With the development of controlled and predictable nanoparticle fabrication, assembling multiple nano-objects into larger functional nanostructure has attracted increasing attention. As the most basic structure, assembly of one-dimensional (1D) structures is a good model for investigating the assembly mechanism of a nanostructure's formation from individual particles. In this dissertation, the dynamics and the growth mechanism of anisotropic 1D nanostructures is investigated. In our first study, we demonstrate a simple method for assembling superparamagnetic nanoparticles (SPIONs) into structure-controlled 1D chains in a rotating magnetic field. The length of the SPION chains can be well described by an exponential distribution, as is also seen in SPION chains in a static field. In addition, the maximum chain length is limited by the field's rotational speed, as is seen in micro-sized beads forming chains in a rotating field. However, due to a combination of thermal fluctuations and hydrodynamic forces, the chain length in our case is shorter than either limit. In addition to chain length, the disorder of chains was also studied. Because of the friction between particles, kinetic potential traps prevent relaxation to the global free energy minimum. The traps are too deep to be overcome through thermal fluctuations, and assemblies captured by the kinetic traps therefore form disordered chains. We demonstrate that this disorder gradually heals over a timescale of tens of minutes and that the healing process can be promoted by increasing particle concentration or solution ionic strength, suggesting that the chain growth process provides the energy required to overcome the kinetic trapping. Next, we introduce a novel optical technique we term Quantitative Optical Anisotropy Imaging (QOAI). A fast and precise single-particle characterizing technique for anisotropic nanostructures, QOAI allows real-time tracking of particle orientation as well as the spectroscopic characterization of polarizabilities of nanoparticles on a microsecond timescale. The abilities of QOAI are demonstrated by the detection and the characterization of single gold nanorods. We also show that single particle diffusions and the process of particle binding to a wall can be tracked through QOAI. The rotational diffusivities of gold nanorods near the wall were determined by autocorrelation analysis, which shows that the diffusivity in the polar direction is slightly smaller than in the azimuthal direction. This result demonstrates that a detailed correlation analysis with QOAI may provide the opportunity to analyze both the translational and rotational motion of particles simultaneously, enabling true 3-dimensional orientation tracking. Finally, optical methods including QOAI are applied to the investigation of magnetic assembly, demonstrating that optical anisotropy is generated during particle binding, which can be used as a probe of the magnetic assembly process. QOAI is employed to track the dynamics of magnetic clusters in real time, attempting to capture insights on the self-assembly of the magnetic nanoparticles. By turning the external magnetic field on and off, the processes of combining superparamagnetic colloidal nanoparticle clusters into chain assemblies are monitored along with the chain growth. This fast and orientation-sensitive single-particle measurement opens the door to detailed studies of self-assembly away from equilibrium. / Doctor of Philosophy / Nanotechnology is the study and application of phenomena at the nanoscale, which is between 1 and 100 nm. Due to quantum effects, nanomaterials exhibit many interesting properties that cannot be found in bulk materials and are highly influenced by the shape of the nanostructures. One of the most promising strategies for forming complex nanostructures is to use smaller nanoparticles as building blocks. Therefore, significant efforts have been spent on the studies of the fabrication and modeling of the assembly of nanostructures. As a good starting point for analyzing the mechanism of self-assembly, we focus on the most basic structure, one-dimensional (1D) nanowires and chains. First, we demonstrate a simple method to fabricate one-dimensional magnetic chains from spherical magnetic nanoparticles in a rotating magnetic field. The growth mechanism of the nanochains is investigated, indicating the theory developed for chains formed with larger beads is not applicable at the nanoscale, and additional factors, such as the effect of temperature, need to be considered. Second, we introduce a fast, sensitive optical technique for characterizing anisotropic nanostructures. Because of their unique optical properties, gold nanorods are used to demonstrate the capabilities of the optical system. Not only static properties (orientation, aspect ratio), but also dynamics properties (rotational motion), of single gold nanorods are characterized quantitatively. Finally, this optical technique is extended to preliminary work on characterizing magnetic chain assembly. The processes of magnetic cluster binding and dissociation in a magnetic field are monitored and analyzed.

