Light absorption in metal catalyst nanoparticles can excite charge carriers to generate hot electron (and complimentary hot holes) with energy higher than the Fermi level. When hot electrons possess energy high enough, they exhibit a high tendency to inject into antibonding orbitals of adsorbates on the photoexcited metal nanoparticles, weakening the corresponding chemical bonds to promote chemical reactions with accelerated reaction kinetics and improved selectivity. Such hot-carrier chemistry has been reported on plasmonic metal nanoparticles, such as silver and gold, which exhibit strong surface plasmon resonances (SPRs) and strong light absorption. However, these metal nanoparticles are not suitable catalysts because their affinity toward interesting molecules is limited. In contrast, most transition metals, such as platinum-group metals and early transition metals, are industrially essential catalysts, but light absorption power in metal nanoparticles is low due to the absence of SPRs in the visible spectral range. Therefore, it is intriguing to explore the potential of hot-carrier catalytic chemistry on photoexcited non-plasmonic metal nanoparticles. Upon the absorption of the same optical power, metal nanoparticles with a small size usually exhibit a high probability of hot electron production and high efficiency of injecting hot electrons into adsorbates. It is challenging to have strong light absorption power and operation stability of the catalyst metal nanoparticles with small sizes. In this thesis, dielectric light antenna, i.e., spherical silica nanoparticles with strong surface scattering resonances near their surfaces, is introduced to support the metal catalyst nanoparticles, enabling improved light absorption power in the metal nanoparticles and operation stability. This thesis focuses on ultrafine rhodium (Rh) nanoparticles (with sizes ranging from 1.7 nm to 4.2 nm) that are widely used as thermal catalysts in many important industry reactions, especially for oxygen-containing species conversion, an oxyphilic feature of Rh nanoparticles. Firstly, this dissertation conducted a comparative study to investigate the influence of silica geometry, nanospheres, and rodlike nanoparticles on the light absorption of Rh nanoparticles. Both silica substrates enhanced the light absorption of loaded Rh nanoparticles due to elongated light scattering paths (random scattering) and enhanced electromagnetic field intensity (resonant scattering). However, silica nanospheres support both resonant scattering and random light scattering modes, exhibiting a higher Rh absorption than the usage of rodlike silica nanoparticles. The light resonant scattering modes on highly symmetrical silica nanospheres enable producing "hot spots" with a much higher electromagnetic field intensity than incident light intensity. This study then investigated the effect of silica geometries on photocatalytic performance. The CO2 hydrogenation was studied as a model reaction. The Rh/silica nanosphere system exhibited a faster photocatalytic kinetic than the case of rodlike silica nanoparticles. It is possibly due to the enhanced light power density around the silica nanospheres. The results give a promise of expanding Rh nanoparticles from thermo-catalysis to photocatalysis. Secondly, this dissertation moves onto accelerating aerobic oxidation of primary alcohols to aldehydes, which was benefited from activated oxygen molecules by hot electron injection. This study found that photoexcited Rh nanoparticles enabled accelerating the alcohol oxidation kinetics by four times at a light power intensity of 0.4 W cm-2, accompanied by a reduced activation energy of 21 kJ mol-1. The derived Langmuir-Hinshelwood rate equation was used to fit the oxygen partial pressure results. Photo-illumination promotes the cleavage of associatively adsorbed oxygen molecules into adsorbed oxygen atoms, reducing the energy barrier. Besides, the silica-supported Rh nanoparticles exhibited a higher photocatalytic performance because of the good colloidal stability and enhanced light absorption of small-sized Rh particles. This part of the dissertation shows the possibility of hot-electron mediated reaction pathways towards a desirable kinetic of alcohol oxidation. Thirdly, it will be meaningful to use the abstracted protons from cheap alcohol sources to reduce other organic molecules rather than dangerous hydrogen gas. This dissertation then investigated the possibility of using an isopropanol solvent as a hydrogen source to reduce nitrobenzene and the feasibility of enhancing the selectivity of the reaction with the light illumination. The results showed that the isopropanol was spontaneously oxidized, producing