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Während die Menschheit bereits seit Jahrtausenden von der Brillanz von Gold und Silber im ausgedehnten Zustand fasziniert ist, bestechen ihre nanoskaligen Gegenstücke mit ihren wundervollen Farben und ihrer breiten Farbpalette. Motiviert durch diese Farben versuchten Wissenschaftler das zugrundeliegende Phänomen dieser Farben, die lokalisierte Oberflächenplasmonenresonanz, zu verstehen, was den Grundstein der Forschung im Bereich Plasmonik legte. Für die Anwendung muss diese lokalisierte Oberflächenplasmonenresonanz umfassend durch Änderung von Material, Größe, Form, Anordnung und Umgebung der Nanopartikel angepasst werden. Es scheint unausweichlich, dass dieser komplexe Parameterraum nur durch die Anwendung von künstlicher Intelligenz verstanden werden kann und die Eigenschaften von solchen komplexen Strukturen — in isolierten oder gekoppelten Strukturen — angepasst werden können. Diese Dissertation untersucht die Anpassung der Plasmonenresonanz in isolierten und gekoppelten Nanostrukturen durch Kombination von Kolloidsynthese, Anordnung und künstlicher Intelligenz. Der erste Teil behandelt die Synthese von Goldnanopartikeln mit Unterstützung des maschinellen Lernens. Durch die Nutzung von baumbasierten Lernalgorithmen wird die Wichtigkeit von bestimmten Syntheseparametern und dessen Auswirkungen auf die finalen Eigenschaften der synthetisierten Nanopartikel beleuchtet. Dabei wird gezeigt, dass der Algorithmus die zugrundeliegenden Chemiekonzepte der Synthese lernen kann, ohne sie explizit zu lehren, sondern ausschließlich durch das Lernen der Synthese- und Charakterisierungsdaten. Der zweite Teil fokussiert sich auf die Anordnung und die optische Charakterisierung von heterogenen Ketten aus Gold- und Silbernanopartikeln. Dabei wird gezeigt, dass nahezu jede Konfiguration bis zu einer Länge von 17 auf einem Quadratzentimeter durch Beschränkungsanordnung angeordnet werden können. Dies löst die synthetische Herausforderung des exponentiell wachsenden Parameterraums, der durch die Einführung eines zweiten Bausteins in der Kette eröffnet wurde. Allerdings ist die Charakterisierung zeitaufwändig und daher für die enorme Menge an Konfigurationen nicht realisierbar. Infolgedessen können elektrodynamische Simulationen hier helfen und diese Lücke schließen. Leider sind diese Simulationen durch ihre Berechnungskomplexität beschränkt, was jedoch durch den Einsatz von rekurrenten neuronalen Netzen im letzten Teil der Dissertation abgemildert wird. Letztlich zeigt diese Dissertation wie innovative Zugänge zu diesen Herausforderungen die Synthese, Charakterisierung und Verständnis von plasmonischen Nanostrukturen ermöglichen und wie die Plasmonenresonanz in Bezug zu ihren Anwendungen angepasst werden kann. / While the brilliance of gold and silver has fascinated humankind for millennia in their bulk state, their nanoscale counterparts captivate with their beautiful colors and broad color range. Motivated by these colors, researchers pursued to understand the underlying phenomenon of these colors, the localized surface plasmon resonance, which sparked the research in the field of plasmonics. In order to be useful, this localized surface plasmon resonance needs to be extensively engineered by variation of material, size, shape, arrangement, and surrounding of the nanoparticles. To explore this complex parameter space, the use of the emerging technology of artificial intelligence seems inevitable to understand and engineer the properties of such complex structures — either in isolated or coupled structures. This thesis investigates the plasmon resonance engineering in isolated and coupled nanostructures by combining colloidal synthesis, assembly, and artificial intelligence. The first part covers the machine learning assisted synthesis of gold nanoparticles, which aims to use tree-based learning algorithms to elucidate the importance of certain synthesis parameters and how they affect the final characteristics of the synthesized nanoparticles. It is shown that the algorithm can learn the underlying concepts of the chemistry of the synthesis without explicitly teaching the algorithm, but purely learning from data that was gathered during synthesis and characterization. The second part focuses on the assembly and optical characterization of heterogeneous chains composed of gold and silver nanospheres. Applying confinement assembly, virtually any configuration up to a length of 17 can be assembled on a square centimeter, which solves the synthetic challenge that is imposed by the exponentially growing configuration space due to the introduction of a second building block in the chain. However, characterization is time-consuming and therefore not feasible for vast amounts of configurations, thus only a tiny subsample is selected for electromagnetic characterization. Consequently, electrodynamicsimulations aid this task and try to fill the gap. Unfortunately, these simulations are limited by computational complexity; however, the use of recurrent neural networks enables to mitigate this problem, as shown in the final part of this thesis. In the end, this thesis showcases how innovative approaches to these challenges can enable the synthesis, characterization, and understanding of plasmonic nanostructures and how they can be used to engineer the plasmonic resonance in accordance with their desired applications.

