Chemical solution approaches to YBa2Cu3O7_delta-Au nanocomposite superconducting thin films.

We explore the feasibility of preparing YBa2CU3O7-Au (YBCO-Au) nanocomposite thin films by chemical solution deposition (CSD). Two approaches were used: (i) A standard in-situ methodology where Au metallorganic salts are added into the precursor solution of YBCO trifluoroacetate (TFA) salts and (ii) a novel approach where stable colloidal solutions of preformed gold nanoparticles (5-15 nm) were homogeneously mixed with TFA-YBCO solutions. A detailed analysis of the microstructure of the films showed that in both cases, there is a strong tendency of gold nanoparticles to migrate to the film surface. However the kinetics of this migration evidences important differences and in the case of preformed nanoparticles their size remains unchanged (a few nanometers) whereas for the in-situ nanocomposites gold ripening leads to large particles (hundreds of nanometers). The grown YBCO-Au films showed good superconducting characteristics (J(c) 2 MA/cm2 at 77 K) but the absence of Au inclusions inside the YBCO matrix explains the fact that no enhancement of vortex pinning was observed.

Two-dimensional quasistatic stationary short range surface plasmons in flat nanoprisms.

We report on the nanometer scale spectral imaging of surface plasmons within individual silver triangular nanoprisms by electron energy loss spectroscopy and on related discrete dipole approximation simulations. A dependence of the energy and intensity of the three detected modes as function of the edge length is clearly identified both experimentally and with simulations. We show that for experimentally available prisms (edge lengths ca. 70 to 300 nm) the energies and intensities of the different modes show a monotonic dependence as function of the aspect ratio of the prisms. For shorter or longer prisms, deviations to this behavior are identified thanks to simulations. These modes have symmetric charge distribution and result from the strong coupling of the upper and lower triangular surfaces. They also form a standing wave in the in-plane direction and are identified as quasistatic short range surface plasmons of different orders as emphasized within a continuum dielectric model. This model explains in simple terms the measured and simulated energy and intensity changes as function of geometric parameters. By providing a unified vision of surface plasmons in platelets, such a model should be useful for engineering of the optical properties of metallic nanoplatelets.

Quantitative determination of the size dependence of surface plasmon resonance damping in single Ag@SiO(2) nanoparticles.

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 plasmon resonance (LSPR). These parameters can thus be directly correlated at a single particle level for the first time. The results show a linear increase of the width of the LSPR with the inverse diameter in the small size regime (less than 25 nm). For these nanoparticles of well-controlled environment, this can be ascribed to quantum confinement of electrons or, classically, to increase of the electron surface scattering processes. The impact of this effect was measured quantitatively and compared to the predictions by theoretical models.

Field gradient imaging of nanoparticle systems: analysis of geometry and surface coating effects.

In this work we compare the standard imaging of various types of nanoparticles deposited on surfaces by atomic force microscopy (AFM) with a complementary analysis of the same samples by either electrostatic force microscopy (EFM) or magnetic force microscopy (MFM). Experiments were carried out on gold nanoparticles (decahedrons and stars) and two different iron oxide systems: goethite (alpha-FeOOH) and hematite (alpha-Fe(2)O(3)). Regardless of the particular geometry, the EFM signal appears to be stronger on edges or tips of pure gold nanoparticles. Both EFM and MFM experiments were also carried out on iron oxide particles. Apart from the structural analysis, we analyzed the influence of a shell layer deposited on the gold and iron oxide particles, the shell being amorphous SiO(2). Although the silica layer was found to have an insulating effect around the particles, in all cases EFM/MFM measurements could still be performed by the proper choice of the scan lift height (with an eventual slight increase of the sample bias, where applicable).

Influence of silver nanoparticles concentration on the alpha- to beta-phase transformation and the physical properties of silver nanoparticles doped poly(vinylidene fluoride) nanocomposites.

This paper describes the processing of silver nanoparticle doped poly(vinylidene fluoride). The effect of the dopant concentration on the alpha- to beta-phase transformation of the polymer as well as in the morphological, thermal, optical and dielectric properties of the nanocomposites was investigated. Spherical silver nanoparticles were incorporated into the poly(vinylidene fluoride) polymeric matrix by the solvent casting method, with different Ag concentrations. Well-dispersed Ag nanoparticles act as nucleation centers, increasing the degree of crystallinity of the nanocomposites. Homogeneous dispersion of silver nanoparticles is demonstrated through the presence of surface plasmon resonance absorption in the nanocomposites. The alpha- to beta-phase transformation was achieved in the polymer matrix and a maximum of approximately equal to 70% of beta-PVDF was reached at 80 degrees C and a stretching ratio of 400%. The dielectric constant of the nanocomposites increases with increasing metal nanoparticle concentration, up to approximately equal to 26 at 0.020 wt% Ag content. The alpha- to beta-phase transformation affects both the dielectric response and the surface plasmon resonance.

Direct imaging of surface plasmon resonances on single triangular silver nanoprisms at optical wavelength using low-loss EFTEM imaging.

Using low-loss energy-filtering transmission electron microscopy (EFTEM) imaging, we map surface plasmon resonances (SPRs) at optical wavelengths on single triangular silver nanoprisms. We show that EFTEM imaging combining high spatial sampling and high energy resolution enables the detection and for the first time, to the best of our knowledge, mapping at the nanoscale of an extra multipolar SPR on these nanoparticles. As illustrated on a 276.5 nm long nanoprism, this eigenmode is found to be enhanced on the three edges where it exhibits a two-lobe distribution.

Self-Assembly of Silver Particle Monolayers on Glass from Ag(+) Solutions in DMF.

The spontaneous reduction of Ag(+) ions in N,N-dimethylformamide (DMF) (in the absence of a protecting agent) leads to the homogeneous deposition of silver nanoparticles on clean glass surfaces in contact with the solution. The process of reduction and deposition can be performed at room temperature and in the dark, but the use of visible or UV radiation affects the reaction rate and the morphology of the deposited films. The deposition conditions can be tuned so that a homogeneous monolayer of silver nanoparticles is deposited on the whole surface. Copyright 2000 Academic Press.