acetone. Light illumination onto Rh particles selectively enhanced the coupling of reduced nitrobenzene intermediates to produce azoxybenzene. The selectivity of nitrobenzene and production rates gradually increased with a higher number of light photons. Photo-illumination promotes both aniline and azoxybenzene production rates. Hot electrons on Rh particles possibly enabled activating nitrobenzene molecules and increasing concentrations of reduced nitrobenzene intermediates. It resulted in a higher possibility of condensation product and azoxybenzene selectivity, which could not be obtained by elevating temperature without light illumination. This part of the work demonstrated the feasibility of hot electrons from Rh nanoparticles to tune the reaction selectivity in a liquid phase. Lastly, it is challenging to modulate the selectivity of CH4 from CO2 hydrogenation because of the competitive CO production. This dissertation moves towards enhancing both kinetic rates and selectivity of CH4 for gaseous CO2 hydrogenation by photoexcited Rh nanoparticles. Light illumination onto Rh/silica nanosphere particles resulted in the selectivity of CH4 over 99% in contrast to ~70% under dark conditions at 330 oC and with an absorbed light power intensity of 1.5 W cm-2. The activation energy of CH4 production and CO2 consumption gradually decreased with higher light power intensity because of the transient injection of hot electrons into adsorbates to activate intermediates. Increasing operating temperature and light power intensity synergistically enhanced the reaction kinetics. Besides, a middle-sized Rh nanoparticle showed a better photocatalytic performance than that of the largest-sized Rh nanoparticles because of the balance in hot-electron production efficiency and intrinsic catalytic performance. Partial pressure dependence and in situ infrared characterizations showed that the critical stable intermediates for CH4 production should be hydrogenated CO2 species (HCOO* COOH*) and hydrogenated CO* species (carbonyl hydride or HxCO*). The light illumination exclusively enhanced the dissociation of CO2 and CO* without apparent influence on CO* desorption. Under high reaction temperature, light illumination preferred a faster CO* conversion than CO2 dissociation, leading to high CH4 selectivity. This result was also supported by higher methanation rates of CO gas under light illumination. The infrared result showed a reduced stretching frequency of CO*, which supported the possibility of the electron from Rh back-donating into antibonding orbitals of strongly adsorbed CO* species. However, hot electrons from silver nanoparticles with a weak COOH* or CO* adsorption could not efficiently activate carbon-species and could not promote CO2 hydrogenation kinetics. This dissertation offers an avenue of enhancing light absorption of small-sized Rh nanoparticles and expanding its usage from thermal catalysis to photocatalysis for driving oxidation and reduction reactions. The reactants share a common feature containing oxygen elements, a strong affinity with rhodium metal for efficient hot electron injection. We studied the light power intensity and temperature-dependence, showing the accelerated reaction kinetics by hot electron-driven pathways. Photo-excited rhodium nanoparticles were believed to promote the cleavage of chemical bonds O-O, N-O, and C-O to drive chemical transformations. The findings offer insights into developing the scope of non-plasmonic metal nanoparticles in photocatalytic reactions for industrial applications. / Chemistry

Effective light energy conversion into other forms of energy in metal and metal compound nanoparticles has been of great interest in past decades. Being illuminated by incident light, electrons in the nanoparticles can be excited to higher energy states followed by deposition of energy into other molecules around their surface and the lattices in the following relaxation process. Ultrafine nanoparticles are thus preferred in these processes due to their high specific surface areas. Moreover, the portion of excited electrons with higher energies is higher in smaller nanoparticles than in larger ones. However, the overall light power absorbed by nanoparticles is proportional to the square of particle size, which causes the ultrafine nanoparticles not to efficiently absorb the incident light, or to drive further chemical or physical processes.Light antennae materials are usually employed to enhance the light absorption of these ultrafine nanoparticles. Plasmonic nanoparticles, e.g., Ag, Au, Cu, and Al nanoparticles, enhance the light absorption of loaded nanoparticles mainly through strong electromagnetic fields generated near their surfaces and