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

This dissertation presents subwavelength optics with focus on the theory and applications of subwavelength apertures in a metal film. Two main issues regarding the optics with subwavelength apertures are investigated. As the first issue, the extraordinary optical transmission (EOT) through a single hole in a metallic waveguide is presented. A total transmission through a single subwavelength aperture is theoretically predicted for a perfect electric conductor regardless of the aperture size, without relying on aperture arrays and surface corrugations as presented in previous works. The waveguide EOT is then applied to boost the optical throughput of an apertured near-field scanning optical microscope (NSOM) probe. Using a new structure for the apertured NSOM probe which allows for waveguide EOT, the optical throughput and the damage threshold are boosted by 100× and 40× as compared to a conventional structure, and the experimental findings are backed-up by comprehensive finite-difference time-domain (FDTD) simulations. Single fluorescent molecules are scanned using the EOT apertured NSOM probe, and a spatial resolution of 62 nm is achieved. As the second issue, subwavelength apertures are found useful for optical trapping. A small dielectric particle can significantly change the optical transmission through an aperture by dielectric loading, and subsequently, a large optical force is induced which favors trapping. A self-induced back-action (SIBA) optical trap is designed using a circular nanohole in a gold film. Trapping of 50 nm polystyrene particle is experimentally achieved, which is not possible using a conventional single beam optical tweezers. The circular nanohole SIBA trap works beyond the perturbative regime, as proven by FDTD simulations and a Maxwell stress tensor analysis. We further improve the nanohole trapping using a double-nanohole, which is more sensitive for small dielectric changes due to the intense local field enhancement between its two sharp tips. A single 12 nm silica sphere is experimentally trapped using the double-nanohole, as the smallest trapped dielectric particle reported. We also achieve the trapping of a single protein – a bovine serum albumin (BSA) protein with a hydrodynamic radius of 3.4 nm in the folded form. The trapped BSA is also unfolded by the large optical force, as confirmed by experiments with changing optical power and changing pH. The high signal-to-noise ratio of 33 in monitoring single protein trapping and unfolding shows a tremendous potential for using the double-nanohole as a sensor for protein binding events at a single molecule level. / Graduate

Acoustic noise pollution is an environmental aggressor in everyday life. Aero- dynamically generated noise annoys and was linked with health issues. It may be caused by high-speed turbulent free flows (e.g. aircraft jet exhausts), by airflow interacting with solid surfaces (e.g. fan noise, wind turbine noise), or it may arise within a confined flow environment (e.g. air ventilation systems, refrigeration systems). Hence, reducing the acoustic noise levels would result in a better life quality, where a systematic approach to decrease the acoustic noise radiation is required to guarantee optimal results. Computational predic- tion methods able to provide all the required flow quantities with the desired temporal and spatial resolutions are perfectly suited in such application areas, when supplementing restricted experimental investigations. This thesis focuses on the use of numerical methodologies in compressible flow applications to understand aerodynamically noise generation mechanisms and to assess technologies used to suppress it. Robust and fast steady-state Reynolds Averaged Navier-Stokes (RANS) based formulations are employed for the optimal design process, while the high fidelity Large Eddy Simulation (LES) approach is utilized to reveal the detailed flow physics and to investigate the acoustic noise production mechanisms. The employment of fast methods on a wide range of cases represents a brute-force strategy used to scrutinize the optimization parameter space and to provide general behavioral trends. This in combination with accurate simulations performed for particular condi- tions of