Computer simulations on sputtering mechanisms: Bombardment of single-crystalline Cu(100) by Ar ions

The sputtering mechanisms of monocrystalline Cu are studied using the binary-collision lattice-simulation code cosipo. Single-crystal Cu (100) is irradiated with normally incident 5-keV Ar ions.
The backward-directed modified recoil flux is compared to the angular distribution of sputtered particles in order to follow the sputtering process. The angular distribution of sputtered particles is directly related to the modified recoil flux and collision cascade anisotropies.
Particular attention is given to different mechanisms acting in single-crystalline sputtering. Both the collision sequence and Lehmann-Sigmund mechanisms are found to take place. The collision chains are mainly of the short-range type, except for the 〈110〉 replacement and directional ones.
The 〈110〉 and 〈100〉 sequences dominate the angular distribution of sputtered particles. The contribution of defocused sequences is higher than that of replacement and focused ones. The sputtering yield and angular distribution of sputtered particles are evaluated as a function of target thickness.
Fifteen atomic layers are sufficient to achieve the bulk yield and spot pattern of sputtered particles that corresponds well to that of a monocrystalline target. The Lehmann-Sigmund model is simulated by employing a target with a varying number of (100) atomic layers on the top of the amorphous bulk.
Calculations show that two atomic layers of regular structure on the top of the amorphous bulk reproduces the main features of the spot pattern of sputtered atoms, but is inadequate in explaining the collision sequence mechanisms of monocrystalline sputtering.