Ionic self-assembled multilayers (ISAMs) can be formed by alternately dipping a substrate in anionic and cationic polyelectrolytes. Each immersion deposits a monolayer via electrostatic attraction, allowing for nanometer-scale control over film thickness. Additionally, ISAM films can be applied to arbitrary substrate geometries and can easily incorporate a variety of polymers and nanoscale organic or inorganic inclusions. The ISAM technique was used to tune and functionalize a rapid, sensitive fiber optic biosensor for textit{Brucella}, a family of bacteria that are detrimental to livestock and can also infect humans. The sensor was based on a turn-around point long period fiber grating (TAP-LPG). Unlike conventional LPGs, in which the attenuation peaks shift wavelength in response to environmental changes, TAP-LPGs have a highly sensitive single wavelength peak with variable attenuation. ISAMs were applied to a TAP-LPG to tune it to maximum sensitivity and to facilitate cross-linking of receptor molecules. Biotin and streptavidin were used to attach biotinylated hybridization probes specific to distinct species of textit{Brucella}. The sensor was then exposed to lysed cell cultures and tissue samples in order to evaluate its performance. The best results were obtained when using samples from textit{Brucella} infected mice, which produced a transmission change of 6.0 ± 1.4% for positive controls and 0.5 ± 2.0% for negative controls. While the sensor was able to distinguish between positive and negative samples, the relatively short dynamic range of the available fiber limited its performance. Attempts to fabricate new TAP-LPGs using a CO2 laser were unsuccessful due to poor laser stability. A second application of the ISAM technique was as a source of second-harmonic generation (SHG). SHG is a nonlinear optical process in which light is instantaneously converted to half its wavelength in the presence of intense electric fields. Localized surface plasmons (LSPs) in metal nanoparticles produce strong electric field enhancements, especially at sharp tips and edges, that can be used to increase SHG. Colloidally grown silver nanoprisms were deposited onto nonlinear ISAM films and conversion of 1064 nm Nd:YAG radiation to its 532 nm second-harmonic was observed. Little enhancement was observed when using nanoprisms with LSP resonance near 1064 nm due to their large size and low concentration. When using shorter wavelength nanoprisms, enhancements of up to 35 times were observed when they were applied by immersion, and up to 1380 times when concentrated nanoprisms were applied via dropcasting at high enough densities to broaden their extinction peak towards the excitation wavelength. A maximum enhancement of 2368 times was obtained when concentrated silver nanoprisms with LSP resonance around 900 nm were spincast with an additional layer of PCBS. / Doctor of Philosophy / Polyelectrolytes are long molecules composed of chains of charged monomers. When a substrate with a net surface charge is dipped into an oppositely charged polyelectrolyte solution, a single layer of molecules will be electrostatically deposited onto the substrate. Because the surface charge now appears to match the charge of the solution, no further deposition occurs. However, the process can be repeated by rinsing the substrate and immersing in a solution with the opposite charge. This technique forms ionic self-assembled multilayers (ISAMs), which can be assembled with nanometer-level control over thickness. The flexibility of polymer chemistry allows ISAMs to be formed from polyelectrolytes with a wide variety of properties. Additionally, the technique can easily incorporate other nanoscale materials, such as nanoparticles, clay platelets, and biological molecules, and has been investigated for applications ranging from dye-sensitized organic solar cells to drug delivery and medical implant coatings. This dissertation presents two applications of ISAM films. In one, ISAM films were used to tune and functionalize an optical biosensor for Brucella. Brucellosis primarily infects livestock, in which it causes significant reproductive problems leading to economic losses, but can also cause flu-like symptoms and more serious complications in humans. A rapid, sensitive test for Brucella is required to monitor herds and adjacent wild carriers, such as elk and bison. Optical biosensors, which operate by detecting changes due to the interaction between light and the stimulus, could satisfy this need. Long period fiber gratings (LPGs) are periodic modulations induced in the core of an optical fiber that cause transmitted light to be scattered at a resonant wavelength, resulting in attenuation. Conventional LPGs respond to changes in strain, temperature, or external refractive index by shifting their resonant wavelength. When special conditions are met, an LPG may exhibit a turn-around point (TAP), where dual peaks coalesce into a single peak with a constant wavelength but variable attenuation depth. TAP-LPGs are more sensitive than ordinary LPGs, and could be developed into inexpensive sensors with single-wavelength light sources and detectors. In this work, ISAMs were deposited onto an LPG to tune it near its TAP. Segments of single-stranded DNA, called hybridization probes, that were specific to individual species of Brucella were attached to the ISAM film before the sensor was exposed to lysed bacterial cultures. It was found that the sensor could distinguish between Brucella and other types of bacteria, but was less successful at distinguishing between Brucella species. The project was limited by the available TAP-LPGs, which had less dynamic range than those used in prior work by this group. Attempts were made to establish a new supply of TAP-LPGs by fabrication with a CO2 laser, but these efforts were unsuccessful due to poor laser stability. The second project discussed in this dissertation investigated ISAM films as a source of second-harmonic generation (SHG), a nonlinear optical process in which light is converted to half its fundamental wavelength in the presence of intense electric fields. Nonlinear ISAMs were constructed by choosing a polyelectrolyte with a hyperpolarizable side group in which SHG can occur. The SHG efficiency was increased by factors of several hundred to several thousand by the addition of silver nanoprisms. Metal nanoparticles can produce strong electric field enhancements, especially at their tips and edges, when incident light causes resonant collective oscillations in their electrons called localized surface plasmons (LSPs). It was found that while silver nanoprisms whose LSP resonant wavelength matched the fundamental wavelength were too dilute to produce noticeable enhancement, better results could be obtained by depositing shorter wavelength nanoprisms at sufficient density to broaden their extinction peak via interparticle interactions. The best enhancement observed was for a sample where concentrated silver nanoprisms with LSP resonance around 900 nm were dropcast onto an ISAM film and coated with an additional polymer layer, resulting in 2368 times more SHG than the plain ISAM film.

