PREFERENTIAL SPUTTERING OF ALLOYS - A MOLECULAR-DYNAMICS STUDY

The preferential sputtering of a series of model alloys CuX by 1 keV Cu and Ar atoms, and by 3 keV Cu atoms, is studied in a molecular-dynamics simulation; both Morse pair potentials and many-body potentials of the tight-binding form are used. The projectiles impinge perpendicularly, or with 10 degrees to the normal direction. As the component X we use several model materials: A heavy Cu with double mass, and weak and strong Cu the cohesive energy of which varies between 50 and 200% of that of natural Cu. The preferential sputtering of heavy Cu is well described by the established analytical theory, if the power exponent m is derived from the potential. However, the distribution of sputtered heavy Cu atoms is characterized by a higher energy loss, and more oblique emission angles; this might be attributed to the last collision which particles experience in sputtering. The preferential sputtering of the more weakly bound species is more pronounced than in the analytical estimate. This feature may be connected to the anisotropy of the collision cascade in the vicinity of the surface; the over-preferentiality is somewhat reduced at 3 keV bombarding energy, and for oblique incidence.