Charge transfer from I₂^- (CO₂)_n cluster anion to silicon surface: Cluster-size dependence

The charge survival yield for a cluster anion, I₂^- (CO₂)_n (n = 0-30) during its collision onto a silicon surface covered with silicon oxide layers of ∼2 nm in thickness was measured as a function of the number of the CO₂ molecules, n, and the collision energy (per I₂^-) in the range of 1-80 eV. A monotonic increase in the charge survival yield with n was observed. This means that the efficiency of the charge transfer from the core ion, I₂^-, to the surface is reduced with the increase of n. It was concluded that the CO₂ molecules suppress the charge transfer by behaving as an electrostatic 'stabilizer' of the core ion and as a 'spacer' between the core ion and the surface.