats encore jamais atteints lors de cette thèse.Le dernier chapitre est consacré à une étude exploratoire sur les NPs de Zn3P2. Le phosphure de zinc est un matériau prometteur du fait de l’abondance de ses constituants non toxiques et des longueurs d’onde potentiellement accessibles. Différents paramètres de synthèse sont étudiés et les propriétés structurales et optiques sont caractérisées. Des résultats préliminaires sur l’enrobage montrent des difficultés liées à la stabilité des NPs de Zn3P2. L’utilisation de l’oxyde de trioctylphosphine (TOPO) semble permettre la passivation de ces NPs à l’air et en travaillant sous H2 une meilleure stabilité est envisageable
Résumé de la thèse en anglais : This PhD investigation focuses on organometallic synthesis of indium phosphide (InP), zinc phosphide (Zn3P2) colloidal semiconductor nanoparticles (NPs) and core/shell structures which were obtained by the growth of a layer of zinc sulfide (ZnS) on the surface. The objectives are to understand and control the synthesis in order to shift the absorption and emission wavelengths to the near infra-red range, interesting for biomedical imaging.The first chapter presents the state of the art on the InP and InP/ZnS nanocrystals (NCx). A brief recall on the physical and chemical properties of semiconductor NCx is presented and various syntheses are described. Particular attention was paid to the size of NCx, the shift of the fluorescence emission to higher wavelengths and the optimization of quantum yields. The potential of these objects for white light emitting diodes (LED) or biomedical imaging shows the value added of using InP/ZnS NCx rather than other materials based on toxic elements such as cadmium, lead elements…The second chapter focuses on a synthesis from indium carboxylates known in the literature. The goal is to characterize the structure of NPs to understand the procedure of the synthesis and the coating. Measurements by Nuclear Magnetic Resonance (NMR) in solid state and Photoelectronic X-ray spectroscopy (XPS) revealed the oxidation of InP of the NPs. This oxide layer increases during the coating. This originates from a decarboxylating coupling of carboxylic acids at high temperature in the presence of NPs. This oxidation is believed to inhibit the growth of the object, which restricts the attainable range of wavelengths.The third chapter provides a novel synthesis from indium amidinate instead of indium carboxylate. The advantage of this approach is the potential to lower significantly the reaction temperature (150°C instead of 280°C) and to avoid secondary decarboxylation reaction. A coating with ZnS at low temperature (150°C) is also developed. The synthesis of InP NPs also causes an oxidation of the surface. A coupling takes place again between the ligands, palmitic acid and hexadecylamine providing new oxidizing conditions. The study of different ratios of ligands shows that when the reaction medium is modified, the InP NPs do not exhibit a conclusive luminescence response. Synthesis and coating are carried out under an atmosphere of hydrogen (H2) in Fisher-Porter reactor in order to counter these oxidizing conditions. NPs with diameters of the order of 3,4 nm (a necessary condition to approach the infra-red emission) and a quantum yield of 18-20% are thus obtained. These had never been observed before during this thesis.The last chapter is devoted to an exploratory study on Zn3P2 NPs. Zinc phosphide is a promising material because of non-toxic and abundant constituents, and potential access to near infra-red wavelengths. Different synthesis parameters are studied and the structural and optical properties are characterized. Preliminary results on the coating show instabilities of the Zn3P2 NPs. The use of trioctylphoshine oxide (TOPO) appears to allow the passivation of the NPs in the air and a better stability is possible under an atmosphere of H2

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Boonkoom, Thitikorn. "InP quantum dots for hybrid photovoltaic devices." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/17778.

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Significant research efforts have been directed towards the development of solar cells comprising blends of conjugated polymers and II-VI inorganic semiconductors (e.g. CdSe and CdS). Despite recent advances in the power conversion efficiency of such devices, the toxicity of Cd-based materials remains a concern with regard to widespread implementation. This thesis focuses on alternative (lower toxicity) InP nanocrystals for use as electron acceptors and light-harvesting materials in solution-processed polymer solar cells. In this thesis a combination of novel materials design/processing, transient absorption spectroscopy (TAS) and time-resolved photoluminescence spectroscopy (TRPL) is used to study the charge generation in InP:polymer photoactive layers. These studies are complimented by morphological characterisation of the photoactive layers as well as device studies. One aim of this thesis is the elucidation of quantitative structure function relationships that can be used to guide the design of new hybrid nanocomposite materials for photovoltaic devices. As such the data presented in this thesis helps to advance the present day understanding how hybrid solar cells work. The first chapter focuses on the synthesis of InP quantum dots (QDs) using an organometallic reaction. The aim of the work in this chapter was to prepare InP QDs with a size that provides an appropriate energy offset relative to the selected the electron donating polymer, poly(3-hexylthiophene) (P3HT). Detailed studies on the growth of InP QDs and how the reaction conditions affect the particle size are provided. The process of ligand exchange from hexadecylamine (HDA) to pyridine prior to blending with P3HT is also described. The second chapter focuses on charge transfer between the P3HT and the InP QDs which is a key process for achieving efficient photovoltaic device operation. Steady state and time-resolved photoluminescence and absorption spectroscopy were used to better understand the parameters influencing charge separation. After the blending and annealing conditions had been optimised to maximise the yield of photogenerated charges, the P3HT:InP blend was found to provide approximately twice yield of standard P3HT:PCBM blends. In addition, the decay lifetime of the polaron in P3HT:InP was found to be longer than that of P3HT:PCBM, suggesting the P3HT:InP blend is a promising active layer material for hybrid solar cells. The third chapter focuses on the fabrication and characterisation of hybrid solar cells. The fabrication conditions were optimised before carrying out detailed studies on the effect of thermal annealing. Although the device performance improved significantly with increasing annealing temperature, the net photocurrent was found to be low, compared to standard P3HT:PCBM devices, suggesting poor charge transport within the device. Nevertheless, if the charge transport can be improved, P3HT:InP still has potential to provide efficient hybrid solar cells. The last result chapter focuses on preliminary studies of quantum dot based light emitting diodes (QDLEDs) using InP QDs as light emitters. ZnO was used as electron transporting and hole blocking layer and poly(9,9-dioctylfluorene) (PFO) as a host medium and a hole transporting layer. The device structure and the PFO:InP blend composition were investigated to obtain QDLEDs with electroluminescence from the InP quantum dots. The findings suggest that ZnO plays a key role in suppressing the electroluminescence of PFO, most likely due to the hole blocking effect of the ZnO layer. Despite the low efficiencies of the InP-based QDLEDs, the results suggest that InP QDs are potential candidates for emitters in QDLEDs.

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Winzell, Ann. "Surface Modification of CdSe(ZnS) quantum dots for biomedical applications." Thesis, Linköping University, Department of Physics, Chemistry and Biology, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-56022.

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Quantum dots are inorganic nanocrystals of semiconductor metals that have unique light emitting properties. Due to their tunable and narrow emission profile, broad absorption spectra, resistance to photobleaching and high level of brightness they have emerged as inorganic fluorophores and numerous applicabilities for in vitro, in situ as well as in vivo studies are present. The chemical nature of the quantum dot surface needs to be altered in order to make the inorganic nanoparticles applicable to biological systems. Water soluble and biocompatible particles that limit unspecific binding to proteins can be obtained through functionalization of the surface coating with appropriate molecules.

In this pilot study, two surface modification strategies were performed upon two commercially available quantum dots in order to attach the zwitterionic molecules L-cysteine and thiolated sulfobetaine methacrylate, both shown to create non-fouling and biocompatible surfaces.

A biphasic exchange method was successfully used to perform ligand exchange of Qdot® ITK™ Organic Quantum Dots (QD-Organic) in order to exchange the structurally unknown, native lipophilic coating to one consisting of the amino acid L-cysteine (QD-Cysteine). The quantum dots transferred from the organic to the aqueous phase after the natively hydrophobic coating was changed to the hydrophilic L-cysteine. A characteristic mass fragment of protonated trioctylphosphine oxide (TOPO) was found for QD-Organic, using TOF-SIMS, suggesting TOPO is a part of the native coating. Further, the mentioned mass fragment was no longer present after the exchange. The C (1s) XPS-spectrum showed a new peak for carboxylic carbon, characteristic for L-cysteine, and expected changes in elemental composition were consistent with measured changes for all relevant elements. Large amounts of buffer remained after purification, suggesting the purification protocol needs further evaluation. Traces of the native coating were found in the C (1s) XPS-spectrum for QD-Cysteine, indicating not all ligands were exchange.

Additionally, a strategy for surface functionalization of Qdot® 655 ITK™ amino (PEG) quantum dots (QD-PEG-NH₂) with L-cysteine and thiolated sulfobetaine methacrylate was outlined and performed, using Michael addition and the heterobifunctional linker 3-Maleimidobenzoic acid N-hydroxysuccinimide ester. Unfortunately, no indications of successful attachment of the linker to the quantum dot have been found, neither by TOF-SIMS nor XPS, and thus functionalization with L-cysteine and tSBMA was not achieved. In theory, the proposed coupling chemistry used during the pilot study is promising, but further experiments are needed to obtain a successful and optimized protocol for the functionalization.

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Cheriton, Ross. "Electrostatic Control of Single InAs Quantum Dots Using InP Nanotemplates." Thèse, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/22758.

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This thesis focuses on pioneering a scalable route to fabricate quantum information devices based upon single InAs/InP quantum dots emitting in the telecommunications wavelength band around 1550 nm. Using metallic gates in combination with nanotemplate, site-selective epitaxy techniques, arrays of single quantum dots are produced and electrostatically tuned with a high degree of control over the electrical and optical properties of each individual quantum dot. Using metallic gates to apply local electric fields, the number of electrons within each quantum dot can be tuned and the nature of the optical recombination process controlled. Four electrostatic gates mounted along the sides of a square-based, pyramidal nanotemplate in combination with a flat metallic gate on the back of the InP substrate allow the application of electric fields in any direction across a single quantum dot. Using lateral fields provided by the metallic gates on the sidewalls of the pyramid and a vertical electric field able to control the charge state of the quantum dot, the exchange splitting of the exciton, trion and biexciton are measured as a function of gate voltage. A quadrupole electric field configuration is predicted to symmetrize the product of electron and hole wavefunctions within the dot, producing two degenerate exciton states from the two possible optical decay pathways of the biexciton. Building upon these capabilities, the anisotropic exchange splitting between the exciton states within the biexciton cascade is shown to be reversibly tuned through zero for the first time. We show direct control over the electron and hole wavefunction symmetry, thus enabling the entanglement of emitted photon pairs in asymmetric quantum dots. Optical spectroscopy of single InAs/InP quantum dots atop pyramidal nanotemplates in magnetic fields up to 28T is used to examine the dispersion of the s, p and d shell states. The g-factor and diamagnetic shift of the exciton and charged exciton states from over thirty single quantum dots are calculated from the spectra. The g-factor shows a generally linear dependence on dot emission energy, in agreement with previous work on this subject. A positive linear correlation between diamagnetic coefficient and g-factor is observed.

