Femtosecond Laser-Induced Periodic Surface Structures in Titanium-Doped Diamond-like Nanocomposite Films: Effects of the Beam Polarization Rotation

We study the properties of laser-induced periodic surface structures (LIPSS) formed on 12 titanium-doped diamond-like nanocomposite (DLN) a-C:H:Si:O films during ablation processing 13 with linearly-polarized beams of a visible femtosecond laser (wavelength 515 nm, pulse duration 14 320 fs, pulse repetition rates 100 kHz-2 MHz, scanning beam velocity 0.05-1 m/s). The studies are 15 focused on (i) laser ablation characteristics of Ti-DLN films at different pulse frequencies and con-16 stant fluence close to the ablation threshold, (ii) effects of the polarization angle rotation on the 17 properties of low spatial frequency LIPSS (LSFL), and (iii) nanofriction properties of the ‘rotating’ 18 LIPSS using atomic force microscopy (AFM) in a lateral force mode. It is found that (i) all LSFL are 19 oriented perpendicular to the beam polarization direction, so being rotated with the beam polari-20 zation, and (ii) LSFL periods are gradually changed from 360±5 nm for ripples parallel to the beam 21 scanning direction to 420±10 nm for ripples formed perpendicular to the beam scanning. The ob-22 tained results are discussed in the frame of the surface plasmon polaritons model of the LIPSS 23 formation. Also, the findings of the nanoscale friction behavior, dependent on the LIPSS orientation 24 relative to the AFM tip scanning direction, are presented and discussed.