La fotónica sobre silicio se ha convertido en la tecnología más importante en la producción de chips integrados fotónicos. Sus grandes ventajas, entre las cuales destacan su idoneidad para la fabricación a gran escala y su bajo coste de producción, como resultado de la posibilidad del uso tecnología CMOS, son motivo suficiente para justificar su supremacía sobre otras plataformas de integración. Pese a los múltiples dispositivos ya implementados en dicha tecnología, entre los que cabe destacar filtros WDM o moduladores electro-ópticos, todavía hay espacio para la mejora, sobre todo en cuanto a la reducción del foot-print de los dispositivos o a la creación de nuevas funcionalidades para la manipulación de la luz. Dichas mejoras podrían llevarse a cabo mediante la integración de componentes con dimensiones sub-lambda surgidos en el campo conocido como plasmónica. Esta disciplina estudia la interacción entre la luz y los metales, que viene mediada por la existencia de ondas conocidas como plasmones de superficie. Una de las propiedades clave de los plasmones es su capacidad para confinar la luz muy por encima del límite de difracción, lo cual es limitante en el caso de la fotónica sobre silicio. Sin embargo, las pérdidas por absorción de los metales a frecuencias ópticas impiden su uso para el guiado de la luz en grandes distancias. Se hace evidente, por tanto, los beneficios de unificar estos dos mundos. Usando el silicio como material conductor de la señal óptica y el metal como eficiente interactor con la luz en estructuras sub-lambda, se pueden crear nuevos dispositivos para la manipulación de las propiedades de la luz en la nanoescala. Esta Tesis está centrada en la integración de estructuras con dimensiones sub-lambda en guías de silicio y en su aplicación a nuevas funcionalidades de manipulación de la luz en chips de silicio. Dichas nanoestructuras sirven de transductores entre la luz guiada y la radiación en espacio libre, por lo que también pueden ser denominadas nanoantenas. Para empezar, se describen las propiedades de los modos guiados en guías de onda de silicio para la correcta excitación de las nanoantenas, seguido de la demostración de técnicas de integración de estas nanoestructuras en las propias guías para aumentar su eficiencia de interacción con la luz guiada. Además, se demuestra el control coherente de la absorción y el scattering de una nanoantenna metálica integrada en una guía de silicio. Por último, a partir del posicionamiento asimétrico de la nanoestructura con respecto a la guía, se proponen y demuestran nuevos métodos de manipulación de la polarización, como la capacidad para sintetizar estados de polarización deseados a escala nanométrica. Esto desembocará en la demostración teórica y experimental de un nanopolarímetro de Stokes, basado en tecnología fotónica sobre silicio, capaz de determinar el estado de polarización de manera local, óptima, y no destructiva, habilitándose su uso para medidas de polarización en tiempo real en circuitos integrados. / Silicon photonics has become the most important technology in integrated photonic chips production. Its great advantages, including its suitability for large-scale production and low-cost production, as a result of the possibility of using CMOS technology, are sufficient reason to justify its supremacy over other integration platforms. Despite the multiple devices already implemented in this technology, among which include WDM filters or electro-optical modulators, there is still room for improvement, especially in terms of reducing the devices footprint or the creation of new functionalities for the manipulation of light. Such improvements could be carried out by integrating components with sub-lambda dimensions arising in the field known as plasmonics. This discipline studies the interaction between light and metals, which is mediated by the existence of waves known as surface plasmons. One of the key properties of plasmons is their ability to confine light well beyond the diffraction limit, which is limiting in the case of silicon photonics. However, losses due to the absorption of metals at optical frequencies prevent their use for guiding light over long distances. Therefore, the benefits of unifying these two worlds becomes evident. By using silicon as the conductive material of the optical signal and the metal as an efficient light interconnector in subwavelength structures, new devices can be created for the manipulation of the properties of light at the nanoscale. This thesis is focused on the integration of structures with subwavelength dimensions in silicon waveguides and in their application to new functionalities of light manipulation in silicon chips. These nanostructures serve as transducers between guided light and free space radiation, so they can also be termed nanoantennas. To begin with, the guided modes properties in silicon waveguides are described for the correct excitation of the nanoantennas, followed by the demonstration of integration techniques of these nanostructures in these waveguides to increase their interaction efficiency with the guided light. In addition, the coherent control of the absorption and scattering of a metallic nanoantenna integrated in a silicon waveguide is demonstrated. Finally, from the asymmetric positioning of the nanostructure with respect to the waveguide, new polarization manipulation methods are proposed and demonstrated, such as the ability to synthesize desired states of polarization at the nanoscale. This will lead to the theoretical and experimental demonstration of a Stokes nanopolarimeter, based on photon-on-silicon technology, capable of determining the polarization state locally, optimally, and non-destructively, enabling its use for real-time polarization measurements in integrated circuits. / La fotònica sobre silici s'ha convertit en la tecnologia més important en la producció de xips integrats fotònics. Els seus grans avantatges, entre les quals destaquen la seva idoneïtat per a la fabricació a gran escala i el seu baix cost de producció, com a resultat de la possibilitat de l'ús tecnologia CMOS, són motiu suficient per justificar la seva supremacia sobre altres plataformes d'integració. Malgrat els múltiples dispositius ja implementats en aquesta tecnologia, entre els quals cal destacar filtres WDM o moduladors electro-òptics, encara hi ha espai per a la millora, sobretot quant a la reducció del foot-print dels dispositius o a la creació de noves funcionalitats per a la manipulació de la llum. Aquestes millores podrien portar-se a terme mitjançant la integració de components amb dimensions sub-lambda sorgits en el camp conegut com plasmònica. Aquesta disciplina estudia la interacció entre la llum i els metalls, que ve intervinguda per l'existència d'ones conegudes com plasmons de superfície. Una de les propietats clau dels plasmons és la seva capacitat per confinar la llum molt per sobre del límit de difracció, la qual cosa és limitant en el cas de la fotònica sobre silici. No obstant això, les pèrdues per absorció dels metalls a freqüències òptiques impedeixen el seu ús per al guiat de la llum en grans distàncies. Es fa evident, per tant, els beneficis d'unificar aquests dos mons. Usant el silici com a material conductor del senyal òptic i el metall com eficient interactor amb la llum en estructures sub-lambda, es poden crear nous dispositius per a la manipulació de les propietats de la llum en la nanoescala. Aquesta Tesi està centrada en la