have been proven to be effective light antennae to benefit the light energy conversion of ultrafine nanoparticles. On the other hand, spherical dielectric particles, e.g., silicon dioxide nanospheres, represent a different type of light antennae with the advantages of low cost, simple synthesis, and negligible Ohmic loss when being illuminated. When the sizes of high geometric symmetry dielectric nanospheres are comparable with the wavelength of the incident light, Mie scattering can happen based on the difference in refractive index between the sphere and the surrounding medium, generating size-dependent scattering resonances at various wavelengths. At these wavelengths, strong electric fields can be created on the surface of dielectric spheres to enhance the light absorption of the nanoparticles loaded on the surface. Previous works have shown that silica nanospheres with a diameter of several hundreds of nanometers can effectively enhance the light absorption of ultrafine Pt nanoparticles and benefit photocatalytic reactions, e.g., selective oxidation of benzyl alcohol. Over the past few years, this concept has been broadened to other ultrafine nanoparticles to study their novel photo-to-chemical/physical properties. However, the availability and comprehensive understanding of the optical properties of this class of composite particles still need to be improved. These challenges limit the further development of these composite materials in new light energy conversion processes. This dissertation aims at studying this class of novel ultrafine nanoparticles/dielectric sphere composite particles synthesis and optical properties. In Chapter 2, a synthesis protocol of ultrafine ruthenium oxyhydroxide nanoparticles on the surface of silica nanospheres’ surfaces is introduced. Unlike the traditional synthesis of nanoparticles in solution followed by a loading process, the method developed in this chapter only requires the injection of aqueous ruthenium salt solution into a silica nanosphere dispersion. The obtained ultrafine nanoparticles with sizes of 2-3 nm are characterized to be ruthenium oxyhydroxide (RuOOH) nanoparticles. The silica nanospheres are crucial in stabilizing these ultrafine RuOOH nanoparticles and enhancing their light absorption. Due to the presence of ruthenium-oxygen bonds in the nanoparticles, the absorbed photons are converted to heat and transferred to the surrounding media with a photo-to-thermal conversion efficiency close to the unity. Experimental results have shown that heat can be effectively used in accelerating the reaction rate of selective oxidation of benzyl alcohol by molecular oxygen. Kinetics data also have shown that these ultrafine RuOOH nanoparticles are able to activate molecular oxygen adsorbed on their surfaces, which represents a novel property of these ultrafine RuOOH nanoparticles that is not observed in other traditional ruthenium catalysts. In Chapter 3, a more general synthesis method of ultrafine metal and metal oxyhydroxide nanoparticles on silica nanospheres is developed, inspired by the synthetic route in Chapter 2. Instead of functionalizing silica surfaces with silane agents with amino groups, the silica surfaces are selectively etched by an aqueous base to create a high density of surface hydroxyl groups. These hydroxyl groups can provide basic sites to stabilize metal ions in aqueous dispersion, which are nuclei for the further growth of larger metal oxyhydroxide nanoparticles. In this chapter, more than ten kinds of metal ions are loaded onto silica spheres, forming oxyhydroxide nanoparticles with average sizes below 5 nm. Some oxyhydroxide nanoparticles can be reduced by 5% H2/N2 to form metal nanoparticles with their ultrafine sizes maintained. The synthesis protocol is promising in preparation of bimetallic samples. The composition and optical absorption of all obtained composite particles are analyzed, demonstrating the practicability of utilizing the reported method to prepare high-quality light-absorbing composite particles. In Chapter 4, the optical absorption property of the composite particle is systematically studied. Using ultrafine Pt nanoparticles as the light absorbing material, the light absorptions of composite particles consisting of silica spheres with diameters from 100 to 1100 nm loaded with these Pt nanoparticles are studied. Through the combination of theoretical calculation based on Mie theory and the measured optical absorption spectra, the scattering resonance peaks are successfully located in each sample. It is also found that the photonic crystal effect and the general absorption of Pt nanoparticles can contribute to the light absorption spectra, especially at higher wavelengths. The