<p>In this thesis, we discuss the study and realization of surface plasmon polaritons (SPPs) and their devices. Plasmonics is the emerging field that will help technologies advance further into the nano-scale without the concern for delays or size limitations. SPPs are a more advanced field of photonics as they use metals instead of the semiconductors or insulators used in optics. They operate at frequencies in the light and near infrared spectrum, as this range produces their unique characteristics. Plasmonics possess the miniaturization of electronics and the speed of photonics. They do not suffer from both the delays in nano-electronics, and the size limitations faced in optics. In this thesis, we present the optimization of plasmonic slit arrays by designing the parabolic phase profile of the array. Moreover, we present a novel multilevel plasmonic coupler that will aid in the realization of 3-D plasmonic chips, as well as quadrature modulation. The theory, procedures, and results are all presented and discussed.</p> / Master of Applied Science (MASc)

The geometry of a plasmonic nanostructure determines the charge-current distributions of its localized surface plasmon resonances (LSPR), thereby determining the device’s interactions with external electromagnetic fields. To target specific applications, we manipulate the nanostructure geometry to create different electromagnetic multipole moments, from basic electric and magnetic dipoles to more exotic higher order and toroidal multipoles. The nanoscale nature of the resonance phenomena makes electron beam spectromicroscopy techniques uniquely suited to probe LSPRs over a wide spectral range, with nanoscale spatial resolution. We use electron energy loss spectroscopy (EELS) in a monochromated scanning transmission electron microscope and cathodoluminescence spectroscopy (CL) in a scanning electron microscope to probe the near-field and far-field properties of LSPR. Electric dipoles within triangular prisms and apertures in Sierpiński fractals couple as the generation number is advanced, creating predictable spectral bands from hybridized dipole modes of parent generations with hierarchical patterns of high field intensity, as visualized in EELS. A magnetic dipole moment is engineered using a vertical split ring resonator (VSRR), pushing the limits of nanofabrication techniques. On this nanostructure we demonstrate the calculation of spatially resolved Stokes parameters on the emission of the magnetic dipole mode and a series of coupled rim modes. Coupling of the magnetic dipole mode of four VSRRs in a circular array creates an LSPR mode supporting the lesser-known toroidal dipole moment. We further probe the near-field configuration of this 3D array through tilting under the electron beam in EELS, and the far-field emission through CL of higher order rim modes. We also propose further configurations of five and six VSRRs to strengthen the toroidal dipole moment. All of the data presented herein was analyzed using custom Python code, which provides a unique graphical interface to 3D spectromicroscopy datasets, and a parallelized implementation of the Richardson-Lucy deconvolution algorithm. / Thesis / Doctor of Philosophy (PhD) / Certain types of metallic particles are capable of trapping light on a scale far below that which we can see; their light-trapping properties depend on their material and on their geometry. Using these tiny particles, we can manipulate the behaviour of light with greater freedom than is otherwise possible. In this thesis, we study how we can engineer the geometry of these particles to give predictable responses that can then be targeted towards specific applications. We study a fractal structure with predictable self-similar responses useful for high sensitivity detection of disease or hormone biomarkers; a resonating structure emulating a magnetic response which can be used in the design of unique new materials capable of bending light backwards and cloaking objects from sight; and a combination of these resonators in an array to demonstrate exotic electromagnetic behaviour still on the limit of our understanding.