integració d'estructures amb dimensions sub-lambda en guies de silici i en la seva aplicació a noves funcionalitats de manipulació de la llum en xips de silici. Aquestes nanoestructures serveixen de transductors entre la llum guiada i la radiació en espai lliure, de manera que també poden ser denominades nanoantenes. Per començar, es descriuen les propietats de les maneres guiats en guies d'ona de silici per a la correcta excitació de les nanoantenes, seguit de la demostració de tècniques d'integració d'aquestes nanoestructures en les pròpies guies per augmentar la seva eficiència d'interacció amb la llum guiada. A més, es demostra el control coherent de l'absorció i el scattering d'una nanoantenna metàl·lica integrada en una guia de silici. Finalment, a partir del posicionament asimètric de la nanoestructura respecte a la guia, es proposen i demostren nous mètodes de manipulació de la polarització, com la capacitat per sintetitzar estats de polarització desitjats a escala nanomètrica. Això desembocarà en la demostració teòrica i experimental d'un nanopolarímetre de Stokes, basat en tecnologia fotònica sobre silici, capaç de determinar l'estat de polarització de manera local, òptima, i no destructiva, habilitant el seu ús per a mesures de polarització en temps real en circuits integrats. / Espinosa Soria, A. (2018). Design and implementation of nanoantennas on integrated guides and their application on polarization analysis and synthesis [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/105382

Surface modification of colloidal nanoparticles is essential for broadening the scope of nanotechnology. In this dissertation, we discuss novel approaches to functionalize the surface of nanoparticles to tailor their properties for applications including radical polymerization inhibitors, supported heterogeneous catalysts, and building blocks for plasmonic devices. First, we investigate the interaction of hydrogen-terminated silicon nanoparticles (H-SiNPs) with Karstedt's catalyst and report a room‑temperature synthesis of Pt-coated SiNPs with highly tunable Pt loading. Analysis of the Pt on-Si ensemble reveals surface-bound Pt(II) on SiNPs which can undergo ligand exchange. Upon calcination, Pt-loaded SiNPs catalyze the hydrogenation of phenyl acetylene, and the SiNP scaffold enables efficient recovery and reuse of the catalyst. Conditions that favor the reductive elimination of the catalyst and efficient hydrosilylation of olefins are also discussed. Next, we report H-SiNPs as inhibitors for anerobic thermal autopolymerization of methacrylates. Prior to use, these solid-state inhibitors can be easily removed from the methacrylic monomers by low-speed centrifugation, offering great advantage to the traditionally used phenols and quinones. Analysis of SiNPs isolated after heating in methacrylates reveals the grafting of ester groups. As such, thermal hydrosilylation is presented as a powerful yet facile route to attach ester and allyl ester groups onto the surface of SiNPs. Finally, we report a method to rapidly and uniformly assemble gold nanoparticles (AuNPs) and their clusters on cm‑scale unmodified substrates. Cetyltrimethylammonium (CTAC) capped AuNPs were conjugated to a sparse coating of poly(ethylene glycol) and extracted into dichloromethane. The clustered patterns were deposited on hydroxyl terminated surfaces from stable dispersions using centrifugal force. The degree of clustering on substrates was tuned by varying a single parameter, the concentration of CTAC in the deposition dispersion. This approach bridges the gap between methods for depositing isolated AuNPs (typically using electrostatic interactions) and AuNP clusters (using covalent or electrostatic binders) and enables large-scale uniform deposition of isolated AuNPs, as well as clusters with tunable size. The non‑covalent assembly onto the substrate provided a means for depositing AuNPs into nanowells in topographically patterned substrates: after uniform deposition onto these substrates, the AuNPs on the surface were selectively removed using mechanical rubbing. This facile approach enabled large-scale selective deposition of AuNPs into patterned substrates that are attractive as SERS substrates and refractive index sensors.

Raman spectroscopy is an extremely versatile technique with molecular sensitivity and fingerprint specificity. However, the translation of this tool into a deployable technology has been stymied by irreproducibility in sample preparation and the lack of complex data analysis tools. In this dissertation, a droplet microfluidic platform was prototyped to address both sample-to-sample variation and to introduce a level of quantitation to surface enhanced Raman spectroscopy (SERS). Shifting the SERS workflow from a cell-to-cell mapping routine to the mapping of tens to hundreds of cells demanded the development of an automated processing tool to perform basic SERS analyses such as baseline correction, peak feature selection, and SERS map generation. The analysis tool was subsequently expanded for use with a multitude of diverse SERS applications. Specifically, a two-dimensional SERS assay for the detection of sialic acid residues on the cell membrane was translated into a live cell assay by utilizing a droplet microfluidic device. Combining single-cell encapsulation with a chamber array to hold and immobilize droplets allowed for the interrogation of hundreds of droplets. Our novel application of computer vision algorithms to SERS maps revealed that sialic sugars on cancer cell membranes are found in small clusters, or islands, and that these islands typically occupy less than 30% of the cell surface area. Employing an opportunistic mindset for the application of the data processing platform, a number of smaller projects were pursued. Biodegradable aliphatic-aromatic copolyesters with varying aromatic content were characterized using Raman spectroscopy and principal component analysis (PCA). The six different samples could successfully be distinguished from one another and the tool was able to identify spectral feature changes resulting from an increasing number of aryl esters. Uniquely, PCA was performed on the 3,125 spectra collected from each sample to investigate point-to-point heterogeneities. A third set of projects evaluated the ability of the data processing tool to calculate spectral ratios in an automated fashion and were exploited for use with nano-pH probes and Rayleigh hot-spot normalization. / Ph. D. / How can we understand the dynamic behavior of the cell membrane? Do certain polymeric structures in biodegradable plastic favor bacterial growth and subsequent degradation? To answer these and other intriguing scientific questions, techniques and technologies must be borrowed from a diverse array of fields and combined with fundamental understanding to create innovative solutions. In this dissertation, a two-dimensional surface enhanced Raman spectroscopy (SERS) assay was translated into a live cell assay by utilizing a droplet microfluidic device. Combining single-cell encapsulation with a chamber array to hold and immobilize droplets allowed for the interrogation of hundreds of droplets. Shifting the SERS workflow from a manual cell-to-cell mapping routine to the mapping of tens to hundreds of cells demanded the development of an automated processing tool to perform basic SERS analyses such as baseline correction, peak feature selection, and SERS map generation. Our novel application of computer