Im Bereich opto-elektronischer Sensortechnik ist ein eindeutiger Trend hin zu immer kleineren Bauelementen und immer spezifischeren Messanwendungen zu erkennen. Plasmonische Materialien auf der Basis von Nanostrukturen bieten sich hierbei hervorragend für dieses Aufgabenfeld an. Deren optische Absorbanzpeaks lassen sich über die geometrischen Parameter der Nanostrukturen einfach und präzise steuern und reagieren äußerst empfindlich auf Brechungsindexänderungen im Umgebungsmedium. Die Herstellung von aufrecht stehenden, teppichartig angeordneten Nanorods auf Basis von anodisierten Aluminiumoxidmatrizen bietet als skalierbares Bottom-up-Verfahren eine einzigartige Kombination aus Prozessgeschwindigkeit, Steuerbarkeit und Kosteneffizienz. In der vorliegenden Dissertation wurde untersucht, wie sich verschiedene Sputterparameter während der Herstellung von Aluminiumdünnschichten auf deren Anodisierungseigenschaften, sowie die anschließende Porenbefüllung und die plasmonischen Eigenschaften des so erzeugten Materials auswirken. Hierzu wurde reines Aluminium bei verschiedenen Sputterleistungen und -raten abgeschieden und hinsichtlich seiner Oberflächenkonfiguration und Prozessierbarkeit im bereits etablierten Nanorodproduktionsverfahren untersucht. Gleichwohl fanden Versuche statt, Aluminiumschichten mit einer schwachen Siliziumlegierung sowie durch reaktives Sputtern mit Sauerstoff voroxidiertes Aluminium zu anodisieren und für die Nanorodherstellung zu nutzen. Als typisches Ergebnis dieser Versuche zeigt sich eine deutliche Verbesserung des Anodisierungs- und Abscheideverhaltens, wenn die Sputterparameter so gewählt werden, dass eine möglichst feinkristalline Schicht abgeschieden wird. Während die Variation der Sputterleistung nur in einer mäßigen Verbesserung und die Siliziumlegierung sogar in einer Verschlechterung der optischen Eigenschaften resultieren, zeigt sich die Sauerstoffzugabe als äußerst vorteilhaft für den Herstellungsprozess sowie die plasmonischen Eigenschaften der fertigen Strukturen. Hierbei weisen Aluminiumschichten mit einem Sauerstoffanteil von 10 22 at.% die gleichmäßigste Anodisierung sowie die schmalsten Plasmonenresonanzpeaks auf, bei gleichzeitig hoher Reproduzierbarkeit. Für derartige Proben konnte eine annähernd vollständige Porenbefüllung erreicht werden. Weiterhin ist die Breite der Plasmonenresonanz hier vergleichbar mit der eines simulierten, defektfreien Nanorodarrays mit perfekt hexagonaler Nanorodanordnung, sodass von einer deutlichen Optimierung gesprochen werden kann, welche nun weitere Untersuchungen an diesem System oder sogar eine großtechnische Produktion ermöglicht Letztendlich offenbart eine quantitative Analyse der Strom-Zeit-Kurve der Anodisierung, dass diese in Form und Ausprägung mit der Güte der plasmonischen Eigenschaften der so produzierten Strukturen korreliert. Somit bietet sich diese als schnelles und günstiges Verfahren zur Qualitätskontrolle in einem sehr frühen Prozessstadium an. / Optical sensing witnesses an increasing trend towards smaller components and more specific applications. Nanostructure-based materials excellently fulfil these kinds of task. Their optical absorbance peaks are easily and precisely controllable by changing the structures‘ geometrical parameters, and have shown to be highly sensitive to refractive index changes of the surrounding medium. The fabrication of free-standing arrays of metallic nanorods based on anodised aluminium oxide matrices as a scalable bottom-up process offers a unique combination of throughput in production, process control and cost efficiency. The scope of the present dissertation thesis is the exploration of different sputtering parameters and techniques for the fabrication of aluminium thin-films, their influence on the anodisation properties as well as subsequent pore filling, and of course the optical properties of the final plasmonic structure. For this, pure aluminium was deposited at different sputtering powers and rates, and was investigated regarding its surface configuration as well as its usability within the well-established nanorod fabrication process. Similarly, attempts were made to anodise aluminium alloyed with small quantities of silicon as well as substoichiometric aluminium oxide, which was prepared by reactive sputtering under partial oxygen pressure. As a typical result of these studies, it was found that a considerable improvement of anodisation and electroplating behaviour could be achieved, provided the sputtering conditions were chosen such that the deposited films\' crystal size becomes as small as possible. While the variation of the sputtering power lead only to a marginal improvement and the silicon admixture even deteriorated the sample quality, the use of partially oxidised aluminium layers proved to be highly advantageous for the fabrication process as well as the plasmonic properties of the final structures. The optimal oxygen content was found to be 10 22 at.%, with these samples showing the most regular anodisation behaviour, the smallest absorbance peak width, and at the same time a high reproducibility. Furthermore, the peak width of these samples is comparable to that of simulated, defect-free nanorod arrays in a perfect hexagonal arrangement. These fabrication parameters can therefore be viewed as highly optimised and well-suited for further investigations of this material or even a large-scale production process. Finally, a quantitative analysis of the current-time-curve of an anodisation process reveals a correlation between its characteristics and the samples’ plasmonic qualities. Hence, the analysis of this curve may be used as a fast and cheap method of quality control at the early stages of the fabrication process.