Surface-enhanced Raman spectroscopy (SERS) is a powerful analytical technique that combines molecular specificity of vibrational fingerprints offered by Raman spectroscopy with single-molecule detection sensitivity from plasmonic hotspots of noble metal nanostructures. Label-free SERS has attracted tremendous interest in bioanalysis over the last two decades due to minimal sample preparation, non-invasive measurement without water background interference, and multiplexing capability from rich chemical information of narrow Raman bands. Nevertheless, significant challenges should be addressed to become a widely accepted technique in bio-related communities. In this dissertation, limitations from different aspects (performance, reliability, and analysis) are articulated with state-of-the-art, followed by how introduced works resolve them. For high SERS performance, SERS substrates consisting of vertically-stacked multiple metal-insulator-metal layers, named nanolaminate, were designed to simultaneously achieve high sensitivity and excellent uniformity, two previously deemed mutually exclusive properties. Two unique factors of nanolaminate SERS substrates were exploited for the improved reliability of label-free in situ classification using living cancer cells, including background refractive index (RI) insensitivity from 1.30 to 1.60, covering extracellular components, and 3D protruding nanostructures that can generate a tight nano-bio interface (e.g., hotspot-cell coupling). Discrete nanolamination by new nanofabrication additionally provides optical transparency, offering backside-excitation, thereby label-free glucose sensing on a skin-phantom model. Towards reliable quantitative SERS analysis, an electronic Raman scattering (ERS) calibration method was developed. ERS from metal is omnipresent in plasmonic constructs and experiences identical hotspot enhancements. Rigorous experimental results support that ERS can serve as internal standards for spatial and temporal calibration of SERS signals with significant potential for complex samples by overcoming intrinsic limitations of state-of-art Raman tags. ERS calibration was successfully applied to label-free living cell SERS datasets for classifying cancer subtypes and cellular drug responses. Furthermore, dual-recognition label-SERS with digital assay revealed improved accuracy in quantitative dopamine analysis. Artificial neural network-based advanced machine learning method was exploited to improve the interpretability of bioanalytical SERS for multiple living cell responses. Finally, this dissertation provides future perspectives with different aspects to design bio-interfaced SERS devices for clinical translation, followed by guidance for SERS to become a standard analytical method that can compete with or complement existing technologies. / Doctor of Philosophy / In photonics, metals were thought to be not very useful, except mirrors. However, at a length scale smaller than wavelength, it has been realized that metallic structures can provide unique ways of light manipulation. Maxwell's equations show that an interface between dielectric and metal can support surface plasmons, resulting in collective oscillations of electrons and light confinement. Surface-enhanced Raman spectroscopy (SERS) is a sensing technique that combines enhanced local fields arising from plasmon excitation with molecular fingerprint specificity of vibrational Raman spectroscopy. The million-fold enhancement of Raman signals at hotspots has driven an explosion of research, providing tons of publications over the last two decades with a broad spectrum of physical, chemical, and biological applications. Nevertheless, significant challenges should be addressed for SERS to become a widely accepted technique, especially in bio-related communities. In this dissertation, limitations from different aspects (performance, reliability, and analysis) are articulated with state-of-the-art, followed by how innovative strategies addressed them. Each chapter's unique approach consists of a combination of five aspects, including nanoplasmonics, nanofabrication, nano-bio interface, cancer biology, statistical machine learning. First, high-performance SERS substrates were designed to simultaneously achieve high sensitivity and excellent uniformity, two previously deemed mutually exclusive properties, by vertically stacking multiple metal-insulator-metal layers (i.e., nanolaminate). Their 3D protruding nanotopography and refractive-index-insensitive SERS response enabled label-free in situ classification of living cancer cells. Tweaked nanofabrication produced discrete nanolamination with optical transparency, enabling label-free glucose sensing on a skin phantom. Towards reliable quantitative SERS analysis, an electronic Raman scattering (ERS) calibration method was developed that can overcome the intrinsic limitations of Raman tags, and it was successfully applied to label-free living cell SERS datasets for classifying cancer subtypes and cellular drug responses. Furthermore, dual-recognition label-SERS with digital assay revealed improved accuracy in quantitative dopamine analysis. Advanced machine learning (artificial neural network) was exploited to improve the interpretability of SERS bioanalysis for multiple cellular drug responses. Finally, this dissertation provides future perspectives with different aspects, including SERS, biology, and statistics, for SERS to potentially become a standard analytical method that can compete with or complement existing technologies.

