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.

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

Linking Ag nanoparticles by aliphatic α,ω-dithiols: A study of the aggregation and formation of interparticle hot spots

Linear α,ω-dithiols have been used as linkers to control the aggregation of silver nanoparticles. The characterization of the resulting nanoparticle clusters thus formed was carried out using plasmon resonance spectroscopy and transmission electron microscopy in both independent and correlated measurements. The obtained nanoparticle assemblies present morphologies that vary according to the dithiol length, displaying controllable-size interparticle gaps (plasmonic hot spots) with potential application in the detection of a large list of hydrophobic analytes. © 2013 American Chemical Society.ACKNOWLEDGMENTS This work has been supported by the Spanish Ministerio de Economía y Competitividad (grant FIS2010-15405), by the Comunidad de Madrid, through MICROSERES II network (grant S2009/TIC-1476). I.I.-L. also acknowledges CSIC and FSE 2007- 2013 for a JAE-CSIC predoctoral grant.Peer Reviewe

Single gold bipyramids on a silanized substrate as robust plasmonic sensors for liquid environments

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Structural and Optical Properties of Silver-Indium and Silver-Aluminium Nanoalloys: Stability Against Oxidation

International audienceBimetallic nanoparticles (BNPs) are promising candidates for fundamental research and applications as their physico-chemical properties can in many cases be tuned continuously or enhanced with respect to the mono-metallic particles. Here we investigate the possibility of fabricating silver-indium and silver-aluminium BNPs in the range of 4-5 nm diameter and of varying stoichiometry by laser vaporization and gas condensation in the gas phase. We analyse their crystalline structure and segregation behaviour using transmission electron microscopy and probe their oxidation state in optical absorption measurements by tracking spectral changes of the localized surface plasmon resonance (LSPR). These complementary techniques show that, despite the small size and the high reactivity especially of aluminium, the BNPs form a silver-rich alloyed core surrounded by an oxide shell. Exposure to air leads to consecutive oxidation, whereas annealing the BNPs in a reducing atmosphere stabilizes the alloyed particle cores, as demonstrated by a narrow and blue-shifted LSPR. This is a first step towards the stabilization of non-oxidized bimetallic nanoparticles combining a noble and a trivalent metal

Inelastic Light Scattering by Multiple Vibrational Modes in Individual Gold Nanodimers

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Tracking the restructuring of oxidized silver–indium nanoparticles under a reducing atmosphere by environmental HRTEM

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Acoustic Mode Hybridization in a Single Dimer of Gold Nanoparticles

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Surface Plasmon Resonance Damping in Spheroidal Metal Particles: Quantum Confinement, Shape, and Polarization Dependences

A key parameter for optimizing nanosized optical devices involving small metal particles is the spectral width of their localized surface plasmon resonances (LSPR). In the small size range the homogeneous LSPR line width is to a large extent ruled by the spatial confinement-induced broadening contribution which, within a classical description, underlies the popular phenomenological limited mean free path model. This unavoidable contribution to the LSPR line width is basically a quantum finite-size effect rooted in the finite extent of the electronic wave functions. This broadening reflects the surface-induced decay of the coherent collective plasmon excitations into particle–hole (<i>p</i>–<i>h</i>) excitations (Landau damping), the signature of which is a size-dependent fragmented LSPR band pattern which is clearly evidenced in absorption spectra computed within the time-dependent local density approximation (TDLDA). In this work we analyze the spatial confinement-induced LSPR damping contribution in the framework on an exact Hamiltonian formalism, assuming for convenience a jellium-type ionic density. In resorting to the harmonic potential theorem (HPT), a theorem stating that in the case of a harmonic external interaction the electronic center-of-mass coordinates separate strictly from the intrinsic motions of the individual electrons, we derive a simple approximate formula allowing to (i) quantify the size dependence of the LSPR damping in spherical nanoparticles (1/<i>R</i> law, where <i>R</i> is the sphere radius) and (ii) bring to the fore the main factors ruling the confinement-induced LSPR broadening. Then the modeling is straightforwardly generalized to the case of spheroidal (prolate or oblate) metal particles. Our investigations show that the LSPR damping is expected to depend strongly on both the aspect ratio of the spheroidal particles and the polarization of the irradiating electric field, that is, on the naturetransverse or longitudinalof the collective excitation. It is found that the magnitude of the damping is tightly related to that of the LSPR frequency which rules the number of <i>p</i>–<i>h</i> excitations degenerate with the plasmon energy. Qualitative analysis suggests that the results are quite general and probably hold for other nonspherical particle shapes. In particular, in the case of elongated particles, as rods, the enlargement of the longitudinal LSPR band by the confinement effects is predicted to be much smaller than that of the transverse LSPR band

Plasmon Coupling in Silver Nanocube Dimers : Resonance Splitting Induced by Edge Rounding

International audienceAbsolute extinction cross sections of individual silver nanocube dimers are measured using spatial modulation spectroscopy in correlation with their transmission electron microscopy images. For very small interparticle distances and an incident light polarized along the dimer axis, we give evidence for a clear splitting of the main dipolar surface plasmon resonance which is found to be essentially induced by cube edge rounding effects. Supported by discrete dipole approximation and finite element method calculations, this phenomenon highlights the high sensitivity of the plasmonic coupling to the exact shape of the effective capacitor formed by the facing surfaces of both particles, especially in the regime of very close proximity