Runaway lattice-mismatched interface in an atomistic simulation of femtosecond laser irradiation of Ag film–Cu substrate system

Generation of subsurface voids and a nanocrystalline surface layer in femtosecond laser irradiation of a single-crystal Ag target

“…Although the potential is fitted to low-temperature values of the equilibrium lattice constant, sublimation energy, elastic constants, and vacancy formation energy, it also provides a good description of high-temperature thermodynamic properties of Ag [35] relevant to the simulation of laser-induced processes. In particular, the equilibrium melting temperature, T m , determined in liquid-crystal coexistence simulations, is 1139 ± 2 K [8], about 8% below the experimental values of 1235 K [36]. The threshold temperature for the onset of the explosive phase separation into liquid and vapor, T*, determined in simulations of slow heating of a metastable liquid, is found to be ~3450 K at zero pressure and ~4850 K at 0.5 GPa [37].…”

“…The source term simulates excitation of the conduction band electrons by a laser pulse with a Gaussian temporal profile and reproduces the exponential attenuation of laser intensity with depth under the surface (Beer-Lambert law). In order to account for the energy transport occurring before the thermalization of the excited electrons [8,45,46], the optical absorption depth, L p = 12 nm at laser wavelength of 800 nm [47], is combined with the effective depth of the "ballistic" energy transport, L b = 56 nm, roughly estimated here as a product of the Fermi velocity and the Drude relaxation time [48]. This estimate is in a good agreement with a prediction of 53±7 nm derived from experiment [49].…”

“…[51] and modified in Ref. [8] to improve the accuracy of identification of crystal structures in the presence of small lattice distortions. This method allows for unambiguous identification of different crystal structures (fcc, bcc, hcp) regardless of their crystallographic orientation.…”

“…The ability of short (pico-and femtosecond) pulse laser irradiation to produce unique surface morphologies [1][2][3][4][5], metastable phases [6][7][8] and microstructure (arrangement of crystal defects) [5,[9][10][11][12][13][14] has been demonstrated in numerous studies and is generally attributed to the conditions of strong electronic, thermal, phase, and mechanical non-equilibrium created in irradiated targets by the fast laser excitation. Detailed understanding of the relations between the basic mechanisms of laser interaction with materials, non-equilibrium processes caused by the fast deposition of laser energy, and the resulting microstructure and properties of laser-treated regions of the targets, however, is still lacking, thus limiting the expansion of laser technologies into the new domain of nanoscale material processing and fabrication.…”

Atomistic Simulation Study of Short Pulse Laser-Induced Generation of Crystal Defects in Metal Targets

“…Under conditions when laser irradiation results in permanent surface modification or material ejection (ablation), the relevant processes discussed in literature are the transient melting and solidification of a thin surface layer [86,120,[141][142][143], the explosive boiling (phase explosion) of a surface region superheated beyond the limit of thermodynamic stability of the molten material [23,114,120,[144][145][146][147], the melt expulsion or sputtering due to the action of ablation recoil pressure [120,148], the ejection of large droplets or fractured solid fragments caused by the relaxation of photomechanical stresses [113,117,118,120,[149][150][151][152][153], as well as non-thermal phase transformations induced by the electronic excitations [154][155][156][157], photochemical reactions [158] or charge separation and Coulomb explosion [159].…”