Surface microstructure and chemistry of polyimide by single pulse ablation of picosecond laser

Abstract

Polyimide (PI) surface was ablated by the single pulse of picosecond laser, and the effects of laser wavelength (λ=355nm and 1064nm) and fluence on surface microstructure and chemistry were explored. Scanning electron microscopy (SEM) analysis found that different surface microstructures, i.e., the concave of concentric ring and the convex of porous circular disk, were generated by 355nm and 1064nm picosecond laser ablation, respectively. X-ray photoelectron spectroscopy (XPS) characterization indicated that due to the high peak energy density of picosecond laser, oxygen and nitrogen from the ambient were incorporated into the PI surface mainly in the form of CO and CNC groups. Thus, both of the O/C and N/C atomic content ratios increased, but the increase caused by 1064nm wavelength laser was larger. It inferred that the differences of PI surface microstructures and chemistry resulted from different laser parameters were related to different laser-matter interaction effects. For 355nm picosecond laser, no obvious thermal features were observed and the probable ablation process of PI was mainly governed by photochemical effect; while for 1064nm picosecond laser, obvious thermal feature appeared and photothermal effect was thought to be dominant.