To see the other types of publications on this topic, follow the link: CdSe/CdS.
Dissertations / Theses on the topic 'CdSe/CdS'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'CdSe/CdS.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Manceau, Mathieu. "Single CdSe/CdS dot-in-rods fluorescence properties." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066362/document.
Full textAbstract:
Les nanocristaux colloïdaux synthétisés par voie chimique sont des sources prometteuses de lumière non-Classique à température ambiante. Ce travail est consacré à l'étude des propriétés optiques d'un type particulier de nanocristaux colloïdaux, appelé coeur-Bâtonnet, dans lequel un noyau de Seleniure de Cadmium (CdSe) sphérique est entouré d'une coquille de Sulfure de Cadmium (CdS) de forme cylindrique. En étudiant des particules de type coeur-Bâtonnet à température ambiante avec un microscope confocal, une caractérisation complète des propriétés optiques de ces émetteurs est réalisée. Nous étudions d'abord la statistique de clignotement de ces émetteurs. Nous montrons que les émetteurs coeur-Bâtonnet avec des coquilles épaisses se caractérisent par un clignotement réduit sur des échelles de temps courts, inférieurs à quelques millisecondes. Ensuite, une caractérisation détaillée de la statistique de photons des émetteurs coeur-Bâtonnet tenant compte du phénomène de clignotement est réalisée. La polarisation de l'émission est également étudié. Nous montrons que la polarisation d'émission peut être controlée en changeant la géométrie de la structure.Enfin, nous présentons également des expériences de couplage de ces émetteurs avec des dispositifs photoniques. Nous montrons la possibilité d'exciter un émetteur coeur-Bâtonnet en utilisant un nanofil d'oxyde de Zinc (ZnO). Nous montrons aussi que nous sommes en mesure d'orienter efficacement des nanoémetteurs uniques en utilisant la formation controlée de défauts dans des cristaux liquidesWet-Chemically synthesized colloidal nanocrystals are promising room temperature non-Classical light sources. This work is devoted to the study of the optical properties of a particular type of colloidal nanocrystals, called dot-In-Rods, in which a spherical Cadmium Selenide (CdSe) core is surrounded by a rod-Like Cadmium Sulfide (CdS) shell. By studying single dot-In-Rods at room-Temperature with a confocal microscope, a complete characterization of the optical, and especially quantum optical, properties of dot-In-Rods is provided for several geometrical parameters. We first study the blinking statistics of such emitters. We show that dot-In-Rods with thick shells are characterized by a reduced blinking that happens on fast timescales, typically on millisecond timescales. We then go on with a detailed characterization of the photon statistics of dot-In-Rods. A complete description of the photon statistics taking into account the blinking process is realized. The polarization of the emission is also investigated. We show that the emission polarization can be tuned by engineering the geometry. Finally, we also present experiments where we couple dot-In-Rods with various photonic devices. We demonstrate the possibility of excitation of a single emitter using a Zinc Oxyde (ZnO) nanowire. Using defects in liquid crystals, we also show that we are able to efficiently orientate single nanoemitters
2
Müller, Josef. "Elektrische Manipulation der Lichtemission von einzelnen CdSe/CdS Nanostäbchen." Diss., lmu, 2005. http://nbn-resolving.de/urn:nbn:de:bvb:19-51297.
Full text
3
Müller, Josef. "Elektrische Manipulation der Lichtemission von einzelnen CdSe-, CdS-Nanostäbchen." [S.l.] : [s.n.], 2005. http://edoc.ub.uni-muenchen.de/archive/00005129.
Full text
4
Coropceanu, Igor. "Colloidal CdSe/CdS nanostructures : synthesis, optical characterization and applications." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/107563.
Full textAbstract:
Thesis: Ph. D. in Physical Chemistry, Massachusetts Institute of Technology, Department of Chemistry, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references.
The focus of this thesis is the study of CdSe/CdS nanostructures, from their fundamental properties to their integration in practical devices. This material system has proven to be remarkably robust both as a platform for studying physics in confined semiconductors, as well as for enabling various optical and optoelectronic applications. In this thesis, we will discuss our recent efforts to improve the synthesis of CdSe/CdS structures, to better understand their optical properties and to use them to create highly performing luminescent solar concentrators. In the first part of the thesis we will discuss our efforts to improve the synthesis of CdSe/CdS nanostructures of different dimensionalities. In particular, we discuss the synthesis of CdSe/CdS quantum dots and seeded CdSe/CdS nanorods that have a near unity photoluminescence quantum yield and complete energy transfer from the shell to the core. Next, we discuss the fabrication of luminescent solar concentrators using these materials and the optical characterization of these devices. Finally, in the last section, we use a combination of synthesis, spectroscopy, and modeling to gain better insight into the photoluminescence lineshape of CdSe/CdS quantum dots.
by Igor Coropceanu.
Ph. D. in Physical Chemistry
5
Hill, Lawrence J. "Synthesis and Dipolar Assembly of Cobalt-Tipped CdSe@CdS Nanorods." Diss., The University of Arizona, 2014. http://hdl.handle.net/10150/332684.
Full textAbstract:
This dissertation contains four chapters with advances relevant to the fields of nanoparticle synthesis and nanoparticle self-assembly: a review of nanoparticle self-assembly, or “colloidal polymers”; dumbbell heterostructured nanorod synthesis; dipolar matchstick heterostructured nanorod synthesis; and self-assembly of dipolar matchsticks to form colloidal polymers. These chapters are followed by appendices containing supporting data for chapters two through four. The first chapter is a review summarizing current research involving the 1-D assembly of nanocrystals to form “colloidal polymers.” One of the major goals of materials chemistry is to synthesize hierarchical materials with precise controlled particle ordering covering all length scales of interest (termed, the “bottom up” approach). Recent advances in the synthesis of inorganic colloids have enabled the construction of complex morphologies for particles in the range of 1 – 100 nm. The next level of structural order is to control the structure of assemblies formed from these materials. Linear nanoparticle assemblies are particularly challenging to achieve due to the need to impart functionality to colloids such that (typically) only two sites are active per particle. An emerging idea in the literature which addresses this challenge is to consider linear assemblies of inorganic nanoparticles as colloidal analogs to traditional polymers. This conceptual framework has enabled the formation of linear assemblies having controlled composition (to form segmented and statistical copolymers), architecture (linear, branched, cyclic), and degree of polymerization (chain length). However, this emerging field of synthesizing colloidal polymers has not yet been reviewed in terms of methods to control fundamental polymer parameters. Therefore, linear nanoparticle assembly is reviewed in chapter 1 by applying concepts from traditional polymer science to nanoparticle assembly. The emphasis of chapter 1 is on controlling degree of polymerization, architecture, and composition for colloidal polymers, and seminal examples are highlighted which control these parameters. The second chapter is centered on a novel methodology to install ferromagnetic cobalt domains onto core@shell, “CdSe@CdS” nanorods. While the structures synthesized in this work were novel, the key advance from this work was the development of a methodology to separate nanorod activation from deposition of ferromagnetic cobalt domains onto semiconductor nanorods. As synthesized CdSe@CdS nanorods are passivated with strongly binding phosphonic acid ligands, and these ligands prevent direct deposition of many materials (such as cobalt). Synthetic methods must therefore modify nanorod surfaces prior to deposition of additional nanoparticle domains (tips). Previous synthetic methods for the deposition of magnetic domains onto nanorod termini typically combined activation of nanorod termini and metal deposition into a single synthetic step. While these previous reports were successful in achieving tipped nanorods, the coupling of these two reactions required matching the kinetics of nanorod activation and decomposition/reduction of metal precursors in order to achieve the desired heterostructure morphology. However, the presence of ligands used for nanorod activation can also affect the rate of metal precursor decomposition/reduction and the propensity of the metal to form free nanoparticles through homogeneous nucleation. Thus, simultaneous nanorod activation and metal deposition hinders modification of these syntheses to obtain differing heterostructured morphologies. In the work presented in chapter 2, we chemically activate nanorod termini towards cobalt deposition in a separate chemical step from deposition of metallic cobalt nanoparticle domains. First, reductive platinum deposition conditions were utilized to activate nanorod termini towards the deposition of cobalt domains, which were deposited in a subsequent reaction step. Then, the kinetics of nanorod activation during platinum deposition were tracked, and the platinum-tipped nanorod morphologies were correlated with the results of subsequent cobalt deposition reactions. Ultimately, controlled placement of cobalt domains onto one or both nanorod termini was demonstrated based on the degree of activation during platinum deposition. Cobalt nanoparticle tips were then selectively oxidized to form CoₓOy-tipped nanorods, which were a novel class of p-n type nanomaterials achieved over a total of five synthetic steps. Relevant supporting details for the synthesis of these dumbbell tipped nanorods are provided in Appendix A. The third chapter describes the synthesis of CoNP-tipped nanorods with a single, strongly dipolar, ferromagnetic CoNP-tip per nanorod. The key synthetic advance was the ability to activate a single terminus per nanorod without activation of lateral nanorod facets, which was vital in achieving these larger, dipolar, cobalt tips (rather than lateral decoration of cobalt onto nanorod lateral facets). These dipolar “matchstick” CoNP-tipped nanorods then spontaneously formed linear assemblies carrying nanorod side chains as pendant functionality. Activation of CdSe@CdS nanorods was found to occur through the deposition of small (< 2 nm) PtNP-tips which were not readily observable by standard characterization techniques. The finding that small (< 2 nm) PtNP-tips altered nanorod reactivity towards cobalt deposition emphasized the effect of subtle changes to nanorod surface chemistry. Relevant supporting details for the synthesis of these dipolar matchstick tipped nanorods are provided in appendix B. The fourth chapter is centered on the self-assembly of dipolar matchstick cobalt-tipped nanorods to form colloidal (co)polymers reminiscent of traditional bottlebrush polymers, with controlled composition and phase behavior on carbon surfaces. Similar to earlier findings in traditional polymer science, nanorod side chain length was found to significantly impact surface assembly of these colloidal analogs of bottlebrush copolymers, which provided a useful parameter for affecting surface wetting and phase behavior of nanoparticle thin films. This work was also the first demonstration of colloidal copolymers from the dipolar assembly of magnetic nanoparticles, where both segmented and statistical copolymer compositions were achieved. We then demonstrated, for the first time, that a colloidal copolymer with segmented composition can form a mesoscopic phase separated morphology which is similar to that observed for traditional block copolymers. This key advance opens the possibility of controlling structural ordering over still longer length scales by the development of methods to control phase separated morphologies in a manner similar to traditional block copolymers. Relevant supporting details for the synthesis and assembly of these colloidal bottlebrush polymers are provided in appendix C.