<p>The demand for the faster information transport and better computational abilities is ever increasing. In the last few decades, the electronic industry has met this requirement by increasing the number of transistors per square inch. This lead to the scaling of devices to tens of nm. However, the speed of the electronics is limited to few GHz. Using light, the operating speed of photonic devices can be much larger than GHz. But the photonic devices are diffraction limited and hence the size of photonic device is much larger than the electronic components. Plasmonics is an emerging field with light-induced surface excitations, and can manipulate the light at nanoscale. It can bridge the gap between electronics and photonics. </p> <p>With the present scaling of devices to few nm, the scientific community is looking for alternatives for continued progress. This has opened up several promising routes recently, including two-dimensional materials, quantum computing, topological computing, spintronics and valleytronics. The discovery of graphene has led to the immense interest in the field of two-dimensional materials. Two dimensional-materials have extraordinary properties compared to its bulk. This work discusses the applications of plasmonics in this emerging field of two-dimensional materials and for heat assisted magnetic recording.</p> <p>Black phosphorus is an emerging low-direct bandgap two-dimensional semiconductor, with anisotropic optical and electronic properties. It has high mobility and is promising for photo detection at infrared wavelengths due to its low band gap. We demonstrate two different plasmonic designs to enhance the photo responsivity of black phosphours by localized surface plasmons. We use bowtie antenna and bowtie apertures to increase the absorption and polarization selectivity respectively. Plasmonic structures are designed by numerical electromagnetic simulations, and are fabricated to experimentally demonstrate the enhanced photo responsivity of black phosphorus. </p> <p>Next, we look at another emerging two-dimensional material, bismuth telluride selenide (Bi₂Te₂Se). It is a topological insulator with an insulating bulk but conducting electronic surface states. These surface states are Dirac like, similar to graphene and can lead to exotic plasmonic phenomena. We investigated the optical properties of Bi₂Te₂Se and found that the bulk is plasmonic below 650 nm wavelength. We study the distinct surface plasmons arising from the bulk and surface state of the topological insulator, Bi₂Te₂Se. The propagating surface plasmons at a nanoscale slit in Bi₂Te₂Se are imaged using near-field scanning optical microscopy. The surface state plasmons are studied with a below band gap excitation of 10.6 µm wavelength and the surface plasmons of the bulk are studied with a visible wavelength of 633 nm. The surface state plasmon wavelength is 100 times shorter than the incident wavelength in sharp contrast to the plasmon wavelength of the bulk. </p> <p>Next, we look at the application of plasmonics in heat assisted magnetic recording (HAMR). HAMR is one of the next generation data storage technology that can increase the areal density to beyond 1 Tb/in². Near-field transducer (NFT) is a key component of the HAMR system that locally heats the recording medium by concentrating light below the diffraction limit using surface plasmons. In this work, we use density-based topology optimization for inverse design of NFT for a desired temperature profile in the recording medium. We first perform an inverse thermal calculation to obtain the required volumetric heat generation (electric field) for a desired temperature profile. Then an inverse electromagnetic design of NFT is performed for achieving the desired electric field. NFT designs for both generating a small heated spot size and a heated spot with desired aspect ratio in recording medium are demonstrated. The effect of waveguide, write pole and moving recording medium on the heated spot size is also investigated. </p>