Owing to its centrosymmetric structure, the critical optical component of a silica fiber cannot to possess a second-order nonlinear optical susceptibility, Χ(²), preventing a silica fiber from many potential applications. Here, we theoretically and experimentally demonstrate a new technique to generate large and thermodynamically stable second-order nonlinearity into silica optical tapered fibers without breaking the centrosymmetry of the silica glass. The nonlinearity is introduced by surface layers with high polar-ordering fabricated by a novel hybrid covalent/ionic self-assembly multilayer technique. Despite the overall rotational symmetry of the nonlinear fiber, we observe significant second harmonic generation with ~ 400–500 fold enhancement of the SHG power compared to the traditional tapers. Phase matching for a SHG process in second-order nonlinear tapered fibers is also realized by the compensation of waveguide modal dispersion with material chromatic dispersion, which occurs only for submicron tapers where the modal dispersion is large. In addition, quasi-phase-matching for a nonlinear taper can be accomplished by introducing a periodic pattern into the nonlinear film coating. We use UV laser ablation for the controlled removal of particular nonlinear film segments on a taper surface in order to produce a Χ(²) grating structure. A resulting SHG enhancement from quasi-phase-matching is observed over a broadband spectrum of the pump light mainly due to the non-uniform shape of a taper waveguide. The laser ablation is a clean and fast technique able to produce well-define patterns of polymer films on either flat or curved substrate geometry. With surface layers containing reactive functional groups e.g. primary amines, we demonstrate that the resulting patterned film obtained from the laser ablation can be used as a template for further self-assembly of nanoparticles with high selectivity. A pattern feature size down to ~ 2μm or smaller can be fabricated using this approach. We also discuss preliminary results on a novel technique to further improve spatial accuracy for selective self-assembly of nanoparticles at an unprecedented level. Different types of nanoparticles are joined in order to form well-defined, molecular-like superstructures with nanoscale accuracy and precision. The technique is based on a selective surface functionalization of photosensitive molecules coated on metallic nanoparticles utilizing enhanced two-photon photocleavage at the plasmonically-active sites (hot spots) of the nanoparticles in resonance with an applied electromagnetic wave. As a result, the surface functional groups at the nanoparticle hot spots are different from the the other areas, allowing other kinds of nanoparticles to self-assemble at the hot spots with high degree of selectivity. / Ph. D.

Nanoparticles present a myriad of physical, optical, electrical, and chemical properties that provide valuable functionality to thin-film technologies. In order to successfully exploit these aspects of nanoparticles, appropriate dispersion and stability measures must be implemented. In this dissertation, different types of nanoparticles are coated with polymer and metallic layers to enable their effectiveness in both anti-reflection coatings (ARCs) and organic photovoltaics (OPVs). Ionic self-assembled multilayers (ISAMs) fabrication of poly(allylamine hydrochloride) (PAH) and silica nanoparticles (SiO2 NPs) results in highly-transparent, porous ARCs. However, the ionic bonding and low contact area between the film constituents lack sufficient mechanical and chemical stability necessary for commercial application. Chemical stability was established in the film by the encapsulation of SiO2 NPs by a photo-crosslinkable polyelectrolyte, diazo-resin (DAR) to make modified silica nanoparticles (MSNPs). UV-irradiation induced decomposition of the diazonium group and the development of covalent bonds with polyanions. Crosslinked MSNP/poly(styrene sulfonate) (PSS) ISAMs exhibited excellent anti-reflectivity (transmittance >98%, reflectance <0.2% in the visible range) and chemical stability against dissolution in a ternary solvent. Mechanical stability was also achieved by the incorporation of two additional PAH and poly(acrylic acid) (PAA) layers to create PAH/PAA/PAH/SiO2 NP interlayer ISAM ARCs. Thermal crosslinking of PAH and PAA facilitates the formation of covalent amide bonds between the two polyelectrolytes, as confirmed by FTIR. Since PAH and PAA are both weak polyelectrolytes, adjustment of the solution pH causes significant variations in the polymer chain charge densities. At low PAA pH, the decreased chain charge densities caused large SiO2 NP encapsulation thicknesses in the film with great mechanical stability, but poor anti-reflection (≤97% transmittance). At high PAA pH, the high chain charge densities induced thin encapsulation layers, insufficient mechanical stability, but excellent anti-reflection. At trade-off between the two extremes was founded at a PAA pH of 5.2 with excellent anti-reflection (less than 99% transmittance) and sufficient