Dissertations / Theses on the topic 'Colloidal Synthesis - Nanocrystals'
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IMRAN, MUHAMMAD. "Synthesis and Post-synthesis Transformations of Colloidal Semiconductor Nanocrystals." Doctoral thesis, Università degli studi di Genova, 2018. http://hdl.handle.net/11567/945513.
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The present PhD thesis focuses on two main classes of semiconductor colloidal nanocrystals, i.e. lead halide perovskite and copper chalcogenides. The former class of semiconductor NCs are promising materials for many high performance optoelectronics applications, as they exhibit a tunable band gap in the range of 1.4 to 2.9 eV and an efficient photoluminescence characterized by narrow emission linewidths and have been explored the most in the last years. Following the standard hot injection based synthesis and selecting a combination of short chain acid (octanoic acid or hexanoic acid) together with alkyl amines (octylamine and oleylamine) we prepared strongly fluorescent CsPbBr3 perovskite nanowires with tuneable width, in the range from 20 nm (exhibiting no quantum confinement, hence emitting in the green) to 3 nm (in the strong quantum-confinement regime, emitting in the blue) for the first time. However the main limitation of the colloidal synthesis protocols that was followed in aforementioned case including the ligand assisted reprecipitation routes which is the second most frequently used method for preparation of LHPs, is that they employ PbX2 (X= Cl, Br, or I) salts as both lead and halide precursors which consequently limit the precise tunability of the amount of reaction species such as metals or halides precursors and are not applicable to entire family of APbX3 (A=FA, MA and Cs; X=Cl, Br, I). To overcome this issue we developed benzoyl halide based colloidal synthesis route i.e broadly applicable to the entire family of LHP NCs and not only ensures the independent tunability of reaction precursors but also maintain the overall integrity of the NCs such as phase purity and high PLQY. Despite the significant advances in synthesis procedures, the control over size monodispersity, shape and phase purity remains another long standing challenge. This is in fact due to the tendency of primary alkyl amine in the form of alkylammonium ions that could compete with Cs+ ions and leads to the anisotropic growth such as NPLs or their use in excess permotes the Pb-depleted Cs4PbX6 phases. We develop here a strategy to achieve size, shape and phase pure CsPbBr3 nanocubes by substituting primary alkyl amines with secondary alkyl amines. We attributed this excellent control over the shape and phase purity to the inability of secondary amines to find the right steric conditions at the surface of the nanocrystals which consequently limits the formation of low dimensional structures. The shape purity and narrow size distribution leads to their ease of self-assembly in superlattices reaching up to 50 microns in lateral dimensions, which are the largest dimensions reported to date for superlattices of LHP NCs. The second class of materials studied here, i.e. copper chalcogenides, are mainly attractive due to their tunable composition via post synthesis chemical transformations, plasmonic properties, low toxicity and environmental friendliness. Taking the advantage of colloidal synthesis and using Cu2S as a template we develop a strategy to obtain novel AuCuS-Cu2S heterostructure through cation exchange, which cannot be realized through conventional synthesis approaches. We further investigated the stability of Cu2S NCs with different dimensionalities and their thermal evolution subsequent to the metal decoration. Interestingly the presence of additional metallic NCs, such as Au and Pt not only improves their thermal stability but also leads to the formation of bi-metallic alloys semiconductor heterostructure.
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Söderlind, Fredrik. "Colloidal synthesis of metal oxide nanocrystals and thin films." Doctoral thesis, Linköpings universitet, Institutionen för fysik, kemi och biologi, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-11831.
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A main driving force behind the recent years’ immense interest in nanoscience and nanotechnology is the possibility of achieving new material properties and functionalities within, e.g., material physics, biomedicine, sensor technology, chemical catalysis, energy storing systems, and so on. New (theoretical) possibilities represent, in turn, a challenging task for chemists and physicists. An important feature of the present nanoscience surge is its strongly interdisciplinary character, which is reflected in the present work. In this thesis, nanocrystals and thin films of magnetic and ferroelectric metal oxides, e.g. RE2O3 (RE = Y, Gd, Dy), GdFeO3, Gd3Fe5O12, Na0.5K0.5NbO3, have been prepared by colloidal and sol-gel methods. The sizes of the nanocrystals were in the range 3-15 nm and different carboxylic acids, e.g. oleic or citric acid, were chemisorbed onto the surface of the nanoparticles. From FT-IR measurements it is concluded that the bonding to the surface takes place via the carboxylate group in a bidentate or bridging fashion, with some preference for the latter coordination mode. The magnetic properties of nanocrystalline Gd2O3 and GdFeO3 were measured, both with respect to magnetic resonance relaxivity and magnetic susceptibility. Both types of materials exhibit promising relaxivity properties, and may have the potential for use as positive contrast enhancing agents in magnetic resonance imaging (MRI). The nanocrystalline samples were also characterised by transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), and quantum chemical calculations. Thin films of Na0.5K0.5NbO3, GdFeO3 and Gd3Fe5O12 were prepared by sol-gel methods and characterized by x-ray powder diffraction (XRPD) and scanning electron microscopy (SEM). Under appropriate synthesis conditions, rather pure phase materials could be obtained with grain sizes ranging from 50 to 300 nm. Magnetic measurements in the temperature range 2-350 K indicated that the magnetization of the perovskite phase GdFeO3 can be described as the sum of two contributing terms. One term (mainly) due to the spontaneous magnetic ordering of the iron containing sublattice, and the other a susceptibility term, attributable to the paramagnetic gadolinium sublattice. The two terms yield the relationship M(T)=M0(T)+χ(T)*H for the magnetization. The garnet phase Gd3Fe5O12 is ferrimagnetic and showed a compensation temperature Tcomp ≈ 295 K.
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Sayevich, Uladzimir. "Synthesis, Surface Design and Assembling of Colloidal Semiconductor Nanocrystals." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-209074.
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The work presented in the thesis is focused on the synthesis of diverse colloidal semiconductor NCs in organic media, their surface design with tiny inorganic and hybrid capping species in solution phase, and subsequent assembling of these NC building units into two-dimensional close-packed thin-films and three-dimensional non-ordered porous superstructures.
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SHAMSI, JAVAD. "Colloidal Synthesis of Lead Halide Perovskite Nanocrystals for Optoelectronic Application." Doctoral thesis, Università degli studi di Genova, 2018. http://hdl.handle.net/11567/929994.
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Berestok, Taisiia. "Assembly of colloidal nanocrystals into porous nanomaterials." Doctoral thesis, Universitat de Barcelona, 2018. http://hdl.handle.net/10803/663275.
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This thesis focuses on different aspects of NCs colloidal synthesis, the exploration of the relevant surface chemistries that afford NC assembly and the NC implementation into porous nanomaterials.
The work is divided into two blocks. The first block is devoted to developing and optimizing the synthesis of NCs followed by the examination of their suitability for potential applications in catalysis and photocatalysis. The second block is dedicated to establish procedures to fabricate single-component or multicomponent porous nanomaterials from NC building blocks. To embrace the use of the developed strategies in different application fields, several kind of materials were under research. Namely, metals (e.g. Au), metal oxides (e.g. CeO2, TiO2, Fe2O3), metal chalcogenides (e.g. In2S3, ZnS, PbS, CuGaS2 and Cu2ZnSnSe4), and their composites.
CeO2 NCs synthesis was deeply investigated with the aim to achieve a proper control on the NCs morphology, facets exposed, crystal phase, composition, etc., required for application. Overall, CeO2 NCs with spherical, octapod-like branched, cubic hyperbranched, and kite-like morphology with sizes in the range 7 to 45 nm were produced by adjusting experimental conditions of the synthetic protocol. Branched and hyperbranched NCs showed higher surface areas, porosities and oxygen capacity storage values compared to quasi-spherical NCs.
The NCs morphology-controlled synthesis has been extended to quaternary Cu2ZnSnSe4 (CZTSe). CZTSe NCs with narrow size distribution and controlled composition were produced. It was shown how off-stoichiometric CZTSe compositions were characterized by higher charge carrier concentrations and thus electrical conductivities.
The strategy to functionalize the metal oxide NC surface composition by applying different ligands is proposed. This enables to develop a novel approach to assemble metal oxide NCs into porous gel and aerogel structures. Propylene oxide has been found to trigger the gelation process of glutamine functionalized NCs. The detailed investigation of the gelation mechanism is demonstrated for the case of ceria. The method is applied for NCs with different morphologies. Eventually, the versatility of the concept is proved by using of the proposed approach for the TiO2 and Fe2O3 nanocrystals.
