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A healthy immune system's core challenge is to mount appropriate responses to an immense and unknown variety of antigenic stimuli. By unraveling the regulatory networks that drive and control immune-cell behaviors, we can begin to identify the means by which proper balance can be achieved and aberrant behaviors clinically corrected. Traditionally, major advances in our understanding of cellular immunological processes depended critically on both improved perturbation and enhanced observation methods. In my doctoral research, I have pursued both strategies to elucidate the differentiation and effector functions of adaptive immune Th17 cells. These cells exemplify the need for balance: while Th17 cells are needed to induce clearance of fungal infections and extracellular bacteria, irregular responses have been strongly implicated in autoimmunity. / Chemistry and Chemical Biology

Central to the implementation of colloidal nanomaterials in commercial applications is the development of high throughput synthesis strategies for technologically relevant materials. Solution based synthesis approaches provide the controllability, high throughput, and scalability needed to meet commercial demand. A flow through supercritical fluid reactor was used to synthesize silicon nanowires in high yield with production rates of ~45 mg/hr. The high temperature and high pressure of the supercritical medium facilitated the decomposition of monophenylsilane and seeded growth of silicon nanowires by gold seeds. Crystalline nanowires with diameters of ~25 nm and lengths greater than 20 [micrometers] were routinely synthesized. Accumulation of nanowires in the reactor resulted in deposition of a conformal amorphous shell on the crystalline surface of the wire. X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and energy dispersive X-ray spectroscopy were used to determine the shell composition. The shell was identified as polyphenylsilane formed by polymerization of the silicon precursor monophenylsilane. A post synthesis etch was developed to remove the shell while still maintaining the integrity of the crystalline silicon nanowire core. Subsequent surface passivation was achieved through thermal hydrosilylation with a terminal alkene. The development colloidal nanomaterials into commercial applications also requires simple and robust bottom-up assembly strategies to facilitate device fabrication. A Langmuir-Blodgett trough was used to assemble continuous monolayers of hexagonally ordered spherical nanocrystals over areas greater than 1 cm². Patterned monolayers and multilayers of FePt nanocrystals were printed onto substrates using pre-patterned polydimethylsiloxane (PDMS) stamps and a modified Langmuir Schaefer transfer technique. Patterned features, including micrometer-size circles, lines, and squares, could be printed using this approach. The magnetic properties of the printed nanocrystal films were also measured using magnetic force microscopy (MFM). Room temperature MFM could detect a remanent (permanent) magnetization from multilayers (>3 nanocrystals thick) films of chemically-ordered L1₀ FePt nanocrystals. Grazing incidence small angle X-ray scattering was used to quantitatively characterize the grain size, crystal structure, lattice disorder, and edge-to-edge spacing of the nanocrystal films prepared on the Langmuir-Blodgett trough both on the air-water interface and after transfer. / text

