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Abstract Some interesting aspects of the dynamical behavior of aqueous electrolyte solutions have been summarized. They are based on the ability of these systems to form glasses providing ‘ideal’ conditions to study the glass transition... more
Abstract Some interesting aspects of the dynamical behavior of aqueous electrolyte solutions have been summarized. They are based on the ability of these systems to form glasses providing ‘ideal’ conditions to study the glass transition phenomena and to characterize the different thermodynamical states in connection with the non-linear behavior of the static properties. Structural relaxation analysis and collective vibrational dynamics are discussed pointing out their connection with the state of the system. The existence of two different scaling behaviors of the relaxation time connected to the change in the multiplicity of microscopic states is given in addition, with some information on the intramolecular stretching vibrations at the glass transition.
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... glass substrates at room temperature (RT), between two pre-deposited Cr electrodes in order to per-form in-situ electrical conductivity ... table 2). Taking into account the uncertainty in thedetermination of the numbers of neighbours... more
... glass substrates at room temperature (RT), between two pre-deposited Cr electrodes in order to per-form in-situ electrical conductivity ... table 2). Taking into account the uncertainty in thedetermination of the numbers of neighbours from EXAFS spectra ... Cobalt and nickel thin firms ...
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ABSTRACT 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... more
ABSTRACT 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 differences in the optical properties of the various samples reflect finite size effects. Time Dependent Local-Density-Approximation (TDLDA) calculations, taking into account the d-electrons and matrix screening effects, are consistent with observed size evolutions of the Mie frequency. Low frequency Roman scattering spectra exhibit a strong size-dependent band related to quadrupolar vibration modes of the clusters.
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Optical properties of gold clusters in the size range 24 nm. B. Palpant Laboratoire de Spectrométrie Ionique et Moléculaire, Université Claude Bernard Lyon 1, 43boulevard du 11 novembre 1918, 69622 Villeurbanne Cedex, France. ...
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ABSTRACT 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... more
ABSTRACT 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 ruled by quantum effects. For a given size, we measure a steady evolution of the surface plasmon frequency versus x. For a given relative composition, the blueshift (relative to the prediction of Mie’s theory), damping, and broadening of the resonance all become more important as the size decreases and as the gold concentration increases. These spectra are compared with model calculations, based on the time-dependent local-density-approximation formalism, including both the porosity of the matrix and an inner skin of reduced ionic-core polarizability. Two models are introduced to describe the effective dielectric function of the ionic background in the bimetallic cluster. Agreement between experimental results and both models is discussed.
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ABSTRACT The formation of gold films obtained by low-energy cluster beam deposition at room temperature in ultrahigh vacuum on a gold (111) surface has been analyzed in situ by scanning probe microscopy. Neither diffusion of the clusters... more
ABSTRACT The formation of gold films obtained by low-energy cluster beam deposition at room temperature in ultrahigh vacuum on a gold (111) surface has been analyzed in situ by scanning probe microscopy. Neither diffusion of the clusters on the surface, nor coalescence between clusters has been detected. The films are formed by a random pavement of the surface and as a consequence submonolayer films are composed by three-dimensional isolated particles, whereas multilayer films exhibit a nanostructured morphology. Molecular-dynamics simulations, using the same size distribution of incident clusters as in the experiment, reveal the influence of the impact energy on the film morphology. For a low kinetic energy of the incident clusters (0.25 eV/atom), the simulated morphology is in excellent agreement with experimental measurements.
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ABSTRACT Magnetic nanostructures from clusters preformed in the gas phase constitute a fascinating field of research both from the fundamental point of view to understand the key parameters which govern the properties of nanosized... more
ABSTRACT Magnetic nanostructures from clusters preformed in the gas phase constitute a fascinating field of research both from the fundamental point of view to understand the key parameters which govern the properties of nanosized magnetic systems, and for applications in various fields of interest (ultrahigh density storage, spin electronics, sensors, magneto-optics systems). In this context the LECBD-technique specially developed for the preparation of original nanostructures, offers some unique potentialities directly related with the non-equilibrium conditions which prevail to the formation of clusters in the gas phase independently of the deposition and stabilization conditions on the substrate. The studies of the magnetic properties of an individual isolated nanocluster and of cluster assemblies emphasize the dominant role of the surface/interface effects on the intrinsic properties of nanoscale systems and the competition with the interactions in the case of assemblies leading to characteristic magnetic behaviours. A further step in these fundamental studies will concern the dynamic aspects of the phenomena. In parallel to the studies of simple and well controlled systems, generally based on pure transition metal clusters, more complex systems such as bimetallic clusters are prepared and studied in view of applications. In this field, the final association of functionalised clusters (i.e. high magnetic anisotropy cluster blocked at room temperature) on functionalised substrates (i.e. 2D-ordered cluster arrays) will be the ultimate stage prior to the realization of novel nanomagnetic devices in the Tbit range.
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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... more
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 with electron-electron scattering acceleration due to surface induced reduction of the Coulomb interaction screening by the conduction and core electrons.
