Resonant Raman Scattering by quadrupolar vibrations of Ni-Ag Core-shell Nanoparticles

Low-frequency Raman scattering experiments have been performed on thin films consisting of nickel-silver composite nanoparticles embedded in alumina matrix. It is observed that the Raman scattering by the quadrupolar modes, strongly enhanced when the light excitation is resonant with the surface dipolar excitation, is mainly governed by the silver electron contribution to the plasmon excitation. The Raman results are in agreement with a core-shell structure of the nanoparticles, the silver shell being loosely bonded to the nickel core.Comment: 3 figures. To be published in Phys. Rev.

Influence de la morphologie sur les propriétés optiques de nano-objets métalliques uniques

On a nanometric scale, noble metal particles have fascinating optical properties. They are dominated by the phenomenon of Surface Plasmon Resonance whose spectral profile is very sensitive to the size, form and environment of the particles (external dielectric medium, other close particles ). The purpose of this thesis is a better comprehension of the fundamental processes responsible of the plasmon resonance modifications: on one hand by carrying out the extinction spectroscopy of single nanoparticles by the original technique of Spatial Modulation Spectroscopy and on the other by characterizing the morphology of these same objects by a direct observation in Transmission Electronic Microscopy. This double approach makes it possible to correlate the optical response of nanoparticles (isolated or in interaction (dimers)) with their form or their spacial arrangement, and thus to facilitate its theoretical modellingA l'échelle nanométrique, les particules de métaux nobles possèdent des propriétés optiques fascinantes. Elles sont dominées par le phénomène de Résonance de Plasmon de Surface dont le profil spectral est très sensible à la taille, à la forme et à l'environnement des particules (milieu diélectrique extérieur, autres particules proches...). Ce travail de thèse a pour but une meilleure compréhension des processus fondamentaux responsables des modifications de la résonance de plasmon : d'une part en réalisant la spectroscopie d'extinction de nanoparticules uniques par la technique originale de Spectroscopie à Modulation Spatiale et d'autre part en caractérisant la morphologie de ces mêmes objets par une observation directe en Microscopie Electronique à Transmission. Cette double approche permet de corréler la réponse optique de nanoparticules (isolées ou bien en interaction (dimères)) avec leur forme ou leur arrangement spatial, et d'en faciliter ainsi la modélisation théoriqueLYON1-BU.Sciences (692662101) / SudocSudocFranceF

Plasmon spectroscopy of small indium-silver clusters: Monitoring the indium shell oxidation

cited By 9International audienceOwing to the very different electrovalences of indium and silver, nanoparticles made of these elements are among the simplest examples of hybrid plasmonic systems retaining a full metallic character. The optical properties of small indium-silver clusters are investigated here for the first time in relation to their structural characterization. They are produced in the gas phase by a laser vaporization source and co-deposited in a silica matrix. The optical absorption of fresh samples is dominated by a strong surface plasmon resonance (SPR) in the near UV, in an intermediate position between those of pure elements. A combination of SPR analysis and electron microscopy imaging provides evidence for the favourable surface segregation of indium. After a prolonged exposure to ambient air and because of the silica matrix porosity, changes in the SPR reflect the spontaneous formation of a dielectric indium oxide shell around a metallic silver core. The metallic character of indium can nevertheless be recovered by annealing under a reducing atmosphere. The reversibility of these processes is directly mirrored in optical measurements through SPR shifts and broadenings as supported by multi-shell Mie theory calculations. By controlling their oxidation level, In-Ag clusters can be considered as new candidates to extend SPR spectroscopy in the UV range and model plasmonic systems consisting of a silver particle of potentially very small size, fully protected by a dielectric oxide shell. © 2014 the Owner Societies

In situ environmental HRTEM study of the restructuration under reducing atmosphere of small oxidized silver-indium nanoparticles

International audienc

In situ environmental HRTEM study of the restructuration under reducing atmosphere of small oxidized silver-indium nanoparticles

International audienc

In situ reduction of core-shell Ag@In2O3 nanoparticles observed through environmental electronic microscopy

International audienc

In situ reduction of core-shell Ag@In2O3 nanoparticles observed through environmental electronic microscopy

International audienc

In situ environmental HRTEM study of the restructuration under reducing atmosphere of small oxidized silver-indium nanoparticles

International audienc

Probing Elasticity at the Nanoscale: Terahertz Acoustic Vibration of Small Metal Nanoparticles

International audienceThe acoustic response of surface-controlled metal (Pt) nanoparticles is investigated in the small size range, between 1.3 and 3 nm (i.e., 75-950 atoms), using time-resolved spectroscopy. Acoustic vibration of the nanoparticles is demonstrated, with frequencies ranging from 1.1 to 2.6 THz, opening the way to the development of THz acoustic resonators. The frequencies, measured with a noncontact optical method, are in excellent agreement with the prediction of a macroscopic approach based on the continuous elastic model, together with the bulk material elastic constants. This demonstrates the validity of this model at the nanoscale and the weak impact of size reduction on the elastic properties of a material, even for nanoparticles formed by less than 100 atoms