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Kors, Andrei [Verfasser]. "InP - based quantum dots for telecom wavelengths ranges / Andrei Kors." Kassel : Universitätsbibliothek Kassel, 2020. http://d-nb.info/1222555239/34.

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Angell, Joshua James. "SYNTHESIS AND CHARACTERIZATION OF CdSe-ZnS CORE-SHELL QUANTUM DOTS FOR INCREASED QUANTUM YIELD." DigitalCommons@CalPoly, 2011. https://digitalcommons.calpoly.edu/theses/594.

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Quantum dots are semiconductor nanocrystals that have tunable emission through changes in their size. Producing bright, efficient quantum dots with stable fluorescence is important for using them in applications in lighting, photovoltaics, and biological imaging. This study aimed to optimize the process for coating CdSe quantum dots (which are colloidally suspended in octadecene) with a ZnS shell through the pyrolysis of organometallic precursors to increase their fluorescence and stability. This process was optimized by determining the ZnS shell thickness between 0.53 and 5.47 monolayers and the Zn:S ratio in the precursor solution between 0.23:1 and 1.6:1 that maximized the relative photoluminescence quantum yield (PLQY) while maintaining a small size dispersion and minimizing the shift in the center wavelength (CWL) of the fluorescence curve. The process that was developed introduced a greater amount of control in the coating procedure than previously available at Cal Poly. Quantum yield was observed to increase with increasing shell thickness until 3 monolayers, after which quantum yield decreased and the likelihood of flocculation of the colloid increased. The quantum yield also increased with increasing Zn:S ratio, possibly indicating that zinc atoms may substitute for missing cadmium atoms at the CdSe surface. The full-width at half-maximum (FWHM) of the fluorescence spectrum did not change more than ±5 nm due to the coating process, indicating that a small size dispersion was maintained. The center wavelength (CWL) of the fluorescence spectrum red shifted less than 35 nm on average, with CWL shifts tending to decrease with increasing Zn:S ratio and larger CdSe particle size. The highest quantum yield was achieved by using a Zn:S ratio of 1.37:1 in the precursor solution and a ZnS shell thickness of approximately 3 monolayers, which had a red shift of less than 30 nm and a change in FWHM of ±3 nm. Photostability increased with ZnS coating as well. Intense UV irradiation over 12 hours caused dissolution of CdSe samples, while ZnS coated samples flocculated but remained fluorescent. Atomic absorption spectroscopy was investigated as a method for determining the thickness of the ZnS shell, and it was concluded that improved sample preparation techniques, such as further purification and complete removal of unreacted precursors, could make this testing method viable for obtaining quantitative results in conjunction with other methods. However, the ZnS coating process is subject to variations due to factors that were not controlled, such as slight variations in temperature, injection speed, and rate and degree of precursor decomposition, resulting in standard deviations in quantum yield of up to half of the mean and flocculation of some samples, indicating a need for as much process control as possible.

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Qejvanaj, Fatjon. "Correlation of size and photoluminescence of single CdSe/ZnS quantum dots." Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-99562.

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In this thesis the correlation between size and emission wavelength of single CdSe/ZnS quantum dots (QDs) has been studied. Based on the quantum confinement model QDs of different size emit light of different wavelength. In order to characterize individual QDs, experiments were carried out using a high-resolution atomic force microscope (AFM) placed on top of an inverted optical microscope. The quantum dots were exited with a high-power diode laser (405 nm) and the spectral response was recorded with a CCD camera attached to a spectrometer. Samples with two different average-sized QDs exhibiting photoluminescence maximum at 600 and 621 nm were prepared by spin-coating a highly diluted QD/toluene solution on cleaned glass cover slides. The results of this thesis verify the theoretical prediction and show on single particle level that with decreasing QD size the emission energy increases.

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Bryan, Caroline. "Optical and structural characterisation of InP based quantum wells and dots." Thesis, Imperial College London, 2000. http://hdl.handle.net/10044/1/7276.

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Coe-Sullivan, Seth (Seth Alexander). "Efficient light emitting devices utilizing CdSe(ZnS) quantum dots in organic host matrices." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/28354.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2002.
Includes bibliographical references (leaves 29-32).
We demonstrate efficient electroluminescence from thin film structures containing core-shell CdSe(ZnS) quantum dots dispersed in molecular organic host materials. In the most efficient devices, excitons are created on the quantum dot sites via energy transfer from organic host molecules, and direct charge injection into the quantum dots is minimized. For quantum dots with core diameter 38 [Angstroms], the electroluminescence spectra peak at 562nm and have full width at half maximum as narrow as 32nm. Saturated color devices have external quantum efficiencies as high as 0.61% at the current density of 7mA/cm². At 125mA/cm², the device luminance is 1900cd/m², which corresponds to a luminescence efficiency of 1.5 cd/A. The yield over hundreds of devices is greater than 90%, indicating a robust material system.
by Seth Alexander Coe.
S.M.

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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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Katmis, Asli Ugur. "Growth and characterization of InP/In0.48Ga0.52P quantum dots optimized for single-photon emission." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2013. http://dx.doi.org/10.18452/16696.

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In dieser Forschungsarbeit wird das selbstorganisierte Wachstum von InP/InGaP-Quantenpunkten (QP) sowie ihre optischen und strukturellen Eigenschaften untersucht. Die QP wurden auf GaAsgitterangepasstem InGaP gewachsen.Selbstorganisierte InP-QP werden mittels Gasquellen-Molekularstrahlepitaxie gewachsen, wobei die InP-Abscheidungsrate uber einen weiten Bereich variiert wird. Bei besonders geringer Wachstumsratevon rund 0,01 Atomlagen/s wird eine Flachendichte von 1 QP/μm2 erreicht. Die daraus resultierenden InP QP, konnen einzeln charakterisiert werden ohne vorher das Substrat lithografisch behandeln zu mussen. Sowohl exzitonische als auch biexzitonische Emission kann dabei an einzelnen QPn als Doublett mit einer Feinstrukturaufspaltung von 320μeV beobachtet warden. Hanbury-Brown-Twiss Korrelationsmessungen der exzitonischen Emission unter Dauerstrichanregung zeigen Antibunching mit einem Autokorrelationskoeffizienten von g(2)(0)=0.2. Dieses System liee sich beispielsweise als Einzelphotonenquelle in Anwendungsbereichen wie der Quantenkryptographie einsetzen. Daruber hinaus wird die Bildung wohlgeordneter Quantenpunktketten auf GaAs (001)-Substraten unter Ausnutzung einer selbstorganisierten InGaP-Oberflachenwellung demonstriert. Diese Anordnung basiert weder auf gestapelten Quantenpunktschichten noch einem intentionalen Substratschragschnitt. Die Strukturen warden mittels polarisationsabhangiger Photolumineszenzspektroskopie sowie Transmissionselektronenmikroskopie untersucht. Die Lumineszenz der InGaP-Matrix ist in eine kristallografische Richtung polarisiert, bedingt durch anisotrope Verspannung, welche ihrerseits aus der lateralen Variation der Materialzusammensetzung entsteht. Photolumineszenzmessungen der QP zeigen eine lineare Polarisation entlang [-110], der Richtung der Ketten. Der Polarisationsgrad liegt bei 66%. Diese optische Anisotropie wird direkt in einer Heterostruktur hervorgerufen, die lediglich eine Quantenpunktschicht beinhaltet.
In this work the growth of self-assembled InP/InGaP quantum dots, as well as their optical and structural properties are presented and discussed. The QDs were grown on InGaP, lattice matched to GaAs.Self-assembled InP quantum dots are grown using gas-source molecular beam epitaxy over a wide range of InP deposition rates, using an ultra-low growth rate of about 0.01 atomic monolayers/s, a quantum-dot density of 1 dot/μm2 is realized. The resulting isolated InP quantum dots are individually characterized without the need for lithographical patterning and masks on the substrate. Both excitionic and biexcitonic emissions are observed from single dots, appearing as doublets with a fine-structure splitting of 320 μeV. Hanbury Brown-Twiss correlation measurements for the excitonic emission under cw excitation show anti-bunching behavior with an autocorrelation value of g(2)(0)=0.2. This system is applicable as a single-photon source for applications such as quantum cryptography. The formation of well-ordered chains of InP quantum dots on GaAs (001) substrates by using self-organized InGaP surface undulations as a template is also demonstrated. The ordering requires neither stacked layers of quantum dots nor substrate misorientation. The structures are investigated by polarization-dependent photoluminescence together with transmission electron microscopy. Luminescence from the InGaP matrix is polarized in one crystallographic direction due to anisotropic strain arising from a lateral compositional modulation. The photoluminescence measurements show enhanced linear polarization in the alignment direction of quantum dots, [-110]. A polarization degree of 66% is observed. The optical anisotropy is achieved with a straightforward heterostructure, requiring only a single layer of QDs.

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Vannoy, Charles Harvey. "Behavioral Effects of Functionalized CdSe/ZnS Quantum Dots in Self-Organization and Protein Fibrillation." Scholarly Repository, 2010. http://scholarlyrepository.miami.edu/oa_dissertations/431.

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Advances in recent nanoscience technologies have generated a new compilation of biocompatible, fluorescent nanoparticles derived from semiconductor quantum dots (QDs). QDs are extremely small in size and possess very large surface areas, which gives them unique physical properties and applications distinct from those of bulk systems. When exposed to biological fluid, these QDs may become coated with proteins and other biomolecules given their dynamic nature. These protein-QD systems may affect or enhance the changes in protein structure and stability, leading to the destruction of biological function. It is believed that these QDs can act as nucleation centers and subsequently promote protein fibril formation. Protein fibrillation is closely associated with many fatal human diseases, including neurodegenerative diseases and a variety of systemic amyloidoses. This topic of protein-QD interaction brings about many key issues and concerns, especially with respect to the potential risks to human health and the environment. Herein, the behavioral effects of dihydrolipoic acid (DHLA)-capped CdSe/ZnS (core/shell) QDs in hen egg-white lysozyme (HEWL) and human serum albumin (HSA) protein systems were systematically analyzed. This study gives rise to a better understanding of the potentially useful application of these protein-QD systems in nanobiotechnology and nanomedicine as a bioimaging tool and/or as a reference for controlled biological self-assembly processes.

