Studies of KrF laser-induced long periodic structures on polyimide

KrF excimer laser-induced long periodic structures on polyimide were investigated. At a low laser fluence slightly above the material ablation threshold, traces of micron-scale irregular ripples were observed, whereas at a fluence much higher than the ablation threshold, long-period (10-μm) and regular ripple structures were clearly visible. By examining the transition region between the peaks and valleys using a transmission electron microscope (TEM), we observed two phases within the region: amorphous structure in the vicinity of the peak and crystalline structure in the vicinity of the valley. The amorphous region was formed probably due to rapid cooling as a result of polymer melting and re-solidification, which did not allow sufficient time for the molecular chains to become completely aligned. The two distinctive regions of different degrees of crystallinity within the periodic structure can provide opportunities for industrial applications as polymer crystallinity affects mechanical and optical properties, as well as surface wettability.