Plasmons, i.e. collective oscillations of conduction electrons, have a strong influence on the optical properties of metal micro- and nanostructures and are of great interest for novel photonic devices. Here, plasmons on metal-dielectric interfaces are investigated using near-field optical microscopy and differential angular reflectance spectroscopy. Emphasis is placed on the study of plasmon interaction with individual nanostructures and on the nonlinear process of surface plasmon amplification. Specifically, plasmon transmission across single grooves in thin silver films is investigated with the help of a near-field optical microscope. It is found that plasmon transmittance as a function of groove width shows a non-monotonic behavior, exhibiting certain favorable groove widths with strongly decreased transmittance values. Additionally, evidence of groove-mediated plasmon mode coupling is observed. Spatial beating due to different plasmon wave vectors produces distinct interference features in near-field optical images. A theoretical approach explains these observations and gives estimated coupling effciencies deduced from visibility considerations. Furthermore, stimulated emission of surface plasmons induced by optical pumping using an organic dye solution is demonstrated for the first time. For this a novel twin-attenuated-total-reflection scheme is introduced. The experiment is described by a theoretical model which exhibits very good agreement. Together they provide clear evidence of the claimed process.

Integrierte optoelektronische Anwendungen sind allgegenwärtig in moderner Technologie. Sie sind einerseits Schlüsselkomponenten in bekannten kommerziellen Produkten wie mobilen Geräten oder Flachbildschirmen, aber sie ermöglichen auch schnelle Netzwerke in Datenzentren. Um drängende Probleme im Zusammenhang mit dieser Technologie zu lösen, z.B. der hohe Energieverbrauch und die Verwendung und Rückgewinnung von seltenen Materialien, sucht die Forschung nach Alternativen. Insbesondere effiziente, nicht-lineare Prozesse werden benötigt, um Signale zu schalten. Einige vielversprechende Konzepte wurden in der Nanooptik vorgeschlagen. Diese basieren insbesondere auf plasmonischen Prozessen, die im Frequenzbereich von sichtbarem Licht stattfinden. Drei dieser Konzepte werden in dieser Arbeit diskutiert und untersucht. Teil 1 der Arbeit handelt von der konkreten Umsetzung eines Konzepts, das eine starke Interaktion zwischen einzelnen Quantenemittern und dem geführten Lichtfeld an metallischen Wellenleitern ausnutzt. Hierdurch können prinzipiell extrem schwache Lichtsignale zum Schalten verwendet werden. In Teil 2 wird die Miniaturisierung von Lasern untersucht. Kleine Lasersysteme finden schon heute Anwendungen in verschiedensten Bereichen der Optoelektronik. Diese Arbeit behandelt die kleinstmögliche Realisierung von Lasern, sogenannte Nanolaser, und untersucht deren Anwendbarkeit. Teil 3 widmet sich dem relativ neuen Materialsystem Graphen. In dieser Arbeit wird untersucht, in wie weit sich Graphen zur Manipulation von sichtbarem Licht verwenden lässt, beziehungsweise, in wie weit Graphen plasmonische Eigenschaften aufweist. Die Analyse der Konzepte liefert neue Erkenntnisse zu kontrovers diskutierten Themen bezüglich der Vorzüge und Nachteile der Miniaturisierung mit Hilfe der Plasmonik. Die Erkenntnisse geben des Weiteren klare Richtlinien zur Optimierung der Konzepte hin zu effizienteren und praktikableren Designs. / Integrated optoelectronic applications are omnipresent in modern technology. They are key constituents of familiar commercial products such as mobile devices and flat screens but also enable fast networks in data centers. In order to solve pressing problems induced by the technology, such as high power consumption and the use and recycling of rare materials, research tries to explore alternatives. In particular, there is a need for efficient, non-linear processes that could be employed for switching of signals. Some promising concepts have been proposed using nanooptics, especially based on plasmonic processes that take place at frequencies of visible light. Three of these concepts are discussed and investigated in this work. Part 1 of this work is about a concrete realization of a concept which makes use of a strong interaction between individual quantum emitters and guided light-fields of metallic waveguides. With this approach, in principle extremely weak light-signals can be sufficient for switching. In part 2 the miniaturization of lasers is investigated. Small laser-systems are already used today for a broad range of applications in optoelectronics. This works examines the smallest possible realization of lasers, so-called nanolasers, and investigates their applicability. Part 3 focuses on the relatively young material graphene. In this work it is investigated in which way graphene could be used for the manipulation of visible light, and accordingly, whether graphene features plasmonic properties. The analysis of these concepts provides new insights to controversial discussed topics with respect to the advantages and disadvantages of miniaturization with the help of plasmonics. Further, the findings give clear advice for the optimization of the concepts towards more efficient and practicable designs.

