Towards Plasmon-Band Engineering in Ordered Plasmonic Nanostructures

In this thesis, the hybridization of localized surface plasmons to generate continuous plasmonic excitation bands was investigated. Localized surface plasmons are quasi-particles corresponding to collective oscillations of charge carriers (for example, conduction electrons in metals). They arise at interfaces between nanoparticles and their surroundings if the signs of the dielectric functions of the facing materials are opposite. If the spatial extension of the plasmon is confined to the nanoparticle, standing plasmon waves (so-called plasmon modes) with localized and amplified electromagnetic fields emerge. The field enhancement is confined to the boundaries of the nanoparticle, with material-dependent evanescent damping (decrease to 1/e in the range of several 10 nm). The penetration of the fields into the environment allows interaction of plasmon modes of different individual nanoparticles arranged in assemblies with interparticle distances of several nanometers. This interaction can lead to hybridization, i.e., spectral splitting of the coupled plasmons into bonding and anti-bonding modes, which is the basis for the emergence of continuous plasmonic excitation bands. In analogy to electronic band structures, which arise by multiple hybridization of atomic orbitals in periodic lattices, plasmonic band structures can be created in large periodic arrays of plasmonic nanoparticles. Also, tuning of the bands to generate desired band properties is possible in principle by periodically varying either the individual building blocks of the arrangement (shape, size, material) or the coupling strength (distance, dielectric spacer). In the present dissertation, the spectral and spatial characteristics (excitation energy, localization, etc.) of different arrangements of plasmonic nanostructures and their plasmonic response were investigated. Using a focused electron beam (probe) in a conventional transmission electron microscope, the plasmons were excited by the evanescent electromagnetic fields of the fast beam electrons (around half of the speed of light). By analyzing the energy loss of the beam electrons (which is caused by plasmon excitation) at different probe positions on the sample, the plasmons were characterized in terms of excitation energies and spatial localization. In addition, the measured data were supported by numerical simulations to verify the experiments. To gain a theoretical understanding, appropriate models were adapted to the present experiments. For example, the classical Mie theory (which describes the plasmonic response of a sphere to transverse electromagnetic waves) was generalized to the inhomogeneous case corresponding to the plasmon excitation by the evanescent field of the beam electrons. Furthermore, surface effects (the so-called axion mixing of magnetic and electric field components), for example, present in topological insulators, were taken into account in the generalization of the Mie theory. As a first step towards plasmon band engineering, the plasmonic response of gold nanoparticles of different shapes was studied to get a comprehensive understanding of the plasmonic behavior of isolated single nanoparticles, which can later be arranged into coupled plasmonic nanostructures. In the next step, gold nanospheres were arranged into chains of different lengths to observe the formation of plasmonic band structures. By examining the hybridization as a function of chain length, the formation of a quasi-continuous plasmonic band with strong dispersion was observed. To create more complex band structures with band gaps or crossings, gold and silver nanospheres were assembled to heterogeneous chains. Focusing on plasmon hybridization in coupled nanoparticles of different kinds, all possible permutations of four coupled gold and silver nanospheres were analyzed. Considering first pure gold and silver tetra chains, similar hybridized plasmon modes, differing only in a