interest becomes a very powerful approach. Advance post-processing techniques (i.e. Proper Orthogonal Decomposition and Dynamic Mode Decomposition) have been employed to analyze the intricate, highly turbulent flows. The impact of using fluidic injection inside a convergent-divergent nozzle for acoustic noise suppression is analyzed, first using steady-state RANS simulations. More than 250 cases are investigated for the optimal injection location and angle, amount of injected flow and operating conditions. Based on a-priori established criteria, a few optimal candidate solutions are detected from which one geometrical configuration is selected for being thoroughly investigated by using detailed LES calculations. This allows analyzing the unsteady shock pattern movement and the flow structures resulting with fluidic injec- tion. When investigating external fluidic injection configurations, some lead to a high amplitude shock associated noise, so-called screech tones. Such unsteady phenomena can be captured and explained only by using unsteady simulations. Another complex flow scenario demonstrated using LES is that of a high ve- locity jet ejected into a confined convergent-divergent ejector (i.e. a jet pump). The standing wave pattern developed in the confined channel and captured by LES, significantly alters the acoustic noise production. Steady-state methods failed to predict such events. The unsteady highly resolved simulations proved to be essential for analyzing flow and acoustics phenomena in complex problems. This becomes a very powerful approach when is used together with steady-state, low time-consuming formulations and when complemented with experimental measurements. / <p>QC 20141202</p>

Most electromagnetic interference standards specify that measurements of radiated emissions must be performed in the far field (FF), e.g. at an open-area test site or in a semi-anechoic chamber. Since near field (NF) measurements are cheaper, quicker and more flexible compared to FF tests, establishing a correlation between NF and FF data is of great research interest. One strategy to achieve this goal is to find a set of basic radiators comprising electric and magnetic dipoles that generate the same NF as the original source at selected observation points. This set of dipoles, based on the uniqueness theorem, can then be used to predict the FF radiation patterns. The uniqueness theorem requires that electric or magnetic fields are matched on a closed surface with respect to the magnitude and phase. The focus of this thesis is the investigation of FF prediction based on NF magnitude-only data. In this thesis, a robust NF-FF conversion model based on Genetic Algorithms (GAs) is built up to predict the radiation of printed circuit boards (PCBs). This is done by introducing a dipole moment magnitude range pre-selection before the initialisation step of GAs, customising the processes of selection, crossover and mutation for anti-sticking and checking the correlation between NF and FF fitness values. Since the performance of GAs is tightly related to the number of dipoles in the GA model, FF characteristics of generic radiation sources (such as a long wire and a large loop) are analysed using both analytical calculation and source modelling by GAs. For structures with simple FF patterns, if more dipoles than necessary are used, the computational cost of GAs is unnecessarily high. On the other side, for structures with complicated FF patterns, the GA modelling may not be able to well approximate the FF radiation, due to the limitation for GAs to tackle too many unknowns. Therefore the scope of the model applicability is discussed, and a dipole number N, depending on the electrical size of the source, is recommended for GA modelling. By applying GAs to get the equivalent dipole set of a radiating PCB from the magnetic NF magnitudes, NF sampling approaches are investigated in detail, including where to locate NF sampling planes, what plane coverage angle to choose, how many points to observe, what type of data to collect, what dynamic range to allow for the data, and how many planes to choose. Two case studies are presented for predicting the FF radiation of PCBs from magnetic NF magnitude-only observations, and validate the NF sampling approaches in this thesis.