relationship between the general absorption of Pt nanoparticles and the packing density of the powder is further studied. The successful deconvolution of several components in the absorption spectra can guide the further rational design of composite particles in optical-related applications. In Chapter 5, the composite particle system is further broadened to using high refractive index zinc sulfide nanospheres as a light antenna. The use of a higher refractive index light antenna is promising for obtaining higher light absorption enhancement in loaded ultrafine nanoparticles, even though the sample is dispersed in organic media with a high refractive index as well. After the successful loading of Pt nanoparticles to the surface of silica-coated zinc sulfide nanospheres, a protocol for analyzing their light absorption spectra in organic media is proposed. Size-dependent scattering resonance peaks are observed in bare zinc sulfide nanospheres and can be utilized to enhance the light absorption of Pt nanoparticles, even when the sample is sealed in high refractive index polymeric matrices. The composite particles are further employed in photothermal tests, the results prove that the better light absorption enhancement using zinc sulfide than silica nanospheres. The results introduced in this dissertation represent the first systematic and comprehensive study of ultrafine metal and metal oxyhydroxide nanoparticles loaded on the surface of dielectric light antenna particles. The conclusions open an avenue to further rational design of high-performance light-absorbing composite particles to be used in photo-to-thermal/chemical processes. / Chemistry

nÃo hà / A expansÃo das redes de telecomunicaÃÃes sem fio e o fenÃmeno da convergÃncia digital trazem a inerente necessidade da pesquisa de novos componentes que assegurem a sustentabilidade e a evoluÃÃo dos sistemas. Novos tipos de antenas, menores e mais eficientes, sÃo exigidas à medida que novos dispositivos vÃo surgindo. Neste contexto, as antenas ressoadoras dielÃtricas, construÃdas com novos materiais, aparecem como excelente opÃÃo para substituir as antenas metÃlicas tradicionais. Este trabalho apresenta uma proposta de antena ressoadora dielÃtrica circularmente polarizada, operando na frequÃncia central de 2,25 GHz, na qual um esquema de alimentaÃÃo por sonda Ãnica à empregado para excitar dois modos ressonantes em um dielÃtrico em forma de quarto de cilindro. Este leiaute permite a ativaÃÃo de modos de baixa ordem, com distribuiÃÃo ortogonal dos campos eletromagnÃticos, ressoando em frequÃncias prÃximas com uma diferenÃa de fase de 90Â. SÃo introduzidos conceitos da teoria eletromagnÃtica envolvendo cavidades ressonantes e caracterÃsticas dos materiais cerÃmicos que compÃem o dielÃtrico. AlÃm disso, os processos de modelagem por computador e de construÃÃo de um protÃtipo sÃo explicados. Os resultados sÃo discutidos comparativamente entre o modelo computacional e as medidas experimentais executadas em laboratÃrio. O estudo demonstra uma boa concordÃncia entre os resultados simulados e os experimentais e evidencia a viabilidade da antena para aplicaÃÃes que necessitem de polarizaÃÃo circular na regiÃo do espectro de frequÃncias prÃximas a 2,25 GHz. / The expansion of wireless telecommunications networks and the phenomenon of digital convergence bring the inherent need for research of new components to ensure the sustainability and evolution of the systems. New types of antenna, smaller and more efficient, are required as new devices emerge. In this context, the dielectric resonator antennas, built with new materials, appear as an excellent option to replace the conventional metallic antennas. This work presents a proposal for a circularly polarized dielectric resonator antenna to operate at the center frequency of 2.25 GHz in which a single probe feeding scheme is used to excite two resonant modes in a quarter-cylinder-shaped dielectric. This layout allows the activation of low-order modes with orthogonal distribution of electromagnetic fields, resonating at near frequencies with a 90 phase difference. The concepts of electromagnetic theory related to resonant cavities and the characteristics of dielectric ceramic materials are introduced. Furthermore, the processes of computer modeling and constructing of a prototype are explained. The results are discussed by comparison between the computational model and experimental measurements performed in the laboratory. The study shows a good agreement between the simulated and experimental results and demonstrates the feasibility of the antenna for applications requiring circular polarization for operating at the region of the frequency spectrum close to 2.25 GHz.

