A COMPARATIVE-STUDY OF PRIMARY ION ENERGY-DEPENDENCE OF SECONDARY-IONYIELDS FROM SI AND GE SURFACES UNDER INERT AND REACTIVE ION-BOMBARDMENT

Primary ion energy variation curves (I(n+)alpha E, where E = 3-10 keV; n = 1, 2) for secondary ions emitted from Si and Ge targets at differ ent target current densities (J(p) approximate to 60-400 mu A/cm(2)) h ave been studied, both under inert (Ar+) and reactive ion (N-2(+), O-2 (+)) bombardment. It is interesting to note that while I-n+ increases with E under Ar+ bombardment the same parameter under the same bombard ment conditions exhibits a steady fall under N-2(+) or O-2(+) bombardm ent, at least for E up to similar to 5 keV. Not only this, the changes in the slopes of the above curves with J(p) in the two cases are also in the opposite direction. In the former case, the increase in the sl opes of the curves with J(p) can be accounted for by taking into accou nt target current density effects which are now known to occur even fo r J(p) < 1 mA/cm(2), due to ionization of sputtered neutrals above the target surface. In the latter case however, the results can only be i nterpreted in terms of our recent publication which presents some evid ence regarding gradual build-up of primary atom concentration at the t arget surface with increase in target current density - a phenomenon, which is rather unexpected from theoretical considerations.