The assembly method has been extended to metal chalcogenides - In2S3 NCs - starting from the NCs synthesis, with further surface chemistry manipulation and eventually follows by the NC assembly into gels and aerogels. The optimization of NC surface chemistry was achieved by testing different ligand exchange approaches via applying short-chain organic and inorganic ligands. The assembly method based on ligand desorption from the NC surface and chalcogenide-chalcogenide bond formation has been established for In2S3. The comparison of the different ligands impact on the NC performance in colloidal form, when assembled into gels and when supported onto substrate is investigated towards photoelectrocatalysis.
The oxidative ligand desorption assembly approach has been extended for multicomponent NCs for the case of CuGaS2 and CuGaS2-ZnS. Optimization of spin-coating process of the formed NCs inks followed by applying of sol-gel chemistry led to formation of highly porous layers from TGA-CuGaS2 and TGA-ZnS. Applied results of CuGaS2/ZnS nanocrystal-based bilayers and CuGaS2–ZnS nanocrystal-based composite layers have been shown by testing their photoelectrochemical energy conversion capabilities.
The approach to adjust NC surface chemistry has been proposed and tested for performing multicomponent NC assemblies. Applying of different ligands for NC surface functionalization endows their surface with different charges which usually provides colloidal NCs stabilization. It has been found that mixing of oppositely
charged NCs with certain concentration enabled their assembly/gelation via electrostatic interaction. The proposed approach has been applied and optimized to produce multicomponent NC gels and aerogels. The detailed investigation of the gelation mechanism is shown for combination of metal-metal oxide and metal oxide-metal chalcogenide NCs (Au-CeO2, CeO2-PbS). Applied results of the Au-CeO2 aerogels were demonstrated for CO-oxidation.Esta tesis se centra en la síntesis coloidal de nanocristales (NCs), en la exploración de su química de superficie y en su ensabanado en nanomateriales porosos funcionales. Para demostrar la versatilidad de aplicación de dichas estructuras, en este estudio se han considerado NCs de distintos tipos de materiales: metales (Au), óxidos metálicos (CeO2, TiO2, Fe2O3), calcogenuros metálicos (In2S3, ZnS, PbS, CuGaS2,Cu2ZnSnSe4) y sus materiales compuestos. El trabajo se dividió en dos bloques. En el primero se desarrolló y optimizó la síntesis de NCs de óxidos y calcogenuros metálicos y se evaluó su potencial para aplicaciones de catálisis y fotocatálisis. Se investigó en profundidad la síntesis de NCs de CeO2, poniendo énfasis en controlar su morfología. Se consiguió producir NCs de CeO2 de forma controlada (esférica, octapodo ramificado, cúbico ramificado y romboidal) y con tamaño controlado (7-45 nm). Asimismo, se obtuvieron NCs de Cu2ZnSnSe4 con una fina distribución de tamaños y composición controlada. En el segundo bloque se establecieron y estudiaron procedimientos para fabricar nanomateriales porosos mono- o multicomponentes a partir del ensamblado de NCs. Se desarrolló una estrategia basada en el ajuste de la química de superficie de NCs de óxidos metálicos (CeO2, Fe2O3,TiO2) y de calcogenuros metálicos (In2S3, CuGaS2-ZnS) que permitió su ensamblaje controlado en estructuras porosas de tipo gel y aerogel. En el caso de los óxidos metálicos, se determinó que el ensamblado se inicia con la adición de un epóxido a NCs funcionalizados con glutamina, causando la gelación. La desorción oxidativa de ligandos basada en la formación de enlaces calcogenuro-calcogenuro se propuso como mecanismo de gelación en calcogenuros mono- (In2S3) y multicomponente (CuGaS2-ZnS). Se investigó el impacto del empleo de distintos ligandos en la eficiencia foto-electrocatalítica de NCs en forma coloidal, ensamblados en geles y soportados en sustratos. Se desarrolló y estudió el ajuste de la química de superficie de NCs para la obtención de ensamblajes multicomponente mediante interacción electrostática de coloides en suspensión. El mecanismo de gelación fue investigado al detalle para materiales compuestos de NCs de oxido metálico (CeO2) con NCs de óxido de calcogenuro (PbS-CeO2) y metálicos (Au-CeO2). Los aerogeles de Au-CeO2 demostraron potencial para la oxidación de CO.
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Fisher, Aidan Antony Edward. "Colloidal synthesis, structural characterisation and single molecule spectroscopy of semiconducting nanocrystals." Thesis, University of Sussex, 2018. http://sro.sussex.ac.uk/id/eprint/73443/.
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Panthani, Matthew George. "Colloidal Nanocrystals with Near-infrared Optical Properties| Synthesis, Characterization, and Applications." Thesis, The University of Texas at Austin, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=3572875.
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Colloidal nanocrystals with optical properties in the near-infrared (NIR) are of interest for many applications such as photovoltaic (PV) energy conversion, bioimaging, and therapeutics. For PVs and other electronic devices, challenges in using colloidal nanomaterials often deal with the surfaces. Because of the high surface-to-volume ratio of small nanocrystals, surfaces and interfaces play an enhanced role in the properties of nanocrystal films and devices.
Organic ligand-capped CuInSe2 (CIS) and Cu(InXGa 1-X)Se2 (CIGS) nanocrystals were synthesized and used as the absorber layer in prototype solar cells. By fabricating devices from spray-coated CuInSe nanocrystals under ambient conditions, solar-to-electric power conversion efficiencies as high as 3.1% were achieved. Many treatments of the nanocrystal films were explored. Although some treatments increased the conductivity of the nanocrystal films, the best devices were from untreated CIS films. By modifying the reaction chemistry, quantum-confined CuInSe XS2-X (CISS) nanocrystals were produced. The potential of the CISS nanocrystals for targeted bioimaging was demonstrated via oral delivery to mice and imaging of nanocrystal fluorescence.
The size-dependent photoluminescence of Si nanocrystals was measured. Si nanocrystals supported on graphene were characterized by conventional transmission electron microscopy and spherical aberration (Cs)-corrected scanning transmission electron microscopy (STEM). Enhanced imaging contrast and resolution was achieved by using Cs-corrected STEM with a graphene support. In addition, clear imaging of defects and the organic-inorganic interface was enabled by utilizing this technique.
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Ho, Minh Q. "Colloidal Synthesis and Optical Characterizations of Semiconductor Nanocrystals from Nontoxic Elements." VCU Scholars Compass, 2015. http://scholarscompass.vcu.edu/etd/3915.
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To date, the search efforts have shifted from the toxic II-VI, III-V and IV-VI semiconductors to more environmentally friendly materials. Among Group II-V semiconductors, Zn3P2 has shown to be a more benign option, similar to Group IV (Ge, Si) materials, for future applications in photovoltaics and optoelectronics. This work is dedicated to the development of wet-chemical synthetic routes of (1) Zn3P2 and (2) Group IV (Ge, Si, Si1-xGex) nanocrystals with precise control over composition, crystal structure, size and dispersity by adjusting different reaction parameters such as temperature, time and solvent composition. Different characterizations will also be employed to probe the size- and composition-dependent physical and optical properties of resulting products.
The first part of this work illustrates the synthesis of luminescent Zn3P2 nanocrystals, an earth-abundant and a direct-gap semiconductor possessing high absorption coefficient and long carrier diffusion length, which uphold promising potential in many optoelectronic applications. A hot injection method by using highly reactive P and Zn precursors (P[Si(CH3)3]3 and diethyl zinc) in hexadecylamine and octadecene was developed to prepare a series of alkyl-amine-passivated tetragonal Zn3P2 crystallites with varying size sizes. Substantial blue shifts in the absorption onsets (2.11−2.73 eV) in comparison to the bulk counterpart (1.4−1.5 eV) and a clear red shift with increasing particle size indicates the quantum confinement effects. This is also consistent with the photoluminescent studies with the size-tunable maxima in the visible region (469−545 nm) as a function of growth temperature and time. The phase purity and alkyl-amine passivation of the nanocrystals were determined by structural and surface analysis, confirming the presence of N–Zn and N–P bonds on the tetragonal Zn3P2 crystallites.
The second part of this works focuses on the development of a colloidal synthetic strategy of alkyl-amine capped Si1-xGex nanocrystals with control over size- and composition-dependent optical properties. Despite their high miscibility at all compositions, developing a wet-chemical synthesis of Si1-xGex alloys in the nanoscale remains a challenging task, owing to the difference of their crystallization temperatures and the high surface oxidation of Si. Thus an adapted colloidal method is utilized to fabricate single-element Ge and Si nanocrystals. Powder X-ray diffraction indicates successful production of cubic crystalline Ge and amorphous Si nanoparticles individually in oleylamine/octadecene (surfactant/solvent) mixture at 300°C. Absorption onset values of 1.28 eV and 3.11 eV are obtained for resulting Ge and Si colloids, respectively. By alloying these two materials in their nano-regime, tunable optical properties can be achieved throughout the visible to the near IR region by simply varying their elemental compositions. The success of this bandgap engineering process offers more options for new material design by taking advantage of unique properties from each component material.
