Refined interpretation of optical extinction spectra of nanoparticles in plasma polymer films

Nanoparticles of silver and gold in plasma polymer matrices were analyzed a ccording to their size and shape using transmission electron microscopy and optical image processing. The particles could be approximated as prolate s pheroids with major and minor half axes A and B. Extinction spectra of plas ma polymer films containing particles with various sizes were measured in t he range 4000 cm(-1) to 50 000 cm(-1), exhibiting an extinction maximum tha t could be assigned to the corresponding long-axis surface plasmon excitati on in the spheroidal noble metal particles. For simulation of the measured spectra, the model of Gans [Ann. Phys. 37, 881 (1912)] was used to calculat e the optical extinction spectrum for each analyzed particle in a sample. T he various spectra of more than 500 particles were added up to get the tota l extinction spectrum of the sample, yielding very good agreement with the measured spectra. A remaining blueshift of the computed spectra compared to the measured spectra could be explained by considering electromagnetic int eraction among the particles.