6
Furlong, Mark Justin. "Structural and photoelectrochemical properties of CdSe and CdS thin films." Thesis, University of Bath, 1996. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.481609.
Full text
7
Давиденко, М. О. "Енергетичний спектр та кінетика електронних збуджень в наночастинках CdSe та CdS." Diss. of Candidate of Physical and Mathematical Sciences, КНУТШ, 2011.
Find full text
8
Xu, Yang. "Synthesis and Characterization of Silica Coated CdSe/CdS Core/Shell Quantum Dots." Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/29974.
Full textAbstract:
A great deal of interest has been dawn on the colloidal chemistry based semiconductor nanocrysallites, also known as quantum dots (QDs). Because of the strong quantum confinement, quantum dots have unique size-dependent optical properties, which are much more superior to the conventional organic fluorescence materials. In addition, strong chemical resistant makes inorganic semiconductor QDs ideal candidate for next-generation of bio-labels and drug delivery vehicles. This report presents a user friendly approach to synthesize high quality biocompatible CdSe QDs in aqueous solution. Size of the dots can be controlled by adjusting the temperature, pH of the solution, and ratio of the precursors. A thin CdS layer was grown on CdSe QDs, forming a CdSe/CdS core/shell structure, to improve the photoluminescence. In order to use these QDs in-vivo, a more chemically robust coating, silica, was grown on the core/shell structure QD. The optical properties of the QDs were characterized by absorption and photoluminescence spectra. X-ray diffraction and transmission electron microscopy were conducted to verify the QDs composition and structure.Ph. D.
9
Halsall, Matthew Peter. "Growth and spectroscopic studies of CdS/CdSe single layers and superlattice structures." Thesis, University of Hull, 1990. http://hydra.hull.ac.uk/resources/hull:3893.
Full text
10
Dzhagan, V., A. G. Milekhin, M. Ya Valakh, S. Pedetti, M. Tessier, B. Dubertret, and D. R. T. Zahn. "Morphology-induced phonon spectra of CdSe/CdS nanoplatelets: core/shell vs. core–crown." Universitätsbibliothek Chemnitz, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-219936.
Full textAbstract:
Recently developed two-dimensional colloidal semiconductor nanocrystals, or nanoplatelets (NPLs), extend the palette of solution-processable free-standing 2D nanomaterials of high performance. Growing CdSe and CdS parts subsequently in either side-by-side or stacked manner results in core–crown or core/shell structures, respectively. Both kinds of heterogeneous NPLs find efficient applications and represent interesting materials to study the electronic and lattice excitations and interaction between them under strong one-directional confinement. Here, we investigated by Raman and infrared spectroscopy the phonon spectra and electron–phonon coupling in CdSe/CdS core/shell and core–crown NPLs. A number of distinct spectral features of the two NPL morphologies are observed, which are further modified by tuning the laser excitation energy Eexc between in- and off-resonant conditions. The general difference is the larger number of phonon modes in core/shell NPLs and their spectral shifts with increasing shell thickness, as well as with Eexc. This behaviour is explained by strong mutual influence of the core and shell and formation of combined phonon modes. In the core–crown structure, the CdSe and CdS modes preserve more independent behaviour with only interface modes forming the phonon overtones with phonons of the coreDieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich
11
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.
Full textAbstract:
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 fiablesTemperature 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
12
Mallek-Zouari, Ikbel. "Propriétés quantiques de la fluorescence de nanocristaux CdSe/CdS déposés sur des nanostructures métalliques." Phd thesis, Université de Versailles-Saint Quentin en Yvelines, 2011. http://tel.archives-ouvertes.fr/tel-00606995.
Full textAbstract:
Nous présentons les principales propriétés quantiques de fluorescence de nanocristaux de CdSe/CdS individuels à température ambiante. Nous montrons la quasi-suppression de scintillement et l'allongement des durées de vie radiative de ces nanocristaux à la coquille épaisse et de leur rendement quantique. Nous prouvons expérimentalement, par microscopie confocale en champ lointain, que l'interaction d'un nanocristal avec des nanostructures métalliques, réduit sa durée de vie radiative et modifie les efficacités des processus radiatifs et non-radiatifs. Nous montrons que, le couplage dépend bien de la position du nanocristal et que pour certains nanocristaux une large fraction des plasmons est diffractée par la structure spatiale de la couche. Nous obtenons des facteurs de Purcell très importants. Enfin, nous expliquons la relation entre les états d'émission et la compétition entre processus Auger et radiatifs.
13
Poirot, David. "Développement de marqueurs photoluminescents à base de nanocristaux de CdSe/CdS pour l'anti-contrefaçon." Thesis, Toulouse, INSA, 2017. http://www.theses.fr/2017ISAT0035.
Full textAbstract:
Ces travaux de thèse s'inscrivent dans le cadre d'un transfert vers l’industrie d’une technologie de marquage à base de nanoparticules photoluminescentes, développée au sein de l’équipe Nanotech du LPCNO et destinée au domaine de l’anti-contrefaçon. Ces travaux ont porté sur la réalisation de marqueurs micrométriques constitués d’assemblées de nanocristaux de CdSe/CdS présentant une émission de photoluminescence dans le visible avec un rendement quantique élevé et stable. Ces nanocristaux sont déposés de façon dirigée sur des surfaces par nanoxérographie: cette technique consiste à injecter des charges électrostatiques dans un matériau électret afin de former des motifs micrométriques servant ensuite de pièges électrostatiques pour assembler, en surface de l’électret, des nano-objets chargés et/ou polarisables depuis leur suspension colloïdale. Afin de permettre une production à échelle industrielle, l’injection de charges est assurée par la technique de « microcontact printing électrique » permettant la réalisation d’un grand nombre de motifs chargés en parallèle, grâce à un timbre microstructuré et conducteur. Des études portant sur la fabrication de ces timbres et sur l’injection parallèle de charges par leur intermédiaire ont permis de fiabiliser le procédé en termes de répétabilité et d’homogénéité d’injection. Des assemblages denses et multicouches de nanocristaux ont été réalisés grâce à la mise en place d’une stratégie d’assemblage visant à favoriser et maximiser les forces diélectrophorétiques. La photoluminescence émise par ces assemblées de nanocristaux est ainsi suffisante pour être observée à l’œil ou par la caméra d’un smartphone lors d’une excitation de faible puissance à 450 nm. Un protocole de transfert des marqueurs depuis leur substrat de fabrication vers un substrat de destination a été développé permettant ensuite de valider une intégration non-destructive au sein de documents officielsThis work is part of a transfer to industry of a tagging technology based on photoluminescent nanoparticles, developed within the Nanotech team of the LPCNO and intended for the field of anti-counterfeiting. This work was focused on the realization of micrometric tags made of assemblies of CdSe/CdS nanocrystals exhibiting an emission of photoluminescence in the visible range with a high and stable quantum yield. These nanocrystals are selectively deposited on surfaces by nanoxerography: this technique involves injecting electrostatic charges into an electret material to form micrometric patterns which then serve as electrostatic traps to assemble, on the surface of the electret, charged and/or polarizable nano-objects from their colloidal suspension. In order to scale-up the tag production on an industrial level, the charge injection step is ensured by the “electrical microcontact printing” technique, allowing to charge a large number of patterns in parallel, thanks to a microstructured and conductive patch. Studies on the manufacture of these stamps, and the injection of charges through them, have led to make the process more reliable in terms of repeatability and homogeneity of injection of charges. Dense and multilayer nanocrystal assemblies have been realized through the implementation of an assembly strategy aimed at promoting and maximizing the dielectrophoretic forces. The photoluminescence emitted by these assemblies of nanocrystals is thereby sufficient to be observed by the eye or the camera of a smartphone for a low-power optical excitation at 450 nm. A transfer protocol of the photoluminescent tags from their manufacturing substrate to a destination substrate has been developed which then allowed the validation of a non-destructive integration within official documents
14
DIB, MOHAMED. "Structure electronique au voisinage de la bande interdite des nanocristaux de cdse et cds." Paris 7, 1999. http://www.theses.fr/1999PA077073.
Full textAbstract:
Les nanocristaux (ncs) de semiconducteurs sont des boites quantiques dans lesquelles les porteurs de charge sont confines dans les trois directions spatiales. Leur structure electronique est une fonction de leur taille. Une des difficultes experimentales de l'etude des ncs est liee a la distribution des tailles des ncs dans l'echantillon. Cette distribution est responsable de l'elargissement inhomogene des bandes dans les spectres d'absorption et de luminescence. Pour s'affranchir de cette difficulte, nous avons utilise des techniques spectroscopiques qui permettent l'observation des proprietes optiques des ncs d'une taille selectionnee dans la distribution, telles que l'excitation selective et la detection selective de la luminescence. Nous avons montre que l'etat responsable de la luminescence des ncs de cdse et de cds de rayons compris entre 15 et 35 angstroms, est un etat optiquement interdit par spin et que l'interaction d'echange electron-trou, tres faible dans les materiaux massifs, augmente de deux ordres de grandeur dans les petits ncs (de 15 angstroms de rayon). Nous avons egalement mis en evidence le fait que l'ecart en energie observe experimentalement entre l'absorption et la luminescence est caracteristique du materiau etudie. Il est interprete par la prise en compte simultanee de l'interaction d'echange electron-trou d'une part et du couplage spin-orbite, dans les ncs de cds ou de l'anisotropie du champ cristallin de la structure cristalline wurtzite dans les ncs de cdse, d'autre part.
15
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.
Full textAbstract:
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
16
Canneson, Damien. "Modification de l'émission d'un nanocristal semi-conducteur individuel de CdSe-CdS à l'aide de nanostructures métalliques." Phd thesis, Université de Versailles-Saint Quentin en Yvelines, 2013. http://tel.archives-ouvertes.fr/tel-00911775.