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Veloso, Aline Bessa. "Propriedades ópticas de pontos quânticos empilhados de InP/GaAs." [s.n.], 2007. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277760.

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Orientador: Fernando Iikawa
Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
Made available in DSpace on 2018-08-09T11:09:31Z (GMT). No. of bitstreams: 1 Veloso_AlineBessa_M.pdf: 2273008 bytes, checksum: 19cf5ce00aebec12cc1795518a811244 (MD5) Previous issue date: 2007
Resumo: Nesta dissertação, estudamos as propriedades ópticas e estruturais de pontos quânticos (QDs) empilhados de InP/GaAs, crescidos por método de auto-formação, conhecido como o modo Stranskii-Krastanov, em um sistema de epitaxia por feixe químico. Os pontos quânticos de InP/GaAs possuem alinhamento das bandas tipo-II nas interfaces, onde somente o elétron fica confinado no QD, enquanto o buraco fica localizado em volta dele na camada de GaAs atraído pelo elétron. Investigamos amostras com diferentes separação d entre duas camadas de QDs de InP, variando de 3 a 12 nm. As análises estruturais foram feitas por técnica microscopia eletrônica de transmissão (TEM) e as análises ópticas por fotoluminescência de feixe contínuo (PL-CW) e de resolvida no tempo (PL-RT) com a temperatura variando de 2 a 120 K. As imagens de TEM mostram alinhamento vertical dos QDs e maiores tamanhos para os que estão na segunda camada. As medidas de PL-CW, a baixas temperaturas, apresentam largura de linha da banda de emissão mais estreita e simétrica nas amostras de QDs empilhados do que a de amostra de uma camada simples. Isso é atribuído à maior uniformidade de tamanhos de QDs da segunda camada. Atribuímos aos efeitos de acoplamento quântico e de tunelamento dos portadores entre QDs, à redução de energia do pico de PL com a diminuição de d. Observamos que o decaimento temporal de PL é independente de d e é relativamente rápido, ~0,6 ns, para uma estrutura com alinhamento de banda tipo-II. Isso sugere a presença de outros canais de captura de portadores de cargas reduzindo o tempo de vida dos éxcitons em nossos QDs. Observamos também uma redução do tempo de vida na região de maior energia de emissão em todas as amostras, indicando a transferência de portadores de cargas dos QDs muito pequenos para os grandes. O aumento da temperatura resultou na redução da energia de transição e da intensidade integrada nas medidas de PL-CW, bem como, do tempo de vida dos éxcitons. A redução da energia de transição se deve à transferência de elétrons dos QDs pequenos para grandes via wetting layer, devido à excitação térmica. Mas a contribuição desse efeito é menor nas amostras de QDs empilhados, devido aos efeitos de tunelamento dos elétrons entre QDs alinhados e à uniformidade dos tamanhos. A redução da intensidade integrada de PL e no tempo de decaimento se deve a excitação térmica do elétron para o estado contínuo da wetting layer
Abstract: We studied the optical and structural properties of stacked InP/GaAs quantum dots (QD) grown by the self-organized Stranskii-Krastanov mode in a chemical beam epitaxy system. The InP/GaAs quantum dots present type-II band alignment, where only the electron is confined in the QD, while the hole is localized around it, in the GaAs layer, due to the Coulomb attraction. We investigated samples with different space-layer d between two stacked InP QDs varying from 3 to 12 nm. The structural analysis was performed by using transmission electronic microscopy (TEM) and the optical analysis by using continuous wave (CW) and time-resolved (TR) photoluminescence (PL) techniques with temperature varying from 2 to 120 K. The TEM images show clear vertical alignment of quantum dots and slightly larger size for QDs of the second layer. The CW-PL spectra measured at low temperatures present narrower QD emission band and more symmetric for stacked QDs samples than single layer one. This is attributed to the uniformity of the QDs in double layers samples. We also observed the PL red-shift with the reduction of d, which is attributed to the quantum coupling and the tunneling effects of the carriers between aligned QDs. We observed that the PL decay time is independent of d and is relatively fast, ~0,6 ns, for a structure with type-II band alignment. This suggests the presence of other carrier capture channels that reduce significantly the exciton lifetime in our QDs. The carrier lifetime is shorter in the higher emission energy region in all samples, indicating the carrier transference from the smaller QDs to the larger ones. Increasing the temperature we observed a reduction of the transition energy and the integrated CW-PL intensity, as well as, of the exciton lifetime. The energy shift is due to the electron transference from the small QDs to the larger ones, through wetting layer, due to the thermal excitation. The contribution of this effect is smaller on the stacked QDs, due to the dot uniformity and the electron tunneling effect. The reduction of the CW-PL integrated intensity and the carrier decay time is due to the thermal excitation of the electron to the continuous state of the wetting layer
Mestrado
Física da Matéria Condensada
Mestre em Física

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Ministro, José João Henrique. "A study on the synthesis and the optical properties of InP-based quantum dots." Master's thesis, Universidade de Aveiro, 2014. http://hdl.handle.net/10773/16836.

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Mestrado em Química - Química Inorgânica e Materiais
The aim of this work is the study of the optical properties of InP quantum dots (QDs) and the exploration of a new method for the synthesis of InP/CdS core-shell QDs. A multitude of research on colloidal QDs requires detailed knowledge of the relation between optical and structural properties, namely the sizing curve, the intrinsic absorption coefficient and the molar extinction coefficient. In this work, InP QDs were synthesized and structurally and optically characterized. The sizing curve was established from the average QD diameter, obtained by transmission electron microscopy, and the position of the first excitonic absorption peak. The intrinsic absorption coefficient and molar extinction coefficient were determined from quantitative elemental analysis and the absorbance of the nanocrystals at short wavelengths. We found that the intrinsic absorption coefficient is size-independent in this wavelength region and the molar extinction coefficient increases linearly with the QD volume. The focus of our study was then shifted to the fabrication of core-shell QD heterostructures, based on a recently reported method that used a more sustainable and much cheaper phosphorus precursor for the synthesis of high-quality InP/ZnS QDs. Using this procedure, we synthesized highly luminescent InP/CdS QDs and their emission could be tuned in the visible and near-infrared spectral regions. Furthermore, time-resolved photoluminescence measurements were performed on samples of InP/ZnS and InP/CdS QDs. We also report an exploratory study on the mechanism of formation of InP QDs with this new method. A thorough understanding of the reaction mechanism will enable a better control over the synthesis products and is potentially relevant for the fabrication of QDs consisting of other III-V semiconductors (e.g. GaP).

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Li, Li. "Time-Resolved Optical Properties of Colloidal CdSe-CdS/ZnS Core-Multishell Quantum Dots in Bioimaging." Doctoral thesis, KTH, Cellens fysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-160939.

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Semiconductor quantum dots (QDs) have attracted great attention as a novel fluorescent material in the last twenty years. Their superior optical properties such as high brightness and photostability, broad absorption spectrum, narrow and size-tunable emission spectrum, enable them great application in bioimaging. However, the fluorescence from single QDs shows irregular on (bright) and off (dark) switches under continuous irradiation which is known as blinking. QD blinking may lead to information loss in single particle tracking and lower brightness in other bioimaging applications. We studied the blinking behavior and its mechanism by using CdSe-core QDs with different shell thicknesses under different excitations. We observed two types of fluorescence behavior, blinking with apparent on and off states and flickering without distinguishable on and off states under low (1.8 and 3.9 W/cm2) and high (12.1 and 25 W/cm2) excitations, respectively. The transfer of photoexcited electron or hole from CdSe core to the QD surface is responsible for QD blinking under low excitations. And further intraband excitation of photoexcited electron and hole is responsible for QD flickering under high excitations. Ca2+ serves as the second messenger in signal transduction. Monitoring Ca2+ concentration in live cell is a key technique in biological research especially in neuroscience. Most of the commercial Ca2+ indicators are organic dyes which are easy to be photobleached. In order to develop QD-based Ca2+ indicator, we investigated the effect of Ca2+ on the QD fluorescence. We found that the fluorescence intensity, lifetime, and on-state ratio in single QD fluorescence were all decreased by Ca2+ ion. Theoretical study shows that one free Ca2+ could attach stably to the surface of one QD, attracting the photogenerated electron and repel the photogenerated hole, suppressing the radiative recombination between them, and resulting in the reduction of fluorescence intensity, lifetime and on-state ratio. Overexpression of vascular adhesion molecule-1 (VCAM-1) in endothelial cells is a hallmark of inflammation-induced activation of endothelium and may serve as a target for evaluation atherogenesis in early stages. We conjugated VCAM-1 binding peptide to amino-coated QDs and employed the functionalized QDs (VQDs) to specifically image activated endothelial cells. Upon the interaction between VQDs and endothelial cells, a blue-shift of about 30 nm in the QD fluorescence peak was observed. We anticipate that the VQDs and the blue-shift phenomenon could be very useful for VCAM-1 detection in vitro and in vivo. Furthermore, we studied the fluorescence of QDs embedded in a porous alumina membrane which is widely used as biomolecule and cell filter for biological research. We found that the fluorescence spectrum has small peaks superimposed on the principle curve. Theoretical study identifies that this modulation is due to the photonic band structure introduced by the membrane pores. This work could supply information about the interaction between QD fluorescence and porous membrane structure which would be useful when applying QDs to image biomolecules or cells filtered by the porous alumina membrane.

QC 20150306

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Yan, Yueran. "CdTe, CdTe/CdS Core/Shell, and CdTe/CdS/ZnS Core/Shell/Shell Quantum Dots Study." Ohio University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1327614907.

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Donat, Florian. "Microréacteurs photocatalytiques utilisant des oxydes métalliques semi-conducteurs sensibilisés par des Quantum Dots CuInS2/ZnS." Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0085/document.

