High-energy particle emission from galena and pyrite bombarded with Cs and O ions

The ejection of energetic particles during steady-state ion surface bombardment has been investigated by means of a dynamic computer simulation as well as in a secondary ion mass spectrometry (SIMS)/low-energy ion scattering from surfaces (LEIS) experiment. The emphasis of this comparative study is on the mass dependence of high-energy tails in sputtering and backscattering for the bombardment of galena (PbS) and pyrite (FeS2) with keV energy ion beam of cesium and oxygen. In the experiment, kinetic energy distributions of sputtered secondary ions ( S + , Fe + , Pb + , S − ), as well as backscattered or re-sputtered primary ions ( Cs + , O + , O − ), have been measured on a modified Cameca IMS-3f magnetic sector mass spectrometer for keV cesium (Cs+) and oxygen ( O 2 + , O − ) bombardment of galena and pyrite. Ejection of high-energy particles, with emission energies of up to ∼40% or up to ∼60% of the bombarding energy for sputtering of the lighter component (S±) with cesium or oxygen, respectively, and of up to ∼40% (Cs+) and ∼80% (O±) for backscattering, has been observed for PbS. The computer simulations were based on the well-known MARLOWE code. In order to model the change of the stoichiometry of the binary compounds, dynamic modification of the target composition in the near-surface region was introduced. Cs incorporation was included, and a relative enrichment of the metallic component (Pb, Fe) in the top few layers due to preferential sputtering of sulfur was allowed. The computer simulations provide information on the formation of altered layer under sputter equilibrium as well as on the energy and angular emission distributions of sputtered and backscattered particles in steady-state conditions. Multiple scattering of Cs projectiles and dynamic re-sputtering of cesium that was previously incorporated in the altered near-surface region can be distinguished in the simulation, and matched with the experimental observations. In addition, information on the inverse velocity dependence of ion formation can be obtained from the comparison of the SIMS/LEIS experiment and the computer simulation.