Servicio de Información Comunitario sobre Investigación y Desarrollo - CORDIS

Final Activity Report Summary - POLYION (Polymer Surface Modification by Ion Implantation)

The aim of the project was to develop polymer / silver-nanoparticle thin films for biosensor applications. Silver nanoparticles exhibit surface plasmon polariton resonances in the visible region of the optical spectrum. These resonances enhance the electric fields in the vicinity of the particles by many orders of magnitude, and consequently enhance the Raman signal of organic molecules adsorbed on or near the particles. This effect, known as Surface enhanced Raman spectroscopy (SERS), has the capability to detect single organic molecules. The incorporation of silver nanoparticles in thin polymer films is expected to provide stable, reproducible and re-usable substrates for SERS. Investigating the formation of the nanoparticles is also of fundamental importance.

The films were produced by two methods; dual magnetron sputtering of silver and poly(tetrafluoroethylene), and; temperature induced formation of silver nanoparticles in spin coated polystyrene and poly(vinyl alcohol). Real time monitoring of the material optical properties during processing was achieved by in situ Spectroscopic ellipsometry (SE). The deposition of silver nanoparticles by magneton sputtering was recorded using in situ SE. Extraction of the optical properties of the films by appropriate modelling revealed the evolution of the surface plasmon polariton resonances during the particle growth.

The plasmon resonances provide a unique opportunity to indirectly monitor the size of the particles growing in polymer matrices by modelling the ellipsometric data. Temperature induced decomposition of organometallic precursors dissolved in a polystyrene film, approximately 100 nm thick, resulted in the diffusion, nucleation and growth of silver nanoparticles. Subsequent heating of the film evaporates the polymer and the particles can be left partially or completely uncovered on the substrate surface. By depositing polymer films of different thickness the concentration of the silver particles after evaporation of the polymer can be controlled. Heating silver ions dispersed in a poly(vinyl alcohol) thin film reduces them to silver atoms which then also diffuse to form nanoparticles. This process was recorded and modelled using real time spectroscopic ellipsometry.

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