Tailoring of Silver Nanoparticle Size Distributions in Hydrogenated Amorphous Diamond-like Carbon Nanocomposite Thin Films by Direct Femtosecond Laser Interference Patterning

Patterning of composites and especially nanocomposites employing conventional lithography processes is typically problematic due to differences in physical properties of a matrix and filler. Direct laser interference patterning (DLIP) promises rapid micromachining of virtually any material by imposing sub-wavelength resolution structures. At the same time, moderate control of intense laser light can also serve for modification of the metal filler particle size distribution in the nanocomposite films. In this paper, we demonstrate capabilities of femtosecond DLIP for imposing periodic patterns with pitches of 564 nm and 1306 nm in reactive magnetron sputtered diamond-like carbon nanocomposite thin films with embedded silver nanoparticles (DLC:Ag). The 1D periodic patterns and, at the same time, regularly repeating areas containing modified size distribution silver nanoparticles were obtained by a range of fluences and number of pulses employing second harmonic of the Yb:KGW femtosecond laser. The investigations of laser-material interaction with metal filler-free DLC as well as pure silver thin films enabled to explain the DLIP ablation processes of DLC:Ag nanocomposite thin films. It was found that, depending on the silver content in nanocomposite films, nanoparticle size distributions were either bimodal (12.6 at.% Ag containing films) or unimodal (7.8 at.%) with effective average diameters shifting from 13 nm to 69 nm, depending on the applied laser processing parameters. We demonstrate importance of the localised surface plasmon absorption and localized field enhancement at the DLC-Ag interface on the ablation threshold of DLC:Ag nanocomposite, that was found to be at least 4 times lower (below 6 mJ/cm2 at 1k pulses) than for pure DLC.