On the formation of oriented nanometer scale patterns on amorphous polymer surfaces studied by atomic force microscopy

Nanometer scale patterns were formed on the surface of several amorphous polystyrenes by a scanning probe microscope (SPM) operating in the contact mode. In order to better understand the nature of their formation, samples of several molar masses were systematically examined at room temperature in ambient conditions as well as in a liquid cell. The formation of the surface patterns was found to depend strongly upon the apparent tip radius, applied normal loading and time of scanning. The experimental results are analyzed by considering the plastic deformation of the glassy polymer subjected to high stresses by the sharp stylus of the scanning probe. Contact mechanics theory is applied to provide an estimate of the normal and shear stresses. Limitations of these theories are discussed. New results are presented that show that surface deformation occurs beyond a critical normal loading.