Full textAbstract:
Les nanocristaux semi-conducteurs sont des objets de dimensions nanométriques aux niveaux d'énergie quantifiés. Grâce à leurs propriétés de fluorescence, ils trouvent des applications dans des domaines aussi variés que la biologie, l'opto-électronique ou l'optique quantique. Pour toutes ces applications, un contrôle de leurs propriétés d'émission est primordial. Dans ce cadre, après une étude fine de leurs propriétés d'émission à température cryogénique, nous nous sommes intéressés à leur couplage avec les plasmons de couches d'or désordonnées. Nous montrons alors la possibilité de supprimer efficacement les fluctuations d'intensité d'émission, d'accélérer drastiquement l'émission de photons et de créer des cascades bi-excitoniques.
17
Santos, José Augusto Lucena dos. "Síntese e caracterização de pontos quânticos de CdS, CdSe E CdTe para aplicação em células solares." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2016. http://hdl.handle.net/10183/143887.
Full textAbstract:
Este trabalho foi desenvolvido em duas etapas: i) síntese, caracterização e aplicação de pontos quânticos de CdS, CdSe e CdTe em células solares. ii) modificação da superfície dos pontos quânticos de CdSe através de troca de ligante, seguida de caracterização e aplicação em células solares. Os pontos quânticos foram sintetizados utilizando acetatos de cádmio, selênio, telúrio e enxofre como precursores e ácido oleico como agente de estabilização. Na segunda etapa o ácido oleico foi substituído por ligantes com maior afinidade eletrônica pelos sítios de Cd2+: ácido 3-mercaptopropiônico, 4-ácido-mercaptobenzóico e ácido 11-mercaptoundecanóico. As amostras foram caracterizadas por UV-Vis, fluorescência, microscopia eletrônica de transmissão, difratometria de raios-X e voltametria cíclica. Adicionalmente, testes de solubilidade, análises de TGA e de RMN foram realizadas para confirmar a troca de ligante. Através dos resultados, verificou-se que todos os pontos quânticos sintetizados são adequados para sensibilização de TiO2 em dispositivos fotovoltaicos. No entanto, os pontos quânticos de CdSe e CdTe apresentaram fatores que evidenciam maior confinamento quântico, sendo que a maior estabilidade do éxciton foi obtida para o CdSe. Através das análises de RMN foi possível verificar que não existe apenas uma confirguração espacial preferencial para a adsorção do ligante sobre a superfície deste ponto quântico enquanto que curvas de corrente versus potencial e de eficiência de conversão de fóton incidente mostraram que a eficiência do dispositivo é fracamente dependente do ligante. Contudo, a troca de ligantes favorece a solubilidade em solventes com diferentes polaridades, inclusive água, o que amplia as possibilidades de aplicação dos pontos quânticos sintetizados neste trabalho.This work was developed in two stages: i) synthesis, characterization and application of CdS, CdSe and CdTe quantum dots to assemble solar cells, ii) surface modification, characterization and application of CdSe quantum dots to assemble solar cells. The quantum dots were synthesized by using cadmium acetate, Se, S or Te as precursors and oleic acid as stabilizing agent. In the second stage the oleic acid capping layer was replaced by other ligands with higher electron affinity to Cd2+: 3-mercaptopropionic acid, 4-mercaptobenzoic acid and 11-mercaptoundecanoic acid. The samples were characterized by UV-Vis, fluorescence, transmission electron microscopy, x-ray diffractometry and cyclic voltammetry. Additionally, solubility tests, TGA analysis and NMR were performed to evaluate the CdSe surface modification. The results showed that all quantum dots synthesized are adequate to sensitize TiO2 in photovoltaic devices. However, CdSe and CdTe quantum dots presented better quantum confinement and the exciton generated in CdSe presented the higher stability. NMR analysis provided information about the non-preferential orientation for adsorption of the ligands on the CdSe surface, meanwhile measurements of current vs. potential and incident photon current efficiency showed a weak dependence of photovoltaic device efficiency with the nature of the ligand. On the other side, the surface modification favors the solubility in solvents with different polarizabilities, including water, widening the range for applications of the quantum dots synthesized in this work.
18
Carvalho, Andre Luiz Braga de. "Síntese e caracterização de nanopartículas semicondutoras com nanoestruturas tipo núcleolcasca CdS/CdSe obtidas por rota coloidal." Universidade Federal de Minas Gerais, 2012. http://hdl.handle.net/1843/BUOS-96CFW5.
Full textAbstract:
Quantum Dots (QDs) are semiconductor nanoparticles with quantum confinement properties. The synthesis of these nanocrystals via aqueous route, when compared to other synthesis methods, is reproducible, less toxic and capable of forming biocompatible materials. Poly (vinyl alcohol), PVA, has significant importance in the stabilization and control of nucleation and growth of cadmium sulfide QDs (CdS), as it is a semicrystalline polymer which is soluble in water with good interfacial characteristics. Some aspects have been studied as the influence of temperature and variation of the molar ratio of cadmium and sulfur in the synthesis of CdS QDs core. The morphological characterization was performed by transmission electron microscopy (TEM), the analysis of the size of QDs was made by the program ImageJ. A spectroscopic characterization by ultraviolet visible (UV-Vis) was also carried out to monitor the formation and stability of quantum dots of CdS core and CdS/CdSe setting in core/shell. Finally a spectroscopic characterization by photoluminescence (PL) was
performed to monitor the emission spectra of CdS QDs core and CdS/CdSe core/shell. It was then possible to synthesize CdS QDs with average core diameters of 3,4 nm in the QDs and CdS / CdSe core / shell with an average diameter of 3,9 to 4,4 nm, stable colloidal solution.Quantum Dots (QDs) são nanopartículas semicondutoras com propriedades de confinamento quântico. A síntese via rota aquosa destes nanocristais, quando comparada a outros métodos de síntese, é reprodutível, menos tóxica e capaz de formar materiais biocompatíveis. O poli (álcool vinílico), PVA, tem importância significativa na estabilização e no controle da nucleação e do crescimento dos QDs de sulfetos de cádmio (CdS), núcleo e sulfeto de cádmio passivados com uma casca de seleneto de cádmio (CdS/CdSe), além de ser um dos poucos polímeros semicristalinos solúveis em água com boas características interfaciais. Alguns aspectos foram estudados como a influência da temperatura e da variação da razão molar de cádmio e enxofre na síntese dos QDs de CdS núcleo. A caracterização morfológica foi realizada por microscopia eletrônica de transmissão (TEM), em seguida, uma análise de tamanho dos QDs foi feita pelo programa ImageJ. Foi realizada também uma caracterização espectroscópica por ultravioleta visível (UV-Vis) para monitorar a formação e a estabilidade coloidal dos pontos quânticos de CdS núcleo e CdS/CdSe em configuração núcleo/casca. Por fim uma caracterização espectroscópica por fotoluminescência (PL) foi realizada para monitorar os espectros de emissão dos QDs de CdS núcleo e CdS/CdSe núcleo/casca. Com isso foi possível sintetizar QDs de CdS núcleo com média no diâmetros de 3,4 nm e QDs de CdS/CdSe núcleo/casca com média do diâmetro de 3,9 a 4,4 nm, estáveis em solução coloidal.
19
Espinobarro, Velazquez Daniel. "Photoluminescent properties of novel colloidal quantum dots." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/photoluminescent-properties-of-novel-colloidal-quantum-dots(a524a8c2-6304-4ce7-9bbe-d07d7205a53a).html.
Full textAbstract:
In this thesis type II colloidal quantum dots (CQDs) with zinc blende crystal structure were investigated. The optical properties were characterized by steady state absorption and photoluminescence (PL) spectroscopy for all the samples, and the PL quantum yield was measured for selected samples by using both absolute and relative methods. Exciton dynamics and interactions were investigated by time-resolved PL (TRPL).The exciton-exciton interaction energy for CdSe, CdSe/CdTe and CdSe/CdTe/CdS CQDs was investigated using TRPL spectroscopy, an established method. The TRPL results were compared with previous results from ultrafast transient absorption (TA) measurements and theoretical predictions. The discrepancies between the TRPL and TA results and the theoretical calculations suggest that TRPL data has been misinterpreted in the literature. The single exciton recombination dynamics for CdSe, CdSe/CdTe and CdSe/CdTe/CdS CQDs were investigated. The effects of non-radiative recombination were identified from the PL transients by using a theoretically-calculated radiative lifetime as a fitting parameter. The combined rate of the non-radiative processes thus found was consistent with the localisation of holes into shallow traps by an Auger-mediated process. A rate equation analysis also showed how shallow trapping can give rise to the tri-exponential PL dynamics observed experimentally. Chloride passivation of CdTe CQDs resulted in a near-complete suppression of surface traps, producing a significant enhancement of the optical properties. PL quantum yield (PLQY) and PL lifetime in particular benefit from the chloride treatment. The radiative recombination rate that now could be extracted from PL transients for chloride treated samples was used to calculate the non-radiative recombination rate for the untreated samples. In addition, a study of the effects of air exposure on the PL, observed for both treated and untreated samples was undertaken and revealed the importance of the influence of the dielectric environment surrounding the traps states on recombination dynamics.
20
Pavlopoulos, Nicholas George, and Nicholas George Pavlopoulos. "Designing Selectivity in Metal-Semiconductor Nanocrystals: Synthesis, Characterization, and Self-Assembly." Diss., The University of Arizona, 2017. http://hdl.handle.net/10150/626149.
Full textAbstract:
This dissertation contains six chapters detailing recent advances that have been made in the synthesis and characterization of metal-semiconductor hybrid nanocrystals (HNCs), and the applications of these materials. Primarily focused on the synthesis of well-defined II-VI semiconductor nanorod (NR) and tetrapod (TP) based constructs of interest for photocatalytic and solar energy applications, the research described herein discusses progress towards the realization of key design rules for the synthesis of functional semiconductor nanocrystals (NCs). As such, a blend of novel synthesis, advanced characterization, and direct application of heterostructured nanoparticles are presented. Additionally, for chapters two through six, a corresponding appendix is included containing supporting data pertinent to the experiments described in the chapter.
