Metal clusters in plasma polymer matrices - Part II. Silver clusters

By means of an inert gas evaporation technique in combination with a simultaneous plasma polymerisation process silver clusters have been prepared within plasma polymer matrices from vinyltrimethylsilane (VTMS) with mean diameters between 1.3 and 4.5 nm and from tetraethoxysilane (TEOS) between 4.8 and 6.2 nm, respectively. The materials were characterised by transmission electron microscopy (TEM), electron diffraction (ED), X-ray photoelectron spectroscopy (XPS) and UV-visible spectrophotometry. From the decrease of the Ag-lattice parameter with decreasing size of the silver clusters a value of the surface stress coefficient f(ss)=5.4 +/- 1.1 N m(-1) could be deduced. UV-visible spectrophotometry of Ag-VTMS composites revealed a damping layer around the metal clusters, which prevents oxidation of the silver particles. A strong blue shift of the plasmon resonance frequency from lambda(max)=557 nm to lambda(max)=450 nm with decreasing filling factor could be observed for the Ag-TEOS composites. The plasma polymer matrix from tetraethoxysilane monomer shows a strong chemical damping of the surface plasmon resonance. The measured UV-visible spectra were fitted with the Maxwell-Garnett theory.