Z-VARIATIONS IN YIELDS OF MULTICHARGED IONS SCATTERED AND RECOILED FROM A SILICON SURFACE

The doubly charged and triply charged ion yields from keV ion-silicon surface scattering are found to have a strong dependence on the atomic number Z1 of the incident ion. For Z1 < Z2 the yield of scattered multicharged ions increases with Z1, so that these ions dominate the recoiling Si2+ and Si3+ ions by Z1 = 9. In contrast, when Z1 > Z2, there are large yields of Si2+ and Si3+ ions, and the multicharged scattered ion yields are too small to detect. The interaction radius at which shell vacancies are produced is also found to change, suggesting that electron promotion occurs at a different level crossing on either side of Z1 = Z2.