Dissertationen: „Advanced nanomaterials“

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Tsikourkitoudi, Vasiliki P. „Development of advanced nanomaterials for lithium-ion batteries“. Thesis, Kingston University, 2016. http://eprints.kingston.ac.uk/37347/.

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The scope of the present study was to demonstrate the capability of Flame Spray Pyrolysis (FSP) process as a unique facility for the one-step synthesis of lithium titanate (Li[sub]4Ti[sub]5O[sub]12, LTO) nanoparticles with tailored properties. FSP offers a versatile technology to produce a wide range of high-purity oxide nanoparticles with desired properties. The ability of FSP to manipulate nanoparticles' properties was demonstrated by controlling operating conditions and selecting appropriate precursors. More precisely, the effect of FSP processing conditions on LTO properties were thoroughly investigated both experimentally in a pilot-scale reactor (production rates up to 1 kg h[sup]-1) and theoretically by the development of models describing particle dynamics in the spray flame. The main aim was to obtain LTO nanoparticles of different particle sizes. The produced nanoparticles were used as active materials for the fabrication of lithium-ion battery anodes and electrochemical characterisation was performed in order to examine the influence of the particles' physical properties on the battery performance. The control of the flame synthesis parameters is crucial, since the properties of the final product depend on the nanoparticles' size distribution, morphology, extent of agglomeration, as well as phase compostition. Initially, the influence of liquid feed properties (precursor concentration and solvent) on LTO physical properties was established. LTO particle size increazsed when the precursor concentration was increased due to particle concentration increase in the flame followed by the enhancement of particle collisions and hence particle growth. Moreover, high precursor concentration caused a variation of physical properties of the precursor mixture, affecting the atomisation process, and subsequently led to the formation of larger droplets. Larger droplets generated larger particle. Additionally, the choice of solvent for the dissolution of metal precursors was proven to be an important issue for LTO synthesis by FSP. The physical properties of the solvents in relation to metal precursor properties affected the formation of LTO nanoparticles. Inhomogenous particle size distribution was observed for LTO synthesised by a precursor mixture containing isopropanoil, due to its low boiling point inducing particle formation via droplet-to-particle mechanism, whereas pure 2-ethylhexanoic acid was used, LTO particles were formed by gas-to-particle route and had homogenous size distribution. The droplets generated during atomisation by the precursor solution of pure 2- ethylhexanoic acid had the largest diameter due to the high viscosity and density of the mixture. Despite this, the obtained nanoparticles were the smallest in comparison to those obtained from other precursor solutions. In such cases, the boiling point and specific combustion enthalpy of the solvents should be taken into consideration. Apart from the liquid feed properties, the effect of FSP operating conditions (O[sub]2 dispersion gas and precursor flow rate) were also investigated in the present study. By increasing the O[sub]2 dispersion gas rate, LTO nanoparticles' diameter was decreased due to a decrease of the droplet diameter. Particle sintering was also prevented due to the faster transport of primary particles through a shorter flame. An increase of the precursor flow rate at first increased and then decreased the LTO nanoparticles' size. The initial increase of particle size occurred due to a flame temperature increase. At higher precursor flow rates, the droplets disintegrated and generated many smaller fragmented droplets due to higher temperature, which subsequently formed smaller particles. Moreover, particle growth in the spray flames was studied theoretically, and numerical models were developed. The monodisperse model developed assumed that all primary particles had the same size. However, it overestimated the primary particle diameter values. Polydispersity was taken into consideration in the development of an additional model which was solved by the quadrature method of moments. The results obtained from the polydisperse model were closer to the experimental values, both for low and high production rates. Finally, the synthesised LTO nanoparticles were used as active materials in lithium-ion battery half cells and their electrochemical behaviour was elucidated, demonstrating the effect of the particles' physical properties on their electrochemical performance. LTO of particle size 18 and 21 nm showed the best electrochemical performance with capacity retention of almost 100% after 500 cycles, whereas the smallest particle deteriorated the electrochemical performance with a capacity loss of more than 60%.

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Zamani, Reza. „Structure nanoengineering of functional nanomaterials. Advanced electron microscopy study“. Doctoral thesis, Universitat de Barcelona, 2013. http://hdl.handle.net/10803/145318.

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In this report novel materials for advanced applications are studied by means of the latest microscopy technologies and methodologies which have had a dramatic impact on progress of materials science. The aim was to study phenomena such as polytypism, unusual morphologies, polytypic branching, cation ordering, polarity, epitaxial growth and interface, etc, in order to find adequate explanations for the influence of the phenomena on the properties and applications such as thermoelectricity, p-n junction functionality, photovoltaic efficiency, optoelectronic properties, and sensing response. Various semiconducting materials, i.e. complex chalcogenides, metal oxides, and III-V nanostructures were characterized for this purpose. Here, nanoengineered structures of functional materials at nanoscale are studied by means of advanced electron microscopy methods. Chapter 1 gives a brief introduction to the report; the main purpose of the work, state-of-the-art, challenges and possibilities. In chapter 2 the methodology is described. The results are provided in Chapter 3, 4, and 5, and Chapter 6 is the general conclusions and the outlook. Note that Chapters 3-5 have their own introduction and conclusion. Therefore, chapter 1 consists of a short introduction to the general idea of the study, its importance and the state-of-the-art, and a preface of the thesis. In Chapter 2, after a brief history and the basic concepts of EM, the TEM methodology is described; the advanced TEM techniques used to study the nanostructured semiconductors at atomic scale. In general, it consists of brief descriptions of basic principles of TEM techniques. As experimental results are corroborated by theoretical studies and simulations, these procedures (image processing, simulations, etc) are also described shortly. Chapter 3 is dedicated to nanoengineering crystal structure and morphology of nanocrystals of complex copper-based chalcogenide, from binaries to complex ternaries and quaternaries. In this chapter it is shown that there is a wide range of possibilities for engineering, as many elements can be substituted with the primary cations and anions. Advanced TEM studies are performed in order to figure out the physics behind the property modifications. Phenomena such as morphology change, polytypism, ordering, polarity, electronic band change, strain, etc are elaborately studied, and correlated to the physical properties such as thermoelectricity. CCTSe polypods are the case of a complete structure study to understand the branching mechanism. Therefore, by means of an aberration-corrected TEM the polarity and cation ordering was determined. Polarity-driven morphology and branching mechanism is explained. Moreover, electronic band structure in this polytypic structure is simulated. Chapter 4 is based on the study of nanojunctions in metal oxide heterostructured NWs, structures that can enhance the functionality of the targeted devices, such as photovoltaic cells, or gas sensors. Production of nanojunctions is a successful approach in the context. In this chapter it is shown how coaxial heterostructuring of NWs, e.g. formation of core-shell structures increase the efficiency of the solar cells or enhance the sensitivity/selectivity of the gas sensors. In chapter 5 almost the same approach was followed, nevertheless, this time with III-V NWs. The importance of axial heterostructures and fully-epitaxial and relaxed structure are emphasized. The optoelectronic properties of the GaN NWs, such promising p-n junctions, are examined. Polarity issue, as a remarkably influencing parameter, is precisely studied experimentally. Its effect on electronic band structure in the heterointerface is also proven by the theoretical simulations. In the end, a general conclusion of the whole work and room for further study and future work is discussed in Chapter 6. The ample freedom of structural nanoengineering in the materials, together with development of novel electron microscopy techniques, opens the way towards the new possibilities for the future work.
En este trabajo hemos estudiado materiales avanzados con las últimas tecnologías y metodologías de microscopía electrónica, las que tienen un impacto importante en el desarrollo de la ciencia de materiales. El objetivo principal ha sido estudiar fenómenos como el politipismo, morfologías inusuales, ramificación, ‘ramificación politípica’, manipulación de la estructura de banda, ordenación de los cationes, polaridad, crecimiento e interfase epitaxial, alojamiento de una fase secundaria en una base, etc. para razonar la influencia de aquellos fenómenos en las propiedades y aplicaciones, por ejemplo la termoelectricidad, el funcionamiento de unión p-n, la eficiencia de las celdas solares, las propiedades optoelectrónicas, la respuesta de los sensores, etc. Distintos semiconductores han sido caracterizados: nanopartículas de calcogenuros complejos, nanohilos de óxidos de metales, y nanohilos del grupo III-V. Hemos estudiado los materiales en escala nanométrica por medio de métodos avanzados de microscopía electrónica de transmisión (TEM). El capítulo 1 es una breve introducción a la tesis, en la que se exponen los objetivos principales del trabajo, los últimos avances (state-of-the-art), los retos, y las nuevas posibilidades. En el capítulo 2 se explica la metodología de TEM utilizada para estudiar los semiconductores. Los capítulos 3 a 5 se componen de los resultados. El capítulo 3 está basado en el análisis de las nanopartículas de calcogenuros complejos. La sección de resultados contiene tres partes: monoestructurados, multiestructurados, y heteroestructuradas de tipo core-shell. En caso de nanopartículas cuaternarias de CCTSe, las nanopartículas ramifican y forman polipodes, que es el caso de un estudio elaborado porque el mecanismo de la ramificación es interesante. En capítulo 4 se trabaja con los nanohilos de óxidos de metales que sirven para muchas aplicaciones como celdas solares o sensores de gas. En nuestro caso, con el objetivo de mejorar la funcionalidad de los aparatos, hemos estudiado heteroestructuras. En el capítulo 5 prácticamente la misma aproximación está escogida, pero esta vez con nanohilos del grupo III-V. Aquí hemos enfatizado la importancia del crecimiento epitaxial de heteroestructuras. Por último, en el capítulo 6 hemos hablado de las conclusiones generales y las perspectivas para la investigación futura.

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Russo, Lorenzo. „Designing advanced nanomaterials for next generation in vitro diagnostics: development of optical and electrochemical biosensors for determination of viral and bacterial infections based on hollow AuAg nanoparticles“. Doctoral thesis, Universitat Autònoma de Barcelona, 2019. http://hdl.handle.net/10803/666751.

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En esta tesis doctoral. El dibujo racional de nanomateriales avanzados con propiedades controladas se aplicó para su empleo en biosensing, y condujo al desarrollo de dos plataformas diagnosticas para la determinación de infecciones virales y bacterianas. Primero, se desarrolló un método sintético altamente reproducible y robusto para la producción de nanoshells de una aleación AuAg monodispersas basado en remplazamiento galvánico. El protocolo descrito permite el controlo preciso sobre la morfología de las partículas, en términos de grosor de la capa externa y de tamaño del vacío interior, la composición relativa y distribución topológica de los metales noble constituyentes, y su rugosidad y porosidad superficial. Esta predictibilidad sintética, testeada sobre un rango de tamaños, se ha conseguido a través de un estudio sistemático de la relación entre de cada reactivo, juntos a una detallada caracterización de la composición y estructura del material con diferentes técnicas. Además, el análisis de las propiedades plasmonicas de las NSs de AuAg durante su transformación estructural, que se extiende por casi todo el espectro visible hasta las longitudes de ondas del Near-Infrared, reveló una dependencia estricta con sus características morfológicas y composicionales. Estos resultados, también confirmados con cálculos basados en la teoría de Mie, proveyeron la base para su aplicación como amplificadores de señal en un immunoensayo basado en SERS. Segundo, por la primera vez el comportamiento electroquímico de las NSs de AuAg fe reportado. Causado por la corrosión controlada de átomos de Ag contenidos en los núcleos residuales de las partículas y las capas finas de aleación, el estudio voltametrico de estos nanocristales vacíos se reveló fuertemente dependiente de su composición elemental relativa y, parcialmente, de su tamaño y morfología. Un efecto electrocatalitico peculiar apareció solamente para NSs de AuAg con un ratio Au/Ag suficiente para permitir la electrodeposición catalítica de Ag+ encima de la superficie de las partículas a potenciales menos negativos que el potencial de redacción estándar de Ag. Este comportamiento no previamente reportado está causado solo por el carácter levemente oxidante del electrolito utilizado, sin la necesidad de ningún otro co-reactivo u oxidante. Estos resultados constituyeron la base racional para desarrollar NSs de AuAg con propiedades desiderables para su aplicación en el ensayo electroquímico descrito. Aventajándose de las propiedades plasmonicas de las NSs de AuAg, el desarrollo de un ensayo immunocromatografico basad ene SERS para la detección sensible y cuantitativa de MxA, un biomarcador comúnmente asociado a infecciones virales, fue realizado. Gracias a las intensidades plasmonicas amplificadas enseñadas por las NSs de AuAg, resultante por el efecto de cavidad plasmonica comúnmente observado in nanoestructuras vacias, su superifices se portan como un continuo hot-spot, amplificando cualquier señal Raman emitido por reporters inmovilizados encima. Además, la posibilidad de ajustar precisamente la longitud máxima de LSPR de las NSs de AuAg de manera de coincidir con el láser NIR durante la mesura SERS permitió de mejorar la performance analítica. Entonces, las NSs de AuAg fueron fácilmente conjugadas con anticuerpos anti-MxA e integrados en un ensayo immunocromatografico para revelar su presencia en muestras de suero. Después de atenta optimización de los parámetros de la plataforma point-of-care, al proteína MxA pudo ser detectada a un limite de detección de pocos ng/mL. En fin, la capacidad de modular precisamente la composición elemental de las NSs de AuAg portó al diseño de un ensayo electroquímico para la detección rápida de dos bacterias modelos, Escherichia coli and Salmonella typhimurium. Las NSs de AuAg se utilizaron como reporters electroquímicos por la facilidad de generar la señal electroquímica, causada solamente por el carácter levemente oxidante de la matriz biológica. Por otro lado, el recubrimiento polimérico de las partículas confirió la interacción non específica basada en afinidad con las células bacterianas en solución, evitando de necesitar anticuerpos caros y frágiles. A través de esta estrategia de bajo coste, E.coli puso ser detectado en PBS a concentraciones de 102 CFU/mL, mientras también se consiguió la discriminación semi-selectiva de los perfiles corriente-concentración de las dos bacterias modelos.
In this PhD thesis, the rational design of advanced nanomaterials with controlled properties was applied for their employment in biosensing, leading to the development of two diagnostic platforms for the determination of viral and bacterial infections. Firstly, a highly reproducible and robust synthetic method for the production of monodisperse AuAg alloy NSs based on GRR was developed. The protocol described allows the precise control over the particles’ morphology, in terms of shell thicknesses and void sizes, the relative composition and topological distribution of their constituting noble metals, as well as their surface roughness and porosity. This synthetic predictability, tested over a range of sizes, has been achieved through a systematic study of the convoluted interplay of each co-reagent, together with a detailed characterization of the material’s composition and structure through an array of techniques. Moreover, the analysis of AuAg NSs’ plasmonic properties evolution during their structural transformation, which spanned through almost the whole visible spectrum up to NIR wavelengths, revealed a tight dependence with their morphological and compositional features. These results, also confirmed by calculations based on Mie’s theory, provided the basis for their application as signal enhancers in the SERS-based LFA developed. Secondly, for the first time the electrochemical behavior of AuAg NSs was reported. Triggered by the controlled corrosion of Ag atoms contained in the particles’ residual cores and thin alloy shells, the voltammetric study of these hollow nanocrystals has been found to be strongly dependent on their relative elemental composition and, partially, to their size and morphology. Indeed, a peculiar electrocatalytic effect appeared only for AuAg NSs possessing a high-enough Au/Ag ratio to let the catalytic electrodeposition of Ag+ on the NSs’ surfaces occur at potentials less negative than Ag standard reduction one. Interestingly, this unreported feature was shown to be triggered only by the mild oxidating character of the electrolyte used, without the need of any other co-reagent or oxidizer. These findings constituted the rational basis for developing AuAg NSs with desirable properties to be applied in the electrochemical assay described. Taking advantage of the tunable plasmonic properties of AuAg NSs, the development of a SERS-based LFA for the sensitive and quantitative detection of MxA, a biomarker commonly associated to viral infections, was achieved. Thanks to the enhanced plasmons intensities displayed by AuAg NSs, resulting from the plasmonic cavity effect commonly observed in hollow nanostructures, their surfaces acted as a continuous hot-spot, amplifying any Raman signal emitted by the reporters thereby attached. Moreover, the possibility to precisely adjust AuAg NSs’ LSPR maximum wavelength to match the NIR excitation laser used during SERS measurements allowed to further improve the overall analytical performance. Thus, AuAg NSs were easily conjugated with anti-MxA antibodies and integrated in a LFA in order to reveal its presence in spiked serum samples. After careful optimization of the point-of-care platform parameters, MxA protein could be successfully detected down to the analytically-relevant LOD of few ng/mL. Finally, the capability to precisely modulate AuAg NSs elemental composition lead to the design of a proof-of-concept electrochemical assay for the rapid detection of two model bacterial strains, Escherichia coli and Salmonella typhimurium. AuAg NSs were used as electrochemical reporters because of the ease of generation of the electrochemical signal, triggered by the sole mild oxidating character of the biological sample matrix. Besides, the polymeric coating of the hollow particles provided the non-specific, affinity-based interaction with bacterial cells in solution, avoiding the need for costly and fragile antibodies. With this low-cost strategy, E.coli could be detected in PBS down to 102 CFU/mL, while the semi-selective discrimination of the current-concentration profiles of the two model bacterial strains was also achieved.

