Anomalous production of Gen+ (n=2,3) secondary ions in the case of 3-10 keV Ar+ bombarded Ge

Secondary emission of singly and multiply charged positive atomic ions (Isn+) from 3-10 keV Ar+ -bombarded Si and Ge targets at target current densities (Jp) in the range 0-820 μA cm-2 has been studied in detail, both as functions of primary ion energy (E) and target current density Jp = Ip/A (A constant). While Is+/Is+ (Si) at a fixed value of E is found to correspond to the usual experimental results (∼ 1%), Is2+/Is+(Ge) is observed to be > I, which is rather anomalous at such low bombarding energies. The Is2+ vs Ip curves, however, clearly indicate that, in both cases, the charge transfer process in vacuum (ionization of neutrally sputtered particles by projectile ions) plays a dominant part in the secondary ionization phenomena, especially at increased target current densities. The excessive yield for Ge2+ ions is attributed to near-resonance conditions for the charge-transfer process, that are satisfied for the Ge2+ ions only, at such low kiloelectronvolt energies. Again, a surprisingly high fraction of Ge3+ ions is also observed in the SIMS spectra. In this case, it is however, suggested that there probably exists an excited state into which electron capture can occur with nearly exact resonance so that at the energies concerned, the near-adiabatic region is attained. Both Is3+ (Ge) vs Ip and ls3+ (Ge) vs E curves support this idea. (Author)