This thesis examines and exploits the optical properties of pairs of MNPs. Pairs of MNPs offer two further parameters not existent at single MNPs, which both affect the local optical fields in their vicinity: the distance between them, and their relative orientation with respect to the polarisation of the excitation light. These properties are subject of three chapters: One section examines the distance-dependent and orientation-sensitive scattering cross section (SCS) of two equally sized MNPs. Both near- and far-field interactions affect the spectral position and spectral width of the SCS. Far-field coupling affects the SCS even in such a way that a two-particle system may show both a blue- and redshifted SCS, depending only on the distance between the two MNPs. The maximum distance for this effect is the coherence length of the illumination source – a fact of importance for SCS-based experiments using laser sources. Another part of this thesis examines the near-field between two MNPs and the dependence of the locally enhanced field on the relative particle orientation with respect to the polarisation of the excitation light. To attain a figure of merit, the intensity of fluorescence light from dye molecules in the surrounding medium was measured at various directions of polarisation. The field enhancement was turned into fluorescence enhancement, even providing a means for sensing the presence of very small MNPs of 12 nm in diameter. In order to quantify the near-field experimentally, a different technique is devised in a third section of this thesis – scanning particle-enhanced Raman microscopy (SPRM). This device comprises a scanning probe carrying an MNP which in turn is coated with a molecule of known Raman signature. By manoeuvring this outfit MNP into the vicinity of an illuminated second MNP and by measuring the Raman signal intensity, a spatial mapping of the field enhancement was possible. / Diese Dissertation untersucht und nutzt die optischen Eigenschaften von Paaren von Metall-Nanopartikeln (MNP). MNP-Paare bieten gegenüber einzelnen MNP zwei weitere Parameter, welche beide auf das optische Nahfeld der zwei MNPs wirken: zum Einen der Abstand der zwei MNPs zueinander, zum Anderen die relative Ausrichtung des Paares bezüglich der Polarisation des anregenden Lichts. Diese Eigenschaften sind Thema der Arbeit: Ein Abschnitt untersucht den abstands- und orientierungsabhängigen Streuquerschnitt (SQS) zweier gleichgroßer MNPs. Die spektrale Position und die Breite des SQS wird von Wechselwirkungen sowohl im Nah- als auch im Fernfeld beeinflusst. Der Einfluß der Fernfeld-Wechselwirkung geht so weit, daß ein Zwei-MNP-System sowohl einen blau- als auch einen rotverschobenen SQS haben kann – dies hängt lediglich vom Abstand der zwei MNPs ab. Die Reichweite dieser Fernfeld-Wechselwirkung wird durch die Kohärenzlänge der Beleuchtungsquelle bestimmt – eine wichtige Tatsache für SQS-Untersuchungen, welche Laserquellen verwenden. Ein weiterer Teil der Dissertation untersucht das Nahfeld zwischen zwei MNPs. Insbesondere wird dargestellt, inwieweit die Überhöhung des Nahfelds von der Orientierung des Partikelpaares bezüglich der Polarisation des Anregungslichts abhängt. Um den Effekt quantifizieren zu können, wurde die Intensität der Fluoreszenz des umgebenden Mediums für verschiedene Polarisationsrichtungen gemessen. Die lokale Feldverstärkung konnte in eine Fluoreszenzverstärkung gewandelt werden, mit deren Hilfe sich sogar die Anwesenheit sehr kleiner MNPs von nur 12 nm Durchmesser nachweisen ließ. Wie Nahfeld-Intensitäten experimentell quantifiziert werden können, stellt ein dritter Abschnitt dieser Dissertation vor – per MNP-verstärkter Raman-Rastersonden-Mikroskopie. Diese Technik besteht aus einer Rastersonde, welcher ein MNP anheftet, welches wiederum mit einem Molekül bekannter Ramansignatur überzogen ist. Indem solch eine Sonde in die unmittelbare Nähe eines zweiten, beleuchteten MNPs gebracht wurde und dabei die Intensität des Raman-Signals aufgezeichnet wurde, ließ sich die räumliche Verteilung der Ramanverstärkung vermessen.

<div>The response time of magnetization switching in current spintronic devices is limited to nanosecond timescales due to the precessional motion of the magnetization during reversal. To overcome this limit two routes of investigation leading to novel recording and logic devices are considered in this thesis: 1) Magnetic tunnel junction structures where the recording and reference layers are replaced by synthetic ferrimagnets and switching is induced by spin transfer torque and 2) Hybrid magneto-photonic devices where switching is induced by plasmon-enhanced all-optical switching. To circumvent limitations of the materials and magnetic properties of CoFeB, the most utilized alloy in spintronics, hcp-CoCrPt, a material that exhibits superior perpendicular anisotropy and thermal stability, is chosen as the ferromagnetic electrode in this work. Whereas actual devices based on the two schemes aforementioned are still in the process of being fabricated, through collaborative work with our international collaborators, this thesis describes fundamental magnetic and structural characterization needed for the realization of said ultrafast switching devices. The magnetic