Дисертації: "Nanomaterials- Semiconductors"

1

Cozzarini, Luca. "Nanomaterials based on II-VI Semiconductors." Doctoral thesis, Università degli studi di Trieste, 2012. http://hdl.handle.net/10077/7359.

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2010/2011
This thesis describes: (i) synthesis and characterization of colloidal nanocrystals of II-VI semiconductor compounds; (II) development of two novel materials using such nanocrystals as “building blocks”: (IIa) a nanocrystals/polymer composite, to be used as phosphor in LED-based lighting devices; (IIb) an inorganic, nano-structured multiphase material, showing a promising geometry as an electronic intermediate band material. Different typologies of nanocrystals (single-phase, alloyed or core-shells) were successfully synthesized using air-stable, safe reagents. Their optical properties (absorption spectrum, fluorescence wavelength and fluorescence quantum yield) were mapped as function of different parameters. Good results in engineering optical properties were achieved by: (a) changing size and/or composition in single-phase nanocrystals; (b) tuning shell composition and thickness and/or mutually diffusing one material into the other in multi-phase nanocrystals. The influence of different surface ligands on optical properties and on solubility in different media was also studied. Nanocrystal/polymer composite lenses were obtained from nanocrystals with desired fluorescence wavelength and quantum yield, mixed in an appropriate solvent with polymer pellets. The mixture was drop casted or tape casted on a solid substrate, obtaining solid, transparent lenses after solvent evaporation. A nano-structured, all-inorganic material (composed of semiconducor nanocrystals embedded into a wider bandgap semiconductor) was obtained through self-assembly and densification of colloidal core-shells nanocrystals. The realization of this composite supracrystal was achieved via a multi-step process: (i) colloidal synthesis of core-shell nanocrystals; (ii) surface ligands exchange; (iii) assembly; (iv) heat treatment. Evolution of the optical properties during heat treatment suggests that it is possible to sinter the shell material without altering the internal nano-heterostructure, if temperature and time of the treatment are controlled properly.
In questa tesi sono descritti: (I) la sintesi colloidale e la caratterizzazione di nanocristalli di semiconduttori II-VI; (II) lo sviluppo, utilizzando i suddetti nanocristalli quali “unità da costruzione”, di due materiali innovativi: (IIa) un composito nanocristalli/polimero, da usare come fosforo in dispositivi per illuminazione basati su LED; (IIb) un materiale inorganico nano-strutturato multifase, con una geometria promettente quale materiale a banda elettronica intermedia. Differenti semiconduttori II-VI sono stati sintetizzati in forma di nanocristalli (monofasici, in forma di lega o in struttura di tipo “core-shell”) usando reagenti sicuri e stabili in atmosfera. Le loro proprietà ottiche (spettro di assorbimento, lunghezza d’onda di fluorescenze e resa quantica di fluorescenza) sono state mappate in funzione di numerosi parametri. Sono stati raggiunti ottimi risultati nel controllo delle proprietà ottiche sia in nanocristalli a fase singola (modificandone le dimensioni o la composizione chimica) che in nanocristalli multifase (regolandone la composizione e lo spessore della “shell”, nonché mutualmente diffondendo un materiale nell’altro). È stata anche studiata l’influenza di differenti leganti superficiali sulle proprietà ottiche e sulla solubilità dei nanocristalli in differenti solventi. Lenti composite di nanocristalli/polimero sono state ottenute a partire da nanocristalli aventi la lunghezza d’onda e la resa quantica di fluorescenza desiderate, mescolandoli con pellet di polimero in solventi appropriati. La miscela è stata depositata su un supporto, tramite drop casting o tape casting, ottenendo lenti solide trasparenti dopo l’evaporazione del solvente. Un materiale inorganico nano strutturato (costituito da nanocristalli di semiconduttore racchiusi all’interno di un secondo materiale semiconduttore a bandgap maggiore) è stato ottenuto tramite l’autoassemblaggio e la densificazione di nanocristalli core-shell sintetizzati con procedure di chimica colloidale. La realizzazione di suddetto sovra-cristallo si è svolta in più fasi: (i) sintesi colloidale; (ii) sostituzione dei leganti superficiali; (iii) assemblaggio; (iv) trattamento termico. I risultati derivanti dallo studio dell’evoluzione delle proprietà ottiche durante il trattamento termico suggeriscono che sia possibile sinterizzare il materiale della shell senza alterare la nano-eterostruttura interna, se la temperatura e il tempo del trattamento sono scelti opportunamente.
XXIV Ciclo
1983

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2

Tassi, Nancy Gattuso. "Manipulation of organic nanomaterials." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 51 p, 2008. http://proquest.umi.com/pqdweb?did=1459918081&sid=5&Fmt=2&clientId=8331&RQT=309&VName=PQD.

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3

Zhang, Shaolin. "Wide band gap nanomaterials and their applications." Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B41758225.

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4

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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5

Zhang, Shaolin, and 張少林. "Wide band gap nanomaterials and their applications." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B41758225.

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6

Yu, Zhang. "Solution Processed Chalcogenide Nanomaterials for Thermoelectric Application." Doctoral thesis, Universitat de Barcelona, 2021. http://hdl.handle.net/10803/670923.

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The bottom-up engineering of nanomaterials using solution-processing strategies is of particular interest for reducing cost and optimizing the performance of TE materials and devices. This thesis focuses on the development of scalable methods for the production of TE nanomaterials with optimized performance. The thesis is divided into 5 chapters. Chapter 1 introduces solution-based approaches for producing functional nanomaterials and the general state of the art in the field of thermoelectricity. Chapter 2 and chapter 3 present a fast and simple molecular ink-based method to produce low cost and crystallographically textured SnSe2 and SnSe nanomaterials. Molecular ink printing techniques could offer a scalable approach to fabricate TE devices on flexible substrates. In these chapters, I proved that cost-effective p-type SnSe NPLs could be produced by a molecular ink-based strategy that allowed introducing controlled amounts of Te to achieve unprecedentedly high TE figure of merit. On the other hand, n-type SnSe2 nanomaterials were also intentionally produced from the same strategy to complement an all Sn-Se based device. Both of the bulk nanomaterials displayed significant crystallographic texture after hot pressing, resulting in highly anisotropic charge and heat transport properties. Different approaches were applied to optimize their TE performance: SnSe2 NPLs were blended with metal NPs to produce a metal-semiconductor NC. The electrical conductivities of the blends were significantly improved with respect to bare SnSe2 bulk nanomaterial and a three-fold increase in the TE figure of merit was obtained, reaching unprecedented values up to ZT = 0.65 for SnSe2 material. For SnSe nanomaterials, I demonstrate that the introduction of small amounts of tellurium in the precursor ink allowed reducing the band gap, increasing both charge carrier concentration and mobility, especially cross plane, with a minimal decrease of the Seebeck coefficient. This strategy translated into record out of plane ZT values at 800 K, ZT=1.05 Chapter 4 and chapter 5 describe two different strategies to produce Bi2Te3-Cu2-xTe NCs based on the consolidation of nanostructured building blocks. I first detail a two-step solution-based process to produce the Bi2Te3-Cu2-xTe heteronanostructures, based on the growth of Cu2-xTe nanocrystals on the surface of Bi2Te3 nanowires. The transport properties of the NCs are investigated as a function of the amount of Cu introduced, which reveal that the presence of Cu decreases the material thermal conductivity through promotion of phonon scattering, modulates the charge carrier concentration through electron spillover, and increases the Seebeck coefficient through filtering of charge carriers at energy barriers. These effects result in an improvement of over 50% of the TE figure of merit of Bi2Te3. As comparison, I produced Bi2Te3-Cu2-xTe NCs by directly mixing proper ratio of individual Bi2Te3 nanowires with Cu2-xTe nanocubes and consolidating the resulting NP mixture by hot-press. A significant difference of transport properties was detected when compared with NCs fabricated by hot-pressing heterostructured Bi2Te3-Cu2-xTe nanowires. On the contrary to the composite obtained from hetero- nanostructures, the presence of Cu2-xTe nanodomains did not lead to a significant reduction of the lattice thermal conductivity of the reference Bi2Te3, which is already very low here, but it resulted in a nearly threefold increase of its power factor. Additionally, the presence of Cu2-xTe resulted in a strong increase of the Seebeck coefficient. This increase is related to the energy filtering of charge carriers at energy barriers within Bi2Te3 domains created by the accumulation of electrons in the regions nearby Cu2-xTe/Bi2Te3 junctions. Overall, a significant improvement of figure of merit, up to a 250%, was obtained with the suitable combination of Cu2-xTe NPs and Bi2Te3 nanowires. Finally, the main conclusions of this thesis and some perspectives for future work are presented.
La ingeniería de nanomateriales a partir del procesado en solución es de particular interés para optimizar el rendimiento de los materiales y dispositivos termoeléctricos. . Esta tesis estáse centra en el diseño y el ensamblaje racional de nanomateriales termoeléctricos de alto rendimiento a través de procesado en solución. La tesis se divide en 5 capítulos. El Capítulo 1 aborda la introducción fundamental del enfoque sintético para producir nanomateriales funcionales. Los capítulos 2 y 3 presentan un método rápido y simple basado en soluciones para producir nanomateriales SnSe2 y SnSe con textura cristalográfica. Dado que los calcogenuros de estaño son materiales especialmente interesantes para la conversión de energía termoeléctrica, se sintetizaron nanoplacas SnSe y SnSe2 controlables por forma mediante una estrategia basada en tinta molecular para lograr una figura de mérito termoeléctrica sin precedentes por dopaje con Te/Cu. Ambos nanomateriales mostraron una textura cristalográfica significativa después del prensado en caliente, lo que dio como resultado unas propiedades de transporte de carga calor altamente anisotrópicas. Los capítulos 4 y 5 describen dos estrategias diferentes para producir nanocompuestos Bi2Te3-Cu2-xTe basados en la consolidación de nanoestructuras. La presencia de Cu2-xTe da como resultado un fuerte aumento del coeficiente de Seebeck. Este aumento está relacionado con el filtrado de los portadores de carga en función de su energía en las barreras de energía dentro de los dominios Bi2Te3 creados por la acumulación de electrones en las regiones cercanas a las uniones Cu2-xTe / Bi2Te3. En general, se obtiene una mejora significativa de la figura de mérito con nanocompuestos Bi2Te3-Cu2-xTe. Finalmente, en el último capítulo se presentan las principales conclusiones de esta tesis y algunas perspectivas para trabajos futuros.

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7

Liu, Yu. "Bottom-up Engineering of Chalcogenide Thermoelectric Nanomaterials." Doctoral thesis, Universitat de Barcelona, 2018. http://hdl.handle.net/10803/663274.

