Kinetic electron emission in the near-threshold region studied for different projectile charges

Total yields for ion-induced electron emission from atomically clean polycr ystalline gold have been measured with an accuracy of less than or equal to +/-5% for normal incidence of Cq+(q less than or equal to 5), Nq+(q less t han or equal to 6), Oq+(q less than or equal to 7), and Neq+(q less than or equal to 9) at impact velocities from the exclusive potential emission (PE ) regime up to 10(6) m/s (approximate to 5 keV/amu). The contribution by ki netic emission (KE) to these total electron yields, which is commonly assum ed as independent of projectile charge, can be estimated by subtracting the respective PE contribution after precise determination of KE impact veloci ty thresholds for the corresponding singly charged ions. At given projectil e atomic number and impact velocity we have searched for a possible q depen dence of the KE yield. For 1 less than or equal to q less than or equal to 3 the KE yields decrease slightly with increasing q, whereas no significant q dependence could be found for higher charged ions. These results are dis cussed by regarding the q dependencies of two different mechanisms which ar e believed to be relevant for KE. (C) 1999 Elsevier Science B.V.