vision algorithms to SERS maps was able to reveal that sialic sugars on cancer cell membranes are found in small clusters, or islands, and that these islands typically occupy less than 30% of the cell surface area. With an opportunistic mindset, several smaller projects that combine Raman and SERS with extensive data analysis were also pursued. Biodegradable plastics of varying content were studied with Raman spectroscopy. The aliphatic and aromatic polymeric units within these plastics both contain esters, but it is hypothesized that enzymatic hydrolysis occurs at the units asymmetrically. For each of six different samples, five maps were collected, processed using the analysis tool, and then analyzed using a multivariate analysis toolbox. Principal component analysis (PCA) was used to distinguish the polymers and to identify spectral feature changes resulting from an increasing v number of aryl esters. Uniquely, PCA was performed on the 3,125 spectra collected from each sample to investigate point-to-point heterogeneities. A third set of projects evaluated the ability of the data processing tool to calculate spectral ratios in an automated fashion and it was exploited for use with nano-pH probes and Rayleigh hot-spot normalization

Nanofabrication techniques continue to advance and are rapidly becoming the primary route to enhancement for the electrical, thermal, and optical properties of materials. The work presented in this dissertation details fabrication and characterization techniques of thin films and nanoparticles for these purposes. The four primary areas of research presented here are thermoelectric enhancement through nanostructured thin films, an alternative frequency-domain thermoreflectance method for thin film thermal conductivity measurement, thermal rectification in nanodendritic porous silicon, and plasmonic enhancement in silver nanospheroids as a reverse photolithography technique. Nanostructured thermoelectrics have been proposed to greatly increase thermopower efficiency and to bring thermoelectrics to mainstream power generation and cooling applications. In our work, thermoelectric thin films of SbTe, BiTe, and PbTe grown by atomic layer deposition and electrochemical atomic layer deposition were characterized for enhanced performance over corresponding bulk materials. Seebeck coefficient measurements were performed at temperatures ranging from 77 K to 380 K. Atomic composition was verified by energy-dispersive X-ray spectroscopy and structures were imaged by scanning electron microscopy. All thin films measured were ultimately found to have a comparable or smaller Seebeck coefficient to corresponding materials made by conventional techniques, likely due to issues with the growth process. Frequency-domain thermoreflectance offers a minimally invasive optical pump-probe technique for measuring thermal conductivity. Like time-domain thermoreflectance, the version of frequency-domain thermoreflectance demonstrated here relies on a non-zero thermo-optic coefficient in the sample, but uses moderate cost continuous wave lasers modulated at kHz or MHz frequencies rather than a more expensive ultrafast laser system. The longer timescales of these frequency ranges enables this technique to take measurements of films with thicknesses ranging from 100 nm to 10 um, complimentary to time-domain thermoreflectance. This method differentiates itself from other frequency-domain methods in that it is also capable of simultaneous independent measurements of both the in plane and out of plane values of the thermal conductivity in anisotropic samples through relative reflective magnitude, rather than phase, measurements. We validated this alternate technique by measuring the thermal conductivity of Al2O3 and soda-lime and found agreement both with literature values and with separate measurements obtained with a conventional time-domain thermoreflectance setup. Thermal rectification has the potential to enhance microcircuit performance, improve thermoelectric efficiency, and enable the creation of thermal logic circuits. Passive thermal rectification has been proposed to occur in geometrically asymmetric nanostructures when heat conduction is dominated by ballistic phonons. Here, nanodendritic structures with branch widths of ~ 10 nm and lengths of ~ 20 nm connected to ~ 50 um long trunks were electrochemically etched from <111> silicon wafers. Thermal rectification measurements were performed at temperatures ranging from 80 K to 250 K by symmetric thermal conductivity measurements. No thermal rectification was ultimately found in these samples within the margin of thermal conductivity measurement error 1%. This result is consistent with another study which found thermal rectification with greater conduction in the direction opposite to what ballistic phonon heat conduction theories predicted. Plasmonic resonance concentrates incident photon energy and enables channeling of that energy into sub-wavelength volumes where it can be used for nanoscale applications. We demonstrated that surface plasmon polaritons induced in silver nanosphereoid films by 532 nm light defunctionalize previously photocleaved ligands adsorbed onto the films, to yield a reverse photolithographic technique. In this method, gold nanosphere conjugation were conjugated to a photocleaved ligand, however conjugation could be inhibited by exposing the cleaved ligand to 532 nm light and consequently yield a reversal technique. This defunctionalizion effect did not occur on gold films or nanoparticles conjugated with the ligand in IR spectroscopy, and was observed to have a reduced effect in silver films relative to silver nanospheroid film. As silver nanospheroid films and gold nanospheres of the size used in this study are known to have plasmon resonance in the green wavelengths, while gold and silver continuous films do not, this defunctionalization likely results from plasmonic effects. / Ph. D. / The increasing trend toward smaller and more efficient electronic devices requires continuous refinement of manufacturing and materials technology. From communication devices to temperature management, miniaturization in electronic components allows for greater versatility in applications. In battery powered devices, increasing efficiency both extends operational lifetime and reduces operational costs in terms of kilowatt hours as well as carbon footprint resulting from powering the devices. Through the application of miniaturization, conventional fabrication techniques are rapidly approaching the physical limits of their applicability, and newer techniques must be developed. Nanofabrication methods involve working with materials at scales where quantum mechanical effects can dominate over classical effects. Some examples of these effects are unique heat and electrical conduction properties in, effectively, one or two dimensional materials as in the case of quantum dots or thin films. This size regime not only allows for construction at smaller scales, but also enables the manipulation of quantum mechanical effects to produce different types of devices which were not possible to make previously. For example, materials can be built up one atomic layer at a time, enabling the creation of a material with perfect atomic ordering, as opposed to common methods which yield many imperfections. This dissertation details fabrication and characterization techniques of nanoscale devices focusing on thermoelectrics, thin film thermal