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In this thesis, it is detailed the bottom-up production and characterization of thermoelectric (TE) nanomaterials with significant enhanced performance by using colloidal nanocrystals (NCs) as building blocks. The production of TE nanomaterials with significant improved figure of merit (ZT), has to do, not only with the precise control of the NCs properties, but also with the further fine control over the crystallographic alignment of nanograins of highly anisotropic materials. The first part of the thesis correspond to the study of synthetic routes to produce high quality chalcogenide NCs that are doped during the NC synthesis, in order to control the charge carrier concentration. The system studied was I−V−VI chalcogenide semiconductor, specifically it was produced the materials: AgSbSe2 and Cu3SbSe4. A low-cost, high-yield and scalable synthesis route to produce monodisperse of AgSbSe2 and Cu3SbSe4 NCs was obtained. After ligand displacement, the NCs were used as building blocks to produce TE nanomaterials. Additionally, by means of substitutional doping, a large increment in the power factor and relatively lower thermal conductivities were observed. The optimization of the doping concentration resulted in ZT values of 1.10 at 640 K for AgSb0.98Bi0.02Se2, and of 1.26 at 673 K for Cu3Sb0.88Sn0.10Bi0.02Se4, which represents a significant increase beyond the state of the art in Te-free multinary Ag/Cu-based chalcogenide materials. In the second part of the thesis, the work about PbS-metal (Cu and Sn) nanocomposites produced by blending procedure is presented. The low work function metal is able to inject electrons to the intrinsic PbS matrix, which is another strategy to control the charge carrier concentration. The power factor is dramatically enhanced due to the increase of the electrical conductivity in the nanocomposites. Consequently, the ZTmax was remarkably enhanced by two times as compared with the pristine PbS. Furthermore, we also compared the TE performance of microcrystalline composites with the same composition as in nanocrystalline composites; commercial PbS host with Cu particles. The results revealed that with the same metal addition, higher electrical conductivities were obtained in the nanocomposite, but higher Seebeck coefficients were maintained in the microcomposite. Moreover, higher thermal conductivities were also obtained in the microcomposite. Finally, the figure of merit ZT were higher for the microcomposite system in the low temperature range, but much lower in the higher temperature range compared with the nanocomposites system. In the last block, the process of production of crystallographically textured materials is presented. We face here the challenge of bottom-up approaches to control the crystallographic alignment of nanograins. The production of nanostructured Bi2Te3-based alloys is presented. This can be done with controlled stoichiometry by solution-processing, and crystallographic texture by liquid-phase sintering using multiple pressure and release steps at 480 °C, above the tellurium melting point. Additionally, we explain the possible mechanism to produce the highly textured nanomaterials. This strategy results in record TE figures of merit: ZT=1.83 at 420 K for Bi0.5Sb2.5Te3 and ZT=1.31 for Bi2Te2.7Se0.3 at 440 K when averaged over 5 materials in the c direction, respectively. These high figures of merit extended over a wide temperature range, which results in energy conversion efficiencies a 50% higher than commercial ingots in the similar temperature range. In summary, different strategies to improve the TE performance of bulk nanostructured materials produced by bottom-up engineering of NCs, have been studied and confirmed in this thesis. Additionally, it has been proven that the solution-processed synthesis approach is low-cost, compatible with the scale-up engineering, and also versatile in tuning the size, shape, composition, and microstructure, among others parameters of different nanomaterials to optimize their TE properties.
Los nanocristales (NCs) coloidales tienen excelentes propiedades para diferentes aplicaciones, como la conversión de energía, la catálisis, los dispositivos electrónicos y optoelectrónicos, entre otros. Así mismo, la síntesis coloidal de NCs tiene ventajas en el control del tamaño, forma y composición a nivel de la nanoescala; las bajas temperaturas de reacción; y la no necesidad de equipos especializados. Este proyecto se concentra en el diseño racional y la ingeniería de materiales termoeléctricos (TE) nanoestructurados de alta eficiencia, usando la estrategia del ensamblado ascendente (bottom-up) de NCs coloidales. Primero, se diseñó una ruta de síntesis de bajo costo, alto rendimiento, con la cual, se obtuvieron NCs de AgSbSe2 y Cu3SbSe4. La optimización de la concentración de dopaje resultó en valores para la figura de mérito TE, ZT, de 1.10 a 640 K para AgSb0.98Bi0.02Se2, y de 1.26 at 673 K para Cu3Sb0.88Sn0.10Bi0.02Se4. El material con mejores propiedades se usó para la producción de un generador TE en forma de anillo, para acoplarlo a los tubos de escape de gases, obteniendo una potencia eléctrica de 1mW por elemento TE con una diferencia de temperatura de 160 °C. En la segunda parte, se presenta el trabajo de la producción de nanocopuestos de PbS-metal (Cu y Sn) usando un procedimiento versátil de mezcla de NCs. La función de trabajo del metal es capaz de inyectar electrones a la matriz intrínseca de PbS. El factor de potencia TE, se ve dramáticamente incrementado debido al aumento en la conductividad eléctrica en los nanocompuestos TE. Consecuentemente, el valor máximo de ZT se vio excepcionalmente incrementado por el doble del valor comparado con el material original PbS. Finalmente, se presenta el proceso de producción de materiales texturizados cristalográficamente, produciendo materiales tipo p BixSb2-xTe3 y tipo n Bi2Te3-xSex. Se controló la estequiometria durante el procesamiento en solución y la textura cristalográfica, por medio de la sinterización en fase líquida con un procedimiento de múltiples pasos de presión y relajación a una temperatura de 480°C. Los valores de la figura de mérito TE presentan el record de: ZT=1.83 a 420 K para Bi0.5Sb2.5Te3 y ZT=1.31 para Bi2Te2.7Se0.3 a 440 K.

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8

Cress, Cory D. "Effects of ionizing radiation on nanomaterials and III-V semiconductor devices /." Online version of thesis, 2008. http://hdl.handle.net/1850/6278.

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9

Hsieh, Chien-Wen. "Formation of composite organic thin film transistors with one-dimensional nanomaterials." Thesis, University of Cambridge, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609276.

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10

Becerril-Garcia, Hector Alejandro. "DNA-Templated Nanomaterials." Diss., CLICK HERE for online access, 2007. http://contentdm.lib.byu.edu/ETD/image/etd1823.pdf.

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11

Lee, Michael M. "Organic-inorganic hybrid photovoltaics based on organometal halide perovskites." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:9384fc54-30de-4f0d-86fc-71c22d350102.

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This thesis details the development of a novel photovoltaic device based on organometal halide perovskites. The initial focus of this thesis begins with the study of lighttrapping strategies in solid-state dye-sensitised solar cells (detailed in chapter 3). While I report enhancement in device performance through the application of near and far-ﬁeld light-trapping techniques, I ﬁnd that improvements remain step-wise due to fundamental limitations currently employed in dye-sensitised solar cell technology— notably, the available light-sensitising materials. I found a promising yet under researched family of materials in the methyl ammonium tri-halide plumbate perovskite (detailed in chapter 4). The perovskite light-sensitiser was applied to the traditional mesoscopic sensitised solar cell device architecture as a replacement to conventional dye yielding world-record breaking photo-conversion e!ciencies for solid-state sensitised solar cells as high as 8.5%. The system was further developed leading to the conception of a novel device architecture, termed the mesoporous superstructured solar cell (MSSC), this new architecture replaces the conventional mesoporous titanium dioxide semiconductor with a porous insulating oxide in aluminium oxide, resulting in very low fundamental losses evidenced through high photo-generated open-circuit voltages of over 1.1 V. This development has delivered striking photo-conversion ef- ﬁciencies of 10.9% (detailed in chapter 6).

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Leijtens, Tomas. "Charge transport in disordered semiconductors in solid state sensitized solar cells : influence on performance and stability." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:04b2a950-59f1-4a3b-bf99-1b7a4492f88b.

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This thesis studies parameters influencing both the performance and stability of solid state sensitized solar cells (ssSSCs). ssSSCs benefit from their low materials and manufacturing processing costs, a consequence of using solution processed materials. However, solution processed materials are often structurally and electronically disordered. By characterizing fully operational ssSSCs and their charge transport properties, this thesis elucidates the factors limiting charge transport and proposes routes towards both improved photovoltaic conversion efficiency and long-term stability. Chapter 2 provides an explanation of the operation of ssSSCs, while Chapter 3 discusses the basic methods used in this thesis. Having set this background, Chapter 4 explores the interaction between atmospheric oxygen and charge doping mechanisms in the organic semiconductors used in ssSSCs. To understand the implications of the findings presented in Chapter 4, a new technique, “transient mobility spectroscopy”, was developed to understand the evolution of balanced charge transport behaviour of disordered semiconductors at different operating conditions in ssSSCs. This technique is presented in full in Chapter 5. The understanding gained in Chapters 4 and 5 suggest that alternative light absorbers with higher extinction coefficients may be beneficial to improving the performance of ssSSCs. Chapter 6 discusses the use of an organometal trihalide perovskite, as light absorber in ssSSCs. Using time resolved techniques, the charge transport and recombination mechanisms in various device architectures are explored, allowing suggestions to be made towards future improvements. Chapter 7 uses the technique presented in Chapter 5 to understand a rapid degradation mechanism of working ssSSCs. Particular focus is placed on the titanium dioxide charge-transporting layer. Building on this newfound understanding, two methods for attaining stable photovoltaic performance are provided, a great step forward for this technology.

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13

Benaissa, Manel. "ÉLABORATION D'OXYDES DOPÉS DE TYPE DMS (semi-conducteurs magnétiques dilués) PAR ÉLECTRODÉPOSITION SOUS CHAMP MAGNÉTIQUE." Thesis, Reims, 2016. http://www.theses.fr/2016REIMS011/document.

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Nos travaux concernent la synthèse et la caractérisation d'oxydes dopés par la méthode d'électrodéposition sous champ magnétique.L'enjeu d'une telle recherche est double puisqu'il associe une étude de synthèses électrochimiques et l'obtention de matériaux associant des propriétés semi-conductrices et magnétiques.Les oxydes étudiés sont l'oxyde de cuivre (I) dopé par le manganèse ou par le cobalt, et l'oxyde de zinc dopé par le cuivre.Notre objectif est l'élaboration sous champ magnétique d'oxydes de type DMS (semi-conducteurs magnétiques dilués), et leurs caractérisations physiques et chimiques.En effet, l'addition du dopage et celui du champ magnétique appliqué pendant l'électrodéposition génèrent des effets sur les matériaux électrodéposés.Nous avons ainsi mis en évidence des modifications au niveau de la morphologie, de la texture, de la composition, et des propriétés optiques ou magnétiques des matériaux obtenus
Our work focuses on the synthesis and characterization of doped oxides by electrodeposition method under magnetic field superimposition.The goal of this research presents two challenges, because it combines a study of electrochemical synthesis and obtaining materials with optical and magnetic properties. The materials which have been studied are manganese or cobalt doped copper (I) oxide on the one hand, and the copper doped zinc oxide in the other hand.Our goal is the elaboration of diluted magnetic oxides, and the study of their physical and chemical characterizations.Indeed, the effects of doping and of the magnetic field applied during the electrodeposition can provide interesting changes in morphology, texture, composition and optical and magnetic properties of the obtained materials

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14

Kong, Liang. "Bismuth oxybromide-based photocatalysts for solar energy utilisation and environmental remediation." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:c95ee3cc-b276-4c69-8b3f-eb60cc64e1c0.

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This thesis reports the investigation of Bismuth oxybromide (BiOBr) semiconductor material as an efficient photocatalyst for the sunlight harvesting as well as environmental cleanup. I have utilised different synthetic methodologies to obtain BiOBr and its derivatives, such as co-precipitation, ultrasonification, and photo-deposition; and have studied their structural and optical properties by X-ray diffraction and surface analysis techniques. I report the synthesis and characterisation of two new p-n heterojunction systems, AgBr-BiOBr and BiOBr-ZnFe₂O₄, and have performed initial studies on photocatalytic reaction and their catalytic decomposition mechanisms. I have also reported the surface modification method including the deposition of noble metal on BiOBr to investigate the role played by the noble metal and the interactions between semiconductor and metal using various characterisation measurements. Furthermore, a continuous series of BiOBr-BiOI solid solutions were synthesised, characterised and the photocatalytic degradation was performed on the as-obtained semiconductors, to study the band structure properties of the solid solutions.

