Evaluation of organic coatings condition with AFM-based method

Abstract

The paper presents an atomic force microscopy (AFM)-based approach to evaluation of local protective properties of organic coatings. Apart from topography, it provides local AC and DC characteristics of examined coating. The method consists in application of AC voltage perturbation signal between conductive AFM tip and coated metal substrate. The resulting current is used to determine local impedance characteristics. Both impedance imaging and impedance spectroscopy modes are available. The measurements are performed in contact AFM regime either for continuous scanning of the tip over the surface or for stationary positioning of the tip over the area of interest. Application of DC bias voltage between the AFM tip and the coated metal substrate makes it possible to verify coating continuity and to identify the potential sites with through-the-coating defects, which penetrate the coating down to the metal substrate. Description of the fundamentals of the technique is supported with selected examples of research results. The obtained topographical images, impedance images, local impedance spectra and DC current maps are correlated as well as supplementary with respect to each other showing that the proposed approach is capable of providing additional information about local behaviour and durability of organic coatings.