Atomistic simulations of spallation dynamics in multilayer thin-film interface excited by femtosecond laser

This paper presents an atomic-scale analysis of delaminating dynamics for characterizing microscopic mechanisms of interfacial spallation at multilayer thin-film interface excited by femtosecond pulse laser. For the first time via a molecular dynamics (MD) approach to investigate the interfacial spallation induced by pulse laser, the standard form of 12-6 Lennard-Jones (L-J) model and a solid-state argon interface are introduced. To allow MD modeling of interfacial spallation being conducted effectively, various laser incident energy densities and pulse durations are employed to characterize the dynamic behaviors and evolutions of interfacial spallation at multilayer thin-film interface. Based on the results of simulation, three different progressive stages, including void nucleation, coalescence leading to crack, and interfacial spallation, are classified via the transient temperature, pressure and density trajectories. The extraordinary expansive dynamics and tension stress induced by relaxation of thermal and pressure wave are major factors leading to detrimental defects growth and enlargement. The same conclusion can be further verified from the viewpoint of energy trajectories. Moreover, the ultra-high strain rate of the order 10⁹ s^-1 is estimated. The result is analogous to that of the experimental result of metal-film spallation excited by pulse laser. Finally, a critical strain-rate is evaluated and the dominant mechanism of the interfacial fracture is also presented.