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15

Cheng, Cheng. "Semiconductor colloidal quantum dots for photovoltaic applications." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:07baccd0-2098-4306-8a9a-49160ec6a15a.

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This thesis studies lead suphide (PbS) colloidal quantum dots and their photovoltaic applications. Different sizes of PbS QDs were synthesised and characterised using absorption spectroscopy and transmission electron microscopes. PbS QD Schottky junction devices were fabricated with AM1.5 power conversion efficiency up to 1.8 %. The Schottky junction geometry limits the device performance. A semiconductor heterojunction using ZnO as an electron acceptor was built and the device efficiency increased to 3%. By studying the light absorption and charge extraction profile of the bilayer device, the absorber layer has a charge extraction dead zone which is beyond the reach of the built-in electric field. Therefore, strategies to create a QD bulk heterojunction were considered to address this issue by distributing the junction interface throughout the absorber layer. However, the charge separation mechanism of the QD heterojunction is not clearly understood: whether it operates as an excitonic or a depleted p-n junction, as the junction operating mechanism determines the scale of phase separation in the bulk morphology. This study shows a transitional behaviour of the PbS/ZnO heterojunction from excitonic to depletion by increasing the doping density of ZnO. To utilise the excitonic mechanism, a PbS/ZnO nanocrystal bulk heterojunction was created by blending the two nanocrystals in solution such that a large interface between the two materials could facilitate fast exciton dissociation. However, the devices show poor performance due to a coarse morphology and formation of germinate pairs. To create a bulk heterojunction where a built-in electric field could assist the charge separation, a TiO₂ porous structure with the pore size matching with the depletion width was fabricated and successfully in-filled by PbS QDs. The porous device produces 5.7% power conversion efficiency, among one of the highest in literature. The enhancement comes from increased light absorption and suppression of charge recombination.

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16

Eley, Clive William. "The rational design of photocatalytic semiconductor nanocrystals." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:ee29c922-857c-432a-8316-a7e04c822b1d.

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This thesis reports the successful rational design of three highly active photocatalytic semiconductor nanocrystal (SNC) systems by exploiting morphology effects and the electronic properties of type II semiconductor heterojunctions. Novel architectures of colloidal SNCs are produced with the aim of suppressing exciton recombination and improving charge extraction for the successful initiation of desirable redox chemistry. Rod-shaped niobium pentoxide Nb₂O₅ nanocrystals (NCs) are shown to exhibit significantly enhanced activity (10-fold increase in rate constant) relative to spherical-shaped NCs of the same material. The increase is attributed to Nb5⁺ Lewis acid site rich (001) surfaces, present in higher proportions in the rod morphology, which bind organic substrates from solution resulting in direct interaction with photogenerated charges on the surface of the NC. Building on the insights into morphology-activity dependence, type II semiconductor heterojunctions are exploited for their ability to increase exciton lifetimes and spatially separate charges. Two novel II-VI heterostructured semiconductor nanocrystals (HSNCs) systems are investigated: a series of CdX/ZnO (X = S, Se, Te) HSNCs and ZnS/ZnO HSNCs capped with two different surface ligands. In the first case, substantial photocatalytic activity improvement is observed for HSNCs (relative to pure ZnO analogues) according to the following trend: CdTe/ZnO > CdS/ZnO > CdSe/ZnO. The observed trend is explained in terms of heterojunction structure and fundamental chalcogenide chemistry. In the second case, both ZnS/ZnO HSNCs exhibit activity enhancement over analogous pure ZnO, but the degree of enhancement is found to be a function of surface ligand chemistry. Photocatalytic activity testing of all the materials investigated in this work is performed via the photodecomposition of methylene blue dye in aerated aqueous conditions under UVA (350 nm) irradiation. The synthetic techniques employed for the synthesis of colloidal SNCs investigated in this thesis range from chemical precipitation and solvothermal techniques to several different organometallic approaches. A wide variety of analytical techniques are employed for the chemical, structural and optical characterisation of SNC photocatalysts including: XRD, XPS, TEM, UV-vis absorption, PL spectroscopy and FTIR. Atom Probe Tomography (APT) is employed for the first time in the structural characterisation of II-VI heterojunctions in colloidal HSNCs. Overall, this thesis provides a useful contribution to the growing body of knowledge pertaining to the enhancement of photocatalytic SNCs for useful applications including: solar energy conversion to chemical fuels, the photodecomposition of pollutants and light-driven synthetic chemistry.

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17

Parkinson, Patrick. "Ultrafast electronic processes at nanoscale organic-inorganic semiconductor interfaces." Thesis, University of Oxford, 2009. http://ora.ox.ac.uk/objects/uuid:e68168c6-bcc0-437d-9133-1bfaf955c80a.

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This thesis is concerned with the influence of nanoscale boundaries and interfaces upon the electronic processes that occur within both organic and inorganic semiconductors. Photoluminescent polymers, highly conducting polymers and nanoscale inorganic semiconductors have been investigated using state-of-the-art ultrafast optical techniques, to provide information on the sub-picosecond photoexcitation dynamics in these systems. The influence of dimensionality on the excitation transfer dynamics in a conjugated polymer blend is studied. Using time-resolved photoluminescence spectroscopy, the transfer transients both for a three-dimensional blend film, and for quasi-two-dimensional monolayers formed through intercalation of the polymer blend between the crystal planes of a SnS2 matrix have been measured. A comparison of the experimental data with a simple, dimensionality-dependent model is presented, based on point dipole electronic coupling between electronic transition moments. Within this approximation, the energy transfer dynamics are found to adopt a three-dimensional character in the solid film, and a two-dimensional nature in the monolayers present in the SnS2 -polymer nanocomposite. The time-resolved conductivity of isolated GaAs nanowires has been investigated by optical-pump terahertz-probe time-domain spectroscopy. The electronic response exhibits a pronounced surface plasmon mode that forms within 300 fs, before decaying within 10 ps as a result of charge trapping at the nanowire surface. The mobility has been extracted using the Drude model for a plasmon and is found to be remarkably high, being roughly one third of that typical for bulk GaAs at room-temperature and indicating the high quality and low bulk defect density in the nanowires studied. Finally, the time-resolved conductivity dynamics of photoexcited polymer-fullerene bulk heterojunction blends for two model polymers, P3HT and MDMO-PPV, blended with PCBM are presented. The observed terahertz-frequency conductivity is characteristic of dispersive charge transport for photoexcitation both at the π−π* absorption peak (560 nm for P3HT), and significantly below it (800 nm). The photoconductivity at 800 nm is unexpectedly high, which is attributed to the presence of a charge transfer complex. In addition, the excitation-fluence dependence of the photoconductivity is studied over more than four orders of magnitude. The time-averaged photoconductivity of the P3HT:PCBM blend is over 20 times larger than that of P3HT, indicating that long-lived positive polarons are responsible for the high photovoltaic efficiency of polymer:fullerene blends. At early times (~ ps) the linear dependence of photoconductivity upon fluence indicates that interfacial charge transfer dominates as an exciton decay pathway, generating charges with mobility of at least ~0.1cm2 V−1 s−1. At later times, a sub-linear relationship shows that carrier-carrier recombination effects influence the conductivity on a longer timescale (> 1 μs).

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18

Shpilevaya, Inga. "Surface characterisation and functional properties of modified diamond electrodes." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:55c8243f-3779-4bcc-878a-999a067cc9c4.

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In this work, the use of modified diamond as an electrode material with superlative physical and electrochemical properties was investigated in a number of electrochemical applications. The surface chemistry of three differing forms of diamond, namely boron-doped microcrystalline diamond, boron-doped diamond powder and detonation nanodiamond powder was modified utilising such strategies as hydrogen plasma treatment, reactive ion plasma etching along with various chemical treatments. The surface and functional properties of the modified diamond electrodes were studied using a wide spectrum of techniques. The electrochemical activity of these materials was concomitantly investigated in order to expand the knowledge of diamond electrochemistry and to establish an understanding of how the surface chemistry of these materials impacts their electrochemical performance. In the first study, the nanostructuring strategies of boron-doped diamond surface with platinum nanoparticles were developed. In particular, two types of diamond nanostructures were produced: one consisting of platinum particles located on the top of diamond nanorods, the other with platinum particles located in the bottom of diamond nanopits. For the first time, the experimental evidence proving the mechanism of the diamond nanostructuring process was reported. The electrochemical activity of these nanostructured diamond electrodes with regard to the electrochemical oxidation of glucose and methanol was investigated. In the second study, the relationship between the surface chemistry of three differing forms of diamond, including microcrystalline boron-doped diamond, boron-doped diamond powder as well as detonation nanodiamond powder, and the electrode fouling in the result of the adsorption processes in methyl viologen and anthraquinonedisulfonate solutions was investigated. The influence of two dissimilar surface terminations: hydrophobic H-terminated and hydrophilic O-terminated on the electrode performance was studied in detail. This work provides a useful insight on the likely reasons for the undesirable adsorption occurrence which may be experienced in many electroanalytical applications that utilise solid and powdered forms of diamond. The third project extends the discussion on the study of the diamond electrodes, modified with detonation nanodiamond and boron-doped diamond powders and investigates the electrochemical behaviour of these materials. In this work, charge transport within the diamond powder films, partition coefficients of different redox mediators along with heterogeneous electron transfer constants were identified. The chemical modification of these electrodes with platinum nanoparticles along with the mechanism of nucleation and growth of the latter were studied. The enhanced electrode performance with regard to methanol electrooxidation reaction was demonstrated. The fourth study investigates the preparation of nickel modified boron-doped diamond electrodes and ascertains the relationship between the surface chemistry of the modified diamond and the associated electrocatalytic performance of nickel nanoparticles in hydrogen peroxide and glucose electrooxidation. The fifth study reports on the development of a novel surface functionalization strategy, based on porphyrin and amide coupling chemistry, which allows the creation of hybrid biomimetic diamond interface that was used as the artificial β-alanine receptor.

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19

Lang, Volker. "Electrically detected magnetic resonance in semiconductor and carbon nanodevices." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:614ed1d1-0304-4356-8bd3-eb0ce7bd6c9d.

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Анотація:

Electrically detected magnetic resonance (EDMR) is a sensitive spectroscopic technique, which can be used to readout few to single electron spins in semiconductor and carbon nanodevices for applications in solid state quantum information processing (QIP). Since only electrically active defects contribute to the EDMR signal, this technique can be used further to investigate defects and impurities in photovoltaic devices, in which they limit the sunlight-to-energy conversion efficiency significantly. Here, I employ X-band EDMR for semiconductor defect analysis and identify the most important recombination centres in Czochralski silicon with oxide precipitates, which can be intentionally grown to confine detrimental metallic impurities to inactive regions of the wafer in order to serve as a defect-free substrate for modern silicon photovoltaic devices. Those experiments show that oxide precipitation is accompanied by the formation of silicon dangling bonds. Furthermore, I describe a very promising route towards the fabrication and readout of few to single electron spins in carbon nanotube devices, which can be characterised structurally via transmission electron microscopy in order to relate their electrical and spin properties with their structure. Finally, I employ EDMR to read out electron spin states in donor-doped silicon field-effect transistors as a prerequisite for their application in QIP. I report on a novel cryogenic probe head for EDMR experiments in resonant microwave cavities operating at 0.35 T (9.7 GHz, X-band) and 3.34 T (94 GHz, W-band). This approach overcomes the inherent limitations of conventional X-band EDMR and permits the investigation of paramagnetic states with a higher spectroscopic resolution and signal intensity. Both advantages are demonstrated and discussed. I further report on a novel mechanism giving rise to the EDMR effect in donor-doped silicon field-effect transistors, which is capable of explaining why the EDMR signal intensities of the conduction electrons are enhanced by a factor of ∼100, while the donor resonance signals increase by a factor of ∼20 from X- to W-band only. The spin-relaxation and dephasing times are extracted from a series of pulsed-EDMR measurements and confirm this model. The author gratefully acknowledges funding from Trinity College Oxford, Department of Materials, EPSRC DTA, and Konrad-Adenauer-Stiftung e.V. (Begabtenförderung).