mechanical stability. The normal force required for scratch initiation was increased by a factor of seven for films made from a pH of 5.2 compared to those made from a pH of 6.0. Organic photovoltaics (OPVs) are an attractive area of solar cell research due to their inexpensive nature, ease of large-scale fabrication, flexibility, and low-weight. The introduction of the bulk heterojunction greatly improved charge transport and OPV performance by the blending of the active layer electron donor and acceptor materials, poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), into an interpenetrating network with high interfacial area between adjacent nanodomains. However, constrained active layer thicknesses restrict the total optical absorption and device performance. The localized surface plasmon resonance (LSPR) of plasmonic nanoparticles, such as anisotropic silver nanoplates (AgNPs), provides large local field enhancements and in coupling with the active layer, substantial optical absorption improvements can be realized. AgNPs were first integrated into the hole-transport layer (PEDOT:PSS) by ISAM deposition. Here, PEDOT:PSS was used as a negatively-charged ISAM layer. Encapsulation of the AgNPs by PAH (ENPs) provided a positive surface charge and allowed for the creation of ENP/PEDOT:PSS ISAMs. Stability against acidic etching by PEDOT:PSS was imparted to the AgNPs by coating the edges with gold (AuAgNPs). The AuAgNP ISAMs substantially improved the optical absorption, but were ineffective at increasing the device performance. The dispersion effects of functionalized polymer coatings on AgNPs were also deeply investigated. Functionalized AgNPs were dispersed in methanol and spin-coated onto the active layer. When the AgNPs possessed hydrophilic properties, such as unfunctionalized or functionalized by poly(ethylene glycol) methyl ether thiol (PEG-SH), they formed large aggregates due to unfavorable interactions with the hydrophobic P3HT:PCBM layer. However, the hydrophobic functionalization of AgNPs with thiol-terminated polystyrene (PS-SH) (PS-AgNPs) resulted in excellent dispersion, optical absorption enhancements, and device performance improvements. At a PS-AgNP concentration of 0.57 nM, the device efficiency was increased by 32% over the reference devices. / Ph. D. / Investigations are presented on the quality of distribution or dispersion of functional inorganic (composed of silicon dioxide or silver) particles that have dimensions of less than 100 nanometers, called nanoparticles. The nanoparticle surfaces were covered with polymer layers, where polymers are organic materials with repeating molecular structures. The study of these nanoparticle distribution effects were first examined in anti-reflection coatings (ARCs). ARCs induce transparency of windows or glasses through a reduction in the reflection of light. Here, the ARCs were fabricated as self-assembled thin-films (films with thicknesses ranging from 1 to 2000 nanometers). The self-assembly process here was carried out by immersing a charged substrate (microscope slide) into a solution with an oppositely-charged material. The attraction of the material to the substrate leads to thin-film growth. The process can continue by sequentially immersing the thin-film into oppositely-charged solutions for a desired number of thin-film layers. This technique is called ionic self-assembled multilayers (ISAMs). ARCs created by ISAM with charged polymers (polyelectrolytes) and silicon dioxide nanoparticles (SiO2 NPs) can lead to highly-transparent films, but unfortunately, they lack the stability and scratch-resistance necessary for commercial applications. In this dissertation, we address the lack of stability in the ISAM ARCs by adding additional polyelectrolyte layers that can develop strong, covalent bonds, while also examining nanoparticle dispersive properties. First, SiO2 NP surfaces were coated in solution with a polyelectrolyte called diazo-resin, which can form covalent bonds by UV-light exposure of the film. After tuning the concentration for the added diazo-resin, the coated SiO2 NPs were used to make ARCs ISAM films. The ARCs had excellent nanoparticle dispersion, high levels of transparency, and chemical stability. Chemically stability entails that the integrity of the film was unaffected by exposure to polar organic solvents or strong polyelectrolytes. In a second method, two additional v polyelectrolyte layers were added into the original polyelectrolyte/SiO2 NP design. Here, heating of the film to 200 oC temperatures induced strong covalent bonding between the polyelectrolytes. Variation of the solution pH dramatically changed the polyelectrolyte thickness, the nanoparticle dispersion, the scratch-resistance, and the anti-reflection. An optimum trade-off was discovered at a pH of 5.2, where the anti-reflection was excellent (amount of transmitted light over 99%), along with a substantially improved scratch-resistance. A change of pH from 6.0 (highest tested pH) to 5.2 (optimal) caused a difference in the scratch-resistance by a factor of seven. In these findings, we