Optical response of thin plasma-polymer films with non-spherical silver nanoparticles

The size and shape of silver nanoparticles which are embedded in a plasma-polymer matrix were obtained by transmission electron microscopy and analyzed with optical image processing. We used a sample in which silver particles were present before and after reshaping caused by thermal annealing in adjacent regions. As most of the particles appeared as elongated rotational ellipsoids, the major and minor half axis were determined for each particle. We adopted the model of Gans in the Rayleigh approximation to calculate for each investigated particle the extinction spectra from 4000 cm(-1) to 35 000 cm(-1) using the data from the image processing. The various spectra for 368 silver particles were added to get total extinction spectra for the sample as deposited and after reshaping, respectively. We found good agreement with the experimental spectra. The blue shift of the plasma-resonance absorption, which occurs due to the reshaping of the silver particles during thermal annealing, was also confirmed by using only changes in the particle sizes and shapes.