Three-dimensional carbon fiber networks with self-orienting nano-textures enabled by femtosecond laser processing

Here, an interconnected three-dimensional (3D) network of carbon fibers possessing nano-scaled ripples, or laser-induced periodic surface structures (LIPSS), is fabricated via laser processing with an 800-nm femtosecond laser. The unique architecture of the CF network realizes the coexistence of both ∼800-nm low-spatial frequency LIPSS (LSFL) and ∼100-nm high-spatial frequency LIPSS (HSFL) overlapping on the same fiber surface. It is suggested that LSFL formed through the interference with Fresnel diffraction patterns projected by the fiber edges, while HSFL formed through LSFL-splitting assisted by surface plasmons. Moreover, the fundamentally different formation mechanisms of the two types result in distinctively different LIPSS orientations, where the LSFL is structure-dependent and self-orients according to the fiber propagation direction, while the HSFL is structure-independent and self-orients perpendicularly to the polarization direction of the incident pulses. The findings not only introduce an optical approach to prepare nano-textured carbon materials for future energy and regenerative-medicine applications but also reveal important insights into the underlying formation mechanisms of LIPSS on complex three-dimensional surfaces.