Non-invasive and continuous spatiotemporal pathogen monitoring at biological interfaces (e.g., human tissue) holds promise for transformative applications in personalized healthcare (e.g., wound infection monitoring) and environmental surveillance (e.g., airborne virus surveillance). Despite notable progress, current receptor-based biosensors encounter inherent limitations, including inadequate long-term performance, restricted spatial resolutions and length scales, and challenges in obtaining multianalyte information. Surface-enhanced Raman spectroscopy (SERS) has emerged as a robust analytical method, merging the molecular specificity of Raman spectroscopy's vibrational fingerprinting with the enhanced detection sensitivity from strong light-matter interaction in plasmonic nanostructures. As a receptor-free and noninvasive detection tool capable of capturing multianalyte chemical information, SERS holds the potential to actualize bio-interfaced spatiotemporal pathogen monitoring. Nonetheless, several challenges must be addressed before practical adoption, including the development of plasmonic bio-interfaces, sensitive capture of multianalyte information from pathogens, regeneration of nanogap hotspots for long-term sensing, and extraction of meaningful information from spatiotemporal SERS datasets. This dissertation tackles these fundamental challenges. Plasmonic bio-interfaces were created using innovative nanoimprint lithography-based scalable nanofabrication methods for reliable bio-interfaced spatiotemporal measurements. These plasmonic bio-interfaces feature sensitive, dense, and uniformly distributed plasmonic transducers (e.g., plasmonic nano dome arrays, optically-coupled plasmonic nanodome and nanohole arrays, self-assembled nanoparticle micro patches) on ultra-flexible and porous platforms (e.g., biomimetic polymeric meshes, textiles). Using these plasmonic bio-interfaces, advancements were made in SERS signal transduction, machine-learning-enabled data analysis, and sensor regeneration. Large-area multianalyte spatiotemporal monitoring of bacterial biofilm components and pH was demonstrated in in-vitro biofilm models, crucial for wound biofilm diagnostics. Additionally, novel approaches for sensitive virus detection were introduced, including monitoring spectral changes during viral infection in living biofilms and direct detection of decomposed viral components. Spatiotemporal SERS datasets were analyzed using unsupervised machine-learning methods to extract biologically relevant spatiotemporal information and supervised machine-learning tools to classify and predict biological outcomes. Finally, a sensor regeneration method based on plasmon-induced nanocavitation was developed to enable long-term continuous detection in protein-rich backgrounds. Through continuous implementation of spatiotemporal SERS signal transduction, machine-learning-enabled data analysis, and sensor regeneration in a closed loop, our solution has the potential to enable spatiotemporal pathogen monitoring at the bio-interface. / Doctor of Philosophy / Continuous monitoring of pathogens within our bodies and surrounding environments is indispensable for various applications in personalized healthcare (e.g., monitoring wound infections) and environmental surveillance (e.g., airborne virus tracking). To accomplish this, we require sensors capable of seamlessly interfacing with biological systems, such as human tissue, and consistently providing pathogen-related information (e.g., spatial location and pathogen type) over prolonged periods. Our research relies on Surface-enhanced Raman spectroscopy (SERS) to address this challenge. SERS enables noninvasive sensing by providing unique fingerprints of molecules near the sensor's surface. SERS holds the potential to enable bio-interfaced spatiotemporal pathogen monitoring, but several challenges must be tackled before practical adoption. In this dissertation, we address various fundamental challenges in SERS, including constructing SERS devices that can seamlessly interface with biological systems while maintaining performance, sensitively capturing pathogen-related information, extracting meaningful insights from SERS datasets, and continuously regenerating the sensor surface to ensure long-term performance. We developed SERS devices capable of seamlessly interfacing with biological systems using innovative scalable nanofabrication methods. These devices contain sensitive, dense, and uniformly distributed SERS sensors on flexible and porous platforms, such as polymeric scaffolds and textiles. Leveraging these SERS devices, we made advancements in pathogen sensing, data analysis, and sensor regeneration. We demonstrated large-area spatiotemporal monitoring of biofilm components and pH in lab-grown biofilm models, critical for wound biofilm diagnostics. Additionally, we introduced novel approaches for sensitive virus detection, including monitoring changes in SERS signals during viral infection in living biofilms and directly detecting decomposed viral components. The SERS datasets were analyzed using machine learning models to extract biologically relevant spatial and temporal information, such as the spatial location of pathogen components and the temporal stage of pathogen growth, and to predict biological outcomes. Finally, we developed a sensor regeneration method to enable long-term continuous detection in complex backgrounds, such as blood. By continuously performing spatiotemporal pathogen sensing, data analysis, and sensor regeneration in a closed loop, our solution has the potential to realize bio-interfaced spatiotemporal pathogen monitoring.

