Effect of film thickness on laser induced surface structures formation on optically transparent polymer films

Laser-induced periodic surface structures can be prepared on polymer thin films, despite the absence of light absorption at the wavelength of the irradiating laser, by using a bilayer approach. Nanostructuring of a poly(3-hexylthiophene-2,5-diyl) (P3HT) layer, by laser irradiation at 532 nm, covered by a thin layer of a non-absorbing polymer, in this case, the ferroelectric copolymer poly(vinylidene fluoride -trifluoro ethylene),P(VDF-TrFE), allows the development of a grating-like structure on the surface. The range of thicknesses of the upper layer, which leads to the formation of LIPSS, has been determined. It is verified that for a thickness larger than 40 nm, no periodic structures are formed, neither in the upper layer nor in the bottom P3HT one. This can be explained considering a mechanical restriction which prevents P3HT rearrangement. The upper nanostructured surface layer exhibits ferroelectric properties as proven by piezoresponse force microscopy measurements.

Automated summary

A bilayer approach is used to create laser-induced periodic surface structures on polymer thin films, even without light absorption at the laser's wavelength. The technique involves nanosctructuring a layer of poly(3-hexylthiophene-2,5-diyl) (P3HT) using 532 nm laser irradiation, and then covering it with a thin layer of a non-absorbing polymer called poly(vinylidene fluoride-trifluoro ethylene) (P(VDF-TrFE)), resulting in a grating-like structure on the surface. The thickness range of the upper layer that leads to the formation of these structures has been determined, and it has been found that a thickness greater than 40 nm inhibits the formation of periodic structures due to mechanical restrictions on P3HT rearrangement. The upper nanostructured surface layer also displays ferroelectric properties.