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GONCALVES, GUILHERME. "Colloidal synthesis and characterization of two- and three-dimensional semiconductor nanocrystals." Doctoral thesis, Università degli studi di Genova, 2018. http://hdl.handle.net/11567/930563.
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Yuan, Ying [Verfasser], and Michael [Akademischer Betreuer] Krüger. "Colloidal CdE (E= S, Se and Te) nanocrystals: from synthesis to applications." Freiburg : Universität, 2016. http://d-nb.info/1122831633/34.
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CAPITANI, CHIARA. "Synthesis of semiconductor colloidal nanocrystals with large Stokes-shift for luminescent solar concentrators." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2022. http://hdl.handle.net/10281/366195.
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I concentratori solari luminescenti (LSCs) sono delle guide d’onda composti da una matrice polimerica drogata o ricoperta con fluorofori. La luce solare diretta e/o diffusa che penetra nella matrice è assorbita dai fluorofori e poi riemessa dagli stessi con energia minore. La luce emessa, grazie alla riflessione totale interna, propaga fino a raggiungere i bordi della guida d’onda dove è convertita in elettricità da celle fotovoltaiche poste sul perimetro della matrice.
L’efficienza del dispositivo è ridotta da numerosi processi di perdita, sia dovuti alla riflessione della matrice e al cono di fuga, sia quelli che dipendono dalle caratteristiche dei fluorofori, come il coefficiente di assorbimento, il quantum yield (QY) di fotoluminescenza (PL) e il riassorbimento.
Per minimizzare tali perdite, una buona alternativa ai tradizionali fluorofori sono i quantum dots (QDs) colloidali che presentano solitamente un elevato QY, un alto coefficiente di assorbimento e una lunghezza d’onda di emissione controllabile cambiando le dimensioni dei nanocristalli tramite modifiche dei parametri di sintesi. Inoltre, ingegnerizzando opportunamente i QDs, è possibile realizzare particelle con elevato Stokes-shift tra gli spettri di assorbimento ed emissione, in modo da ridurre quanto più possibile il riassorbimento.
Il progetto si è quindi focalizzato sullo sviluppo della sintesi di QDs, al fine di ottimizzare il QY di fotoluminescenza, la compatibilizzazione con la matrice polimerica e la fotostabilità, limitando comunque il riassorbimento.
Inoltre. la procedura di sintesi deve essere facilmente trasportabile su volumi industriali, per soddisfare il fabbisogno di produzioni di elevati metri quadrati di LSCs.
Durante i tre anni di progetto di dottorato in Alto Apprendistato ho potuto sviluppare una procedura di sintesi che consiste in quattro step:
• crescita di nanocristalli di CuInS2 core;
• formazione del quaternario tramite aggiunta di zinco (ZnCuInS2); passaggio cruciale per aumentare il QY e controllare la lunghezza d’onda di emissione;
• crescita di una shell di solfuro di zinco (ZnCuINS2/ZnS) per passivare la superficie dei nanocristalli, aumentare il QY e la fotostabilità;
• trattamento post sintesi di scambio di leganti parziale per migliorare la solubilità nella matrice polimerica.
I nanocristalli così prodotti mostrano un QY del 60% ed un’ottima solubilità nella matrice polimerica. Infatti, è stato prodotto un LSC di grande dimensione (30 cm x 30 cm x 0.7 cm) la cui optical power efficiency, OPE = 6.8%.
Inizialmente ho sviluppato la procedura di sintesi in un pallone di vetro da 25 mL, producendo 250 mg a sintesi. Grazie all’attrezzatura fornita da Glass to Power S.p.A ho potuto studiare lo scale-up della sintesi. Dapprima ho effettuato studi preliminare, per approfondire alcune possibili problematiche dovute all’aumento dei volumi, su palloni di maggiori dimensioni, 500 mL e 2 L. Analizzate e risolte le tematiche di riscaldamento e stop della sintesi ho effettuato sintesi in un reattore preindustriale producendo 300 g di nanocristalli di ZnCuINS2/ZnS.
Oltre ad incrementare la produzione di sintesi da 250 mg a 300 g mi sono occupata dell’ottimizzazione della procedura di sintesi. Ho testato diverse strategie per incrementare il QY senza danneggiare la solubilità nel polimero. Grazie ad una variazione di reagente nel secondo step e ad un incremento dei layer della shell ho ottenuto nanocristalli con 80% di QY.
Il prossimo step sarà effettuare lo scale-up di questa nuova procedura e produrre LSC di grandi dimensioni.
Grazie alle collaborazioni con altri studenti di dottorato ho sintetizzato nanocristalli di calcogenuro drogati oro e opportunamente decorati con molecole coniugate per sistemi di up-conversion. Grazie all’introduzione dell’oro in questi sistemi si è ottenuta un’efficienza di up-conversion del 12%.Luminescent solar concentrators (LSCs) are waveguides composed of a polymeric matrix doped or coated with fluorophores. The direct and/or diffuse sunlight that penetrates the matrix is absorbed by the fluorophores and then re-emitted by them with less energy. The light emitted, thanks to the total internal reflection, propagates until it reaches the edges of the wave guide where it is converted into electricity by photovoltaic cells placed on the perimeter of the matrix. The efficiency of the device is reduced by numerous loss processes, due to the reflection of the matrix and the escape cone, and/or due to the characteristics of the fluorophores, such as the absorption coefficient, the quantum yield (QY) of photoluminescence (PL) and the reabsorption. To minimize losses due to fluorophores, a good alternative are colloidal quantum dots (QDs) that usually have a high QY, a high absorption coefficient and a controllable emission wavelength by changing the size of the nanocrystals. Furthermore, by properly engineering the QDs, it is possible to realize particles with high Stokes-shift between the absorption and emission spectra, in order to reduce the reabsorption as much as possible. The project is focused on the development of the synthesis of QDs, in order to optimize the QY of photoluminescence, compatibility with the polymer matrix and photostability, while limiting the reabsorption. Besides. the synthesis procedure must be easily transferable on industrial volumes, to meet the production needs of high square meters of LSCs. During the three years of the doctoral project in High Apprenticeship I was able to develop a synthesis procedure consisting of four steps: • growth of CuInS2 core nanocrystals; • quaternary formation with zinc addition (ZnCuInS2); crucial step to increase the QY and control the emission wavelength; • growth of a zinc sulphide shell (ZnCuInS2/ZnS) to passivate the surface of nanocrystals, increase QY and photostability; • post-synthesis treatment of the partial exchange of ligands to improve solubility in the polymer matrix. The nanocrystals thus produced show 60% QY and excellent solubility in the polymer matrix. In fact, a large size LSC (30 cm x 30 cm x 0.7 cm) was produced, whose optical power efficiency, OPE = 6.8%. Initially, I developed the synthesis procedure in a 25 ml glass flask, producing 250 mg for batch. Thanks to the equipment provided by Glass to Power s.p.A I was able to study the increase in the scale of the synthesis. Firstly, in order to investigate some possible problems due to the increase in volumes, I have carried out preliminary studies on larger balloons, 500 mL and 2 L. After analysis of heating and quenching of synthesis, I have performed the synthesis in a preindustrial reactor producing 300 g of nanocrystals of ZnCuInS2/ZnS. In addition I also optimized the synthesis procedure. I tested several strategies to increase QY without damaging solubility in the polymer. Thanks to a variation of the reagent in the second step and an increase of the shell layers, I obtained nanocrystals with 80% of QY. The next step will be to scale up this new procedure and produce large LSCs. I collaborated with other PhD students, in particular, I synthesized with a heat-up method CdSe nanocrystals doped with Au7 clusters and decorated with conjugated dyes as efficient triplet sensitizers or up-conversion applications (gold doping improves up-conversion efficiency). The beneficial effects of the doping strategy result in a maximum UC efficiency of 12%, which is an unprecedented result for up-conversion based on decorated NCs as triplet sensitizers.
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Premathilaka, Shashini M. "Synthesis and Optical Properties of Colloidal PbS Nanosheets." Bowling Green State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1561463157379607.
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Razgoniaeva, Natalia Razgoniaeva. "Photochemical energy conversion in metal-semiconductor hybrid nanocrystals." Bowling Green State University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1465822519.
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ROSINA, IRENE. "Exploiting Cation Exchange Reactions in Doped Colloidal NIR Semiconductor Nanocrystals: from synthesis to applications." Doctoral thesis, Università degli studi di Genova, 2020. http://hdl.handle.net/11567/1019427.