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20

Zhao, Yixin. "Developing Nanomaterials for Energy Conversion." Cleveland, Ohio : Case Western Reserve University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=case1270172686.

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21

Brent, John. "Exfoliation and synthesis of two-dimensional semiconductor nanomaterials." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/exfoliation-and-synthesis-of-twodimensional-semiconductor-nanomaterials(289ba930-19ff-4fae-8d84-e46560620c18).html.

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Анотація:

2-Dimensional (2D) materials are characterised by atomic thickness and significantly larger edge-lengths, producing particles which are highly confined in 1 direction. Reducing a material to one or few atomic layers gives rise to structural and electronic properties that deviate significantly from those of the bulk crystal. For this reason 2D nanosheets have been investigated for potential application in sensing, catalysis, capacitance, photovoltaics and for flexible circuits (among others).Despite rapid progress in understanding the synthesis and properties of 2D nanosheets in recent years, there remain significant problems surrounding the development of scalable production methods, understanding and tuning fundamental properties, and controlling the size and monodispersity of semiconductor crystals. In addition, new materials with novel properties are constantly sought in order to meet specific requirements. Although the tools developed over the last 12 years can often be applied to the fabrication of these materials, understanding their behaviour and limitations is ongoing. The following thesis discusses the routes to the fabrication of 2-dimensional materials and explores the production of MoS2, black phosphorus and tin(II) sulfide nanosheets. The aim of each piece of work is determined by the level of development of the field; MoS2 nanosheets have been known for several years and therefore the work presented was motivated by a desire to impart size control for specific applications. The study of phosphorene and 2D tin(II) sulfide is in its infancy; as such the focus remains on scalable nanosheet exfoliation and developing an understanding of their properties. The following studies on phosphorene report the exfoliation of nanosheets in organic and aqueous surfactant solutions and an investigation of the stability and breakdown products of the resulting colloidal suspensions. The stabilisation of phosphorene in aqueous media paves the way for its use in biological systems. Band-gap tuning in IV-VI analogues of phosphorene is demonstrated by size-selection of exfoliated SnS nanosheets. Although the physical characteristics of nanosheets and their incorporation into devices receive some attention, this thesis will focus mainly on the synthetic aspects of 2D materials research.

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22

Holmes, Mark J. "Optical spectroscopy of wide bandgap semiconductor nanoscale structures." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:b8318654-dd3a-4875-8a8e-1e57d877b0f2.

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The optical properties of GaN nanocolumn structures containing InGaN quantum disks are investigated by optical microphotoluminescence spectroscopy using pulsed lasers, and cathodo- luminescence. The results are analyzed in the context of current theories regarding an inho- mogeneous strain distribution in the disk which has been theorized to generate lateral charge separation in the disks by strain induced band bending, an inhomogeneous polarization field distribution, and Fermi surface pinning. Simulations of the strain distribution for the relevant materials and structures are also performed, and the results analysed. It is concluded from ex- perimental measurements that no extreme lateral separation of carriers occurs in the quantum disks under investigation. Internal field screening by an increased carrier density in the QDisks at higher excitation densities is observed via a blue-shift of the emission and a dynamically changing decay time. Other possible explanations for these effects are discussed and discounted. Microphotoluminescence studies are also carried out on a single GaN nanocolumn struc- ture that has been removed from its growth substrate and dispersed onto a patterned grid. An analysis of the dynamics of the carriers in the nanocolumn is presented. Suppression of the GaN luminescence from the area of the column in the vicinity of the InGaN QDisk in addition to a delayed emission from the QDisk relative to the GaN is observed. Time resolved spatial maps of the luminescence intensity from the column are also presented, illustrating the evolution of the carrier density in the system. Additional, albeit early-stage, work on novel structures based on the production of GaN nanocolumns, namely nanotubes and nanopyramids, is also presented.

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23

Sugunan, Abhilash. "Photochemical and Photoelectric Applications of II-VI Semiconductor Nanomaterials." Licentiate thesis, KTH, Functional Materials, FNM, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-12808.

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In this work we investigated fabrication of semiconductor nanomaterials and evaluated their potential for photo-chemical and photovoltaic applications. We investigated two different II-VI semiconductor nanomaterial systems; (i) ZnO oriented nanowire arrays non-epitaxially grown from a substrate; and (ii) colloidal CdTe nanotetrapods synthesized by solution-based thermal decomposition of organo-metallic precursors. In both the cases our main focus has been optimizing material synthesis for improving potential applications based on photon-electron interactions.

We have studied the synthesis of vertically aligned ZnO nanowire arrays (NWA), by a wet chemical process on various substrates. The synthesis is based on epitaxial growth of ZnO seed-layer on a substrate in a chemical bath consisting of an aqueous solution of zinc nitrate and hexamethylenetetramine (HMT). We have suggested an additional role played by HMT during the synthesis of ZnO nanowire arrays. We have also extended this synthesis method to fabricate hierarchical nanostructures of nanofibers of poly-L-lactide acting as a substrate for the radially oriented growth of ZnO nanowires. The combination of high surface area of the nanofibrous substrate with the flexibility of the PLLA-ZnO hierarchical nanostructure enabled the proof-of-principle demonstration of a ‘continuous-flow’ water treatment system that could effectively decompose single and combination of known organic pollutants in water, as well as render common waterborne bacteria nonviable.

We have studied another chemical synthesis that is commonly used for size controlled synthesis of colloidal quantum dots, which was modified to obtain anisotropic nanocrystals mainly for CdE (E=S, Se, Te) compositions. In this work we demonstrate by use of oleic acid (instead of alkylphosphonic acids) it is possible to synthesize CdTe and CdSe nanotetrapods at much lower temperatures (~180 ºC) than what is commonly reported in the literature, with significantly different formation mechanism in the low-temperature reaction.

Finally, we have performed preliminary photoconduction measurements with CdTe nanotetrapods using gold ‘nanogap’ electrodes fabricated in-house, and obtain up to 100 times enhancement in current levels in the I–V measurements under illumination with a white light source.

QC20100607

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24

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.

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Анотація:

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

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25

Mao, Baodong. "Synthesis and Property Characterization of Novel Ternary Semiconductor Nanomaterials." Case Western Reserve University School of Graduate Studies / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=case1334065821.

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26

Wu, Fanxin. "Synthesis and characterization of semiconductor nanomaterials : PbS, CdS, and CdTe /." Diss., Digital Dissertations Database. Restricted to UC campuses, 2004. http://uclibs.org/PID/11984.

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27

Yong, Chaw Keong. "Ultrafast carrier dynamics in organic-inorganic semiconductor nanostructures." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:b2efdc6a-1531-4d3f-8af1-e3094747434c.

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Анотація:

This thesis is concerned with the influence of nanoscale boundaries and interfaces upon the electronic processes that occur within the inorganic semiconductors. Inorganic semiconductor nanowires and their blends with semiconducting polymers have been investigated using state-of-the-art ultrafast optical techniques to provide information on the sub-picosecond to nanosecond photoexcitation dynamics in these systems. Chapters 1 and 2 introduce the theory and background behind the work and present a literature review of previous work utilising nanowires in hybrid organic photovoltaic devices, revealing the performances to date. The experimental methods used during the thesis are detailed in Chapter 3. Chapter 4 describes the crucial roles of surface passivation on the ultrafast dynamics of exciton formation in gallium arsenide (GaAs) nanowires. By passivating the surface states of nanowires, exciton formation via the bimolecular conversion of electron-hole plasma can observed over few hundred picoseconds, in-contrast to the fast carrier trapping in 10 ps observed in the uncoated nanowires. Chapter 5 presents a novel method to passivate the surface-states of GaAs nanowires using semiconducting polymer. The carrier lifetime in the nanowires can be strongly enhanced when the ionization potential of the overcoated semiconducting polymer is smaller than the work function of the nanowires and the surface native oxide layers of nanowires are removed. Finally, Chapter 6 shows that the carrier cooling in the type-II wurtzite-zincblend InP nanowires is reduced by order-of magnitude during the spatial charge-transfer across the type-II heterojunction. The works decribed in this thesis reveals the crucial role of surface-states and bulk defects on the carrier dynamics of semiconductor nanowires. In-addition, a novel approach to passivate the surface defect states of nanowires using semiconducting polymers was developed.

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Liu, Jingjing. "Diluted Magnetic Semiconductor Nanomaterials Fabrication by a Chemical Vapor Deposition Method." ScholarWorks@UNO, 2006. http://scholarworks.uno.edu/td/426.

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Well-aligned DMS Zn1-xMnxO nanowires and nanorods were successfully synthesized in-situ using a chemical vapor deposition method. Low-dimensional nanostructures such as bowls and cages were deposited on a silicon surface downstream of the tube furnace. Variation of reaction temperature and Mn doping level were investigated on structure and properties of the as-grown nanomaterials. The as-grown nanowires and naorods are single crystalline wurtzite structure and possess a growth direction along the c axis. At 850 ºC, the most optimistic condition for ZnO crystal growth was obtained. At high reaction temperature 950ºC, Mn2+ were substitutionally doped into ZnO lattice, resulting in room-temperature ferromagnetic coupling with a saturated magnetization of 0.25emu/g. The ferromagnetic interaction is weakened, however, by larger concentration of Mn, due to the antiferromagnetic coupling of direct superexchange interaction between Mn2+. The well-aligned DMS 1-dimensional Mn doped ZnO nanostructures have great potential for application in spintronic nanodevices.

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29

Nagy, Dávidné. "Visible light response semiconductor nanomaterials for heterogeneous photocatalysis in liquid phase." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/33062.