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Lin, Yan. „Advanced nanomaterials for fuel cell catalysts characterization of bimetallic nanoparticles /“. Diss., Online access via UMI:, 2006.

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Shmeliov, Aleksey. „Transmission electron imaging and diffraction characterisation of 2D nanomaterials“. Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:4bc4d60f-4db0-43d2-9119-cb0a0366090e.

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Following the discovery of graphene, 2D nanostructures have been noted for their potential in a range of high-impact applications, such as sensing, catalysis, and composite reinforcement. Liquid-phase exfoliation and chemical vapour deposition have been demonstrated and indicate the feasibility of mass-scale production. With the advent of mass-produced 2D nanostructures a key focus of research is to characterise these materials. This thesis is concerned with imaging and structural properties of the 2D nanomaterials, hexagonal boron nitride (h-BN), molybdenum disulfide (MoS₂), tungsten disulfide (WS₂), titanium disulfide (TiS₂) and hexabenzocoronene (HBC), produced via liquid phase exfoliation. HBC strictly speaking is not 2D nanomaterial, however, it can be viewed as transition molecule from benzene to graphene. The data used for characterisation is based primarily on electron diffraction and, in particular, aberration corrected annular dark field (ADF) scanning transmission electron microscopy (STEM). The incoherent nature of ADF STEM provides direct atomic imaging without the contrast reversals upon focus changes seen in conventional high-resolution transmission electron microscopy (HRTEM). The main structural feature investigated in this thesis was the stacking sequences in few-layers h-BN, MoS₂, WS₂ and TiS₂. Simple stacking (AAA) can be distinguished from Bernal (ABA) and rhombohedral (ABC) on the basis of intensity ratio, I_{10̅10}/I_{11̅20} , in diffraction patterns and indirectly in HRTEM images. Nonetheless acquisition of the diffraction patterns suitable for analysis can be challenging due to the sample issues. Non-bulk stacking sequences were reliably confirmed for all above 2D nanomaterials on the basis of atomically resolved ADF STEM. 20 h-BN, 28 MoS₂, 5 WS₂ and 6 TiS₂ nanoflakes were imaged and analysed. Amongst them 2 h-BN, 9 MoS2, 4 WS2 and 1 TiS2 nanoflakes displayed non-bulk stacking. Hence, it appears that 2D WS2 has the greatest affinity for non-bulk stacking. Finally, an interesting structural transformation was observed in HBC molecules. Under the influence of electron beam HBC agglomerates were transformed into crystalline phase with 90^o symmetry.

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Liu, Kewei. „FABRICATION OF STRUCTURED POLYMER AND NANOMATERIALS FOR ADVANCED ENERGY STORAGE AND CONVERSION“. University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1542022285390711.

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Melinte, Georgian. „Advanced 3D and in-situ TEM approaches applied to carbon-based and zeolitic nanomaterials“. Thesis, Strasbourg, 2015. http://www.theses.fr/2015STRAE009/document.

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Dans le cadre de cette thèse, des techniques avancées de Microscopie électronique à transmission (MET)ont été utilisées dans le but de caractériser et de fabriquer de nouveaux nanomatériaux pour des applications dans les domaines de la nanoélectronique et de la catalyse. Trois types de matériaux fonctionnalisés sont étudiés: le graphène multifeuillets (FLG– Few-Layer Graphene) avec des nanomotifs,des nanotubes de carbone (CNTs - Carbon Nanotubes en anglais) et des zéolithes mésoporeux. La formation de nanomotifs de tranchées et de tunnels sur des flocons de FLG à l’aide de nanoparticules(NPs) de fer est étudiée dans une approche qui combine la tomographie électronique et la MET environnementale. Le rôle des facettes de la nanoparticule et des paramètres topographiques de FLG a été déterminé du point de vue quantitatif, ce qui a mené à la mise en évidence du mécanisme de formation des nanomotifs de tranchées et de tunnels. Le transfert de nanoparticules à base de métal entre deux nanostructures de carbone a été également étudié, en temps réel, en employant un porte-échantillon MET couplé avec un dispositif STM (Scanning Tunneling Microscope en anglais). Le protocole de contrôle du transfert des nanoparticules, les transformations chimiques et structurales subies par celles-ci, le mécanisme de croissance de nouvelles nanoparticules et d’autres phénomènes liés à ces effets ont été étudiés avec attention. La dernière partie de la thèse est centrée sur l’étude de la tomographie électronique à faible dose de la porosité induite dans deux classes de zéolithes, ZSM-5 et zéolithe Y, en utilisant un traitement chimique novateur à base de fluor
In this thesis, advanced Transmission Electron Microscopy (TEM) techniques are used to characterize and fabricate new nanomaterials with applications in nanoelectronics and catalysis. Three types of functionalized materials are investigated: nanopatterned few-layer graphene (FLG), carbon nanotubes(CNTs) and mesoporous zeolites. The nanopatterning process of FLG flakes by iron nanoparticles (NPs) is studied using an approach combining electron tomography (ET) and environmental TEM. The role of the nanoparticle faceting and of the FLG topographic parameters has been quantitatively determined leading to the first determination of the operating mechanism of the patterning process. The mass transfer of metallic-based NPs between two carbon nanostructures was studied as well in real-time by using a TEMSTMholder. The protocol of controlling the mass transfer, the chemical and structural transformations of the NPs, the growth mechanism of the new NPs and other related phenomena were carefully investigated.The last part deals with the low-dose ET investigation of the porosity induced in two classes of zeolites,ZSM-5 and zeolite Y, by an innovative fluoride-based chemical treatment

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Oben, Delphine. „Synthesis of advanced hybrid polymeric nanomaterials and characterization of novel silsesquioxanes with desirable superhydrophobic coating properties“. Thesis, Open University, 2016. http://oro.open.ac.uk/48062/.

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Understanding and controlling the hydrolysis and condensation of trialkoxy and tetraalkoxy silanes in acidic medium (Figure A) has not been fully realised. In this research study, both the understanding and control has been achieved using methods developed from the VitolaneTM process invented by TWI Ltd1 our industrial collaborators. The VitolaneTM process involves the synthesis of 3-methacryloxypropylsilsesquioxane resin from the hydrolytic condensation of 3-methacryloxy-propyltrimethoxysilane (MPTMS) in the presence of methanol, water and an acid catalyst (A-system). The reaction was repeated with two starting materials; 3-methacryloxy-propyltrimethoxysilane (MPTMS) and n-propyltrimethoxysilane (nPTMS) to form the AZ-system. It was found that with certain compositions, the reaction quickly reaches a pseudo equilibrium hence the hydrolysis rate constant could be determined. The instrumental analysis using Maldi-ToF-MS, HPLC, GPC, TGA, GCMS, DLS, DSC, FTIR and CHN analysis of both types of resins gave results that suggested the organic-inorganic hybrid silsesquioxanes obtained had the expected chemical composition and unique physical properties. This study was further extended to Stöber sphere silica nanoparticles aimed at extending our understanding from the above hydrolysis and condensation mechanistic study to the synthesis of Stöber silica nanoparticles 2 of various sizes (Figure B). The synthesis follows a similar pattern as the Vitolane™ process but using TEOS as starting material and ammonium hydroxide base instead of acid as in the original VitolaneTM process. The Stöber spheres study was carried out so we could add them to Vitolane in order to give rough (on the nanoscale) surfaces that would be superhydrophobic. The Stöber spheres were characterized using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and dynamic light scattering (DLS) to investigate the particle size formation. The Stöber spheres obtained were of varied sizes depending upon the way they were prepared (Figure B).

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Wang, Weiliang. „Novel functional nano-coatings on glass by spray deposition“. Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:45bd0d35-111e-4855-96f1-edf109e65b7b.

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Nanocomposite thin films with gold nanoparticles embedded in a host metal oxide prepared by spray pyrolysis deposition have been investigated. A single-step process has been developed using a one-pot solution containing precursors for both gold nanoparticles and host metal oxides. The films obtained display combined features of colouration, electrical conductivity and solar control. In this study two precursors for gold nanoparticles were used: preformed gold colloids and HAuCl₄. Three metal oxide host materials, TiO₂, SnO₂ and ZnO, were investigated. These films were deposited at a substrate temperature of 200-600 °C. Powder X-ray diffraction analysis reveals the presence of metallic gold. SEM inspection typically showed particulate gold of 5-20 nm in diameter, distributed at the surface or within the host matrix. Optical spectroscopy showed an intense absorption in the visible region due to the characteristic surface plasmon resonance (SPR) effects of gold nanoparticles. The wavelength of the SPR peaks varies depending on the refractive index of surrounding host material which is significantly influenced by the substrate deposition temperature. On the other hand, SnO₂ and ZnO, together with the introduction of dopants, were further investigated as suitable materials for transparent conducting oxides (TCO). SnO₂:F films were found to attain very low electrical resistivity, while ZnO films exhibit higher transparency in the visible. A double layered structure with a TCO layer of SnO₂:F on top of a layer embedded with gold nanoparticles has been employed to achieve the combined functionalities of conductivity and colouration. The electrical conductivity is significantly enhanced compared to a nanocomposite single layer film due to the introduction of the TCO top layer. In this thesis, spray pyrolysis deposition has demonstrated a simple and rapid approach to the production of a variety of thin films. It can be immediately integrated with current industrial coating equipment and scaled up for large-scale production process.

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Searle, Andrew. „Application of nanostructured emitters for high efficiency lighting“. Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:81731b64-c40b-4c76-9c90-dae7c956e29f.