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Colloidal quantum dots (CQDs) have tunable optical properties through manipulation of their size, shape, and surface chemistry. Among pholuminescent QDs, near-infrared (NIR) emitting ones are of particular interest since they can be used in several applications, from the labeling in living tissues, to the integration in commercial optoelectronic devices, like photovoltaics for solar energy conversion or photodetectors from visible to the near-infrared and mid-infrared. In addition, the exciting promise of CQDs is that is associated with easy and low-cost device fabrication process. In fact, solution-based techniques like spin-coating, dip coating and ink-jet printing are typically used for solution CQDs readily to be used in large-area processing techniques.
Thus, to obtain an ink solution of nanocrystals (NCs) ready to be used in device fabrication process, in this thesis, cation exchange (CE) reactions have been used as a convenient tool to finely transform NCs directly in solution or deposited as thin films. These reactions allow to substitute a fraction or all “host” metal cations of pre-synthesized NCs with new “guest” cations while preserving both NCs’ size, shape and, typically, crystal structure. Depending on the miscibility of the reactant and product materials, and on the kinetics of the CE reaction, different types of nanostructures can be accessed ranging from alloy NCs, doped systems, dimers, core@shell (or core@graded-shell) heterostructures even with elaborated architectures (i.e., quantum wells, multiple-cores@shell). Unlike ion substitution in solids, cation exchange at nanoscale results in fast reaction rate and an easy modulation of the thermodynamics through selective ion coordination in solution.
This study provides an overview of the CE on semiconductor NCs, in particular on II-VI, I-III-VI2 and III-VI compounds. We first explore the exchange between cadmium chalcogenides and mercury ions to produce Cd1-xHgxTe CQDs which can be potentially employed in NIR photodetectors and photovoltaic devices. Our developed synthesis is a result of a wide systematic investigation process, in which we varied specific physical parameters, such as the reaction temperature, the feed molar ratio of the precursor and the solvent. More specifically, these aspects were studied to have control on the size, shape, surface composition and crystalline phase after mild conditions of annealing into stable connected crystals. This peculiarity could be exploited to boost the photogenerated charges diffusion in polycrystalline photoconducting films fabricated by means of an ink of NCs solution.
Additionally, another aspect studied was the surface passivation of Cd1-xHgxTe colloidal NCs, in order to understand how to optimize the charge transfer efficiency among the nanocrystals. The carrier transport in QD devices differs fundamentally from band transport in bulk semiconductors. In nanocrystal film it is of fundamental relevance to improve the mobility of the photogenerated charges. Noteworthy, the granularity of the system and the consequent coupling between adjacent dots can produce additional physical parameters, as charge recombination. The carrier diffusion length can be limited by trapping sites1. To overcome these limitations, post-synthetic strategies that couple the high quality NCs solutions with ideal properties (band gap, absorption, monodispersivity) and high-quality films (quantum dot packing, passivation, and absorptive/conductive properties) are necessary. Indeed, to improve the inter-NCs conductivity in a NC film, ligand exchange and stripping procedures are widely used, with the aim of replacing insulating surfactants with more conductive species. These procedures have some drawbacks, for example metal cations can desorb from the surface of the NCs during the stripping. On the contrary, here we will show how our nano heterostructures (NHCs) enable to avoid the post-process ligand stripping and to perform the final annealing step in milder conditions.
Above these considerations, CE can be exploited to address NCs solution through surface uniformity from the nano- to the macroscopic scale. This is the first step toward electronic coupling between the separate building blocks of nanocrystals.
Apart from III-V QDs, we shifted our research activity on valid alternative material which do not contain toxic heavy metals such as Cd, Pb, As or Hg, and that offer a high flexibility for tuning band gap in the NIR window. In chapter 5, the results about the study of a III-V system are reported. Thus, we studied InP system, which is probably the only one that could provide a compatible emission color range similar to that of Cd-based QDs but without intrinsic toxicity. Nevertheless, the synthesis of III-V NCs, due to their covalent-bond character, is limited by long reaction times or an uncontrollably fast nucleation that may lead to the formation of amorphous or bulk compounds. The role of our work is to explore the reported InP synthesis and to further improve the luminescent properties of these systems Here we study the effect of different parameter (molar concentration in reaction mixture, the use of different phosphorous precursors) to enhance the control over the particle size and size distribution. After that, we studied different Sulphur source precursors to obtain InP@ZnS core@shell NCs with high quantum Yield (QY).
In the last chapter, we describe also I-III-VI2 system as CuInS2 for photoluminescence modulation. In this Chapter Copper Indium Sulfide nanocrystals are prepared using a single-step heating up method relying on the low thermal stability of ter- dodecanethiol used as stabilizing agent, solvent, and sulfur precursors. The obtained particles exhibit an emission varying from 710 to 940 nm. This range depends on the extent of the heating time (pre-heating) before the threshold temperature of 230°C for the growth process of ternary semiconductor NCs such as of CIS nanocrystals. Afterwards we report on the procedure for the growth of a ZnS shell, which enables a blueshift of the PL emission wavelength with respect to those of their parent CIS, due to the widening of the band gap for the entrance of zinc ions into the CIS structures.
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Pedetti, Silvia. "Synthesis and optical properties of II-VI colloidal two-dimensional nanocrystals : homo- and hetero-structures." Electronic Thesis or Diss., Paris 6, 2015. http://www.theses.fr/2015PA066755.
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Ces travaux de thèse ont porté sur une nouvelle classe de semi-conducteurs colloïdaux sous forme de nanoplaquettes composées de chalcogénures de cadmium. Ces nanocristaux, comparables à des puits quantiques, présentent un confinement excitonique dans une seule direction, l’épaisseur, qui est contrôlée au niveau atomique. Les nanoplaquettes sont caractérisées par une excellente résolution spectrale et de bons rendements quantiques. Par conséquence, elles représentent de potentiels candidats pour développer des dispositifs optoélectroniques comme des diodes électroluminescentes ou bien des photo-détecteurs. Toutefois, dans ce but, il est nécessaire d’élargir la gamme de longueurs d’ondes d’absorption et d’émission et d’augmenter leur rendement quantique. Pour cela, nous avons étudié la synthèse colloïdale de nanoplaquettes à base d’homo- et d’hétèro-nanoplaquetts des groupes II-VI. Les nanocristaux fabriqués ont été caractérisé par spectroscopie UV-visible et de fluorescence, par diffraction à rayons X et par microscopie électronique. Dans un premier temps, nous avons optimisé la préparation de nanoplaquettes de CdTe en utilisant des procédés de synthèse colloïdale par injection de précurseurs à hautes températures. Ensuite, des structures plus complexes ont été investiguées. Par exemple, nous avons synthétisé nanoplaquettes cœur/couronne de CdSe/CdTe qui possèdent une structure électronique de type-II. Nous avons également étudié la croissance de couches d’un deuxième semi-conducteur dans la direction de l’épaisseur de plaquettes cœur pour la fabrication de structures type cœur/coque. Grâce au contrôle de la composition chimique du cœur et de la coque, l’alignement de bande a été modulé pour obtenir structures électroniques de type-I, quasi type-II et type-IIThis thesis project is based on the development of a novel class of colloidal two-dimensional nanocrystals, i.e. nanoplatelets (NPLs), composed of cadmium chalcogenides. These nanocrystals, in analogy to quantum wells, are characterized by an exciton confinement along one direction, i.e. the thickness, which can be controlled at atomic level. Nanoplatelets possess unique optical features as an excellent spectral resolution and good quantum yields. As consequence these nanocrystals are potential candidates for the fabrication of optoelectronic devices such as electroluminescent diodes or photo-detectors. However, for this aim it is necessary to enlarge the range of the absorption and emission wavelengths and to increase their quantum yield. For this reason, we investigated the colloidal synthesis of II-VI homo- and hetero-nanoplatelets which have been characterized by UV-Vis and photoluminescence spectroscopy, by X-ray diffraction and by electronic microscopy. First, we optimized the synthesis of CdTe NPLs using colloidal synthesis based on precursors injection at high temperatures. Then, we focused on more complexes hetero-structures. For example, through lateral extension reactions we obtained CdSe/CdTe core/crown NPLs which possess a type-II electronic structure. Successively, we studied the synthesis of core/shell NPLs by the growth of a second semiconductor layer along the thickness of NPLs cores. Depending on the core and shell chemical composition we could engineer the band gap of the nanoplatelets between type-I, quasi type-II and type-II electronic structures
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Sayevich, Uladzimir Verfasser], Alexander [Akademischer Betreuer] [Gutachter] Eychmüller, and Eike [Gutachter] [Brunner. "Synthesis, Surface Design and Assembling of Colloidal Semiconductor Nanocrystals / Uladzimir Sayevich ; Gutachter: Alexander Eychmüller, Eike Brunner ; Betreuer: Alexander Eychmüller." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://d-nb.info/1114068004/34.
