Subwavelength LIPSS-based nanopatterning of thin titanium films

Precise nanopatterning of thin films is an important task in production of modern optoelectronics and photonics elements. Direct recording of laser-induced periodic surface structures (LIPSS) is a promising tool for direct subwavelength nanopatterning. Recent studies show that the dynamics of LIPSS formation changes significantly if the film is relatively thin. Here we present a comprehensive analytical model aiming to bridge the gap between the expected dynamics of electromagnetic fields during LIPSS formation and experimentally obtainable nanopatterning results. The phenomenological model of surface electromagnetic wave (SEW) propagation at the film–substrate interface illustrates the mechanism of LIPSS formation using a periodic distribution of SEW energy concentration. SEW features are calculated depending on metal film thickness, and positive feedback between the local thickness of the growing oxide layer and the SEW energy concentration is unveiled. Changes in LIPPS formation mechanisms are confirmed experimentally on titanium films with different thickness. These findings shed light on the intrinsic physical mechanisms of LIPSS formation on thin metal films and ease the possibilities for LIPPS applications for nanopatterning.