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This is the first study comparing morphologies of CNT films on Kanthal wire, with their field emission properties, and as such offers ways to design better cylindrical emitter devices. A low turn-on field was achieved (0.35 V/µm), the field emission results have been explained using a simple model, and a fluorescent lamp was fabricated. Whilst previous work has been done on the link between “as grown” CNT films and their respective field emission properties on flat substrates, very little work has been done on linking morphology to emission performance on wire substrates, where the morphology can be very different. Microscopic structures such as towers, ridges and clumps consisting of many aligned or entangled CNTs were grown using an aerosol chemical vapour deposition (a-CVD) technique. Hydrogen added to the carrier gas resulted in a decrease in defect density in the growth of undoped CNTs, and an increase in defect density in the growth of nitrogen doped CNTs (N-CNTs) and boron doped CNTs (BCNTs). In-situ transmission electron microscopy (TEM) studies show that damage to CNT tips results in a significantly higher turn-on field compared to undamaged tips. This can be recovered by making the CNT emit current for several minutes which makes the tip recrystallize due to heat caused by the Nottingham effect. The field emission properties of the “as grown” CNT films are dominated by protruding CNTs found at the edges of ridge and tower microscopic structures. The field emission properties are also related to the dimensions of these structures with the longest ridges (hence those with the longest protruding CNTs) resulting in the lowest turn-on electric field. The ridge and tower structures act to accommodate protruding CNTs at their edges and their physical dimensions (mainly width) act to separate these emitters so that screening is minimised. This work shows that efficient emitters can be fabricated effectively from simple a-CVD techniques and microscopic structures act to improve, not degrade, field emission properties.

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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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Huang, Wen-Yen. „Responsive theranostic nanoparticles“. Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:275e12ca-e5a4-4f63-af9e-3c73948f8001.

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The development and use of nanotechnology towards theranostics (all-in-one disease diagnostics and therapeutic delivery) have been increasing in popularity in recent years, in particular the use of high capacity of nanomaterials to transport both imaging and therapeutic agents into pathological tissues or abnormal cells. In this work, biocompatible mesoporous silica nanoparticles (MSNs) that can be reliably endocytosed by cells are employed in the investigation of novel cancer treatment and magnetic resonance imaging (MRI). One of the principal aims is to develop T₁ contrast nanoparticles not only with extraordinarily high MRI contrast characteristics, but also tunability through surface chemistry and functional protein conjugation. In coupling paramagnetic Gd³⁺-centres to MSNs, one can effectively marry the advantages afforded by increased molecular bulk with those engendered by confined water environment inside the porous network. Specifically, through exclusively biasing paramagnetic Gd³⁺-centres in the internal spaces of nanoparticles, their mobility and interaction with water protons can be altered, significantly, with beneficial changes in molecular tumbling (τ_R), proton exchange (τ_M) and water diffusion (τ_D) within relaxation dynamics. These MRI nanoparticles with internalised Gd³⁺-centres are additionally used in the development of tunable/responsive contrast agents through vectoring protein conjugation. The relaxivity of MSNs can be tailored depending on the separation distances between proteins and nanoparticles; significantly, the simultaneous retention of both high MRI contrast and protein vectoring is achieved by the insertion of long polyethylene glycol (PEG) chain. The image contrast can also be reversibly gated through the competitive displacement of surface proteins by their partner proteins. Specifically, these responsive nanoparticles possess a low contrast resulting from restricted water accessibility when protein moieties are conjugated on the particles, whereas the removal of proteins causes a transition of contrast from a low to high state. The MSNs synthesised in this work are used not only in diagnostic imaging but also in the delivery of therapeutic agents for cancer therapy. The agents can be either physically encapsulated inside the pores or chemically conjugated on the nanoparticles. For the former, their loading and release efficiencies are tunable by the electrostatic interactions with particle surface functional groups; while in the latter case, their retention on nanoparticles, as opposed to being released, plays an important role in the effectiveness of cancer treatment that is achieved by trigging programmed cell death (apoptosis) in this work. This nanoparticle conjugation secures the proteins’ activity by facilitating their bypass of proteolytic degradation. Significantly, specially designed nanoparticles that demonstrate endo/lysosomal escape capability can reliably deliver therapeutic cytochrome c to cell cytosols for the initiation of a caspase cascade within apoptosis with high efficacy.

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Liška, Petr. „Optická charakterizace pokročilých nanomateriálů s vysokým laterálním rozlišením“. Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2021. http://www.nusl.cz/ntk/nusl-443725.

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Advanced nanomaterials show a significant improvement in certain physical or functional properties compared to conventional materials. Such advanced materials are, for example, lead halide perovskites (LHP). It is a group of hybrid organic-inorganic materials with a direct bandgap exhibiting unique optical properties. The high quantum efficiency of photoluminescence makes nanocrystals or thin films of LHP suitable candidates for the production of light-emitting diodes, solar cells and LCD displays. Their inexpensive and simple fabrication together with their unique optical properties makes LHP one of the most developed materials of the last decade. This diploma thesis aims to study the optical properties of CsPbBr3 perovskite nanocrystals using high lateral resolution methods. CsPbBr3 perovskite nanocrystals show intense anti-Stokes photoluminescence. These nanocrystals can emit light with a lower wavelength than that of the light that causes their photoluminescence. The nanocrystals are prepared in two different ways: by evaporation or by crystallization of the precursor in a solution of dimethylformamide. The morphology, photoluminescence properties and chemical composition of individual nanocrystals are studied. Each nanocrystal is studied individually and its size, shape, photoluminescence properties and chemical compounds are determined, which leads to a deeper understanding of the anti-Stokes photoluminescence of perovskite nanocrystals.

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Huang, Chun. „Processing and properties of nanostructured solid-state energy storage devices“. Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:f97b7c40-35cc-4cd8-96d4-9928ec62b368.

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A scalable spray processing technique was used to fabricate carbon nanotube (CNT)-based film electrodes and solid-state supercapacitors. The sprayed CNT-based electrodes comprised a randomly interconnected meso-porous network with a high electrical conductivity. Layer-by-layer (LbL) deposition of functionalised and oppositely charged single-wall carbon nanotubes (SWNTs) increased the electrode density and improved charging and discharging kinetics when compared with carboxylic functionalised only SWNT electrodes. The capacitance was further increased to 151 F g-1 at 2 mV s-1 and 120 F g-1 at 100 mV s-1 after vacuum and H2 heat treatments that removed the functional groups, and resulted in a hybrid microstructure of SWNTs and multi-layer graphene sheets from unzipped SWNTs. Flexible solid-state supercapacitors were fabricated by directly spraying multi-wall carbon nanotube (MWNT)-based aqueous suspensions onto both sides of a Nafion membrane and dried. A single cell with MWNT-only electrodes had a capacitance of 57 F g-1 per electrode at 2 mV s-1 and 44 F g-1 at 150 mV s-1. Cells with MWNT/ionomer electrodes showed a higher H+ mobility and a lower charge transfer resistance, and the capacitance increased to 145 F g-1 at 2 mV s-1 and 91 F g-1 at 150 mV s-1. Finally, MWNT/TiO2 nanoparticle/ionomer hybrid electrodes were used in the same solid-state supercapacitor configuration and provided a capacitance of 484 F g-1 per electrode at 5 mV s-1 and 322 F g-1 at 100 mV s-1. A qualitative model of the charge storage mechanism was developed, where TiO2 promoted H+ ions via redox reactions that fed protons into the proton-conducting ionomer coating over the MWNTs (in which the TiO2 was embedded), while electrons were readily conducted through the MWNT scaffold. This solid-state supercapacitor provided both attractive energy (31.8 Wh kg-1) and power (14.9 kW kg-1) densities, where such high energy density is difficult to achieve for MWNTs alone and such high power density is difficult for metal oxides alone, especially in the solid state.

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Cattley, Christopher Andrew. „Quaternary nanocrystal solar cells“. Thesis, University of Oxford, 2016. http://ora.ox.ac.uk/objects/uuid:977e0f75-e597-4c7a-8f72-6a26031f8f0b.

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This thesis studies quaternary chalcogenide nanocrystals and their photovoltaic applications. A temperature-dependent phase change between two distinct crystallographic phases of stoichiometric Cu₂ZnSnS₄ is investigated through the development of a one pot synthesis method. Characterisation of the Cu₂ZnSnS₄ nanocrystals was performed using absorption spectroscopy, transmission electron microscopy (TEM) and powder X-ray diffraction (XRD). An investigation was conducted into the effects of using hexamethyldisilathiane (a volatile sulphur precursor) in the nucleation of small (<7nm), mono-dispersed and solution-stable quaternary Cu₂ZnSnS₄ nanocrystals. A strategy to synthesize high quality thermodynamically stable kesterite Cu₂ZnSnS₄ nanocrystals is established, which subsequently enabled the systematic study of Cu₂ZnSnS₄ nanocrystal formation mechanisms, using optical characterization, XRD, TEM and Raman spectroscopy. Further studies employed scanning transmission electron microscopy (STEM) energy dispersive x-ray (EDX) mapping to examine the elemental spatial distributions of Cu₂ZnSnS₄ nanocrystals, in order to analyse their compositional uniformity. In addition, the stability of nanocrystals synthesised using alternative ligands is investigated using Fourier transform infrared spectroscopy, without solution based ligand substitution protocol is used to replace aliphatic reaction ligands with short, aromatic pyridine ligands in order to further improve Cu₂ZnSnS₄ colloid stability. A layer-by-layer spin coating method is developed to fabricate a semiconductor heterojunction, using CdS as an n-type window, which is utilised to investigate the photovoltaic properties of Cu₂ZnSnS₄ nanocrystals. Finally, three novel passivation techniques are investigated, in order to optimise the optoelectronic properties of the solar cells to the point where a power conversion efficiency (PCE) of 1.00±0.04% is achieved. Although seemingly modest when compared to the performance of leading devices (PCE>12%) this represents one of the highest obtained for a Cu₂ZnSnS₄ nanocrystal solar cell, fabricated completely under ambient conditions at low temperatures.

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Bekermann, Daniela [Verfasser], Roland A. [Gutachter] Fischer und Davide [Gutachter] Barreca. „Advanced perspectives in the vapor-phase deposition of multifunctional metal oxide nanomaterials / Daniela Bekermann ; Gutachter: Roland A. Fischer, Davide Barreca ; Fakultät für Chemie und Biochemie“. Bochum : Ruhr-Universität Bochum, 2012. http://d-nb.info/1199609145/34.

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17

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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Nish, Adrian. „Studies on optical characterisation of carbon nanotube suspensions“. Thesis, University of Oxford, 2008. http://ora.ox.ac.uk/objects/uuid:1ecd4f04-0178-4d8b-bf3a-cd6f8d744b92.

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This thesis reports studies done on single-walled carbon nanotubes (SWNTs) using optical spectroscopy as the primary investigative technique. It focuses on advances in sample preparation which have been made possible through improvements to the method of photo-luminescence excitation (PLE) mapping of nanotubes. An introduction to the field and some theoretical models are presented initially to provide a background to the experimental chapters which follow. A description of the standard procedure for sample preparation in aqueous surfactants is then followed by a detailed introduction to PLE mapping, including modeling of SWNT spectra. The next chapter discusses improvements to the sample preparation method by using organic polymer solutions instead of aqueous surfactants for suspending the nanotubes. The results show reductions in the distribution of SWNT species which are solubilised, leading to significant improvements in the resolution of the optical absorbance spectra and an increased photoluminescence yield. Two experiments which were performed on the novel polymer-SWNT systems are then described. The first shows (via PLE mapping) that energy is transfered to the SWNTs when the polymer is photo-excited. The possible mechanisms behind this, as well as the implications for using carbon nanotubes as an additive in polymer photovoltaics, are discussed. The second experiment details a recent magneto-PL study of SWNTs embedded in films produced from the polymer solutions. Here, the improved optical signatures and absence of strain at low temperatures have revealed a previously unseen high field intensity dependence. The behavior has been explained by the magnetic field induced mixing of the excitonic states.

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Chan, Matthew Yunho. „Visualization, Characterization, and Analysis of Gold Nanoparticles Fate and Transport in Aqueous Porous Media Environment with Advanced Photonics Technique“. Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/85437.

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Increased proliferation of nanotechnology has led to concerns regarding its implication to the water environment. Gold nanoparticles (AuNP) were used as a model nanomaterial to investigate the fate and dynamics of nanoparticles in the complex water environment. A column study was performed to examine the fate and transport of gold nanoparticles with two different coatings in porous media. The resulting data suggested that gold nanoparticles aggregate significantly in the porespace of the column interior, a finding that is not predicted by traditional colloidal filtration theory or Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Surface-enhanced Raman spectroscopy (SERS) was developed as a new technique to investigate AuNP aggregation in water with varying salt levels. The SERS technique proved valuable as an analytical technique, elucidating information about aggregation as well as AuNP surface interactions with dissolved halides in water. A thorough investigation examining Aunt aggregation with monovalent and divalent salts utilizing SERS, ultraviolet-visible light (UV-Vis) spectroscopy, and dynamic light scattering (DLS) was conducted. Each technique provided data describing different aspects of the dynamic behavior of AuNPs in complex water environments. Results suggest that in addition to attractive and repulsive interactions described by DLVO theory, chemical interactions between the AuNP surface and dissolved halides were also a significant driving force for aggregation and other transformative behaviors of AuNPs in water. The SERS technique developed in this work was shown to be a viable tool to help unveil the vastly complex dynamics of nanomaterial in the water environment.
Ph. D.

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Malik, Adnan Muhammad. „Development of High Aspect Ratio Nano-Focusing Si and Diamond Refractive X-ray optics using deep reactive ion etching“. Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:588ca438-e4c6-4d51-8f13-30bcb3c437a3.