switching behavior of CoCrPt-Ru-CoCrPt synthetic ferrimagnets with perpendicular magnetic anisotropy have been studied in the temperature range from 2K to 300K. It was found that two sets of magnetic transitions occur in the CoCrPt-Ru-CoCrPt ferrimagnet systems studied. The first set exhibits three magnetization states in the 50K – 370K range, whereas the second involves only two states in the 2K and 50K range. The magnetic hysteresis curves of the synthetic ferrimagnet are assessed using an energy diagram technique which accurately describes the competition between interlayer exchange coupling energy, Zeeman energy, and anisotropy energy in the system. This energy diagram analysis is then used to predict the changes in the magnetic hysteresis curves of the synthetic ferrimagnet from 200K to 370K. This represents the potential operation temperature extrema that a synthetic ferrimagnet could be expected to operate at, were it to be utilized as a free layer in a memory or sensor spintronic device in the device configuration described in this dissertation.</div><div>Circularly polarized fs laser pulses generate large opto-magnetic fields in magnetic materials, through the inverse Faraday effect. These fields are attributed to be largely responsible for achieving ultrafast all-optical magnetization switching (AOS). All experimental demonstrations of AOS thus far have been realized on thin films over micron-sized irradiated regions. To achieve magnetization switching speeds in the ps and potentially fs time regimes, this work proposes the use of surface plasmon resonances at the interface of hybrid magneto-photonic heterostructures. In addition to the ability of plasmon resonances to confine light in the nm scale, the resonant excitation can largely enhance induced opto-magnetic fields in perpendicular magnetic anisotropy materials. This requires strong spin-photon coupling between the plasmonic and the magnetic materials, which thus requires the minimization of seed layers used for growth of the magnetic layer. This work reports on the development of ultrathin (1 nm thick) interlayers to control the growth orientation of hcp-Co alloys grown on the refractory plasmonic material, TiN, to align the magnetic axis out-of-plane. CoCrPtTa seed layers down to 1 nm were developed to seed the growth of CoCrPt, and the dependence of the quality of the CoCrPt is investigated as Ta composition is varied in the seed layer. Whereas bismuth iron garnet (BIG) meets the magneto-optical requirements for a hybrid magneto-photonic material, its magnetic and structural properties are highly sensitive to the Bi:Fe ratio and must be grown epitaxially on single crystalline substrates. Therefore, in this work we have investigated alternative materials that offer superior magnetic properties and are amenable to growth on inexpensive substrates. Opto-magnetic field enhancements up to 2.6x in Co-ferrite magneto-photonic heterostructures have been obtained via finite element analysis modelling. Alternative materials for plasmon-enhanced all-optical switching such as Co/Pd multilayers have also been investigated. Successful growth of Co/Pd multilayers on TiN using ultrathin Ti interlayers has been achieved. </div><div><br></div>

Atoms change their optical properties drastically when combined into molecules or crystals. This becomes evident when comparing isolated carbon atoms with their solid-state polymorphs graphite and diamond. Plasmonic meta-surfaces adopt this concept to design the optical properties of thin films at will. In analogy to natural materials, the optical response of a meta-surface is dictated by the arrangement and plasmonic coupling (hybridization) of sub-wavelength metallic objects, so-called meta-atoms, rather than by the individual components. Although traditional direct writing approaches offer a high degree of freedom in design of nanostructures, reconfiguration of meta-atoms is usually limited. Especially their spatial rearrangement remains a huge challenge. Postfabrication tunability, however, would be crucial to advance device miniaturization and optical computing, by introducing dynamically tunable optics and optical switches. This thesis investigates colloidal assembly as a cost-efficient approach to fabricate meta-surfaces on cm²-areas whose optical properties can be tuned by geometrical reconfiguration. Hydrodynamic fields and topographical templates guide the deposition of colloidal nanoparticles with precise orientational and/or positional control. In the course of this work, the level of particle assembly complexity is successively increased to realize 1-, 2-, and 3-dimensional (1D, 2D, 3D) plasmonic assemblies. Strongly correlated with assembly geometry, different aspects of light are controllable. (I) 1D alignment of silver nanowires (AgNWs) produces differential transmission for linear polarization states (linear dichroism). (II) Single particles in a 2D square array interact coherently to produce a sharp, so-called surface lattice resonance (SLR). This effect confines strong electromagnetic fields in the lattice plane, which is promising for plasmonic lasing. (III) 3D chiral, cross-stacked particle chains control the transmission of circular polarization states (circular dichroism, CD). The unique advantages of colloidal assembly are demonstrated. (I) Spray coating allows rapid deposition of oriented AgNWs over large areas and is compatible with roll-to-roll processing. Employing wrinkle-structured receiver substrates, gradients of continuously varying linear dichroism are feasible in a single step. (II) Capillary assembly is able to realize ~1 nm inter-particle spacing, which is not achievable by conventional top-down lithographical methods. The small spacing enhances inter-particle plasmon coupling and boosts CD in cross-stacked, chiral particle chains, as presented in this thesis. (III) Such hierarchical and restackable, chiral structures make large volumes of superchiral fields accessible for ultrasensitive, enantioselective detection of analytes. This is in vast contrast to stacked nanobars produced via lithography where the most pronounced fields in the inter-layer gap are blocked by the presence of spacing layers. A central focus of this thesis is the postfabrication reconfiguration of the systems presented. This in-situ tunability is realized by elastic and reversibly stackable templates. (I) Uniaxial, mechanical strain converts the 2D square lattice into a rectangular one. This splits the SLR into two polarization-dependent modes whose resonance position is shifted reversibly when load is applied. (II) The cross-stacked, chiral particle chains are restackable. This allows adjustment of the stacking angle to tune CD magnitude and sign. (III) Reversible compression of this chiral stack induces a bending of the chains to shift the spectral position of CD modes. In a proof of concept, locally varying compression is shown to create a gradient of CD response as important step towards on-chip CD spectroscopy. Overall, this thesis (I) tests the limits of colloidal assembly by going from single-particle arrays to complex 3D arrangements; (II) explores geometrical reconfiguration of these plasmonic nanostructures to tune pronounced optical effects. The strategies presented herein can be extended to other colloidal particle shapes and materials. Moreover, the concepts of restackable meta-surfaces and local compression for tuning optical response open an intriguing playground and might inspire top-down approaches as well. / Atome ändern ihre optischen Eigenschaften drastisch, wenn sie sich zu Molekülen oder Kristallen vereinigen. Dies wird deutlich, wenn man isolierte Kohlenstoffatome mit ihren Festkörperpolymorphen Graphit und Diamant vergleicht. Plasmonische Meta-Oberflächen übernehmen dieses Konzept, um die optischen Eigenschaften dünner Schichten nach Belieben einzustellen. In Analogie zu natürlichen Materialien wird die optische Antwort einer Meta-Oberfläche durch die Anordnung und plasmonische Kopplung (Hybridisierung) metallischer Mikro- und Nano-Objekte, den sogenannten Meta-Atomen, bestimmt und kann sich stark von den Eigenschaften der Einzelkomponenten unterscheiden. Obwohl traditionelle Direktschreibverfahren ein hohes Maß an Gestaltungsfreiheit in der Nanostrukturierung bieten, ist die Rekonfiguration von Meta-Atomen in der Regel begrenzt. Vor allem ihre räumliche Neuordnung bleibt eine große Herausforderung. Eine Durchstimmbarkeit auch nach der Herstellung zu gewährleisten wäre jedoch entscheidend, um die Miniaturisierung von Geräten und die Realisierung optischer Computer—durch die Einführung dynamisch durchstimmbarer optischer Bauteile und optischer Schalter—voranzutreiben. Diese Dissertation untersucht kolloidale Assemblierung als kostengünstigen Ansatz zur Herstellung von Meta-Oberflächen im cm²-Maßstab, deren optische Eigenschaften durch geometrische Rekonfiguration durchgestimmt werden können. Hydrodynamische Felder und topographische Template steuern die Ablagerung kolloidaler Nanopartikel mit präziser Orientierungs- und/oder Positionskontrolle. Im Verlauf dieser Arbeit wird die Komplexität der Partikelanordnung sukzessive erhöht, um 1-, 2- und 3-dimensionale (1D, 2D, 3D), plasmonische Anordnungen zu realisieren. Eng verbunden mit der