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The development of sustainable and green technologies powered by renewable energy sources is highly desired to address the growing global energy need and water scarcity problems. Heterogeneous photocatalysis emerged in the past decades as promising solar-powered technology for environmental remediation applications such as wastewater treatment. The photoactivity of the materials is believed to be governed by complex mechanisms, still it was shown that it may be critically dependent on the following material properties (i) ability and effectiveness to absorb incident photons, (ii) charge separation efficiency, (iii) charge utilization efficiency, (iv) morphology including the size and shape of the nanostructure and its distribution and (v) the crystal structure, phase composition and crystallinity ... etc. Hence, most strategies aiming to improve the performance of photocatalytic materials may focus on one or more of the aforementioned aspects. Beside developing new materials or modifying existing systems, the development of sustainable, easy-to-operate systems are highly desired for developing countries such as Africa where almost half of the population are affected by water scarcity of some sort. For this motivation the immobilization of powder catalyst could be one attractive solution. In this thesis three experimental systems are presented. In the first two the effect of material properties on the photoactivity whereas in the third chapter the immobilization of powder catalyst was investigated. The first experimental project aimed to study the effect of synthesis parameters of WO3 nanostructures on its morphology, phase composition, optical properties and ultimately on the photoactivity. Understanding the role of process parameters to gain control over the material properties is still a challenge but is of great interest in photocatalysis. Here, a hydrothermal synthesis method was employed to synthesize WO3 nanostructures with various morphologies, crystal phases and optical properties. The effect of the solution pH, the polymeric surface modulator and the added EtOH was investigated on the material properties and on the photocatalytic activities. It was found that the crystal structure and the morphology of WO3 was influenced by the solution pH in the first place. It was proposed that stabilization effects between the crystal phase and the morphology could also influence the crystallization process beside supersaturation. It was revealed that despite the highest surface area of W-2.01-P20E, reduced oxidation state did not promote high photo-response. Instead the photoactivity of WO3 was seen as the compromise of the material properties including the optical, structural properties and the oxidation state. In the second experimental project the effect of Ag co-catalysis was studied on TiO2- Cu2O heterostructure formation. Coupling a wide band gap (TiO2) and a narrow band gap (Cu2O) semiconductor could benefit from extended light absorption properties and additionally from enhanced charged separation. In this study a facile wet chemical synthesis method was coupled with a UV treatment step to fabricate TiO2-Ag-CuxO ternary hybrid nano-materials. The effect of the Ag loading (1-5%) and the synthesis sequence of the Ag deposition step was evaluated on the material properties as well as on the visible photocatalytic activity. It was revealed that both the amount and the order of the Ag-deposition altered the material properties considerably. Typically TiO2/CuxO/Ag (TCA) catalysts had better visible light absorption properties but reduced affinity to adsorb methyl orange (MO) to their surface. Whereas, TiO2/Ag/CuxO (TAC) catalysts in general had better dye adsorption properties relative to TCA and had more efficient decoloration properties under visible light. TOC and HPLC-MS analysis revealed that MO and possibly its degradation products were mainly mineralized and/or adsorbed to the surface of TAC catalyst with 5% nominal Ag content in the visible process generating limited amount of byproducts in the final solution. The third experimental project focused on the immobilization of the previously prepared powder TiO2-Cu2O nanostructure. In this work a fluorine-doped tin oxide (FTO) glass sheet was used as a substrate and the doctor-blade coating technique has been employed to make TiO2-Cu2O thin films. Although this technique has a widespread use in the fabrication of solar cells to the best of our knowledge this is the first report on supported TiO2-Cu2O photocatalytic systems prepared by this method. To optimize the performance of the TiO2- Cu2O thin film under visible light irradiation, the chemical composition of the doctor-blading paste and the temperature of the final thermal treatment step was studied. It was found that both the paste composition and the heat treatment step played an important role in the material properties. When the film contained ethyl cellulose the minimum temperature to remove organic additives was 350 °C. Whereas for the films containing only alpha terpineol 300 °C was sufficient. It was revealed that the higher temperature treatment resulted in more oxidized films which were also shown in their deeper colour. The most effective film under visible light irradiation was TC-0-300 which contained no cellulose and was treated at the lowest temperature.

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30

CONCA, ERIKA. "Preparation and investigation of new heterostructures for prospective energetic and biomedical applications." Doctoral thesis, Università degli Studi di Cagliari, 2015. http://hdl.handle.net/11584/266554.

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Nanotechnologies, defined as the ensemble of disciplines aiming at manipulating matter on an atomic or molecular scale and at exploiting the corresponding properties, have recently emerged as one of the most relevant research fields due to its implications in applied science and technological applications. Nanocrystals (NCs) with a uniformly crystalline structure and at least one dimension in the range 1÷100 nanometers, play a key role as building blocks for the assembly of innovative materials and devices for nanotechnology. A wide variety of nanocrystalline materials showing metallic, semiconducting, magnetic properties or their combinations are now available. It is well documented that nanocrystals exhibit physical properties, ranging from mechanical strength, chemical reactivity and conductivity that depend on their size and structure and differ from those of the corresponding bulk materials. For this reason, nanocrystals are regarded as promising building blocks for the fabrication of functional materials with targeted nanotechnological application. In particular, in semiconducting nanocrystals the formation of a set of discrete energy levels, at which the carriers can exist, results in quantum effects. Size restricts the movements of the charge carriers forcing them into a quantum confinement and is responsible for new properties. Again, magnetic materials with nanometric size may exhibit single domain structures, which reflect in unique physical properties such as superparamagnetism, enhanced coercivity, quantum tunnelling of the magnetization and giant magnetoresistance with respect to multi domain bulk magnets. The controlled manufacture of matter at the nanoscale is considered therefore as a promising route to obtain novel materials which can be exploited in optical, electronic, photovoltaic and magnetic nanotechnological applications. Within this framework, this PhD thesis has been focused on the design, preparation and characterization of heterostructures constituted by nanomaterials of different composition, which could be employed in two relevant areas such as energy and biomedicine. In particular, we have addressed the preparation by chemical solution routes of heterostructures which include different domains (metal-semiconductor and metal-magnet) with the aim to develop nanocrystalline new materials with improved and combined functionalities. A key aspect which has been taken into account is how to control the connection between the domains with different functionalities by tuning appropriate synthetic parameters of high temperature colloidal procedures and how this can be exploited to produce heterostructures with well-controlled morphology and microstructure. In particular, metal-semiconductor heterostructures made out of platinum tips deposited at controlled sites of a chalcogenides semiconductor with a branched octapod morphology were achieved. As the semiconducting domain is able to absorb solar light whereas the noble metal tip is capable to catalyze chemical reactions, it is prospected that the developed materials, i.e. CdSe@CdS-Pt octapods, are active as solar conversion devices and photocatalysis, with particular reference to hydrogen production through optimization of the redox process behind the photocatalytic water splitting reaction. Photophysical investigation of CdSe@CdS-Pt octapods enabled us to point out the effect of heterostructure morphology-properties relationship, as it was found that two regimes for capture of photoexcited electrons by Pt domains take place depending on the location of the metal tips onto the semiconductor octapods. When Pt is deposited at the octapod tip a slow capture takes place after energy relaxation in the semiconductor and result in large spatial separation of charges; while when Pt covers the whole octapods surface an ultrafast capture of hot electrons occurs, and charge separation happens faster than energy relaxation and Auger recombination. As an alternative route to the fabrication of multifunctional nanostructures including different domains, the potential of high temperature polymer-mediated hydrolysis in producing magnetic clusters, which are aggregates constituted of many single crystallite approximately 10 nm in size, has been explored. Such magnetic clusters retain the peculiar properties of the constituent nanoparticles such as superparamagnetism, while exhibiting specific features such as higher magnetization and stability which are advantageous for practical use. Here, the possibility to fine-tune the properties of the clusters by varying the composition of the primary particles has been investigated by including metal nanoparticles (Au, Ag, Pt) and through doping the iron oxide with manganese. This research has been achieved in order to perform a systematic study of the correlation between morpho-structural and magnetic and relaxometric properties, which may be employed for their potential use in biomedical field. The development of novel magnetic doped clusters has enabled to investigate the relaxometric and heat mediator behaviour of the novel materials, in order to evaluate their potential in biomedicine as prospective novel contrast agents for detection through Magnetic Resonance Imaging and as therapeutic tools in Magnetic Fluid Hyperthermia. In addition to contributing to the understanding of the mechanisms behind the preparation of functional and multifunctional heterostructures, this thesis also aims at elucidating the structure-properties relationship at the nanoscale in materials with highly controlled compositional and morphological features. To this end, extensive morphological and structural characterization was carried out by a multi technique approach including in particular X-Ray diffraction, conventional and advanced transmission electron microscopy techniques, X-Ray absorption spectroscopy, UV-visible spectroscopy and dynamic light scattering. The research work is presented according to the following thesis outline: - Chapter 1 deals with a short review on theoretical background, synthetic approaches and physical and chemical properties of semiconductor nanocrystals and magnetic nanocrystals. An overview on application of semiconductor and magnetic nanocrystals in two relevant fields such as energy and biomedicine, respectively, is also provided. - Chapter 2 reports on the design and applications of nanometric metal-semiconductor heterostructures. Here we will discuss in detail the formation of CdSe@CdS-Pt nanocrystal hybrid materials, obtained by synthesizing Pt metal nanoparticles onto preformed CdSe@CdS octapod semiconductor obtained by the seeded growth approach. We will present the physico-chemical properties of the developed heterostructures, as obtained by a systematic structural and morphological characterization. The optical properties of these new materials, performed by ultrafast optical spectroscopy in collaboration with Prof. Michele Saba at the Department of Physics of the University of Cagliari, will also be presented and correlated to the dynamics of charges carriers of the nanocrystals, which can in turn be used to predict their prospective use in photocatalysis. - Chapter 3 describes the synthesis and characterization of magnetic nanoclusters heterostructures based on iron oxide which were in part developed under the supervision of Dr. Antonios Kanaras during a research visit at the University of Southampton (UK). Here, a discussion on the hydrolysis approach adopted in order to produce doped magnetic nanoclusters based on iron oxide, i.e. noble metal M-Fe3O4 (M= Au, Ag, Pt) and MnxFe3-xO4 which may used as heat mediators on hyperthermia treatment cancer and as contrast agents for magnetic resonance imaging is reported. In these samples, the morpho-structural data were correlated to their magnetic and relaxometric behaviour, which was investigated through SQUID magnetometry and diffusion curves in collaboration with Dr. Teresa Pellegrino and coworkers at the Italian Institute of Technology (IIT, Genova). Finally, conclusive remarks and future developments arising from this work are discussed.

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31

Sushko, O. A., and О. М. Bilash. "Use of semiconductor nanomaterials for polycyclic aromatic hydrocarbons detection in water object." Thesis, B. Verkin Institute of Low Temperature Physics and Engineering, NASU, 2013. http://openarchive.nure.ua/handle/document/8874.

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This paper considers a novel method of PAHs in particular BP detection in water solutions with the use of semiconductor nanomaterials. The method constitutes a combination of electrochemical (EC) and electrochemiluminescent (ECL) analysis with the application of nanomaterials (semiconductor QDs) and nanotechnologies for sensor’s electrodes modification.

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32

Shahine, Issraa. "A chemical route to design plasmonic-semiconductor nanomaterials heterojunction for photocatalysis applications." Thesis, Université de Lorraine, 2019. http://www.theses.fr/2019LORR0105/document.