Hybride Nanostrukturen verbinden die Vorzüge von individuellen Materialien, die neue Eigenschaften hervorrufen können. In dieser Arbeit wurden verschiedene Metal Nanostrukturen synthetisiert und deren optische Eigenschaften analysiert. Die Herstellung eines Spasers oder Lichteinfang in Solarzellen wurde untersucht. Der Einfluß von Größe, Form und Brechungsindex auf die Metal-Plasmonen wurde erforscht. Die gewonnen Erkenntnisse genutzt um Metal Nanopartikel mit gezielten Eigenschaften herzustellen. Hybride Gold Nanostrukturen (funktionalisiert mit Farbstoffen oder Quantenpunkten) wurden hergestellt und Energie-Transfereffekte untersucht. Diese hybriden Nanostrukturen wurden optisch gepumpt um Spasing zu erreichen. Allerdings wurde festgestellt, dass eine unrealistisch hohe Verstärkung benötigen wird, um die charakteristischen Verluste im Metal zu überwinden. Silber und Gold Nanopartikel wurden synthetisiert um diese in Dünnschichtsolarzellen einzusetzen. Es konnte gezeigt werden, dass Silber chemisch instabil ist und, wenn oxidiert, hohe Absorption auftritt. Durch hohe Temperaturen konnte die Oxidschicht auf den Silberpartikeln reduziert werden und damit auch die Verluste. Stabilere Gold Partikel wurden in Perovskit-Solarzellen eingebaut, wodurch die Effizienz einer solch modifizierten Solarzelle um ~40% gesteigert werden konnte. Dies wurde durch eine erhöhte Anzahl an generierten Ladungsträgern mittels metallischen Lichtfallen erreicht. Zusätzlich wurden anisotrope Janus Trägerpartikel synthetisiert und mit Metal Nano-partikeln funktionalisiert. Gold Nanopartikel wurden abgeschieden und zu einer Gold Hülle gewachsen. Dies erfolgte entweder gleichförmig über das gesamte Hantel-Trägerpartikel oder einseitig unter Ausnutzung der chemischen Anisotropie. Desweiteren wurden Platin Nano-partikel einseitig abgeschieden und in Wasserstoffperoxid Lösung gegeben. Die Partikel wurden daraufhin mittels dynamischer Lichtstreuung auf Selbstvortrieb untersucht. / Hybrid nanostructures combine the assets of the individual materials with a vast amount of new properties. In this work various metal nanoparticles have been synthesized and investigated on their optical properties. The synthesized metal nanoparticles have been implemented for potential applications, e.g. fabrication of a spaser or in solar cells. At first, the size, shape and refractive index effects of gold and silver nanoparticles have been investigated. The insight gained helps to optimize the synthesis of metal nanoparticles with specific optical properties needed for further applications. Optimized hybrid gold nanostructures have been synthesized and functionalized with dye molecules or quantum dots to investigate energy transfer effects. These hybrid structures have been optically pumped to achieve spasing. However, comparison with a theory showed that such metal nanostructures need unrealistic high gain to overcome the inherent losses and achieve spasing. Silver and gold nanoparticles have been synthesized for applications in thin film solar cells. It has been shown that silver lacks chemical stability and thus, if oxidized, the nanoparticles exhibit weak scattering and strong Ohmic losses. The oxide layer of silver nano-spheres could be via annealing. By contrast, gold nanoparticles, known for their higher stability, have been implemented in a perovskite solar cell. Such a modified solar cell showed an increase in efficiency by ~40% through increased generation of carriers. Anisotropic Janus carrier systems have been synthesized and functionalized with metal nanoparticles. Gold nanoparticles have been deposited either uniformly or on one lobe only of the dumbbell-shaped carrier system by using its chemical anisotropy. These gold nano¬particles have been grown to a gold shell. Platinum nanoparticles have been deposited on a single lobe and its self-propelling ability in a chemical fuel was investigated by means of dynamic light scattering.