introduce stability enhancing properties from films composed purely of polyelectrolytes into nanoparticle-containing ISAM films. We also show that a simple adjustment of solution parameters, such as the pH value, can cause substantial differences in the film properties. Nanoparticle dispersion properties were next investigated in organic photovoltaics (OPVs) OPVs use semiconducting polymers to convert sunlight into usable electricity. They have many advantages over traditional solar cells, including their simple processing, low-cost, flexibility, and lightweight. However, OPVs are limited by their total optical absorption or the amount of light that can potentially be converted to electricity. The addition of plasmonic nanoparticles into an OPV device is a suitable way to increase optical absorption without changing the other device properties. Plasmonic nanoparticles, which are composed of noble metals (such as silver or gold), act as “light antennas” that concentrate incoming light and radiate it around the particle. In this dissertation, we investigate the dispersion and stability effects of polymer or metallic layers on silver nanoplates (AgNPs). The stability of the AgNPs was found to be greatly enhanced by coating the nanoparticle edges with a thin gold layer (AuAgNPs). AuAgNPs could then be introduced into a conductive, acidic layer of the OPVs (PEDOT:PSS) to increase the overall light absorption, which otherwise would be impossible with uncoated AgNPs. Next, the AgNPs were distributed on top of the photoactive layer or the layer that is responsible for absorbing light. Coating the AgNPs with a polystyrene polymer layer (PS-AgNPs) allowed for excellent dispersion on this layer and contrastingly, dispersion of the uncoated AgNPs was poor. An increased amount PS-AgNPs added on top of the photoactive layer progressively increased the optical absorption of the OPV devices. However, trends were quite different for the power conversion efficiency or the ratio of electricity power to sunlight power in the OPV device. The greatest PCE enhancements (27 – 32%) were found at a relatively low coverage level (using a solution concentration of 0.29 to 0.57 nM) of the PS-AgNPs on the photoactive layer.

Esta tesis trata sobre el fascinante fenómeno de la transmisión extraordinaria a través de láminas metálicas nonoestructuradas periódicamente con aperturas al corte. Un efecto relacionado con la excitación de un tipo de ondas superficiales como son los plasmones de superficie. Además, en aquellas estructuras formadas por el apilamiento de dos o más láminas metálicas se consiguen nuevas funcionalidades, como magnetismo artificial que da lugar a resonancias magnéticas y por tanto la posibilidad de obtener un índice de refracción negativo.Mediante un estudio teórico y numérico se ha comprobado que este tipo de respuesta magnética efectiva se debe a la excitación de resonancias plasmónicas internas en la estructura. Obteniéndose, bajo incidencia normal, un índice de refracción efectivo negativo en la dirección de propagación en el caso de que dichas resonancias se produzcan en zonas del espectro donde se obtenga la permitividad negativa, conectando el mundo de la plasmónica con el de los metamateriales. Uno de los principales objetivos en el diseño de metamateriales es obtener un índice de refracción negativo en un gran ancho de banda. Sin embargo, este objetivo suele ser complicado de conseguier al basar los diseños en fenómenos resonantes. Es por ello que en esta tesis se ha propuesto un diseño basado en el apilamiento de estructuras fishnet con diferentes grosores de dieléctrico para conseguir aumentar el ancho de banda en el cual se consigue un índice negativo. Básicamente, la obtención de tal efecto se basa en la excitación de resonancias plasmónicas a distintas frecuencias al estar formada la celda unidad por difentes grososres de dieléctrico. La hibridación que se produce entre dichas resonancias permite aumentar el ancho de banda con índice negativo. Aunque la transmisión extraordinaria esta principalmente relacionada con excitación de plasmones de superficie, los resultados mostrados en la tesis demuestran que para el caso de láminas metálicas rodeadas por dieléctricos también se consigue transmisión extraordinaria debido a la adaptación de la luz incidente a los modos soportados por los medios dieléctricos siempre y cuando el metal se encuentre estructurado periódicamente. / Ortuño Molinero, R. (2012). Extraordinary Transmission Filtering Structures based on Plasmonic Metamaterials [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/14639

