Impact of Plasmonic Modes and Metal Thermophysical Properties on the Formation of Self-Organised Nano-Patterns in Thin Films

Nanoscale laser-induced periodic surface structures in thin metal films (of the size of the optical penetration depth) is a yet unexplored area that is expected to open new routes for laser patterning and a wealth of exciting applications in optics, photonics, and sensing. In contrast to the common belief that excitation of Surface Plasmon Polaritons (SPPs) on the air/metal interface plays the dominant role in the features of the induced topographies, in this work, we demonstrate that the excitation of coupled SPPs in both air/metal and metal/substrate interfaces (Fig. 1a), along with other parameters such as the thickness of the material, the photon energy, and the substrate refractive index, dictate the spatial modulation of the absorbed energy. Results are shown for Au while the methodology can be followed for any metal. A detailed theoretical analysis of the excited plasmonic waves and a multiscale modelling of laser-induced physical phenomena manifests that depending on the laser conditions and thickness of the irradiated solid, topographies with periodic features of diverse sizes (ranging from
$\lambda_{L}/3$
to
$\lambda_{L}$
, where
$\lambda_{L}$
stands for the laser wavelength) and different orientation can be realized (Fig. 1b) [1].