conductivity, thermal rectification, and plasmonic enhancement. Thermoelectrics are devices that use temperature differences across the device to produce electric power or, conversely, create a temperature difference across the device when electrically driven. Theoretical studies have proposed that the efficiency of thermoelectric materials can be greatly increased through nanofabrication. Here, thin film thermoelectric devices made from commonly employed bulk materials such as SbTe, BiTe, and PbTe produced by atomic layer deposition and electrochemical atomic layer deposition, were characterized to test these theories. Ultimately, no notable enhancement was found in our samples over conventionally produced materials, but this may have been due to difficulties in the fabrication process of the thin films. Thermoreflectance is a purely optical technique for thermal conductivity (the measure of how well a material conducts heat) measurement which can measure thin film materials. Other benefits of the technique are its speed and that samples measured by it are not damaged, unlike other methods which effectively ruin the sample for any purpose beyond the measurement. Cost, however, is a major downside to conventional thermoreflectance, as it requires pricey ultrafast laser systems. Presented here is an alternative method of thermoreflectance which used much more economical diode lasers to achieve thermal conductivity measurements. This system costs approximately a tenth of what a conventional system would, while also being capable of measuring in-plane and cross-plane thermal conductivity simultaneously. The drawbacks of this method are thicker film requirements and the necessity of having well-defined control samples of similar thermal conductivity to the sample of interest. Management of waste heat is one of the major design limitations in modern circuitry. Removal of waste heat is most often performed by adhering large surface area heat sinks to heat generating areas and/or mechanical fans to aid in heat radiation. One proposed method of reducing the amount of space required for heat management is through the development and implementation of thermal rectifiers, which are materials that conduct heat more efficiently in one direction than the opposite. The thermal rectification properties of nanodendritic porous silicon is explored here. This material is made by electrochemically etching silicon wafers such that the surface is formed into an array of pine-tree-like structures on the nanoscale. While it was proposed that these structures would manifest thermal rectification under the right conditions, no rectification was observed. This result is consistent with previous experimental work which observed preferential heat conduction in the opposite direction to that proposed by this theory, likely caused by a different effect. Plasmonic enhancement enables absorption and manipulation of light energy in structures far smaller than conventional techniques permit. In the case of photolithography, a go-to method of commercial microfabrication, the smallest feature size is a function of the wavelength of light used and is typically around 100 nm. Plasmonic techniques enable optical manipulation in structures of sizes down to a few nm. The plasmonic enhancement technique demonstrated here is a photolithography technique in which selective nanosphere-to-nanosphere binding occurs This technique offers another method of directed self-assembly, where nanoparticles can come together to form larger structures. A benefit of this method is that large quantities of nanoparticle assemblies can occur simultaneously, allowing for rapid production of assembled nanostructures.

Since Ebbesen's seminal work in 1998 observing extraordinary optical transmission (EOT) through nanohole arrays, much research has focused on the role of surface plasmon polaritons (SPPs) in EOT. While the energy and momentum conditions have become clear, no consensus has been reached on the role of incident light polarization. This study presents a simple model that captures Bloch-SPP excitation, including the role of polarization, in general periodic plasmonic structures. Our model predicts that under certain conditions polarization conversion should occur in EOT light transmitted through the nanohole array. We experimentally measure polarization conversion in EOT and compare the experimentally obtained results to the predictions of our model. Using numerical simulations, we tie the far field experimental results to the near field underlying physics described by our model. In using polarization conversion to provide evidence supporting our model, we also establish a novel approach to achieving polarization conversion based on SPPs instead of hole shape or other techniques in literature, and present reasons why this approach to achieving polarization conversion may be better suited for applications in biomedical sensing and optical elements. / Master of Science / In 1998, Ebbesen et al¹ observed that when light is shown on a metal nanofilm perforated with nanoholes more light appears on the other side of the metal film than was incident on the nanoholes. The unexpectedly high transmission of light through the nanohole array was termed extraordinary optical transmission (EOT), and quickly found applications in diverse fields such as biomedical sensing^13,14, energy harvesting^12,31, and nonlinear optics^12–14,24 . As the importance of EOT in applications became clear, interest developed in understanding the fundamental physics involved. Over the next 20 years, researchers showed that the incident light (made up of electromagnetic fields) excites conduction electrons on the surface of the metal film¹¹ . Specifically, the light and the electrons couple to form quasiparticles known as surface plasmon polaritons (SPP) which propagate along the surfaces of the metal film. The SPPs on the back surface of the metal film then radiate free space transmitted light, which is observed as EOT. However, much of the physics involved how SPPs mediate EOT has remained unclear. The first focus of this work is theoretical, presenting a microscopic model for SPP mediated EOT. In contrast to many groups which aim to characterize SPPs from their far field properties, our model focuses on the near field microscopic physics and presents the far field properties as a consequence of the near field physics. Since the near field cannot be probed iv experimentally, we use numerical simulations to both verify our model’s predictions in the near field and predict the properties that should be measured in the far field. The second focus of this work is more applications driven. We notice that our model predicts that under certain conditions SPPs should cause a phenomenon known as polarization conversion to occur, which is when the polarization of the transmitted light is different from the polarization of the incident light. We experimentally measure the predicted polarization conversion, thereby providing substantial experimental evidence in support of our theoretical model. Our novel approach to achieving polarization conversion based on the behavior of SPPs differs substantially from the approaches in literature (usually based on hole shape²⁴). We present the reasons why our SPP-based approach to achieving polarization conversion is more robust to fabrication imperfections than the conventional approaches, and describe how our approach could affect various applications.

