Picosecond Laser Processing of Copper and Gold

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Abstract
Non-equilibrium Molecular Dynamics Simulation methods have been used to study the ability of Embedded Atom Method models of the metals copper and gold to reproduce the equilibrium and non-equilibrium behavior of metals at a stationary and at a moving solid/liquid interface. The equilibrium solid/vapor interface was shown to display a simple termination of the bulk until the temperature of the solid reaches ≊90% of the bulk melting point. At and above such temperatures the systems exhibit a surface disordering known as surface melting. Non-equilibrium simulations emulating the action of a picosecond laser on the metal were performed to determine the regrowth velocity. For copper, the action of a 20 ps laser with an absorbed energy of 2–5 mJ/cm2 produced a regrowth velocity of 83–100 m/s, in reasonable agreement with the value obtained by experient (> 60 m/s). For gold, similar conditions produced a slower regrowth velocity of 63 m/s at an absorbed energy of 5 mJ/c2. This is almost a factor of two too low in comparison to experiment (> 100m/s). The regrowth velocities of the metals seems unexpecteldy close to experiment consisdering that the efree-electron contribution is ignored in the Embeeded Atom Method mothod models used.