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La pollution actuelle des effluents hospitaliers par des médicaments, nécessite le développement de nouvelles techniques de traitement, la photocatalyse étant l’une des plus efficaces pour remédier à ce type de pollution. Cependant, les oxydes métalliques utilisés pour la photocatalyse (TiO2, ZnO, …) ne sont activables que sous irradiation UV. L’association de ces oxydes à des Quantum Dots (QDs), crée une hétérojonction qui étend la zone d’activation du photocatalyseur vers les rayonnements visibles et diminue les recombinaisons des porteurs de charges. La première partie de ce travail décrit le développement d’un photocatalyseur activable sous irradiation solaire pour la dégradation du colorant Orange II. Nous avons d’abord caractérisé l’hétérojonction créée entre ZnO et les QDs CuInS2/ZnS (ZCIS) puis étudié leur efficacité photocatalytique, en regardant notamment leurs capacités à générer des espèces réactives de l’oxygène. Dans la seconde partie, nous avons évalué la photodégradation d’un agent anticancéreux, l’Ifosfamide, présent dans les effluents hospitaliers. Pour cela, des réacteurs fermés agités et des microréacteurs ont été utilisés. Dans les deux cas, l’Ifosfamide, ainsi que ses intermédiaires de dégradation, sont photodégradés efficacement par le catalyseur ZnO/ZCIS sous une irradiation solaire de faible intensité (5 mW/cm2). Dans le cas des microréacteurs, le dépôt du catalyseur dans le microcanal a été optimisé et sa stabilité évaluée. Les résultats montrent que le catalyseur ZnO/ZCIS est réutilisable cinq fois sans perte d’activité, témoignant d’une bonne recyclabilité, ce qui en fait un bon candidat pour des applications photocatalytiques
The pollution of hospital effluents by pharmaceutical drugs, requires the development of new treatment techniques. Among these processes, photocatalysis is one of the most efficient one and allows the remediation of this kind of pollution. However, metal oxides used for photocatalysis (TiO2, ZnO, …) can only be activated by UV light. The association of these oxides with quantum dots (QDs) creates an heterojunction, which not only allows to extend the activation spectrum of the photocatalyst to the visible region but also decreases the charge carriers recombinations. The first part of this work describes the development of a catalyst responding to solar light irradiation for the degradation of the Orange II dye. First, we characterized the heterojunction created between ZnO and the CuInS2/ZnS (ZCIS) QDs and evaluated their photocatalytic efficiency. This work was undertaken by evaluating the capacity of the ZnO/ZCIS catalyst to produce reactive oxygen species (ROS). In the second part, we studied the photodegradation of the antineoplastic agent Ifosfamide commonly found in hospital effluents. For this purpose, closed and agitated reactors but also microreactors were used. In both cases, Ifosfamide, and the compounds originating from its degradation, can be fully photodegraded under simulated light of weak intensity (5 mW/cm2) using the ZnO/ZCIS catalyst. In the case of microreactors, the deposition of the catalyst was optimized and its stability evaluated. Results obtained demonstrate that the ZnO/ZCIS catalyst can be reused, at least five times, without significant loss in activity, thus demonstrating its ability to be used in real photocatalytic applications

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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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Keßler, Christian [Verfasser]. "Electrically Driven Single-Photon Sources Based on InP/GaInP Quantum Dots: Characterization and Application in Quantum Communication / Christian Keßler." München : Verlag Dr. Hut, 2015. http://d-nb.info/1077403941/34.

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Keßler, Christian Alexander [Verfasser]. "Electrically Driven Single-Photon Sources Based on InP/GaInP Quantum Dots: Characterization and Application in Quantum Communication / Christian Keßler." München : Verlag Dr. Hut, 2015. http://d-nb.info/1077403941/34.

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Adegoke, Oluwasesan, Tebello Nyokong, and Patricia B. C. Forbes. "Structural and optical properties of alloyed quaternary CdSeTeS core and CdSeTeS/ZnS core–shell quantum dots." Elsevier, 2015. http://hdl.handle.net/10962/d1020248.

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Synthesis of fluorescent alloyed quantum dots (QDs) with unique optical properties suitable for a wide array of chemical, physical and biological applications is of research interest. In this work, highly luminescent and photostable alloyed quaternary CdSeTeS core QDs of two different sizes were fabricated via the organometallic hot-injection synthetic route. Characterization of the nanocrystals were performed using TEM, XRD, UV/vis and fluorescence spectrophotometric techniques. We have demonstrated in this work that the well fabricated alloyed quaternary CdSeTeS core QDs possess unique optical properties that are advantageous over conventional core/shell systems. Formation of the CdSeTeS/ZnS core/shell with the desired optical properties comes with a number of challenges, hence the advantages of the quaternary alloyed core over the core/shell QDs are (i) avoidance of the challenging process of determining the proper shell thickness which can provide the desired optical properties in the core/shell system and (ii) avoidance of the lattice-induced mismatch between the core and the shell material which can either lead to incomplete exciton confinement or dislocation at the core/shell interface.
Original publication is available at http://dx.doi.org/10.1016/j.jallcom.2015.05.083

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Shen, Yaoming. "Photoluminescence spectral study of single CdSe/ZnS Colloidal Nanocrystals in Poly(methyl methacrylate) and Quantum Dots molecules." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2008. http://wwwlib.umi.com/cr/ucsd/fullcit?p3304209.

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Thesis (Ph. D.)--University of California, San Diego, 2008.
Title from first page of PDF file (viewed June 17, 2008). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 91-99).

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Bouwer, James Christopher. "Preparation, theory, and biological applications of highly luminescent CdSe/ZnS quantum dots in optical and electron microscopy /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC IP addresses, 2002. http://wwwlib.umi.com/cr/ucsd/fullcit?p3061628.

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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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Chauviré, Timothée. "Développement de systèmes photochimiques à base de Quantum Dots hydrosolubles de type coeur CdSe et coeur-coquille CdSe/ZnS." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENV039/document.

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L'utilisation de nanoparticules semi-conductrices colloïdales, appelées quantum dots, est nouvelle pour des applications en photocatalyse redox. Ces nano-objets possèdent une forte absorption dans le visible modulable avec leur taille. De plus, la présence d'une couche de ligands peut rendre ces nanostructures éco-compatibles. Dans ce manuscrit de thèse, une étude de la photocatalyse redox avec des nanoparticules cœur CdSe et cœur-coquille CdSe/ZnS a été réalisée dans le visible en solvant aqueux. Les quantum-dots hydrosolubles sont tout d'abord fonctionnalisés par des ligands de type acide aminé. Trois systèmes photochimiques ont ensuite été testés avec les substrats suivants : dérivés d'acides aminés, vanilline et 8oxodG. L'activité photochimique des nanoparticules semi-conductrices a pu être démontrée et évaluée par la détection de produits de réaction. Le mécanisme de transfert de charge photoinduit a par ailleurs été élucidé par des techniques spectroscopiques durant l'irradiation
The use of colloidal semiconductor nanoparticles, called quantum dots, is recent in redox photocatalysis. Those nanostructures exhibit strong and size depending visible absorption properties. The ligand shell on the nanoparticle surface can be furthermore managed to realize green applications. Thus the study of redox photocatalysis with core CdSe nanoparticles and core-shell CdSe/ZnS was carried out with visible light in aqueous solvent. Firstly, we synthetized hydrophilic quantum-dots stabilized by amino acids ligands. Secondly, we perform three different studies of photocatalytic systems with the following substrates : modified amino acids, vanillin and 8oxodG. The nanoparticle's photochemical activity was first demonstrated and evaluated by the detection of photochemical products. The photoinduced charge transfer mechanism was elucidated during irradiation by spectroscopic techniques

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Kristukat, Christian. "High pressure study of the electronic structure of self-assembled InAs/GaAs and InP/GaP quantum dots." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=97877339X.

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Raevskaya, Alexandra, Vladimir Lesnyak, Danny Haubold, Volodymyr Dzhagan, Oleksandr Stroyuk, Nikolai Gaponik, Dietrich R. T. Zahn, and Alexander Eychmüller. "A Fine Size Selection of Brightly Luminescent Water-Soluble Ag-In-S and Ag-In-S/ZnS Quantum Dots." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-226647.

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A size-selected series of water-soluble luminescent Ag–In–S (AIS) and core/shell AIS/ZnS QDs were produced by a precipitation technique. Up to 10–11 fractions of size-selected AIS (AIS/ZnS) QDs emitting in a broad color range from deep-red to bluish-green were isolated with the photoluminescence (PL) quantum yield reaching 47% for intermediate fractions. The size of the isolated AIS (AIS/ZnS) QDs varied from ~2 nm to ~3.5 nm at a roughly constant chemical compo- sition of the particles throughout the fractions as shown by the X-ray photoelectron spectroscopy. The decrease of the mean AIS QD size in consecutive fractions was accompanied by an increase of the structural QD imperfection/disorder as deduced from a notable Urbach absorption “tail” below the fundamental absorption edge. The Urbach increased from 90–100 meV for the largest QDs up to 350 meV for the smallest QDs, indicating a broadening of the distribution of sub-bandgap states. Both the Urbach energy and the PL bandwidth of the size-selected AIS QDs increased with QD size reduction from 3–4 nm to ~2 nm and a distinct correlation was observed between these parameters. A study of size-selected AIS and AIS/ZnS QDs by UV photoelectron spectroscopy on Au and FTO substrates revealed their valence band level EVB at ~6.6 eV (on Au) and ~7 eV (on FTO) and pinned to the Fermi level of conductive substrates resulting in a masking of any possible size- dependence of the valence band edge position.

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Krasselt, Cornelius, Jörg Schuster, and Borczyskowski Christian von. "Photoinduced hole trapping in single semiconductor quantum dots at specific sites at silicon oxide interfaces." Universitätsbibliothek Chemnitz, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-122745.

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Blinking dynamics of CdSe/ZnS semiconductor quantum dots (QD) are characterized by (truncated) power law distributions exhibiting a wide dynamic range in probability densities and time scales both for off- and on-times. QDs were immobilized on silicon oxide surfaces with varying grades of hydroxylation and silanol group densities, respectively. While the off-time distributions remain unaffected by changing the surface properties of the silicon oxide, a deviation from the power law dependence is observed in the case of on-times. This deviation can be described by a superimposed single exponential function and depends critically on the local silanol group density. Furthermore, QDs in close proximity to silanol groups exhibit both high average photoluminescence intensities and large on-time fractions. The effect is attributed to an interaction between the QDs and the silanol groups which creates new or deepens already existing hole trap states within the ZnS shell. This interpretation is consistent with the trapping model introduced by Verberk et al. (R. Verberk, A. M. van Oijen and M. Orrit, Phys. Rev. B, 2002, 66, 233202).

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Junior, João Batista Souza. "Síntese de nanoestruturas core/shell de Co/Au magnetoplasmônica e pontos quânticos de CdSe/ZnS." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/75/75134/tde-28072017-170738/.