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Bhandari, Khagendra P. "Characterization and Application of Colloidal Nanocrystalline Materials for Advanced Photovoltaics." University of Toledo / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1430327894.
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Stroyuk, Oleksandr, Alexandra Raevskaya, Oleksandr Selyshchev, Volodymyr Dzhagan, Nikolai Gaponik, Dietrich R. T. Zahn, and Alexander Eychmüller. "“Green” Aqueous Synthesis and Advanced Spectral Characterization of Size-Selected Cu2ZnSnS4 Nanocrystal Inks." Macmillan Publishers Limited, 2018. https://tud.qucosa.de/id/qucosa%3A33825.
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Structure, composition, and optical properties of colloidal mercaptoacetate-stabilized Cu2ZnSnS4 (CZTS) nanocrystal inks produced by a “green” method directly in aqueous solutions were characterized. A size-selective precipitation procedure using 2-propanol as a non-solvent allows separating a series of fractions of CZTS nanocrystals with an average size (bandgap) varying from 3 nm (1.72 eV) to 2 nm (2.04 eV). The size-selected CZTS nanocrystals revealed also phonon confinement, with the main phonon mode frequency varying by about 4 cm−1 between 2 nm and 3 nm NCs.
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Kirsanova, Maria. "ZnSe/CdS Core/Shell Nanostructures and Their Catalytic Properties." Bowling Green State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1342565590.
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Dorfs, Dirk [Verfasser]. "Advanced shape, composition, and property control in colloidal nanocrystal synthesis / Dirk Dorfs." Hannover : Gottfried Wilhelm Leibniz Universität, 2018. http://d-nb.info/1172414203/34.
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Herz, Erik. "Colloidal Semiconductor Nanocrystals: A Study of the Syntheses of and Capping Structures for CdSe." Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/10147.
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Luminescent quantum dots (QDs) or rods are semiconductor nano-particles that may be used for a wide array of applications such as in electro-optical devices, spectral bar coding, tagging and light filtering. In the case under investigation, the nano-particles are cadmium-selenide (CdSe), though they can be made from cadmium-sulfide, cadmium-telluride or a number of other II-VI and III-V material combinations. The CdSe quantum dots emit visible light at a repeatable wavelength when excited by an ultraviolet source. The synthesis of colloidal quantum dot nanoparticles is usually an organo-metallic precursor, high temperature, solvent based, airless chemical procedure that begins with the raw materials CdO, a high boiling point ligand, and a Se-trioctylphosphine conjugate. This investigation explores the means to produce quantum dots by this method and to activate the surface or modify the reaction chemistry with such molecules as trioctylphosphine oxide, stearic acid, dodecylamine, phenyl sulfone, aminophenyl sulfone, 4,4'dichlorodiphenyl sulfone, 4,4'difluorodiphenyl sulfone, sulfanilamide and zinc sulfide during the production to allow for further applications of quantum dots involving new chemistries of the outer surface. Overall, the project has been an interesting and successful one, producing a piece of equipment, a lot of ideas, and many dots with varied capping structures that have been purified, characterized, and stored in such a way that they are ready for immediate use in future projects.Master of Science
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Cable, Robert E. "Synthesis and characterization of patterned surfaces and catalytically relevant binary nanocrystalline intermetallic compounds." [College Station, Tex. : Texas A&M University, 2007. http://hdl.handle.net/1969.1/ETD-TAMU-2026.
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Stott, Nathan E. 1973. "Novel synthetic routes to high-quality II-VI colloidal nanocrystals : controlled growth using mild precursors in the presence of selected ligands." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/26719.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2004.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references.
by Nathan E. Stott.
Ph.D.
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Tamang, Sudarsan. "Synthèse et fonctionnalisation des nanocristaux émettant dans le proche infrarouge pour l'imagerie biologique." Phd thesis, Université de Grenoble, 2011. http://tel.archives-ouvertes.fr/tel-00665109.
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Cette thèse concerne le développement de nanocristaux (NCs) cœur/coquille d'InP/ZnS émettant dans le proche infrarouge pour l'imagerie biologique. Dans la synthèse chimique des NCs cœur d'InP, nous avons utilisé la phosphine générée in situ comme précurseur de phosphore en combinaison avec le myristate d'indium comme précuseur d'indium et l'1-octadécène comme solvant. Les NCs obtenus sont hautement cristallins et présentent une fluorescence dans la gamme 720-750 nm, selon leur taille. La croissance d'une ou deux monocouches (coquille) de ZnS sur la surface des NCs d'InP a considérablement amélioré leur rendement quantique de fluorescence. Nous avons de plus étudié le transfert de phase de ces NCs InP/ZnS du milieu organique au milieu aqueux en utilisant diverses molécules hydrophiles contenant un groupe thiol. En particulier, nous nous sommes intéressés au transfert de phase avec des molécules zwitterioniques tels que la penicillamine et la cystéine afin d'obtenir une taille hydrodynamique compacte, et de réduire les interactions non-spécifiques en milieu biologique. Dans l'étude du transfert de phase, l'accent a été mis sur la stabilité colloïdale des NCs et sur la préservation de leur efficacité de fluorescence en milieu aqueux. La cytotoxicité des NCs InP/ZnS fonctionnalisés avec la pencillamine a été évaluée en culture cellulaire. Puis la bio-distribution de ces NCs a été étudiée dans des souris vivantes par imagerie de fluorescence grâce à leur émission dans le proche infrarouge. Pour finir, les fonctionnalisations de NCs InP/ZnS d'une part avec un peptide de pénétration cellulaire, d'autre part avec des agents de contraste IRM (complexes de gadolinium) et enfin avec un nombre contrôlé de molécules streptavidine ont été explorées, démontrant le grand intérêt de ces NCs pour l'imagerie biologique. Mots clés: phosphure d'indium, boîtes quantiques, nanocristaux, imagerie biologique de fluorescence, infrarouge, transfert de phase, fonctionnalisation de surface
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Stowell, Cynthia Ann. "Aspects of colloidal nanocrystals: patterning, catalysis and doping." Thesis, 2005. http://hdl.handle.net/2152/1735.
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Hendricks, Mark Patrick. "The Synthesis of Colloidal Metal Sulfide Nanocrystals." Thesis, 2015. https://doi.org/10.7916/D8HD7V35.
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As nanotechnology becomes ever more pervasive in everyday life, the ability to control the bottom-up synthesis of nanomaterials is of great technological interest. In particular, colloidal semiconducting nanocrystals, or quantum dots, are beginning to find applications in biological imaging, solar cells, and as down-converters for LED-driven light bulbs and displays. Herein we report various experimental endeavors that explore the role of the precursors used to make these nanocrystals, with a special interest in the kinetics of their reactivity. In doing so, we highlight the influence that precursor conversion rate has on the size of nanocrystals, which is essential to optimizing their performance
in optoelectronic devices, catalysis, and imaging applications.
After surveying the history, applications, and theoretical models describing the synthesis of semiconductor nanocrystals, we focus on phosphine-based precursors. We describe the synthesis of cadmium bis(diphenyldithiophosphinate) (Cd(S₂PPh₂)₂) from secondary phosphine sulfides and its conversion to cadmium sulfide nanocrystals. Heating Cd(S₂PPh₂)₂ and
cadmium tetradecanoate to 240 °C results in complete
conversion of Cd(S₂PPh₂)₂ to cadmium sulfide nanocrystals with tetradecanoate surface termination. The nanocrystals have a narrow size distribution that is evident from the line width of the
lowest energy absorption feature and
display bright photoluminescence. Monitoring the reaction with ³¹P NMR, UV-Visible, and infrared absorption spectroscopies shows that the production of cadmium diphenylphosphinate (Cd(O₂PPh₂)₂) and tetradecanoic anhydride co-products is coupled with the formation of cadmium sulfide. From these measurements we propose a balanced chemical equation for the conversion reaction and use it to optimize a synthesis that affords CdS nanocrystals in quantitative yield. Interestingly, the final diameter is insensitive to the reaction conditions, including the total concentration of precursors, which we attribute to a first-order rate of precursor conversion.