Diese Arbeit präsentiert eine vollständige quantenmechanische Beschreibung eines Systems bestehend aus einem Molekül und einem metallischem Nanopartikel (MNP) in der Gegenwart eines Strahlungsfeldes. Zuerst wird ein System aus einem Molekül und einem Gold-MNP betrachtet. Das Emissionsund Absorptionsspektrum zeigt viele scharfe molekulare Schwingungssatelliten auf einem breiten Plasmonmaximum. Eine Verstärkung der Schwingungssatelliten um drei Größenordnungen ist auf effiziente Absorption und Emission durch die MNP zurückzuführen. Dann wird ein System aus einer molekularen Kette mit einem Gold-MNP untersucht. Alle zuvor genannten Phänomene treten auch hier auf, jedoch werden die Schwingungssatelliten durch das Exzitonenband der molekularen Kette ersetzt. Anschließend wird ein Nano-Laser aus vielen Molekülen und einem Gold-MNP betrachtet. Die Moleküle werden durch inkohärentes optisches Pumpen angeregt. Dabei wird eine starke Plasmonanregung durch die gemeinsame Kopplung an die Moleküle erreicht. Die Photonenemission des Lasers zeigt, dass die Intensität ansteigt, während die Linienbreite schmaler wird. Die Korrelationsfunktion in zweiter Ordnung für die Photonen in Verbindung mit der schmaler Emission könnte dabei sogar einen Hinweis auf Lasing geben. Zuletzt wird eine Nanoverbindung aus einem Molekül und zwei sphärischen metallischen Elektroden betrachtet. Das Molekül wird durch den sequentiellen Ladungstransfer angeregt. Durch die Kopplung an die Moleküle werden die Elektrodenplasmonen angeregt. Die Photonenemission der Verbindung zeigt, dass die scharfen molekularen Schwingungssatelliten um das Tausendfache verstärkt werden. Anschließend ist ein System aus zwei pyramidalen Elektroden, die seitlich von zwei Gold-MNP eingeschlossen werden, untersucht. Hier können die Schwingungssatelliten einzeln verstärkt werden, indem der Abstand zwischen den MNP variiert wird. Wir zeigen auch, dass das Lasing in einer Verbindung aus vielen Molekülen theoretisch möglich ist. / This thesis presents a unified quantum description of the combined molecule-metal nano-particle system in the presence of a radiation field. Firstly, a single molecule coupled to a gold nano-sphere is investigated. The emission and absorption spectrum show many sharp molecular vibrational satellites over one broad plasmon peak. The three orders of magnitude enhancement of the vibrational satellites is due to the great ability of the sphere to absorb and emit photons. Secondly, a molecular chain coupled to a gold nano-sphere is investigated. All the phenomena mentioned above appear also for such system, except that the vibrational satellites are replaced by the Frenkel exciton band of the molecular chain. Thirdly, a plasmonic nano-laser consisting of many dye molecules and a gold nano-sphere is considered. The molecules are initially excited by incoherent optical pump. The strong plasmon excitation of the sphere is achieved due to the concerted coupling with the molecules. The emission of the laser shows that the intensity is enlarged while the line-width is reduced. The second-order correlation function of photons together with the emission narrowing can be utilized to determine lasing operation. Finally, a nano-junction formed by a molecule and two spherical metallic leads is investigated. The molecule is excited through sequential electron transfer. The lead plasmons get excited due to the coupling with the excited molecule. The emission of the junction shows that the molecular vibrational satellites are about one thousand times enhanced by the lead plasmons. Then, a junction with two pyramidal metallic leads sandwiched by two gold nano-spheres is investigated. The simulations show that the molecular vibrational satellites can be selectively enhanced by varying the inter-sphere distance. It is also proved that the lasing can be realized by a junction with many molecules.

Diese Arbeit ist der theoretische Untersuchung nichtlinearer optischer Prozesse in metall-dielektrischen Medien gewidmet, wobei Möglichkeiten zur Ausnutzung der erhöhten nichtlinearen Koeffizienten und der Feldüberhöhung durch metallische Nanoteilchen untersucht wurden. Die wichtigsten Ergebnisse beziehen sich auf eine Untersuchung der zeitabhängigen sättigbaren Absorption in Gläsern, die mit metallischen Nanoteilchen dotiert sind, ihrer physikalischen Ursache sowie verschiedener Anwendungen in der nichtlinearen Optik. Zur Untersuchung der Zeitabhängigkeit der nichtlinearen Rückwirkung wird unter Verwendung des semi-klassischen Zwei-Temperatur-Modells eine zeitabhängige Gleichung für die nichtlineare dielektrische Funktion der Metalle hergeleitet. Die Ergebnisse zeigen, dass solche Gläser, sich als sehr effiziente sättigbare Absorber im Spektralbereich vom sichtbaren bis nahen IR eignen. Für kurzwellige Laser im blau/violetten Spektralbereich wird die Dynamik der Modenkopplung in Festkörper- und Halbleiter-Scheibenlaser untersucht. Weiterhin wird ein neuer Mechanismus für die Realisierung von langsamem Licht vorgeschlagen und im Detail untersucht, der in solchen dotierten Gläsern in einem Pump-Probe Regime infolge der sättigbaren Absorption in der Nähe der Plasmonresonanz realisierbar ist. Weiterhin untersuchten wir die Möglichkeit einer Femtosekunden Plasmon Impulserzeugung durch Modenkopplung eines Oberflächen Plasmonlasers mit einem Bragg Resonator, der aus einer dünnen Schicht aus Silber sowie einem sättigbaren Absorbers und einem Verstärker besteht. Im letzten Teil der Arbeit werden Ergebnisse zur Erzeugung hoher Harmonischer in Edelgasen in der Nähe einer metallischen fraktalen rauen Oberfläche untersucht. Die Berechnungen zeigen eine Reduzierung der geforderten Intensität um drei Größenordnungen und eine um zwei Größenordnungen erhöhte Effizienz gegenüber der bisher experimentell realisierten HHG in der Nähe von metallischen "bow-tie"Nanostrukturen. / This work reports results of a theoretical study of nonlinear optical processes in metal-dielectric nanocomposites used for the increase of the nonlinear coefficients and for plasmonic field enhancement. The main results include the study of the transient saturable nonlinearity in dielectric composites doped with