El propósito de esta tesis es diseñar y optimizar dispositivos fotónicos en el régimen no lineal. En particular, se han elegido dos tipos de dispositivos, que se clasifican según los fenómenos físicos de interés. La primera clase corresponde a fibras convencionales o de cristal fotónico, diseñadas para que la dinámica temporal de los paquetes de onda que se propagan en su interior genere espectros con las características deseadas, en el contexto del supercontinuo. La segunda clase explota la fenomenología espacial asociada a las ondas electromagnéticas que se propagan sobre la superficie de un metal. Estas ondas permiten, desde diseñar dispositivos tipo chip fotónico cuyas dimensiones típicas están muy por debajo de la longitud de onda de la luz, hasta la generación de estados no lineales híbridos de dinámica singular. Todos estos efectos tienen lugar dentro del marco proporcionado por las ecuaciones de Maxwell macroscópicas, las cuales han sido resueltas numéricamente. En algunos casos se emplean grandes aproximaciones teóricas para estudiar sistemas 1D, mientras que en otros se integran directamente en 3D. En el caso en el que la optimización del dispositivo resulta no trivial tras haber adquirido un conocimiento teórico profundo del mismo, se emplea una novedosa herramienta numérica que nace de la combinación de algoritmos genéticos con plataforma Grid. / Milián Enrique, C. (2012). Optimisation of nonlinear photonic devices: design of optical fibre spectra and plasmonic systems [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/14670

[EN] This thesis studies the optical properties of random arrays of metal nanoparticles in multilayered substrates such as a solar cell, as well as the electrooptic consequences for those substrates. This study difers from traditional models which assume independent spherical particles in an homogeneous medium. Moreover, the efects beyond the near field range are studied because substrates thicker than 150µm are used. The study in this thesis uses two main approaches: a) A theoretical approach based on simulations and analytical models. Starting with the traditional methods (Mie), alternatives are considered for considering the substrate efect, the shape of the nanoparticles as well as the efect of the surrounding nanoparticles. For this, the use of Green functions and the Sommerfeld identity are presented as interesting strategies against traditional numerical model that are not suitable due to the complexity of the system that leads to huge power, time and memory consumptions. Nevertheless, the analytical approach has its limits and dificulties, that are analysed in this thesis. The results obtained in the thesis are compared with experimental data and a critical analysis is performed to check the real suitability and the scope of this strategy for simulating these kinds of systems. b) An experimental approach, in which special attention has been paid to the self-aggregation method as a quick way of integrating the nanoparticles on the final device. Some issues have been detected and studied related with the degradation of the nanoparticles, and some strategies to minimise this efect are presented. Integrated samples have been prepared using diferent integration approaches. From the measurements and their analysis the infuence of the substrate and other factors on the nanoparticle behaviour is confrmed, and the enhancement potential of the solar cell is studied. This thesis has been carried out at Valencia Nanophotonics Technology Center (NTC, in Spain) partly in the context of the LIMA european project (FP7-ICT-2009.3.8) and has included a short term scientific mission at the Laboratory of Photonics and Nanostructures (CNRS-LPN) at Marcoussis (France). / [ES] En esta tesis se realiza un estudio de las propiedades ópticas de agrupaciones aleatorias de nanopartículas metálicas cuando éstas se depositan en un sustrato multicapa como una célula solar, así como las consecuencias electroópticas sobre dicho sustrato. Este estudio supone una diferencia importante con respecto a las hipótesis de modelos tradicionales en los que se suponen partículas individuales, perfectamente esféricas y en medios homogéneos. Además, estudia los efectos más allá del campo cercano al utilizar sustratos de más de 150µm de grosor. El trabajo de esta tesis gira en torno a dos enfoques principales: a) Un enfoque más teórico basado en simulaciones y modelos analíticos. Partiendo de los métodos tradicionales (Mie), se estudian métodos para incluir el efecto del sustrato, de la forma de las partículas y el efecto de las partículas cercanas. Para este fin, el uso de funciones de Green y de la identidad matemática de Sommerfeld se presentan como alternativas de gran interés frente al uso de modelos numéricos, inviables dada la complejidad del sistema y los recursos de memoria y tiempo necesarios. Aún así, los modelos analíticos presentan sus propias limitaciones y difcultades que son analizadas en esta tesis. Las soluciones obtenidas con estos modelos se han comparado con datos experimentales y un análisis crítico se ha llevado a cabo para determinar el alcance y la fabilidad de estas estrategias de simulación. b) Un enfoque más experimental, en el que se ha hecho especial hincapié en la autoagregación de capas finas como vía rápida para integrar las partículas en el dispositivo fnal. También se han estudiado los problemas asociados a la estabilidad de las nanopartículas con el tiempo y a cómo minimizar la degradación. Por otro lado, se han preparado varios dispositivos integrados siguiendo distintas estrategias y de cuyas medidas y