Το οξείδιο του ψευδαργύρου είναι ένας ημιαγωγός της ομάδας II-VI και έχει μεγάλη ποικιλία σε τεχνολογικές εφαρμογές όπως οι αισθητήρες διαφόρων χημικών αερίων, τα lasers, οι δίοδοι εκπομπής φωτός, οι νανο-γεννήτριες, τα ηλιακά κύτταρα και πολλές άλλες. Το ευρύ του ενεργειακό κενό (3.445 eV) το καθιστά ένα πολλά υποσχόμενο υλικό για φωτονικές εφαρμογές στην περιοχή του UV ή του ιώδους, ενώ ταυτόχρονα η υψηλή ενέργεια συνοχής του εξιτονίου που το χαρακτηρίζει (περίπου στα 60 meV) επιτρέπει την αποτελεσματική εξιτονική εκπομπή σε θερμοκρασία δωματίου. Οι πιο πρόσφατες εξελίξεις στον τομέα του νανοδομημένου ZnO είναι οι νανοδρόμοι, οι νανογέφυρες, οι νανοπροπέλες, οι νανοδακτύλιοι, τα νανονήματα κ.α. Στην παρούσα διπλωματική εργασία μελετώνται οι ηλεκτρονιακές και οπτικές ιδιότητες νανονημάτων οξειδίου του ψευδαργύρου (ZnO) για ένα εύρος διαμέτρων από 2 έως 6 nm και με την βοήθεια της εμπειρικής μεθόδου των ψευδοδυναμικών και της Configuration Interaction (CI). Μια ανασκόπηση των ιδιοτήτων και χαρακτηριστικών του bulk ZnO, όπως η κρυσταλλική και η ενεργειακή του δομή, κάποιες τεχνολογικές εφαρμογές και μέθοδοι ανάπτυξης δίνονται στο πρώτο κεφάλαιο. Το δεύτερο κεφάλαιο περιέχει την περιγραφή διαφόρων υπολογιστικών μεθόδων όπως της προσέγγισης ενεργούς μάζας ( Effective Mass Approximation), της θεωρίας του συναρτησιακού της πυκνότητας (Density Functional Theory) και τέλος, της εμπειρικής μεθόδου των ψευδοδυναμικών που χρησιμοποιείται στους υπολογισμούς των ηλεκτρονιακών και οπτικών ιδιοτήτων των νανοδομών που μελετάμε. Στο τρίτο και τελευταίο κεφάλαιο, παρατίθενται τα αριθμητικά αποτελέσματα . Αυτά, αφορούν στο εξαρτώμενο από το μέγεθος, οπτικό ενεργειακό κενό, το Stokes shift, και το φάσμα φωτοφωταύγειας. Στο τέλος του κεφαλαίου περιγράφονται τα συμπεράσματα. / Zinc oxide (ZnO), a typical group II-VI compound, has a great variety of device applications, such as chemical sensors, lasers, light-emitting diodes, nanogenerators, solar cells and so forth. The wide band gap (3.445 eV) makes it a promising material for photonic applications in the UV or the blue range, while the high exciton binding energy (around 60 meV at room temperature) allows efficient excitonic emission at room temperature. The most recent developments are towards the nanostructured ZnO, such as nanorods, nanobridges, nanopropellers, nanorings, nanowires, et al. In the present master thesis, the electronic and optical properties of ZnO nanowires within the range of 2-6 nm in diameter are studied by means of atomistic empirical pseudopotential method and configuration interaction. A review of the bulk ZnO, such as the crystal and band structures, technological applications and synthesis methods, is presented in chapter one. The second chapter is devoted to the discussion of various types of methods, e.g., effective-mass approximation, density-functional theory (DFT), and especially the empirical pseudopotential method used herein, for the calculations of the electronic and optical properties of nanostructured ZnO. The numerical results, based on the empirical pseudopotential methods and configuration interaction approach, are present in the following chapter. These results cover the size-dependent optical band gap, Stokes shift and photoluminescence spectrum. A summarization of the results is given in the last chapter.

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This dissertation describes a novel methodology to prepare, functionalize, and assemble polymer-coated ferromagnetic cobalt nanoparticles (PS-CoNPs) and cobalt oxide nanowires. This research demonstrated the ability to use dipolar nanoparticles as `colloidal monomers' to form electroactive 1-D mesostructures via self- and field-induced assembly. The central focus of this dissertation is in developing a novel methodology termed as `Colloidal Polymerization', in the synthesis of well-defined cobalt oxide nanowires as nanostructured electrode materials for potential applications in energy storage and conversion.Ferromagnetic nanoparticles are versatile building blocks due to their inherent spin dipole, which drive 1-D self-assembly of colloids. However, the preparation and utilization of ferromagnetic nanoparticles have not been extensively examined due to the synthetic challenges in preparing well-defined materials that can be easily handled. This dissertation has overcome these challenges through the hybridization of polymeric surfactants with an inorganic colloid to impart functionality, colloidal stability and improved processing characteristics. This modular synthetic approach was further simplified to prepare ferromagnetic nanoparticles in gram scale, which enabled further investigations to develop new chemistry and materials science with these materials. These polymer-coated magnetic nanoparticles self-assembled into extended linear chains due to strong dipolar attractions between colloids. Additionally, novel dipolar assemblies, such as, flux-closure nanorings and lamellae type mesostructures were demonstrated by controlling the interparticle of attractive forces (dipolar versus van der Waals).The research presented herein focused on utilizing polymer-coated ferromagnetic cobalt nanoparticles as `colloidal molecules' to form interconnected 1-D mesostructures via `Colloidal Polymerization'. This process exploited the magnetic organization of dipolar colloids into 1-D mesostructures followed by a facile oxidation reaction to form interconnected electroactive cobalt oxide nanowires. This facile and template free approach enabled the large scale synthesis of semiconductor cobalt oxide nanowires, in which the electronic and electrochemical properties were confirmed for potential applications for energy storage and conversion. This work served as a platform in fabricating a wide range of semiconductor heterostructures, which allowed for structure-property investigation of new nanostructured electrodes.