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Nanomateriais apresentam propriedades ajustáveis pelo seu tamanho e forma, como o fenômeno de superparamagnetismo em nanopartículas magnéticas ou o confinamento quântico dos portadores de carga em pontos quânticos (quantum dots). Assim, a síntese de nanopartículas esféricas monodispersas torna-se um fator extremamente importante, haja visto que tais propriedades podem ser ajustáveis para diferentes aplicações na área de tecnologia e biomedicina. Nanopartículas magnéticas e quantum dots podem ser apontados como promissores materiais para diagnóstico e terapia de neoplasias (câncer), e o desenvolvimento desses sistemas busca, atualmente, intensificar a magnetização e a eficiência de emissão, respectivamente, relativo às propriedades magnéticas e ópticas, além de outros requisitos. Neste trabalho, nanopartículas esféricas de cobalto metálico foram sintetizadas com diâmetro médio de 5,3 nm e desvio padrão de 0,4 nm, distribuição de tamanhos lognormal. A equação de Langevin modificada pelo modelo de partículas interagentes foi utilizada no ajuste da curva de magnetização M(H) para obtenção do diâmetro magnético médio e desvio padrão, 4,7 nm e 1,0 nm, respectivamente. Comparando os dois diâmetros, encontra-se uma camada morta de magnetização de aproximadamente 3,0 Å a qual, praticamente, não contribui para a magnetização da amostra, sendo a magnetização de saturação de 125 emu g-1. Nanoestruturas core/shell de Co/Au apresentaram a propriedade de ressonância plamon de superfície, uma propriedade adicional também desejada para aplicações biomédicas, sendo este sistema denominado magnetoplasmônico. Quantum dots de CdSe foram sintetizados como elevado controle de tamanho e forma. Utilizando rotas de síntese diferentes dos clássicos procedimentos denominados TOP-TOPO, e dióxido de selênio como precursor, estudos mostraram que na presença de um agente redutor no meio de reação e do solvente 1-octadeceno, as amostras apresentaram melhores propriedades óticas. A estrutura cristalina das amostras de CdSe corresponde à formação da fase blenda de zinco, diferentemente das sínteses TOP-TOPO que levam à formação da fase hexagonal wurtzita. A cinética de crescimento dos quantum dots de CdSe também foram avaliadas através de alíquotas retiras com o tempo de reação mostrando um crescimento exponencial do diâmetro das partículas, como previsto pelas teorias de nucleação e crescimento. Estudos por microscopia de fluorescência mostraram que os quantum dots apresentaram o comportamento de intermitência de fluorescência relatado na literatura como um dos fatores que levam a uma diminuição do rendimento quântico de fluorescência. Nanoestruturas core/shell de CdSe/ZnS foram obtidas com elevado controle da espessura da camada de recobrimento e a intensificação das propriedades de fotoluminescência foram mostradas. Os objetivos do trabalho foram alcançados com sucesso, onde foi possível observar a estabilização e a intensificação da magnetização da fase de cobalto metálico, pouco relatado na literatura. Ainda, foi possível conferir maior estabilidade química, versatilidade de funcionalização da superfície e uma segunda propriedade de ressonância plasmônica com o recobrimento com ouro, sem grande prejuízo da propriedade magnética. Em relação aos sistemas ópticos, os semicondutores de CdSe foram obtidos por nova rota de síntese com expressivo controle de tamanho e forma, recobertos com ZnS intensificando as propriedades ópticas do sistema.
Nanomaterials properties are size- and shape-controlled, such as the superparamagnetism phenomenon of magnetic nanoparticles or the quantum confinement of charge carriers of quantum dots. Therefore, synthesis of monodisperse spherical nanoparticles became extremely important over the past few deacades, since nanoparticles can be used for plenty of applications in technology and biomedicine. Magnetic nanoparticles and quantum dots are promising materials for diagnosis and therapy of cancer. Spherical nanoparticles of metallic cobalt were synthesized with mean diameter of 5,3 nm and standard deviation of 0,4 nm, lognormal distribution. A modified Langevin equation using the interacting superparamagnetic model was used to fit magnetization curves obtaining the mean magnetic diameter and standard deviation, 4,7 nm and 1,0 nm, respectively. The difference between these two diameters was assigned to the magnetic dead layer (∼3.0 Å), which does not contribute to the sample magnetization, being the saturation magnetization of cobalt nanoparticles around 125 emu g-1. Co/Au core/shell nanostructures were synthesized and the surface plasmon ressonance property was observed, an additional property also desired for biomedical applications, being the Co/Au core/shell system called magnetoplasmonic. CdSe quantum dots were synthesized with high size- and shape-controlled. Using different synthetic routes from the classic TOP-TOPO synthesis, and selenium dioxide as a precursor, the results show that and reducing agent is necessary and 1-octadecene solvent leads to better optical properties. CdSe samples showed a zinc blend (cubic phase) crystal structure, different from TOP-TOPO syntheses that leads to wurtzite structure (hexagonal phase). The growth kinetics of CdSe particles were also evaluated through aliquots from reaction showing exponential growth of particles diameter, as predicted on the theory of nucleation and growth. Fluorescence microscopy studies showed that quantum dots exhibited fluorescence intermittence behavior already reported in the literature as one fo the reasons for the quantum yield decrease. CdSe/ZnS core/shell nanostructures were obtained with high control of the coating layer thickness and the increase of the photoluminescence properties were shown.

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Oluwole, David O., Jonathan Britton, Philani Mashazi, and Tebello Nyokong. "Synthesis and photophysical properties of nanocomposites of aluminum tetrasulfonated phthalocyanine covalently linked to glutathione capped CdTe/CdS/ZnS quantum dots." Elsevier, 2015. http://hdl.handle.net/10962/d1020291.

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Aluminum tetrasulfonated phthalocyanine (ClAlTSPc) was covalently linked with different sizes of glutathione capped CdTe/CdS/ZnS quantum dots (QDs). The photophysical and Förster resonance energy transfer (FRET) properties of the nanoconjugates were investigated. The CdTe/CdS/ZnS(6.3) nanocomposite showed the highest enhancement in its photophysical properties while (CdTe/CdS/ZnS(3.2) nanocomposite showed the least. Highest FRET efficiency was observed in the linked CdTe/CdS/ZnS(6.3) nanocomposites at 93%. Hence, the combination of CdTe/CdS/ZnS with ClAlTSPc exhibited excellent photophysical properties.
Original publication is available at http://dx.doi.org/10.1016/j.synthmet.2015.04.015

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Adegoke, Oluwasesan, Tebello Nyokong, and Patricia B. C. Forbes. "Deposition of CdS, CdS/ZnSe and CdS/ZnSe/ZnS shells around CdSeTe alloyed core quantum dots: effects on optical properties." Wiley, 2015. http://hdl.handle.net/10962/d1020342.

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In this work, we synthesized water-soluble L-cysteine-capped alloyed CdSeTe core quantum dots (QDs) and investigated the structural and optical properties of deposition of each of CdS, CdS/ZnSe and CdS/ZnSe/ZnS shell layers. Photophysical results showed that the overcoating of a CdS shell around the alloyed CdSeTe core [quantum yield (QY) = 8.4%] resulted in effective confinement of the radiative exciton with an improved QY value of 93.5%. Subsequent deposition of a ZnSe shell around the CdSeTe/CdS surface decreased the QY value to 24.7%, but an increase in the QY value of up to 49.5% was observed when a ZnS shell was overcoated around the CdSeTe/CdS/ZnSe surface. QDs with shell layers showed improved stability relative to the core. Data obtained from time-resolved fluorescence measurements provided useful insight into variations in the photophysical properties of the QDs upon the formation of each shell layer. Our study suggests that the formation of CdSeTe/CdS core/shell QDs meets the requirements of quality QDs in terms of high photoluminescence QY and stability, hence further deposition of additional shells are not necessary in improving the optical properties of the core/shell QDs. Copyright © 2015 John Wiley & Sons, Ltd.
Original publication is available at http://dx.doi.org/10.1002/bio.3013

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Bump, Buddy J. "Synthesis and Characterization of CdSe/ZnS Core/Shell Quantum Dot Sensitized PCPDTBT-P3HT:PCBM Organic Photovoltaics." DigitalCommons@CalPoly, 2014. https://digitalcommons.calpoly.edu/theses/1309.

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Durable, cheap, and lightweight polymer based solar cells are needed, if simply to meet the demand for decentralized electrical power production in traditionally “off-grid” areas. Using a blend of Poly(3-hexylthiophene-2,5-diyl) (P3HT), Phenyl-C61-butyric acid methyl ester (PCBM), and the low band-gap polymer Poly[2,6-(4,4-bis-(2- ethylhexyl)-4H-cyclopenta [2,1-b;3,4-b′]dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT), we have fabricated devices with a wide spectral response and 3% power conversion efficiency in AM 1.5 conditions; however, this thin film system exhibits only 0.43 optical density at 500 nm. To improve the performance of this polymer blend photovoltaic, we aim to increase absorption by adding CdSe(ZnS) core (shell) quantum dots. Four groups of devices are fabricated: a control group with an active polymer layer of 16 mg/mL P3HT, 16 mg/mL PCBM, and 4 mg/mL PCPDTBT; and three groups with dispersed quantum dots at 4 mg/ml, 1 mg/mL, and 0.25 mg/mL. The (CdSe)ZnS quantum dots are coated with octadecylamine ligands and have a peak absorbance at 560 nm and peak emission at 577 nm. The active layer was dissolved in chlorobenzene solvent and spun on glass substrates, patterned with indium tin oxide. The devices were then annealed for fifteen minutes at 110° C, 140° C, and 170° C. Current-voltage characteristic curves v and optical density data were taken before and after the anneal step. Finally, surface characterization was conducted with atomic force microscopy and electrostatic force microscopy. When compared to the control, the sensitized devices exhibited increased absorption and depressed electrical performance with increasing quantum dot loading. The surface morphology, both electrical and physical, showed deviation from the typical values and patterns shown by the control that increased with quantum dot loading. When the degrading electrical characteristics, increasing optical absorbance, and surface changes, are considered together, it becomes likely that the quantum dots interact in a significant manner with the morphology of the P3HT phase, which leads to an overall decrease in performance.

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Salverson, Lynsey Alexandra-McLennan. "An Engineering Approach Investigating the Uptake and Phytotoxicity of One Type of Engineered Nanoparticle (CdSe/ZnS Quantum Dots) by Solanum lycopersicum." Digital Commons at Loyola Marymount University and Loyola Law School, 2012. https://digitalcommons.lmu.edu/etd/42.