Dans cette thèse, nous associons mesures expérimentales et modélisation des données pour étudier l'émission spontanée d'émetteurs fluorescents en environnement nano-structuré. Le mémoire est organisé en deux parties.Dans la première partie, nous étudions le transfert d'énergie entre émetteurs fluorescents en environnement plasmonique et sur des distances micrométriques. Pour commencer, nous caractérisons le transfert d'énergie entre deux ensembles d'émetteurs situés en champ proche d'une surface d'argent. Nous déterminons ainsi la dépendance en distance du taux de transfert d'énergie sur des distances micrométriques. Nous couplons ensuite une boite quantique et une bille fluorescente à un nano-fil d'argent et nous étudions le transfert d’énergie entre ces deux émetteurs, distants de plusieurs micromètres. Nous démontrons notamment le clignotement corrélé de ces deux émetteurs grâce à l'étude de la fonction de corrélation de leur intensité de fluorescence.Dans la seconde partie, nous sondons les variations spatiales de densité locale d'états électromagnétiques induites par des environnements nano-structurés grâce à différentes techniques de microscopie à super-résolution. A l'aide d'un microscope à balayage, nous réalisons tout d’abord une étude en trois dimensions de l’interaction de champ proche entre une bille fluorescente et différentes antennes en silicium. Nous introduisons ensuite une technique stochastique permettant de déterminer expérimentalement la position et le taux d'amortissement de molécules uniques photo-activées, avec une précision de localisation de l'ordre de 10 nm. Enfin, nous utilisons l'information de Fisher afin d'estimer les bornes inférieures de l'erreur type des estimations de positions et de taux d'amortissement réalisées dans le cadre de mesures sur molécules uniques. / In this thesis, we perform experimental measurements and data modelling to investigate spontaneous emission of fluorescent emitters in nanostructured environments. The manuscript is organised into two main parts.In the first part, we study micrometre-range energy transfer between fluorescent emitters in plasmonic environments. First of all, we characterise plasmon-mediated energy transfer between ensembles of fluorescent emitters located in the near field of a silver film. We thus determine the distance dependence of the energy transfer rate over micrometre distances. We then couple a single quantum dot and a fluorescent nanobead to a silver nanowire and we study evidences of the energy transfer between the two emitters, separated by several micrometres. We notably demonstrate a correlated blinking of the two emitters through the study of the correlation function of their fluorescence intensity.In the second part, we probe sub-wavelength spatial variations of the local density of electromagnetic states induced by nanostructured environments by means of different super-resolution microscopy techniques. To start with, we perform a three-dimensional study of the near-field interaction between a fluorescent nanobead and different silicon nanoantennas using a scanning-probe microscope. We then introduce a stochastic technique to experimentally determine the position and the fluorescence decay rate of single photo-activated molecules, with a localisation precision of the order of 10 nm. Finally, we use the Fisher information to estimate lower bounds on the standard errors on position and decay rate estimates performed in the context of single-molecule microscopy.

The dielectric antenna is an interesting alternative to a metallic antenna. This is mainlydue to its low manufacturing cost and the possibility to fabricate complex antennageometry with the aid of additive manufacturing (AM). Sophisticated AM technologyprovides new degrees of freedom in shaping the outer and inner geometry of antennas.This feature can be utilized to optimize various properties of antenna, such as itsbandwidth, radiation pattern etc, while maintaining a compact geometry.This master thesis investigates the possibility of improving the bandwidth of acompact dielectric antenna by modifying its geometry. Specifically, dielectricresonator antennas (DRAs) have been considered here. In this connection, twoembedded cylindrical DRAs operating within 8 GHz-17 GHz frequency band havebeen designed and simulated using Ansys HFSS. For the first design (Design-1), abandwidth (corresponding to reflection coefficient ≤ -10dB) of approximately 63%has been obtained and the second design (Design-2) has a bandwidth (correspondingto reflection coefficient ≤ -10dB) of about 57%. However, in terms of radiationcharacteristics, the performance of Design-2 has been found to be superior comparedto Design-1, mainly due to its symmetrical geometry. Furthermore, the two designshave been compared to an existing compact rectangular embedded DRA. It has beenfound that both Design-1 and Design-2 have comparatively wider bandwidth. Withrespect to the radiation characteristics, the performance of the reference antenna andDesign-2 are similar. While, the radiation performance of the reference antenna isfound to be better than Design-1. / Dielektriska antenner är ett intressant alternativ till metalliska diton. Detta beror delspå lägre tillverkningskostnader men också, tack vare additiva tillverkningsmetoder,på grund av möjligheten att använda komplexa geometrier. De senaste årens framsteginom additiv tillverkning har öppnat upp nya möjligheter vid designen av den externaoch den inre geometrin hos dielektriska antenner. Detta kan utnyttjas till att optimeraolika aspekter hos antennen, exempelvis bandbredd och strålningsmönster, utan attpåverka de yttre måtten.Denna avhandling studerar möjligheten att förbättra bandbredden hos dielektriskaresonansantenner (DRA) genom att modifiera deras inre. Två cylindriska DRA:er,verksamma inom 8-17 GHz, har designats och simulerats i Ansys HFSS. Bandbredderom 63 % för Design-1, samt 57 % för Design-2, erhölls. Trots den första designensstörre bandbredd uppvisar Design-2 bättre strålningsegenskaper, främst avseendeantennens strålningsmönster. De simulerade antennerna har också visat sig hastörre bandbredd jämfört med en redan existerande kompakt, inbäddad DRA. Sett tillstrålningsegenskaper är prestandan hos Design-2 jämförbar med referensantennen,medan design ett uppvisar sämre prestanda.