Thermally activated nanowear modes of a polymer surface induced by a heated tip.

We report on nanoscale wear induced by atomic force microscopy using a heated cantilever/tip on a 20 nm thick film of polystyrene. Wear modes dependent on tip temperature characteristics were identified. Below the glass transition temperature of the polymer, the formation of quasi one-dimensional surface ripples with a typical period on the order of 100 nm was observed. We found that the ripple height typically saturates at 20 nm and that the buildup rate depends on temperature and load. From these observations we can calculate an activation energy for the ripple formation, which is on the order of 0.4 eV, at temperatures close to but below the glass transition temperature of the polymer. In the glass transition regime the ripple formation is strongly enhanced. An abrupt change of the wear mode is observed as the polymer in contact with the tip is heated above the glass transition temperature. Here, polymer material is transported along with the propagating tip.