abstract: To detect and resolve sub-wavelength features at optical frequencies, beyond the diffraction limit, requires sensors that interact with the electromagnetic near-field of those features. Most instruments operating in this modality scan a single detector element across the surface under inspection because the scattered signals from a multiplicity of such elements would end up interfering with each other. However, an alternative massively parallelized configuration, consisting of a remotely interrogating array of dipoles, capable of interrogating multiple adjacent areas of the surface at the same time, was proposed in 2002. In the present work a remotely interrogating slot antenna inside a 60nm silver slab is designed which increases the signal to noise ratio of the original system. The antenna is tuned to resonance at 600nm range by taking advantage of the plasmon resonance properties of the metal’s negative permittivity and judicious shaping of the slot element. Full-physics simulations show the capability of detecting an 8nm particle using red light illumination. The sensitivity to the λ/78 particle is attained by detecting the change induced on the antenna’s far field signature by the proximate particle, a change that is 15dB greater than the scattering signature of the particle by itself. To verify the capabilities of this technology in a readily accessible experimental environment, a radiofrequency scale model is designed using a meta-material to mimic the optical properties of silver in the 2GHz to 5GHz range. Various approaches to the replication of the metal’s behavior are explored in a trade-off between fidelity to the metal’s natural plasmon response, desired bandwidth of the demonstration, and ii manufacturability of the meta-material. The simulation and experimental results successfully verify the capability of the proposed near-field sensor in sub-wavelength detection and imaging not only as a proof of concept for optical frequencies but also as a potential imaging device for radio frequencies. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2016

abstract: Recently, nanostructured metamaterials have attracted lots of attentions due to its tunable artificial properties. In particular, nanowire/nanohole based metamaterials which are known of the capability of large area fabrication were intensively studied. Most of the studies are only based on the electrical responses of the metamaterials; however, magnetic response, is usually neglected since magnetic material does not exist naturally within the visible or infrared range. For the past few years, artificial magnetic response from nanostructure based metamaterials has been proposed. This reveals the possibility of exciting resonance modes based on magnetic responses in nanowire/nanohole metamaterials which can potentially provide additional enhancement on radiative transport. On the other hand, beyond classical far-field radiative heat transfer, near-field radiation which is known of exceeding the Planck’s blackbody limit has also become a hot topic in the field. This PhD dissertation aims to obtain a deep fundamental understanding of nanowire/nanohole based metamaterials in both far-field and near-field in terms of both electrical and magnetic responses. The underlying mechanisms that can be excited by nanowire/nanohole metamaterials such as electrical surface plasmon polariton, magnetic hyperbolic mode, magnetic polariton, etc., will be theoretically studied in both far-field and near-field. Furthermore, other than conventional effective medium theory which only considers the electrical response of metamaterials, the artificial magnetic response of metamaterials will also be studied through parameter retrieval of far-field optical and radiative properties for studying near-field radiative transport. Moreover, a custom-made AFM tip based metrology will be employed to experimentally study near-field radiative transfer between a plate and a sphere separated by nanometer vacuum gaps in vacuum. This transformative research will break new ground in nanoscale radiative heat transfer for various applications in energy systems, thermal management, and thermal imaging and sensing. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2017

This thesis provides novel contribution to the field of body-centric wireless communications (BCWC) with the development of a measurement methodology for wearable antenna characterisation on the human body, the implementation of fully-textile wearable antennas and the on-body channel modelling considering different antenna types and user's dynamic effects. More specifically, a measurement methodology is developed for characterising wearable antennas on different locations of the human body. A cylindrical near-field (CNF) technique is employed, which facilitates wearable antenna measurements on a full-body solid anthropomorphic mannequin (SAM) phantom. This technique allows the fast extraction of the full spherical radiation pattern and the corresponding radiation efficiency, which is an important parameter for optimising wearable system design. It appears as a cost- effective and easy to implement solution that does not require expensive positioning systems to rotate the phantom, in contrast to conventional roll-over-azimuth far-field systems. Furthermore, a flexible fully-textile wearable antenna is designed, fabricated and measured at 2.4 GHz that can be easily integrated in smart clothing. It supports surface wave propagation and exhibits an omni-directional radiation pattern that makes it suitable for on-body communications. It is based on a multilayer low-profile higher-mode patch antenna (HMMPA) design with embroidered shorting vias. Emphasis is given to the fabrication process of the textile vias with conductive sewing thread that play an important role in generating the optimal mode for on-body radiation. The radiation pattern shape of the proposed fully-textile antenna was found to be similar to a copper rigid antenna, exhibiting a high on-body radiation efficiency of 50 %. The potential of the embroidery technique for creating wearable antennas is also demonstrated with the fabrication of a circularly polarised spiral antenna that achieves a broadband performance from 0.9-3 GHz, which is suitable for off-body communications. By testing the textile spiral antenna on the SAM phantom, the antenna-body interaction is examined in a wide frequency range. Finally, a statistical characterisation of on-body communication channels is undertaken both with EM simulations and channel measurements including user's dynamic movement (walking and running). By using antenna types of different polarisation, the on-body channels are examined for different propagation conditions. Four on-body channels are examined with the one part fixed on the waist of the human body while the other part located on the chest, back, wrist and foot. Channel path gain is derived, while large-scale and small-scale fading are modelled by best-fit statistical distributions.