The first chapter is a review summarizing the design, synthesis, properties, and applications of multicomponent nanomaterials composed of disparate semiconductor and metal domains. By coupling two compositionally distinct materials onto a single nanocrystal, synergistic properties can arise that are not present in the isolated components, ranging from self-assembly to photocatalysis. While much progress was made in the late 1990s and early 2000s on the preparation of a variety of semiconductor/metal hybrids towards goals of photocatalysis, comprehensive understanding of nanoscale reactivity and energetics required the development of synthetic methods to prepare well-defined multidimensional constructs. For semiconductor nanomaterials, this was first realized in the ability to tune nanomaterial dimensions from 0-D quantum dot (QD) structures to cylindrical (NR) and branched (TP) structures by exploitation of advanced colloidal synthesis techniques and understandings of NC facet reactivities. Another key advance in this field was the preparation of "seeded" NR and TP constructs, for which an initial semiconductor QD (often CdSe) is used to "seed" the growth of a second semiconductor material (for example, CdS). These advances led to exquisite levels of control of semiconductor nanomaterial composition, shape, and size. Concurrently, many developments were made in the functionalization of these NCs with metallic nanoparticles, allowing for precise tuning of metal nanoparticle deposition position on the surface of preformed semiconductor NCs. To date, photoinduced and thermally induced methods are most widely used for this, providing access to metal-semiconductor hybrid structures functionalized with Au, Pt, Ag2S, Pd, Au/Pt, Ni, and Co nanoparticles (to name a few). With colloidal nanomaterial preparation becoming analogous to traditional molecular systems in terms of selectivity, property modulation, and compositional control, the field of nanomaterial total synthesis has thus emerged in the past decade. With a large toolbox of reactions which afford selectivity at the nanoscale developed, to date it is possible to design a wider array of materials than ever before. Only recently (the past ~ 5 years), however, has the transition from design of model systems for fundamental characterization to realization of functional materials with optimized properties begun to be demonstrated. The emphasis of chapter 1 is thus on the key advances in the preparation of metal-semiconductor hybrid nanoparticles made to date, with seminal synthetic, characterization, and application milestones being highlighted.
The second chapter is focused on the synthesis and characterization of well-defined CdSe-seeded-CdS (CdSe@CdS) NR systems synthesized by overcoating of wurtzite (W) CdSe quantum dots with W-CdS shells. 1-dimensional NRs have been interesting constructs for applications such as solar concentrators, optical gains, and photocatalysis. In each of these cases, a critical step is the localization of photoexcited excitons from the light-harvesting CdS NR "antenna" into the CdSe QD seed, from which emission is primarily observed. However, effects of seed size and NR length on this process remained unexplored prior to this work. Previous work had demonstrated that, for core@shell CdSe@CdS systems, small CdSe seed sizes (< 2.8 nm in diameter) resulted in quasi-type II alignment between semiconductor components (with photoexcited electrons delocalized across the structure and holes localized in the CdSe seed), and large seed sizes (> 2.8 nm) resulted in type I alignment (with photoexcited electrons and holes localized in the CdSe seed). Through synthetic control over CdSe@CdS NR systems, materials with small and large CdSe seeds were prepared, and for each seed size, multiple NR lengths were prepared. Through transient absorption studies, it was found that band alignment did not affect the efficiency of charge localization in the CdSe core, whereas NR length had a profound effect. This work indicated that longer NRs resulted in poor exciton localization efficiencies owing to ultrafast trapping of photoexcited excitons generated in the CdS NR. Thus, with increasing rod length, poorer efficiencies were observed. This work served to highlight the ideal size range for CdSe@CdS NR constructs targeted towards photocatalysis, with ~ 40 nm NRs exhibiting the best rod-to-seed localization efficiencies. Additionally, it served to expand the understanding of exciton trapping in colloidal NC systems, allowing development of a predictive model to help guide the preparation of other nanorod based photocatalytic systems.
The third chapter describes the synthesis of Au-tipped CdSe NRs and studies of the effects of selective metal nanoparticle deposition on the band edge energetics of these model photocatalytic systems. Previous studies had demonstrated ultrafast localization of photoexcited electrons in Au nanoparticles (AuNP) (and PtNP) deposited at the termini of CdSe and CdSe@CdS NR constructs. Also, for similar systems, the hydrogen evolution reaction (HER) had been studied, for which it was found that noble metal nanoparticle tips were necessary to extract photoexcited electrons from the NR constructs and drive catalytic reactions. However, in these studies, energetic trap states, generally ascribed to surface defects on the NC surface, are often cited as contributing to loss of catalytic efficiency. In this study, we found that the literature trend of assuming the band-edge energetics of the parent semiconductor NC applies to the final metal-functionalized catalyst did not present a complete picture of these systems. Through a combination of ultraviolet photoelectron spectroscopy and waveguide based spectroelectrochemistry on films of 40 nm long CdSe NRs before and after AuNP functionalization, we found that metal deposition resulted in the formation of mid-gap energy states, which were assigned as metal-semiconductor interface states. Previously these states had only been seen in single particle STS studies, and their identification in this study from complementary characterization techniques highlighted a need to further understand the nature of the interface between metal/semiconductor components for the design of photoelectrochemical systems with appropriate band alignments for efficient photocatalysis.
The fourth chapter transitions from NR constructs to highly absorbing CdSe@CdS TP materials, for which a single zincblende (ZB) CdSe NC is used to seed the growth of four identical CdS arms. These arms act as highly efficient light absorbers, resulting in absorption cross sections an order of magnitude greater than for comparable NR systems. In the past, many studies have been published on the striking properties of TP nanocrystals, such as dual wavelength fluorescence, multiple exciton generation, and inherent self-assembly owing to their unique geometry. Nonetheless, these materials have not been exploited for photocatalysis, primarily owing to challenges in preparing TP from ultrasmall ZB-CdSe seed size (owing to phase instability of the zincblende crystal structure), thus preventing access to quasi-type II structures necessary for efficient photocatalysis. In this study, we successfully break through the type I/quasi-type II barrier for TP NCs, reclaiming lost ground in this field and demonstrating for the first time quasi-type II behavior in CdSe@CdS TPs through transient absorption measurements. This was enabled by new synthetic protocols for the synthesis and stabilization of ultrasmall (1.8 – 2.8 nm) ZB-CdSe seeds, as well as for the synthesis of CdSe@CdS TPs with arm lengths of 40 nm. Easily scalable, TPs were prepared on gram scales, and the quasi-type II systems showed dramatically enhanced rates of selective photodeposition of AuNP tips under ultraviolet and solar irradiation. These are promising materials for photocatalytic and solar energy applications.
The fifth chapter continues with the study of CdSe@CdS TPs, and elaborates on a new method for the selective functionalization of the highly symmetrical TP construct. Previous studies had demonstrated that access to single noble metal NP tips was vital for efficient photocatalytic HER from NR constructs. However, TP materials have been notoriously difficult to selectively functionalize, owing to their symmetric nature. Using a novel photoinduced electrochemical Ostwald ripening process, we found that initially randomly deposited AuNPs could be ripened to a single, large (~ 7 nm) AuNP tip at the end of one arm of a type I CdSe@CdS TP with 40 nm arms. To demonstrate the selectivity of this tipping process, dipolar cobalt was selectively overcoated onto the AuNP tips of these TPs, resulting in dipolar Au@Co-CdSe@CdS TP nanocrystals. These particles were observed to spontaneous self-assemble into 1-D mesoscopic chains, owing to pairing of N-S dipoles of the ferromagnetic CoNPs, resulting in the first example of “colloidal polymers” (CPs) bearing bulky, tetrapod ("giant t-butyl") pendant groups.
The sixth chapter elaborates further on the preparation of colloidal polymers, further extending the analogy between molecular and colloidal levels of synthetic control. One challenge in the field of colloidal science is the realization of new modes of self-assemble for compositionally distinct nanoparticles. In this work, it was found that Au@Co nanoparticle dipole strength could be systematically varied by tuning of AuNP size on CdSe@CdS nanorods/tetrapods. In the first example of a colloidal analogue to reactivity ratios observed for traditional chain growth polymerization systems, highly disparate AuNP tip sizes (and thus final Au@Co NP dipole strength) were found to result in segmented colloidal copolymers upon dipolar self-assembly, whereas similar AuNP tip sizes ultimately led to random dipolar assemblies. Clearly visualized through incorporation of NR and TP sidechains into these colloidal polymers, this study presented a compelling case for continued exploration of colloidal analogues to traditional molecular levels of synthetic control.
21
Siebers, Benjamin [Verfasser], Dmitri R. [Akademischer Betreuer] Yakovlev, and Heinz [Gutachter] Hövel. "Spectroscopy of excitons in CdSe/CdS colloidal nanocrystals / Benjamin Siebers. Betreuer: Dmitri R. Yakovlev. Gutachter: Heinz Hövel." Dortmund : Universitätsbibliothek Dortmund, 2015. http://d-nb.info/1101606290/34.
Full text
22
Hinsch, Alexandra [Verfasser]. "Fluoreszenzspektroskopie an einzelnen elongierten CdSe/CdS-Nanopartikeln zur Erklärung ensemblecharakteristischer Eigenschaften wie die wellenlängenabhängige Quantenausbeute / Alexandra Hinsch." Hamburg : Staats- und Universitätsbibliothek Hamburg Carl von Ossietzky, 2020. http://d-nb.info/1236695135/34.
Full text
23
Ramanery, Fábio Pereira. "Síntese e Caracterização de Nanopartículas Semicondutoras com Estrutura tipo Núcleo/Casca CdSe/CdS obtidas por Rota Coloidal Aquosa." Universidade Federal de Minas Gerais, 2012. http://hdl.handle.net/1843/BUOS-967HPQ.
