Formation and Coherent Propagation of Femtosecond-Laser-Induced Periodic Surface Structures (LIPSS) in Fluorine-Doped...

We have analyzed the formation and coherent propagation of laser-induced periodic surface structures (LIPSS) upon fs-laser irradiation of fluorine-doped tin oxide (FTO) films. The aim is the generation of large electrical anisotropies in macroscopic areas for applications including laser-written transparent heaters, sensors, or substrates for electrically controllable wettability, among others. The films have been processed with high-repetition-rate (hundreds of kHz) fs-laser pulses at 1030 nm using different laser (fluence and pulse duration) and scanning parameters (speed and line overlap). Optimal LIPSS formation and coherent propagation are conditioned by the dynamic evolution of the F content in the laser-processed regions that can be controlled via processing parameters. However, the homogeneity in the spatial distribution of F in the microscale in the pristine samples can generate important issues that are carefully considered and discussed in the present work. Still, the formation of optically and electrically highly anisotropic surfaces for laser scanning speeds well above 1.0 m/s has been demonstrated, reaching electrical resistivity anisotropy factors of >10³. Consequently, the potential development of large-area applications using LIPSS-structured FTO films seems feasible, as we have demonstrated by fabricating an efficient laser-written electrothermal transparent device as a proof-of-concept.