In the widely accepted Stern model, an adsorption layer of an ionic surfactant at the air-water interface consists of a charged topmost amphiphilic monolayer, a so-called compact Stern layer of directly adsorbed counterions, and the Gouy-Chapman layer characterized by a diffuse ion distribution. The crux of Sterns treatment is the estimation of to what extent ions enter the compact layer and reduce the surface potential.This issue is addressed in this paper by optical means. Surface second harmonic generation, ellipsometry, and surface tension measurements have been used for an investigation of the prevai領(lǐng) ion distribution.Each technique probes different structural elements of the interfacial architecture, and their combination yields a deeper insight into the internal composition of the interface. 組合式多功能橢偏儀