Attenuated total reflection measurements on poly-carbonate surfaces structured by laser illumination

Periodic structures were studied on spin-coated poly-carbonate (PC) films: (a) sub-micrometer laser induced periodic surface structures (LIPSS) were generated by polarized ArF excimer laser beam; (b) micrometer periodic lines were ablated by imaging a mask onto the samples. The change in the thickness and the surface roughness was determined by an attenuated total reflection setup. The difference between the resonance places measured on the structured and untreated surfaces was very small in the case (a), proving that there is no significant material removal during LIPSS formation. The plasmon scattering caused by the sub-micrometer roughness weakly depends on the direction of the plasmon propagation. The broadening of the resonance curve started after 400 laser pulses, the roughness increased up to 800 laser pulses and after 1000 pulses the curve became more narrow corresponding to the changes in the topography detected by atomic force microscopy. The shift of the resonance peak measured on the ablated samples (b) indicated a change in thickness corresponding to the rate of ablation. The effect of the micrometer structures on the broadening of resonance curves depends on the direction of plasmon propagation.