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L’ingénierie de nanomatériaux hybrides semi-conducteurs/plasmoniques représente une technologie durable en raison de l’efficacité parfaite du couplage pour améliorer, rénover et enrichir les propriétés des composants intégrés. Ce couplage a pour résultat la variation des propriétés fonctionnelles du système, grâce auquel les plasmons de surface générés par les métaux peuvent améliorer la séparation des charges, l’absorption de la lumière et la luminescence du semi-conducteur. Ce phénomène permet de fortes interactions avec d'autres éléments photoniques tels que les émetteurs quantiques. Ces fonctionnalités aux multiples facettes découlent de l'interaction synergique exciton-plasmon entre les unités liées. Ainsi, les nanomatériaux hybrides conviennent à diverses applications, notamment : conversion de l'énergie solaire, dispositifs optoélectroniques, diodes électroluminescentes (LED), photocatalyse, détection biomédicale, etc. Les nanostructures Au-ZnO suscitent un intérêt croissant dans ces applications où le couplage de ZnO à de nanoparticules d’or (GNPs) favorise la réponse du système dans le domaine du visible grâce à leur résonance plasmon de surface (SPR). En fonction de la taille de deux nanomatériaux, de la distance qui les sépare et leurs rapports massiques dans un échantillon, les propriétés des particules hybrides peuvent varier. Dans ce contexte, nous nous sommes concentrés sur la construction de nano-cristaux (NCs) de ZnO purs de dimensions contrôlables, puis incorporés dans des solutions de GNPs par une simple voie chimique. Ce travail est divisé en deux parties : la première consiste à effectuer une synthèse de nanocristaux de ZnO (NCs) purs présentant d'excellentes propriétés de photoluminescence dans l’UV. Ceci a été réalisé par une synthèse à basse température, aboutissant à des structures rugueuses et amorphes. La synthèse a été suivie d'un traitement post-thermique afin de cristalliser les nanoparticules obtenues. Une étude structurale et optique poussée a été établie à la suite de la synthèse (SEM, TEM, DRX, photoluminescence). Les activités photocatalytiques des ZnO NCs ont été étudiées en mesurant leur capacité à dégrader le bleu de méthylène (MB). De plus, la relation entre les structures en ZnO, la luminescence et les propriétés photocatalytiques a été explorée en détail. Dans la deuxième étape, les ZnO NCs obtenus ont été couplés ajoutés à des nanoparticules d'or de tailles et fractions volumiques variables. Le rôle effectif des GNPs concernant leur morphologie, leur contenu et leur effet SPR sur la photoémission des nanostructures de ZnO est souligné par le transfert de charge et / ou d'énergie entre les constituants du système hybride. De plus, l’activité photocatalytique du système hybride a été examinée. Comme débouché et perspective de ce travail de thèse, l'intégration des ZnO NC dans une couche nanoporeuse de polymère (PMMA) a été réalisée et caractérisée afin d'obtenir un substrat de large surface à base de ZnO. Les ZnO NCs assemblés dans du PMMA pourraient être des substrats prometteurs en tant que catalyseurs pour la croissance de nanofils de ZnO, de nanomatériaux métalliques et de matériaux hybrides
Hybrid heterojunctions composed of semiconductors and metallic nanostructures have perceived as a sustainable technology, due to their perfect effectiveness in improving, renovating, and enriching the properties of the integrated components. The cooperative coupling results in the variation of the system’s functional properties, by which the metal-generated surface plasmon resonance can enhance the charge separation, light absorption, as well as luminescence of the semiconductor. This phenomenon enables strong interactions with other photonic elements such as quantum emitters. These multifaceted functionalities arise from the synergic exciton-plasmon interaction between the linked units. Thereby, hybrid systems become suitable for various applications including: solar energy conversion, optoelectronic devices, light-emitting diodes (LED), photocatalysis, biomedical sensing, etc. Au-ZnO nanostructures have received growing interest in these applications, where the deposition of gold nanoparticles (GNPs) promotes the system’s response towards the visible region of the light spectrum through their surface plasmon resonance (SPR). Based on a specific size and purity of ZnO nanostructures, as well as the GNPs, and a definite inter-distance between the nanoparticles, the properties of the ZnO nanostructures are varied, especially the photoemission and photocatalytic ones. In this context, we have focused on the construction of size-tunable ZnO nanocrystals (NCs), then incorporated into GNPs solutions using a simple chemical way. This work is divided into two parts: the first is to perform synthesis of pure ZnO NCs having excellent UV photoluminescence. This was achieved through a low-temperature aqueous synthesis, resulting in rough and amorphous structures. The synthesis was followed by a post-thermal treatment in order to crystallize the obtained particles. The synthesis was followed by structural and optical studies (SEM, TEM, XRD, photoluminescence). The photocatalytic activities of ZnO NCs were studied through tailoring their ability to degrade the methylene blue (MB) dye. In addition, the relationship between ZnO structures, luminescence, and photocatalytic properties was explored in details. In the second step, the obtained ZnO NCs were added to gold nanoparticles of various sizes and volume fractions. The effective role of GNPs concerning their size, amount, and their capping molecule on the photoemission of the ZnO nanostructures was emphasized through the charge and/or energy transfer between the constituents in the hybrid system. In the same way, the systems photocatalytic activities were examined after coupling ZnO to GNPs. Further advancement in the integration of the ZnO NCs into PMMA polymer layers was featured in order to obtain large area template of homogenous ZnO properties. The PMMA-assembled ZnO nanoparticles could be promising substrates as catalysts for growing ZnO nanowires, metallic nanoparticles and hybrid nanomaterials

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33

Aryal, Basu Ram. "Bottom-Up Fabrication and Characterization of DNA Origami-Templated Electronic Nanomaterials." BYU ScholarsArchive, 2021. https://scholarsarchive.byu.edu/etd/9041.

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This work presents the bottom-up fabrication of DNA origami-assembled metal nanowires and metal-semiconductor junctions, and their electrical characterization. Integration of metal and semiconductor nanomaterials into prescribed sites on self-assembled DNA origami has facilitated the fabrication of electronic nanomaterials, whereas use of conventional tools in their characterization combines bottom-up and top-down technologies. To expand the contemporary DNA-based nanofabrication into nanoelectronics, I performed site-specific metallization of DNA origami to create arbitrarily arranged gold nanostructures. I reported improved yields and conductivity measurements for Au nanowires created on DNA origami tile substrates. I measured the conductivity of C-shaped Au nanowires created on DNA tiles (âˆ¼130 nm long, 10 nm diameter, and 40 nm spacing between measurement points) with a four-point measurement technique which revealed the resistivity of the gold nanowires was as low as 4.24 Ã— 10-5 Î© m. Next, I fabricated DNA origami-templated metal-semiconductor junctions and performed electrical characterization. Au and Te nanorods were attached to DNA origami in an alternating fashion. Electroless gold plating was used to create nanoscale metal--semiconductor interfaces by filling the gaps between Au and Te nanorods. Two-point electrical characterization indicated that the Au--Te--Au junctions were electrically connected, with non-linear current--voltage curves. Finally, I formed metal-semiconductor nanowires on DNA origami by annealing polymer-encased nanorods. Polymer-coated Au and Te nanorods pre-attached to ribbon-shaped DNA origami were annealed at 170°C for 2 min. Gold migration occurred onto Te nanorods during annealing and established electrically continuous interfaces to give Au/Te nanowires. Electrical characterization of these Au/Te/Au assemblies revealed both nonlinear current-voltage curves and linear plots that are explained. The creation of electronic nanomaterials such as metal nanowires and metal-semiconductor junctions on DNA origami with multiple techniques advances DNA nanofabrication as a promising path toward future bottom-up fabrication of nanoelectronics.

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34

Naik, A. J. T. "Hetero-junction and nanomaterial systems for metal oxide semiconductor based gas sensing." Thesis, University College London (University of London), 2015. http://discovery.ucl.ac.uk/1463687/.

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Investigations into a number of hetero-junction and nanoceramic materials systems for metal oxide semiconductor (MOS) gas sensing for potential environmental and bio-sensing applications are presented. The hetero-junction study encompasses investigations into various composite n-n hetero-contact systems such as WO3-ZnO and SnO2-ZnO and a p-n hetero-contact system, specifically CTO (Chromium Titanium Oxide) - ZnO. The facile fabrication of various arrays of hetero-junction MOS gas sensor devices has been demonstrated. A simple change in the compositional contribution of an individual metal oxide within a composite, exhibits the ability to tune the composite’s responsivity and selectivity. The hetero-junction systems were characterized by various techniques including Scanning Electron Microscopy (SEM), Raman spectroscopy, X-Ray Diffraction (XRD) and X-Ray Photoelectron Spectroscopy (XPS) and the influence of the physical and chemical properties of these materials towards the associated gas sensing properties, deduced. Further, the influence of fundamental properties of junctions such as contact potential and packing structure, towards the sensing properties, are also discussed. The nanomaterials study encompasses investigation into ZnO semiconducting oxides fabricated by various emerging fabrication technologies including Continuous Hydrothermal Flow Synthesis (CHFS) and other relatively high temperature routes. The chemical and physical properties of the nanoceramics have been investigated by various techniques including Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) and Brunauer Emmett Teller (BET) surface area measurements. The investigation demonstrates emerging techniques for the production of nanomaterials, which can be successfully used in MOS gas sensing for the desired applications. Further, the study shows that the behaviour of the nanomaterials is complex and material surface area is not the only deterministic factor of enhanced responsivities, but microstructural factors such as morphology and particle size, as well as heat-treatment conditions are all influential over the overall sensing properties. This thesis presents an overview of emerging material systems for MOS gas sensing applications.

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35

Al-Saadi, Ali. "Preparation and characterisation of encapsulation magnetic metal iron oxide nanoparticles." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:57bdcf38-9d45-48ab-a971-a2d60e2e4391.

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One of the most challenging goals in nanoparticle research is to develop successful protocols for the large-scale, simple and possibly low-cost preparation of morphologically pure nanoparticles with enhanced properties. The work presented in this thesis was focused on the synthesis, characterisation and testing of magnetic nanoparticles and their potential applications. There are a number of magnetic nano-materials prepared for specific applications such as metal oxide nanoparticles encapsulated with various porous materials including Fe₃O₄/Fe₂O₃ coated with soft bio-organic materials such as glycol chitosan and bovine serum albumin and hard materials such as silica (SiO₂) and zinc sulphide (ZnS). The preparation of these materials was achieved principally by bottom-up methods with different approaches including micro-emulsion, precipitation, electrostatic and thermolysis processes. The thesis also presents the uses of various analytical techniques for characterising different types of nano-materials including Attenuated Total Reflection Fourier Transformer Infrared Vibrational Spectroscopy (ATR-FTIR), Ultraviolet Visible- Near Infrared (UV-Vis-NIR) Spectroscopy, Zeta Potentiometric Surface Charge Analysis, Superconducting Quantum Interference Device (SQUID) and Vibration Sample Magnetometry (VSM) for magnetic analysis and powder X-Ray Diffraction (XRD) for crystallographic pattern analysis. There are many applications of magnetic nanoparticles, including nano-carriers for biological and catalytic reagents. The magnetic nanoparticles can facilitate separation in order to isolate the carriers from solution mixtures as compared to many inefficient and expensive classic methods, which include dialysis membrane, electrophoresis, ultracentrifugation, precipitation and column separation methods. There are six key chapters in this thesis: the first chapter introduces the up-to-date literature regarding magnetic nano-materials. The uses of magnetic nano-materials in drug binding and for protein separation are discussed in the second and third chapters. The fourth chapter presents the use of magnetic nanoparticle in conjunction with a photo-catalytic porous overlayer for the photo-catalytic reduction of organic molecules. The fifth chapter describes different analytical techniques used for the characterisation of nanoparticles and the underlying principles and the experimental details are also given. The sixth chapter summarises the results and provides an overview of the work in a wider context of future applications of magnetic nanoparticles.

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36

Bidaud, Thomas. "Characterization of nanomaterials by cathodoluminescence for photovoltaic applications." Thesis, université Paris-Saclay, 2021. http://www.theses.fr/2021UPAST010.