Anordnungsgeometrie können verschiedene Aspekte des Lichts gesteuert werden. (I) Die 1D-Ausrichtung von Silbernanodrähten ruft unterschiedliche Transmission für lineare Polarisationszustände hervor (linearer Dichroismus). (II) Einzelpartikel in einem quadratischen 2D-Kristall wechselwirken kohärent, was eine scharfe, sogenannte Oberflächengitterresonanz (surface lattice resonance) erzeugt. Dieser Effekt konzentriert starke elektromagnetische Felder in der Gitterebene, was ihn für plasmonische Laser interessant macht. (III) 3D-chirale, über Kreuz geschichtete Partikelketten beeinflussen die Transmission zirkularer Polarisationszustände (zirkularer Dichroismus). Die einzigartigen Vorzüge der kolloidalen Assemblierung werden aufgezeigt. (I) Die Sprühbeschichtung ermöglicht eine rasche Abscheidung orientierter Silbernanodrähte auf großen Flächen und lässt sich mit kontinuierlicher Fertigung (Rolle-zu-Rolle) verbinden. Mit Hilfe faltenstrukturierter Substrate können Gradienten mit kontinuierlich variierendem Lineardichroismus in einem einzigen Schritt erzeugt werden. (II) Partikelanordnung mittels Kapillarkräften ermöglicht Partikelabstände von ~1 nm, was mit herkömmlichen, lithographischen Methoden nicht erreichbar ist. Dieser geringe Abstand verbessert die Plasmonenkopplung zwischen den Partikeln und verstärkt den Zirkulardichroismus in gekreuzten, chiralen Partikelketten, wie in dieser Arbeit vorgestellt wird. (III) Solche hierarchischen und wiederholt stapelbaren, chiralen Strukturen machen große Volumina an superchiralen Feldern für Analytmoleküle zugänglich, was deren ultrasensitive, enantioselektive Detektion ermöglicht. Dies steht in starkem Gegensatz zu gestapelten, lithographisch hergestellten Nanostäbchen, bei denen die stärksten Felder im Zwischenschichtspalt durch die Anwesenheit von Abstandsschichten versperrt bleiben. Ein zentrales Thema dieser Arbeit ist die Rekonfiguration der vorgestellten Systeme im Anschluss an deren Fertigung. Diese in-situ-Durchstimmbarkeit wird durch elastische und reversibel stapelbare Template realisiert. (I) Mechanische Deformation entlang einer Achse überführt den quadratischen 2D-Kristall in einen rechteckigen. Dadurch wird die Oberflächengitterresonanz in zwei polarisationsabhängige Moden aufgespalten, deren Resonanzposition unter Krafteinwirkung reversibel verschoben wird. (II) Die über Kreuz gestapelten, chiralen Partikelketten sind wiederholt stapelbar. Dies ermöglicht die Anpassung des Stapelwinkels, um die Stärke und das Vorzeichen des Zirkulardichroismus einzustellen. (III) Reversible Kompression dieses chiralen Stapels verursacht ein Verbiegen der Ketten und verschiebt so die spektrale Position der zirkulardichroitischen Moden. In einer Machbarkeitsstudie konnte gezeigt werden, dass lokal variierende Kompression einen Gradienten des Zirkulardichroismus hervorruft. Dies stellt einen wichtigen Schritt in Richtung Ein-Chip-Spektroskopie dar. Diese Arbeit (I) lotet die Grenzen der kolloidalen Assemblierung aus, indem sie von Einzelpartikel-Anordnungen zu komplexen 3D-Arrangements übergeht; (II) untersucht die geometrische Rekonfiguration dieser plasmonischen Nanostrukturen, um ausgeprägte optische Effekte zu modulieren. Die hier vorgestellten Strategien können auf andere kolloidale Partikelformen und materialien übertragen werden. Darüber hinaus bereiten die Konzepte wiederholt stapelbarer Meta-Oberflächen und der lokalen Kompression zum Einstellen der optischen Eigenschaften eine faszinierende Spielwiese. Auch der Top-Down-Fertigung könnten diese Ansätze als Blaupause dienen.

Plazmonika, tedy vědní obor zabývající se interakcí světla s kovovými materiály, nabízí ve spojení s nanotechnologiemi nezvyklé možnosti, jak světlo ovládat a využívat. Výsledkem tohoto spojení může být například zaostřování světla pod difrakční limit, zesilování emise nebo absorbce kvantových zářičů, či extrémně citlivá detekce molekul. Tato práce se zabývá zejména možnostmi využití plazmoniky pro vývoj plošných optických prvků, tzv. metapovrchů, a pro fotokatalytické aplikace založené na plazmonicky generovaných elektronech s vysokou energií, tzv. horkých elektronech. Nejprve jsou vysvětleny teoretické základy plazmoniky a je poskytnut přehled jejích nejvýznamnějších aplikací. Poté jsou představeny tři studie zabývající se využitím plazmonických nanostruktur pro ovládání fáze a polarizace světla, pro vytváření dynamicky laditelných metapovrchů, a pro foto-elektrochemii s horkými elektrony. Společným prvkem těchto studií je pak používání pokročilých, resp. v rámci těchto oblastí netradičních, materiálů, jako např. oxidu vanadičitého nebo dichalkogenidů přechodných kovů.