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This thesis is devoted to the development of nano-focusing refractive optics for high energy X-rays using planar microelectronic technology. The availability of such optics is the key for the exploitation of high brilliance third and fourth generation X-ray sources. Advancements in the quality of optics available are commensurate with advancements in the fabrication technology. The fabrication process directly influences the quality and performance, so must be understood and controlled. In the first part of this thesis, the development of high aspect ratio Si kinoform lenses is examined. It is shown that control of the re-entrance angle is critical for successful fabrication; in fact, a large re-entrance angle can destroy the lens during the fabrication process. Through an etch study, it was found that as aspect ratio increases, control of the re-entrance angle becomes harder. To control the re-entrance angle for very high aspect ratios, a novel approach based on sacrificial structures was proposed and initial results presented. The second part is dedicated to an experimental study of refractive lenses made from diamond. Due to its low atomic number, relatively high density and very high thermal conductivity, diamond is one of the most desirable lens materials for refractive X-ray optics. However, due to its extreme hardness, it is very difficult to structure into a form suitable for X-ray lenses. To overcome this difficulty a Si moulding technique was used and focusing down to a 400 nm wide spot was achieved. Several obstacles were encountered and successfully overcome. The hardest obstacle was to obtain selective void-free filling in the Si moulds. Several methods were investigated. A method based on a sacrificial oxide layer and an Electrostatic Self-Assembly process was found to be the most useful. The approach discovered in this thesis is not limited to X-ray lenses, but can be applied to a wide variety of high aspect ratio MEMS requiring void-free diamond filling and smooth sidewalls.

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Murdock, Adrian T. „Chemical vapour deposition growth of large-area graphene on metals“. Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:07fa91ef-0d61-4086-a7d8-a53537dcb54b.

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Graphene has unrivalled properties and is heralded as a revolutionary material for the 21^st century. Chemical vapour deposition (CVD) on metals is a promising method to produce large-area graphene. Controlling the properties of CVD graphene is vital for its integration in a wide-range of future applications. Many factors can influence the CVD growth of graphene and its properties, therefore further investigations will be beneficial to fully understand and control this technique. In this thesis I expand the knowledge about the growth of pure and heteroatom-doped graphene by low pressure chemical vapour deposition (LPCVD) and atmospheric pressure chemical vapour deposition (APCVD) on commercially available Cu and Pt foils. Using a range of characterisation techniques, I investigate the influence of the substrate’s properties and the synthesis conditions on the growth of graphene, in pursuit of improved, controlled or optimised production, which can promote high quality, large-area, single-layer graphene, or other as desired. By characterising the topography, surface roughness, crystallographic orientations, and chemical composition of six Cu foils, I find that their properties vary greatly and this influences the growth of CVD graphene. I elucidate that the commonly used 99.8 % Alfa Aesar Cu foil has a surface coating composed of calcium, chromium, and phosphorus, which detrimentally influences graphene growth. Cleaning Cu foils with CH₃COOH is shown to reduce the concentration of surface contaminants, consequently reducing the nucleation density and increasing the growth rate of CVD graphene. I also demonstrate that the shape, orientation, edge-geometry and thickness of CVD graphene domains can be controlled by the Cu crystallographic orientations. Single layer LPCVD graphene domains align with zigzag edges parallel to a single <101> direction on Cu{111} and Cu{101}, while bilayer domains align to two directions on Cu{001}. Hexagonal APCVD domains also preferentially align with edges parallel to the <101> direction(s). This discovery resolves a key challenge of controlling the orientation of individual graphene domains and opens a new avenue for tailored production of large-area CVD graphene with improved properties. By controlling the synthesis conditions of APCVD graphene on Pt foils I optimise production of ~0.5 mm single layer graphene domains with reduced nucleation density and increased growth rate of ~100 μm/min by synthesis at 1150°C, a higher temperature than previously reported. The absence of large, hexagonal, single-crystal domains on pristine Pt foil, and observation of a reaction between quartz and Pt that promotes hexagonal domains, suggests that a silicon or platinum silicide surface layer may be advantageous for improved growth of graphene. Finally, I demonstrate that the dopant concentration of nitrogen-doped graphene is increased at lower synthesis temperatures and higher NH₃ concentration, up to 1.3 %, but with an associated decrease in the growth rate. Direct visualisation, elemental confirmation, and electronic characterisation of individual nitrogen atoms is shown for the first time using aberration corrected scanning transmission electron microscopy and electron energy loss spectroscopy. Boron-doped graphene is also synthesised. The implications of these findings, and many additional minor contributions, are wide-ranging and of considerable importance for the future understanding of CVD growth of graphene on metals, and more generally for the advancement of scientific knowledge for manufacturing large-area graphene. Collectively, these discoveries represent a significant body of work that can improve the efficiency of production and assist with controlling the properties of large-area CVD graphene.

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Robertson, Alexander William. „Synthesis and characterisation of large area graphene“. Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:aee750dd-41b8-4462-9efa-4e89e06e0ed7.

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The pursuit of high quality, large area graphene has been a major research focus of contemporary materials science research, in the wake of the discovery of the multitude of exceptional properties exhibited by the material. The DPhil project was undertaken with the objective of developing an understanding of the growth of large graphene sheets by chemical vapour deposition (CVD), and also in the subsequent characterisation of their material properties. By conducting atmospheric pressure CVD growth at high methane flow rates, it was found that few-layered graphene (FLG) could be deposited on a copper catalyst. It is demonstrated that the self-limiting property of a copper catalyst is not universal to all deposition conditions, and shown that FLG grows in a terrace-like configuration. In depth transmission electron microscopy (TEM) studies were carried out on FLG. By selective image reconstruction from the inverse power spectrum of the TEM images, it was possible to elucidate the inter-grain connectivity of few-layer graphenes. It was determined that there were two possible inter-grain configurations possible; specifically an overlap of graphene layers or a discrete atomic bonding edge. The perturbation of the few-layer structure when subject to an out of plane distortion was found to incur a shift in the conventional AB-Bernal stacking of FLG. By utilising the aberration corrected TEM (AC-TEM) at Oxford it was possible to resolve atomic detail in CVD synthesised monolayer films, including atomic bond rotations and vacancies. The use of a high current density at low accelerating voltage (80 kV) was demonstrated to allow for the controlled defect creation in graphene sheets. This permitted the creation of monovacancies and iron doped vacancy complexes suitable for further study. The behaviour of these two defect types under electron beam irradiation was subsequently studied.

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Holder, Jenna Ka Ling. „Quantum structures in photovoltaic devices“. Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:d23c2660-bdba-4a4f-9d43-9860b9aabdb8.

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A study of three novel solar cells is presented, all of which incorporate a low-dimensional quantum confined component in a bid to enhance device performance. Firstly, intermediate band solar cells (IBSCs) based on InAs quantum dots (QDs) in a GaAs p-i-n structure are studied. The aim is to isolate the InAs QDs from the GaAs conduction band by surrounding them with wider band gap aluminium arsenide. An increase in open circuit voltage (V_OC) and decrease in short circuit current (J_sc) is observed, causing no overall change in power conversion efficiency. Dark current - voltage measurements show that the increase in V_OC is due to reduced recombination. Electroreflectance and external quantum efficiency measurements attribute the decrease in J_sc primarily to a reduction in InGaAs states between the InAs QD and GaAs which act as an extraction pathway for charges in the control device. A colloidal quantum dot (CQD) bulk heterojunction (BHJ) solar cell composed of a blend of PbS CQDs and ZnO nanoparticles is examined next. The aim of the BHJ is to increase charge separation by increasing the heterojunction interface. Different concentration ratios of each phase are tested and show no change in J_sc, due primarily to poor overall charge transport in the blend. V_OC increases for a 30 wt% ZnO blend, and this is attributed largely to a reduction in shunt resistance in the BHJ devices. Finally, graphene is compared to indium tin oxide (ITO) as an alternative transparent electrode in squaraine/ C₇₀ solar cells. Due to graphene’s high transparency, graphene devices have enhanced J_sc, however, its poor sheet resistance increases the series resistance through the device, leading to a poorer fill factor. V_OC is raised by using MoO₃ as a hole blocking layer. Absorption in the squaraine layer is found to be more conducive to current extraction than in the C₇₀ layer. This is due to better matching of exciton diffusion length and layer thickness in the squaraine and to the minority carrier blocking layer adjacent to the squaraine being more effective than the one adjacent to the C₇₀.

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Saliba, Michael. „Plasmonic nanostructures and film crystallization in perovskite solar cells“. Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:fdb36a9e-ddf5-4d27-a8dc-23fffe32a2c5.

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The aim of this thesis is to develop a deeper understanding and the technology in the nascent field of solid-state organic-inorganic perovskite solar cells. In recent years, perovskite materials have emerged as a low-cost, thin-film technology with efficiencies exceeding 16% challenging the quasi-paradigm that high efficiency photovoltaics must come at high costs. This thesis investigates perovskite solar cells in more detail with a focus on incorporating plasmonic nanostructures and perovskite film formation. Chapter 1 motivates the present work further followed by Chapter 2 which offers a brief background for solar cell fabrication and characterisation, perovskites in general, perovskite solar cells in specific, and plasmonics. Chapter 3 presents the field of plasmonics including simulation methods for various core-shell nanostructures such as gold-silica and silver-titania nanoparticles. The following Chapters 4 and 5 analyze plasmonic core-shell metal-dielectric nanoparticles embedded in perovskite solar cells. It is shown that using gold@silica or silver@titania NPs results in enhanced photocurrent and thus increased efficiency. After photoluminescence studies, this effect was attributed to an unexpected phenomenon in solar cells in which a lowered exciton binding energy generates a higher fraction of free charge. Embedding thermally unstable silver NPs required a low-temperature fabrication method which would not melt the Ag NPs. This work offers a new general direction for temperature sensitive elements. In Chapters 6 and 7, perovskite film formation is studied. Chapter 6 shows the existence of a previously unknown crystalline precursor state and an improved surface coverage by introducing a ramped annealing procedure. Based on this, Chapter 7 investigates different perovskite annealing protocols. The main finding was that an additional 130°C flash annealing step changed the film crystallinity dramatically and yielded a higher orientation of the perovskite crystals. The according solar cells showed an increased photocurrent attributed to a decrease in charge carrier recombination at the grain boundaries. Chapter 8 presents on-going work showing noteworthy first results for silica scaffolds, and layered, 2D perovskite structures for application in solar cells.

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25

Lee, Jeonyoon. „Nanomaterial-enabled manufacturing for next-generation multifunctional advanced composite prepreg laminate architectures“. Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/120256.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 179-193).
Manufacturing of advanced aerospace-grade structural composites has traditionally utilized autoclaves to impart heat and pressure, in addition to vacuum, to create high-quality, void (defect)- free, reproducible structures. Carbon (micro) fiber reinforced polymer (CFRP) composites, which are pre-impregnated with a thermoset or thermoplastic polymer to form prepreg sheets, are in widespread use via autoclave processing due to their ease of use and high fiber volume fraction. However, autoclaves have high capital costs, and incur high operating costs due to the convective heating and applied pressure. Furthermore, the fixed capacity of an autoclave limits the size and design of composite parts, and the production rate is limited by autoclave availability. As a result, there has been an increasing interest in the development of alternatives, for example, out-of-autoclave (OoA) specially-formulated prepregs that only require heat and vacuum (i.e., pressure is not required). OoA prepreg processing also has drawbacks due to their specialized morphological and chemical formulation for vacuum-only conditions, as well as part quality (especially, composite interlaminar properties) that is below autoclave-processed materials. In light of the limitations described above, this dissertation (1) develops a novel prepreg processing technique, termed 'out-of- oven' (OoO) curing, that conductively cures OoA prepregs via nanoengineered resistive heating; (2) expands the applicability of the OoO process to conventional autoclave-formulated prepregs; and (3) introduces multifunctionality in the form of cure status sensing. Characteristics of the OoO process using a CNT film as a heating element are first examined and compared to those of an oven curing process, focusing on an aerospace-grade OoA-formulated unidirectional aerospace-grade CFRP prepreg system. Thermophysical and mechanical property comparisons suggest that there is no difference in laminates cured via OoO and oven curing as evaluated by void content, degree of cure analysis, short beam shear interlaminar testing, dynamic mechanical analysis, and double-edge notch tensile testing. The OoO process reduces electrical energy consumption by two orders of magnitude (from 13.7 to 0.12 MJ) due to conductive vs. convective heating, under a typical industrial curing condition for a small (60 mm x 50 mm) test panel. Modeling shows that for parts beyond a meter-scale, energy savings will also be at least two orders of magnitude. Moreover, comparative finite element modeling of the OoO and oven curing shows excellent agreement with measured values, including the reduction in electrical energy and instantaneous power consumption. Altogether, these findings show that OoO curing works for OoA prepreg systems, with significant energy savings. Given the results of the first study, the next study effectively removes the need for an autoclave by adapting the OoO process to conventional autoclave-formulated prepreg systems that currently require applied pressure of ~700 kPa in addition to vacuum. This technique entails OoO curing plus insertion of a nanoporous network (NPN, e.g., vertically aligned CNT arrays) into the interlaminar regions of autoclave-formulated composite laminates. Capillary pressure due to the NPN is calculated to be of the same order as the pressure applied in conventional autoclave processing. Results show that capillary-enhanced polymer wetting by the NPN enables sufficient reduction of interlaminar voids to levels commensurate with autoclave-processed composites. Thermophysical property comparisons and short beam shear interlaminar strength testing show that OoO-processed composites with NPN are equivalent to those of autoclave-cured composites, with energy and other savings similar to OoO curing with OoA prepreg in the first study. Conformability of the NPN to the micron-scale topology of the prepreg surface, and continuous vacuum channels created by the NPN, are identified as key factors underlying interlaminar void reduction. Finally, this dissertation introduces a multifunctional aspect of the OoO manufacturing: an in situ cure status monitoring technique utilizing the nanostructured CNT-based heating element of the OoO process. The OoO heating elements are nanoporous and CNT-based, but in this study have different morphology (randomly-oriented or in-plane aligned CNTs) than the NPN (vertically aligned CNTs, A-CNTs). As OoO curing proceeds and the heating element is powered, the adjacent polymer flows into the nanoporous heater via capillary action. Based on cure status sensing experiments and theoretical models, it is found that electrical resistance changes of the heating element correspond to several mechanisms associated with different stages in the cure process, including polymer infiltration into the CNT network that causes the average CNT-CNT junction distance to increase, giving a resistance increase. Later in the manufacturing, as the polymer cross-linking occurs after infiltration into the heating element, chemical cure shrinkage decreases the CNT-CNT junction distance, leading to a decrease in resistance. Thus, the heating element is multifunctional as a cure status sensor, and is found to be highly repeatable, demonstrating a new capability to enhance both quality and productivity of composite manufacturing. OoO curing and related processing techniques introduced here are expected to contribute to the design and manufacturing of next-generation multifunctional composite architectures. These processing techniques have several advantages, including: (1) compatibility with a wide range of composite materials, including OoA- and autoclave-formulated prepregs; (2) removal of size and shape constraints on composite components imposed by the use of a heating vessel; (3) manufacturing cost savings by efficient conductive (as opposed to convective) thermal processing; (4) production improvements via the in situ cure status monitoring by multifunctional heating elements as cure sensors; and (5) the potential for spatial heating control to accommodate structural features such as thick and thin transitions. Future work will expand the techniques to thermoplastics and other high-temperature polymers. The OoO techniques are expected to enable several systems-level production and operational savings, such as accelerated cure cycles, that require further study. Other areas of exploration include on-site composite curing and repair, and leveraging the spatial control of heat flux from the OoO technique into other OoA composite processes, such as resin infusion and resin transfer molding.
by Jeonyoon Lee.
Ph. D.

