The term “electroluminescence” refers to light emission resulting from the application of an electrical bias. Electron tunneling across a biased, nanoscale junction can serve as the excitation source for photon emission. This effect is also mediated by the plasmonic environment of the junction, where a strong local field can enhance light emission by orders of magnitude. This dissertation presents measurements of electroluminescence from nanoscale gaps and single-molecule junctions. These measurements are made possible by a custom light emission detection system coupled to a scanning tunneling microscope break junction (STM-BJ) instrument. Conductance and light emission data are obtained simultaneously for thousands of junctions. Chapter 1 discusses molecular optoelectronics, a field at the intersection of plasmonic phenomena and molecular electronics, and introduces the STM-BJ technique for measuring molecular junctions. Chapter 2 describes the light emission detection setup that is operated in tandem with the STM-BJ instrument. Chapter 3 presents a study of Au tunnel junctions. This lays the groundwork for the plasmonics at play in these electroluminescent systems, detangling how gap size, electrical bias, and emission wavelength affect plasmonic enhancement. In Chapters 4 and 5, Au-molecule-Au junctions are investigated in some of the first experimental studies of single-molecule electroluminescence at ambient conditions. Chapter 4 uses light emission data from molecular junctions to estimate finite-frequency shot noise and uncover critical information about transmission characteristics. Chapter 5 presents one of the first examples of single-molecule strong light-matter coupling in an electroluminescent system, substantiated by spectroscopy data. This dissertation greatly expands on existing knowledge of plasmonic phenomena, particularly in relation to electroluminescent devices. Furthermore, it lays a strong foundation for single-molecule spectroscopy studies using the STM-BJ technique.

Lateral flow assay (LFA) has been demonstrated as a promising point-of-care biosensor due to its facile use and low cost. These immunoassays utilize nanoparticles as a colorimetric label to conjugate with the antibody and create a colored signal for antigen detection. Typically, gold or silver nanoparticles are used for this procedure. However, the sensitivity of these materials is not high enough to detect certain biomarkers such as the prostate specific antigen (PSA) which is a biomarker for prostate cancer. Replacing the nanoparticles with dual metal nanocages with a hollow interior has potential to improve the state of the flow test. Dual metal nanocages generated through galvanic replacement have been studied for their unique plasmonic and catalytic properties. In this study, silver-palladium nanocages were synthesized using a galvanic replacement reaction to create dual-metal, hollow nanocages. The particles were characterized for their bimetallic nature with x-ray photoelectron spectroscopy, their hollow structure with transmission electron microscopy, and their plasmonic properties with UV-Vis spectroscopy. Particles of three different sizes were created to investigate a size effect on antigen detection. The nanocages were used to as the label for immunoassay which produced a black, colored signal, and the medium and large AgPd NPs improved the tests’ naked eye limit of detection against standard 40 nm gold nanoparticles by tenfold and twenty-fivefold respectively. The medium and large AgPd NPs also had a considerable increase in calibration sensitivity when converting qualitative measurement into quantitative signal. With this work, it is our hope to improve the sensitivity of lateral flow assay and sustain the procedure as a reliable form of point-of-care testing.

