Electrochemical porosity evaluation of thin films on iron base materials

Corrosion properties of bulk materials coated with thin protective films are not only dependent on the electrochemical properties of the bulk materials and the intrinsic corrosion properties of thin protective films but also to a high degree on the films porosity. It is therefore necessary to know about the porosity in order to be able to control and optimize it with the deposition process. In this contribution we introduce a technique to measure the porosity by means of an electrochemical technique. Model systems are chosen, i.e. thin iron films deposited on silicon wafers were coated with tungsten and carbon thin protective films. The depositions were done with coaxial arc deposition, evaporation, and plasma immersion ion assisted sputter deposition. Raman measurements, Rutherford backscattering spectroscopy, raster electron microscopy, atomic force microscopy and electrochemical measurements were carried out to characterize the films.