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The novel and extraordinary physiochemical properties of engineered nanoparticles (ENPs) are certain; however, their unique characteristics raise growing concerns regarding potentially adverse effects on biological and ecological systems. It is becoming increasingly evident that, before the full potential of nanotechnology can be realized, standardized characterization of ENP behavior, fate, and effects on the ecosystem are essential to ensure the safe manufacturing and use of ENP products. Otherwise, the promise of such extraordinary advancements may find itself limited to applications such as electronics and sporting equipment, industries in which ENPs currently reside. The current toxicity profile of engineered nanomaterials is not only preliminary, but highly variable amongst researchers. Consequently, there is great need for the development of a highly organized, efficient, and precise approach to assess the hazardous potential ENPs may pose, while addressing the safety concerns surrounding and limiting nanotechnology. In response to such concerns, the present study took an engineering approach, in an otherwise traditionally viewed discipline, to assess the potential impact of one type of engineered nanoparticle, water-soluble (MUA) CdSe/ZnS- quantum dots (QDs), on tomato (Solanum lycopersicum) seedlings, by implementing a full factorial design of experiment (FDOE), in an effort to identify which factors, and their interactions, have a significant (p ≤ 0.05) effect on root and shoot elongation, and if any observed effects are a result of particle uptake, evaluated via fluorescence microscopy imaging. By implementing factorial experimental design methodologies, not only are we efficiently identifying the factors that affect phytotoxicity, we are providing, for the first time to our knowledge, the first scientific data to report the significant interaction effects between the factors responsible for ENP toxicity. (MUA) CdSe/ZnS quantum dots had a negative influence on root and shoot lengths of tomato seedlings exposed for 3 days, as well as those exposed for 6 days. The observed influence depended on QD concentration and exposure time, as statistical analyses found QD concentration, exposure time, and the concentration-exposure time interaction significantly (p ≤ 0.05) affected root and shoot lengths of tomato seedlings. Additionally, to minimize the observed phytotoxicity effects (i.e., to maximize tomato root lengths), our results suggest that exposure of tomato seeds to low QD concentration levels (125 mg/L) for short periods of time (maximum of 3 days) to yield maximum root lengths of approximately 2.21 cm, that is – minimal phytotoxicity effects.

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Bufon, Carlos César Bof\'. "Propriedades eletrônicas de pontos quânticos de InAs1-xPx sobre GaAs." Universidade de São Paulo, 2003. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-09032009-152432/.

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O crescimento de pontos quânticos a partir do descasamento dos parâmetros de rede tem sido alvo de intensos estudos nos últimos dez anos. Conhecer as propriedades eletrônicas destes materiais é chave para a engenharia de sistemas quânticos. O objetivo deste trabalho é estudar as propriedades eletrônicas de pontos quânticos (QD) de InAS1-x Px enterrados em GaAs, através de Espectroscopia de Capacitância (CV). A Espectroscopia CV é uma técnica que permite determinar os estados eletrônicos e a distribuição de cargas do sistema. As amostras de InAS1-x Px foram crescidas por MOCVD (Low-Pressure Metalorganic Chemical Vapor Deposition) sobre um substrato de GaAs:Cr (001). A estrutura das amostras é do tipo MIS (Metal-Isolante-Semicondutor) com um contato traseiro do tipo n. As medidas de capacitância foram feitas a 4,2 K para diferentes valores de freqüência e campo magnético. A partir da dispersão dos estados confinados com o campo magnético aplicado perpendicular ao plano dos pontos quânticos, pode-se determinar, ◚, a freqüência natural do sistema. A partir de ◚, determinou-se 𕖮, o comprimento característico da função de onda. A concordância entre os valores de 𕖮 com as dimensões laterais dos pontos quânticos obtidos por microscopia eletrônica de transmissão (TEM) é boa. Finalmente, através das medidas de espectroscopia CV pode-se separar os efeitos de confinamento lateral e vertical, permitindo um melhor entendimento dos espectros de fotoluminescência (PL), assim como os detalhes da forma dos QD obtidos por TEM.
The growth of quantum dots in the Stranski-Krastranov mode has been subject of intense investigation in the last decade. Knowing the electronics properties of these materials is key for performing quantum systems engineering. The objective of this work is to study the quantum dots (QD) electronic properties of the InAS1-x Px embedded in GaAs. The study was done by capacitance spectroscopy (CV), which is an experimental tool that allows the evaluation of the electronic states and the charge distribution of a given quantum device. The samples of InAS1-x Px were grown by Low-Pressure Metalorganic Chemical Vapor Deposition on GaAs:Cr (001) substrates. They consist of metalinsulator-semiconductor structures with an n-type back contact. The measurements were performed at 4.2 K for different values of frequencies and magnetic field. From the confined states dispersion as a function of the applied magnetic field, perpendicular to the QD plane, the system natural frequency, ◚, was determined. From the ◚, we could determine the wave function characteristic length, 𕖮. The concordance between the 𕖮, values and the lateral sizes obtained by Transmission Electronic Microscopy (TEM) is good. Finally, by CV spectroscopy we could separate the lateral and vertical confinement effects, leading to a more complete understanding of the Photoluminescence (PL) spectra, as well as the details of the QD shape obtained by TEM.

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Akanuma, Y., I. Yamakawa, Y. Sakuma, T. Usuki, and A. Nakamura. "Sharp Interfacial Structure of InAs/InP Quantum Dots Grown by a Double-Cap Method: A Cross-Sectional Scanning Tunneling Microscopy Study." American Institite of Physics, 2007. http://hdl.handle.net/2237/12037.

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Clift, Martin James David. "Quantum dots : an investigation into how differing surface characteristics affect their interaction with macrophages in vitro." Thesis, Edinburgh Napier University, 2009. http://researchrepository.napier.ac.uk/Output/2557.

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Quantum dots (QDs) are potentially advantageous tools for both diagnostics and therapeutics due to their light emitting characteristics. The impact of QDs on biological systems however, is not fully understood. The aim of this project therefore, was to investigate the interaction of a series of different surface modifies QDs with macrophages and their subsequent toxicity. CdTe/CdSe (core), ZnS (shell) QDs with either an organic, COOH or NH2 polyethylene glycol (PEG) surface coatings were used. Fluorescent COOH polystyrene beads (PBs) at (Ø) 20nm and 200nm were also studied. J774.A1 murine ‘macrophage-like' cells were treated for two hours with QDs (40nM) of PBs ($50μg.ml^{-1}$) in the presence of 10% FCS prior to assessment of cellular uptake via confocal microscopy and flow cytometry. COOH and $NH_{2}$ (PEG) QDs, as well as 20nm and 200nm PBs entered macrophages within 30 minutes, and were found to locate within endosomes, lysosomes and the mitochondria. T.E.M. also illustrated particles, including organic QDs, to be present inside J774.A1 cells within membrane- bound vesicles at two hours. Organic QDs were unable to be visualised via fixed cell confocal microscopy. Live cell confocal microscopy (without 10% FCS) did suggest however, that organic QDs entered cells in low quantities up to 30 minutes, after which fluorescence declined. Particle toxicity was determined over 48 hours via the MTT, LDH and GSH assays, as well as via assessment of their potential to produce the pro-inflammatory cytokine (TNF-α) and effect cytosolic $Ca^{2+}$ signalling in the J774.A1 cells. Organic QDs were found to be highly toxic at all time points and concentrations used. Both COOH and $NH_{2 }$ (PEG) QDs induced significant (p<0.0001) cytotoxicity (MTT and LDH assays) at 80nM after 48 hours, as well as significant (p<0.01) GSH depletion over 24 hours at all doses, as well as increasing the level of cytosolic $Ca^{2+}$ at 40nM when assessed over 30 minutes. Organic and NH2 (PEG) QDs were found to significantly increase TNF-α production after 24 hours at 80nM. The findings of this study demonstrate that QDs differ in their uptake by macrophages according to their surface coating, with the organic surface coated QDs being the most toxic. At sub-lethal concentrations, in the presence of 10% FCS, the COOH and $NH_{2}$ (PEG) QDs are taken up resulting in GSH depletion and modulated $Ca^{2+}$ signalling, with $NH_{2}$ (PEG) QDs and organic QDs only eliciting limited TNF-α production. Interestingly however, despite these observations, QD surface coating does not affect the intracellular fate of these NPs, with all of the different surface coated QDs observed to be present in endosomes, lysosomes and the mitochondria within J774.A1 macrophage cells. Therefore, in conclusion, the surface coating of QDs plays a significant role in their interaction with macrophages, their uptake and their subsequent toxicity.

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MONTEIRO, Thatyara Oliveira. "Sensores fotoeletroquímicos explorando o tetracianoetileneto de lítio (LiTCNE) na determinação do antioxidante terc-butil hidroquinona (TBHQ)." Universidade Federal do Maranhão, 2017. https://tedebc.ufma.br/jspui/handle/tede/tede/1949.

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Two novel and pioneering photoelectrochemical sensors were developed for determination of tert-butyl hydroquinone (TBHQ) in biodiesel and edible oil samples. The former based on composite formed by TiO2 nanoparticles and lithium tetracyanethylene (LiTCNE), and the last based on the sensitization of CdSe/ZnS quantum dots with LiTCNE. In both cases, indium tin oxide (ITO) was used as the work electrode surface. The LiTCNE/TiO2/ITO sensor showed a TBHQ photocurrent about 28-fold higher than the TiO2 sensor. The same was observed for the CdSe/ZnS/LiTCNE/ITO sensor, which presented a photocurrent for TBHQ about 13-fold higher than that presented by the electrode modified with CdSe/ZnS. Both developed sensors showed lower resistance to charge transfer than their non-sensitized components. They also demonstrated high selectivity to TBHQ, with high photocurrent for this compound in comparison to photocurrent responses to other phenolic antioxidants. The experimental conditions optimized for both sensors were: 0.1 mol L-1 of phosphate buffer solution pH 7.0 and applied potential to the working electrode of 450 mV, for the LiTCNE/TiO2/ITO sensor, and 0.1 mol L-1 of phosphate buffer solution pH 6.0, and potential of 400 mV for the CdSe/ZnS/LiTCNE/ITO sensor. In these conditions, the sensors presented a linear range of TBHQ response between 0.4 and 500 μmol L-1 for LiTCNE/TiO2/ITO sensor and between 0.6 and 250 μmol L-1 for the CdSe/ZnS/LiTCNE/ITO sensor, with limits of detection of 0.10 and 0.21 μmol L-1, respectively. The LiTCNE/TiO2/ITO sensor was applied in biodiesel samples for determination of TBHQ using standard addition method, showing recovery values between 96.8 and 98.2%. The CdSe/ZnS/LiTCNE/ITO sensor was applied in edible oil samples to detect TBHQ using an external calibration method, with recovery values between 98.25 and 99.83%. The photoelectrochemical sensors were successfully used to determine the TBHQ antioxidant in real samples of biodiesel and vegetable oil.
Dois novos e pioneiros sensores fotoeletroquímicos foram desenvolvidos para determinação de tert-butil hidroquinona (TBHQ) em amostras de biodiesel e de óleo comestível. O primeiro baseado no compósito formado por nanopartículas de TiO2 e tetracianoetileneto de lítio (LiTCNE), e o segundo baseado na sensibilização de quantum dots CdSe/ZnS com o LiTCNE. Em ambos os casos utilizou-se como eletrodo de trabalho o óxido de índio e estanho (ITO) como superfície eletródica. O sensor à base de LiTCNE/TiO2/ITO apresentou uma fotocorrente para o TBHQ cerca de 28 vezes mais elevada que o sensor à base de TiO2. O mesmo foi observado para o sensor à base de CdSe/ZnS/LiTCNE/ITO, que apresentou fotocorrente para o TBHQ cerca de 13 vezes maior do que à apresentada pelo eletrodo modificado com CdSe/ZnS. Ambos os sensores desenvolvidos apresentaram baixa resistência à transferência de carga em comparação a seus componentes não sensibilizados. Também demonstraram grande seletividade ao TBHQ, com alta fotocorrente para esse composto em comparação às respostas de fotocorrente para outros antioxidantes fenólicos. As condições experimentais otimizadas para ambos os sensores desenvolvidos foram, respectivamente: 0,1 mol L-1 de solução tampão fosfato pH 7,0 e potencial aplicado ao eletrodo de trabalho de 450 mV, para o sensor LiTCNE/TiO2/ITO, e 0,1 mol L-1 de solução tampão fosfato pH 6,0, e potencial de 400 mV, para o sensor CdSe/ZnS/LiTCNE/ITO. Nessas condições, os sensores apresentaram faixa linear de resposta de TBHQ entre 0,4 a 500 µmol L-1 para sensor LiTCNE/TiO2/ITO e entre 0,6 a 250 µmol L-1 para o sensor CdSe/ZnS/LiTCNE/ITO, apresentando limites de detecção de 0,10 e 0,21 µmol L-1 , respectivamente. O sensor LiTCNE/TiO2/ITO foi aplicado em amostras de biodiesel para determinação de TBHQ usando método de adição de padrão, mostrando valores de recuperação entre 96,8 e 98,2%. Já o sensor CdSe/ZnS/LiTCNE/ITO foi aplicado em amostras de óleo comestível para detecção de TBHQ usando método de calibração externa, com valores de recuperação entre 98,25 e 99,83%. Os sensores fotoeletroquímicos foram empregados com sucesso para determinação de antioxidante TBHQ em amostras reais de biodiesel e óleo vegetal.

