Laser-induced electron dynamics and surface modification in ruthenium thin films

TL;DR

This study combines experimental and theoretical approaches to understand laser-induced heating, damage, and surface modifications in ruthenium thin films, revealing the roles of electron dynamics and surface stresses.

Contribution

It introduces a comprehensive analysis of laser-induced damage in ruthenium films, linking electron behavior to surface morphology changes and providing thresholds for optical applications.

Findings

Surface morphology evolves from oxide growth to cracking and grooving with increasing laser fluence.

Theoretical models show melting thresholds are higher than damage thresholds due to surface stresses.

Fermi smearing mechanism influences hot electron behavior in ruthenium.

Abstract

We performed the experimental and theoretical study of the heating and damaging of ruthenium thin films induced by femtosecond laser irradiation. Results of an optical pump-probe thermoreflectance experiment with rotating sample allowing to significantly reduce heat accumulation in irradiated spot are presented. We show the evolution of surface morphology from growth of a heat-induced oxide layer at low and intermediate laser fluences to cracking and grooving at high fluences. Theoretical analysis of pump-probe signal allows us to relate behavior of hot electrons in ruthenium to the Fermi smearing mechanism. The analysis of heating is performed with the two-temperature modeling and molecular dynamics simulation, results of which demonstrate that the calculated melting threshold is higher than experimental damage threshold. We attribute it to heat-induced surface stresses leading to cracking which accumulates to more severe damage morphology. Our results provide an upper limit for operational conditions for ruthenium optics and also direct to further studies of the Fermi smearing mechanism in other transition metals.