Using CdS nanocrystals synthesized from Cd(S₂PPh₂)₂ as a model system, we demonstrate that metal carboxylate complexes (L− Cd(O₂CR)₂, R = oleyl, tetradecyl) are
readily displaced from carboxylate-terminated nanocrystals. Removal of up to 90% of surface-bound Cd(O₂CR)₂ from the CdS nanocrystals is possible with N,N,N’,N’-tetramethylethylenediamine (TMEDA), decreasing the photoluminescence quantum yield (PLQY) from 20% to <1% and broadening the 1Sₑ-2S_(3/2)h absorption feature. These changes are partially reversed upon rebinding of M(O₂CR)₂ at room temperature (∼60%) and fully reversed at elevated temperature. A model is proposed in which electron-accepting M(O₂CR)₂ complexes (Z-type ligands) reversibly bind to nanocrystals, leading to a range of stoichiometries for a given core size. The results demonstrate that nanocrystals lack a single chemical formula, and are instead dynamic structures with concentration-dependent compositions.
Following the precursor reactivity and rate study undertaken on Cd(S₂PPh₂)₂, we establish a novel method of controlling the number and size of nanocrystals produced from a reaction through the use of a precursor library. We report a library of thioureas whose substitution pattern tunes their conversion reactivity over more than five orders of magnitude and demonstrate that faster thiourea conversion kinetics increases the extent of crystal nucleation. Tunable kinetics thereby allows the nanocrystal concentration to be adjusted and a desired crystal size to be prepared at full conversion. Controlled precursor reactivity and quantitative conversion improve the batch-to-batch consistency of the final nanocrystal size at industrially relevant reaction scales and open up new synthetic routes towards commercially-relevant core/shell heterostuctures. The ability to tune reaction rate independent of the reaction conditions for the first time also enables new studies of the underlying mechanisms of nanocrystal synthesis.
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Sigman, Michael Barron Korgel Brian Allan. "Solventless synthesis, characterization, self-assembly of colloidal nanocrystals." 2005. http://repositories.lib.utexas.edu/bitstream/handle/2152/1725/sigmanm10116.pdf.
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Sigman, Michael Barron. "Solventless synthesis, characterization, self-assembly of colloidal nanocrystals." Thesis, 2005. http://hdl.handle.net/2152/1725.
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Saunders, Aaron Edward. "Colloidal nanocrystals: synthesis and shape-control, interparticle interactions & self-assembly." Thesis, 2005. http://hdl.handle.net/2152/2299.
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Zanella, Marco [Verfasser]. "Synthesis of advanced inorganic colloidal nanocrystals / vorgelegt von Marco Zanella." 2008. http://d-nb.info/990495698/34.
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Abulikemu, Mutalifu. "Synthesis and Characterization of Colloidal Metal and Photovoltaic Semiconductor Nanocrystals." Diss., 2014. http://hdl.handle.net/10754/335794.
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Metal and semiconducting nanocrystals have received a great deal of attention from fundamental scientists and application-oriented researchers due to their physical and chemical properties, which differ from those of bulk materials. Nanocrystals are essential building blocks in the development of nanostructured devices for energy conversion. Colloidal metals and metal chalcogenides have been developed for use as nanocrystal inks to produce efficient solar cells with lower costs. All high-performing photovoltaic nanocrystals contain toxic elements, such as Pb, or scarce elements, such as In; thus, the production of solution-processable nanocrystals from earth-abundant materials using environmentally benign synthesis and processing methods has become a major challenge for the inorganic semiconductor-based solar field. This dissertation, divided into two parts, addresses several aspects of these emerging challenges.
The first portion of the thesis describes the synthesis and characterization of nanocrystals of antimony sulfide, which is composed of non-scarce and non-toxic elements, and examines their performance in photovoltaic devices. The effect of various synthetic parameters on the final morphology is explored. The structural, optical and morphological properties of the nanocrystals were investigated, and Sb2S3 nanocrystal-based solid-state semiconductor-sensitized solar cells were fabricated using different deposition processes. We achieved promising power conversion efficiencies of 1.48%.
The second part of the thesis demonstrates a novel method for the in situ synthesis and patterning of nanocrystals via reactive inkjet printing. The use of low-cost manufacturing approaches for the synthesis of nanocrystals is critical for many applications, including photonics and electronics. In this work, a simple, low-cost method for the synthesis of nanocrystals with minimum size variation and waste using reactive inkjet printing is introduced. As a proof of concept, the method was used for the in situ synthesis of gold nanoparticles as a model system. Relatively monodisperse gold nanoparticles were produced. The size and shape of gold nanoparticles can be controlled by the gold precursor and surfactant concentration in the ‘ink.’ This approach can be extended to the synthesis of other nanocrystals and is thus a truly impactful process for the low-cost synthesis of materials and devices incorporating nanocrystals.
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Wang, J., P. Liu, Colin C. Seaton, and K. M. Ryan. "Complete Colloidal Synthesis of Cu2SnSe3 Nanocrystals with Crystal Phase and Shape Control." 2014. http://hdl.handle.net/10454/10193.
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NoHere we report an investigation of systematic control of crystal phase in the ternary nanocrystal system, dicopper tin triselenide. Optimizing the synthetic parameters allows modulation between nucleation and growth in either the hexagonal or cubic phase. In addition to size controlled single crystals, the particles can be tuned to occur as 1D linear heterostructures or 3D tetrapods with growth in one phase and termination in the alternate.
SFI, IRCSET
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Ghezelbash, Hossein-Ali. "Topics in colloidal nanocrystals: synthesis and characterization, polymorphism, and self-assembly." Thesis, 2006. http://hdl.handle.net/2152/2485.
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Panthani, Matthew George. "Colloidal nanocrystals with near-infrared optical properties : synthesis, characterization, and applications." 2011. http://hdl.handle.net/2152/19825.
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Colloidal nanocrystals with optical properties in the near-infrared (NIR) are of interest for many applications such as photovoltaic (PV) energy conversion, bioimaging, and therapeutics. For PVs and other electronic devices, challenges in using colloidal nanomaterials often deal with the surfaces. Because of the high surface-to-volume ratio of small nanocrystals, surfaces and interfaces play an enhanced role in the properties of nanocrystal films and devices.
Organic ligand-capped CuInSe2 (CIS) and Cu(InXGa1-X)Se2 (CIGS) nanocrystals were synthesized and used as the absorber layer in prototype solar cells. By fabricating devices from spray-coated CuInSe nanocrystals under ambient conditions, solar-to-electric power conversion efficiencies as high as 3.1% were achieved. Many treatments of the nanocrystal films were explored. Although some treatments increased the conductivity of the nanocrystal films, the best devices were from untreated CIS films. By modifying the reaction chemistry, quantum-confined CuInSeXS2-X (CISS) nanocrystals were produced. The potential of the CISS nanocrystals for targeted bioimaging was demonstrated via oral delivery to mice and imaging of nanocrystal fluorescence.
The size-dependent photoluminescence of Si nanocrystals was measured. Si nanocrystals supported on graphene were characterized by conventional transmission electron microscopy and spherical aberration (Cs)-corrected scanning transmission electron microscopy (STEM). Enhanced imaging contrast and resolution was achieved by using Cs-corrected STEM with a graphene support. In addition, clear imaging of defects and the organic-inorganic interface was enabled by utilizing this technique.text
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Campos, Michael Paul. "The Synthesis and Surface Chemistry of Colloidal Quantum Dots." Thesis, 2017. https://doi.org/10.7916/D86H4VZG.
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Colloidal semiconductor nanocrystals, also known as quantum dots, are an extraordinary class of material, combining many of the most attractive properties of semiconductors with the practicality of solution chemistry. As such, they lie at a unique interface between inorganic chemistry, organic chemistry, solid-state physics, and colloidal chemistry. The rapid advance in knowledge of quantum dots over the past 30 years has largely been driven by interest in their fundamental physical properties and their broad applicability to challenges in nanoscience. However, much less attention has been paid to the chemistry underlying these features. In this dissertation, we discuss the state of nanocrystal chemistry and new insights we have unlocked by taking a bottom-up, chemistry-based approach to nanocrystal synthesis. We will cover these in a case-by-case fashion in the context of four chapters.
Chapter 1 covers our CdTe nanocrystal synthesis surface chemistry studies with an eye toward CdTe photovoltaic technology, in which the role of CdTe surfaces is poorly understood. CdTe nanocrystals are traditionally a difficult material to synthesize, particularly with well-defined surface chemistry. In order to enable quantitative surface studies, we looked upstream and re-evaluated CdTe synthesis from the ground up. We identified a CdTe precursor largely overlooked since 1990, cadmium bis(phenyltellurolate) (Cd(TePh)2), and harnessed its excellent reactivity toward a synthesis of CdTe nanocrystals solely bound by cadmium carboxylate (Cd(O2CR)2) ligands. We then use this well-defined material to show that Cd(O2CR)2 ligands bind less tightly to CdTe nanocrystals than CdSe nanocrystals. This finding holds promise for the development of photovoltaics from colloidal CdTe feedstocks.
