EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Thanks to the non-linear absorption nature of ultrafast laser-matter interaction, femtosecond lasers offer a means to modify materials in their volume and to induce localized density changes, self-organized nanoscale patterns and phase transitions. Specifically, laser-induced crystallization has been reported for a variety of materials and exposure conditions, and ultrashort pulses have been shown to induce crystallization in bulk and thin film dielectrics alike.

In this work, we explore the behavior of dielectric multilayer systems exposed to femtosecond laser pulses. In particular, we show that in systems having individual layers with sub-wavelength thicknesses, ultrafast laser exposure offers a versatile method of achieving localized crystallization and atomic intermixing in systems composed of SiNx and SiO2 layers materials.
Specifically, we report the formation of embedded, localized clusters of crystallites, both in the multilayer structure and in the substrate nearby. Due to the samples’ geometry and the intrinsic parameters of ultrafast laser systems, the experimental framework is a complex entity where pulse parameters (wavelength, pulse duration, chirp), optical parameters (beam waist, beam quality) and samples’ design (materials selection, multilayers thickness), all contribute to the unfolding of this physical process. Understanding the influence of these parameters on the dynamics and the spatial extension of the phase transition areas enables a finer control over the direct writing of these structures as well as their localization.