En la presente tesis doctoral se ha realizado un estudio computacional de las propiedades electrónicas de sistemas basados en cadenas metálicas monodimensionales de la familia de los llamados nanowires, concretamente su magnetismo y conductividad. Estas cadenas lineales se sustentan gracias a los ligandos orgánicos que se organizan a su alrededor, cuyo número de sitios de unión determina la nuclearidad de la cadena. Para estas moléculas, llamadas cadenas metálicas extendidas, se han calculado los parámetros de acoplamiento magnético con el método CASPT2. El uso del Hamiltoniano de Heisenberg estándar para los sistemas M3(dpa)4Cl2 cuando hay dos electrones no desapareados en cada centro, ha sido examinado mediante el cálculo del valor de λ mediante cálculos DFT. Las diferentes conductividades eléctricas observadas en las cadenas MMX [Ni2(dta)4I]∞ y [Pt2(dta)4I]∞ (dta = CH3CS2) y sus estados de ordenación de carga han sido analizados con parámetros de estructura electrónica extraídos a partir de cálculos DFT periódicos y de correlación combinados con la teoría del Hamiltoniano efectivo. / In the present thesis, magnetic and conducting properties of systems, one-dimensional chains of the family of so-called nanowires, have been studied computationally. These linear chains are supported by organic ligands surrounding the metal backbone where the number of binding sites determines the nuclearity of the chain. For these molecules, also called extended metal atom chains, magnetic coupling parameters have been calculated with the CASPT2 method. The use of standard Heisenberg Hamiltonian for systems M3(dpa)4Cl2 when two unpaired electrons are localized on each magnetic center has been examined by calculating the value of λ from DFT calculations. The different electrical conductivities observed in MMX chains [Ni2(dta)4I]∞ and [Pt2(dta)4I]∞ (dta = CH3CS2) and the charge ordering state have been analyzed with DFT periodic calculations and also through the comparison of extracted electronic structure parameters from ab initio calculations combined with the effective Hamiltonian theory.

Zinc oxide (ZnO) nanostructures, especially nanowires, have been one of the most important semiconductive materials used for photocatalysis due to their unique material properties and remarkable performance. In this project, vertically-aligned ZnO nanowires on glass substrate have been synthesized by using the facile hydrothermal methods with the help of pre-coated ZnO seeding layer. The crystalline structure, morphology and UV-Vis transmission spectra of the as-synthesized sample were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and Ultra-violet Visible (UV-Vis) Spectrophotometer. The photocatalytic activity of the sample was examined for the photocatalytic degradation of methyl orange (MO) as the test dye in aqueous solution under UV-A irradiation. The extent of direct hydrolysis of the MO dye under UV light without the photocatalysts was first measured to eliminate the possible contribution from the undesired variables to the overall efficiency. The effects of pH and initial concentration of the MO solution, as well as the nanowire growth time, on the photocatalytic efficiency have been investigated, in order to determine the optimal conditions for photocatalytic applications of ZnO nanowires in the industry. Furthermore, the reproducibility of the experimental methods used in this project was tested to ensure the reliability of the experimental results obtained; and the reusability of the prepared ZnO nanowire arrays were also evaluated to investigate the stability of the products for photocatalytic applications in a large scale. In addition, a micro-chamber based microfluidic device with integrated ZnO nanowire arrays has been fabricated and used for photodegradation studies of MO solution under continuous-flow conditions. As expected, the micro-chamber based approach exhibited much improved photodegradation efficiency as compared to the conventional method using bulk dye solution. The effects of the flow rate and chamber height of the microfluidic device have also been investigated in order to determine the optimal experimental conditions for photodegradation reactions in microfluidic devices.

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