Ellipsometry porosimetry (EP): Thin film porosimetry by coupling an adsorption setting with an optical measurement, highlights on diffusion results

Ellipsometry porosimetry (EP) is an emerging technique that is dedicated to porous thin films analysis; it is non-contact and non-destructive. EP tools developed at SOPRALAB, allows us to obtain adsorption isotherms with many different adsorptives at an ambient temperature. EP leads to the same results as classical adsorption experiments (e.g. porosity and pore size distribution), but it also has some particular features leading to new information. For instance, our optical setup (Spectroscopic Ellipsometry) allows us to determine the variation of the thickness of the samples during the adsorption experiment. It is also very sensitive to interfaces; it is thus possible to detect a porosity gradient or to study a bi-layer sample and plot the two corresponding adsorption isotherms at the same time [A. Bourgeois, A. Brunet-Bruneau, V. Jousseaume, N. Rochat, S. Fisson, B. Demarets, J. Rivory, Description of the porosity of inhomogeneous MSQ films using solvent adsorption studied by spectroscopic ellipsometry in the visible range, Thin solid films 455-456 (2004) 366]. For porous thin films with a non-porous barrier layer deposited on top, it is also possible to study the lateral diffusion phenomenon in the film (see figure below). In this paper, we will illustrate a part of the different features of EP for adsorption on porous thin films and more particularly for diffusion phenomenon.