El silicio es la plataforma más prometedora para la integración fotónica, asegurando la compatibilidad con los procesos de fabricación CMOS y la producción en masa de dispositivos a bajo coste. Durante las últimas décadas, la tecnología fotónica basada en la plataforma de silicio ha mostrado un gran crecimiento, desarrollando diferentes tipos de dispositivos ópticos de alto rendimiento. Una de las posibilidades para continuar mejorando las prestaciones de los dispositivos fotónicos es mediante la combinación con otras tecnologías como la plasmónica o con nuevos materiales con propiedades excepcionales y compatibilidad CMOS. Las tecnologías híbridas pueden superar las limitaciones de la tecnología de silicio, dando lugar a nuevos dispositivos capaces de superar las prestaciones de sus homólogos electrónicos. La tecnología híbrida dióxido de vanadio/ silicio permite el desarrollo de dispositivos de altas prestaciones, con gran ancho de banda, mayor velocidad de operación y mayor eficiencia energética con dimensiones de la escala de la longitud de onda. El objetivo principal de esta tesis ha sido la propuesta y desarrollo de dispositivos fotónicos de altas prestaciones para aplicaciones de conmutación. En este contexto, diferentes estructuras basadas en silicio, tecnología plasmónica y las propiedades sintonizables del dióxido de vanadio han sido investigadas para controlar la polarización de la luz y para desarrollar otras funcionalidades electro-ópticas como la modulación. / Silicon is the most promising platform for photonic integration, ensuring CMOS fabrication compatibility and mass production of cost-effective devices. During the last decades, photonic technology based on the Silicon on Insulator (SOI) platform has shown a great evolution, developing different sorts of high performance optical devices. One way to continue improving the performance of photonic optical devices is the combination of the silicon platform with another technologies like plasmonics or CMOS compatible materials with unique properties. Hybrid technologies can overcome the current limits of the silicon technology and develop new devices exceeding the performance metrics of its counterparts electronic devices. The vanadium dioxide/silicon hybrid technology allows the development of new high-performance devices with broadband performance, faster operating speed and energy efficient optical response with wavelength-scale device dimensions. The main goal of this thesis has been the proposal and development of high performance photonic devices for switching applications. In this context, different structures, based on silicon, plasmonics and the tunable properties of vanadium dioxide, have been investigated to control the polarization of light and for enabling other electro-optical functionalities, like optical modulation. / El silici és la plataforma més prometedora per a la integració fotònica, assegurant la compatibilitat amb els processos de fabricació CMOS i la producció en massa de dispositius a baix cost. Durant les últimes dècades, la tecnologia fotònica basada en la plataforma de silici ha mostrat un gran creixement, desenvolupant diferents tipus de dispositius òptics d'alt rendiment. Una de les possibilitats per a continuar millorant el rendiment dels dispositius fotònics és per mitjà de la combinació amb altres tecnologies com la plasmònica o amb nous materials amb propietats excepcionals i compatibilitat CMOS. Les tecnologies híbrides poden superar les limitacions de la tecnologia de silici, donant lloc a nous dispositius capaços de superar el rendiment dels seus homòlegs electrònics. La tecnologia híbrida diòxid de vanadi/silici permet el desenvolupament de dispositius d'alt