Refined interpretation of optical extinction spectra of nanoparticles in plasma polymer films
Nanoparticles of silver and gold in plasma polymer matrices were analyzed according to their size and shape using transmission electron microscopy and optical image processing. The particles could be approximated as prolate spheroids with major and minor half axes A and B. Extinction spectra of plasma polymer films containing particles with various sizes were measured in the range 4000 cm(-1) to 50000 cm(-1), exhibiting an extinction maximum that could be assigned to the spheroidal noble metal particles. For simulation of the measured spectra, the model of Gans was used to calculate the optical extinction spectrum for each analyzed particle in a sample. The various spectra of more than 500 particles were added upto get the total 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 interaction among the particles.