Full textAbstract:
Nanoparticles of semiconductor materials with diameters of less than 10nm are particles called quantum dots (PQ's, English, quantum dots, QD's) and have unique size-dependent optical properties. The present FPs dimensions intermediate between the macro-molecules and the crystals and their optical properties, physical and chemical properties are distinct from the material presented in the form of extended solid. The effect of confinement in quantum dots allows for diverse applications in several areas of technological interest as optoelectronic devices, photovoltaic and biological markers in the biomedical area. The synthesis of nanoparticles with structure type core / shell (CS) for semiconductors, particularly semiconductor cadmium selenide (CdSe) and cadmium sulfide (CdS), among others, have been prepared by different methods, with an aqueous colloidal
promising route to not use toxic precursors in normal temperature and pressure compatible with biological systems. In this study were synthesized cores quantum dots with a structure NC-type semiconductor core CdSe and CdS aqueous colloidal route by using poly (vinyl alcohol) as a stabilizer. We investigated the changes in optical properties of CdSe PQs for the formation of different thicknesses of CdS shell. The property of luminescence, formation and evaluation of the dispersion particle size was backed by photoluminescence (PL) and characterized by spectroscopy ultraviolet-visible (UV-vis). The morphological characteristics were investigated by transmission
electron microscopy (TEM) and chemical evaluation of the particles with core / shell structure was analyzed by EDS.Nanopartículas de materiais semicondutores dos com diâmetros inferiores a 10nm são partículas designadas por pontos quânticos (PQs, do inglês, quantum dots, QDs) e apresentam peculiares propriedades ópticas dependentes do tamanho. Os PQs apresentam dimensões intermediárias entre as moléculas e os macro-cristais e as suas propriedades ópticas, físicas e químicas são distintos das apresentadas pelo material na forma de sólido estendido. O efeito do confinamento nos pontos quânticos permite diversas aplicações em várias áreas de interesse tecnológico como dispositivos optoeletrônicos, fotovoltaicos e marcadores biológicos na área biomédica. A síntese de nanopartículas com estrutura do tipo núcleo/casca (NC, do inglês core/shell, CS) de semicondutores, em particular semicondutores de seleneto de cádmio (CdSe) e sulfeto de cádmio (CdS), além de outros, têm sido preparados por diferentes métodos, sendo a rota coloidal aquosa promissora por não utilizar precursores tóxicos em condições normais de temperatura e pressão e compatíveis com sistemas biológicos. Neste trabalho foram sintetizados núcleos de pontos quânticos com estrutura do tipo NC de semicondutores de núcleo de CdSe e CdS, por rota coloidal aquosa utilizando poli(álcool vinílico) como agente estabilizante. Foram investigadas as alterações nas propriedades ópticas dos PQs de CdSe pela formação de diferentes espessuras de casca de CdS. A propriedade de luminescência, formação e avaliação da dispersão de tamanho das partículas foram avalizadas por fotoluminescência (PL) e caracterizadas por espectroscopia de na região do ultravioleta-visível (UV-vis). As características morfológicas foram investigadas por microscopia eletrônica de transmissão (MET) e a avaliação química das partículas com estrutura núcleo/casca foi avaliada por EDS.
24
Hao, Junjie. "Revisiter la chiralité induite et la photodéposition d'or sur des semi-conducteurs CdSe/CdS possédant différentes morphologies contrôlées." Thesis, Bordeaux, 2020. http://www.theses.fr/2020BORD0186.
Full textAbstract:
Des morphologies contrôlées de nanocristaux de semi-conducteurs II – VI traditionnels à base de cadmium (NCs) sont présentées. Différentes morphologies peuvent être obtenues en utilisant le processus d'extraction et de purification à la tri-n-octylphosphine (TOP), tels que les nanodots, les nanofleurs, les têtards, les bâtonnets (dot-in-rods) et les tétrapodes. Les objets appelés CdSe/CdS (DRs) ont été spécifiquement choisis pour la poursuite de l'étude sur la chiralité et la photodéposition en raison de leur chiralité potentielle induite par le ligand et de leurs performances catalytiques. Le mécanisme de transmission chirale induite par un ligand a été étudié par un procédé top-down de gravure de domaine sélectif. Les résultats ont montré que lors de la comparaison des signaux de chiralité d'une nanoparticule individuelle, la couche de coquille avait un impact négatif sur la chiralité du premier pic d'exciton, mais une corrélation positive sur la chiralité d'absorption de la coquille. Nous présentons pour la première fois les signaux de luminescence à polarisation circulaire (CPL) de chiralité induite dans des nanoplaquettes deCdSe / CdS (NPL) synthétisées par une approche en une étape. La chiralité des nanocristaux semi-conducteurs de morphologies différentes induite par le ligand est étudiée plus en détail, et les activités de dichroïsme circulaire (CD) et de CPL observées sont étroitement associées aux caractères géométriques des nanostructures tels que l'épaisseur de la coque et le rapport d'aspect des NR CdSe/CdS . Enfin, le mécanisme de croissance par photodéposition induite par laser de nanocristaux d'or sur des bâtonnets préformés de CdSe/CdS (DRs) est abordé. Les nanoparticules HNPs Au-CdSe/CdS sont obtenues en utilisant une lumière laser bleue. Les effets du capteur de trous pour la synthèse des HNPs à pointe unique sont étudiés en profondeur pour la première fois. De plus, d'autres paramètres sont également étudiés, tels que l'intensité d'irradiation, le temps de dépôt, le rapport Au / DRs, etc. Nos résultats sont en bon accord avec un modèle développé pour la croissance d'un seul nanocristal Au en surface du DRControlled morphologies of traditional cadmium-based II–VI semiconductor nanocrystals (NCs) are presented. Different morphologies can be achieved by using the tri-n-octylphosphine (TOP) extraction and purification process, such as nanodots, nanoflowers, tadpoles, dot-in-rods and tetrapods. CdSe/CdS dot-in-rods (DRs) were specifically chosen for the further study on chirality and photodeposition due to its potential ligand-induced chirality and catalytic performances. The mechanism of ligand-induced chiral transmission was studied by the top-down selective domain etching process. The results showed that when comparing the chirality signals of an individual nanoparticle, the shell layer had a negative correlation with the first exciton peak chirality, but positive correlation with the shell absorption chirality. We present the induced chirality circularly polarized luminescence (CPL) signals in CdSe/CdS nanoplates (NPLs) synthesized by a one-pot approach for the first time. The ligand induced chirality of semiconductor nanocrystals with different morphologies are further studied, and the observed circular dichroism (CD) and CPL activities are closely associated to the geometrical characters of the nanostructures such as the shell thickness and the aspect ratio of the CdSe/CdS Tadpoles. Finally, the laser-induced photodeposition growth mechanism of gold nanocrystals onto preformed CdSe@CdS dot-in-rods (DRs) is presented. The hybrid NPs (HNPs) Au-CdSe/CdS are achieved by using a blue-laser light. The effects of the hole scavenger for the synthesis of single-tipped HNPs are studied deeply for the first time. Additionally, other parameters are also studied, such as the irradiation intensity, the deposition time, the Au/DRs ratio and so on. Our results compare quite well with a model developed for the growth of single Au nanocrystal
25
Gomes, de Castro Neto Antonio. "Nanocristais fluorescentes de seleneto de cádmio/sulfeto de cádmio (CdSe/CdS): síntese coloidal em meio aquoso, caracterização óptica e estrutural." Universidade Federal de Pernambuco, 2011. https://repositorio.ufpe.br/handle/123456789/1618.
Full textAbstract:
Made available in DSpace on 2014-06-12T15:51:31Z (GMT). No. of bitstreams: 2
arquivo5719_1.pdf: 2389208 bytes, checksum: fd3ee770e606c50de4354c931bb7ce22 (MD5)
license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5)
Previous issue date: 2011Conselho Nacional de Desenvolvimento Científico e Tecnológico
Nanocristais fluorescentes de semicondutores, quantum dots (QDs) vêm sendo obtidos para diversas aplicações por vários grupos de pesquisa em todo o mundo. A maioria das rotas sintéticas encontradas na literatura refere-se à produção desta classe de nanomateriais em meio orgânico e condições de alta temperatura. A síntese em meio aquoso consiste em uma metodologia simples para a obtenção de nanocristais com estrutura core-shell de CdSe/CdS altamente fluorescentes em regime de confinamento quântico. Estes QDs dispersos em água foram sintetizados através da adição de sal de cádmio, selênio reduzido e ácidos orgânicos com radicais tióis. Tais compostos orgânicos nesse caso são fundamentais para a estabilização das partículas coloidais, além de fornecerem íons sulfeto, que participam da formação da camada de passivação. A caracterização dos QDs obtidos foi realizada através de medidas espectroscópicas e análises estruturais. Foram feitos também planejamentos quimiométricos e avaliações temporais da luminescência para se saber quais os melhores parâmetros e quando os QDs apresentam a melhor intensidade de luminescência após serem sintetizados. Devido sua elevada luminescência, estabilidade em meio aquoso e baixa fotodegradação, os QDs de CdSe/CdS foram utilizados para a marcação de fluorescência de cromossomos metafásicos. Apesar do grande interesse e crescente aumento na produção de QDs, os mesmos apresentam muitas vezes, metais de elevada toxicidade, tais como o Cádmio. Assim, o tratamento dos resíduos oriundos da produção de quantum dots, que ainda é alvo de poucos trabalhos, é aqui abordado mais especificamente com relação ao tratamento através de processos oxidativos avançados, de rejeitos oriundos da síntese dos QDs de CdSe/CdS, objetos do presente trabalho
26
Javaux, Clémentine. "Etude de la réduction du phénomène de clignotement dans les nanocristaux semi-conducteurs de CdSe/CdS à coque épaisse." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2012. http://pastel.archives-ouvertes.fr/pastel-00799228.
Full textAbstract:
Les nanocristaux semi-conducteurs colloïdaux présentent un phénomène de clignotement qui s'avère être un obstacle pour de nombreuses applications. Dans cette thèse, nous nous sommes intéressés à la suppression du phénomène de clignotement dans les nanocristaux constitués d'un coeur de CdSe et d'une coque épaisse de CdS. Nous avons mis au point un protocole facile à mettre en oeuvre, rapide et robuste, permettant de synthétiser des nanocristaux semi-conducteurs de CdSe/CdS à coque épaisse non-clignotants. L'étude de la dépendance en température des propriétés optiques de ces nanocristaux mesurés à l'échelle individuelle nous a permis de déterminer l'origine de la réduction du clignotement. Nous avons mis en évidence l'activation thermique de la recombinaison Auger non-radiative, cette dernière étant responsable du clignotement dans ces nanocristaux. Cette activation thermique est liée à la dépendence en température de la localisation de l'électron. A basse température, les nanocristaux sont chargés négativement et présentent d'excellentes propriétés optiques : un temps de vie radiatif inférieur à 10 ns et un rendement quantique de 100 %. Ces caractéristiques remarquables ont permis l'étude directe des propriétés magnéto-optiques des nanocristaux. Ces résultats ouvrent la voie à la conception de nanocristaux ayant un rendement quantique de 100 % à température ambiante.
