Modelling the directional and energy dependence of 5–10 keV Ar + ion-induced secondary electron yields from Cu crystals

Abstract

The primary ion directional effects observed in secondary electron yields induced by ion bombardment [5 keV Ar + → Cu(100)] are simulated using a semi-empirical molecular dynamics model. The directional effects are presumed to arise from inelastic energy transfers that take place in close binary atomic encounters. The latter are estimated using the Oen-Robinson model, in combination with a critical apsidal distance ( R c). The connection between the measured kinetic electron emission (KEE) yields ( γ KEE ) and the predicted inelastic energy loss in a binary atomic collision (Δ E i ) is established through a semi-empirical fitting procedure involving R c and other parameters in the following model: γ e = γ 0 + γ KEE = γ 0 + 〈 ΔE i ( z)exp(− z/ λ)〉, where z is the collision depth. The directional effects are best reproduced by fitting the model to Ar–Cu inelastic collisions for two azimuthal incident directions: R c is estimated to be 0.47 ± 0.03 Å; the parameter, λ (an effective electron attenuation length), is estimated to be 18 ± 2 Å. The same model also describes the γ KEE energy dependence for 5–10 keV Ar + normally incident on low-index Cu crystal targets [Phys. Rev. 129 (1963) 2409]. The spatial and temporal distributions of the hard collisions that initiate KEE are discussed on the basis of the model.