Impact of plasmonic modes on the formation of self-organised nano-patterns in thin films

TL;DR

This paper investigates how coupled surface plasmon polaritons influence the formation of nanoscale periodic surface structures on thin metal films during laser irradiation, revealing new control mechanisms for laser patterning.

Contribution

It demonstrates that coupled SPPs at both interfaces and various parameters govern the surface topographies, providing a detailed theoretical and multiscale modeling analysis of laser-induced nanostructures.

Findings

Coupled SPPs influence surface pattern formation.

Surface topographies can range from λ_L/3 to λ_L.

Control over nanostructure characteristics is achievable.

Abstract

Formation of nanoscale laser-induced periodic surface structures on 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, 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. 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. The capability to control and tune the characteristics of the produced structures on thin films is expected to enable novel surface patterning approaches.