Velocity effect in secondary electron emission below and above the electronic stopping power maximum

We studied secondary electron emission yields gamma from a carbon surface w ith helium projectiles near the electronic stopping power maximum (0.2-2 Me V). We ask the question: "Does gamma depend on the electronic stopping powe r (dE/dx)(e) only or is there an additional dependence on the projectile ve locity V-P?" A velocity effect is indeed found for backward emission. The r esults are discussed in the framework of recent electron transport and trac k models and compared with the yield of secondary ions from the same collis ion system. (C) 1998 Elsevier Science B.V. All rights reserved.