Sub-Threshold Fabrication of Laser-Induced Periodic Surface Structures on Diamond-like Nanocomposite Films with IR Femtosecond Pulses

In the paper, we study the formation of laser-induced periodic surface structures (LIPSS) on diamond-like nanocomposite (DLN) a-C:H:Si:O films during nanoscale ablation processing at low fluences-below the single-pulse graphitization and spallation thresholds-using an IR fs-laser (wavelength 1030 nm, pulse duration 320 fs, pulse repetition rate 100 kHz, scanning beam velocity 0.04-0.08 m/s). The studies are focused on microscopic analysis of the nanostructured DLN film surface at different stages of LIPSS formation and numerical modeling of surface plasmon polaritons in a thin graphitized surface layer. Important findings are concerned with (i) sub-threshold fabrication of high spatial frequency LIPSS (HSFL) and low spatial frequency LIPSS (LSFL) under negligible surface graphitization of hard DLN films, (ii) transition from the HSFL (periods of 140 +/- 30 and 230 +/- 40 nm) to LSFL (period of 830-900 nm) within a narrow fluence range of 0.21-0.32 J/cm(2), (iii) visualization of equi-field lines by ablated nanoparticles at an initial stage of the LIPSS formation, providing proof of larger electric fields in the valleys and weaker fields at the ridges of a growing surface grating, (iv) influence of the thickness of a laser-excited glassy carbon (GC) layer on the period of surface plasmon polaritons excited in a three-layer system air/GC layer/DLN film.

Automated summary

In this paper, we studied the formation of laser-induced periodic surface structures (LIPSS) on nanocomposite films at low fluences during nanoscale ablation processing. The study focused on microscopic analysis of the nanostructured film surface at different stages of LIPSS formation and numerical modeling of surface plasmon polaritons. Important findings include sub-threshold fabrication of high and low spatial frequency LIPSS, transition of LIPSS from high to low spatial frequency within a narrow fluence range, visualization of equi-field lines in the valleys and ridges of a growing surface grating, and influence of a laser-excited layer on the period of surface plasmon polaritons.