Atomic collisions in secondary ion production by hydrogen near the electronic stopping power maximum

Abstract

H+ projectiles from a 2.5 MV van de Graaff accelerator were used to bombard a carbon target (500 Å) under high vacuum conditions. By varying the H+ projectile energy (50–160 keV/u) it was possible to scan the low energetic Lindhard–Scharff–Schiøtt region (LSS), the maximum, and the high energetic Bethe–Bloch region (BB) of the electronic stopping power (dE/dx)e. The secondary ion yields Y(H+,C2Hx+,C3Hx+,C4Hx+,C5Hx+) from the beam entrance surface were measured with a time of flight spectrometer (TOF). The measurements reveal a non-linear behaviour between the electronic stopping power (dE/dx)e calculated with TRIM, in the maximum and the Bethe–Bloch region, and the secondary ion yields. However, the experimental results show good agreement with a new Pereira et al. [Int. J. Mass Spectrom. Ion Proc. 174 (1998) 179] effective energy loss model.