Angular dependence of the sputtering yield from a cylindrical track

The dependence of the sputtering yield on the incident angle, Θ, is determined using molecular dynamics (MD) simulations for a cylindrical track produced by a fast ion. For a ‘small' spike radius and for the mean energy in the track, E_exc, smaller than the binding energy, U, a (cosΘ)^−1.7 dependence is found, close to the linear collision cascade (LCC) result and to some thermal spike models. On the other hand, when E_exc>U, the incident angle dependence is (cosΘ)⁻¹. For a larger spike radius we obtain a (cosΘ)^−1.6 dependence for both high and low energy densities. Analytic spike models based on diffusive transport are shown not to give satisfactory results. In addition, at low energy densities we see correlated atom ejection ignored in analytic models. Applying the MD results to the experimental data for electronic sputtering of solid O₂ at large excitation densities suggests that the effective spike radius is larger than the initial Bohr adiabatic radius indicating that energy is rapidly transported from the initially narrow track.