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Le développement récent de dispositifs photovoltaïques solaires fait appel à des matériaux dont les propriétés peuvent varier à l’échelle sub-micronique, par exemple des cellules solaires à base de nanofils III-V, ou des films minces polycristallins de CdTe. Cette thèse a pour but de développer de nouvelles méthodes et techniques basées sur l’utilisation de la cathodoluminescence (CL) et la CL résolue en temps (TRCL) pour sonder ces matériaux à l’échelle nanoscopique. Une première partie est consacrée aux films minces polycristallins en CdTe. L’impact du recuit sous CdCl₂ sur la formation et la passivation de défauts dans les grains et aux joints de grains a été analysé en combinant les cartographies de CL à haute résolution, à température ambiante et à basse température. L’incorporation de Se à différentes concentrations et son effet sur la passivation des défauts et sur l’efficacité radiative de films minces de CdSeₓTe₁-ₓ ont ensuite été étudiés et corrélés à des mesures macroscopiques (tension Voc et mesures de temps de vie). Dans un second temps, des nanofils en GaAs ont été étudiés. Les propriétés optiques et de transport des phases wurtzite (WZ) et zinc-blende (ZB) ont été comparées dans des nanofils uniques, et des déclins radiatifs ont été mesurés (τ(WZ)=0.55 ns et τ(ZB)=0.62 ns). Le dopage n obtenu par incorporation d’élément Te a été déterminé quantitativement, et son homogénéité à l’échelle d’un nanofil unique a été étudiée par cartographie de CL. Des dopages atteignant n=3.3×10¹⁸ cm⁻³, et un gradient de dopage le long des nanofils, ont été mis en évidence. Enfin, la passivation des nanofils de GaAs par ajout d’une coquille en AlGaAs ou en InGaP a été caractérisée par des mesures de l’intensité radiative de CL, de la longueur de diffusion et de la durée de vie des porteurs. Les méthodologies et techniques décrites dans cette thèse peuvent être utilisées pour le développement d’un large éventail de matériaux semiconducteurs, pour des applications photovoltaïques et optoélectroniques
The recent development of photovoltaic devices makes use of materials with properties that may vary at the sub-micrometer scale, for instance nanowire-based III-V solar cells based or CdTe polycrystalline thin films. This thesis aims at developing new methods and techniques based on cathodoluminescence (CL) and time-resolved CL (TRCL) in order to probe material properties at the nanometer scale. A first part is devoted to CdTe polycrystalline thin films. The role of CdCl₂ annealing on the formation and passivation of defects in the grain interior and at the grain boundaries is analyzed by combining high-resolution CL maps at room- and low-temperature. The incorporation of Se at different concentrations and its effect on defect passivation and radiative efficiency of CdSeₓTe₁-ₓ thin films is investigated and correlated to macroscopic measurements (Voc, lifetimes). A second part is devoted to GaAs nanowires. The optical and transport properties of wurtzite (WZ) and zinc-blende (ZB) phases are compared in single nanowires, and radiative decay measurements are presented (τ(WZ)=0.55 ns et τ(ZB)=0.62 ns). N-doping obtained by incorporation of Te is determined quantitatively, and its homogeneity is studied in single nanowires by CL maps. We evidence doping levels up to n=3.3×10¹⁸ cm⁻³, and a doping gradient along nanowires. Finally, the passivation of GaAs nanowires by an AlGaAs or InGaP shell is characterized by CL measurement of the radiative intensity, diffusion length and lifetime of charge carriers. The techniques and methodologies presented in this thesis may be applied to a wide variety of semiconductor materials for photovoltaic or optoelectronic applications

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37

Fairclough, Simon Michael. "Carrier dynamics within semiconductor nanocrystals." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:857f624d-d93d-498d-910b-73cce12c4e0b.

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This thesis explores how the carrier dynamics within semiconductor nanocrystals can be directly engineered through specific core-shell design. Emphasis is placed on how material characteristics, such as strain or alloying at a core-shell interface, can influence the exciton energies and the recombination dynamics within semiconductor nanocrystals. This study synthesises type-II heterojunction ZnTe/ZnSe core-shell nanocrystals via a diethyl zinc-free synthesis method, producing small size distributions and quantum yields as high as 12%. It was found that the 7% lattice mismatch between the core and shell materials places limitations on the range of structures in which coherent growth is achieved. By developing compositional and strained atomistic core-shell models a variety of physical and optical properties could be simulated and has led to a clear picture of the core-shell architecture to be built. This characterisation provides evidence that the low bulk modulus ZnTe cores are compressed by the higher bulk modulus smaller lattice constant ZnSe shells. Further studies show how strain is manifested in structures with 'sharp' core-shell interfaces and how intentional alloying the interface can influence the growth and exciton energies. A (2-6)-band effective mass model was able to distinguish between the as-grown 'sharp' and 'alloyed' interfaces which indicated that strain accentuates the redshift of the excitonic state whilst reduced strain within an alloyed interface sees a reduced redshift. Single nanocrystal spectroscopy investigations of brightly emitting single graded alloyed nanocrystals and of a size series of commercially available CdSe/ZnS nanocrystals showed almost no fluorescence intermittency (nearly 'non-blinking'). These investigations also identified trion recombination as the main mechanism within the blinking 'off' state. Ultimately this thesis adds to the growing understanding of how specific core-shell architectures manipulate the electronic structure and develops techniques to identify specific material characteristics and how these characteristics influence the physical and optical properties within semiconductor nanocrystals.

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38

Jiang, Zhoufeng Jiang. "Zero-dimensional and two-dimensional colloidal nanomaterials and their photophysics." Bowling Green State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1522964027555741.

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39

Dooley, Chad Johnathan. "New Nanomaterials for Photovoltaic Applications: A Study on the Chemistry and Photophysics of II-VI Semiconductor Nanostructures." Thesis, Boston College, 2009. http://hdl.handle.net/2345/705.

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Thesis advisor: Torsten Fiebig
This dissertation examines the chemistry and photophysics of semiconductor quantum dots with the intent of studying their capabilities and limitations as they pertain to photovoltaic technologies. Specifically, experiments are presented detailing the first time-resolved measurements of electron transfer in electronically coupled quantum rods. Electron transfer from the conduction band of CdTe was measured to occur on the 400 fs timescale (k_ET = 2.5 x 1012 s-1), more than 500x faster than previously believed. Additionally, the direct optical promotion of an electron from the valence band of CdTe was observed, occurring on the timescale of the pump pulse (~50 fs). Based on the determined injection rates, a carrier separation efficiency of > 90% has been calculated suggesting these materials are sufficient for use in solar energy capture applications where efficient carrier separation is critical. To this end, model photovoltaic cells were fabricated, and their power conversion efficiency and photon-to-current generation efficiency characterized. In devices based of CdSe and heteromaterial quantum rods we observed fill-factors on the order of 10-20% though with power conversion efficiencies of < 0.02%. It was discovered that using a high temperature annealing step, while critical to get electrochemically stable photoelectrodes, was detrimental to quantum confinement effects and likely removed any hQR specific capabilities. Additionally, a detailed study on the role of nucleotide triphosphate chemistry in stabilizing emissive CdS nanoparticles is presented. Specifically it was observed that in a neutral pH environment, GTP selectively stabilizes CdS quantum dots with diameters of ~4 nm while the other naturally occurring ribonucleotides do not yield emissive product. The selectivity is dependent on the presence of the nucleophilic N-7 electrons near a triphosphate pocket for Cd2+ complexation as well as an exocyclic amine to stabilize the resulting product particles. However, in an elevated pH environment, the nucleobase specificity is relaxed and all NTPs yield photo-emissive quantum dots with PLQEs as high as 10%
Thesis (PhD) — Boston College, 2009
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry

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40

Shao, Hui. "Functional nanomaterials derived from self-assembly of peptide hybrids and amino acid amphiphiles: from diseases to devices." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1267225830.

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41

Parala, Harish. "Precursor routes to selected metal and semiconductor nanomaterials crystals, composites, colloids of Au, GaN, InN, CdSe and TiO₂ /." [S.l.] : [s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=96870901X.

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42

Parala, Harish. "Precursor routes to selected metal and semiconductor nanomaterials crystals, composites, colloids of Au, GaN, InN, CdSe and TiO2 /." [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=96870901X.

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43

Farzinpour, Pouyan. "DYNAMIC TEMPLATING: A NEW PATHWAY FOR THE ASSEMBLY OF LARGE-AREA ARRAYS OF PLASMONIC, MAGNETIC AND SEMICONDUCTOR NANOMATERIALS." Diss., Temple University Libraries, 2014. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/280637.

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Mechanical Engineering
Ph.D.
Substrate-based nanostructures are of great importance due to their applications in microelectronic devices, chemical sensors, catalysis and photovoltaics. This dissertation describes a novel fabrication technique for the formation of periodic arrays of substrate-based nanoparticles. The prescribed route, referred to as dynamic templating, requires modest levels of instrumentation consisting of a sputter coater, micrometer-scale shadow masks and a tube furnace. The route has broad applicability, having already produced periodic arrays of gold, silver, copper, platinum, nickel, cobalt, germanium and Au-Ag alloys on substrates as diverse as silicon, sapphire, silicon-carbide, and glass. The newly devised method offers large-area, high-throughput capabilities for the fabrication of periodic arrays of sub-micrometer and nanometer-scale structures and overcomes a significant technological barrier to the widespread use of substrate-based templated assembly by eliminating the need for periodic templates having nanoscale features. Because this technique only requires modest levels of instrumentation, researchers are now able to fabricate periodic arrays of nanostructures that would otherwise require advanced fabrication facilities.
Temple University--Theses

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44

Lin, Yu-Pu. "Functionalization of two-dimensional nanomaterials based on graphene." Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM4727.

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Cette étude de la fonctionnalisation de graphène se base principalement sur la monocouche de graphène épitaxiée sur SiC. Les propriétés électroniques, structurales et les compositions chimiques du graphène fonctionnalisé sont étudiées. L'incorporation d'azote dans le graphène réalisée par les procédures à base de plasma montre un décalage de niveaux inoccupés du graphène vers EF , obtenue par les analyses spectroscopie de photoémission inverse en résolution angulaire. Ce dopage-n est attribué à la présence de graphitique-N. De plus, la configuration des espèces de N substitués dans le graphène peut être contrôlée efficacement par l'énergie, les espèces d'azote incidentes, et l'épaisseur du graphène de départ. L'hydrogénation de la couche tampon de graphène (BLG) à température variante sature les liaisons pendantes de Si de l'interface différemment, soit par la formation de nouvelles liaisons C-Si à température ambiente, soit par les hydrogènes intercalés. Le BLG devient fortement-isolant dans le premier cas, et devient une monocouche de graphène quasi-autoportante (QFSG) dans le second, permettant un nouveau concept de fabrication des dispositifs à base de graphène sur SiC. La réaction/couplage entre des molécules pi-conjugué et les graphène vierge ou fonctionnalisé est aussi étudiée. Les états inoccupés des molécules à base de perylene sont légèrement modiffiées sur le graphène dopé N à cause d'un renforcement de transfert de charge. Des réactions chimiques entre les molécules perylenes et le graphène sont observées aprés l'exposition aux électrons de basse énergie. En résumé, cette étude permettra une meilleure maîtrise des propriétés des matériaux 2D comme le graphène
In order to promote 2D materials like graphene to their numerous applications, new methodsaltering their electronic and chemical properties have to be mastered. In this thesis, theprocesses of chemical doping and hydrogenation of monolayer graphene grown on SiC are investigated. Nitrogen atoms are successfully substituted in the graphene lattice using plasma-basedmethods. The bonding configurations of the incorporated N can be controlled via the nature and energy of exposing species and the thickness of the pristine graphene. An n-type doping, revealed by angle-resolved inverse photoemission spectroscopy (ARIPES), is found in most N-doped graphene and is assigned to the presence of graphitic-N. Hydrogenations of the buffer layer of graphene (BLG) on SiC at ambient or high temperatures saturate the remaining Si dangling bonds at BLG/SiC interface in two different ways, either by inducing additional C-Si bonds or by H intercalation. This results in 2D materials with distinct characters, an insulating, graphane-like H-BLG or a quasi-free-standing graphene, which may be used as a new concept for the engineering of graphene-based devices. The interactions between pi-conjugated molecules and the functionalized graphene are also investigated. The unoccupied states of molecules are altered by the presence of incorporated N, but the degradation of molecules due to low-energy electron exposure seems not enhanced by the doping nitrogen under the studied conditions. Nevertheless, the functionalization of graphene is demonstrated and its electronic and chemical properties are carefully studied, which should help to faster further applications employing functionalized graphene

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45

Wu, Yimin A. "Towards large area single crystalline two dimensional atomic crystals for nanotechnology applications." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:bdb827e5-f3fd-4806-8085-0206e67c7144.

