Jean Lermé

• French National Centre for Scientific Research

Localized Surface Plasmon Resonances are ubiquitous for the characterization and in applications of noble metal nanoparticles. Their dependence on chemical composition, size, shape and environment is widely studied since decades but still many aspects are subject of controversy. In this article we experimentally investigate surfactant-free and mass...

The coupling effects affecting the vibrations of two close nanostructures (e.g., two metal nanoplates or nanospheres separated by a thin dielectric layer) may considerably alter their vibrational eigenfrequencies, as demonstrated by several recent experimental studies. In this work, we present theoretical investigations of these coupling processes...

The coupling effects affecting the vibrations of two close nanostructures (e.g., two metal nanoplates or nanospheres separated by a thin dielectric layer) may considerably alter their vibrational eigenfrequencies, as demonstrated by several recent experimental studies. In this work, we present theoretical investigations of these coupling processes...

The intrinsic optical response of a scattering object is known to be modified when it is placed on a substrate. Moreover, the total extinction through ohmic losses and Rayleigh scattering is basically dependent on the reversal of the direction of the excitation wave. Considering, as stated by the generalized optical theorem, that the total extincti...

In most conventional optical experiments on substrate-supported nanoparticles, detectors are located in the far-field space whereas their intrinsic properties (scattering, absorption cross-sections) are commonly computed in the near-field by using numerical approaches. In this respect, a connection between experiment and theory can be usefully made...

The chemical structure and the localized surface plasmon resonance (LSPR) of size-selected AgxFe1-x (x=0.5, 0.8) nanoparticles (NPs), produced by laser vaporization, were investigated experimentally and theoretically. Monte Carlo simulations employing a many-body-embedded-atom model show that small isolated Ag-Fe NPs should preferentially adopt [em...

The physical properties of metals change when their dimensions are reduced to the nano-scale and new phenomena such as the localized surface-plasmon resonance (LSPR) appear. This collective electronic excitation can be tuned over a large spectral range by adapting the material, size and shape. The existing literature is as rich as it is controversi...

Plasmonic sensors owe their sensitivity to the susceptibility of collective electron modes to tiny changes of the local environment. Simple sensors are based on metal nanoparticles where spectral shifts of the resonance are frequently treated in view of an "effective" dielectric medium surrounding each particle. Using single-object spectroscopy pro...

Sensitive, robust and stable sensors are required to bring biosensing techniques from the forefront of research to clinical and commercial settings. To this end, we report on the development of new robust plasmonic sensors consisting of gold nano-bipyramids (BPs) grafted to a glass substrate via silanization, associated with a novel setup based on...

The acoustic vibrations of single monomers and dimers of gold nanoparticles were investigated by measuring for the first time their ultra-low frequency micro-Raman scattering. This experiment provides access not only to the frequency of the detected vibrational modes, but also to their damping rate, which is obscured by inhomogeneous effects in mea...

The low frequency Raman scattering from gold nanoparticle bimodal assemblies with controlled size distributions has been studied. Special care has been paid to determining the size dependence of the Raman intensity corresponding to the quadrupolar Lamb mode. Existing models based on a microscopic description of the scattering mechanism in small par...

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 linewidth is to a large extent ruled by the spatial confinement-induced broadening contribution which, within a classical description, under...

Homodimers of noble metal nanocubes form model plasmonic systems where the localized plasmon resonances sustained by each particle not only hybridize but also coexist with excitations of a different nature: surface plasmon polaritons confined within the Fabry-Perot cavity delimited by facing cube surfaces (i.e. gap plasmons). Destructive interferen...

The optical absorption of bimetallic nanoparticles M-Ag involving silver as an active plasmonic compound has been the subject of very extensive experimental studies, both for a large range of sizes and a large variety of associated metals. Considering the most commonly encountered core-shell segregated configuration M@Ag involving a transition meta...

In the presence of a nearby highly reflecting dielectric substrate, the optical response of a metal nanoparticle exhibits a rich multipolar plasmonic structure. For quantifying the multimodal plasmonic response of such hybrid particle/interface systems, the hydrodynamic plasmon hybridization (PH) method has been applied in the simple case of a soli...