Light interaction with matter has long been an area of interest throughout history, spanning many fields of study. In recent decades, the investigation of light-matter interactions with nanostructures has become an intense area of research in the field of photonics. Metallic nanostructures, in particular, are of interest due to the interesting properties that arise when interacting with light. The properties are a result of the excitation of surface plasmons which are the collective oscillation of the conduction electrons in the metal. Since the conduction electrons can be thought of as harmonic oscillators, they are quantized in a similar fashion. Just as a photon is a quantum of oscillations of an electromagnetic field, the plasmon is a quantum of electron oscillations of a metal. There are three types of plasmons: 1. Bulk plasmons, also called volume plasmons, are longitudinal density fluctuations which propagate through a bulk metal with an eigenfrequency of �� called the plasma frequency. 2. Localized surface plasmons are non-propagating excitations of the conduction electrons of a metallic nanoparticle coupled to an electromagnetic field. 3. Surface plasmon polaritons are evanescent, dispersive propagating electromagnetic waves formed by a coupled state between a photon and the excitation of the surface plasmons. They propagate along the surface of a metal-dielectric interface with a broad spectrum of eigenfrequencies from � = 0 to � = ��⁄√2. iv Plasmonics is a subfield of photonics which focuses on the study of surface plasmons and the optical properties that result from light interacting with metal films and nanostructures on the deep subwavelength scale. In this thesis, plasmonic nanostructures are investigated for optical waveguides and other nanophotonic applications through computational simulations primarily base on electrodynamic theory. The theory was formulated by several key figures and established by James Clerk Maxwell after he published a set of relations which describe all classical electromagnetic phenomena, known as Maxwell’s equations. Using methods based on Maxwell’s equations, the optical properties of metallic nanostructures utilizing surface plasmons is explored. In Chapter 3, light propagation of bright and dark modes of a partially and fully illuminated silver nanorod is investigated for waveguide applications. Then, the origin of the Fano resonance line shape in the scattering spectra of a silver nanorod is investigated. Next, in Chapter 4, the reflection and transmission of a multilayer silver film is simulated to observe the effects of varying the dielectric media between the layers on light propagation. Building on the multilayer film work, metal-insulator-metal waveguides are explored by perforating holes in the bottom layer of a two layer a silver film to investigate the limits of subwavelength light trapping, confinement, and propagation. Lastly, in Chapter 5, the effect of surface plasmons on the propagation direction of electromagnetic wave around a spherical silver nanoparticle which shows an effective negative index of refraction is examined. In addition, light manipulation using a film of silver prisms with an effective negative index of refraction is also investigated. The silver prisms demonstrate v polarization selective propagation for waveguide and optical filter applications. These studies provide insight into plasmonic mechanisms utilized to overcome the diffraction limit of light. Through better understanding of how to manipulating light with plasmonic nanostructures, further advancements in nanophotonic technologies for applications such as extremely subwavelength waveguides, sensitive optical detection, optical filters, polarizers, beam splitters, optical data storage devices, high speed data transmission, and integrated subwavelength photonic circuits can be achieved.

The utilization of plasmonic energy in the form of heat, resonance energy, and/or hot carriers offers unique possibilities for various applications, like in catalytic and medical applications, due to their simple recyclability or administration. A common strategy to make this plasmonic energy available to the direct environment is to introduce conductive polymer coatings to transfer the energy and to increase the excitons lifetime. However, their practical use is limited due to the limited spectral match of gold with commonly used polymeric materials and semiconductors, the oxidation vulnerability of silver, and the short range of the required strong plasmonic interactions. To overcome these challenges, we developed the synthesis of conjugated polymer–gold–silver hybrid colloids that simultaneously enable silver as the central plasmonic material and prolong the internal relaxation by a heterojunction with a conductive polymer shell. The introduced thin gold layer focuses the plasmonic energy to the metal surface, enhancing and enabling the photocatalyzed polymerization of polypyrrole (PPy) while maintaining the plasmonic properties of silver. Hence, the introduced hybrid particles allow the foreseeable use of plasmonic energy in real-world applications via the strong plasmonics of silver and compatible conductive polymer shells as mediators.

Plasmonische Substrate stellen ein leistungsstarkes Werkzeug für analytische Anwendungen dar. Neue plasmonische Substrate werden entwickelt, um das Spektrum ihrer Anwendungen und die Nachweisgrenzen der analytischen Spektroskopie zu erweitern. Diese Arbeit setzte sich zum Ziel, plasmonische Nanostrukturen mit Magnesiumfluorid zu beschichten. Magnesiumfluoridbeschichtungen sind zwar porös, weisen aber eine hohe mechanische Stabilität und außergewöhnliche optische Eigenschaften auf (niedrigen Brechungsindexes, großen optischen Fensters). Die Kombination dieser Eigenschaften mit den positiven Eigenschaften von plasmonischen Nanostrukturen kann zu fortschrittlichen plasmonischen Substraten für analytische Anwendungen führen. Diese Arbeit bietet zwei Ansätze für die Beschichtung der plasmonischen Nanostrukturen an die Core-Shell-Nanopartikelherstellung, die einen plasmonischen Core enthält und die Beschichtung von auf Glas immobilisierten plasmonischen Nanostrukturen. Über Metal@metal Fluoride Core-Shell-Nanopartikel wurde in der Literatur noch nichts