Artifacts in AFM images revealed using friction maps

We have retrieved a clear wavy pattern form and AFM image taken in the friction mode, over a highly polished stainless steel surface, which is usually assumed to be due to an optical interference phenomenon. A clear spatial correlation has been found between the best resolved parts of the pattern observed, and the smoothest part of the original topographical image, which clearly support the idea that the observed effect (not appeared in the topographical image), is effectively due to an optical interference phenomenon.