Pressure-induced solid-state lattice mending of nanopores by pulse laser annealing

This paper presents the pressure-induced solid-state lattice mending of nanopores in single-crystal copper by femtosecond laser annealing processes. The microscopic mechanism of lattice mending is investigated by a modified continuum-atomistic modeling approach. Three typical lattice mending phases, including (i) the incubation of dislocation nucleation, (ii) plastic deformation under the combined effect of pressure and atomic thermal diffusion, and (iii) lattice recovery and reconstruction, are characterized via the microscopic structure changes and transient thermodynamic trajectories. The simulation results reveal that the structural mending of a pore is originated in heterogeneous nucleation of dislocations from the pore surface. The shear-induced multiple lattice glides are found to significantly contribute to the mending of a nanopore in the process of solid-state structural mending. The mending rates of two different modes, the pressure-induced and the classical unsteady-state atomic diffusion, are estimated and found to be very different from each other, by an order of 10(4). In addition, the location of the pore is also found to significantly influence the annealing threshold. Since the largest amplitude of the pressure wave is built up at a characteristic depth of approximately 45 nm below the irradiated surface, the shock wave will directly impinge on the pore and induce a fast solid-state lattice mending if the pore is located within the lower limit of the range of the characteristic depth. Furthermore, it is also interesting to note that the mending of a nanopore close to the characteristic depth by annealing fluence is generally lower than that of a pore near the surface. These results provide vital insights of photomechanical interactions with the microstructure of metallic solid, and the proposed approach can be further considered and enhanced to predict the mending depth for various defects in the future.