The deposition of energetic (5 to 80eV) Cu atoms onto (001)Cu was simulated by molecular dynamics. The Cu-Cu interaction potential used was a spline of an embedded atom potential developed from equilibrium data and the universal scattering potential. Incident Cu atoms substituted for first-layer substrate atoms, via an exchange process, at energies as low as 5eV. Incident 20eV Cu atoms penetrated to the second substrate layer, and 20eV of energy was sufficient to produce interstitial defects. Incident 80eV atoms penetrated to the third atomic layer, produced interstitials 12 atomic layers into the substrate by focussed replacement collision sequences, and produced sputtered atoms with a yield of 16%. Interstitial clusters containing up to 7 atoms were observed. The observed mechanisms of film growth included the direct deposition of atoms into film equilibrium-atom positions, the exchange of substrate atoms at equilibrium film-atom positions and the migration of interstitials to equilibrium film-atom positions. The relative frequency of each process was a function of the incident energy. Since all of the observed growth mechanisms resulted in film atoms being in equilibrium atomic positions, the simulations suggested that stresses in homo-epitaxial Cu thin films were due to point

 
defects. Vacancies were expected to produce tensile strains, and interstitial atoms were expected to produce compressive strains in the films. It was proposed that immobile interstitial clusters could be responsible for retaining interstitial atoms and clusters in growing thin metal films.

Molecular Dynamics Simulation of Defect Formation during Energetic Cu Deposition. C.M.Gilmore, J.A.Sprague: Thin Solid Films, 2002, 419[1-2], 18-26