Au cours de cette thèse nous avons étudié les effets des interactions entre électrons dansles contacts ponctuels quantiques (QPCs). Les contacts ponctuels quantiques sont des petitscanaux quasi-unidimensionnels, définis à partir de gaz électroniques bidimensionnelsde haute mobilité (2DEG). Une tension négative appliquée sur des grilles métalliques audessus de la surface permet d’ouvrir ou fermer le QPC. Lorsqu’un QPC s’ouvre, de plusen plus de modes électroniques peuvent traverser le QPC, et sa conductance augmente parpas discrets, séparés par un quantum de conductance 2e2/h. On peut le comprendre parle transport unidimensionnel d’une seule particule, car chaque mode transverse contribuepour un quantum de conductance.Mais depuis leurs premières réalisations, les QPCs ont montré des déviations par rapportà ce modèle à une particule. Les plus connues sont un épaulement sous le premier plateau,autour de 0.7×2e2/h, appelé "l’anomalie 0.7", et un pic dans la conductance différentiellequi apparaît à basse température: l’anomalie à zéro polarisation (ZBA).L’instrument que nous avons utilisé pour étudier ces effets d’interactions est un microscopeà effet de grille local (SGM). Cette technique consiste à modifier localement le potentield’un dispositif à l’aide d’une pointe de microscope à force atomique (AFM) chargée négativement,et enregistrer les modifications de la conductance en fonction de la position dela pointe. En utilisant cette technique à très basse température, nous avons montré quenous pouvons moduler les anomalies de conductance du QPC. Nous avons interprété nosrésultats comme la signature d’un cristal d’électrons se formant spontanément à bassedensité dans le QPC à cause de la répulsion Coulombienne: un cristal de Wigner. Onpeut modifier le nombre d’électrons cristallisés en approchant la pointe, et obtenir dessignatures de la parité du nombre d’électrons localisés dans le transport électronique.En fonction de cette parité, le cristal de Wigner présente un état de spin différent, etl’écrantage de ce spin par les électrons de conduction au travers d’un mécanisme appeléeffet Kondo donne une anomalie à zéro polarisation formant alternativement un simplepic ou un double pic. Cette découverte apporte une avancée significative à ce domaine,qui a concentré les efforts de plusieurs groupes importants ces 15 dernières années.Nous avons ensuite réalisé des mesures interférométriques à l’aide du microscope SGM,en créant in situ des interféromètres dans le gaz 2D. Nous avons obtenu les signaturesd’un déphasage supplémentaire dans le régime de la ZBA. Nous attribuons cet effet audéphasage universel accumulé par les électrons à la traversée d’un singulet Kondo, ce quirenforce le fait que la ZBA trouve son origine dans les phénomènes Kondo.Enfin, nous avons adapté la technique SGM au transport thermoélectrique dans les QPCs,et avons imagé pour la première fois les interférences d’électrons se déplaçant sous l’effetd’une différence de température. / In this thesis, we studied the effect of electron electron interactions in quantum pointcontacts (QPCs). Quantum point contacts are small quasi-one dimensional channels,designed on a high mobility two-dimensional electron gas (2DEG). A negative voltageapplied on a pair of metallic split gates above the sample surface allows to open or closethe QPC. As a QPC opens, more and more electronic modes are allowed to cross theQPC, and its conductance increases by discrete steps, separated by a conductance quantum2e2/h. This can be understood from a single-particle picture in one-dimensionaltransport, as each transverse mode carries a conductance quantum.But from their first realization 25 years ago, quantum point contacts have shown deviationsfrom this picture, attributed to electron electron interactions. The most well knownare a shoulder below the first plateau, around 0.7×2e2/h, called the "0.7 anomaly", and apeak in the differential conductance that arises at low temperature: the zero bias anomaly(ZBA).The tool we used to study these interaction effects is a scanning gate microscope (SGM).It consists by changing locally the device’s potential with the polarized tip of an atomicforce microscope (AFM), and record the changes in conductance as a function of the tipposition. By performing this technique at very low temperature, we showed that we canmodulate