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Bouchonville, Nicolas. "Nouveau nano-matériau hybride – nanocristaux de CdSe/ZnS couplés à la bactériorhodopsine – pour des applications en optoélectronique et en biologie : élaboration et caractérisations structurale et optique." Thesis, Reims, 2011. http://www.theses.fr/2011REIMS017/document.

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Ce travail est consacré à l’élaboration et à la caractérisation d’un nouveau matériau hybride présentant des propriétés de transfert d’énergie, à base de la protéine photochromique bactériorhodopsine (bR) acceptrice d’énergie et de boites quantiques (QDs) de CdSe/ZnS fluorescentes donneuses d’énergie. Le but est d’essayer d’améliorer et d’utiliser les propriétés photochromiques et photochimiques de la bR en utilisant un transfert d’énergie par résonancede Förster (FRET) qui peut exister avec des QDs semiconductrices. Ce nouveau matériau hybride pourrait servir dans divers domaines, tels que des commutateurs optiques ou lescellules photovoltaïques.Les propriétés physiques d’un tel composé et son efficacité dépendant fortement de sa structure, ce travail à consister à élaborer le complexe bR/QD et à le caractériser par microscopie à force atomique (AFM) et par spectrométries optiques (fluorescence,absorption) afin de mettre en évidence un éventuel effet FRET entre bR/QDs. Nous avons montré qu’en modifiant la charge de surface des QDs nous pouvions optimiser l’efficacité duFRET. Cet effet provient d’une modification des forces électrostatiques entraînant un arrangement des QDs différent à la surface des membranes en fonction de leur charge de surface. En renforçant la liaison bR/QD à l’aide de biotine et de streptavidine, nous avons atteint une efficacité maximale de FRET de 80 %.Lors de nombreuses expériences que nous avons menées, nous avons montré parAFM et dichroïsme circulaire que la présence de QDs accélère fortement le processus de monomérisation de la bR par du détergent ce qui pourrait avoir des applications en biologie
In this work, we built and characterized a new hybrid material with energy transfer properties made from photochromic protein Bacteriorhodopsin (bR) which is the energy acceptor and CdSe/ZnS fluorescent quantum dots (QDs) which are the energy donor. Our aim was to improve the photochromic and photo-physical bR properties by using a Förster resonance energy transfer (FRET) which should exist in presence of semiconductor QDs. This new hybrid material should have applications in many fields such as optical switching or photovoltaics.Since optical properties and efficiency of such a material are highly dependent of its structure, our work was to develop and characterize bR/QD complex by atomic force microscopy (AFM) and optical spectrometries (fluorescence, absorption) in order to demonstrate FRET between bR and QDs. By tuning QDs surface charges, we proved that we were able to optimize FRET, by optimization of the electrostatic interactions between bR and QDs. This effect was due to a better organization of QDs on the membrane surface when interactions were optimized. We also showed that when QD and bR are linked by biotin streptavidin link they revealed the maximum FRET efficiency of 80 %.During all these experiments, we showed that QDs could induce a quicker detergent monomerization of bR. This is supported by AFM images and circular dichroïsm measurements. This effect should find applications in biology

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Godoy, Marcio Peron Franco de. "Propriedades de pontos quânticos de InP/GaAs." [s.n.], 2006. http://repositorio.unicamp.br/jspui/handle/REPOSIP/277715.

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Orientador: Fernando Iikawa
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
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Resumo: Neste trabalho estudamos as propriedade estruturais e ópticas de pontos quânticos auto-organizados de InP crescidos sobre o substrato de GaAs. Esta estrutura apresenta o alinhamento de bandas tipo-II na interface, confinando o elétron no ponto quântico, enquanto o buraco mantém-se na barreira, próximo à interface devido à interação coulombiana atrativa. As amostras foram crescidas por epitaxia de feixe químico (CBE) no modo Stranskii-Krastanov. Os pontos quânticos apresentam raio médio de 25 nm e grande dispersão de altura (1-5 nm) e ocorre a relaxação parcial do parâmetro de rede, chegando a 2 %, em pontos quânticos superficiais. Do ponto de vista de propriedades ópticas, a fotoluminescência de pontos quânticos superficiais exibe uma eficiente emissão óptica, devido a baixa velocidade de recombinação dos estados superficiais do InP, e reflete a densidade e distribuição bimodal de tamanhos. Além disso, sua emissão óptica em função da intensidade de excitação exibe comportamento diverso em comparação com pontos quânticos cobertos com uma camada de GaAs. Em pontos quânticos cobertos, determinamos a energia de ativação térmica, que varia de 6 a 8 meV, e é associada à energia de ligação do éxciton ou energia de ionização do buraco. O decaimento temporal da luminescência de pontos quânticos é de 1,2 ns, um tempo relativamente curto para um ponto quântico tipo-II. A análise das propriedades magneto-ópticas em pontos quânticos individuais, inédita em QDs tipo-II, permitiu verificar que o fator-g do éxciton é praticamente constante, independentemente do tamanho dos QDs, devido ao fato dos buracos estarem levemente ligados. Por fim, mostramos a versatilidade do sistema acoplando-o a um poço quântico de InGaAs. Este acoplamento introduz mudanças na superposição das funções de onda do par elétron-buraco que permitem a manipulação do tempo de decaimento da luminescência e da energia de ligação excitônica
Abstract: We have investigated structural and optical properties of InP self-assembled quantum dots grown on GaAs substrate. This system presents a type-II band lineup where only electrons are confined in the InP quantum dots. The InP/GaAs quantum dots were grown by chemical beam epitaxy in the Stranskii-Krastanov mode. Our quantum dots present a mean radius of 25 nm and large height dispersion, 1-5 nm, and a partial relieve of the strain up to 2 % is observed. The photoluminescence spectra of surface quantum dots show an efficient optical emission, which is attributed to the low surface recombination velocity in InP. We observed a bimodal dispersion of the dots size distribution, giving rise to two distinct emission bands. A remarkable result is the relatively large blue shift of the emission band from uncapped samples as compared to those for capped dots. In capped quantum dots, we obtained the thermal activation energy, from 6 to 8 meV, which is associated to the exciton binding energy or hole ionization energy. The observed luminescence decay time is about 1.2 ns, relatively short decay time for type II system. We investigated magneto-optical properties using single-dot spectroscopy. The values of the exciton g factor obtained for a large number of single InP/GaAs dots are mainly constant independent of the emission energy and, therefore, of the quantum dot size. The result is attributed to the weak confinement of the holes in InP/GaAs QDs. We have also investigated structures where InP quantum dots are coupled to a InGaAs quantum well. This system permits the manipulation of the wave function overlap between electron-hole in order to control the optical emission decay time and exciton binding energy
Doutorado
Física
Doutor em Ciências

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Ugur, Katmis Asli [Verfasser], W. Ted [Akademischer Betreuer] Masselink, Mete [Akademischer Betreuer] Atat¨ure, and Henning [Akademischer Betreuer] Riechert. "Growth and characterization of InP/In0.48Ga0.52P quantum dots optimized for single-photon emission / Asli Ugur Katmis. Gutachter: W. Ted Masselink ; Mete Atat¨ure ; Henning Riechert." Berlin : Humboldt Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2013. http://d-nb.info/1032944218/34.

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Grimes, Logan. "DEVELOPENT OF A PHOSPHOLIPID ENCAPSULATION PROCESS FOR QUANTUM DOTS TO BE USED IN BIOLOGIC APPLICATIONS." DigitalCommons@CalPoly, 2014. https://digitalcommons.calpoly.edu/theses/1237.