27
Reich, Aina Johanna [Verfasser], and Alf [Akademischer Betreuer] Mews. "Single charge carrier–defect complexes in CdSe and CdS nanowires observed by photoluminescence spectroscopy / Aina Johanna Reich ; Betreuer: Alf Mews." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2019. http://d-nb.info/1201087104/34.
Full text
28
Nemchinov, Alexander. "Using Colloidal Nanocrystal Matrix Encapsulation Technique for the Development of Novel Infrared Light Emitting Arrays." Bowling Green State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1339806993.
Full text
29
Tchakpele, Komi Paalamwé. "Contribution à l'étude théorique des états localisés dus aux défauts et impuretés dans les semiconducteurs II-VI de structure Wurtzite (CdSe, CdS, ZnS et ZnO)." Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb37610232r.
Full text
30
Biermann, Amelie Laura [Verfasser], Axel [Akademischer Betreuer] Hoffmann, Christian [Akademischer Betreuer] Thomsen, Axel [Gutachter] Hoffmann, and Anna [Gutachter] Rodina. "Phonons and excitons in colloidal CdSe/CdS quantum dots with wurtzite and zincblende crystal structure / Amelie Laura Biermann ; Gutachter: Axel Hoffmann, Anna Rodina ; Axel Hoffmann, Christian Thomsen." Berlin : Technische Universität Berlin, 2018. http://d-nb.info/1168722160/34.
Full text
31
Sugunan, Abhilash. "Fabrication and Photoelectrochemical Applications of II-VI Semiconductor Nanomaterials." Doctoral thesis, KTH, Funktionella material, FNM, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-95410.
Full textAbstract:
In this work we investigated fabrication of semiconductor nanomaterials and evaluated their potential for photo-chemical and photovoltaic applications. We investigated different II-VI semiconductor nanomaterial systems; (i) ZnO oriented nanowire arrays non-epitaxially grown from a substrate; and (ii) colloidal CdE (E=Te,Se,S) quantum structures synthesized by solution-based thermal decomposition of organo-metallic precursors. We have studied the synthesis of vertically aligned ZnO nanowire arrays (NWA), by a wet chemical process on various substrates. We have extended this method wherein nanofibers of poly-L-lactide act as a substrate for the radially oriented growth of ZnO nanowires. By combining the large surface area and the flexibility of the PLLA-ZnO hierarchical nanostructure we have shown the proof-of-principle demonstration of a ‘continuous-flow’ water treatment system to decompose known organic pollutants in water, as well as render common waterborne bacteria non-viable. We have studied synthesis of colloidal quantum dots (QD), and show size, morphology and composition tailored nanocrystals for CdE (E=S, Se, Te) compositions. We have studied the influence of crystal growth habits of the nanocrtsyals on the final morphology. Furthermore we have synthesized core-shell, CdSe-CdS QDs with spherical and tetrahedral morphologies by varying the reaction conditions. We show that these core-shell quantum dots show quasi-type II characteristics, and demonstrate with I-V measurements, the spatial localization of the charge carriers in these hetero-nanocrystals. For this purpose, we developed hybrid materials consisting of the core-shell quantum dots with electron acceptors (ZnO nanowires) and hole acceptors (polymeric P3HT nanofibers). In addition we have also compared the synthesis reaction when carried out with conventional heating and microwave-mediated heating. We find that the reaction is enhanced, and the yield is qualitatively better when using microwave induced heating.QC 20120525
32
Darugar, Qusai A. "Surface effects on the ultrafast electronic relaxation of some semiconductor and metallic nanoparticles." Diss., Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-06272006-160645/.
Full textAbstract:
Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2007.Zhang, John, Committee Member ; Wang, Zhong, Committee Member ; El-Sayed, Mostafa, Committee Chair ; Orlando, Thomas, Committee Member ; Lyon, Andrew, Committee Member.
33
Liu, Bei [Verfasser], Benjamin [Gutachter] Dietzek, and Wolfgang [Gutachter] Weigand. "From the inside out : colloidal CdSe/CdS semiconductor nanorods : a study on the influence of their structures, surface ligands, and interactions with Redox-Active (Poly)Dopamine / Bei Liu ; Gutachter: Benjamin Dietzek, Wolfgang Weigand." Jena : Friedrich-Schiller-Universität Jena, 2020. http://d-nb.info/1223981800/34.
Full text
34
Al-Brasi, Enteisar. "The growth and characterization of films of noble metal nanocrystals and inorganic semiconductors at the interface of two immiscible liquids." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/the-growth-and-characterization-of-films-of-noble-metal-nanocrystals-and-inorganic-semiconductors-at-the-interface-of-two-immiscible-liquids(5652496a-6e6d-4e91-a21b-6ae1b3f36a87).html.
Full textAbstract:
Deposition of noble metal and semiconductor nanocrystalline thin films has received much attention. CdS and CdSe are important semiconductors used in optical devices. A wet chemical route which uses the interface of two immiscible liquids to control the growth and deposition of nanocrystalline thin films forms the basis of the current study. In this method, a metal precursor dissolved in toluene or decane is held in contact with a water layer containing a reducing or sulphiding agent. The reaction proceeds at the interface of the liquids and results in deposits adhering to the interfacial region. The products of such reactions typically consist of nanocrystals forming a thin film. Stable sols of Au, Ag were found to metathesize on contact with alkylamine in oil to form monolayer films that spread across large areas at the water/oil interface. The nature and properties of interfacial thin films depend on the alkylamine. Nanocrystalline thin films consisting of CdS adhering to the interface starting with a polydispersed aqueous sol of crystallites and alkylamine were obtained. The optical band gaps of the films formed are dependent on the alkylamine chain length, with the shortest chain yielding the largest gap. A systematic increase in particle diameters following adsorption is responsible for changes in the electronic structure of films. The formation of nanocrystalline films of CdS adhering at the interface using a toluene solution of cadmium diethyldithiocarbamate and aqueous Na2S solution, in the presence of tetraoctylammonium bromide (TOAB) in the aqueous phase, was investigated under various reaction parameters, while CdSe was obtained using Na2SeSO3 solution and the influences of deposition temperature and solution concentration were studied. A ternary water/decane/2-butoxyethanol /salt system was used to grow deposits of CdSe and CdS. Nanostructured thin films were obtained at the upper interface of the ternary system, between the emulsive middle layer and oil rich top phase. The influence of deposition conditions such as precursor concentrations and temperature, as well as the nature of the medium on the properties of the deposits was studied. Deposits grown using the ternary system were compared with those obtained using water/decane and water/toluene systems. Reaction parameters such as temperature, solution concentration and the size of CdS and CdSe were controlled. A thin film of CdS and CdSe nanocrystals was formed at the interface. The grain size was found to be dependent on reaction temperature and solution concentration, with higher temperatures and solution concentration resulting in larger grains. The nature of thin films obtained at the interface of two immiscible liquids and of a water/decane/2-butoxyethanol/salt ternary system were studied using Scanning and Transmission electron microscopy, X-ray diffraction and UV-visible spectroscopy.
35
Krasselt, Cornelius. "Dynamik der Photo-Lumineszenz-Unterbrechung von Halbleiter-Nanokristallen in elektrischen Feldern." Doctoral thesis, Universitätsbibliothek Chemnitz, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-172910.
Full textAbstract:
Diese Arbeit untersucht die Photo-Lumineszenz (PL)-Unterbrechung (Blinken) einzelner in Polymer-Nanopartikeln eingebetteter CdSe/CdS Halbleiter-Nanokristalle (Quantenpunkte) im Einfluss elektrischer Gleich- und Wechselfelder mittels Weitfeld-Mikroskopie. Hierbei emittieren die einzelnen Quantenpunkte trotz kontinuierlicher Anregung mit einer zwischen hellen An- und dunklen Aus-Zuständen variierenden PL-Intensität.
Die Ergebnisse zeigen, dass die Dynamik dieses Blinkens durch Wechselfelder stark beeinflusst wird und von deren Feldstärke, teilweise auch deren Feldfrequenz abhängt. Für zunehmende Feldstärken lässt sich ein schnellerer Wechsel zwischen An- und Aus-Zuständen (erhöhte Blinkfrequenz) beobachten, der von einer reduzierten Häufigkeit langer An- und Aus-Ereignisse begleitet wird. Der Verlauf der An-Zeit-Verteilungen bei kleinen Zeiten wird zunehmend (monoton) flacher, während die Verteilungen der Aus-Zeiten zunächst ebenfalls einem analogen Trend folgen, ab einer bestimmten und von der Feldfrequenz abhängenden Feldstärke jedoch wieder steiler verlaufen. Ein solcher Monotonie-Wechsel in der Blinkdynamik im Fall einer gleichbleibenden Variation einer äußeren Bedingung wurde bei Halbleiter-Nanokristallen so erstmalig beobachtet.
Für Gleichfelder zeigen sich hingegen nahezu keine Auswirkungen. Lediglich die An-Zeit-Verteilungen sowie die Blinkfrequenz im Fall hoher Feldstärken werden modifiziert.
Die Ergebnisse werden im Kontext verschiedener aktueller Modelle zur PL-Unterbrechung wie dem trapping-Modell, dem self-trapping-Mechanismus oder dem Modell multipler Rekombinationszentren diskutiert und diese entsprechend erweitert. Dabei stehen die dielektrischen Eigenschaften und die Relaxationsdynamik der lokalen Quantenpunkt-Umgebung im Mittelpunkt, deren Reaktion auf die externen Felder durch eine zeitabhängige Ausrichtung permanenter Dipole beschrieben werden kann.
36
Hua, Muchuan. "Optical refrigeration on CdSe/CdS quantum dots." Thesis, 2019. http://hdl.handle.net/1805/20964.