Chapter 2 covers a tunable library of substituted thiourea precursors to metal sulfide nanocrystals. Controlling the size of nanocrystals produced in a given reaction is paramount to their use in opto-electronic devices, but the most widely used technique to control size is prematurely arresting crystal growth. We introduce a library of thiourea precursors whose organic substituents tune the rate of precursor conversion, which dictates the number of nanocrystals formed and the final nanocrystal size following complete precursor conversion. We use PbS as a model system to 1) demonstrate the concept of kinetically controlled nanocrystal size, 2) quantify substituent trends, and 3) optimize multigram scale syntheses. We then expand the thiourea methodology to a broad range of materials and nanocrystal morphologies. This work represents a paradigm shift that will greatly accelerate the pace of progress in nanocrystal science as it transitions from academia to a multibillion-dollar industry.
Chapter 3 covers an analogously tunable library of substituted selenourea precursors, but focuses on the synthesis of PbSe nanocrystals. PbSe nanocrystal synthesis is notoriously low-yielding and poorly tunable, but the remarkable properties of PbSe nanocrystals in photovoltaics and electrical transport have driven interest in the material for decades. We develop a library of N,N,N’-trisubstituted selenourea precursors and leverage their fine conversion rate tunability to synthesize PbSe nanocrystals of many sizes in quantitative yields. Interestingly, the nanocrystals produced in this reaction are demonstrably less polydisperse than literature samples, exhibiting absorption linewidths approaching the single-particle limit. We quantify this narrowness using a transient absorption spectroscopy technique called spectral hole burning.
Chapter 4 covers our efforts to dig deeper into nanocrystal nucleation and growth and use that new knowledge to develop luminescent downconverters ready for on-chip integration into LED lighting. By studying early time points in PbS and PbSe nanocrystal synthesis, we estimate solute concentrations, nucleation thresholds, and nanocrystal growth rates. In particular, we find that metal selenides and sulfides have very different nucleation and growth behavior, as well as that PbS nucleation is a surprisingly slow process. The lessons learned from these fundamental experiments have enabled us to rapidly develop red-emitting CdS/CdSe/CdS “spherical quantum well” emitters whose photoluminescence quantum yields are 90 – 95%.
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Shiding, M., A. Eychmüller, and Stephen G. Hickey. "Artificial Supermolecule: Progress in the Study of II-V Colloidal Semiconductor Nanocrystals." 2012. http://hdl.handle.net/10454/16721.
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Johnson, Noah John Joe. "Sodium lanthanide fluoride nanocrystals: colloidal synthesis, applications as nano-bioprobes, and fundamental investigations on epitaxial growth." Thesis, 2012. http://hdl.handle.net/1828/4377.
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The ability to grow materials in the nanometric size regime with controlled shape and size provide a fundamental synthetic challenge, while allowing for evaluation of such unique nanostructures in multiple applications. In this dissertation, colloidal sodium lanthanide fluoride (NaLnF4) nanocrystals are described with an overall emphasis on i) size control, ii) surface chemistry related towards their applications as nano-bioprobes, and iii) the synthesis and fundamental aspects of epitaxial layer growth generally referred as core-shell nanocrystals.
Chapter 1 provides a brief overview on the basic aspects of colloidal nanocrystals. In Chapter 2, synthesis and surface modification of colloidal sodium lanthanide fluoride nanocrystals, epitaxial growth, and their applications in optical and magnetic resonance imaging is reviewed. Chapter 3 describes a phase transfer protocol utilizing polyvinylpyrrolidone and subsequent silica coating of initially hydrophobic upconverting nanocrystals. This protocol is extended in Chapter 4 using end-group functionalized polyvinylpyrrolidone and demonstrates tunability of surface charge and functional groups on upconverting nanocrystals for targeted labeling of human prostate cancer cells. The synthesis of size-tunable NaGdF4 nanocrystals below 10 nm is described in Chapter 5. These nanocrystals are evaluated for their efficacy in magnetic resonance imaging (MRI), and a fundamental insight into the effect of surface gadolinium ions in T1 MRI contrast enhancement is presented. Chapter 6 demonstrates the synthesis of tunable, epitaxial layers on upconverting (core) nanocrystals. A novel synthetic strategy is demonstrated, by deliberate defocusing and self-focusing of differently sized nanocrystals driven by the common physical phenomenon of Ostwald ripening. Utilizing the contraction of lanthanide ions along the series, a fundamental investigation on the effect of compressive/tensile strain epitaxial layer growth is presented in Chapter 7. The fundamental rule of minimal lattice mismatch for epitaxial growth takes into account only the magnitude of mismatch and not the sign of mismatch caused by a compressive/tensile strained layer. A strong asymmetric effect between the compressive/tensile layer growth given the same magnitude of lattice mismatch is observed, demonstrating the necessity of including the sign of mismatch to generate isotropic (conformal)/ pseudomorphic (coherent) epitaxial growth. Finally, in Chapter 8 conclusions and possible future work are discussed.Graduate
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Patel, Reken Niranjan. "Aspects of bottom-up engineering : synthesis of silicon nanowires and Langmuir-Blodgett assembly of colloidal nanocrystals." Thesis, 2010. http://hdl.handle.net/2152/ETD-UT-2010-08-1595.
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Central to the implementation of colloidal nanomaterials in commercial applications is the development of high throughput synthesis strategies for technologically relevant materials. Solution based synthesis approaches provide the controllability, high throughput, and scalability needed to meet commercial demand. A flow through supercritical fluid reactor was used to synthesize silicon nanowires in high yield with production rates of ~45 mg/hr. The high temperature and high pressure of the supercritical medium facilitated the decomposition of monophenylsilane and seeded growth of silicon nanowires by gold seeds. Crystalline nanowires with diameters of ~25 nm and lengths greater than 20 [micrometers] were routinely synthesized. Accumulation of nanowires in the reactor resulted in deposition of a conformal amorphous shell on the crystalline surface of the wire. X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and energy dispersive X-ray spectroscopy were used to determine the shell composition. The shell was identified as polyphenylsilane formed by polymerization of the silicon precursor monophenylsilane. A post synthesis etch was developed to remove the shell while still maintaining the integrity of the crystalline silicon nanowire core. Subsequent surface passivation was achieved through thermal hydrosilylation with a terminal alkene. The development colloidal nanomaterials into commercial applications also requires simple and robust bottom-up assembly strategies to facilitate device fabrication. A Langmuir-Blodgett trough was used to assemble continuous monolayers of hexagonally ordered spherical nanocrystals over areas greater than 1 cm². Patterned monolayers and multilayers of FePt nanocrystals were printed onto substrates using pre-patterned polydimethylsiloxane (PDMS) stamps and a modified Langmuir Schaefer transfer technique. Patterned features, including micrometer-size circles, lines, and squares, could be printed using this approach. The magnetic properties of the printed nanocrystal films were also measured using magnetic force microscopy (MFM). Room temperature MFM could detect a remanent (permanent) magnetization from multilayers (>3 nanocrystals thick) films of chemically-ordered L1₀ FePt nanocrystals. Grazing incidence small angle X-ray scattering was used to quantitatively characterize the grain size, crystal structure, lattice disorder, and edge-to-edge spacing of the nanocrystal films prepared on the Langmuir-Blodgett trough both on the air-water interface and after transfer.text
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Lesnyak, Vladimir. "Colloidal Semiconductor Nanoparticles as Functional Materials: Design, Assembly and Applications." 2021. https://tud.qucosa.de/id/qucosa%3A73651.
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This work summarizes results of about ten years of the author’s own research activities in the field of colloidal synthesis of semiconductor nanoparticles, their postsynthetic chemical modification, assembly, and applications. I attempted to provide a concise yet comprehensive overview presenting my own results as a part of the knowledge framework created in close collaboration with many colleagues from all over the world. This habilitation thesis consists of an introduction, explaining the motivation of the research accomplished, followed by a main part which briefly presents key achievements of the author with links to appropriate annexes, i.e. original published articles in peer review journals which are attached to this cumulative script, and completed by conclusions.
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Singh, Tejinder. "Atomic-scale Modeling of Transition-metal Doping of Semiconductor Nanocrystals." 2011. https://scholarworks.umass.edu/open_access_dissertations/356.