rendiment, amb gran ample de banda, major velocitat d'operació i major eficiència energètica en l'escala de la longitud d'ona. L'objectiu principal d'esta tesi ha sigut la proposta i desenvolupament de dispositius fotònics d'alt rendiment per a aplicacions de commutació. En este context, diferents estructures basades en silici, tecnologia plasmònica i les propietats sintonitzables del diòxid de vanadi han sigut investigades per a controlar la polarització de la llum i per a desenvolupar altres funcionalitats electró-òptiques com la modulació. / Sánchez Diana, LD. (2016). High performance photonic devices for switching applications in silicon photonics [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/77150

In dieser Arbeit werden die nichtlokalen sowie nichtlinearen Eigenschaften plasmonischer Nanopartikel behandelt, wie sie im hydrodynamischen Modell enthalten sind. Das hydrodynamische Materialmodell stellt eine Erweiterung des Drude Modells dar, in der Korrekturen in der Beschreibung des Elektronenplasmas berücksichtigt werden. Einer ausführlichen Einführung des Materialmodells folgt eine analytische Diskussion der Auswirkungen der Nichtlokalität am Beispiel eines einzelnen Zylinders. Hierbei werden die durch die Nichtlokalität herbeigeführten Frequenzverschiebungen in den Streu- und Absorptionsspektren quantifiziert und asymptotisch behandelt. Des Weiteren wird mit Hilfe einer konformen Abbildung das Problem eines zylindrischen Dimers in der Elektrostatischen Näherung gelöst und die Moden der Struktur bestimmt. Diese Untersuchungen dienen als maßgebliche Grundlage für weiterführende numerische Studien die mit der diskontinuierlichen Galerkin Zeitraummethode durchgeführt werden. Die durch die analytischen Betrachtungen gewonnene Kenntnis der Moden ermöglicht es, im Zusammenhang mit gruppentheoretischen Betrachtungen und numerischen Untersuchungen, rigorose Auswahlregeln für die Anregung der Moden durch lineare und nichtlineare Prozesse aufzustellen. In weiterführenden numerischen Simulationen werden außerdem Strukturen niedrigerer Symmetrie, auf die sich die Auswahlregeln übertragen lassen, untersucht. Zudem werden numerische Studien präsentiert in denen der Einfluss der Nichtlokalität auf Feldüberhöhungen in Dimeren und doppel-resonantes Verhalten (es liegt sowohl bei der Frequenz des eingestrahlten Lichtes als auch bei der zweiten harmonischen eine Resonanz vor) untersucht werden. / This thesis deals with the nonlocal and nonlinear properties of plasmonic nanoparticles, as described by the hydrodynamic model. The hydrodynamic material model represents an extension of the Drude model that contains corrections to the descriptions of the electron plasma. After a thorough derivation of the material model, analytical discussions of nonlocality are presented for the example of a single cylinder. The frequency shifts in the scattering and absorption spectra are quantified and treated asymptotically. Furthermore, by applying a conformal map, the problem of a cylindrical dimer is solved in the electrostatic limit and the modes of the structure are determined. These investigations lay the foundations for numerical investigations which are performed employing the discontinuous Galerkin time domain method. The analytical knowledge of the modes, in conjunction with group theoretical considerations and numerical analysis, enables the formulation of rigorous selection rules for the excitation of modes by linear and nonlinear processes. In further numerical studies, the influence of nonlocality on the field enhancement in dimer structures and double-resonant behavior (a resonance is found at the frequency of the incoming light and at the second harmonic) are investigated.