análisis se ha confrmado el efecto del sustrato y otros factores sobre el comportamiento de las nanopartículas, así como estudiado la potencial mejora de la eficiencia en células solares. Esta tesis se ha realizado en su mayoría en el Centro de Tecnología Nanofotónica de Valéncia (NTC, en España) enmarcada parcialmente en el proyecto europeo LIMA (FP7-ICT-2009.3.8) y ha incluido una estancia investigadora en el Laboratorio de Fotónica y Nanoestructuras (CNRS-LPN) en Marcoussis (Francia). / [CA] En aquesta tesi es realitza un estudi de les propietats òptiques d'agrupacions aleatòries de nanopartícules metàl·liques quan aquestes es depositen sobre un substrat multicapa com una cel·lula solar, així com les consequències electroòptiques resultants en el substrat. Aquest estudi presenta una difèrencia important amb les hipotesis de models tradicionals en els quals es suposa una partícula tota sola, perfectament esfèrica i en un medi homogeni. A més a més, s'estudiaran els efectes més enlla del camp proper a l'utilitzar substrats de més de 150µm d'espessor. El treball d'aquesta tesi es fara mitjançant dues estratègies principalment: a) Un enfocament més teòric emprant simulacions i models analítics. Començant amb models tradicionals (Mie), s'estudiaran estratègies per a incloure l'efecte d'un substrat, de la forma de les partícules així com el de la presència de partícules al voltant. Amb aquesta fnalitat, les funcions de Green i la identitat matemàtica de Sommerfeld es presenten com unes eines de gran interés comparat amb l'ús de mètodes numèrics tradicionals, els quals tenen uns requeriments excessius de memòria i temps de càlcul. Amb tot, aquests models analítics també tenen les seues limitacions i dificultats que són estudiades en la tesi. Les solucions obteses amb aquests models s'han comparat amb dades experimentals i s'ha fet un anàlisi crític per determinar l'abast de la validesa i la fiabilitat d'aquestes estrategies de simulació. b) Un enfocament més experimental, en el qual s'ha posat l'accent en l'auto-agregació de pel·lícules fines com a estratègia per a l'integració de les partícules en el dispositiu fnal. També s'han estudiat els problemes associats a l'estabilitat de les partícules amb el temps així com vies per a minimitzar aquesta degradació. D'altra banda, s'han preparat diversos dispositius integrats mitjannant diferents estratègies i a partir de les mesures de les quals s'ha confirmat l'efecte del substrat i d'altres factors en el comportament de les nanopartícules i s'ha estudiat la potencial millora de l'eficiència de la cèl·lula solar. Aquesta tesi s'ha dut a terme majoritàriament en el Centre de Tecnologia Nanofotonica de Valéncia (NTC) parcialment enmarcada en el projecte europeu LIMA (FP7-ICT-2009.3.8), i inclou la realització d'una estància al Laboratori de Fotònica i Nanoestructures (CNRS-LPN) en Marcoussis (França). / Cortés Juan, F. (2015). Theoretical and experimental study of light-nanoparticle interactions in high efficiency solar cells [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/59404

The unprecedented ability of plasmonic metal nano-structures to concentrate light into deep-subwavelength volumes has propelled their use in a vast array of nanophotonics technologies and research endeavors. They are used in sensing, super-resolution imaging, SPP lithography, SPP assisted absorption, SPP-based antennas, light manipulation, etc. To take full advantage of the attractive capabilities of CMOS compatible low-cost plasmonic structures based on Al and Cu, nanolaminate coatings are investigated to improve their long-term stability in corrosive physiological environments. The structures are fabricated using phase-shifting PDMS masks, e-beam deposition, RIE, Atomic Layer Deposition and Rapid Thermal Annealing. An alternate approach using Nanosphere Lithography (NSL) was also investigated. Films were examined using ellipsometry, atomic force microscopy and transmission measurements. Accelerated in-situ tests of Hafnium Oxide/Aluminum Oxide nanolaminate shells in a mildly pH environment with temperatures akin to physiological environments emulated using PBS show greatly enhanced endurance, with stable structures that last for more than one year. / Master of Science / When light (electromagnetic radiation) interacts with the free (conduction) electrons of a metallic nanostructure it leads to a coupling resulting in collective excitations (oscillations) that lead to strong enhancements of the local electromagnetic fields surrounding the nanoparticles, this phenomenon is called Localized Surface Plasmon Resonance (LSPR) and plasmonics are structures that are capable of exhibiting this phenomenon. The condition for LSPR to occur is that the dimension scale of the structure is less than the wavelength of the electromagnetic radiation interacting with it. This implies that the structure has to be in nanoscale dimensions. LSPR based plasmonic structures are compact, sensitive and can be integrated with electronic devices and can be used in various applications like implantable biological sensors (blood pH sensing, diabetics