The optical properties of small Cu-Ag bimetallic clusters have been experimentally and theoretically investigated in relation with their chemical structure analyzed by high resolution transmission electron microscopy (HRTEM). Cu (1-x)Agx clusters of about 5nm in diameter are produced in a laser vaporization source with a well-defined stoichiometry...

Anisotropic gold nanoparticles and in particular with shapes exhibiting tips are known to present extremely strong localized electromagnetic field. This field is mostly located at the top of the tips and can be used in various optical applications. Moreover, as a consequence of their anisotropy, they present two plasmon resonance bands correspondin...

In the presence of a nearby highly reflecting dielectric substrate the optical response of a metal nanoparticle exhibits a rich multipolar plasmonic structure. For interpreting and quantifying the spectral patterns the quasistatic hydrodynamic plasmon hybridization (PH) method developed by the Nordlander’group has been applied to the particle/inter...

In this article, we show for the first time, both theoretically and empirically, that plasmonic coupling can be used to generate Localized Surface Plasmon Resonances (LSPRs) in transition metal dimeric nano-antennas (NAs) over a broad spectral range (from the visible to the near infrared) and that the spectral position of the resonance can be contr...

A great number of studies focus their interest on the photophysical properties of fluorescent hybrid gold nanoparticles for potential applications in biotechnologies such as imaging and/or treatment. Spherical gold nanoparticles are known to quench a chromophore fluorescent signal, when moieties are located in their close vicinity. The use of a pol...

Owing 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...

We show that the optical properties of a particle above a plane dielectric interface differ dramatically from those of the same particle embedded in a homogeneous matrix. Calculations for gold and silver spheres have been carried out in using the exact multipole expansion method, providing thus benchmark results for testing the accuracy of the avai...

Absolute extinction measurements on individual silver nanoparticles under illumination show a steady evolution of their localized surface plasmon resonance. Their progressive transformation during light exposure and the influence of various parameters such as the nature of stabilizers, the local environment (oxygen rate), the spectral range of the...

In this paper the specific properties of free clusters and the formation of new cluster-assembled materials using the low energy cluster beam deposition (LECBD) technique are discussed. Recent results obtained for free clusters are summarized with special attention to new observed structures. As for the specific structures and properties of cluster...

A great number of works focus their interest on the study of gold nanoparticle plasmonic properties. Among those, sharp nanostructures appear to exhibit the more interesting features for further developments. In this paper, a complete study on bipyramidal-like gold nanostructures is presented. The nano-objects are prepared in high yield using an or...

Absolute 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...

A key parameter for optimizing nanosized optical devices involving small metal particles is the spectral width of their localized surface plasmon resonances (LSPR), which is intrinsically limited by the confinement-induced broadening (quantum finite size effects). I have investigated the size evolution of the LSPR width induced by quantum confineme...

Numerous research efforts are investigating the possibility of using light interactions with metallic nanoparticles to improve the fluorescence properties of nearby molecules. Few investigations have considered the encapsulation of molecules in metallic nanocavities. In this paper, we present the optical properties of new hybrid nanoparticles consi...

The impact of quantum confinement on the width of the surface plasmon resonance of a metal nanoparticle is theoretically investigated in a model system formed by a silver nanosphere in different environments. Calculations are performed using the time-dependent local density approximation (TDLDA) for nanoparticle diameters up to about 11 nm, permitt...

This article describes a high sensitivity spectrophotometer designed to detect the overall extinction of light by a single nanoparticle (NP) in the 10(-4)-10(-5) relative range, using a transmission measurement configuration. We focus here on the simple and low cost scheme where a white lamp is used as a light source, permitting easy and broadband...

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The optical extinction spectra of single silver nanoparticles coated with a silica shell were investigated in the size range 10-50 nm. Measurements were performed using the spatial modulation spectroscopy technique which permits independent determination of both the size of the metal nanoparticle under study and the width of its localized surface p...

