The existence of sub-micrometer micromechanical modulation generated by polarized UV laser illumination on polymer surfaces

Sub-micrometer grating-like structures were generated on the surface of poly-carbonate (PC) films by polarized ArF excimer laser illumination well below the material ablation threshold. The period of the laser-induced surface structures was tuned by modifying the angle of incidence of the laser beam. The depth of the modulation was enlarged increasing the number of the laser pulses. The surface changes caused by the laser illumination were investigated by atomic force microscope operating in pulsed force mode. It was proven that not only the topography, but also the micromechanical properties are modulated with sub-micrometer period. Interestingly, the measured adhesion modulation is different from the adhesion modulation calculated by taking into account the tip and sample geometry. The co-existence of a reversed adhesion modulation was proven: the adhesion is increased at the hills caused by material changes, which may over-compensate the topographical effects. FTIR investigations have shown that chemical changes accompany the phase transitions leading to the structure formation.