sensing, etc.), devices that integrate several laboratory testing functionalities on a single chip, studies to determine the dynamics of chemical reactions, increasing the efficiency of solar power generation, etc. LSPR is exhibited by metallic nano-particles like gold, silver, copper and aluminum. Metals like copper corrode at a rapid rate in water at room temperature and hence nano scale structures made from them that can exhibit LSPR cannot be used in higher temperature ionic environments without a protective coating. High density, uniform coatings with less defect density can be deposited using Atomic layer deposition (ALD). In this research Atomic Layer Deposited Aluminum Oxide and Hafnium Oxide nanolaminate structures are explored to increase the long-term stability of plasmonic structures in physiological solutions. In-situ tests are carried out in a Phosphate-buffered Saline (PBS) solution with a pH value of 7.2 (simulating physiological conditions) at a temperature of 37℃ (physiological temperature) and 85.1℃ (accelerated testing). The results demonstrate that the dielectric nano coatings investigated in this project can increase the stability of the plasmonic structures in the corrosive physiological environment from a few days to more than one year.

During the last decades, the continuing need for faster and smaller sensors has indeed triggered the rapid growth of more sophisticated technologies. This has led to the development of new optical-based sensors, able to detect and measure different phenomena using light. Furthermore, material processing technologies and micro fabrication methods have exponentially advanced, allowing engineers and scientists to develop new and more complex sensors on optical fibers platforms; specifically attractive for life science and biomedical research. All these substantial developments have brought biosensors to a point where multifunctionality is needed, this has led to envision the "Lab-on-Fiber" concept. Which promotes the integration of different sensing components into a single platform, an optical fiber. In this work, an integrated system with non-conventional polymer optical fibers and their further surface modification has been developed. With these different approaches, electrodes, hollow channels and plasmonic nanostructures can be incorporated into a single optical fiber-based sensor, allowing for both electrical and optical sensing with the capabilities of tuning and signal enhancement thanks to the metallic nanostructures. Different fiber substrates can be designed and modified in order to satisfy multiple requirements for a wide variety of applications. / MS / Silica optical fibers have been used since the 1960’s to guide optical signals, such as light, with low losses through long distances; making them an attractive platform to use in large communication systems. However, over the past couple of decades researchers have been trying to implement these low-loss platforms in sensing devices for many different fields, such as environmental and structural monitoring, and chemical and biomedical research. Unfortunately, their high brittleness has prompted researchers to introduce different materials in the same technology, leveraging the development of multimaterial non-conventional fibers. Where different polymers and even metals have replaced silica as the structural material, making these fibers more cost-affordable, flexible, and allow for multi-sensing capabilities of both electrical and optical signals. Although these multimaterial fibers are able to transmit light, they need to be functionalized or modified in order for them to be able to sense different phenomena occurring in their surrounding media. This can be achieved by integrating small particles or structures onto the fibers end-faces, these small structures are known as plasmonic nanostructures. When light (electromagnetic radiation) travels through a fiber and interacts with the free (conduction) electrons of a metallic nanostructure, it leads to a coupling that results in collective oscillations, which produce strong enhancement of the local electromagnetic fields surrounding the nanostructures. The latter can be easily detected with the help of an optical spectrum analyzer that iv stores the transmitted light as a function of the transmitted wavelength. Noble metals like gold and silver produce unprecedented electromagnetic field enhancements and are also biocompatible, making them very attractive in biosensing applications. In this research metallic plasmonic nanostructures were deposited on the end face of multimaterial polymer fibers to enhance the optical properties and potentially the electrical properties as well, creating new sensing devices. The enhancement produced by these structures was studied with both experimental measurements and theoretical simulations. The results demonstrate that the nanostructures investigated in this work can indeed enhance the optical properties of the used polymer fibers, enabling them to work as sensing probes for a many different applications, especially biosensing research.