spectral red shift in the case of gold were observed. The mixed chains also show similar hybridized modes with intermediate spectral positions depending on the number of gold and silver spheres in the chains, which proves hybridization in heterogeneous arrangements. In addition, it was found that in particular silver nanoparticles degrade in air, resulting in a bad and undefined plasmonic response. The latter hampers the use of silver for plasmonic band engineering, although it has relatively low dielectric loss. To address the degradation and to deliberately tune the distance between the coupled nanoparticles, the use of a silicon dioxide shell as a dielectric spacer and protection layer was elicited. Silver nanocubes were encapsulated in silica shells of various controllable thicknesses and investigated in terms of the plasmonic properties. It was found that the coating significantly reduces both degradation and influence of the substrate, resulting in a highly predictable and reproducible plasmonic response. The dielectric silica shell can additionally sustain Mie type resonances, which may couple to plasmons and thus mediate effective plasmonic coupling over relatively large distances (about a factor of two compared to the coupling of uncoated nanoparticles). In contrast to the delocalized quasi-continuous plasmon bands in periodic nanostructures, localized (spectral and spatial) plasmonic modes can occur in disordered geometries. This effect can hamper the formation of plasmonic bands if the plasmons localize at imperfections (shape, size, or distance deviation) of the coupled nanoparticles. Related to this, the effect of plasmon localization in randomly disordered 2-dimensional gold webs was studied. Stronger localization with increasing plasmon excitation energy was found here. Finally, a geometry-dependent spectral threshold of vanishing localized plasmon modes was observed. In summary, several fundamental aspects of plasmonic band engineering were investigated, providing a basis for the specific design of plasmonic nanostructures with desired properties.:Abstract Acronyms List of Symbols List of Figures List of Tables Contents 1 Introduction 1.1 Synthesis of Plasmonic Systems 1.2 State of the Art 1.3 Outline 2 Theory 2.1 Surface Plasmons at Planar Interfaces 2.2 Modeling Dielectric Functions - the Drude Model 2.3 Axion Electrodynamics of Topological Insulators 2.4 Surface Plasmons at Spherical Geometries - Mie Theory and Generalization to Topological Insulators 2.4.1 Vector Spherical Harmonic Expansion 2.4.2 Axion Boundary Conditions 2.4.3 Homogeneous Case 2.4.4 Inhomogeneous Case 2.5 Complex Geometries and Coupled Nanoparticles 2.5.1 Plasmon Mode Hybridization 2.5.2 Numerical Solvers 2.5.3 Discrete Dipole Model 2.6 Plasmon Mode Classification 2.7 Plasmonics in the Transmission Electron Microscope 2.7.1 Electron Energy-Loss Probability 3 Methods 3.1 Experimental Setup 3.1.1 Energy Filter 3.1.2 Spectroscopy Mode - Direct Imaging of the Energy-Dispersive Plane 3.1.3 Imaging Mode - Energy-filtered Imaging of the Filter Entrance Plane 3.1.4 Alternative Modes 3.1.5 High-Angle Annular Dark Field-Detector 3.2 Data Post-Processing 3.2.1 Zero-Loss Peak Subtraction and Deconvolution 3.2.2 Correction of the Scattering Absorption 3.2.3 Enhancement of the Signal-to-Noise Ratio 3.3 Uncertainties of the Measurement 3.4 Plasma Cleaning of the Sample 4 Results 4.1 Interplay of the Nanoparticle’s Shape and Plasmonic Response 4.2 Self-Assembly of Spherical Nanoparticles to Homogeneous Chains 4.3 Self-Assembly of Spherical Nanoparticles to Heterogeneous Chains 4.4 Silica Encapsulation of Air Sensitive Nanoparticles 4.5 Localization of Surface Plasmon Modes in Disordered 2-Dimensional Webs 5 Summary and Outlook 5.1 Summary 5.2 Outlook 5.2.1 Measurement of the Plasmon Band Dispersion 5.2.2 Generalization of Anderson Localization to Plasmons 5.2.3 Measurement of the Axion Contribution in TIs 5.2.4 Non-Local Measurements Bibliography List of Publications Danksagung Erklärun