We have studied the spectral response of individual pairs of gold nanoparticles chemically synthesized and stabilized on a transparent thin film. Very thin interspacing distances are explored by taking advantage of a residual layer of surfactant molecules at the metal surface. Absolute extinction cross section measurements by the spatial modulation...

We present a general formalism for describing the optical response of spherical nano-objects located in the focus region of a tightly convergent light beam. The theory can be applied to any polarized light beam emerging from axially symmetric focusing optical devices. The approach is based on the generalized Mie theory equations and the expansion o...

We develop a new and numerically efficient formalism to describe the general problem of the scattering and absorption of light by a spherical metal or dielectric particle illuminated by a tightly focused beam. The theory is based on (i) the generalized Mie theory equations, (ii) the plane-wave decomposition of the converging light beam, and (iii) t...

The optical properties of Au-Ag and Ni-Ag clusters are measured by linear optical absorption spectroscopy and the time-resolved pump-probe femtosecond technique allowing a study of the influence of alloy or core-shell structure.

The absolute extinction cross-section spectrum of a single nanoparticle measured using spatial modulation spectroscopy (SMS) is correlated with its transmission electron microscopy (TEM) image. The sizes of quasi-spherical particles obtained by the two methods are found to be in good quantitative agreement. The possibilities opened up by combinatio...

Metal cluster cations are produced in a laser vaporization source, size selected in the gas phase by an electrostatic quadrupole deflector, and deposited on transmission electron microscopy grids coated with various substrates. The morphology of cluster assemblies is very dependent on the occurrence of diffusion, collision, and coalescence of incid...

The extinction spectrum of single silver nanoparticles with size ranging from 20 to 80nm is investigated with the spatial modulation spectroscopy technique using either a tunable laser or a white lamp as the broadband source. Results are in good agreement with the prediction of the Mie theory, permitting to extract the nanoparticle size from t...

The clusters and colloids discussed in this chapter are structures made up of anything from a few tens to a few thousand or tens of thousands of atoms, with diameters between 1 and 10 nm, which are intermediate states of matter between the molecule and the bulk solid. In this nanoscale world, where the range of interactions is equal to or exceeds t...

The optical properties of noble metal clusters are measured and compared in the size range 1.4–7nm in diameter. The clusters of copper, silver and gold are produced by the same experimental technique, the deposition of preformed clusters in a transparent matrix. The size dependence is found to be different for the three metals. As the size decrease...

Metal cluster cations are produced in a laser vaporization source, size selected in the gas phase by an electrostatic quadrupole deflector, and deposited without coalescence on carbon coated electron microscopy grids for further observation. For platinum clusters, a transition from spherical to strongly ramified shapes is observed when the cluster...

Effects of confinement on the electron-electron (e-e) and electron-phonon (e-ph) thermalization dynamics in noble metal clusters are calculated using simple approaches. The model predictions are compared with femtosecond pump-probe measurements which display an acceleration of the e-e and e-ph relaxation dynamics. The size-effects on the e-e relaxa...

Copper nanocrystals characterized by various sizes and shapes are synthesized in reverse micelles. The average size of the metallic nanocrystals increases from 3 to 8.4 nm. Experimental (UV spectroscopy) and theoretical (TDLDA formalism) optical studies permit to correlate the optical response to size and shape effects of the nanocrystals.

Optical properties of copper clusters of 3 to 5 nm in diameter, produced by laser vaporization and embed-ded in alumina, are investigated and compared to a semi-quantal model [based on time-dependent local-density approximation (TDLDA) and density functional theory (DFT)], including the absorption and screening prop-erties of the ionic core backgro...

An electrostatic quadrupole deviator is used to separate charged from neutral clusters produced by a laser vaporization source. Because of their rather constant velocity, this device which is basically an energy selector also acts as an efficient mass filter. We have simulated and studied its capability to generate beams of size-selected charged cl...

The conduction electron energy exchanges are investigated in gold and silver nanoparticles with average size ranging from 2 to 26 nm, embedded in different matrices. The experimental studies were performed by following the internal thermalization dynamics of photoexcited nonequilibrium electrons with a femtosecond pump-probe technique. The probe wa...

