Nucleation and propagation of dislocations during nanopore lattice mending by laser annealing: Modified continuum-atomistic modeling

Abstract

This paper investigates the atomic-level microscopic dynamic behavior of a solid-state nanopore lattice mending process by femtosecond laser annealing using a modified continuum-atomistic modeling approach. The nucleation and propagation of dislocation are also depicted via quantitative dislocation analyses. Three typical lattice mending phases, including (i) the incubation of dislocation nucleation, (ii) pressure-induced dislocation propagation and plastic deformation, and (iii) lattice recovery and reconstruction via thermal diffusion, are thoroughly characterized by the evolution of microscopic dislocation and the slope change of atomic mean-squared displacement curve. The results of the analyses indicate that the structural mending originated from the heterogeneous nucleation of dislocation from the pore surface. The laser-induced shock waves provide considerable mechanical work and, consequently, are transferred largely to become an equivalent applied stress on the activated glide planes. These pressure-induced multiple glides on a lattice near the pore rapidly and effectively enable the mending operations in solid-state structural transition processes. Subsequently, the relaxation of the compression stress leads to the target material that is rapidly swelled in the $z$ direction with an expansive strain rate of $2.2\ifmmode\times\else\texttimes\fi{}{10}^{9}\phantom{\rule{0.3em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$. The expansion dynamics and associated tension stress further induce drastic emissions of dislocation after the pore is completely mended. Moreover, it is also observed that the dislocation of sessile stair rods can act as a strong barrier to prevent further glide on slip planes, thus leading to a local strain-hardening effect. The simulation results presented in this paper provide comprehensive insights for a better understanding of the laser-induced solid-state nanopore mending process. The approach proposed here can also be modified and used to further investigate the mechanisms of laser-induced surface hardening with various advanced functional materials.