<p>As global population continue to rise, the demand for energy is slated to increase substantially. To combat climate change, large amounts of renewable energy will be needed to feed this growing demand. Of renewable energy sources, photovoltaics are well positioned to meet this increasing demand due to the immense abundance of solar energy incident on earth. However, existing energy intensive, low throughput, and costly manufacturing techniques for photovoltaics may pose a barrier to continued large scale implementation.</p> <p>Solution processing has emerged as a promising photovoltaics fabrication technique with high throughput, high materials utilization, and lower cost than existing vacuum-based methods. Thin film photovoltaic materials such as Cu(In,Ga)(S,Se)₂ and CdTe have both been fabricated using various solution processing methods. Of the various solution processing routes, colloidal metal chalcogenide nanoparticles have demonstrated promise as a hydrazine-free route for the solution processing of high efficiency Cu(In,Ga)(S,Se)₂ solar cells. However, conventional solution processing with colloidal nanoparticles has long suffered from anionic and carbonaceous impurities, stemming from legacy synthesis methods. The work in this dissertation aims to solve these issues through the development of novel synthetic methods, ligand engineering, and ultimately improved scalability through slot-die coating.</p> <p> Typical colloidal syntheses rely on the use of metal salts as precursors such as metal halides, nitrates, acetates, and so forth, where the anions may incorporate and alter the electrical properties of the targeted nanomaterials. In this work, the recent advances in amine-thiol chemistry and its unique ability to solubilize many metal containing species are expanded upon. Alkylammonium metal thiolate species are easily formed upon addition of monoamine and dithiol to elemental Cu, In, Ga, Sn, Zn, Se, or metal chalcogenides such as Cu₂S and Ag₂S. These species were then used directly for the synthesis of colloidal nanoparticles without the need for any additional purification. The metal thiolate thermal decomposition pathway was studied, verifying that only metal chalcogenides and volatile byproducts are formed, providing a flexible route to compositionally uniform, phase pure, and anionic impurity-free colloidal nanoparticles including successful syntheses of In₂S₃, (In_xGa_1–x)₂S₃, CuInS₂, CuIn(S_xSe_1–x)₂, Cu(In_xGa_1–x)S₂, Cu₂ZnSnS₄, and AgInS₂. </p> <p>However, further impurities from deleterious carbonaceous residues originating from long chain native ligands were still a persistent problem. This impurity carbon has been observed to hinder grain formation during selenization and leave a discrete residue layer between the absorber layer and the back contact. An exhaustive hybrid organic/inorganic ligand exchange was developed in this work to remove tightly bound oleyalmine ligands through a combination of microwave-assisted solvothermal pyridine ligand stripping followed by inorganic capping with diammonium sulfide, yielding greater than 98% removal of native ligands via a rapid process. Despite the aggressive ligand removal, the nanoparticle stoichiometry remained largely unaffected when making use of the hybrid ligand exchange. Scalable blade coating of the ligand exchanged nanoparticle inks from non-toxic dimethyl sulfoxide inks yielded remarkably smooth and crack free films with RMS roughness less than 7 nm. Selenization of ligand exchanged nanoparticle films afforded substantially improved grain growth as compared to conventional non-ligand exchanged methods yielding an absolute improvement in device efficiency of 2.8%. Hybrid ligand exchange nanoparticle-based devices reached total-area power conversion efficiencies of 12.0%.</p> <p>While extremely effective in ligand removal, ligand exchange pathways increase process complexity and solvent usage substantially, which may limit the cost advantage solution processing aims to provide. Further synthesis improvement was developed through a ligand exchange free, direct sulfide capped strategy. Using sulfolane as a benign solvent, CuInS₂ nanoparticles with thermally degradable thioacetamide ligands were synthesized using thermal decomposition of isolated metal thiolates from Cu₂S and In precursors. Through gentle thermal treatment, these ligands decomposed into non-contaminating gaseous byproducts leaving carbon free nanoparticle films without the need for ligand exchange.</p> <p>With the development of virtually contamination free colloidal nanoparticle inks, focus was shifted to scalability using slot die coating. Unlike typical lab-scale coating techniques such as spin coating, slot die coating is a widely used industrial coating technique with nearly 100% materials utilization, and high throughput roll-to-roll compatibility. A custom lab-scale slot-die coater was used to rapidly proof coating conditions, which were rapidly analyzed for uniformity using absorbance scanning in conjunction with profilometry. A cosolvent chlorobenzene/dichlorobenzene ink was developed to yield highly uniform, crack free thin films from non-ligand-exchanged Cu(In,Ga)S₂ nanoparticles, which were finished into devices with champion total are efficiencies of 10.7%. To the best of our knowledge, this represents the first report of slot die coated Cu(In,Ga)(S,Se)₂ photovoltaics. The methods presented in this work offer a pathway towards low impurity, high efficiency, scalable solution processed Cu(In,Ga)(S,Se)₂ photovoltaics to enable low cost renewable energy.</p>

