Ordered rippling of polymer surfaces by nanolithography: influence of scan pattern and boundary effects.

We demonstrate how AFM nanolithography, with a proper choice of scan pattern, can induce an exceptionally ordered alignment of ripples on the surface of polymer films on the first scan. By analogy with the manipulation of nanoparticles, the orientation of the ripples is determined by the material flow, which is ultimately fixed by the direction of motion of the probing tip. This makes a raster scan pattern the best choice for orienting the ripples, as opposed to the zigzag scan pattern commonly adopted by most AFM setups. Our hypothesis is substantiated by a series of measurements on a solvent-enriched ultrathin film of PET, which allowed ripple formation on the first scan. We also show how the ripple orientation is significantly modified by the boundary conditions appearing when nanolithography is performed on circular, triangular and L-shaped areas on the polymer surface.