Gegenstand der Untersuchungen dieser Arbeit ist die analytische und numerische Studie der plasmonischen Eigenschaften vorhanden in Silbernanodrähten von verschiedener horizontaler Geometrie aufgrund verschiedener Modelle der optischen Antwort der Leitungselektronen. Nach einer hierarchischen Anordnung von linearen Volumen-Materialmodellen, welche innerhalb der plasmonischen Literatur genutzt werden, untersuchen wir die Verwicklung von (nicht)lokaler und dispersiver Antwort mit geometrischen Parametern von Monomeren und Dimeren. Unsere analytischen Studien fokussieren sich auf einzelne zylindrische Drähte, wobei wir das Auftreten von Radius-abhängiger Dämpfung in lokalisierten Oberflächenplasmonen nachweisen, ähnlich dem Konzept der begrenzten mittleren freien Weglänge diskutiert von Kreibig und Mitarbeitern. Weiterhin wird ein Streuproblem mit transversaler Nichtlokalität und "No-slip"- Randbedingung gelöst, gefolgt von einer Diskussion einer Randbedingung, welche zwischen “No-Slip”- und “Slip”-Bedinung interpoliert. Aus numerischer Sicht wird die Streuung an abgerundeten und gleichseitigen dreieckigen und Bowtie-Drähten behandelt mit Fokus auf einer vollanalytischen Beschreibung der Eckenrundung mittels Bézier- Kurven. Dies enthüllt den Krümmungsradius als neuen geometrischen Parameter. Das Variieren der Lückenbreite und Eckenrundung führt zu Verstärkungsfaktoren, welche relevant für oberflächenverstärkte Raman-Streuung einzelner Moleküle sind, in ausgezeichneten räumlichen Bereichen abhängig von der Art der Resonanz. Innerhalb der Extinktionsspektren von dreieckigen und Bowtie-Drähten erscheint eine Sequenz von nichtlokalen Maxima. Diese Sequenz ist am sensitivsten in Bezug auf die Änderung der Krümmung. Die Identifikation der (Hybrid-)Resonanzen basiert auf simulierten Ladungsdichteverteilungen. / Subject of this thesis is the analytical and numerical study of the plasmonic properties present in silver nanowires of different horizontal geometries due to different models of optical response of conduction electrons. Following a hierarchical arrangement of linear bulk material models, used throughout the plasmonic literature, we investigate the intertwining of (non)local and dispersive response with geometrical parameters of monomers and dimers. Our analytical studies focus on single cylindrical wires, revealing the occurrence of radius-dependent damping of localized surface plasmons similar to the concept of limited-mean-free-path discussed by Kreibig and coworkers. Further, a scattering problem with transverse nonlocality and s no-slip condition is solved followed by a discussion of a boundary condition interpolating between the slip and no-slip conditions. On a numerical level, the scattering by rounded and equilateral triangular and bowtie nanowires is treated based on a full analytical description of the corner rounding via Bézier curves revealing the radius of curvature as a new geometrical degree of freedom. Tuning of gap size and corner rounding reveals enhancement factors relevant for surface-enhanced Raman scattering of single molecules in distinguished spatial domains dependent on the type of resonance. Within the extinction spectra a nonlocal peak sequence emerges. This sequence is most sensitive to curvature variations and arises in the triangular monomer and bowtie dimer. The identification of (hybrid) resonances is based on charge density simulations.