the conductance anomalies of QPCs. We interpret our result as the signatureof a small electrons crystal forming spontaneously at low density in the QPC due to theCoulomb repulsion: a Wigner crystal. We can modify the number of crystallized electronsby approaching the tip, and obtain signatures of the parity of the localized electrons numberin transport features. Depending on this parity, the Wigner crystal has a differentspin state, and screening of this spin by the surrounding electrons through the so-calledKondo effect leads alternatively to a single peak or a split ZBA. This discovery bringsa significant advance in this field, that has attracted research efforts of many importantgroups in the world over the past 15 years.We then performed interferometric measurements thanks to the scanning gate microscopeby creating in-situ interferometers in the 2DEG. We obtained signatures of an additionalphase shift accumulated by the electrons in the ZBA regime. We attribute this effect tothe universal phase shift that electrons accumulate when crossing a Kondo singlet, reinforcingthat the debated origin of the ZBA lies in Kondo physics.Finally, we adapted the SGM technique to the study of thermoelectric transport in QPCs,and for the first time imaged interferences of electrons driven by a temperature difference.

Le graphène, une monocouche de graphite, est composé d'atomes de carbone avec une structure en nid d'abeilles. Ses propriétés exceptionnelles ont attiré un intérêt mondial, dont le Prix Nobel de Physique en 2010. Le graphène épitaxié sur métal à rapidement été identifié comme un moyen de production de graphène de haute qualité de taille métrique, et est le sujet d'intenses activités de recherche en sciences de surface pour caractériser ses propriétés. En outre, ces études concernent aussi des systèmes plus complexes avec pour base le graphène, par exemple les réseaux ordonnés de nanoparticules à sa surface. Tout cela a mené à l'étude de la croissance, de la structure et des défauts du graphène épitaxié avec un grande variété de techniques expériementales, tel que la microscopie par effet tunnel, spectroscopie par photo-émission résolue en angle ou encore la microscopie électronique à basse énergie. Ce travail de recherche se concentre sur le graphène obtenu par croissance sur la surface (111) d'un monocristal d'iridium dans des conditions d'ultra vide et étudié avec plusieurs techniques de mesure par diffraction (diffraction de surface des rayons X, diffraction des rayons X en incidence rasante, réflectivité des rayons X et diffraction des électrons à haute énergie en réflexion). Ces expériences ont été faites au synchrotron européen ESRF à Grenoble, en France. La première partie de cette étude a été de déterminer la structure du graphène à l'échelle atomique. Le système montre une tendance à la commensurabilité, mais sa structure précise dépend fortement des conditions de préparation et de la température appliqué au système. En outre, en combinant des techniques de diffraction à haute résolution, une caractérisation précise de la structure, qui fait débat dans la littérature, est dévoilée. Le système étudié présente aussi une surperstructure, typique du graphène épitaxié, nommé moiré pour ses similarités avec l'effet optique du même nom. Celle-ci est utilisée comme gabarit pour faire croître des nanoparticules monodisperses à la surface en réseau auto-organisé. Durant cette étude, trois types de nanoparticules ont été examinés, des particules de platine de deux tailles différentes et des particules composées de platine et de cobalt. Ces systèmes hybrides présentent un fort degré d'organisation, partiellement hérité de la superstructure du moiré. Les nanoparticules forme une interaction forte avec leur support et elles subissent des contraintes de surface causées par leurs petites tailles. Par ailleurs, les nanoparticules de platine-cobalt, dont la croissance est en deux étapes, gardent une structure en couche et non une structure d'alliage métallique. / Graphene, a monolayer of graphite, is composed of carbon atoms arranged in a honeycomb lattice. Its exceptional properties have attracted a worldwide interest, including the Novel Prize in Physics in 2010. Epitaxial graphene on a metal was rapidly identified as an efficient method for large-area production of high quality graphene, and