engleski

Spectroscopic ellipsometry of thin films at solid/liquid and solid/gas interfaces

The optical models used for determining the thickness of the thin organic films by means of spectroscopic ellipsometry, involve the dielectric functions of both the film and the solid support materials. Therefore, a reasonable dielectric function model is necessary for simultaneously fitting the optical constants (refractive index, extinction coefficient) and the film thickness. We report the dielectric functions for thin (10 - 150 nm) films of the poly(sulfonatestyrene) sodium salt (PSS:Na) and poly(3, 4-ethylenedioxythiophene) : polystyrene sulfonate (PEDOT:PSS) polyplex, determined from the ellipsometric angles measured in the visible and near infrared regions. The films were prepared by spin-coating the aqueous dispersions on silicon, and their thicknesses were determined by spectroscopic ellipsometry and AFM. The experimentally determined dielectric function of the PSS:Na can be well described with the Lorentz model, applicable for the non-conducting materials, while for PEDOT:PSS, they can be reasonably well described by the Drude-Lorentz model, indicating the presence of the free charge carriers. In both cases, the film thicknesses obtained by fitting the optical models, are in a very good agreement with those measured with AFM.

Spectroscopic ; ellipsometry ; AFM ; PEDOT:PSS ; film ; conductivity

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