Characterization of sol-gel thin films by ellipsometric porosimetry
As an extension of spectral ellipsometry, ellipsometric porosimetry has gained considerable importance for the characterization of porous thin films. The in-situ measurement of sorption facilitates the evaluation of open porosity, pore radius distribution, film backbone refractive index and even elastic properties. Multilayer assemblies and gradients within films can be characterized. These features are especially interesting for sol-gel derived thin films that are commonly composed of aggregated nanoparticles and thus may retain significant porosity after thermal treatment. In this paper the general features of Ellipsometric Porosimetry are highlighted and related to the characterization of selected sol-gel films. The examples range from simple assessments of porosity and pore radius distribution, film backbone analysis to the characterization of multilayer assemblies and systematic changes induced by thermal treatment or leaching phenomena.