Electron-lattice energy exchanges are investigated in gold and silver nanoparticles with sizes ranging from 30 to 2.2 nm embedded in different environments. Femtosecond pump-probe experiments performed in the low-perturbation regime demonstrate a strong increase of the intrinsic electron-phonon interaction for nanoparticles smaller than 10 nm due t...

The optical properties of mixed (Ni0.5Ag0.5)n and Pt/Ag clusters are investigated in the size range 2−5 nm. Low Energy Ion Spectroscopy (LEIS) experiments show that the cluster surface is entirely covered by silver atoms for the two systems. The optical spectra of Ni/Ag clusters exhibit a large Surface Plasmon Resonance (SPR), damped and widened wh...

Optical properties of mixed clusters Ni/Ag, Co/Ag, and Ni/Au of 2–5 nm in diameter, produced by laser vaporization and embedded in an alumina matrix, are investigated. The first part is devoted to (Ni x Ag 1x) n clusters whose photoabsorption spectra reveal a surface plasmon resonance, damped, broadened, and blue-shifted as compared to pure silver...

(C60)mNan clusters are produced in a tandem laser vaporization source and analyzed by photoionization and photofragmentation time-of-flight mass spectroscopy. At low sodium coverage, the special behavior of (C60)m=1,2Nan clusters (n £ 6m)(n\leq 6m) is consistent with a significant electron transfer from the first six adsorbed atoms towards each of...

(C60)nCq+ cationic clusters are produced in a laser vaporization source by quenching the vapors from C60 and graphite targets. They are analyzed in the gas phase by abundance and photofragmentation time-of-flight mass spectroscopy. Among the large number of expected isomers, the present experiments give evidence for the stability of special arrange...

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...

The effects of surface-induced lattice contraction on the size evolution of the surface plasmon resonance and of the electronic thermalization time in small silver clusters have been investigated in the framework of a mixed classical/quantum model. The increase of the conduction-electron density results in a blue-shift trend for decreasing cluster...

Optical properties of mixed clusters (AuxAg 1 - x ) n and (NixAg 1 - x ) n , produced by laser vaporization and embedded in an alumina matrix, are reported. The size effects are investigated for different concentrations (x = 0.25, 0.5 and 0.75) in the diameter range 2-4 nm. For alloyed clusters (AuxAg 1 - x ) n of a given size an almost li...

This paper deals with a new type of SiC bonding where silicon atom seems to bridge C60 molecules. We have studied films obtained by deposition of (C60)nSim clusters prepared in a laser vaporization source. Prior deposition, free ionized clusters were studied in a time-of-flight mass spectrometer. Mixed clusters (C60)nSim were clearly observed. Abun...

This paper deals with a new type of SiC bonding where silicon atom seems to bridge C60 molecules. We have studied films obtained by deposition of (C60)nSim clusters prepared in a laser vapor-ization source. Prior deposition, free ionized clusters were studied in a time-of-flight mass spectrometer. Mixed clusters (C60)nSim were clearly observed. Abu...

Mixed (AuxAg1-x)n clusters of various relative compositions are produced in a laser vaporization source, and embedded in an alumina matrix. The size and concentration effects in the optical properties are investigated for different stoichiometries (from x=0 up to 1 in steps of 0.25), in the diameter range 1.5–5 nm for which the size evolution is ru...

The low energy cluster beam deposition technique (LECBD) is developed to prepare original nanostructured systems from clusters preformed in the gas phase. The nucleation and growth mechanism specific of the cluster deposits is studied Ln view to control the nanostructured morphology of the cluster assembled films, especially for future applications...

We present the gas phase measurement of the static electric dipole polarizability of C70 fullerenes. The value is 102+/-14 Å3. The increase in polarizability from C60 to C70 is discussed and compared to different theoretical predictions.

The optical properties of nanocomposite thin films of gold, silver and bimetallic silver-gold clusters embedded in a porous alumina matrix have been investigated in the size range 2–6.7 nm. The metallic particles are produced by laser vaporization of either an Au0.5Ag0.5 alloy or a pure metal target whereas the dielectric matrix is evaporated by an...

