Study of cobalt clusters with very narrow size distribution deposited by high-rate cluster source.

Co nanoparticles with an average diameter of 4.8 nm and a very narrow size distribution were prepared in a self-built gas aggregation cluster source without a size-selective filtering system. Ferromagnetic nanoparticle films with a thickness of several hundreds of nanometres were prepared at deposition rates up to 600 nm min(-1). Cluster properties and deposition characteristics were investigated for different deposition parameters. The as-deposited films exhibit high porosity compared to conventionally DC-sputtered films.

Nanostructural and functional properties of Ag-TiO2 coatings prepared by co-sputtering deposition technique.

Ag-TiO2 nanocomposite coatings with varying Ag content were prepared by co-sputtering from two separate sputter sources. This technique allows to prepare coatings not only with a large variation of Ag content and different gradient but also allows much better control of nanocomposite thickness and nanostructure compared with mostly used techniques based on wet chemical approaches. Various thicknesses of nanocomposite layers with different deposition parameters were studied to obtain a better understanding on the growth of Ag nanostructures in the TiO2 films. The metal-volume-fraction was varied between 15% and 47%. Structural and microstructural investigations of the nanocomposite films were carried out by transmission electron microscopy. Special attention was paid to surface segregation of Ag and its suppression. The observed segregation on TiO2 contrasts sharply with the well known embedding tendency of Ag clusters on polymers. Functionality of the Ag-TiO2 nanocomposites was demonstrated via UV-Vis spectroscopy and antibacterial tests. It was shown that a thin layer of TiO2 can be used as an effective barrier to tailor the release behaviour of Ag ions.

Synthesis and characterization of Ag-polymer nanocomposites.

We report the synthesis of Ag nanoparticles in polyethylene terephthalate (PET) matrix using atom beam co-sputtering. Metal filling factor was evaluated by Rutherford backscattering spectrometry. Microstructural evolutions of the nanocomposites films were investigated by transmission electron microscopy, which confirmed the formation of irregular shaped Ag nanoparticles. The X-ray photoelectron spectroscopy measurements of the sputter deposited PET film and co-sputtered deposited Ag-PET as well as PET bulk foil (from Goodfellows) were performed to study chemical composition of the nanocomposite films. The optical properties of these nanocomposites were studied by light absorption/transmission, which revealed a narrow transmission of UV light approximately 320 nm and a broad surface plasmon resonance absorption extending up to infrared region (approximately 2400 nm). Swift heavy ion irradiation of Ag-PET nanocomposite resulted in narrowing the full width at half maximum of transmission band.

Equal intensity double plasmon resonance of bimetallic quasi-nanocomposites based on sandwich geometry.

We report a strategy to achieve a material showing equal intensity double plasmon resonance (EIDPR) based on sandwich geometry. We studied the interaction between localized plasmon resonances associated with different metal clusters (Au/Ag) on Teflon AF (TAF) in sandwich geometry. Engineering the EIDPR was done by tailoring the amount of Au/Ag and changing the TAF thickness. The samples were investigated by transmission electron microscopy (TEM) and UV-visible spectroscopy. Interestingly, and in agreement with the dipole-surface interaction, the critical barrier thickness for an optimum EIDPR was observed at 3.3 nm. The results clearly show a plasmon sequence effect and visualize the role of plasmon decay.

Surface glass transition in bimodal polystyrene mixtures.

Using the cluster-embedding method of V. Zaporojchenko et al. (Macromolecules 34, 1125 (2000)), we measured the glass transition temperature T (g) at the polystyrene/vacuum interface of bimodal mixtures of monodisperse polystyrenes of 3.5k and 1000k. Embedding of approximately 1 nm Au clusters was monitored in situ by X-ray photoelectron spectroscopy (XPS). The clusters were formed by evaporation of Au onto the polymer surface. Only one glass transition was observed in the mixtures. The surface glass transition temperatures are correlated to but are below the bulk values of the mixtures and obey the Gordon-Taylor equation. The results suggest that the earlier reported molecular-weight dependence of the surface glass transition is not due to segregation of short chains to the surface.

Plasmonic properties of Ag nanoclusters in various polymer matrices.

Nanocomposite films containing Ag nanoparticles embedded in a polymer matrix of Teflon AF, poly(methyl methacrylate) (PMMA) and Nylon 6 were prepared by vapour phase co-deposition in high vacuum. A large variation of the particle plasmon resonance frequency in the visible region was obtained by increasing the Ag volume fraction from 4-80%. The metal volume fraction was measured by energy dispersive x-ray spectrometry (EDX) and the film thickness was measured by surface profilometry. The position, width and strength of the plasmon resonance depend strongly on the metal filling factor, cluster size and interparticle distance. The microstructure of the nanocomposites (shape, size, size distribution and interparticle separation of metal clusters) was determined by transmission electron microscopy. The effect of the surrounding dielectric medium on the optical properties of nanocomposites was investigated by comparing the Teflon AF/Ag, PMMA/Ag and Nylon/Ag composites.

X-ray reflectivity study on the surface and bulk glass transition of polystyrene.

The surfaces of polystyrene (PS) films decorated with gold nanoclusters were investigated by x-ray reflectivity measurements. The thicknesses of the films are much larger than the radii of gyration of the different PS samples. By annealing the films above the glass transition temperature T(g) an embedding process of the clusters into the polymer is detected which is accompanied by a substantial increase in the cluster layer thickness due to Brownian motion. These processes start at a sufficiently low viscosity and may be regarded as a probe of the glass transition in the near surface region of the PS films. Simultaneously the thermal expansion of the entire film and hence its approximate bulk behavior were monitored. Two samples of different molecular weight do not show a significant difference between the surface and bulk T(g) values.