Full textAbstract:
Indiana University-Purdue University Indianapolis (IUPUI)Optical refrigeration in quantum dots was carried out in this research. Zinc-blende crystalline CdSe/CdS (core/shell structure) QDs with complete surface passivation were synthesized and been used as the cooling substance. Phonon-assisted up-conversion photoluminescence driven by sub-band gap laser excitation was utilized as the cooling mechanism in the QD samples. A net cooling efficiency was predicted by a semi-empirical model developed during the research, within a range of the laser excitation energy, even after taking into account possible parasitic heating processes. To observe the cooling effect, the experiment was carried out in a thermally isolated environment, which temperature was also monitored. By using an optical thermometry technique developed for this research, a maximum temperature drop around 0.68 K was observed in the experiment. This development paves the way to use QDs' cooling in new industrial and fundamental research approaches.
37
(7373747), Muchuan Hua. "Optical refrigeration on CdSe/CdS quantum dots." Thesis, 2019.
Find full textAbstract:
Implementation of optical refrigeration (OR) in quantum dot (QD) materials was achieved for the first time. An OR experiment was designed and carried out in our lab and a maximum temperature drop around 0.68 K was observed in the zinc-blende crystalline CdSe/CdS (core/shell structure) QD samples under laser excitation. The cooling effect was achieved by utilizing the energy up-conversion photoluminescence (PL) of CdSe/CdS QDs with sub-band excitation. While the cooling efficiency of the system was estimated and optimized by a semi-empirical model built during this research. This work has proved the capability of QD materials to be used as a cooling substance for OR, which significantly expanded the possible candidates for OR. The technique could have many applications, such as harvesting cooling effect from sun light with the help of metamaterials, which can produce quasi-monochromatic light. It may also be used to cool QD in optical traps, which leading may help to develop new ultra-sensitive sensors and application for quantum information science.
38
陳正源. "Optical Properties of CdSe and CdS nanocrystals." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/53757936853090353764.
Full text
39
Liau, Shih-Yi, and 廖士懿. "Photoelectrochemical hydrogen generation by CdS- and CdSe- sensitized TiO2 photoelectrodes." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/66564986011721017671.
Full textAbstract:
碩士國立成功大學
化學工程學系碩博士班
97
These studies utilize the method of chemical bath deposition (CBD) to assemble, CdS and CdSe onto porous TiO2 films as sensitizer for photoelectrochemical hydrogen generation. The sensitizer incorporated amount and co-sensitized effect on photoelectrochemical conversion efficiency were discussed in this study. The results show that the CdS/CdSe co-sensitized photoelectrode has not only a complementary effect in light harvest and the cascade structure, TiO2/CdS(4)/CdSe(4), but leads to a stepwise structure of band-edge levels which is advantageous to the electron injection and hole-recovery of the system. The energy conversion efficiency (ECE) achieved by the TiO2/CdS(4)/CdSe(4) electrode under illumination (AM1.5, UV cut-off, 100 mW/cm2) is 7.4%. Zinc Sulfide (ZnS) was further deposited as passivation layer to improve the photoelectrode stability and reduce leakage current. The corresponding hydrogen evolved rate measured for the TiO2/CdS(4)/ CdSe(4)/ZnS electrode is 210 µmol．cm-2．h-1. Further, thermal-treatment process was used to improve TiO2/sensitizer interface and increase sensitizer crystallinity, the electron transfer ability of photoelectrodes and decrease the electrode defects. At the temperature of 300℃ and 150℃, the electrode TiO2/CdS(4)300℃/CdSe(4)150℃ had the highest photocurrent density about 17 mA/cm2 and ECE is 10.6%.
40
Teixeira, Diogo Manuel Pacheco. "Células fotovoltaicas de Grätzel usando cossensibilização de pontos quânticos de CdS-CdSe." Master's thesis, 2017. http://hdl.handle.net/1822/47176.
Full textAbstract:
Dissertação de mestrado em Ciências do Ambiente – EnergiaA procura incessante por energia tem aumentando nas últimas décadas, o que tem levado a uma busca mais intensiva por fontes de energia renováveis (FER) e sustentáveis. Deste modo, as células solares, que através do efeito fotovoltaico convertem a energia proveniente do sol em energia elétrica, tem ganho especial atenção. Dentro dos vários tipos de células solares, encontram-se as células solares sensibilizadas por corante (DSSC), bem como as células solares por pontos quânticos (QDSSC) que têm ganho interesse de estudiosos da área por apresentarem uma possibilidade de geração de energia elétrica a baixo custo. O estudo de pontos quânticos semicondutores é considerado como uma área emergente em aproveitamento de energia fotovoltaica e novas arquiteturas de dispositivos foram desenvolvidas para a realização de células solares com base em pontos quânticos. As nanopartículas semicondutoras oferecem uma série de vantagens sobre os corantes convencionais, tais como a do hiato energético e baixo custos. Entre os compostos mais utilizados estão os semicondutores CdS e CdSe. Nesta tese está descrito de forma minuciosa os métodos aplicados na construção e caracterização das células de grätzel que são constituídas por um elétrodo, um sensibilizador, um eletrólito e um contra elétrodo. Para a constituição ideal de uma célula solar consiste na deposição de diferentes camadas, em relação ao elétrodo apresenta uma camada de ATO (óxido de estanho dopado com antimónio), uma camada de bloqueio e por fim o revestimento TIO,. O sensibilizador a utilizar diferenciava-se, pois para as QDSSC utilizou-se os pontos quânticos de CdS/CdSe e já para DSSC depositou-se corantes naturais, com os eletrólitos de polissulfeto e lodeto/triodeto respetivamente. Os contra elétrodos mais eficazes foram de platina, latão e o CuSnS3. Este estudo foi baseado na otimização da eficiência destes dispositivos solares, onde verificamos a influência de vários fatores na eficiência destas células, para sua avaliação e análise foi utilizado curvas tensão corrente e o método de Van der Pauw.
The incessant demand for power has increased in recent decades, which has Ied to a more intensive search for renewable and sustainable energy sources. In this way, the solar cells, which through the photovoltaic effect convert the energy from the sun to electric energy, has gained special attention. Among the various types of solar cells, there are the dye-sensitized solar cells (DSSC) as well the quantum dots solar cells (QDSSC) that have gained interest among scientist because generate power at low cost. The study of quantum dots semiconductors is considered as an emerging area in the use of photovoltaic energy and in the new device architectures that were developed for the solar cells based on quantum dots. The semiconductors nanoparticles offer a number of advantages over conventional colorants such as gap energy and 10w costs. Among the most used compounds are the CdS and CdSe semiconductors. This thesis describes in detail the methods applied in the construction and characterization of grätzel cells that consist of an electrode, a sensitizer, an electrolyte and a counter electrode. A solar cell consists of the deposition of different layers. The electrode has a layer of ATO (tin oxide doped with antimony), a blocking layer and finally the TIO, coating. The sensitizers used for the QDSSC were the quantum dots of CdS / CdSe while for DSSC were deposited natural dyes with the polysulfide and iodide / triiodide electrolytes respectively. The most effective counter electrodes were platinum, brass and CuSnS3. This study was based on the optimization of the efficiency of these solar devices, where we verified the influence of several factors on the efficiency of these cells, for their evaluation and analysis we used current voltage curves and Van der Pauw method.
41
Lin, Chi Hung, and 林騏宏. "Detection of Volatile Organic Compounds by Ag/CdSe-CdS/PMMA Electrospun fibers." Thesis, 2019. http://ndltd.ncl.edu.tw/cgi-bin/gs32/gsweb.cgi/login?o=dnclcdr&s=id=%22107CGU05063015%22.&searchmode=basic.
Full text
42
Müller, Joseph [Verfasser]. "Elektrische Manipulation der Lichtemission von einzelnen CdSe-, CdS-Nanostäbchen / vorgelegt von Josef Müller." 2005. http://d-nb.info/979801486/34.
Full text
43
Liu, ShangYing, and 劉尚鷹. "Study on the Synthesis and Characterization of CdSe / CdS Core Shell Quantum Dots." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/79550375024553761128.
Full textAbstract:
碩士國立中正大學
光機電整合工程研究所
101
In this experiment, we used a high thermal decomposition method to cleavage the inorganic metal precursors CdO, which are capped with the surfactants of SA, OA, TOPO, HDA, OLA , that are not aggregating so fast due to the surfactants steric hindrance. CdSe nanoparticles are stable upon the surfactants for at least several months, so that it can control the particles nucleation and growth rate by tuning the reaction temperature and reaction time. It was observed that the growth of the CdSe nanoparticles are strongly dependent on the initial Cd:Se ratio of the precursors, which is a determining factor for the emission properties of the nanoparticles. In this case, a higher nucleation rate will result in a smaller particle size, where by the emission wavelength of the CdSe quantum dots ranged from 400 nm to 700 nm. On the other hand, the CdSe quantum dots were used as a precursor, and then the surfactants and non-coordinating solvents of OA,OLA, ODE are capped on the CdSe precursor. This was then synthesized by SILAR method into the CdSe solution where successive injections of the Cadmium and Sulfur shell stock solution allowed the CdS shell to grow up to desired thickness. Therefore, the CdSe / CdS core shell quantum dots can be shown by tuning the reaction temperature and reaction time. Finally, comparison of the different reaction time of CdSe core quantum dots and the corresponding CdSe / CdS core shell quantum dots were made. Absorption characteristics, crystal structure, particle size distribution and particle uniformity of quantum dots were observed by UV-vis spectra, PL spectra, XRD diffraction, DLS and SEM respectively.
44
Pang, Chia-Chun, and 潘佳駿. "The Preparation of CdSe/CdS/ZnO nanorod array and the Application of Photoelectrochemical." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/qayx47.
