Friction force image of a patterned n-octadecyltrichlorosilane SAM on silicon using bias-assisted nanolithography. The terminal methyl group is converted to a carboxyl group by a redox reaction as the biased tip passes over the film in a predefined pattern. The bright areas in the image are the carboxyl groups which have much higher friction than the surrounding methyl-terminated SAM film. 2 µm scan. Imaged with the MFP-3D AFM.