In the last 20 years there has been a number of synthetic and natural product based molecular replicators published in the literature. The majority of these systems have focused on the minimal model with only a few examples of cross-catalytic or reciprocal replication. Of the cross-catalytic systems investigated the majority focus around the use of natural products, oligonucleotides, peptides etc. This thesis will investigate the design, synthesis and kinetic analysis of both synthetic minimal and reciprocal replicating systems, and how these two forms of replication interact in a complex hypercyclic network. Chapter 1 introduces key concepts such as molecular recognition, intramolecularity/ enzyme kinetic, bisubstrate systems and the work conducted into replication systems to date. Chapter 2 describes the design, synthesis and kinetic analysis of a reciprocal replicating system, based on Diels-Alder and 1,3-dipolar cycloadditions, before going on to discuss what we have learned and how this system can be improved. Chapter 3 focuses on the design, synthesis and kinetic analysis of a replicating network (minimal and reciprocal replication), based on 1,3-dipolar cycloadditions. Initial individual systems are examined in isolation to determine their behavior and nature. After which the systems are combined to observe how each species interacts in a potential complex hypercyclic network. Chapter 4 investigates the redesign of the replicating network in Chapter 3 in order to overcome the problems identified from its kinetic analysis. Chapter 5 introduces the shift in direction away from kinetically controlled replicating networks towards systems in thermodynamic equilibrium.

Im Rahmen der vorliegenden Arbeit wurde eine Auswertemethodik für anomale Röntgenkleinwinkelstreuung (ASAXS) zur nanochemischen Zusammensetzungsanalyse der beteiligten Phasen eines Probensystems entwickelt und auf eine Glaskeramik angewendet. Die nanochemische Analyse unterscheidet sich von den bekannten Verfahren der partiellen Strukturfaktoren bzw. -funktionen (PSF) durch die Anwendbarkeit auf nahezu jedes Probensystem, da keine einschränkenden Annahmen bezüglich der anomalen Korrekturfaktoren der atomaren Streufaktoren der einzelnen Elemente getroffen werden müssen. Im Gegensatz zu den üblicherweise verwendeten PSF''s werden die relevanten Probeneigenschaften, d.h. die Nanostruktur und die nanochemische Zusammensetzung, direkt aus den Verläufen der differenziellen Streuquerschnitte in Abhängigkeit von der Röntgenenergie und des Streuvektorbetrages bestimmt. Es wurden umfangreiche anomale Röntgenkleinwinkelstreuexperimente an einer ausgewählten Oxyfluorid-Glaskeramik durchgeführt und mit der entwickelten Methode analysiert. Die untersuchte Glaskeramik, welche mit den seltenen Lanthanoiden Erbium und Ytterbium dotiert ist, zeigt die nichtlineare optische Eigenschaft der Frequenzerhöhung. Es konnte gezeigt werden, dass es möglich ist, die gemittelte Zusammensetzung der Teilchenphase und die der amorphen Glasmatrix mittels ASAXS quantitativ zu bestimmen. Im Gegensatz zu EDX-Studien liefert ASAXS gemittelte Zusammensetzungen, die das Probensystem aus statistischer Sicht besser repräsentieren. Die nanochemische Zusammensetzungsanalyse der Glaskeramik lieferte das Ergebnis, dass das Cadmium kein Bestandteil der Nanopartikelphase ist, die eine gemittelte Zusammensetzung von 17%Pb 2%Er 17%Yb 64%F (at%) aufweist. TEM-Studien implizieren, dass die Nanopartikel im Glas näherungsweise als Rotationsellipsoide beschrieben werden können. Es wurde gezeigt, dass die Streukurven der ASAXS Studien mit einem solchen Strukturmodell modelliert werden können. / In the present work an evaluation method for anomalous small-angle X-ray scattering (ASAXS) to analyze nanochemical compositions of all involved phases of a sample has been developed and was applied to a glass ceramic. The nanochemical analysis differs from the known methods of partial structure factors or functions (PSF) by the applicability to virtually any system, because the new evaluation method does not require any limiting assumptions regarding the anomalous corrections of the atomic scattering factors of the individual elements. Unlike the PSF''s normally used, the relevant sample properties, i.e. nanostructure and nanochemical compostion, will be determined directly from the differential scattering cross sections as a function of the X-ray energy and the scattering vector. Extensive ASAXS experiments at a selected oxyfluoride glass ceramic were done and analyzed by the developed method. The investigated glass ceramic, which is co-doped with selected lanthanides like erbium and ytterbium, shows the nonlinear optical property of frequency upconversion. It was shown that it is possible to determine quantitatively the average compositions of all phases of a system using ASAXS. In contrast to EDX studies, ASAXS provides average compositions, which represent the sample better from a statistical point of view. The nanochemical composition analysis of the glass ceramic yielded the result that the cadmium is not part of the nanoparticle phase, which has an average composition of 17%Pb 2%Er 17%Yb 64%F (at%). TEM studies imply that the nanoparticles in the glass can be described by ellipsoids. It was shown that the scattering curves of the ASAXS studies can be simulated by such a structural model.