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26

Oulton, Rebekah Lynn. „Development of nanomaterial-enabled advanced oxidation techniques for treatment of organic micropollutants“. Diss., University of Iowa, 2013. https://ir.uiowa.edu/etd/4889.

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Increasing demand for limited fresh water resources necessitates that alternative water sources be developed. Nonpotable reuse of treated wastewater represents one such alternative. However, the ubiquitous presence of organic micropollutants such as pharmaceuticals and personal care products (PPCPs) in wastewater effluents limits use of this resource. Numerous investigations have examined PPCP fate during wastewater treatment, focusing on their removal during conventional and advanced treatment processes. Analysis of influent and effluent data from published studies reveals that at best 1-log10 concentration unit of PPCP removal can generally be achieved with conventional treatment. In contrast, plants employing advanced treatment methods, particularly ozonation and/or membranes, remove most PPCPs often to levels below analytical detection limits. However, membrane treatment is cost prohibitive for many facilities, and ozone treatment can be very selective. Ozone-recalcitrant compounds require the use of Advanced Oxidation Processes (AOPs), which utilize highly reactive hydroxyl radicals (*OH) to target resistant pollutants. Due to cost and energy use concerns associated with current AOPs, alternatives such as catalytic ozonation are under investigation. Catalytic ozonation uses substrates such as activated carbon to promote *OH formation during ozonation. Here, we show that multi-walled carbon nanotubes (MWCNTs) represent another viable substrate, promoting *OH formation during ozonation to levels exceeding activated carbon and equivalent to conventional ozone-based AOPs. Via a series of batch reactions, we observ a strong correlation between *OH formation and MWCNT surface oxygen concentrations. Results suggest that deprotonated carboxyl groups on the CNT surface are integral to their reactivity toward ozone and corresponding *OH formation. From a practical standpoint, we show that industrial grade MWCNTs exhibit similar *OH production as their research-grade counterparts. Accelerated aging studies indicate that MWCNTs maintain surface reactivity for an extended period during ozonation treatment. Further, *OH generation is essentially unaffected in complex water matrices containing known radical scavengers, and is effective for degradation of the ozone-recalcitrant herbicide atrazine. A proof-of-concept study verified that results from batch systems can be replicated in a flow-through reactor utilizing MWCNTs immobilized on a ceramic membrane support. Collective, results suggest that CNT-enhanced ozonation may provide a viable treatment alternative for emerging organic micropollutants.

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Lynn, Geoffrey M. „Polymer carriers of toll-like receptor-7/8 agonists as vaccine adjuvants“. Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:acdb09f7-e690-4cf2-b0e4-3b1611750e49.

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There is currently a need for vaccine adjuvants that are effective for eliciting Th1-type CD4 and CD8 T cell responses when formulated with protein and peptide-based subunit vaccines. Some of the most promising adjuvants in this regard are combined small molecule Toll-like receptor-7/8 agonists (TLR-7/8a). However, poor pharmacokinetic properties have precluded TLR-7/8a for use in vaccines. In this thesis, polymer carriers were used to control pharmacokinetics and to modulate activity of TLR-7/8a for use as vaccine adjuvants. Combinatorial synthesis and in vivo structure-activity studies were used to evaluate how properties of Polymer-TLR-7/8a conjugates (Poly-7/8a) influence innate immune activation in lymph nodes that drain the site of vaccine administration. The most striking finding was that particle formation by Poly-7/8a strongly enhances the magnitude and duration (>14 days) of innate immune activation in lymph nodes by restricting agonist biodistribution and promoting uptake by dendritic cells. Particle-forming Poly-7/8a optimized for activity were found to induce only local innate immune activation (not systemic) and were effective for eliciting Th1-type CD4 and CD8 T cells that mediated protection against infectious challenge. Based on the importance of particle formation for activity of Poly-7/8a, thermo-responsive Poly-7/8a were developed that exist as single water-soluble macromolecules in solution but undergo temperature-driven particle formation in vivo. In conclusion, polymer carriers of TLR-7/8a represent a versatile and effective platform for modulating innate immune activity and warrant further investigation as a class of adjuvants for vaccines.

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28

Otto, Ernst. „Development of superconducting bolometer device technology for millimeter-wave cosmology instruments“. Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:30a1103a-ea7a-4b08-ba92-665cbd9740e0.

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The Cold-Electron Bolometer (CEB) is a sensitive detector of millimeter-wave radiation, in which tunnel junctions are used as temperature sensors of a nanoscale normal metal strip absorber. The absorber is fed by an antenna via two Superconductor-Insulator-Normal metal (SIN) tunnel junctions, fabricated at both ends of the absorber. Incoming photons excite electrons, heating the whole electron system. The incoming RF power is determined by measuring the tunneling current through the SIN junctions. Since electrons at highest energy levels escape the absorber through the tunnel junctions, it causes cooling of the absorber. This electron cooling provides electro-thermal feedback that makes the saturation power of a CEB well above that of other types of millimeter-wave receivers. The key features of CEB detectors are high sensitivity, large dynamic range, fast response, easy integration in arrays on planar substrates, and simple readout. The high dynamic range allows the detector to operate under relatively high background levels. In this thesis, we present the development and successful operation of CEB, focusing on the fabrication technology and different implementations of the CEB for efficient detection of electromagnetic signals. We present the CEB detector integrated across a unilateral finline deposited on a planar substrate. We have measured the finline-integrated CEB performance at 280-315 mK using a calibrated black-body source mounted inside the cryostat. The results have demonstrated strong response to the incoming RF power and reasonable sensitivity. We also present CEB devices fabricated with advanced technologies and integrated in log-periodic, double-dipole and cross-slot antennas. The measured CEB performance satisfied the requirements of the balloon-borne experiment BOOMERANG and could be considered for future balloon-borne and ground-based instruments. In this thesis we also investigated a planar phase switch integrated in a back-to-back finline for modulating the polarization of weak electromagnetic signals. We examine the switching characteristics and demonstrate that the switching speed of the device is well above the speed required for phase modulation in astronomical instruments. We also investigated the combination of a detector and a superconducting phase switch for modulating the polarization of electromagnetic radiation.

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29

Villar, Gabriel. „Aqueous droplet networks for functional tissue-like materials“. Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:602f9161-368c-48c0-9619-7974f743f2f2.

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An aqueous droplet in a solution of lipids in oil acquires a lipid monolayer coat, and two such droplets adhere to form a bilayer at their interface. Networks of droplets have been constructed in this way that function as light sensors, batteries and electrical circuits by using membrane proteins incorporated into the bilayers. However, the droplets have been confined to a bulk oil phase, which precludes direct communication with physiological environments. Further, the networks typically have been assembled manually, which limits their scale and complexity. This thesis addresses these limitations, and thereby enables prospective medical and technological applications for droplet networks. In the first part of the work, defined droplet networks are encapsulated within mm-scale drops of oil in water to form structures called multisomes. The encapsulated droplets adhere to one another and to the surface of the oil drop to form interface bilayers that allow them to communicate with each other and with the surrounding aqueous environment through membrane pores. The contents of the droplets can be released by changing the pH or temperature of the surrounding solution. Multisomes have potential applications in synthetic biology and medicine. In the second part of the work, a three-dimensional printing technique is developed that allows the construction of complex networks of tens of thousands of heterologous droplets ~50 µm in diameter. The droplets form a self-supporting material in bulk oil or water analogous to biological tissue. The mechanical properties of the material are calculated to be similar to those of soft tissues. Membrane proteins can be printed in specific droplets, for example to establish a conductive pathway through an otherwise insulating network. Further, the networks can be programmed by osmolarity gradients to fold into designed shapes. Printed droplet networks can serve as platforms for soft devices, and might be interfaced with living tissues for medical applications.

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30

Belding, Stephen Richard. „Computational electrochemistry“. Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:e997642f-fbaa-469c-98a3-f359b0996f03.

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Electrochemistry is the science of electron transfer. The subject is of great importance and appeal because detailed information can be obtained using relatively simple experimental techniques. In general, the raw data is sufficiently complicated to preclude direct interpretation, yet is readily rationalised using numerical procedures. Computational analysis is therefore central to electrochemistry and is the main topic of this thesis. Chapters 1 and 2 provide an introductory account to electrochemistry and numerical analysis respectively. Chapter 1 explains the origin of the potential difference and describes its relevance to the thermodynamic and kinetic properties of a redox process. Voltammetry is introduced as an experimental means of studying electrode dynamics. Chapter 2 explains the numerical methods used in later chapters. Chapter 3 presents a review of the use of nanoparticles in electrochemistry. Chapter 4 presents the simulation of a random array of spherical nanoparticles. Conclusions obtained theoretically are experimentally confirmed using the Cr³⁺/Cr²⁺ redox couple on a random array of silver nanoparticles. Chapter 5 presents an investigation into the concentration of supporting electrolyte required to make a voltammetric experiment quantitatively diffusional. This study looks at a wide range of experimental conditions. Chapter 6 presents an investigation into the deliberate addition of insufficient supporting electrolyte to an electrochemical experiment. It is shown that this technique can be used to fully study a stepwise two electron transfer. Conclusions obtained theoretically are experimentally confirmed using the reduction of anthracene in acetonitrile. Chapter 7 presents a new method for simulating voltammetry at disc shaped electrodes in the presence of insufficient supporting electrolyte. It is shown that, under certain conditions, the results obtained from this complicated simulation can be quantitatively obtained by means of a much simpler ‘hemispherical approximation’. Conclusions obtained theoretically are experimentally confirmed using the hexammineruthenium ([Ru(NH₃)₆]³⁺/[Ru(NH₃)₆]²⁺) and hexachloroiridate ([IrCl₆]²⁻/[IrCl₆]³⁻) redox couples. Chapter 8 presents an investigation into the voltammetry of stepwise two electron processes using ionic liquids as solvents. It is shown that these solvents can be used to fully study a stepwise two electron transfer. Conclusions obtained theoretically are experimentally confirmed using the oxidation of N,N-dimethyl-p-phenylenediamine in the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([C₄ mim][BF₄]). The work presented in this thesis has been published as 7 scientific papers.

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31

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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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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32

Quigley, John. „Advanced Thermoplastic Nanocomposite Melt Processing Using an Improved Supercritical Carbon Dioxide Pretreatment for the Nanomaterial“. Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/52624.

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Polymer nanocomposites have been proposed as lightweight replacements for traditional composite materials in various applications. Montmorillonite (MMT) and carbon nanotubes (CNTs) are two nanofillers which have accrued significant interest in the past 20 years due to their superior mechanical and electrical properties, respectively. However, efficient dispersion of the nanofiller and damage to CNTs prevent widespread utilization of these materials in polymer nanocomposites. Novel methods of nanocomposite generation combining the use of supercritical carbon dioxide (scCO2) with melt compounding have been investigated to overcome these issues. The focus of this work is on developing the scCO2 treatment of nanomaterial for thermoplastic nanocomposite generation. First, the supercritical carbon dioxide aided melt blending method was applied to nanoclay nanocomposites of Nylon 6/ and organoclay where the polymer may interact with the nanoclay surface. Second, the effect of scCO2 processing of CNTs was investigated with special consideration to the processing variables. Finally, a study was carried out to analyze the electrical conductivity of polycarbonate nanocomposites generated using CNTs deagglomerated by scCO2 processing. The initial focus of this dissertation is the use of supercritical carbon dioxide (scCO2) as a processing aid in the generation of nylon 6 nanocomposites in which the nylon 6 may interact with the nanoclay surface. Wide-angle X-ray diffraction, transmission electron microscopy, rheology, and tensile tests were carried out to investigate the effect of processing with scCO2 on the final composite morphology and properties. It was observed that mechanical properties of composites prepared with the scCO2 aided melt blending method were similar to or higher than those reported in the literature for samples prepared with twin screw compounding. At 7.6 wt% nanoclay the modulus value reaches 4.75 +/- 0.194 GPa which is one of the highest increases (1.7 GPa) reported for these materials processed at intermediate concentrations. Beyond 7.6 wt% the improvement due to scCO2 processing matched that of direct blending. The next objective of this work is to develop a method for the deagglomeration of commercially available multi-walled carbon nanotubes (MWCNTs) by manipulating processing variables and observing carbon nanotube aspect ratios after deagglomeration. High levels of deagglomeration of Baytubes C 150 P and Nanocyl NC-7000 MWCNT agglomerates were observed, resulting in 30 fold and 50 fold decreases in bulk density, respectively, with median agglomerate sizes < 8 um in diameter. These results were obtained while retaining the aspect ratio of the as-received nanomaterial, irrespective of the MWCNT agglomerate morphology. It was found that the supercritical temperature and pressure of 40 deg C and 7.86 MPa were the optimal temperature and pressure for maximum deagglomeration without damaging the MWCNTs. The final goal of this work is to apply the scCO2 aided melt blending process to generate polycarbonate/ carbon nanotube (CNT) nanocomposites with enhanced electrical conductivity and improved dispersion while maintaining the aspect ratio of the as-received CNTs. Different degrees of scCO2 processed Baytubes C 150 P CNT were benignly deagglomerated with scCO2 resulting in 5 fold (5X), 10X, and 15X decreases in bulk density from the as-received CNTs. The CNT were melt compounded with polycarbonate using single screw melt extrusion and compression molded into plaques. A surface conductivity of 4.8 x 10-8 +/- 2.0 x 10-9 S was observed for samples prepared with the scCO2 aided melt blending at 15X scCO2 processing. Electrical percolation thresholds as low as 0.83 wt% were observed for composites prepared with 15X CNTs using the scCO2 aided melt blending method, while concentrations as high as 1.5% are required without scCO2 processing. The percolation concentration in nanocomposites prepared with 15X scCO2 processing and single screw extrusion is competitive with values reported for similar nanocomposites generated using twin screw melt compounding in the literature. Optical microscopy, transmission electron microscopy, and rheology were used to investigate the dispersion and mechanical network of CNTs in the nanocomposites. The dispersion of CNTs generally improved with scCO2 processing compared to direct melt blending but was found to be significantly worse than that of twin screw melt compounded nanocomposites from the literature. Because the percolation thresholds are similar with substantially different extents of dispersion, the importance of maintaining longer CNTs during nanocomposite generation is emphasized.
Ph. D.