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Nanomaterials have attracted great interest due to the unique physical properties and great potential in the applications of nanoscale devices. Two dimensional atomic crystals, which are atomic thickness, especially graphene, have triggered the gold rush recently due to the fascinating high mobility at room temperature for future electronics. The crystal structure of nanomaterials will have great influence on their physical properties. Thus, this thesis is focused on developing the methods to control the crystal structure of nanomaterials, namely quantum dots as semiconductor, boron nitride (BN) as insulator, graphene as semimetal, with low cost for their applications in photonics, structural support and electronics. In this thesis, firstly, Mn doped ZnSe quantum dots have been synthesized using colloidal synthesis. The shape control of Mn doped ZnSe quantum dots has been achieved from branched to spherical by switching the injection temperature from kinetics to thermodynamics region. Injection rates have been found to have effect on controlling the crystal phase from zinc blende to wurtzite. The structural-property relationship has been investigated. It is found that the spherical wurtzite Mn doped ZnSe quantum dots have the highest quantum yield comparing with other shape or crystal phase of the dots. Then, the Mn doped ZnSe quantum dots were deposited onto the BN sheets, which were micron-sized and fabricated by chemical exfoliation, for high resolution imaging. It is the first demonstration of utilizing ultrathin carbon free 2D atomic crystal as support for high resolution imaging. Phase contrast images reveal moiré interference patterns between nanocrystals and BN substrate that are used to determine the relative orientation of the nanocrystals with respect to the BN sheets and interference lattice planes using a newly developed equation method. Double diffraction is observed and has been analyzed using a vector method. As only a few microns sized 2D atomic crystal, like BN, can be fabricated by the chemical exfoliation. Chemical vapour deposition (CVD) is as used as an alternative to fabricate large area graphene. The mechanism and growth dynamics of graphene domains have been investigated using Cu catalyzed atmospheric pressure CVD. Rectangular few layer graphene domains were synthesized for the first time. It only grows on the Cu grains with (111) orientation due to the interplay between atomic structure of Cu lattice and graphene domains. Hexagonal graphene domains can form on nearly all non-(111) Cu surfaces. The few layer hexagonal single crystal graphene domains were aligned in their crystallographic orientation over millimetre scale. In order to improve the alignment and reduce the layer of graphene domains, a novel method is invented to perform the CVD reaction above the melting point of copper (1090 ºC) and using molybdenum or tungsten to prevent the balling of the copper from dewetting. By controlling the amount of hydrogen during the growth, individual single crystal domains of monolayer over 200 µm are produced determined by electron diffraction mapping. Raman mapping shows the monolayer nature of graphene grown by this method. This graphene exhibits a linear dispersion relationship and no sign of doping. The large scale alignment of monolayer hexagonal graphene domains with epitaxial relationship on Cu is the key to get wafer-sized single crystal monolayer graphene films. This paves the way for industry scale production of 2D single crystal graphene.

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46

Docampo, Pablo. "Electronic properties of mesostructured metal oxides in dye-sensitized solar cells." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:e97e90f9-47fe-4259-a462-c97f0bf81469.

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Solid-state dye-sensitized solar cells (ssDSCs) offer the possibility of high power conversion efficiencies (PCEs) of over 20%. However, after more than a decade of research, devices still barely reach over 7% PCEs. In this thesis, limitations to device performance are studied in detail, and solutions for future advancement are put forward. In the first part of the thesis, factors limiting charge generation are explored by studying the crystallization environment of mesoporous TiO2 self-assembled through block copolymers. It was found that the density and distribution of sub band gap states are a function of the synthesis conditions and critically affect the performance characteristics of the self-assembled titania used in ssDSCs. As a result, the self-assembled mesoporous oxide system presented in this thesis outperforms for the first time the conventional nanoparticle based electrodes fabricated and tested under the same conditions, with demonstrated PCEs of over 5%. In chapters 6, 7, and 8, the factors limiting the diffusion length and hence, the thickness of the fabricated devices, are carefully examined. Previous literature points towards insufficient pore-filling of the hole transporting material (HTM) as the main limiting factor. In chapter 6, a pore-filling study is shown where a new technique to evaluate the pore-filling fraction of the HTM in the conventional mesoporous metal oxide electrode is also presented and conclude that sufficient pore-filling of thick films can easily be achieved. Another usual strategy to extend the electron lifetime in the devices and thus, the charge diffusion length, involving thin film coatings of insulating metal oxides is examined in chapter 7, with satisfactory results for SnO2-based ssDSCs. The diffusion length can also be extended if the factors limiting the diffusion of charges through the device are identified and removed, as presented in chapter 8. Finally, a study on the stability of the ssDSC is presented in chapter 9. The developments achieved enable long term stability to be effectively targeted, and represent a key milestone towards commercial realization of ssDSCs.

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47

Jiang, Ye. "Growth mechanism and surface chemistry of II-VI 2D nanomaterials." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS058.

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Grâce à leurs propriétés optiques et électroniques uniques, les nanocristaux de semi-conducteurs colloïdaux bidimensionnels tels que les nanoplaquettes de chalcogénure de cadmium ont émergé comme une nouvelle classe de nanomatériaux. Tout comme les puits quantiques, ces nanocristaux ont un confinement electronique limité à une seule direction, l'épaisseur qui est contrôlée au niveau atomique. Ces nanoplaquettes colloïdales apparaissent ainsi comme de bons candidats pour la fabrication de dispositifs optoélectroniques. Cependant, leur mécanisme de formation reste sujet à discussion. Ainsi, cette thèse se concentre tout d’abord sur l'étude de la synthèse de nanoplaquettes de CdSe zinc blende et l’effet de la longueur de la chaine aliphatique des carboxylates sur ces dernières, ouvrant ainsi la voie à une meilleure compréhension de la croissance des nanocristaux bidimensionnels.Par la suite, la nature et la localisation de ces ligands carboxylates en surface des nanoplaquettes a été étudié par des techniques de RMN. Cette étude semble confirmer l’effet de la gêne stérique sur la croissance des nanoplaquettes. La RMN du solide en corrélation 13C-1H 2D, se basant sur l’interaction dipolaire, indique que les acétates et les carboxylates à longue chaîne sont très probablement distribués de manière homogène à la surface des nanoplaquettes de CdSe. Dans une dernière partie, j’explore la possibilité d’améliorer les propriétés optiques de nanoplaquettes synthetisées par déposition de couches atomiques en voie colloïdale (c-ALD) en utilisant des recuits, visant à améliorer la structure et la surface des matériaux
Colloidal two-dimensional semiconductor nanocrystals such as nanoplatelets of cadmium chalcogenides, have emerged as a new class of nanomaterials due to their unique optical and electronic properties. These nanocrystals possess exciton confinement along one direction in analogy to quantum wells, with their thickness controlled at atomic level.Although colloidal two-dimensional nanoplatelets have been considered as potential candidates for the fabrication of optoelectronic devices, their formation mechanism e.g. zinc blende CdSe nanoplatelets is still under debate. Thereby this thesis first focuses on the study of CdSe nanoplatelets synthesis and size of the aliphatic chain in the carboxylate, paving the way to a better understanding of two-dimensional nanocrystals’ growth.Successively surface carboxylate ligands are investigated by NMR techniques which gives us an idea of how surface ligands are composed and relocated. Our study of ligand quantification on nanoplatelets’ surface appears to support the proposed effect from steric hinderance on NPLs growth. 13C-1H 2D correlation solid state NMR based on the dipolar interaction indicates that acetates and long alkyl chain carboxylates should be distributed homogenously on the surface of the CdSe NPLs. In the last part, I explore the possibility of improving the optical features of nanoplatelets synthesized from colloidal atomic-layer-deposition technique through optimizing both interior and surface structures by an annealing process

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48

Mehdi, Aghaei Sadegh. "Electronic and Magnetic Properties of Two-dimensional Nanomaterials beyond Graphene and Their Gas Sensing Applications: Silicene, Germanene, and Boron Carbide." FIU Digital Commons, 2017. http://digitalcommons.fiu.edu/etd/3389.

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The popularity of graphene owing to its unique properties has triggered huge interest in other two-dimensional (2D) nanomaterials. Among them, silicene shows considerable promise for electronic devices due to the expected compatibility with silicon electronics. However, the high-end potential application of silicene in electronic devices is limited owing to the lack of an energy band gap. Hence, the principal objective of this research is to tune the electronic and magnetic properties of silicene related nanomaterials through first-principles models. I first explored the impact of edge functionalization and doping on the stabilities, electronic, and magnetic properties of silicene nanoribbons (SiNRs) and revealed that the modified structures indicate remarkable spin gapless semiconductor and half-metal behaviors. In order to open and tune a band gap in silicene, SiNRs were perforated with periodic nanoholes. It was found that the band gap varies based on the nanoribbon’s width, nanohole’s repeat periodicity, and nanohole’s position due to the quantum confinement effect. To continue to take advantage of quantum confinement, I also studied the electronic and magnetic properties of hydrogenated silicene nanoflakes (SiNFs). It was discovered that half-hydrogenated SiNFs produce a large spin moment that is directly proportional to the square of the flake’s size. Next, I studied the adsorption behavior of various gas molecules on SiNRs. Based on my results, the SiNR could serve as a highly sensitive gas sensor for CO and NH3 detection and a disposable gas sensor for NO, NO2, and SO2. I also considered adsorption behavior of toxic gas molecules on boron carbide (BC3) and found that unlike graphene, BC3 has good sensitivity to the gas molecules due to the presence of active B atoms. My findings divulged the promising potential of BC3 as a highly sensitive molecular sensor for NO and NH3 detection and a catalyst for NO2 dissociation. Finally, I scrutinized the interactions of CO2 with lithium-functionalized germanene. It was discovered that although a single CO2 molecule was weakly physisorbed on pristine germanene, a significant improvement on its adsorption energy was found by utilizing Li-functionalized germanene as the adsorbent. My results suggest that Li-functionalized germanene shows promise for CO2 capture.

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Pournia, Seyyedesadaf. "Exploring the Photoresponse and Optical Selection Rules in the Semiconductor Nanowires, Topological Quantum Materials and Ferromagnetic Semiconductor Nanoflakes using Polarized Photocurrent Spectroscopy." University of Cincinnati / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1627666632280473.

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50

Jakob, Matthias [Verfasser], Ulrich K. [Akademischer Betreuer] Heiz, Ulrich K. [Gutachter] Heiz, and Bernhard [Gutachter] Rieger. "Optical and Chiroptical Properties of Semiconductor and Noble Metal Nanomaterials / Matthias Jakob ; Gutachter: Ulrich K. Heiz, Bernhard Rieger ; Betreuer: Ulrich K. Heiz." München : Universitätsbibliothek der TU München, 2019. http://d-nb.info/1212178106/34.

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Дисертації з теми "Nanomaterials- Semiconductors"

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