On the work of adhesion of film-substrate solid junctions

A study of the work W of adhesion of a thin film of thickness h deposited on a substrate is reported. The free energy change occurring during the deposition of the coating from the gas phase is assumed to be negative. In these conditions the thermodynamic stability of the deposited film requires W < 0. To obtain a negative value of the work of adhesion the surface tension 7rs of the film-substrate interface has to satisfy inequalities involving the mechanical properties of the film, the surface tension ~,f~ of the film and the parameters that enter into the film-substrate interaction potential. It is also shown that the 7fs--~sgq-)'fg < 0 condition is not always a sufficient condition to have W < 0.