Thesis (M.S.)--Mississippi State University. Department of Chemistry. / Title from title screen. Includes bibliographical references.

Thesis (Ph.D.) -- Mississippi State University. Department of Chemistry. / Title from title screen. Includes bibliographical references.

The design, modeling, fabrication, and validation of an optical magnetic response in dielectric-based metamaterials are studied. These metamaterials consist of either periodic or random arrays of dielectric particle inclusions, which may be spheres, coated spheres, or completely randomly shaped. It is demonstrated that because of the simple particle shapes and dielectric materials, these metamaterials are quite easy and feasible to implement in a bulk, three-dimensional sample, and the response is isotropic. This in is contrast to other predominant designs of optical metamaterials, which are planar and anisotropic arrays of complicated metallic fishnet or split-ring resonator structures, which require stringent tolerances and sophisticated assembly. It is shown that SiC is one of many materials from which such infrared magnetic metamaterials can be constructed. A simple SiC powder is used to verify these claims. The milled micropowder of crystalline SiC is comprised of particles of random shapes and sizes. A model of the electromagnetic response of such powders is developed, whereby the induced magnetic dipole response is modeled by equivalently-sized spheres of SiC, whereas the electric dipole response is modeled by a continuous distribution of ellipsoidal particles. Infrared spectroscopic measurements and numerical calculations are performed, verifying both the magnetic and electric response of the powder. A alternate approach is also described, where uniform SiC microspheres are fabricated using more sophisticated nanochemical techniques. In the final portion of the dissertation, the mutual near-field coupling between ideal magnetic dipoles induced in dielectric spheres is studied. This is implemented for microwave frequencies using large permittivity ceramic spheres. An approximate coupled dipole model of the multiple scattering among the spheres is developed, and a transition matrix method is implemented to calculate the exact scattering by the clusters. Experimental measurements are performed, confirming the two models. The results for pairs, chains, and rings of spheres indicates that the magnetic dipole modes hybridize in analogy to atomic bonding. A notable result is that certain hybridized magnetic dipole modes may have a net electric dipole moment. The similarity to atomic and molecular bonding should prove useful in conceptualizing and designing more sophisticated metamaterials.

