MOLECULAR-DYNAMICS SIMULATION OF ATOM EJECTION FROM THE (0001) SURFACE OF SINGLE-CRYSTAL ZIRCONIUM DUE TO KEV ION-BOMBARDMENT

Atom desorption from the (0001) surface of a HCP single crystal Zr ind uced by 2 keV Ne+, Ar+ and Xe+ ions at four incident angles is studied using molecular dynamics simulations. The atom ejection pattern for n ormal ion incidence has six approximately equal intense spots around a weak central spot, in agreement with the pattern observed experimenta lly. Few surface atoms have a high probability of being sputtered and they contribute significantly to the formation of the intense spots. T he mechanism for the formation of the spots is determined primarily by the first two layers of the crystal and knock-on sputtering by primar y recoil is important for all three ions. The relative importance of p rimary recoil knock-on ejection increases with ion mass. Other mechani sms involve momentum transfer through second layer atoms. The Lehmann- Sigmund mechanism is not applicable for the ion masses and energies us ed in the simulations. Similarities and differences between the HCP (0 001) and FCC (111) surfaces are discussed and it is proposed that, to a certain extent, the atom ejection mechanisms described in this paper may also apply to FCC (111) surfaces under similar sputtering conditi ons. (C) 1995 American Institute of Physics.