The role of original surface roughness in laser-induced periodic surface structure formation process on poly-carbonate films

Poly-carbonate films containing different types of original surface roughness were illuminated by a polarized ArF excimer laser beam having a fluence of 4 mJ/cm2. Atomic force microscopy was applied to study the laser-induced periodic surface structure formation process at 0°, 30° and 45° angles of incidence. The effect of initial surface structures on the intensity distribution was investigated in cases of: (a) grains on oriented and amorphous thick films; (b) holes on thin spin-coated films; and (c) nanoparticles arranged along micrometer long sides of hexagons below the spin-coated films. The presence of the scattering objects caused symmetry breaking, if the samples were illuminated by oblique incident ‘s’ polarized beam. The Fourier analysis of the AFM pictures has shown the competition of structures having different periods. The characteristic of the permanent surface patterns proved that the interference of the incoming beam and the beams scattered on previously existing structures is the LIPSS generating feedback process. Ring-shaped structures having 228 nm diameter were produced.