also was the matter of intense activities exploiting surface science approaches to address the various properties of graphene and of advanced systems based on graphene, for instance ordered lattice of metal nanoparticles on graphene. This resulted in the study of growth, structure and defects of epitaxial graphene on a wide variety of substrates with various techniques such as scanning tunneling microscopy, angle-resolved photoemission spectroscopy or low-energy electron microscopy. This work focuses on graphene grown on the (111) surface of iridium in ultra-high vacuum conditions and studied with several diffraction techniques (surface X-ray diffraction, grazing incidence X-ray diffraction, X-ray reflectivity, and reflection-high energy electron diffraction). These experiments were performed at the European Synchrotron Radiation Facility in Grenoble, France. The first step in our study was to determine the structure of graphene at the atomic scale. The system was found to have a tendency to commensurability, but that the precise structure depends on temperature and on preparation conditions. Moreover, with the combination of high resolution diffraction techniques, a precise characterization about the debated structure of graphene perpendicular to the surface was unveiled. The system, exhibits a superstructure, typical of epitaxial graphene, called a moiré, as an equivalent of the moiré effect in optics. This is used as a template to grown nanoparticles on top of the system to achieve the self-organisation of monodisperse nanoparticles. In this study, three type of nanoparticles were investigated, two different size of pure platinum ones and bimetallic ones, platinum and cobalt. These hybrid systems show very high degree of order, partly inherited by the superstructure lattice. The nanoparticles were found to strongly bond to their support, experience substantial surface strain related to their small size, and that bimetallic ones grown in a sequential manner retain a chemically layered structure.

Orientador: Aleardo Junior Manacero / Banca: Maurício Araújo Dias / Banca: Marcos Antônio Simplício Júnior / Resumo: O desenvolvimento de tecnologias móveis tem criado oportunidades para uso de aplicações remotas executando em dispositivos como smartphones. Para algumas dessas aplicações é essencial que a autenticação seja feita de modo seguro e eficiente. Nesse sentido surge o uso da tecnologia NFC (Near Field Communication) para obter segurança para transações executadas em aplicativos móveis. Esse tipo de aplicação é bastante interessante para a realização de comércio eletrônico, bem como controle de acesso a informações sigilosas, como dados bancários, por exemplo. Neste trabalho, apresentam-se dois protocolos para fazer a autenticação de dispositivos através de etiquetas NFC, com técnicas de criptografia assimétrica usando algoritmos de curvas elípticas. Ao longo do texto são apresentados os principais conceitos sobre NFC, criptografia e a classe de web services REST (Representational State Transfer), que serve como padrão para a construção dos protótipos dos protocolos Protecting Touch aqui desenvolvidos. Os detalhes sobre a implementação desses protocolos são também apresentados, assim como resultados de experimentos para sua avaliação / Abstract: The appearance of mobile technologies created opportunities for remote applications running in devices such as smartphones. In some of these applications it is essential that authentication have to be performed in a secure and ecient way. In this sense the use of NFC (Near Field Communication) technology came to provide safety to transactions executed through mobile applications. This kind of application is rather attractive to perform electronic commerce, as well as access control for sensitive data, such as banking accounts. In this work it is presented two protocols for user authentication through NFC tags, using asymmetric cryptography by elliptic curves. Throughout the text we present the main concepts about NFC, cryptography and the web services REST (Representational State Transfer), which is used as the building framework for the prototypes of the Protecting Touch protocols presented here. Details about the protocols implementation are also presented, as well as results from the evaluation experiments of these protocols / Mestre