Low-frequency Raman scattering experiments have been performed on thin films consisting of pure gold or gold-silver alloy clusters embedded in alumina matrix. It is clearly shown that the quadrupolar vibrational modes are observed by Raman scattering because of the effect of resonance with the excitation of the electronic surface dipolar plasmon. T...

The low energy cluster beam deposition technique (LECBD) is developed to prepare original nanostructured systems from clusters preformed in the gas phase. The nucleation and growth mechanism specific of the cluster deposits is studied in view to control the nanostructured morphology of the cluster assembled films, especially for future applications...

We present the gas phase measurement of the static electric dipole polarizability of C70 fullerenes. The value is 102±14 Å3. The increase in polarizability from C60 to C70 is discussed and compared to different theoretical predictions.

The internal thermalization dynamics of the conduction electrons is investigated in silver nanoparticles with radius ranging from 13 to 1.6 nm using a femtosecond IR pump-UV probe absorption saturation technique. A sharp increase of the electron energy exchange rate is demonstrated for nanoparticles smaller than 5 nm. The results are consistent wit...

The optical properties of bimetallic silver-gold clusters are investigated in the size range 1.9-2.8 nm. Clusters, produced by laser vaporization of an alloy target Au-Ag (50%-50% atomic composition) are embedded with a low concentration in an alumina matrix. The mixed particles have the same stoichiometry as the rod. Absorption spectra exhibit a p...

(C60)nSim+ cationic clusters are produced in a laser vaporization source by quenching the vapors from two independent C60 and silicon targets. They are analyzed in the gas phase by abundance and photofragmentation time-of-flight mass spectroscopy. For complexes containing only one C60 molecule, silicon is unlikely to wet the fullerene surface. Mass...

A mixed classical/quantum model for calculating the optical response of free and matrix-embedded multilayered metal spheres in the dipolar approximation is presented. The conduction electrons are quantum-mechanically treated in the framework of the time-dependent local-density-approximation formalism (TDLDA), whereas the surrounding matrix, the ion...

A theoretical mixed classical/quantal model for describing the optical properties of free and matrix-embedded metal clusters, based on the time-dependent local-density approximation, is presented. As compared to the previous models involving an inner or/and an outer dielectric medium, all the dielectric effects—screening and absorbing properties—ar...

Absorption and low-frequency Raman-scattering experiments have been performed on thin films consisting of small silver clusters embedded in a porous alumina matrix. When the Raman excitation wavelength is close to the maximum (≈420 nm) of the Mie band (dipolar surface plasmon resonance) the Raman spectra exhibit a strong band located around 10 cm-1...

Absorption and low-frequency Raman scattering experiments have been performed on thin films consisting of small silver clusters embedded in a porous alumina matrix. When the Raman excitation wavelength is close to the maximum (˜420nm) of the Mie band (dipolar surface plasmon resonance) the Raman spectra exhibit a strong band located around 10cm -1,...

The optical properties of nanocomposite thin films of gold and silver clusters embedded in an alumina matrix have been investigated. The samples have been characterized by several techniques in order to determine their composition, morphology and cluster size distribution. Ellipsometry and photoabsorption measurements have been performed. The diffe...

High-resolution ion mobility measurements have been used to examine Iny and Inq clusters with ns 2-30. The nn cluster-He scattering cross-sections of the anions are systematically larger than those of the cations. The difference ; 25% . for In to ; 2% for In is attributed to the electron density extending further from the surface of the cluster in...

Silicon carbon binary clusters are generated in a laser vaporization source from SixC1−x mixed targets (x=0 to 50%). We have first analyzed stoichiometric (SiC)n (n⩽40) clusters grown from a silicon carbide target (x=50%). Both high fluence photoionization of (SiC)n neutral clusters and photofragmentation of size-selected (SiC)n+ natural positive i...

We have investigated SiC films, obtained by the low-energy cluster beam deposition (LECBD) technique, and using AFM Raman and XPS spectroscopies. We produce these films at room temperature and in an ultrahigh vacuum environment to protect them from the pollution. The inner morphology of the clusters is close to an amorphous-like structure. However,...

