The aim of this work is to present an interaction reactor which allows us to build very thin organic coatings on metallic substrates. This reactor is coupled to an analytic device which further enables an investigation of the interfacial region by very-surface-sensitive analytical means. The use of such an integrated installation makes it possible to follow the growth of the interfacial region step by step and to focus on the nature of the chemical structure that is identified in the interfacial region between a well-defined polymer phase and an atomically clean metallic substrate. As an illustration we compare the behavior of PA-6,6 on copper and platinum.