Laser-induced periodic surface structure formation on polyethylene-terephthalate

Abstract

Periodic surface structures generated by linearly polarized ArF excimer laser (193 nm) were studied on polyethylene–terephthalate (PET), in a narrow fluence region (3–5 mJ/cm 2). Atomic force microscopy was used to follow the morphological changes caused by subsequent laser pulses on the same part of the surface. A homemade kinematic base plate ensured the reproducible positioning of the sample with respect to the AFM and the laser beam. The main subsequent phases of the Laser-Induced Periodic Surface Structure (LIPSS) formation were identified as: laser light scattering on the originally existing granules, formation of elliptical structures around the granules, and the transformation of ellipses into ripple-shape modulation. The LIPSS generating feedback mechanism was described: the incoming beam and the beams scattered on the granules and already existing LIPSS interfere and cause spatially modulated melting and crystallisation, which develops the structure. The dependence of the LIPSS period on the wavelength and on the angle of incidence was studied. The structure's height and surface-roughness vs. the number of laser shots was measured. The experimental results are in good agreement with the theory of the self-organized diffraction gratings. It was proved experimentally that the LIPSS are formed by redistribution of the material on the surface, without significant material removal.