Collisions between slow highly charged ions and surfaces

The two-center classical trajectory Monte Carlo (CTMC) method has been modified to incorporate multiple target centers. This multiple-center method has been used to investigate the dynamics of collisions between slow, highly charged ions and surfaces. The above-surface dynamics of a projectile with charge q = 6,10,18,36, and 54+, impacting a LiF (100) surface was studied for impact energies ranging from 0.25 eV/u to 2.25 keV/u, with velocities normal to the surface. The critical distance for capture, and the energy levels populated by the captured electrons were calculated. We find that electron recapture from the projectile by the surface begins immediately after the charge transfer begins and dominates over autoionization until the projectile gets very close to the surface. When the projectile is a few atomic units above the surface, the simultaneous capture of electrons becomes evident as a dramatic increase in the number of autoionization events. The projectiles potential energy is deposited to the surface at a much higher rate in the plane of the surface than in the longitudinal direction of the incoming projectile. Above-surface energy gains were found to agree with experimental measurements. A study was also made of Xe44+ moving through amorphous carbon with an impact energy of 3.6 keV/u, directed perpendicular to the surface. Approximately 36% of the projectiles available potential energy was found to be deposited to an area of the surface 4 nm in diameter, consistent with experimental observations. The CTMC results were then employed in a calculation of the deexcitation time. The calculated time for the projectile to deexcite was found to differ from experimental observations by an order of magnitude, an indication that the scaled Auger rates used in the calculation need to be increased by a like amount --Abstract, page iv