Bulky Counterions: Enhancing the Two-Photon Excited Fluorescence of Gold Nanoclusters

International audienc

Nonlinear Refraction and Absorption of Ag 29 Nanoclusters: Evidence for Two-Photon Absorption Saturation

International audienc

Universal scaling of plasmon coupling in metal nanostructures: Checking the validity for higher plasmonic modes using second harmonic generation

The universal scaling of plasmon coupling in metallic nanostructures is now a well-established feature. However, if the interaction between dipolar plasmon modes has been intensively studied, this is not the case of the coupling between higher order ones. Using Mie theory extended to second harmonic generation, we investigate the coupling between quadrupolar plasmon modes in metallic nanoshells. Like in the case of dipolar plasmon modes, a universal scaling behavior is observed in agreement with the plasmon hybridization model

Second harmonic scattering from silver nanocubes

The second harmonic light scattered from silver nanocubes dispersed in an aqueous suspension is investigated. The first hyperpolarizability is determined and corrected for resonance enhancement. It is shown to be similar to that of silver nanospheres with a comparable volume. The polarization-resolved analysis of the scattered harmonic intensity exhibits a surface response strongly modulated by the different multipolar field contributions. As a result, the shape does not play a leading role anymore for nanoparticles with a centrosymmetric shape when retardation must be considered. Comparing the right angle and forward-scattered polarized intensity responses, the unequal balance of the eight nanocube corners' contribution to the total response is revealed despite the high degree of centrosymmetry of the cubic shape. It is then demonstrated with a simple model that the nanocubes' first hyperpolarizability exhibits an octupolar tensorial symmetry. The surface integral equation method calculations are finally provided to investigate further the role of the corners’ and edges’ rounding

Control of the supercrystallinity, nanocrystallinity, morphology and magnetism of cobalt nanoparticle assemblies. Towards novel colloidal crystals with high magnetic anisotropy

International audienceStarting from a colloidal solution of dodecanoic acid-coated Co nanoparticles (NP) of 8.1 nm in size and of low anisotropy and using a solvent-mediated ligand-ligand interaction strategy, we obtain either colloidal crystals or supercrystalline films. The comparison between the structural and magnetic properties of these two different architectures of supercrystals evidences improved magnetic properties for the colloidal crystals. This is interpreted as a result of both an increase in the mesoscopic coherence length and a decrease in the interparticle distance. In this work we extend this comparative study between the two types of supercrystals after annealing treatment. A common batch of NP is used for the native and the annealed samples in order to optimize the accuracy of the comparison. A complete set of structural characterizations and magnetic measurements shows that upon annealing the NP evolve from soft to hard magnetic NP, with changes of both the anisotropy constant and saturation mangnetization, while the supercrystal structures remain unchanged. Both native and annealed colloidal crystals remain characterized by a smaller interparticle distance compared to the corresponding films, inducing higher dipolar interactions, which is evidenced by an increase in the blocking temperature. In this study, we highlight the first fcc colloidal crystals made of hcp-Co single crystals resulting from the annealing of their native counterparts made of fcc-Co polycrystals. In addition, the comparative magnetic study between both the annealed supercrystalline films and colloidal crystals evidences enhanced magnetic properties for the latter ones

Isomeric Effect of Mercaptobenzoic Acids on the Synthesis, Stability, and Optical Properties of Au 25 (MBA) 18 Nanoclusters

International audienc

Second Harmonic Scattering of Molecular Aggregates

International audienceA general model is developed to describe the polarization-resolved second harmonic scattering (SHS) response from a liquid solution of molecular aggregates. In particular, the molecular spatial order is introduced to consider the coherent contribution, also known as the retarded contribution, besides the incoherent contribution. The model is based on the description of a liquid suspension of molecular dyes represented by point-like nonlinear dipoles, locally excited by the fundamental field and radiating at the harmonic frequency. It is shown that for a non-centrosymmetrical spatial arrangement of the nonlinear dipoles, the SHS response is very similar to the purely incoherent response, and is of electric dipole origin. However, for centrosymmetrical or close to centrosymmetrical spatial arrangements of the nonlinear dipoles, the near cancellation of the incoherent contribution due to the inversion symmetry rule allows the observation of the coherent contribution of the SHS response, also known as the electric quadrupole contribution. This model is illustrated with experimental data obtained for aqueous solutions of the dye Crystal Violet (CV) in the presence of sodium dodecyl sulfate (SDS) and mixed water-methanol solutions of the dye 4-(4–dihexadecylaminostyryl)-N-methylpyridinium iodide (DiA), a cationic amphiphilic probe molecule with a strong first hyper-polarizability; both CV and DiA form molecular aggregates in these conditions. The quantitative determination of a retardation parameter opens a window into the spatial arrangements of the dyes in the aggregates, despite the small nanoscale dimensions of the latter

Second Har onic Generation from Metallic Nanoparticles in a Random Medium

International audienc