TRAPPING AT HYPERTHERMAL ENERGIES

Trapping probabilities for 5 eV to 600 eV Na+ incident at 45 degrees a long the [100] azimuth of Cu(001) have been measured. The measurement exploits the fact that the neutralization of scattered Na is very sens itive to Na particles trapped on the surface. Classical trajectory ana lysis indicates that for incident energies below 75 eV the Na traps pr imarily on top of the Cu surface. In the 5 eV to 75 eV range, the meas ured trapping probability is nonmonotonic, and is approximately zero f or an incident energy of 20 eV. This nonmonotonic trend in the top lay er trapping is attributed to changes in trapping trajectories as a fun ction of energy.