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.

Gegenstand der vorliegenden Dissertation ist die Untersuchung von einzelnen nano- und mikrometergroßen Partikeln, zum Verständnis und zur Entwicklung von neuartigen nanooptischen Elementen, wie Lichtquellen und Sensoren, sowie Strukturen zum Aufsammeln und Leiten von Licht. Neben der Charakterisierung stehen dabei verschiedene Methoden zur elektromagnetischen Manipulation im Vordergrund, die auf eine Kontrolle der Position oder der Geometrie der Partikel ausgerichtet sind. Die gezielten Manipulationen werden verwendet, um vorausgewählte Partikel zu isolieren, modifizieren und transferieren. Dadurch können Partikel zu komplexeren photonischen Systemen kombiniert werden, welche die Funktionalität der einzelnen Bestandteile übertreffen. Der Hauptteil der Arbeit behandelt Experimente mit freischwebenden Partikeln in linearen Paul-Fallen. Durch die räumliche Isolation im elektrodynamischen Quadrupolfeld können Partikel mit reduzierter Wechselwirkung untersucht werden. Neben der spektroskopischen Charakterisierung von optisch aktiven Partikeln (farbstoffdotierte Polystyrol-Nanokügelchen, Cluster aus Nanodiamanten mit Stickstoff-Fehlstellen-Zentren, Cluster aus kolloidalen Quantenpunkten) sowie optischen Resonatoren (plasmonische Silber-Nanodrähte, sphärische Siliziumdioxid-Mikroresonatoren) werden neu entwickelte Methoden zur Manipulation vorgestellt, mit denen sich individuelle Partikel freischwebend kombinieren und elektromagnetisch koppeln sowie aus der Falle auf optischen Fasern zur weiteren Untersuchung bzw. zur Funktionalisierung photonischer Strukturen ablegen lassen. In einem weiteren Teil der Arbeit wird eine Methode zur Manipulation der Geometrie von plasmonischen Nanopartikeln vorgestellt. Dabei werden einzelne Goldkugeln auf einem Deckglas mit einem fokussierten Laserstrahl zum Schmelzen gebracht und verformt. Durch die kontrollierte und reversible Veränderung der Symmetrie lassen sich die lokalisierten Oberflächenplasmonen des Partikels gezielt beeinflußen. / The topic of the present thesis is the investigation of single nano- and microsized particles for the understanding and design of novel nanooptical elements as light sources and sensors, as well as light collecting and guiding structures. In addition to particle characterization, the focus is on different methods for electromagnetic particle manipulation aimed at controlling the particle’s position or geometry. The specific manipulations are used for isolation, modification and transfer of preselected particles, enabling combination of particles into more complex photonic systems, which exceed the functionalities of the individual constituents. The main part of this work deals with experiments on levitated particles in linear Paul traps. Due to the spatial isolation in the electrodynamic quadrupole field, particles can be investigated with reduced environmental interaction. In addition to spectroscopic characterization of optically active particles (dye-doped polystyrene nanobeads, clusters of nanodiamonds with nitrogen vacancy defect centers, clusters of colloidal quantum dots) and particles with optical resonances (plasmonic silver nanowires, spherical silica microresonators) new manipulation methods are presented that enable assembly and electromagnetic coupling of individual, levitated particles as well as deposition of particles from the trap on optical fibers for further characterization or functionalization of photonic structures. In a further part of this work a method to manipulate the geometry of plasmonic nanoparticles is presented. Single gold nanospheres on a coverslip are melted and shaped with a focused laser beam. The localized surface plasmons can be influenced specifically by controlled and reversible changes of the particle symmetry.

