Surface structuring of polyimide by pulsed laser ablation

In the present paper, polyimide surfaces were processed with pulsed KrF laser radiation at fluences near the ablation threshold. The morphology of the processed surfaces was studied by scanning electron microscopy and chemical analyses were performed by electron dispersive spectroscopy. The formation of conical structures is observed for radiation fluences lower than 0.5 J/cm²;. The areal density of cones increases with increasing number of pulses and decreases with increasing laser fluence. At low radiation fluences (F < 150 mJ/cm²), cones are formed due to shadowing by calcium phosphate impurities while for higher fluences the main mechanism of cones formation is believed to be radiation hardening. It is shown that cones can be used to change the wettability properties of the polymer surface. Indeed, the contact angle between water and polyimide duplicates after laser processing.