The effect of channeling on MeV ion-induced auger electron production in silicon

We have measured Auger electron emission from single crystal targets of Si(111) bombarded with H⁺ and ⁴He⁺ beams in the 0.5 to 1.8 MeV range under channeled and random directions of incidence. Under channeling conditions (monitored by simultaneous measurement of the Rutherford backscattering yield), a significant reduction is observed in the intensity and also in the energy width of the KLL Auger line. These two characteristics of the Auger signal are influenced by channeling of the incident beam as evidenced by their angular dependence. The measured ratio of the channeled to random Auger signals correlates well with a simple model based on the shadow cone radius for the channeled ion, the lattice vibrational amplitude, the adiabatic K-shell excitation distance, and the electron inelastic mean free path, λ, for the 1620 eV Auger line. We derive a value for the latter quantity of 34 Å.