Remote Sensing methods for power line corridor surveys

AbstractTo secure uninterrupted distribution of electricity, effective monitoring and maintenance of power lines are needed. This literature review article aims to give a wide overview of the possibilities provided by modern remote sensing sensors in power line corridor surveys and to discuss the potential and limitations of different approaches. Monitoring of both power line components and vegetation around them is included. Remotely sensed data sources discussed in the review include synthetic aperture radar (SAR) images, optical satellite and aerial images, thermal images, airborne laser scanner (ALS) data, land-based mobile mapping data, and unmanned aerial vehicle (UAV) data. The review shows that most previous studies have concentrated on the mapping and analysis of network components. In particular, automated extraction of power line conductors has achieved much attention, and promising results have been reported. For example, accuracy levels above 90% have been presented for the extraction of conductors from ALS data or aerial images. However, in many studies datasets have been small and numerical quality analyses have been omitted. Mapping of vegetation near power lines has been a less common research topic than mapping of the components, but several studies have also been carried out in this field, especially using optical aerial and satellite images. Based on the review we conclude that in future research more attention should be given to an integrated use of various data sources to benefit from the various techniques in an optimal way. Knowledge in related fields, such as vegetation monitoring from ALS, SAR and optical image data should be better exploited to develop useful monitoring approaches. Special attention should be given to rapidly developing remote sensing techniques such as UAVs and laser scanning from airborne and land-based platforms. To demonstrate and verify the capabilities of automated monitoring approaches, large tests in various environments and practical monitoring conditions are needed. These should include careful quality analyses and comparisons between different data sources, methods and individual algorithms

Visual localisation of electricity pylons for power line inspection

Inspection of power infrastructure is a regular maintenance event. To date the inspection process has mostly been done manually, but there is growing interest in automating the process. The automation of the inspection process will require an accurate means for the localisation of the power infrastructure components. In this research, we studied the visual localisation of a pylon. The pylon is the most prominent component of the power infrastructure and can provide a context for the inspection of the other components. Point-based descriptors tend to perform poorly on texture less objects such as pylons, therefore we explored the localisation using convolutional neural networks and geometric constraints. The crossings of the pylon, or vertices, are salient points on the pylon. These vertices aid with recognition and pose estimation of the pylon. We were successfully able to use a convolutional neural network for the detection of the vertices. A model-based technique, geometric hashing, was used to establish the correspondence between the stored pylon model and the scene object. We showed the effectiveness of the method as a voting technique to determine the pose estimation from a single image. In a localisation framework, the method serves as the initialization of the tracking process. We were able to incorporate an extended Kalman filter for subsequent incremental tracking of the camera relative to the pylon. Also, we demonstrated an alternative tracking using heatmap details from the vertex detection. We successfully demonstrated the proposed algorithms and evaluated their effectiveness using a model pylon we built in the laboratory. Furthermore, we revalidated the results on a real-world outdoor electricity pylon. Our experiments illustrate that model-based techniques can be deployed as part of the navigation aspect of a robot

Nano-estructuras tridimensionales funcionales (alúmina 3D y redes de nanohilos interconectados en las 3 direcciones del espacio)

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, leída el 09-03-2022This Thesis has been focused on the development of functional nanostructures for a variety of applications, from structural coloring to magnetic nanostructures with tailored properties and highly efficient thermoelectric metamaterials. In all cases, the fabrication of such nanostructures has been based on two processes: aluminum anodization and electrochemical growth. Both are chemical processes, which need no vacuum and that are well known at the industrial level. The results that are presented in this manuscript represent the state of the art of both techniques, which is well endorsed by the publications that have resulted from it.In brief, the main objective pursued in this Ph.D. Thesis has been to prove the versatility of a recent kind of alumina membranes, consisting of longitudinal pores that are transversely perforated by smaller pore channels, in the development of future nanotechnology applications. These 3D-Anodic alumina templates (3D AAO) have been studied by themselves, but also used as templates to grow different materials and tune their properties...Este trabajo de tesis se centra en el desarrollo de nanoestructuras funcionales interconectadas para diversas aplicaciones, desde la obtención de color estructural a la fabricación de metamateriales magnéticos con propiedades modificadas, así como metamateriales termoeléctricos de alta eficiencia. En todos estos casos, la fabricación de estas nanoestructuras se ha basado en dos procesos: anodización de aluminio y crecimiento electroquímico. Ambos son procesos químicos que no requieren de vacío y que son muy conocidos a nivel industrial. Los resultados que se presentan en este manuscrito muestran el estado del arte en ambas técnicas, lo que queda patente por las publicaciones científicas a las que este trabajo ha dado lugar. Brevemente, el objetivo principal de esta Tesis ha sido probar la versatilidad de un tipo de membranas de alúmina desarrolladas recientemente para el desarrollo de futuras aplicaciones nanotecnológicas. Estas membranas consisten en poros longitudinales que están unidos por poros transversales más pequeños que forman canales que los conectan. Estas membranas de alúmina tridimensionales (3D-AAO, del inglés 3D Anodic Aluminum Oxide) se han estudiado, por un lado, como plataformas para la generación de dispositivos en sí mismas, y, por otro lado, como plantillas para crecer en su estructura porosa distintos materiales y nanoestructurarlos, modificando de este modo sus propiedades...Fac. de Ciencias FísicasTRUEunpu