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The American Cancer Society predicts that 1,665,540 people will be diagnosed with cancer, and 585,720 people will die from cancer in 2014. One of the most common types of cancer in the United States is skin cancer. Melanoma alone is predicted to account for 10,000 of the cancer related deaths in 2014. As a highly mobile and aggressive form of cancer, melanoma is difficult to fight once it has metastasized through the body. Early detection in such varieties of cancer is critical in improving survival rates in afflicted patients. Present methods of detection rely on visual examination of suspicious regions of tissue via various forms of biopsies. Accurate assessment of cancerous cells via this method are subjective, and often unreliable in the early stages of cancer formation when only few cancer cells are forming. With fewer cancer cells, it is less likely that a cancer cell will appear in a biopsied tissue. This leads to a lower detection rate, even when cancer is present. This lack of detection when cancer is in fact present is referred to as a false negative. False negatives can have a highly detrimental effect on treating the cancer as soon as possible. More accurate methods of detecting cancer in early stages, in a nonsubjective form would alleviate these problems. A proposed alternative to visual examination of biopsied legions is to utilize fluorescent nanocrystalline biomarker constructs to directly attach to the abnormal markers found on cancerous tissues. Quantum dots (QDs) are hydrophobic nanoscale crystals composed of semiconducting materials which fluoresce when exposed to specific wavelengths of radiation, most commonly in the form of an ultraviolet light source. The QD constructs generated were composed of cadmium-selenium (CdSe) cores encapsulated with zinc-sulfide (ZnS) shells. These QDs were then encapsulated with phospholipids in an effort to create a hydrophilic particle which could interact with polar fluids as found within the human body. The goal of this thesis is to develop a method for the solubilization, encapsulation, and initial functionalization of CdSe/ZnS QDs. The first stage of this thesis focused on the generation of CdSe/ZnS QDs and the fluorescence differences between unshelled and shelled QDs. The second stage focused on utilizing the shelled QDs to generate hydrophilic constructs by utilizing phospholipids to bind with the QDs. Analysis via spectroscopy was performed in an effort to characterize the difference in QDs both prior to and after the encapsulation process. The method generated provides insight on fluorescence trends and the encapsulation of QDs in polar substances. Future research focusing on the repeatability of the process, introducing the QD constructs to a biological material, and eventual interaction with cancer cells are the next steps in generating a new technique to target and reveal skin cancer cells in the earliest possible stages without using a biopsy.

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Dupuy, Emmanuel. "Croissance et spectroscopie de boîtes quantiques diluées d'InAs/InP(001) pour des applications nanophotoniques à 1,55 µm." Phd thesis, Ecole Centrale de Lyon, 2009. http://tel.archives-ouvertes.fr/tel-00616499.

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Ce travail porte sur la croissance épitaxiale et la caractérisation optique de boîtes quantiques d'InAs/InP(001) en faible densité en vue de la réalisation de nouveaux composants nanophotoniques émettant à 1,55 µm. Les propriétés structurales et optiques des îlots ont été corrélés pour différents paramètres de croissance d'un système d'épitaxie par jet moléculaire à sources solides. Nos résultats soulignent l'influence des reconstructions de surface d'InAs sur la forme des îlots. Des boîtes, plutôt que des bâtonnets allongés généralement observés,peuvent être directement formées dans des conditions de croissance adéquates. Une transition de forme de bâtonnets vers des boîtes est également démontrée par des traitements postcroissance sous arsenic. Les faibles densités de boîtes sont obtenues pour des faibles épaisseurs d'InAs déposées. Leur émission est facilement contrôlée à 1,55 µm par une procédure d'encapsulation spécifique appelé " double cap ". Quelques propriétés des boîtes individuelles d'InAs/InP sont ensuite évaluées. Les études de micro-photoluminescence révèlent des pics d'émission très fins et distincts autour de 1,55 µm confirmant les propriétés" quasi-atomiques " de ces boîtes uniques. Enfin, nous proposons pour la première fois une méthode à haute résolution spatiale qui permet d'étudier le transport de charges autour d'une boîte unique grâce à une technique de cathodoluminescence à basse tension d'accélération.Une mesure directe de la longueur de diffusion des porteurs avant capture dans une boîte a été obtenue. Ces résultats ouvrent de nouvelles perspectives quant à l'intégration de ces boîtes uniques dans des microcavités optiques pour la réalisation de sources de lumières quantiques à 1,55 µm.

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Felle, Martin Connor Patrick. "Telecom wavelength quantum devices." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/270019.

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Semiconductor quantum dots (QDs) are well established as sub-Poissonian sources of entangled photon pairs. To improve the utility of a QD light source, it would be advantageous to extend their emission further into the near infrared, into the low absorption wavelength windows utilised in long-haul optical telecommunication. Initial experiments succeeded in interfering O-band (1260—1360 nm) photons from an InAs/GaAs QD with dissimilar photons from a laser, an important mechanism for quantum teleportation. Interference visibilities as high as 60 ± 6 % were recorded, surpassing the 50 % threshold imposed by classical electrodynamics. Later, polarisation-entanglement of a similar QD was observed, with pairs of telecom-wavelength photons from the radiative cascade of the biexciton state exhibiting fidelities of 92.0 ± 0.2 % to the Bell state. Subsequently, an O-band telecom-wavelength quantum relay was realised. Again using an InAs/GaAs QD device, this represents the first implementation of a sub-Poissonian telecom-wavelength quantum relay, to the best knowledge of the author. The relay proved capable of implementing the famous four-state BB84 protocol, with a mean teleportation fidelity as high as 94.5 ± 2.2 %, which would contribute 0.385 secure bits per teleported qubit. After characterisation by way of quantum process tomography, the performance of the relay was also evaluated to be capable of implementing a six-state QKD protocol. In an effort to further extend the emitted light from a QD into the telecom C-band (1530—1565 nm), alternative material systems were investigated. InAs QDs on a substrate of InP were shown to emit much more readily in the fibre-telecom O- and C-bands than their InAs/GaAs counterparts, largely due to the reduced lattice mismatch between the QD and substrate for InAs/InP (~3 %) compared to InAs/GaAs (~7 %). Additionally, to minimize the fine structure splitting (FSS) of the exciton level, which deteriorates the observed polarisation-entanglement, a new mode of dot growth was investigated. Known as droplet epitaxy (D-E), QDs grown in this mode showed a fourfold reduction in the FSS compared to dots grown in the Stranski-Krastanow mode. This improvement would allow observation of polarisation-entanglement in the telecom C-band. In subsequent work performed by colleagues at the Toshiba Cambridge Research Labs, these D-E QDs were embedded in a p-i-n doped optical cavity, processed with electrical contacts, and found to emit entangled pairs of photons under electrical excitation. The work of this thesis provides considerable technological advances to the field of entangled-light sources, that in the near future may allow for deterministic quantum repeaters operating at megahertz rates, and in the further future could facilitate the distribution of coherent multipartite states across a distributed quantum network.

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Tzeng, Jia-Yu, and 曾嘉羽. "Device characterization of InP/ZnS colloidal dots on InGaAs Quantum Dots Solar cells." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/x4zr65.

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碩士
國立中興大學
光電工程研究所
107
We use colloidal InP/ZnS quantum dots coating on InGaAs QD solar cells. The power conversion efficiency of the solar cell is improved by the light absorption of the upper InP/ZnS colloidal quantum dots and the secondary light absorption of the InGaAs quantum dots in the solar cells. The EQE measurement of the solar cells without InP/ZnS quantum dots shows a conversion peak at about 700 nm. In order to increase the light absorption of the solar cells, we use 750 nm quantum dots coating on the solar cells, and grow gold nanoparticles above the solar cells to increase the uniformity of colloidal quantum dots dispersion. First, the samples were deposited by atomic deposition (Atomic Layer Deposition, ALD) with 50 nm HfO2 and 50 nm Al2O3 as the heat collecting layer, then use a thermal evaporation to coat a thin layer of Au and use different annealing time to form gold nanoparticles. And then we take a picture of SEM to confirm the formation of the gold nanoparticles. The effect of gold nanoparticles forming is most significant when the annealing temperature is 450℃ and the annealing time is 90 seconds. Finally, samples proceed to the high-concentration I-V measurement and external quantum efficiency (EQE) measurement. The power conversion efficiency of C536 is enhanced from 8.2% to 9.8% by coating the gold nanoparticles and 15% InP/ZnS colloidal quantum dots.

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Chen, To-Yuan, and 陳鐸元. "Bio-oriented interface of InP/ZnS quantum dots through octenyl succinic anhydride modification." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/76793a.

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碩士
中原大學
生物醫學工程研究所
102
Recently, the unique optical properties of quantum dot gradually replace the traditional organic fluorescent dyes and fluorescent proteins in the field of biomedical technology. It has become important tools in related biomedical areas, such as cell targeting, cell tracking. But the material for the synthesis of traditional quantum dot contains heavy metal, such as Cd2+、Pb2+, which will cause serious toxicity for both biological and environmental pollution. Scientists have investigated the alternative materials to replace heavy metal ions and thereby increase its potential in biomedical applications. This study focused on engineering hydrophobic InP/ZnS quantum dots and on the use of octenyl succinic anhydride (OSA) toward bioconjugation. Using a simple, fast microemulsion method not only can modify the hydrophobic InP/ZnS Quantum dots to be hydrophilic ones but also transfer versatile hydrophobic nanoparticles to aqueous phase successfully. However, the buffer layer structure conposed by the octenyl succinic anhydride was unsteady, it was prone to result in disintegration in diluted condition. Then we further showed that using polyethylene glycol monomethyl ether as the surface modifier can increase the stability of InP/ZnS hydrophilic structure. Subsequently, using DSPE-PEG-X (X: -amine, -carboxyl, -methoxy) can further functionalized the surface which can be verified by gel electrophoresis. In this study, we found that the use of octenyl succinic anhydride can offer superior hydrophilic modification of InP/ZnS quantum dots and that the use of polyethylene glycol monomethyl ether can increase stability of buffer layer to improve the stability after phase transfer. We envision the coating method will expand the nanomaterials applying in biomecial research.

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Hung, Shih-Ting, and 洪詩婷. "Fabrication of High Luminous Efficacy InP/ZnS Core-Shell Quantum dots for Application to Light-Emitting Diodes." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/98448177402680271758.

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碩士
國立臺灣師範大學
化學系
104
Semiconductor quantum dots (QDs), of which particle sizes are in the nanometer scale, have very unusual size-controllable optical properties. However, the well-developed Cadmium-based QDs are restricted in further application due to its acute toxicity, making it necessary to find the alternative materials. Among all the possible alternatives, indium phosphide(InP) shows promising in both optical and electric properties, which can be later introduced into application. The environment-friendly InP quantum dots (QDs) have been synthesized in this paper by the conventional hot injection method using a non-toxic precursor of P(TMS)3. To enhance the material durability, the InP would be covered by ZnS, forming the InP/ZnS core-shell structure. The carefully controlled syntheses of a series of InP/ZnS QDs were designed by varying the core-growth temperature and the concentrations of precursor. The environment-friendly InP/ZnS is set to have further application in electronic devices. Therefore, heat resistance and surface smoothness were also examined in our work. In the test of heat resistant, InP/ZnS quantum dots were annealed under different temperature and time, which shows possible to the light-emitting diodes (LEDs) converters. Over all, using fatty-acid as the surfactant, the InP/ZnS QDs have revealed the potential for the fabrication of solid-state lighting.

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