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33

Chen, Yu-Ming. „The Fabrication of Advanced Electrochemical Energy Storage Devices With the integration of Ordered Nanomaterial Electrodes“. University of Akron / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron148553322128565.

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34

O'Sullivan, Melanie Claire. „Template directed synthesis of porphyrin nanorings“. Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:c500c594-fa28-4857-b74e-b80d14b87202.

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This thesis describes supramolecular approaches to porphyrin nanorings. Cyclic porphyrin arrays resemble natural light harvesting systems, and it is of interest to probe the photophysical effects of bending the porphyrin aromatic π-system. A general overview of the synthesis and photophysical properties of porphyrins and their arrays is carried out in Chapter 1. The electronic structure of porphyrins is examined, and how conformational effects in oligomers, such as inter-porphyrin torsional angle and backbone bending influence the π-conjugation pathway. The structures of light harvesting complexes are discussed. Chapter 2 describes the design and synthesis of a complementary 12-armed template designed to coordinate linear porphyrin oligomers in the correct conformation for cyclisation to give a cyclic porphyrin dodecamer. Chapter 3 demonstrates two approaches to a cyclic porphyrin dodecamer ring. Firstly, a classical templating approach using the 12-armed template is described. The limitations of this approach in the quest for larger nanorings are discussed. Vernier templating, which utilises a mismatch in the number of binding sites between a ligand and its receptor is introduced as a general strategy to the synthesis of large nanorings. This is demonstrated by the synthesis of cyclic dodecamer from a linear porphyrin tetramer and a hexadentate template via a figure-of-eight intermediate. The general utility of the Vernier method to large nanorings is explored in Chapter 4 with steps towards the synthesis of a cyclic tetracosamer, consisting of 24 porphyrin subunits. In preliminary experiments, an improved route to the cyclic porphyrin octamer is described. Finally, the photophysical properties of the nanoring series are explored in Chapter 5 as a function of size and conformation. Femtosecond photoluminescence spectroscopy shows that even in cyclic dodecamer, exciton delocalisation over the entire porphyrin backbone occurs on a sub-picosecond timescale, and parallels are drawn with the dynamics of natural light harvesting complexes.

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Noel, Nakita K. „Advances in hybrid solar cells : from dye-sensitised to perovskite solar cells“. Thesis, University of Oxford, 2014. https://ora.ox.ac.uk/objects/uuid:e0f54943-546a-49cd-8fd9-5ff07ec7bf0a.

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This thesis presents a study of hybrid solar cells, specifically looking at various methods which can be employed in order to increase the power conversion efficiency of these devices. The experiments and results contained herein also present a very accurate picture of how rapidly the field of hybrid solar cells has progressed within the past three years. Chapters 1 and 2 present the background and motivation for the investigations undertaken, as well as the relevant theory underpinning solar cell operation. Chapter 2 also gives a brief review of the literature pertinent to the main types of devices investigated in this thesis; dye-sensitised solar cells, semiconductor sensitized solar cells and perovskite solar cells. Descriptions of the synthetic procedures, as well as the details of device fabrication and any measurement techniques used are outlined in Chapter 3. The first set of experimental results is presented in Chapter 4. This chapter outlines the synthesis of mesoporous single crystals (MSCs) of anatase TiO₂ as well as an investigation of its electronic properties. Having shown that this material has superior electronic properties to the conventionally used nanoparticle films, they were then integrated into low temperature processed dye-sensitised solar cells and achieved power conversion efficiencies of > 3%, exhibiting electron transport rates which were orders of magnitude higher than those obtained for the high temperature processed control films. Chapter 5 further investigates the use of MSCs in photovoltaic devices, this time utilising a more strongly absorbing inorganic sensitiser, Sb₂S₃. Utilising the readily tunable pore size of MSCs, these Sb₂S₃ devices showed an increase in voltage and fill factor which can be attributed to a decrease in recombination within these devices. This chapter also presents the use of Sb₂S₃ in the meso-superstructured configuration. This device architecture showed consistently higher voltages suggesting that in this architecture, charge transport occurs through the absorber and not the mesoporous scaffold. Chapters 6 and 7 focus on the use of hybrid organic-inorganic perovskites in photovoltaic devices. In Chapter 6 the mixed halide, lead-based perovskite, CH₃NH₃PbI_3-xCl_x is employed in a planar heterojunction device architecture. The effects of Lewis base passivation on this material are investigated by determining the photoluminescence (PL) lifetimes and quantum efficiencies of treated and untreated films. It is found that passivating films of this material using Lewis bases causes an increase in the PLQE at low fluences as well as increasing the PL lifetime. By globally fitting these results to a model the trap densities are extracted and it is found that using these surface treatments decreases the trap density of the perovskite films. Finally, these treatments are used in complete solar cells resulting in increased power conversion efficiencies and an improvement in the stabilised power output of the devices. Chapter 7 describes the materials synthesis and characterisation of the tin-based perovskite CH₃NH₃SnI₃ and presents the first operational, lead-free perovskite solar cell. The work presented in this thesis describes significant advances in the field of hybrid solar cells, specifically with regards to improvements made to the nanostructured electrode, and the development and implementation of more highly absorbing sensitizers. The improvements discussed here will prove to be quite important in the drive towards exploiting solar power as a clean, affordable source of energy.

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Baimpas, Nikolaos. „'Hybrid' non-destructive imaging techniques for engineering materials applications“. Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:1aa00fed-34e6-4a5e-951b-c710e21ac23c.

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The combination of X-ray imaging and diffraction techniques provides a unique tool for structural and mechanical analysis of engineering components. A variety of modes can be employed in terms of the spatial resolution (length-scale), time resolution (frequency), and the nature of the physical quantity being interrogated. This thesis describes my contributions towards the development of novel X-ray “rich” imaging experimental techniques and data interpretation. The experimental findings have been validated via comparison with other experimental methods and numerical modelling. The combination of fast acquisition rate and high penetration properties of X-ray beams allows the collection of high-resolution 3-D tomographic data sets at submicron resolution during in situ deformation experiments. Digital Volume Correlation analysis tools developed in this study help understand crack propagation mechanisms in quasi-brittle materials and elasto-plastic deformation in co-sprayed composites. For the cases of crystalline specimens where the knowledge of “live” or residual elastic strain distributions is required, diffraction techniques have been advanced. Diffraction Strain Tomography (DST) allows non-destructive reconstruction of the 2-D (in-plane) variation of the out-of-plane strain component. Another diffraction modality dubbed Laue Orientation Tomography (LOT), a grain mapping approach has been proposed and developed based on the translate-rotate tomographic acquisition strategy. It allows the reconstruction of grain shape and orientation within polycrystalline samples, and provides information about intragranular lattice strain and distortion. The implications of this method have been thoroughly investigated. State-of-the-art engineering characterisation techniques evolve towards scrutinising submicron scale structural features and strain variation using the complementarity of X-ray imaging and diffraction. The first successful feasibility study is reported of in operando stress analysis in an internal combustion engine. Finally, further advancement of ‘rich’ imaging techniques is illustrated via the first successful application of Time-of-Flight Neutron Diffraction Strain (TOF-NDST) tomography for non-destructive reconstruction of the complete strain tensor using an inverse eigenstrain formulation.

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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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38

Chang, Be-Ming, und 張璧名. „Multi-Functional Nanodiamonds Hybrids: Advanced Nanomaterials for Biomedical Applications“. Thesis, 2019. http://ndltd.ncl.edu.tw/handle/v4k8k8.

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39

Arefe, Ghidewon. „Engineered Two-Dimensional Nanomaterials for Advanced Opto-electronic Applications“. Thesis, 2018. https://doi.org/10.7916/D83R29RW.

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Two dimensional (2D) materials have unique properties that make them exciting candidates for various optical and electronic applications. Materials such as graphene and transition metal dichalcogenides (TMDCs) have been intensively studied recently with researchers racing to show advances in 2D device performance while developing a better understanding of the material properties. Despite recent advances,there are still significant roadblocks facing the use of 2D materials for real-world applications. The ability to make reliable, low-resistance electrical contact to TMDCs such as molybdeum disulfide (MoS22) has been a challenge that many researchers have sought to overcome with novel solutions. The work laid out in this dissertation uses novel techniques for addressing these issues through the use of improved device fabrication and with a clean, and potentially scalable doping method to tune 2D material properties.A high-performance field-effect transistor (FET) was fabricated using a new device platform that combined graphene leads with dielectric encapsulation leading to the highest reported value for electron mobility in MoS2. Device fabrication techniques were also investigated and a new, commercially available lithography tool (NanoFrazor) was used to pattern contacts directly onto monolayer MoS2. Through a series of control experiments with conventional lithography, a clear improvement in contact resistance was observed with the use of the NanoFrazor. Plasma-doping, a dry and clean process, was investigated as an alternative to traditional wet-chemistry doping techniques. In addition to developing doping parameters with a chlorine plasma treatment of graphene, a series of experiments on doped graphene were conducted to study its effect on optical properties. Whereas previous studies used electrostatic gating to modify graphene’s optical properties, this work with plasma-doped graphene showed the ability to tune absorbence and plasmon wavelength without the need for an applied bias opening the door to the potential for low-power applications. This work is a just small contribution to the larger body of research in this field but hopefully represents a meaningful step towards a greater understanding of 2D materials and the realization of functional applications.

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(8070293), Zhimin Qi. „MANGANESE-BASED THIN FILM CATHODES FOR ADVANCED LITHIUM ION BATTERY“. Thesis, 2021.

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Lithium ion batteries have been regarded as one of the most promising and intriguing energy storage devices in modern society since 1990s. A lithium ion battery contains three main components, cathode, anode, and electrolyte, and the performance of battery depends on each component and the compatibility between them. Electrolyte acts as a lithium ions conduction medium and two electrodes contribute mainly to the electrochemical performance. Generally, cathode is the limiting factor in terms of capacity and cell potential, which attracts significant research interests in this field.Different from conventional slurry thick film cathodes with additional electrochemically inactive additives, binder-free thin film cathode has become a promising candidate for advanced high-performance lithium ion batteries towards applications such as all-solid-state battery, portable electronics, and microelectronics. However, these electrodes generally require modifications to improve the performance due to intrinsically slow kinetics of cathode materials.

In this thesis work, pulsed laser deposition has been applied to design thin film cathode electrodes with advanced nanostructures and improved electrochemical performance. Both single-phase nanostructure designs and multi-phase nanocomposite designs are explored. In terms of materials, the thesis focuses on manganese based layered oxides because of their high electrochemical performance. In Chapter 3 of the nanocomposite cathode work, well dispersed Au nanoparticles were introduced into highly textured LiNi_0.5Mn_0.3Co_0.2O₂(NMC532) matrix to act as localized current collectors and decrease the charge transfer resistance. To further develop this design, in Chapter 4, tilted Au pillars were incorporated into Li₂MnO₃ with more effective conductive Au distribution using simple one-step oblique angle pulsed laser deposition. In Chapter 5, the same methodology was also applied to grow 3D Li₂MnO₃ with tilted and isolated columnar morphology, which largely increase the lithium ion intercalation and the resulted rate capability. Finally, in Chapter 6, direct cathode integration of NMC532 was attempted on glass substrates for potential industrial applications.

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Davarazar, Mahsa. „Ecotoxicological assessment of industrial effluents treated by the activation of persulfate using CuO nanomaterials“. Master's thesis, 2021. http://hdl.handle.net/10773/31919.