metal nanoparticles, its physical mechanism as well its applications in nonlinear optics. For the study of the transient response, a time-depending equation for the dielectric function of the nanocomposite using the semi-classical two-temperature model is derived. By using this approach, we study the transient nonlinear characteristics of these materials in comparison with preceding experimental measurements. The results show that these materials behave as efficient saturable absorbers for passive mode-locking of lasers in the spectral range from the visible to near IR. We present results for the modelocked dynamics in short-wavelength solid-state and semiconductor disk lasers; in this spectral range other efficient saturable absorbers do not exist. We suggest a new mechanism for the realization of slow light phenomenon by using glasses doped with metal nanoparticles in a pump-probe regime near the plasmonic resonance. Furthermore, we study femtosecond plasmon generation by mode-locked surface plasmon polariton lasers with Bragg reflectors and metal-gain-absorber layered structures. In the final part of the thesis, we present results for high-order harmonic generation near a metallic fractal rough surface. The results show a possible reduction of the pump intensities by three orders of magnitudes and two orders of magnitudes higher efficiency compared with preceding experimental results by using bow-tie nanostructures.

Récemment, la famille des dichalcogénures de métaux de transition (TMDs) (MoS2, WS2, MoSe2...) a suscité l'intérêt de nombreuses équipes de recherche en raison de leurs propriétés optiques, électroniques et spintroniques exceptionnelles. Ma thèse est centrée sur l'association de monocouches de TMDs à des nano-structures plasmoniques. Ces dernières apportent une exaltation des propriétés d'absorption, de diffusion et d'émission optiques qui peuvent être mises à profit dans divers domaines d'applications tels que l'opto-électronique, la photo-catalyse ou les capteurs. Dans une première partie je me suis intéressée à l'interaction plasmon-exciton dans des systèmes hybrides constitués de couches de MoSe2 élaborés par dépôt chimique en phase vapeur (CVD) et transférées sur les nanodisques d'or. La résonance plasmon est contrôlée par le diamètre et la séparation entre les nano-disques. Grâce à des mesures de transmission optique et de photoluminescence, et à une analyse détaillée des réponses spectrales basée sur un modèle analytique et des simulations numériques, j'ai mis en évidence un couplage de type Fano entre les plasmons de surface des nanodisques et les transitions excitoniques de MoSe2. J'ai étudié la dépendance de ce couplage en fonction de la taille des disques, du nombre de monocouches de MoSe2 déposées et aussi en fonction de la température. Une analyse quantitative des résultats a été menée en simulant numériquement non seulement le champ local plasmonique mais aussi son couplage avec le moment dipolaire des transitions excitoniques. Pour compléter l'exploration des propriétés optiques du système MoSe2@Au, je me suis intéressée à la diffusion Raman dans des conditions d'excitation résonante et non-résonante de la transition hybride plasmon-exciton. L'idée principale étant que la résonance plasmonique apporte une exaltation de la diffusion Raman par effet SERS (Surface Enhanced Raman Scattering) tandis que les transitions excitoniques contribuent par l'effet Raman résonnant. Cette combinaison des résonances plasmonique et excitonique conduit à un effet SERS résonant. J'ai ainsi pu distinguer les contributions relatives de ces deux résonances, notamment grâce à l'imagerie confocale de la diffusion Raman. J'ai également montré que, dans ces conditions d'excitation résonnante de la transition plasmon-exciton, un phénomène d'hyperthermie a lieu. la modélisation par simulation numérique du champ proche optique et de la diffusion Raman a été utile pour comprendre les principaux facteurs limitatifs de l'exaltation Raman. Ensuite, la couche de MoSe2 a été utilisée comme substrat de nanoparticules d'Au. Les mesures de photoluminescence ont révélé une extinction quasi-totale de l'émission de la photoluminescence. Afin d'expliquer ce phénomène, deux possibilités ont été discutés : (i) le passage de la structure de bande électronique de la couche de TMD d'un semiconducteur à gap direct à indirect à cause de la contrainte imposée par les nanoparticules d'Au (ii) le désordre structural dû au dépôt des nanoparticules d'Au (iii) le transfert des porteurs photo- générés du semiconducteur vers le métal. Grâce aux mesures Raman, et à l'émission radiative des nanoparticules d'Au, j'ai mis en évidence un phénomène de transfert de charges entre le semi conducteur et le métal. Pour compléter les interprétations proposées, j'ai mené une étude comparative avec les propriétés optiques de couche de TMD couvertes \nolinebreak de silice. Ce travail de thèse a été mené au sein du groupe NeO du CEMES et dans le cadre d'une collaboration avec le groupe du Professeur Jun Lou de l'université de Rice à Houston. / Transition metal dichalcogenide materials (TMDs) are increasingly gaining attention, due to their unique optical, spintronic, and electronic properties. These properties result from the ultimate confinement in 2D monolayers of a direct band-gap semiconductor and the lack of inversion symmetry in the crystallographic structure. To control and enhance the optical response of these materials, it is interesting to integrate them with plasmonic nano-resonators. The TMDs/plasmonic hybrid systems have been extensively studied for plasmon-enhanced optical signals, photocatalysis, photodetectors, and solar cells. In this context, this thesis deals with the interaction between TMD monolayers and gold nanostructures. In a first part, an hybrid system composed of CVD grown MoSe2 monolayers transferred on gold nanodisks was studied. Surface plasmon resonance was tuned by controlling the nanodisks size and the inter-disks separation. The optical properties of the nanostructures are probed by means of spatially resolved optical transmission and photoluminescence spectroscopies. Fano-type coupling regime between the