berichtet. Daher Au@MgF2wurde ein Ansatz verfolgt, der auf dem Wissen über Metall-@Metalloxide und Metallfluoride@Metallfluoride basiert und die Synthese von Core-Shell-Nanopartikeln ermöglicht. Die erhaltenen Strukturen wurden mit elektronenmikroskopischen Methoden charakterisiert. Der zweite Ansatz bestand in der Immobilisierung von Goldnanopartikeln auf Glas und deren Beschichtung mit Magnesiumfluorid. Diese Fertigungsart verleiht eine hohe mechanische Stabilität und wissenswerte optische Eigenschaften an plasmonischen Substraten, die sich durch eine hohe nanoskopische Homogenität der Goldnanopartikelverteilung auszeichnen und optischer Signale, die echte analytische Anwendungen ermöglichen, ermittelt. Die Beschichtung von auf Glas mit Magnesiumfluorid immobilisierten Goldnanopartikeln führt zu einem sehr vielversprechenden Substrat , das in Zukunft für Sensorik und andere Anwendungen verwendet werden kann. / Plasmonic substrates can be a powerful tool for analytical applications. In order to broaden the spectrum of their applications and to push the detection limits of analytical spectroscopy, new plasmonic substrates are developed. The motivation of this work was to coat plasmonic nanostructures with magnesium fluoride. Coatings of magnesium fluoride are porous but exhibit high mechanical stability and extraordinary optical properties including a low refractive index and a wide optical window. Combining these properties with the beneficial properties of plasmonic nanostructures can lead to advanced plasmonic substrates for analytical applications. Two approaches for coating of the plasmonic nanostructures are proposed in this work: a core-shell nanoparticles fabrication and coating of plasmonic nanostructures immobilized on glass. The fabrication of Au@MgF2 core-shell nanoparticles turned out to be an extremely challenging approach. Such systems have not been reported in the literature yet. Therefore, an approach based on knowledge of metal@metal oxides and metal fluorides@metal fluorides core-shell nanoparticles synthesis was undertaken. The obtained structures were characterized using electron microscopy methods. Due to the numerous difficulties in the synthesis and characterization this way of coating plasmonic nanostructures with magnesium fluoride was not further processed. The approach based on immobilization of gold nanoparticles on glass and coating them with magnesium fluoride using a dip-coating method provides plasmonic substrates that are characterized by a high nanoscopic homogeneity of the gold nanoparticles distribution, a high mechanical stability, interesting optical properties and enhancement factors of optical signals that allow for real analytical applications. The coating of gold nanoparticles immobilized on the glass with magnesium fluoride results in very promising substrate that can be used for sensing and other applications in the future.

<p>  </p> <p>Low-dimensional materials (LDMs) are substances that have at least one dimension with thicknesses in the nanometer (nm) scale. They have attracted tremendous research interests in many fields due to their unique properties that are absent in bulk materials. For instance, in quantum optics/photonics, LDMs offer unique advantages for effective light extraction and coupling with photonic/plasmonic structures; in chemistry, the large surface-to-volume ratio of LDMs enables more efficient chemical processes that are useful for numerous applications. In this thesis, several types of LDMs are studied and engineered with the goal to improve their impact in plasmonic and quantum photonic applications. Two-dimensional hexagonal boron nitride (hBN) is receiving increasing attention in quantum optics/photonics as it hosts various types of quantum emitters that are promising for quantum computing, quantum sensing, etc. In the first study, we explore and demonstrate a radiation- and lithography-free route to deterministically create single-photon emitters (SPEs) in hBN by nanoindentation with an atomic force microscopy. The method applies to hBN on flat, chip-compatible silicon-based substrates, and an SPE yield of up to 36% is achieved. This marks an important step toward the deterministic creation and integration of hBN SPEs with photonic and plasmonic devices. In the second study, the recently discovered negatively charged boron vacancy (V_B^-) spin defect in hBN is investigated. V_B^- defects are optically active with spin properties suitable for sensing at extreme scales. To resolve the low brightness issue of V_B^- defects, we couple them with an optimized nano-patch antenna structure and observe emission intensity enhancement that is nearly an order of magnitude higher than previous reports. Our achievements pave the way for the practical integration of V_B^- defects for quantum sensing. Zero-dimensional nanodiamond is another important host material for solid-state SPEs. Specifically, the negatively charged silicon vacancy (SiV) center in nanodiamonds exhibits optical properties that are suitable for quantum information technologies. In the third study, we, for the first time, demonstrate the creation of single SiV centers in nanodiamonds with an average size of ~20 nm using ion implantation. Stable single-photon emission is confirmed at room temperature, with zero-phonon line (ZPL) wavelengths in the range of 730 – 803 nm. This confirms the feasibility of single-photon emitter creation in nanodiamonds with ion implantation, and offers new opportunities to integrate diamond color centers for hybrid quantum photonic systems. Finally, we have also explored using metal-semiconductor hybrid nanoparticles for plasmon-enhanced photocatalysis. A core-shell nanoparticle structure is synthesized, with titanium nitride (TiN) and titanium dioxide (TiO₂) being the core and shell material respectively. It is observed that such core-shell nanoparticles effectively catalyze the generation of single oxygen molecules under 700-nm laser excitation. The main mechanism behind is the hot electron injection from the TiN core to the TiO₂ shell. Considering the chemical inertness and low cost of TiN, TiN@TiO₂ NPs hold great potential as plasmonic photosensitizers for photodynamic therapy and other photocatalytic applications at red-to-near-infrared (NIR) wavelengths.</p>