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Wastewaters originated from industrial activities can cause severe toxic effects to the biota inhabiting the receiving environment. Hence, there is a need for efficient treatment technologies to a) removing the contaminants, and b) providing good quality water resources. In this context, the present thesis main goal is to assess the efficiency of advanced oxidation process (AOP) in the treatment of industrial effluents. To attain this main goal, first a scientometric study was performed to identify the main gaps in the application of various AOps, namely regarding a) optimization of AOPs for the treatment of recalcitrant organic compounds, and b) the need for ecotoxicity characterization after effluent treatment to ensure the good quality of the final treated effluents. Secondly, the efficiency of an AOP, by the activation of persulfate (PS) using CuO nanomaterials, in the treatment of an artificial effluent (with 50 mg/L Rhodamine B) was assessed. For this, different treatment designs were tested in the artificial effluent done in distilled water. The obtained results identified the treatment using 0.5 g/L of CuO, 5 mM of PS to exhibit the highest the effectiveness as it removed 100% of RhB after 120 minutes of reaction. The mentioned treatment conditions were then applied to the artificial effluent performed in ASTM medium (an artificial medium simulating freshwater; [RhB]0=50 mg/L). A drop was observed in RhB removal efficiency to 29% after 30 min, and 57% after 60 min due to the complexity of the medium. Hence, integration of catalytic and thermal activation was adopted under the same experimental condition but with an elevated temperature to 45 °C. As a result, complete degradation of RhB was observed within 60 min of reaction. The lethal toxicity of the artificial effluent to Daphnia magna was assessed before and after the AOP treatment. The toxicity of CuO and PS was also assessed. The results indicated that the treated effluent was still highly toxic to D. magna and that PS was probably the main cause for such high toxicity. Following these results, a complementary set of experiments was performed by treating the effluent with the same conditions except for the PS concentration used that was reduced to 1 mM. After 60 min of the reaction time, complete degradation of RhB was observed. The lethal toxicity of the effluent before and after the AOP treatment was then assessed for the rotifer Brachionus calyciflorus, by exposing these organisms to serial dilutions of the effluents (6.25%, 12.5%, 25%, 50%, 100%). The median lethal concentration of the effluent before treatment was 44.3% while that for the treated effluent was 8.24%, suggesting a much higher lethal toxicity of the treated effluent. It is hypothesised that such high toxicity is due to the PS, since both D. magna and B. calyciflorus exposed to this chemical alone showed 100% mortality. Adding to this, the formation of intermediate compounds during the AOP treatment, may have also contributed to the increased toxicity of the treated effluent. Overall, the obtained results suggested that other oxidant compounds should be considered to be used in AOPs to treat (waste)water effluents, as well the concentrations of CuO must be adjusted or the removal of these nanoparticles and metallic ions should be improved to allow obtaining a treated effluent with no to low environmental toxicity.
As águas residuais oriundas das atividades industriais podem causar elevada toxicidade para o biota que habita os compartimentos ambientais recetoras dessas águas. Deste modo, são necessárias tecnologias de tratamento de águas residuais que sejam eficientes de modo a: a) removerem os contaminants e b) permitirem a sua a conversão em recursos hídricos de boa qualidade. Neste contexto, o objetivo principal da presente tese foi avaliar a eficiência de processos de oxidação avançada (POA) no tratamento de efluentes industriais. Para atingir este objetivo principal, primeiro foi realizado um estudo cienciométrico para identificar as principais lacunas de conhecimento no que respeita a aplicação de vários POA, nomeadamente no que se refere à: a) otimização dos POA para o tratamento de compostos orgânicos recalcitrantes, e b) necessidade da caracterização ecotoxicológica após o tratamento do efluente e garantir a boa qualidade dos efluentes tratados. Em segundo lugar, avaliou-se a eficiência de um POA, pela ativação de persulfato (PS) utilizando nanomateriais de CuO, no tratamento de um efluente artificial (com 50 mg/L de Rodamina B). Para tal, foram testados diferentes tipos de tratamentos num efluente artificial feito em água destilada. Os resultados obtidos identificaram o tratamento que consistiu na aplicação de 0,5 g/L de CuO e 5 mM de PS como o que apresentou maior eficácia na remoção da RhB (100%) após 120 minutos de reação. As condições de tratamento mencionadas foram então aplicadas ao efluente artificial realizado em meio ASTM (um meio artificial que simula água doce; [RhB] 0 = 50 mg/L). Foi observado um decréscimo na eficiência de remoção de RhB para 29% após 30 min e 57% após 60 min de reação, possivelmente devido à complexidade do meio. Assim, a integração da ativação catalítica e térmica foi adotada sob a mesma condição experimental, mas com uma temperatura elevada até 45 °C. Como resultado, a degradação completa de RhB foi observada dentro de 60 min de reação. A toxicidade letal do efluente artificial foi avaliada, antes e após o tratamento POA, para Daphnia magna. A toxicidade de CuO e PS também foi avaliada. Os resultados indicaram que o efluente tratado ainda era altamente tóxico para D. magna e que o PS foi provavelmente a principal causa dessa alta toxicidade. No seguimento destes resultados, foi realizado um conjunto complementar de experiências em que o efluente artificial foi tratado nas mesmas condições, exceto no que respeita À concentração de PS utilizada que foi de 1mM. Após 60 min do tempo de reação, foi observada degradação completa de RhB. A toxicidade letal do efluente, antes e após o tratamento POA, foi então avaliada para o rotífero Brachionus calyciflorus, expondo este organismo a diluições em série dos dois efluentes (6,25%, 12,5%, 25%, 50%, 100%). A concentração letal média do efluente antes do tratamento foi de 44,3%, enquanto para o efluente tratado foi de 8,24%, sugerindo uma toxicidade letal muito maior do efluente tratado. É colocada a hipótese de que esta toxicidade elevada é devida ao PS, uma vez que D. magna e B. calyciflorus expostos apenas a este composto apresentaram mortalidade de 100%. Mais ainda, a formação de compostos intermédios durante o tratamento POA, pode também ter contribuído para o aumento da toxicidade do efluente tratado. De forma geral, os resultados obtidos sugerem que outros compostos oxidantes devem ser considerados para serem utilizados em POA para tratamento de efluentes de águas residuais, bem como as concentrações de CuO devem ser ajustadas ou a remoção destas nanopartículas e iões metálicos deve ser melhorada de forma a permitir a obtenção um efluente tratado que não apresente ou apresente baixa toxicidade para o biota.
Mestrado em Eco-toxicologia e Análise de Risco

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Bessa, Maria João Moura Gonçalves Moutinho de. „Moving into advanced nanomaterials. Toxicity of TiO2 nanoparticles immobilized in clay on human cell line“. Dissertação, 2015. https://repositorio-aberto.up.pt/handle/10216/89207.

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Bessa, Maria João Moura Gonçalves Moutinho de. „Moving into advanced nanomaterials. Toxicity of TiO2 nanoparticles immobilized in clay on human cell line“. Master's thesis, 2015. https://repositorio-aberto.up.pt/handle/10216/89207.

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44

„Advanced Characterization and Optical Properties of Single-Walled Carbon Nanotubes and Graphene Oxide“. Thesis, 2011. http://hdl.handle.net/1911/70369.

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Photophysical, electronic, and compositional properties of single-walled carbon nanotubes (SWCNTs) and bulk nanotube samples were investigated together with graphene oxide photoluminescence. First, we studied the effect of external electric fields on SWCNT photoluminescence. Fields of up to 10 7 V/m caused dramatic, reversible decreases in emission intensity. Quenching efficiency was proportional to the projection of the field on the SWCNT axis, and showed inverse correlation with optical band gap. The magnitude of the effect was experimentally related to exciton binding energy, as consistent with a proposed field-induced exciton dissociation model. Further, the electronic composition of various SWCNT samples was studied. A new method was developed to measure the fraction of semiconducting nanotubes in as- grown or processed samples. SWCNT number densities were compared in images from near-IR photoluminescence (semiconducting species) and AFM (all species) to compute the semiconducting fraction. The results provide important information about SWCNT sample compositions that can guide controlled growth methods and help calibrate bulk characterization techniques. The nature of absorption backgrounds in SWCNT samples was also studied. A number of extrinsic perturbations such as extensive ultrasonication, sidewall functionalization, amorphous carbon impurities, and SWCNT aggregation were applied and their background contributions quantified. Spectral congestion backgrounds from overlapping absorption bands were assessed with spectral modeling. Unlike semiconducting nanotubes, metallic SWCNTs gave broad intrinsic absorption backgrounds. The shape of the metallic background component and its absorptivity coefficient were determined. These results can be used to minimize and evaluate SWCNT absorption backgrounds. Length dependence of SWCNT optical properties was investigated. Samples were dispersed by ultrasonication or shear processing, and then length-fractionated by gel electrophoresis or controlled ultrasonication shortening. Fractions from both methods showed no significant absorbance variations with SWCNT length. The photoluminescence intensity increased linearly with length, and the relative quantum yield gradually increased, approaching a limiting value. Finally, a strong pH dependence of graphene oxide photoluminescence was observed. Sharp and structured excitation/emission features resembling the spectra of molecular fluorophores were obtained in basic conditions. Based on the observed pH-dependence and quantum calculations, these spectral features were assigned to quasi-molecular fluorophores formed by the electronic coupling of oxygen-containing addends with nearby graphene carbon atoms.

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Haorongbam, Bisheshwar. „Prediction Of The Behaviors Of Hollow/Foam-Filled Axially Loaded Steel/Composite Hat Sections For Advanced Vehicle Crash Safety Design“. Thesis, 2015. http://etd.iisc.ernet.in/handle/2005/2634.

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Hat sections, single and double, made of steel are frequently encountered in automotive body structural components such as front rails, B-Pillar, and rockers of unitized-body cars. These thin-walled components can play a significant role in terms of crashworthiness and impact energy absorption, through a nonlinear phenomenon called as progressive dynamic buckling. As modern vehicle safety design relies heavily on computer-aided engineering, there is a great need for analysis-based predictions to yield close correlation with test results. Although hat sections subjected to axial loading have been studied widely in the past, there is scanty information in published literature on modeling procedures that can lead to robust prediction of test responses. In the current study, both single-hat and double-hat components made of mild steel are studied extensively experimentally and numerically to quantify statistical variations in test responses such as peak load, mean load and energy absorption, and formulate modeling conditions for capturing elasto-plastic material behavior, strain rate sensitivity, spot-welds, etc. that can lead to robust predictions of force-time and force-displacement histories as well as failure modes. In addition, keeping initial stages of vehicle design in mind, the effectiveness of soft computing techniques based on polynomial regression analysis, radial basis functions and artificial neural networks for quick assessment of the behaviors of steel hat sections has been demonstrated. The study is extended to double-hat sections subjected to eccentric impact loading which has not been previously reported. A lightweight enhancement of load carrying capacity of steel hat section components has been investigated with PU (polyurethane) foam-filled single and double hat sections, and subjecting the same to quasi-static and axial impact loading. Good predictions of load-displacement responses are again obtained and shortening of fold lengths vis-à-vis hollow sections is observed. Finally, the performance of hat sections made of glass fiber-reinforced composites is studied as a potential lightweight substitute to steel hat section components. The challenging task of numerical prediction of the behaviors of the composite hat sections has been undertaken using a consistent modeling and analysis procedure described earlier and by choosing an appropriate constitutive behavior available in the popular explicit contact-impact analysis solver, LS-DYNA.

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Michálková, Hana. „Nanotoxikologie pokročilých materiálů =:Nanotoxicology of advanced materials /“. Doctoral thesis, 2019. http://www.nusl.cz/ntk/nusl-426247.

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Nowadays, a wide range of nanoparticles is used in different fields of human acti-vities. These relatively are well-researched. However, with the development of new nanomaterials, new possibilities for their use both in nanomedicine and in other fields are possible. This phenomenon is accompanied by potential toxic risks of these mate-rials. The presented thesis deals with the extensive topic of cytotoxicity of both nanoma-terials and their modification for better binding of cytostatics to increase their effi-cacy. Experimental work is focused on the interaction of nanomaterials with the cells and their environment, the determination of the toxicity of nanomaterials and their potential use in nanomedicine. The main aim of my thesis was to prepare a comprehensive summary about nano-materials, their physico-chemical properties, to modify nanoparticles surface to provi-de an entity for targeted drug delivery and to test cytotoxicity on selected cell lines.

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Li, Huifeng. „Development of Advanced Nanomanufacturing: 3D Integration and High Speed Directed Self-assembly“. Thesis, 2010. http://hdl.handle.net/1969.1/ETD-TAMU-2010-08-8550.

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Development of nanoscience and nanotechnology requires rapid and robust nanomanufacturing processes to produce nanoscale materials, structures and devices. The dissertation aims to contribute to two major challenging and attractive topics in nanomanufacturing. Firstly, this research develops fabrication techniques for three dimensional (3D) structures and integrates them into functional devices and systems. Secondly, a novel process is proposed and studied for rapid and efficient manipulation of nanomaterials using a directed self-assembly process. The study begins with the development of nanoimprint lithography for nanopatterning and fabrication of 3D multilayer polymeric structures in the micro- and nano-scale, by optimizing the layer-transfer and transfer-bonding techniques. These techniques allow the integration of microfluidic and photonic systems in a single chip for achieving ultracompact lab-on-a-chip concept. To exemplify the integration capability, a monolithic fluorescence detection system is proposed and the approaches to design and fabricate the components, such as a tunable optical filter and optical antennas are addressed. The nanoimprint lithography can also be employed to prepare nanopatterned polymer structures as a template to guide the self-assembly process of nanomaterials, such as single-walled carbon nanotubes (SWNTs). By introducing the surface functionalization, electric field and ultrasonic agitation into the process, we develop a rapid and robust approach for effective placement and alignment of SWNTs. These nanomanufacturing processes are successfully developed and will provide a pathway to the full realization of the lab-on-a-chip concept and significantly contribute to the applications of nanomaterials.

