Two-level ablation and damage morphology of Ru films under femtosecond extreme UV irradiation

Igor Milov* (Corresponding Author), V. Zhakhovsky, D. Ilnitsky, K. Migdal, V. Khokhlov, Yu. Petrov, N. Inogamov, Vladimir Lipp, Nikita Medvedev, B. Ziaja, V. Medvedev, Igor A. Makhotkin, Eric Louis, F. Bijkerk

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

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Abstract

The dynamics of a thin ruthenium film irradiated by femtosecond extreme UV laser pulses is studied with a hybrid computational approach, which includes Monte Carlo, two-temperature hydrodynamics and molecular dynamics models. This approach is capable of accurate simulations of all stages of material evolution induced by extreme UV or X-ray photons: from nonequilibrium electron kinetics till complete lattice relaxation. We found that fast energy deposition in a subsurface layer leads to a two-level ablation: the top thin layer is ablated as a gas-liquid mixture due to expansion of overheated material at near and above critical conditions, whereas a thicker liquid layer below is ablated via a cavitation process. The latter occurs due to a thermo-mechanically induced tensile pressure wave. The liquid ablating layer exhibits unstable behaviour and disintegrates into droplets soon after detachment from the rest of the target. Our simulations reveal basic processes leading to formation of specific surface morphologies outside and inside the damage craters. The calculated ablation threshold, crater depth and morphological features are in quantitative agreement with the experimental data, which justifies the applicability of our hybrid model to study laser-induced material damage.
Original languageEnglish
Article number146952
JournalApplied surface science
Volume528
Early online date23 Jun 2020
DOIs
Publication statusE-pub ahead of print/First online - 23 Jun 2020

Keywords

  • UT-Hybrid-D
  • free-electron laser
  • extreme ultraviolet
  • molecular dynamics
  • Monte Carlo
  • thin films
  • Femtosecond laser ablation

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