The design, modeling, fabrication, and validation of an optical magnetic response in dielectric-based metamaterials are studied. These metamaterials consist of either periodic or random arrays of dielectric particle inclusions, which may be spheres, coated spheres, or completely randomly shaped. It is demonstrated that because of the simple particle shapes and dielectric materials, these metamaterials are quite easy and feasible to implement in a bulk, three-dimensional sample, and the response is isotropic. This in is contrast to other predominant designs of optical metamaterials, which are planar and anisotropic arrays of complicated metallic fishnet or split-ring resonator structures, which require stringent tolerances and sophisticated assembly. It is shown that SiC is one of many materials from which such infrared magnetic metamaterials can be constructed. A simple SiC powder is used to verify these claims. The milled micropowder of crystalline SiC is comprised of particles of random shapes and sizes. A model of the electromagnetic response of such powders is developed, whereby the induced magnetic dipole response is modeled by equivalently-sized spheres of SiC, whereas the electric dipole response is modeled by a continuous distribution of ellipsoidal particles. Infrared spectroscopic measurements and numerical calculations are performed, verifying both the magnetic and electric response of the powder. A alternate approach is also described, where uniform SiC microspheres are fabricated using more sophisticated nanochemical techniques. In the final portion of the dissertation, the mutual near-field coupling between ideal magnetic dipoles induced in dielectric spheres is studied. This is implemented for microwave frequencies using large permittivity ceramic spheres. An approximate coupled dipole model of the multiple scattering among the spheres is developed, and a transition matrix method is implemented to calculate the exact scattering by the clusters. Experimental measurements are performed, confirming the two models. The results for pairs, chains, and rings of spheres indicates that the magnetic dipole modes hybridize in analogy to atomic bonding. A notable result is that certain hybridized magnetic dipole modes may have a net electric dipole moment. The similarity to atomic and molecular bonding should prove useful in conceptualizing and designing more sophisticated metamaterials.

Submitted by Marco Antonio Oliveira da Silva (maosilva@ipen.br) on 2016-08-25T17:43:02Z No. of bitstreams: 0 / Made available in DSpace on 2016-08-25T17:43:02Z (GMT). No. of bitstreams: 0 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Nesse trabalho foi proposto investigar a estabilidade de fases do sistema zircônia-escândia (ScSZ) por meio do estudo termodinâmico de nanopartículas, na faixa de 0 a 20% em mol de Sc2O3, e a partir da introdução de um segundo aditivo (Dy2O3 e Nb2O5) ao ZrO2 contendo 10% em mol de Sc2O3 (10ScSZ). A estabilidade de fases do ScSZ foi avaliada com base em dados termodinâmicos determinados pelas técnicas de microcalorimetria de adsorção de água e calorimetria de dissolução à alta temperatura. As soluções sólidas foram sintetizadas pelo método de coprecipitação de hidróxidos. Dados termodinâmicos foram determinados para as formas polimórficas encontradas (monoclínica, tetragonal, cúbica, romboédrica &beta; e &gamma;) por difração de raios X no ScSZ. Esse trabalho resultou no diagrama de fases em nanoescala de tamanho de partícula-composição. Os efeitos produzidos pela introdução de aditivos na matriz de 10ScSZ foram investigados visando obter a possível estabilização da estrutura cúbica (c) e a supressão da transformação de fase c-&beta;, característica do sistema binário. As composições foram sintetizadas por coprecipitação de hidróxidos e por reações em estado sólido para fins comparativos. Os materiais foram sinterizados convencionalmente e por sinterização assistida por campo elétrico. A estabilização completa da fase cúbica ocorreu a partir de teores molares de 1% de Dy2O3 e 0,5% de Nb2O5. O menor teor de Nb2O5 necessário para a estabilização da fase foi atribuído à provável formação da fase líquida durante a sinterização e ao menor tamanho do íon Nb5+. Os resultados de difratometria de raios X em alta temperatura e análise térmica mostraram que houve supressão da transição c-&beta;. As amostras contendo 0,5% mol de Nb2O5 apresentaram valores de condutividade iônica similares aos do 10ScSZ sem aditivos em uma ampla faixa de temperatura com elevada estabilidade em um período de 170 h a 600 °C. / Tese (Doutorado em Tecnologia Nuclear) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP / FAPESP: 12/03319-5