Showing papers on "Nanoparticle published in 1989"
TL;DR: It was shown that when sulphur dioxide was dissolved in the cyanoacrylic monomer at a high concentration, subsequent anionic polymerization in an aqueous phase produced particles as small as 10 nm, which displayed an important negative charge which improve their stability against aggregation.
19 citations
TL;DR: In this article, the authors report calculations for various multilayer spherical nanoparticle models in a host dielectric: i) polymeric core and metallic shell, ii) semiconductor core and metal shell, iii) metallic core, polymeric shell and metallic second shell.
Abstract: The effective nonlinear susceptibility X ( 3 ) for a composite that consists of a dilute suspension of structured nanoparticles that utilizes the surface mediated plasmon resonance can be enhanced by orders of magnitude compared to the intrinsic X (3) for a film of the same neat material. Here we report calculations for various multilayer spherical nanoparticle models in a host dielectric: i) polymeric core and metallic shell, ii) semiconductor core and metallic shell, iii) metallic core, polymeric shell and metallic second shell, and iv) metallic core, semiconductor shell and metallic second shell. The polymer is polydiacetylene, FDA, the semiconductor is Si, the metal is Ag, and the host is water, a GaAs 2 glass or Si. Enhancements as great as 10 4 can be obtained in both x (3) and the figure of merit with no degradation in the intrinsic speed of the nonlinearity. The choice of geometrical parameters and of component materials permit tailoring of the wavelength dependence and bandwidth characteristics of the nonlinear response. However, fabrication of these structured nanoparticle suspensions remians the key challenge.
8 citations
TL;DR: In this article, the surface plasmon resonance from the metal dielectric constant that increases the local field in the core material was investigated and the frequency of the resonance and the enhancement depend upon the particle shape and the coating thickness, as well as on the specific materials.
Abstract: We study coated, nanometer-size, ellipsoidal particles that have a semiconductor or polymer core surrounded by a metal coating. We predict that composite materials containing these particles will have much larger enhancement of the nonlinear optical response than had previously been found by using semiconductor colloid suspensions or semiconductor - doped glasses. The enhancement is due to the surface plasmon resonance from the metal dielectric constant that increases the local field in the core material. The frequency of the resonance and the enhancement depend upon the particle shape and the coating thickness, as well as on the specific materials. Also, we predict intrinsic optical bistability in these new materials and show that the threshold intensity for optical bistability can be greatly reduced by using the coated particles. We predict a switching intensity of silver coated GaAs particles below 100W/cm2
3 citations
Dissertation•
01 Jan 1989
TL;DR: In this article, a new radiolytic process for the synthesis at room temperature of metal aggregates within the bulk volume (and/or at the surface) of a perfluorosulfonated ion exchange membrane such as NAFION (French Patent Nr 87-13295).
Abstract: This work describes a new radiolytic process for the synthesis at room temperature of metal aggregates within the bulk volume (and/or at the surface) of a perfluorosulfonated ion exchange membrane such as NAFION (French Patent Nr 87-13295). The membrane is first impregnated with a solution of one (or more) metallic salt(s) in a polar solvent enabling the metal salt(s) to dissolve and the membrane to swell, and then subjected to an ionizing radiation (X rays, 60Co y rays, accelerated electrons), so as to induce a radiolytic reduction of the metal ions down to nascent metal atoms. The latter diffuse in the hydrophilic phase of the membrane and aggregate in the form of nanometer size metal particles (nanoaggregates). The electrocatalytic efficiency of bimetallic nanoparticles (such as Pt-Ru and Ni-Ru), once grafted onto bulk metal electrodes (Ti or Ni), has been investigated by respectively measuring the overpotential for chlorine or hydrogen evolution. Experimental conditions are similar to those of the so-called chlorine-soda industrial process. A synergistic effect is shown when Pt and Ru are alloyed with a 2:1 atomic ratio. Then the chlorine overpotential is minimum. Conversely, there is no synergy between Ni and Ru, but a minimum amount of Ru in Ru-Ni (40% atomic) ensures a very low hydrogen overpotential. Time-resolved studies of aggregation dynamics in a membrane medium have been carried out for the first time by a nanosecond pulse radiolytic reduction of silver ions in NAFION 117 swollen with 2-propanol/water mixtures. Kinetic measurements show that the earliest stages of silver aggregation are quite fast, while the following are far slower. This growth inhibition is interpreted as resulting from a slow diffusion of the transient species of silver aggregation through the hydrophilic phase of the membrane. A computer simulation of silver aggregation, occurring in competition with the corrosion of the earliest species by H30+ ions, has given estimated values of the corresponding rate constants, and an estimation of the size beyond which the diffusion of silver particles is slowed down to zero. Such a model well accounts for the stabilization in the membrane medium of silver species made up of very few atoms.
1 citations