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Structural characterization has been made for the same disordered material in 3 different thermodynamic states: liquid, supercooled and glassy. It concerns the aqueous electrolyte LiCl, 6H2O. Using isotopic substitution, we can analyse... more
Structural characterization has been made for the same disordered material in 3 different thermodynamic states: liquid, supercooled and glassy. It concerns the aqueous electrolyte LiCl, 6H2O. Using isotopic substitution, we can analyse the pair distribution functions and precise the modifications induced by the glass transition and the melting in the short, medium and long range order. Particularly interesting is the
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The morphology and the electronic structure of a single focused ion-beam-induced artificial extended defect is probed by several methods including micro-Raman spectroscopy, atomic force and scanning tunneling microscopies and Monte Carlo... more
The morphology and the electronic structure of a single focused ion-beam-induced artificial extended defect is probed by several methods including micro-Raman spectroscopy, atomic force and scanning tunneling microscopies and Monte Carlo and/or semi-analytical simulation within standard codes. The efficiency of the artificial defect for deposited metallic cluster pinning is also investigated. We show a correlation between the ion dose, morphology, electronic structure and cluster trapping efficiency. At room temperature, cluster pinning is efficient when the displacement per atom is one or more. Well-ordered patterned cluster networks are considered for potential applications.
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ABSTRACT In this paper, we report on the surface patterning of punctual defects onto graphene films grown on 6H–SiC(0001) substrates, using a finely focused gallium (Ga+) ion beam. We present organized arrays of nano-defects, designed... more
ABSTRACT In this paper, we report on the surface patterning of punctual defects onto graphene films grown on 6H–SiC(0001) substrates, using a finely focused gallium (Ga+) ion beam. We present organized arrays of nano-defects, designed using ion doses in the range of 10 –1 × 106 Ga+ ions/dot. Using Conductive Atomic Force Microscopy (CAFM) and Raman spectroscopy we evidence the strong resilience of graphene towards ion irradiation and characterize the morphology and the electronic properties of the FIB-induced local nano-defects. We show that punctual ion irradiation and dose control allow progressive amorphization of graphene leading to the promising perspective of graphene-based tunable templates.
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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... more
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 on the substrate. Depending on the deposition conditions (nature, size and flux
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A brief survey of the structural and dynamical properties of the aqueous electrolyte LiCl, RH2O (R≤6) at various temperatures leads us to the characterization of specific structural reorganizations related to the slowing down of... more
A brief survey of the structural and dynamical properties of the aqueous electrolyte LiCl, RH2O (R≤6) at various temperatures leads us to the characterization of specific structural reorganizations related to the slowing down of structural relaxation. Specific molecular motions are induced by competitions between the H-bond network developing among the hydration shells of ionic clusters and the increasing ion solvent
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ABSTRACT Nanodevices require the elaboration of periodic arrays of nanoparticles with adjustable periodicities. In this way, “bottom-up” and “top-bottom” methods are currently developed. We focus on a “top-down/bottom-up” approach based... more
ABSTRACT Nanodevices require the elaboration of periodic arrays of nanoparticles with adjustable periodicities. In this way, “bottom-up” and “top-bottom” methods are currently developed. We focus on a “top-down/bottom-up” approach based on the direct deposition of nanoclusters on patterned graphite surfaces. In this case, artificial defects (created by Focused Ion Beam (FIB)) are expected to act as nucleation centers for the deposited clusters. Clusters are preformed in free phase from a laser vaporization source. Such clusters (gold and cobalt platinum clusters) are deposited in a soft landing route onto various substrates (free or patterned) at moderate temperature T
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ABSTRACT 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... more
ABSTRACT 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 maximum of which depends on the mean cluster diameter in the sample according to the approximate law ? vib? -1. The Raman band corresponds to the excitation of the quadrupolar vibration mode of the clusters. Moreover, the maximum of the Raman band shifts towards lower frequencies when the excitation light is shifted to the red. This feature, as well as the rather large Mie-band width, is thought to reflect the ellipsoidal shape distribution of part of the embedded clusters.
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ABSTRACT 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... more
ABSTRACT 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-dependence of the 5d core-electron dielectric function in the vicinity of the interband threshold is emphasized. The size evolution of the Mie-frequency in free gold clusters exhibits a noticeable blue-shift trend as the particle size decreases, much stronger than in silver clusters. The width and shape of the resonance, essentially ruled by the decay via the interband transitions, are found closely correlated to the imaginary component of the core-electron dielectric function. In presence of a surrounding matrix the blue-shift trend is largely rubbed out. Agreement with recent experimental results on size-selected gold clusters embedded in an alumina matrix may be achieved by taking into account the porosity effects at the metal/matrix interface. The comparison with the predictions of classical models is also provided.
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Epitaxial graphene on silicon carbide labeled 6H-SiC (0001) substrate has been patterned using high resolution focused ion beam. Atomic force microscopy and Raman spectroscopy measurements give evidence of the strong resilience of the... more
Epitaxial graphene on silicon carbide labeled 6H-SiC (0001) substrate has been patterned using high resolution focused ion beam. Atomic force microscopy and Raman spectroscopy measurements give evidence of the strong resilience of the graphene monolayer to ion irradiation. The morphology and electronic properties of defects versus ion doses exhibit a progressive local amorphization of graphene.
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