Plasmons, i.e. collective oscillations of conduction electrons, have a strong influence on the optical properties of metal micro- and nanostructures and are of great interest for novel photonic devices. Here, plasmons on metal-dielectric interfaces are investigated using near-field optical microscopy and differential angular reflectance spectroscopy. Emphasis is placed on the study of plasmon interaction with individual nanostructures and on the nonlinear process of surface plasmon amplification. Specifically, plasmon transmission across single grooves in thin silver films is investigated with the help of a near-field optical microscope. It is found that plasmon transmittance as a function of groove width shows a non-monotonic behavior, exhibiting certain favorable groove widths with strongly decreased transmittance values. Additionally, evidence of groove-mediated plasmon mode coupling is observed. Spatial beating due to different plasmon wave vectors produces distinct interference features in near-field optical images. A theoretical approach explains these observations and gives estimated coupling effciencies deduced from visibility considerations. Furthermore, stimulated emission of surface plasmons induced by optical pumping using an organic dye solution is demonstrated for the first time. For this a novel twin-attenuated-total-reflection scheme is introduced. The experiment is described by a theoretical model which exhibits very good agreement. Together they provide clear evidence of the claimed process.

Complex systems are ensembles of interconnected elements where mutual interaction and an optimized amount of disorder produce advanced functionalities. These systems are abundant in our daily experience: typical examples are the brain, biological ecosystems, society, and finance. In the last century, researchers have investigated the fundamental properties of disordered systems, unveiling fascinating and counterintuitive dynamics. The main aim of this Dissertation is the study of a new platform of disorder-enhanced photonics systems, denoted as Complex Metamaterials. Due to its ultrafast time scale nanophotonics represents an ideal framework to investigate and harness complex dynamics. Starting from the theoretical modeling of disordered plasmonic systems, I discuss advanced real-life applications, including the generation of highly-resistant structural colors from porous metal surfaces and the realization of early-stage cancer detectors based on surface roughness and self-similarity. In addition to the effects of structural disorder on plasmonic systems I also investigate the complex emission dynamics from non-conventional nanolasers. Lasers represent the quintessential example of a complex photonic system due to the simultaneous presence of strong nonlinearities and multi-mode interactions. At the same time, the integration of nanolasers with silicon-based electronic circuitry represents one of the greatest technological challenges in the field of nanophotonics. By combining ab-initio simulations and analytical modeling, I characterize the nonlinear emission from three-dimensional plasmonic nanolasers known as SPASERs. My results show for the first time the occurrence of a spontaneous rotational emission in spherical SPASERs, which originates from the nonlinear interaction of several lasing modes. I further discuss how rotating nanolasers can be employed as a fundamental building block for integrated quantum simulators, random information sources, and brain-inspired photonics platforms. Leveraging the practical limitations of SPASERs, I also propose a novel concept of near-field nanolaser based on invisible anapole modes. Anapoles constitute a peculiar state of electromagnetic radiation with no far-field emission and they have been recently discovered in dielectric nanoparticles. By integrating anapole lasers in a silicon-compatible platform, I discuss several advanced applications such as spontaneously polarized nanolasers and ultrafast pulse generators on-chip.

Silver (Ag) is an ideal low-loss platform for plasmonic applications, but from a materials standpoint it presents challenges. Development of plasmonic devices based on Ag thin film has been hindered both by the dificulty of fabricating such film and by its fragility out of vacuum. Silver is non-wetting on semiconducting and insulating substrates, but on certain semiconductors and insulators can adopt a metastable atomically at epitaxial film morphology if it is deposited using the "two-step" growth method. This method consists of deposition at low temperature and annealing to room temperature. However, epitaxial Ag is metastable, and dewets out of vacuum. The mechanisms of dewetting in this system remain little understood. The fragility of Ag film presents a particular problem for the engineering of plasmonic devices, which are predicted to have important industrial applications if robust low-loss platforms can be developed. This dissertation presents two sets of experiments. In the first set, scanning probe techniques and low energy electron microscopy have been used to characterize Ag(111) growth and dewetting on two orientations of silicon (Si), Si(111) and Si(100). These studies reveal that multiple mechanisms contribute to Ag film dewetting. Film stability is observed to increase with thickness, and thickness to play a decisive role in determining dewetting processes. A method has been developed to cap Ag film with germanium (Ge) to stabilize it against dewetting. The second set of experiments consists of optical studies that focus on the plasmonic properties of epitaxial Ag film. Because of the problems posed until now by epitaxial Ag growth and stabilization, research and development in the area of plasmonics has been limited to devices based on rough, thermally evaporated Ag film, which is robust and simple to produce. However, plasmonic damping in such film is higher than in epitaxial film. The optical studies presented here establish that Ag film can now be stabilized sufficiently to allow optical probing and device applications out of vacuum. Furthermore, they demonstrate the superiority of epitaxial Ag film relative to thermally evaporated film as a low-loss platform for plasmonic devices spanning the visible and infrared regimes. / text