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Tsai, Dung-Sheng, und 蔡東昇. „Physics and Nanomaterial Designs of Advanced Photodetectors for Extreme Radiation and Temperature Environments“. Thesis, 2012. http://ndltd.ncl.edu.tw/handle/28801541972146201392.

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博士
國立臺灣大學
光電工程學研究所
101
This thesis consists of an introduction, four chapters and a conclusion, with each chapter covering a different topic. In the introduction, we introduce the various limitations of the conventional photodetectors that we study in the later chapters. In chapter 2, we demonstrated Si MSM PDs with ZnO nanorod arrays (NRAs) as a top layer, which absorbs the UV photons (photon energy > band gap of ZnO) effectively and serves as an ARC layer, providing an effective refractive-index gradient between Si and air in the long-wavelength region (photon energy < band gap of ZnO), enabling broadband detection with greatly enhanced responsivity. The responsivity of Si MSM PDs is increased by up to 3 orders of magnitude in the UV region and by 2 orders of magnitude in the visible/NIR regions due to ZnO NRA layers. The huge enhancement of broadband detection by Si MSM PDs with ZnO NRAs could allow the low-cost production of photonic devices and extend the application potential for Si-based optoelectronic devices. In chapter 3, the visible-blind UV PDs employing n-ZnO/LaAlO3 (LAO)/p-Si double heterojunction using pulse laser deposition (PLD) are presented. The n-ZnO/LAO/p-Si PDs exhibit visible-blind UV responsivity with the cutoff wavelength of responsivity at 380 nm, corresponding to the near band edge (NBE) absorption of ZnO. Inserted 10-nm-thick LAO layers effectively eliminate visible light responses via blocking the electrons excited by visible photons in p-Si near the interface owing to the high potential barrier between p-Si and LAO layers (~2.0 eV). This study paves the way for visible-blind UV photosensing applications under outdoor lighting. In chapter 4, we report few-layer MoS2 Schottky PDs with back-to-back MSM geometry, capable of broadband photodetection from visible to UV regions with working temperatures up to 200 °C for use in harsh environments. Until few-layer MoS2 is demonstrated here, the broadband responsivity feature is not previously achievable for harsh environment use since all of photodetection materials for harsh environments are wide-bandgap semiconductors. As a new record, the responsivity of 5.7 A/W, has never been obtained in 2D nanomaterial-based PDs due to very high optical absorption of ~10% (very high absorption coefficient of up to 7.5×105 cm-1) of the few-layer MoS2 and a high photogain of ~13.3. In addition, temporal measurements reveal fast response times (~70 μs) and recovery times (~110 μs). The excellent optical properties of few-layer MoS2 promise a new generation of fast, broadband PDs based on 2D nanomaterials for the applications in harsh environments, such as sensing, imaging, and intrachip optical interconnects at the high temperatures. In chapter 5, we demonstrate the Schottky PDs with back-to-back metal-semiconductor-metal (MSM) geometry by employing AlN thin films on Si(100) substrates from reactive sputtering deposition with working temperature up to 300 °C for use in solar-blind UV detection and harsh environments. For 2 MeV proton irradiation, the PDCR value of AlN MSM PDs is 0.7 under a 5 V bias at proton fluences up to 1013 cm-2, indicating that the PDs are well suited for space applications. The AlN MSM PDs show a fast and stable photoresponse, i.e., ~110 ms of the rise time and ~80 ms of the fall time at 5 V bias. This study paves the way for fast and solar-blind photosensing in the space environment and high-temperature conditions.

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Ribeiro, Maria João Xavier. „dyNaMic - Nanomaterial-corona formation species targeted, advances for NMs mode of action“. Doctoral thesis, 2018. http://hdl.handle.net/10773/25924.

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The growing use of nanomaterials (NMs) in a wide variety of fields is due to the better and innovative properties that they can offer to, e.g., the end-use industry or biomedicine. The release of NMs into the environment during their life-cycle is an actual scenario. Reaching the environment, the NMs will interact with the organisms, but despite the growing efforts to provide conclusive results on the safety of NMs, their impact is still poorly understood, particularly in the terrestrial compartment. There are many knowledge gaps that need to be covered to better understand the mechanisms that drive NMs toxicity, hence this thesis aims to increase the knowledge on the effects of selected NMs in soil invertebrates. Understanding NMs mode of action is key to safer-by-design strategies that will contribute to improve nanotechnology sustainability. Effect assessment of NMs was done at several levels of biological organization, covering different endpoints, which can be integrated in order to understand the toxicity mechanisms. Further, long-term and multigenerational effects were also considered, as they are likely scenarios for NMs exposure. Selected NMs - silver (Ag), tungsten carbide cobalt (WCCo) and copper oxide (CuO) case study (using different surface modifications), along with the corresponding salt forms, were tested at different levels: molecular (oxidative stress and genotoxicity) and organism (survival and reproduction). The standard soil invertebrates Enchytraeus crypticus and Eiseina fetida were used for in vivo and in vitro exposures, respectively. Sub-lethal concentrations of Ag NMs induced distinct and later biochemical effects (oxidative stress and genotoxicity) in E. crypticus compared to the nonnano form (AgNO3). While different responses point to nano-specific effects, possible dissolution of Ag NMs and consequent ion-driven toxicity can also be occurring. WCCo NMs impaired reproduction in E. crypticus, at a higher extent compared to CoCl2 (assuming similar Co concentrations). The lower Co concentrations in the soil:water interface and lower uptake in WCCo exposed organisms suggest that toxicity resulted from a combined effect between WC and Co. Multigenerational exposure did not increase toxicity in terms of survival and reproduction, in spite of Co internalization. Monitoring of Co body burden pointed to Co elimination and storage as the detoxifying strategies in WCCo and CoCl2 exposed organisms, respectively. CuO NMs did not decrease viability of Eisenia fetida’s immune cells, either in the pristine form or with different surface modifications. The interaction with the biomolecules present in the coelomic fluid may have led to the formation of a native corona that interfered with the toxic potential, independently of the surface modification, but the impact of such interaction is unclear. Some technical aspects need further optimization due to the possibility that the effects could have been underestimated, but this constitutes a promising test system for in vitro testing battery.
A crescente utilização de nanomateriais (NMs) numa grande variedade de setores é devida às melhores e mais inovadoras propriedades que estes podem oferecer, por exemplo, à indústria de uso final ou à biomedicina. A libertação de NMs no ambiente durante o seu ciclo de vida é um cenário actual. Ao entrarem no ambiente, os NMs irão interagir com os organismos, e apesar dos crescentes esforços para fornecer resultados conclusivos sobre a segurança dos NMs, o seu impacto ainda é pouco conhecido, particularmente no compartimento terrestre. Existem várias lacunas no conhecimento que necessitam de ser preenchidas de forma a entender melhor os mecanismos que levam à toxicidade dos NMs; assim, esta tese pretende aumentar o conhecimento dos efeitos de NMs selecionados em invertebrados de solo. Perceber o mecanismo de acção dos NMs é a chave para estratégias safer-bydesign, fundamentais para melhorar a sustentabilidade da nanotecnologia. A avaliação dos efeitos dos NMs foi realizada a vários níveis de organização biológica, cobrindo diferentes endpoints, que, sendo integrados, permitem perceber os mecanismos de toxicidade. Os efeitos a longo-prazo e multigeneracionais foram também considerados, uma vez que são possíveis cenários de exposição aos NMs. Os NMs selecionados – prata (Ag), liga de carboneto de tungsténio-cobalto (WCCo) e o caso estudo de óxido de cobre (CuO) (usando diferentes modificações da superfície), juntamente com os correspondentes sais, foram usados a diferentes níveis: molecular (stress oxidativo e genotoxicidade) e do organismo (sobrevivência e reprodução). Os invertebrados modelo de solo Enchytraeus crypticus e Eisenia fetida foram usados em exposições in vivo e in vitro, respectivamente. Concentrações sub-letais de Ag NMs induziram efeitos bioquímicos (de stress oxidativo e genotoxicidade) em E. crypticus, distintos e mais tardios comparados com a forma não-nano (AgNO3). Enquanto diferentes respostas apontam para efeitos nano-específicos, a possível dissolução de Ag NMs e consequente toxicidade induzida pelos iões também pode ocorrer. WCCo NMs comprometeram a reprodução de E. crypticus de forma superior comparado com CoCl2 (assumindo concentrações de Co semelhantes). Menores concentrações de Co na interface solo-água e a menor internalização de Co nos organismos expostos a WCCo, sugere que a toxicidade resulta do efeito combinado entre WC e Co. Apesar da internalização de Co, a exposição multigeneracional não aumentou a toxicidade em termos de sobrevivência e reprodução. A monitorização da quantidade de Co nos organismos aponta para a eliminação e armazenamento como estratégias de detoxificação nos organismos expostos a WCCo NMs e CoCl2, respectivamente. Os CuO NMs não diminuíram a viabilidade das células dos sistema imunitário de Eisenia fetida, quer na forma pristina ou com diferentes modificações da superfície. A interacção com as biomoléculas presentes no fluido celómico terá levado à formação de uma corona nativa que interferiu com o potencial de toxicidade, independentemente da modificação da superfície, mas o impacto dessa interação não é claro. Alguns aspectos técnicos necessitam de otimização devido à possibilidade dos efeitos terem sido subestimados, mas este constitui um sistema de teste promissor para a bateria de testes in vitro.
Programa Doutoral em Biologia

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Ribeijro, Rita Sá. „Aplicação de nanomateriais na oxidação avançada de poluentes orgânicos“. Master's thesis, 2013. http://hdl.handle.net/1822/31047.

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Dissertação de mestrado integrado em Engenharia Civil (área de especialização em Perfil de Hidráulica e Ambiente)
A constante preocupação com a preservação da saúde humana impulsiona o necessário desenvolvimento de novos e mais sustentáveis processos de tratamento para remoção de micropoluentes das águas, dado que alguns deles, como é o caso da matéria orgânica natural (MON), podem ser percussores de substâncias potencialmente cancerígenas e apresentar comportamento refratário às tecnologias convencionais instaladas na grande maioria das estações de tratamento de água (ETA). Estudos científicos recentes têm vindo a evidenciar a potencialidade da fotocatálise heterogénea (FH) e do efeito catalítico do dióxido de titânio (TiO2), na remoção eficaz de MON e outros micropoluentes orgânicos, assumindo-se como alternativa viável a outras formas de oxidação mais dispendiosas. O presente trabalho de investigação tem como objetivo principal o desenvolvimento e avaliação da eficiência da aplicação de técnicas de oxidação avançada na remoção de constituintes orgânicos (MON), baseada na utilização de nanopartículas de TiO2 suspensas na água. Neste documento são apresentadas as metodologias utilizadas na investigação efetuada, nomeadamente a definição da relação entre a concentração de ácido húmico (AH) e a absorvância, bem como a análise dos resultados (absorvância a 254 nm, pH, CQO, cloro livre e total) obtidos em ensaios de degradação de MON sob incidência de radiação solar e UV (TNN 15/32), com e sem o contributo catalítico das nanopartículas de TiO2. A eficiência e cinética de degradação foram estudadas considerando diferentes concentrações iniciais de MON, resultantes das diferentes matrizes aquosas utilizadas: água sintética, obtida por diluição de ácido húmico; água superficial natural, recolhida em dois pontos (com diferentes graus de poluição) da ribeira de Couros, em Guimarães; e água da rede pública de abastecimento à qual se adicionou uma solução com igual concentração inicial de AH. A melhor eficiência de degradação de MON foi de 99% tendo sido obtida sob incidência de radiação UV, numa água sintética com uma concentração inicial de AH igual a 8 mg/L e uma concentração de TiO2 de 5 mg/L. No sentido de avaliar se a oxidação efetuada conduz a águas tratadas ecotoxicologicamente mais seguras, este trabalho contempla ainda uma análise toxicológica dos subprodutos de oxidação da MON. Os testes de toxicidade realizados mostraram que o AH inicial e a solução resultante do tratamento fotocatalítico com TiO2 não induzem toxicidade nas matrizes de água estudadas.
Preservation of human health has always been a main concern for society, drives the development required of new and more sustainable treatment processes for the removal of micropolluants of water, as somo of them, such as the natural organic matter (NOM), may be precursors of potentially carcinogenic substances and present refractory behavior to conventional technologies installed in most water treatment plants (WTP). Given the growing interest in solving this problem, this investigation has as its main goal the development and evaluation of the efficiency of the application of advanced oxidation techniques in the removal of organic constituents (NOM), which is based on the use of titanium dioxide that is suspended in water, assuming as a viable alternative to other forms of more expensive oxidation. This paper presents the methodologies used in research conducted, in particular the definition of the relationship between absorbance and concentration of humic acid (HA), as well as the analysis of the results (absorbance at 254 nm, pH, COD, free and total chlorine) of the trials made, which are based on the degradation of NOM under the incidence of solar radiation and UV (TNN 15/32), with and without the catalytic contribution of titanium dioxide nanosized particles. The efficiency and kinetics of degradation were studied considering different initial concentrations of MON. These different concentrations were the result of different types of water matrices used such as: synthetic water obtained by dilution of humic acid (HA); natural surface water samples collected at two points (with different degrees of pollution) in the Couros stream (Guimarães); and water of supply network with a solution of the same initial concentration of HA. The highest efficiency degradation of NOM recorded was 99%. This value was obtained under UV radiation , in a synthetic water with an initial concentration of HA equal to 8 mg / L and a TiO2 concentration of 5 mg/L. In order to assess if performed oxidation leads to safest ecotoxicological treates waters, this work also addresses a toxicological analysis of the byproducts of oxidation da MON. Toxicity tests have shown that initial HA and the resulting solution of the photocatalytic treatment with TiO2 do not induce toxicity in the water matrices studied.

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