Computer Studies of the Slowing Down of Energetic Atoms in Crystals

The slowing down of 1- to 10-keV Cu atoms in fcc, bcc, and diamond-structure crystals has been investigated by high-speed digital computer techniques, using exponentially screened Coulomb and Born-Mayer potentials to describe the interatomic repulsion. The ranges of these atoms prove to be strongly dependent on their initial directions of motion, the order of ranges being fcc [011]>[001]>[111]≈isotropic, bcc [111]>[001]>[011]>isotropic, diamond [011]>[001]≈[111]>isotropic. This orientation dependence of the range, which has also been observed experimentally, is a consequence of the tendency of the lattice to focus moving particles into channels bordered by relatively closely packed atomic rows. Inclusion of zero-point vibrations reduces the degree of channeling, but does not modify the order of ranges for fcc. The experimental evidence for channeling and some of its implications for radiation damage theory are discussed.