Full textAbstract:
碩士國立臺北科技大學
有機高分子研究所
98
We directly prepared the photoanode by growing the ordered ZnO nanorod arrays (ZnR) vertically on a fluorine-doped tin oxide conducting substrate using chemical bath deposition method. The quantum dots of CdS and CdSe were in turn deposited on ZnO nanorod arrays by using the method of successive ionic layer absorption and reaction (SILAR). Finally,upper layers (ZL) was coated by SILAR. We examined the physical-chemical properties of the CdSe/CdS/ZnR and ZL/CdS/ZnR composite layers using XRD, XPS,UV-Vis, SEM, HR-TEM and EDX. The results of SEM and HR-TEM demonstrated that the quantum dots of CdS and CdSe and ZnO layers are adhered firmly on the surface of the ZnR. Because of the high solar light utilization performance of quantum dots of CdS and CdSe, and the lower electron recombination rate of ZnO layers, the water splitting efficiency as high as 4.07% was achieved and the QDSSC’s photoelectron conversion efficiency as high as 2.09% was achieved when illuminated with simulated AM1.5 spectrum.
45
Wu, Pei-Shin, and 吳佩馨. "Highly efficient solar water splitting using CdS and CdSe sensitized ZnO nanorod arrays." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/6v64hh.
Full textAbstract:
碩士國立臺北科技大學
有機高分子研究所
100
We fabricated CdS quantum dots sensitized ZnO nanorod arrays (CdS/ZNR) as photoanodes that used for solar water splitting. The vertically aligned ZNR was fabricated via a simple chemical bath deposition method (CBD), and the CdS quantum dots were coated on the ZNR by using successive ionic layer adsorption and reaction (SILAR). The prepared electrodes were characterized by FE-SEM, HR-TEM, XRD, UV-Vis, and photoelectrochemical measurements. All the photoelectrochemical measurements were carried out in a three-electrode cell with an Au wire as a counter electrode and an Ag/AgCl electrode as a reference. A mixture of 0.35 M Na2SO3 and 0.25 M Na2S aqueous solution was used as electrolyte. The working electrode was illuminated with a solar-simulated light source (AM 1.5 G filtered, 100 mW/cm2 ). In this study, we changed the solvent (water and ethanol) used in SILAR processes to fabricated various CdS/ZNR photoanodes, such as eight water-based SILAR cycles (CdS/ZNR-8w), six ethanol-based SILAR cycles (CdS/ZNR-6e), and three water-based as well as three ethanol-based SILAR cycles (CdS/ZNR-3w3e). After CdS sensitization, TEM images showed that ZnO nanorod were covered with nanoparticular forme in water solvent but with film form in ethanol solvent. The photoconversion efficiency of CdS/ZNR-8w for 4.14% was much higher than that of CdS/ZNR-6e for 3.86%, so the choice of solvent that water was better than ethanol. Further, the photoconversion efficiency of CdS/ZNR-3w3e had best performance of 5.23%. The photoconversion efficiency was enhanced because of the ZnO nanorod were covered with nanoparticle and then film. Such CdS composite was closely coated on the ZnO nanorod and could collect more excited photoelectrons. Furthermore, we also fabricated CdSe quantum dots sensitized ZNR (CdSe/ZNR) as photoanode. The CdSe quantum dots were coated on the ZNR surface using SILAR methode. The photoconversion efficiency of the single sided CdSe/ZNR was 4.12%. In order to increase the light-harvesting in the full spectrum of visible light region, we used CdS to absorb the short wavelength region (400-550 nm), and CdSe to absorb the long wavelength region (550-750 nm). Therefore, we combined CdS/ZNR electrode with CdSe/ZNR electrode by their non-conductive sides (CdS//CdSe), and the incident light transmitted through the CdS/ZNR substrate to the CdSe/ZNR substrate, thus the light could be absorbed by both substrates. The best photoconversion efficiency of 6.61% was achieved by using the CdS//CdSe as photoelectrode in solar water splitting.
46
Stachowski, G. M., C. Bauer, C. Waurisch, D. Bargheer, P. Nielsen, J. Heeren, Stephen G. Hickey, and A. Eychmüller. "Synthesis of radioactively labelled CdSe/CdS/ZnS quantum dots for in vivo experiments." 2014. http://hdl.handle.net/10454/10537.
Full textAbstract:
NoDuring the last decades of nanoparticles research, many nanomaterials have been developed for applications in the field of bio-labelling. For the visualization of transport processes in the body, organs and cells, luminescent quantum dots (QDs) make for highly useful diagnostic tools. However, intercellular routes, bio-distribution, metabolism during degradation or quantification of the excretion of nanoparticles, and the study of the biological response to the QDs themselves are areas which to date have not been fully investigated. In order to aid in addressing those issues, CdSe/CdS/ZnS QDs were radioactively labelled, which allows quantification of the QD concentration in the whole body or in ex vivo samples by gamma-counting. However, the synthesis of radioactively labelled QDs is not trivial since the coating process must be completely adapted, and material availability, security and avoidance of radioactive waste must be considered. In this contribution, the coating of CdSe/CdS QDs with a radioactive (65)ZnS shell using a modified, operator-safe, SILAR procedure is presented. Under UV illumination, no difference in the photoluminescence of the radioactive and non-radioactive CdSe/CdS/ZnS colloidal solutions was observed. Furthermore, a down-scaled synthesis for the production of very small batches of 5 nmol QDs without loss in the fluorescence quality was developed. Subsequently, the radio-labelled QDs were phase transferred by encapsulation into an amphiphilic polymer. gamma-counting of the radioactivity provided confirmation of the successful labelling and phase transfer of the QDs.
47
Lo, Yi-Siou, and 羅亦修. "Co-Sensitization Effect of CdS/CdSe on The Quantum-Dots Sensitized Solar Cells." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/34479387328439333817.
Full textAbstract:
碩士國立成功大學
化學工程學系碩博士班
96
In this study, cadmium sulfide (CdS) and cadmium selenide (CdSe) quantum dots (QDs) were used as sensitizers of dye-sensitized solar cells (DSSCs). This two QDs were sequentially assembled onto a nanocrystalline TiO2 film, using a chemical bath deposition (CBD) process, to prepare a CdS/CdSe co-sensitized photoelectrode for QDs-sensitized solar cell application. The effects of CBD cycles and the positions of QDs respected to TiO2 on the performance of QDs-DSSCs are studied. The results showed that CdS and CdSe QDs have complementary effect in the light harvest, but the performance of a QDs co-sensitized solar cell is strongly dependent on the order of CdS and CdSe respected to the TiO2. In the cascade structure of TiO2/CdS/CdSe electrode, the alignment of the Fermi level between CdS and CdSe forms a stepwise structure of band-edge levels which is advantageous to the electron injection and hole-recovery of CdS and CdSe QDs. An energy conversion efficiency of 2.48% has been achieved using a ITO/TiO2/CdS(3)/CdSe(4) electrode. Besides, we deposited Zinc sulfide (ZnS) QDs onto the TiO2/CdS/CdSe electrode. The experimental results showed that ZnS can avoid the occurrence of leakage current and increase photostability. An energy conversion efficiency of 3.88% has been achieved in this study using a ITO/TiO2(13.55μm)/CdS(3)/CdSe(4)/ZnS electrode.
48
Rasmussen, Rachel M. "Laser-assisted dielectrophoretic alignment and optoelectronic properties of solution-grown CdS and CdSe semiconductor nanowires." 2009. http://etd.nd.edu/ETD-db/theses/available/etd-07242009-190511/.
Full textAbstract:
Thesis (M.S.)--University of Notre Dame, 2009.Thesis directed by Huili (Grace) Xing and Masaru Kenneth Kuno for the Department of Chemistry and Biochemistry. "July 2009." Includes bibliographical references (leaves 57-58).
49
"Nanowire Synthesis and Characterization: Erbium Chloride Silicate and Two Segment CdS-CdSe Nanowires and Belts." Master's thesis, 2012. http://hdl.handle.net/2286/R.I.14579.
Full textAbstract:
abstract: In this work, I worked on the synthesis and characterization of nanowires and belts, grown using different materials, in Chemical Vapor Deposition (CVD) system with catalytic growth method. Through this thesis, I utilized the Photoluminescence (PL), Secondary Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-ray diffraction (XRD) analyses to find out the properties of Erbium Chloride Silicate (ECS) and two segment CdS-CdSe samples. In the first part of my research, growth of very new material, Erbium Chloride Silicate (ECS), in form of core/shell Si/ECS and pure ECS nanowires, was demonstrated. This new material has very fascinating properties for new Si based photonic devices. The Erbium density in those nanowires is which is very high value compared to the other Erbium doped materials. It was shown that the luminescence peaks of ECS nanowires are very sharp and stronger than their counterparts. Furthermore, both PL and XRD peaks get sharper and stronger as growth temperature increases and this shows that crystalline quality of ECS nanowires gets better with higher temperature. In the second part, I did a very detail research for growing two segment axial nanowires or radial belts and report that the structure type mostly depends on the growth temperature. Since our final step is to create white light LEDs using single axial nanowires which have three different regions grown with distinct materials and give red, green and blue colors simultaneously, we worked on growing CdS-CdSe nanowires or belts for the first step of our aim. Those products were successfully grown and they gave two luminescence peaks with maximum 160 nm wavelength separation depending on the growth conditions. It was observed that products become more likely belt once the substrate temperature increases. Also, dominance between VLS and VS is very critical to determine the shape of the products and the substitution of CdS by CdSe is very effective; hence, CdSe growth time should be chosen accordingly. However, it was shown two segmented products can be synthesized by picking the right conditions and with very careful analyses. We also demonstrated that simultaneous two colors lasing from a single segmented belt structures is possible with strong enough-pumping-power.Dissertation/Thesis
M.S. Electrical Engineering 2012
50
Li, Yen-Ting, and 李彥廷. "Transfer of Hydrophobic CdSe/CdS Core/Shell Quantum Dots from Organic to Aqueous Phase by Poly(vinylamine)." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/87986658401617149327.
Full textAbstract:
碩士國立成功大學
化學工程學系碩博士班
97
In this work, we have synthesized the CdSe/CdS core shell quantum dots（QDs）in organic phase using TOPO as a capping agent. The CdSe/CdS NCs were then transferred to the aqueous phase using poly(vinylamine)（PVAm）as the stabilizer. Through the transfer procedure, QDs prepared from TOPO can retain their high quantum yield in water. The parameters that affect the photoluminescent properties such as the –NH2 amount and pH and ionic strength of the solutions have been systematically investigated. The stability of QDs is most important for application of QDs in the aqueous. We also make an experiment of etching of QDs by 80 �aC in dark surrounding to observe the effect of QDs for different parameters.