Silicon–carbon binary clusters with various mean compositions are generated in a laser vaporization source from targets processed as mixtures of graphite and silicon powders. Their size distribution is first analyzed by time-of-flight mass spectroscopy, which shows the stability of carbon fullerenes doped with silicon atoms in substitutional sites....

The authors report on a high-resolution study of Rydberg levels in the atomic spectrum of francium, performed at CERN with the on-line mass separator ISOLDE. The ns (n=12-22) and nd (n=10-20) levels were investigated using stepwise laser excitation in collinear geometry. From these are deduced the quantum defects of the ns and nd series, as well as...

The authors present an extension to low-lying states of francium (10s, 11s, 8d, 9d) of a previously published high-resolution experiment performed on the ns and nd Rydberg levels. These four levels were investigated at CERN with the on-line mass separator ISOLDE using stepwise laser excitation in collinear geometry. Accurate energy measurements lea...

The authors have applied the collinear laser spectroscopy technique together with a field ionisation detection method to investigate the even parity spectra of atomic argon. The optical excitation is produced by a frequency doubled CW ring dye laser operating in the 300 nm region. The 4s(3/2)20 metastable level populated by means of charge exchange...

An original method of determining the nuclear Lande factor for atoms with a diamagnetic ground state is illustrated with the two odd-A isotopes 135Ba and 137Ba. The method, based on the fast atomic beam laser spectroscopy technique, consists of detecting the in-flight Larmor precession of the nuclear magnetic dipolar moment in a static magnetic fie...

The low-energy cluster beam deposition technique (LECBD) is applied to produce cluster assembled films with hitherto unknown nanostructured morphologies and properties. Neutral clusters having the very low energy gained in the supersonic expansion at the exit of the inert gas condensation-type source are deposited without fragmentation upon impact...

Nanosized neutral silicon-carbon compound clusters produced by a laser vaporization source have been analyzed in the gas phase and deposited at room temperature on various substrates in an ultrahigh vacuum environment to produce nanostructured thin films. The electronic structure has been probed by complementary techniques, such as x-ray photoemiss...

The optical response of free and matrix-embedded gold metal clusters AuN is investigated in the framework of the time-dependent local-density-approximation (TDLDA). The characteristics of the surface plasmon resonance are carefully analyzed as a function of the model parameters and the particle radius. The strong influence of the frequency-dependen...

The electronic shell structure of gallium clusters has been investigated up to N e ≈15000 valence electrons. Two successive supershell nodes located respectively around 2500 and 7500 electrons have been observed. The location of these supershell nodes at a size larger than expected from the standard jellium model is interpreted in the framewor...

The surface plasmon energy of silver clusters is investigated in the framework of the time-dependent local density approximation. The results are in good agreement with experimental data on free Ag+N clusters and on AgN clusters embedded in solid argon and alumina. The size effects are weak and very sensitive to the matrix, the porosity at the inte...

We report on the synthesis of ${\mathrm{C}}_{2n$-${}q}{\mathrm{Si}}_{q}$ clusters with $2n\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}32$-${}100$ and $q<4$. The analysis of the abundance distribution and photofragmentation spectra provides clear evidences that such clusters remain in the fullerene geometry and that the Si atoms are located c...

Distributions of neutral Si-clusters centered around mean sizes of 50 and 200 atoms have been produced using a laser vaporization source and deposited on various substrates at room temperature in ultrahigh vacuum. The Si-cluster assembled films obtained, resulting from the random stacking of incident free nanosize clusters, were subsequently coated...

We report experiments on gold clusters in the size range 2–4 nm, embedded in an alumina matrix. The metallic particles are produced with a laser vaporization source and codeposited with a dielectric vapor as a thin film on a substrate. Our technique allows varying the cluster size at a given metal concentration. These composite materials are studie...

Nanosize neutral silicon clusters produced using a laser vaporization source were analyzed in the gas phase and deposited on various substrates at room temperature in ultrahigh vacuum. Nanostructured thin films with thickness around 100 nm resulting from this nearly ballistic deposition process were subsequently characterized by several complementa...