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Doping in bulk semiconductors (e.g., n- or p- type doping in silicon) allows for precise control of their properties and forms the basis for the development of electronic and photovoltaic devices. Recently, there have been reports on the successful synthesis of doped semiconductor nanocrystals (or quantum dots) for potential applications in solar cells and spintronics. For example, nanocrystals of ZnSe (with zinc-blende lattice structure) and CdSe and ZnO (with wurtzite lattice structure) have been doped successfully with transition-metal (TM) elements (Mn, Co, or Ni). Despite the recent progress, however, the underlying mechanisms of doping in colloidal nanocrystals are not well understood. This thesis reports a comprehensive theoretical analysis toward a fundamental kinetic and thermodynamic understanding of doping in ZnO, CdSe, and ZnSe quantum dots based on first-principles density-functional theory (DFT) calculations. The theoretical predictions of this thesis are consistent with experimental measurements and provide fundamental interpretations for the experimental observations. The mechanisms of doping of colloidal ZnO nanocrystals with the TM elements Mn, Co, and Ni is investigated. The dopant atoms are found to have high binding energies for adsorption onto the Zn-vacancy site of the (0001) basal surface and the O-vacancy site of the (0001) basal surface of ZnO nanocrystals; therefore, these surface vacancies provide viable sites for substitutional doping, which is consistent with experimental measurements. However, the doping efficiencies are affected by the strong tendencies of the TM dopants to segregate at the nanocrystal surface facets, as indicated by the corresponding computed dopant surface segregation energy profiles. Furthermore, using the Mn doping of CdSe as a case study, the effect of nanocrystal size on doping efficiency is explored. It is shown that Mn adsorption onto small clusters of CdSe is characterized by high binding energies, which, in conjunction with the Mn surface segregation characteristics on CdSe nanocrystals, explains experimental reports of high doping efficiency for small-size CdSe clusters. In addition, this thesis presents a systematic analysis of TM doping in ZnSe nanocrystals. The analysis focuses on the adsorption and surface segregation of Mn dopants on ZnSe nanocrystal surface facets, as well as dopant-induced nanocrystal morphological transitions, and leads to a fundamental understanding of the underlying mechanisms of dopant incorporation into growing nanocrystals. Both surface kinetics (dopant adsorption onto the nanocrystal surface facets) and thermodynamics (dopant surface segregation) are found to have a significant effect on the doping efficiencies in ZnSe nanocrystals. The analysis also elucidates the important role in determining the doping efficiency of ZnSe nanocrystals played by the chemical potentials of the growth precursor species, which determine the surface structure and morphology of the nanocrystals.
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Abel, Keith Alexander. "Synthesis and characterization of colloidal lead chalcogenide quantum dots and progress towards single photons on-demand." Thesis, 2011. http://hdl.handle.net/1828/3481.
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Nanometer-sized semiconductor crystals, termed ‘quantum dots’, are of fundamental interest because of their size-tunable properties. Three-dimensional quantum confinement of charge carriers by the small crystal size results in discrete atomic-like electronic states. This dissertation describes the synthesis and in-depth characterization of lead chalcogenide colloidal quantum dots for forthcoming applications as near-infrared single photon emitters. An efficient single photon source that operates at telecommunication wavelengths (between 1.3 and 1.6 µm) is a basic requirement for many photonic quantum technologies, such as quantum computing and quantum cryptography.
Chapters 1 and 2 of this work provide an introduction to colloidal quantum dots and their use as single photon emitters. It includes a description of photonic crystal microcavities and their ability to enhance the spontaneous emission rate of quantum dots. The synthesis and basic characterization of PbSe and PbS quantum dots is then discussed in chapter 3. In particular, a new synthetic method for the preparation of highly photoluminescent PbS quantum dots is presented. PbSe/CdSe core/shell quantum dots prepared by a cation exchange reaction are also described and a significant improvement in photo-stability is shown. Chapter 3 concludes with a description of three different surface modification techniques. PbSe core and PbSe/CdSe core/shell materials are investigated further in chapter 4 by advanced characterization techniques that include high-angle annular dark field (HAADF) imaging, energy-filtered transmission electron microscopy (EF-TEM) imaging, energy-dependent X-ray photo-electron spectroscopy (XPS), small angle X-ray scattering (SAXS), and small angle neutron scattering (SANS). The information obtained from these techniques is combined to form a structural model of the PbSe core and PbSe/CdSe core/shell quantum dots with greater complexity than previously reported. In chapter 5, the temperature-dependent photoluminescence from PbSe and PbSe/CdSe core/shell quantum dots is discussed and a thermal model is presented that accounts for the large (non-trivial) temperature dependence of the Stokes shift and photoluminescence lineshape over the entire temperature range (4.5 to 295 K). Chapter 6 examines two scalable methods to integrate the colloidal quantum dots into silicon two-dimensional photonic crystal slab microcavities (a requirement for efficient single photon emission). Finally, conclusions and possible future work are discussed in chapter 7.Graduate
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Choi, Chang-Ho. "Synthesis of colloidal metal oxide nanocrystals and nanostructured surfaces using a continuous flow microreactor system and their applications in two-phase boiling heat transfer." Thesis, 2013. http://hdl.handle.net/1957/37900.
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Metal oxide nanocrystals have attracted significant interests due to their unique chemical, physical, and electrical properties which depend on their size and structure. In this study, a continuous flow microreactor system was employed to synthesize metal oxide nanocrystals in aqueous solution. Assembly of nanocrystals is considered one of the most promising approaches to design nano-, microstructures, and complex mesoscopic architectures. A variety of strategies to induce nanocrystal assembly have been reported, including directed assembly methods that apply external forces to fabricate assembled structures.
In this study ZnO nanocrystals were synthesized in an aqueous solution using a continuous flow microreactor. The growth mechanism and stability of ZnO nanocrystals were studied by varying the pH and flow conditions of the aqueous solution. It was found that convective fluid flow from Dean vortices in a winding microcapillary tube could be used for the assembly of ZnO nanocrystals. The ZnO
nanocrystal assemblies formed three-dimensional mesoporous structures of different shapes including a tactoid, a retangle and a sphere. The assembly results from a competing interaction between electrostatic forces caused by surface charge of nanocrystals and collision of nanocrystals associated with Dean vortices. The as synthesized colloidal ZnO nanocrystals or assembly were directly deposited onto a substrate to fabricate ZnO nanostructured surfaces. The rectangular assembly led to flower-like ZnO nanostructured films, while the spherical assembly resulted in amorphous ZnO thin film and vertical ZnO nanowire (NW) arrays. In contrast to the formation of flower structure or amorphous thin film, only colloidal ZnO nanocrystals were used as the building blocks for forming vertical ZnO NW arrays. This study demonstrates the versatility of the microreactor-assisted nanomaterial synthesis and deposition process for the production of nanostrucuturesres with various morphologies by tuning the physical parameters while using the same chemical precursors for the synthesis.
ZnO flower structure was coated on a microwick structure to improve the capillary flow. The coated microwick structure showed an enhanced capillary rise, which was attributed to the hydrophilic property and geometrical modification of ZnO nanostructure. Two-phase boiling heat transfer was performed using ZnO nanostructured surfaces. ZnO nanocoating altered the important characteristics including surface roughness and wettability. Hydrophilic nature of the ZnO nanocoating generally enhanced the boiling heat transfer performance, resulting in higher heat transfer coefficient (HTC), higher critical heat flux (CHF), and lower surface superheat comparing to the bare surface. Octahedral SnO and porous NiO
films, fabricated by a continuous flow microreactor system, were suggested as potential boiling surfaces for the high porosity and irregularity of their structures.Graduation date: 2013
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Kumar, Ajay. "Bile Salts in Supramolecular Chemistry: Synthesis of Fluorescent Nanoclusters, Oxide Nanoflowers, and Anion Effect on Metallogels." Thesis, 2019. https://etd.iisc.ac.in/handle/2005/4544.
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In summary, we have explored an interesting pH-dependent sensitization of Tb(III) using methyl salicylate (MS) as a sensitizer in aqueous media. Methyl salicylate was found to be a specific sensitizer for Tb(III) but not for Eu(III). Upon doping Eu(III) in Tb(III)-MS system resulted in the color change from green to orange depending upon the pH of the solutions. Photophysical studies confirm the energy transfer from Tb(III) to Eu(III) in the lanthanide mixed Tb(III)/Eu(III)-MS system
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Huang, Wei-Hsiang, and 黃韋翔. "Colloidal Synthesis of GeSbTe Nanocrystal and Its Phase Change Characteristics & Hydrogen Production by Kerf Loss Corrosion Assisted by Sodium metasilicate and Silicic acid." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/884m4t.
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Suyal, Ganesh [Verfasser]. "Synthesis of nanocomposite glass-like films containing semiconductor nanocrystals and noble bimetallic colloids by sol-gel route and their characterisation / von Ganesh Suyal." 2002. http://d-nb.info/964814498/34.
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