La plasmonique est un domaine de la nano-photonique qui étudie le comportement de la lumière à des échelles sub-longueurs d'ondes en présence de métaux. Les plasmons polaritons de surface (SPPs) sont des modes électromagnétiques qui se propagent à l'interface entre un diélectrique et un métal. Les SPPs trouvent des applications dans plusieurs domaines comme la communication et le traitement tout-optique du signal, la spectroscopie, la détection en biologie et en chimie. De nombreux composants plasmoniques (modulateurs, coupleurs, détecteurs ...) ont été démontrés ces dernières années. Cependant, leur l'intégration reste conditionnée par l'absence d'un générateur compact (pompage électrique, dimensions réduites) et par les grandes pertes ohmiques. Les techniques standards de génération de SPs nécessitent l'alignement d'un laser externe sur un prisme ou un réseau de diffraction afin d'adapter le vecteur d'onde incident avec celui du plasmon. L'approche que nous avons choisie est basée sur l'utilisation de lasers à semiconducteur ayant une polarisation transverse magnétique (TM) comme source d'excitation et de gain. Notre approche, permet d'obtenir des dispositifs compacts et facilement intégrables sur puce. Pendant ma thèse j'ai étudié expérimentalement et numériquement les performances d'un laser en fonction rapprochement du contact métallique à sa région active. La proximité du gain optique au métal est nécessaire pour la réalisation de dispositifs plasmoniques actifs. J'ai démontré la génération et l'amplification des plasmons de surface dans la bande télécom (λ=1.3µm), avec des dispositifs compacts, à base de semiconducteurs, fonctionnant par injection électrique et à température ambiante. Notamment, j'ai réalisé une architecture élégante, avec coupleur intégré, pour la génération de SPPs accessibles sur le sommet du dispositif. Un dispositif avec gaine superficielle ultrafine a permis de démontrer un mode hybride plasmonique avec une fraction consistante de champ électrique à l'interface métal/semiconducteur. Finalement, j'ai montrée que la structuration nanométrique du contact métallique réduit les pertes du mode laser. Les résultats sont renforcés par une nouvelle technique de imagerie de champ proche (SNOM) qui a permis de mesurer les SPPs à l'interface métal/or et à l'interface métal/ semiconducteur. Grâce aux mesures SNOM, il a aussi été possible de démontrer sans aucune ambiguïté l'effet de la structuration du métal sur le mode optique. / The field of plasmonics is experiencing a rapid development, due to the interest in studying the behavior of light at the nanometer scale. Key ingredients of plasmonics are the surface plasmons (SPs), electromagnetic modes localized at the interface between a metal and a dielectric. SPs rely on the interaction between electromagnetic radiation and conduction electrons at metallic interfaces or in "small" metallic nanostructures. The recent intense activity on plasmonics has been also enabled by state-of-the-art nano fabrication techniques and by high-sensitivity optical characterization techniques. These tools pave the way to promising applications (integration in electronics, chemical and biological detection...), which exploit the SP peculiarity of confining optical fields over sub-wavelength mode volumes. The number of publications concerning plasmonics has been continuously increasing over the last twenty years giving rise to a dynamic research context. Several plasmonic devices have been demonstrated during the last years (modulators, couplers, detectors ...). However their integration is limited by the absence of a compact generator (electrical pumping, small dimensions) and by the huge ohmic losses. Standard techniques for surface plasmon polariton (SPP) generation need an external alignment with a laser source on a prism or on a grating. Our approach is based on semiconductor lasers sources with a transverse magnetic (TM) polarization. Therefore, it is possible to obtain compact semiconductor devices suitable for the on chip integration. During my thesis I studied experimentally and numerically the performance of a diode laser as a function of the metal distance from its active region. The proximity of the gain to the metal is necessary to realize active plasmonic devices. I demonstrated the generation and the amplification of SPP in the telecom range (λ=1.3µm) with compact semiconductor based devices, operating at room temperature and by electrical injection. I realized an elegant architecture with an integrated coupler grating for the SPP generation. The SPPs are directly accessible at the device surface. An ultra-thin cladding device allowed the demonstration of a hybrid plasmonic laser with a consistent fraction of electric field at the metal/semiconductor interface. Finally I demonstrated that the metal patterning allows a loss reduction, decreasing the laser threshold. The results are strengthened by a new near-field technique (NSOM) which permitted to measure the SPPs at the metal/air interface and at the metal/semiconductor interface. Thanks to the NSOM we showed unambiguously the effect of the metal patterning on the optical mode.