A molecular dynamics model for the Coulomb explosion

The impact of positively charged Arn+ ions, n = 1, 4, 8, incident normally on the (1 0 0) surface of NaCl is studied by Molecular Dynamics (MD) simulations for energies up to 1 keV. The model assumes fixed charges on the ions and the effect of projectile charge is investigated as a function of energy. It is shown that there is a significant enhancement in the sputtering yield at low impact energies due to the attachment of Cl ions to the impacting Ar, which is subsequently ejected from the lattice. The low energy Ar ions can also experience acceleration towards the NaCl crystal due to Coulombic attraction. At energies greater than a few hundred eV the Ar ions implant within the crystal which accommodates the extra charge from these ions. As a result the sputtering yield from the initial impact is reduced but as the dose increases, the yield rises as Na+ ions are preferentially ejected from the lattice. A large proportion of the ejected material is in the form of clusters.