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

Structural transformations in a shallow surface region of a bulk Ag (001) target irradiated by a femtosecond laser pulse are investigated in large-scale atomistic simulations and experiments. The simulations reveal a complex interplay of fast laser melting, rapid resolidification, and dynamic relaxa...

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Bibliographic Details
Published in:Physical review. B, Condensed matter and materials physics Condensed matter and materials physics, 2015-01, Vol.91 (3), Article 035413
Main Authors: Wu, Chengping, Christensen, Martin S., Savolainen, Juha-Matti, Balling, Peter, Zhigilei, Leonid V.
Format: Article
Language:English
Subjects:
Condensed matter
CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY
Femtosecond
incubation effect in laser ablation
Irradiation
laser-induced swelling
laser-materials interactions
Lasers
MATERIALS SCIENCE
molecular dynamics simulations
nanocrystalline materials
Nanocrystals
Nanostructure
pentagonal structural elements
Silver
Simulation
Surface layer
twins
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Summary:Structural transformations in a shallow surface region of a bulk Ag (001) target irradiated by a femtosecond laser pulse are investigated in large-scale atomistic simulations and experiments. The simulations reveal a complex interplay of fast laser melting, rapid resolidification, and dynamic relaxation of laser-induced stresses that leads to the formation of a subsurface porous region covered by a nanocrystalline surface layer. The generation of the porous region is consistent with the experimental observation of surface "swelling" occurring at laser fluences below the spallation/ablation threshold and may be related to the incubation effect in multipulse laser ablation of metals. The nanocrystalline layer is produced by massive nucleation of crystallites triggered by a deep undercooling of the melted surface region experiencing fast quenching at a rate on the order of 10 super(11) K/s. The predicted surface structure features random crystallographic orientation of nanograins and a high density of stacking faults, twins, and nanoscale twinned structural elements with fivefold symmetry, which suggests high hardness and possible enhancement of catalytic activity of the surface.
ISSN:1098-0121
1550-235X
DOI:10.1103/PhysRevB.91.035413