A Review of 2D and 3D Plasmonic Nanostructure Array Patterns: Fabrication, Light Management and Sensing Applications

Abstract: This review article discusses progress in surface plasmon resonance (SPR) of two-dimensional (2D) and three-dimensional (3D) chip-based nanostructure array patterns. Recent advancements in fabrication techniques for nano-arrays have endowed researchers with tools to explore a material’s plasmonic optical properties. In this review, fabrication techniques including electron-beam lithography, focused-ion lithography, dip-pen lithography, laser interference lithography, nanosphere lithography, nanoimprint lithography, and anodic aluminum oxide (AAO) template-based lithography are introduced and discussed. Nano-arrays have gained increased attention because of their optical property dependency (lightmatter interactions) on size, shape, and periodicity. In particular, nano-array architectures can be tailored to produce and tune plasmonic modes such as localized surface plasmon resonance (LSPR), surface plasmon polariton (SPP), extraordinary transmission, surface lattice resonance (SLR), Fano resonance, plasmonic whisperinggallery modes (WGMs), and plasmonic gap mode. Thus, light management (absorption, scattering, transmission, and guided wave propagation), as well as electromagnetic (EM) field enhancement, can be controlled by rational design and fabrication of plasmonic nano-arrays. Because of their optical properties, these plasmonic modes can be utilized for designing plasmonic sensors and surfaceenhanced Raman scattering (SERS) sensors

Piezoresponse Force Microscopy: A Window into Electromechanical Behavior at the Nanoscale

Piezoresponse force microscopy (PFM) is a powerful method widely used for nanoscale studies of the electromechanical coupling effect in various materials systems. Here, we review recent progress in this field that demonstrates great potential of PFM for the investigation of static and dynamic properties of ferroelectric domains, nanofabrication and lithography, local functional control, and structural imaging in a variety of inorganic and organic materials, including piezoelectrics, semiconductors, polymers, biomolecules, and biological systems. Future pathways for PFM application in high-density data storage, nanofabrication, and spectroscopy are discussed

Plasma Nanoscience: from Nano-Solids in Plasmas to Nano-Plasmas in Solids

The unique plasma-specific features and physical phenomena in the organization of nanoscale solid-state systems in a broad range of elemental composition, structure, and dimensionality are critically reviewed. These effects lead to the possibility to localize and control energy and matter at nanoscales and to produce self-organized nano-solids with highly unusual and superior properties. A unifying conceptual framework based on the control of production, transport, and self-organization of precursor species is introduced and a variety of plasma-specific non-equilibrium and kinetics-driven phenomena across the many temporal and spatial scales is explained. When the plasma is localized to micrometer and nanometer dimensions, new emergent phenomena arise. The examples range from semiconducting quantum dots and nanowires, chirality control of single-walled carbon nanotubes, ultra-fine manipulation of graphenes, nano-diamond, and organic matter, to nano-plasma effects and nano-plasmas of different states of matter.Comment: This is an essential interdisciplinary reference which can be used by both advanced and early career researchers as well as in undergraduate teaching and postgraduate research trainin