Experimental Determination of the Fluorescence Quantum Yield of Semiconductor Nanocrystals

Many studies have considered the luminescence of colloidal II–VI nanocrystals, both in solution at a collective scale and at an individual scale by confocal microscopy. The quantum yield is an important figure of merit for the optical quality of a fluorophore. We detail here a simple method to determine the quantum yield of nanocrystals in solution as a function of the absorption. For this purpose, we choose rhodamine 101 as a reference dye to measure the nanocrystal fluorescence quantum yield. The influence of the concentration on quantum yield is therefore studied for both the reference and the solutions of nanocrystals and is found to be critical for the acuity of the method. Different types of nanocrystals are studied to illustrate different quantum yield evolutions with the concentration

Nanosources exaltées pour la spectroscopie non-linéaire en champ proche optique

The yield of sub-microscopic non-linear optical processes are very low. Therefore, intensive researches are done to study the electromagnetic field confinement by metallic structures on sub-wavelength areas.This describe relates the optical properties of granular metallic films on nanometer scale. These samples show linear local field enhancements in nanometer-sized regions due to surface plasmon resonances (SPR).In order to study these samples, aperture near-field optical microscopy (SNOM) has been chosen. Our results display high local field enhancements in sub-wavelength areas. These fields depend on both wavelength and polarization. When SPR are not excited, only scattering occurs. When increasing the wavelength, enhancements are observed together with scattering. Finally, these two regimes are statistically analysed with the autocorrelation function.Les processus non-linéaires optiques à l'échelle nanométrique ont des rendements très faibles. Ainsi les structures métalliques permettant de confiner les champs électromagnétiques sur des zones sub-longueur d'onde sont intensivement étudiées.Ce mémoire présente l'étude des propriétés optiques à l'échelle nanométrique de films granulaires métalliques. Les modes de résonances plasmons, quand ils sont excités, génèrent des pics d'exaltation localisés.Pour faire les études expérimentales de ces échantillons, nous avons choisi la microscopie optique de champ proche à ouverture (SNOM). Nos résultats montrent la localisation de champs intenses dans des zones nanométriques. Ces exaltations dépendent de la longueur d'onde et de la polarisation. Il existe un régime purement diffusif quand les résonances plasmons ne sont pas excitées. En augmentant la longueur d'onde, les exaltations apparaissent, mais la diffusion est toujours présente. Une étude statistique par la fonction d'autocorrélation analyse ces deux régimes

Nanosources exaltées pour la spectroscopie non-linéaire en champ proche optique

The yield of sub-microscopic non-linear optical processes are very low. Therefore, intensive researches are done to study the electromagnetic field confinement by metallic structures on sub-wavelength areas.This describe relates the optical properties of granular metallic films on nanometer scale. These samples show linear local field enhancements in nanometer-sized regions due to surface plasmon resonances (SPR). In order to study these samples, aperture near-field optical microscopy (SNOM) has been chosen. Our results display high local field enhancements in sub-wavelength areas. These fields depend on both wavelength and polarization. When SPR are not excited, only scattering occurs. When increasing the wavelength, enhancements are observed together with scattering. Finally, these two regimes are statistically analysed with the autocorrelation function.VERSAILLES-BU Sciences et IUT (786462101) / SudocSudocFranceF

From scattering regime to strong localization: a statistical analysis of the near-field intensity on random gold films

International audienceRandom metallic films have very specific optical properties due to disorder. Strong localization of electromagnetic fields can be observed due to plasmons. This localization strongly depends on excitation conditions, and different optical regimes can exist. To characterize these regimes, we investigated the spatial intensity correlation functions using near-field scanning optical microscopy for different excitation wavelengths and different incident polarization states. The transition between a weak scattering regime where no plasmon resonances are excited and a regime where strong plasmon resonances occur has clearly been observed. In the strong plasmonic regime, by varying the incident polarization direction, the shape of the correlation function has been correlated to the intensity enhancement which raises the possibility to control the intensity localization using the incident polarization state

Plasmon excitation and induced emission with a plasmonic self-organized crystal

International audienceIn this paper, we describe the plasmonic and plasmon-photon coupling properties of nanostructured metallic films obtained by a self-assembly protocol. A gold layer is deposited on top of a self-assembled deposition of silica beads (artificial opal), which thus acts as a template. Atomic-force and scanning-electron microscopies demonstrates a periodic pattern on the metal surface with groove depth (here labelled h) ranging from 55 to 150 nm. By optical gonioreflectometry, the surface plasmon modes of this structure are probed: plasmon creation appears as an absorption dip in the reflection spectra. The plasmon dispersion relation is probed as a function of h and shows, for the smaller values of h, a good agreement with an analytical model for vanishing h. By depositing nanocrystals on the structure and measuring the fluorescence radiation pattern, we demonstrate a method to estimate the plasmon extraction (plasmon-to-photon coupling) efficiency. Finally, we use photo-emission electron microscopy to map the electric field of the plasmonic modes and characterize both propagative surface plasmon and localized (" hot spot ") plasmon modes

Leakage interferences applied to surface plasmon analysis

International audienceWe report the experimental combination of leakage radiation microscopy with a Young slit experiment to address the spatial coherence properties of surface waves. We applied this method to measurements of surface plasmon polaritons (SPPs). The relationship between the spatial decay and interference contrast allows us to extract the degree of coherence. In a second step, we investigate the coherence properties of the plasmon in the weak coupling regime between fluorophores and metallic surfaces. Finally, a method is proposed to extract the propagation length of SPPs in a large variety of systems

FDTD simulations of localization and enhancements on fractal plasmonics nanostructures

International audienceA parallelized 3D FDTD (Finite-Difference Time-Domain) solver has been used to study the near-field electromagnetic intensity upon plasmonics nanostructures. The studied structures are obtained from AFM (Atomic Force Microscopy) topography measured on real disordered gold layers deposited by thermal evaporation under ultra-high vacuum. The simulation results obtained with these 3D metallic nanostructures are in good agreement with previous experimental results: the localization of the electromagnetic intensity in subwavelength areas (" hot spots ") is demonstrated; the spectral and polarization dependences of the position of these " hot spots " are also satisfactory; the enhancement factors obtained are realistic compared to the experimental ones. These results could be useful to further our understanding of the electromagnetic behavior of random metal layers

Strong Coupling between Plasmons and Organic Semiconductors

In this paper we describe the properties of organic material in strong coupling with plasmon, mainly based on our work in this field of research. The strong coupling modifies the optical transitions of the structure, and occurs when the interaction between molecules and plasmon prevails on the damping of the system. We describe the dispersion relation of different plasmonic systems, delocalized and localized plasmon, coupled to aggregated dyes and the typical properties of these systems in strong coupling. The modification of the dye emission is also studied. In the second part, the effect of the microscopic structure of the organics, which can be seen as a disordered film, is described. As the different molecules couple to the same plasmon mode, an extended coherent state on several microns is observed