surface plasmon of the gold nanodisks and the MoSe2 exciton was evidenced by a quantitative analysis of the optical extinction spectra based on an analytical model. Our interpretations were supported by numerical simulations. The number of MoSe2 monolayer dependence as well as the Temperature dependence of the plasmon-exciton interaction was investigated. Our results were quantatively analysed on the nanometric scale by studying the local electromagnetic near-field and the excitonic transition dipole momentum interaction. Furthermore, the Raman scattering of MoSe2@Au system was carried out. A particular situation was investigated where a resonant interaction between the surface plasmon of nanodisks and A exciton of v occur. The contribution of these two resonances leads to a resonant surface enhanced Raman scattering (SERRS) effect. The Raman Scattering excitation is selected to resonantly excite the Surface Plasmon resonance and MoSe2 excitonic transition simultaneously. The relative contribution of the surface Plasmon and the confined exciton to the resonant Raman scattering signal is pointed out. In this resonant condition, a hyperthermia effect was detected. Numerical simulations of the SERS gain were useful to figure out the main factors affecting the SERS intensity enhancement in MoSe2@Au. In a second part, the TMD monolayer was used as a substrate of Au nanoparticles. Au nanoislands were deposited on mono- and few-layered MoSe2 flakes. Photoluminescence (PL) measurements revealed a net quenching of the MoSe2 photoluminescence. To figure out the origin of this quenching three possibilities were discussed (i) the charge transfer between the TMD monolayer and the Au particles (ii) the direct to indirect gap transition of the TMD electronic band structure caused by the strain induced by the metal deposition (iii) structural disorder imparted by the nanoparticles in the TMD/metal interface. Owing to the Raman scattering measurements and using the radiative emission of the gold nanoparticles, we evidenced a charge transfetrt between the metallic nanostructures and the semiconductor. In order to complement our interpretations a comparative study with respect to optical properties of TMD covered by a silica film was carried out. The present work was held within the NeO group in CEMES, in a frame of a collaboration with the group of thr Pr. Jun Lou from Rice university, Houston.

<div>My dissertation research is in the field of plasmonics. Specifically, my focus is on the use of plasmonics for various applications such as solar energy harvesting and optically addressable magnetic memory devices. Plasmonics is the study of collective oscillations of free electrons in a metal coupled to an electromagnetic field. Such oscillations are characterized by large electromagnetic field intensities confined in nanoscale volumes and are called plasmons. Plasmons can be excited on a thin metal film, in which case they are called surface plasmon polaritons or in nanoscale metallic particles, in which case they are called localized surface plasmon resonances. Researchers have taken advantage of this electromagnetic field enhancement resulting from the excitation of plasmons in metallic structures and demonstrated phenomenon such as plasmon-assisted photocatalysis, plasmon-induced local heating, plasmon-enhanced chemical sensing, optical modulators, nanolasers, etc.</div><div>In the first half of my dissertation, I study the role of plasmonics in hydrogen production from water using solar energy. Hydrogen is believed to be a very viable source of alternative green fuel to meet the growing energy demands of the world. There are significant efforts in government and private sectors worldwide to implement hydrogen fuel cells as the future of the automotive and transportation industry. In this regard, water splitting using solar energy to produce hydrogen is a widely researched topic. It is believed that a Solar-to-Hydrogen (STH) conversion efficiency of 10% is good enough to be considered for practical applications. Iron oxide (alpha-Fe2O3) or hematite is one of the candidate materials for hydrogen generation by water splitting with a theoretical STH efficiency of about 15%. In this work, I experimentally show that through metallic gold nanostructures we can enhance the water oxidation photocurrent in hematite by two times for above bandgap wavelengths, thereby increasing hydrogen production. Moreover, I also show that gold nanostructures can result in a hematite photocurrent enhancement of six times for below bandgap wavelengths. The latter, I believe, is due to the excitation of plasmons in the gold nanostructures and their subsequent decay into hot holes which are harvested by hematite.</div><div>The second part of my dissertation involves data storage in magnetic media. Memory devices based on magnetic media have been widely investigated as a compact information storage platform with bit densities exceeding 1Tb/in2. As the size of nanomagnets continue to reduce to achieve higher bit densities, the magnetic fields required to write information in these bits increases. To counter this, the field of heat-assisted magnetic recording (HAMR) was developed where a laser is used to locally heat up a magnet and make it susceptible to smaller magnetic switching fields. About two decades ago, it was realized that a single femtosecond laser pulse can switch magnetic media and therefore could be used to write information in magnetic bits. This field is now known as All-Optical Magnetic Switching (AOMS). My research aims to bring together the two fields of HAMR and AOMS to create optically addressable nanomagnets for information storage. Specifically, I want to show that plasmonic resonators can couple the laser field to nanomagnets more efficiently. This can therefore be used not only to heat the nanomagnets but also switch them with lower optical energy compared to free-standing nanomagnets without any plasmonic resonator. The results of my research show that by coupling metallic resonators, supporting surface plasmons, to nanomagnets, one can reduce the light intensity required for laser induced magnetization reversal.</div>