Transient to steady-state morphology evolution of carbon surfaces under ion bombardment: Monte Carlo simulations

Molecular dynamics (MD) simulations have established the sputtering yields of carbon under the low-energy bombardment of noble gas ions. Here, we upscale these MD results to account for the evolving surface morphology and sputtering yield with ion fluence using a Monte Carlo model, which considers the shadowing of the incident ion flux, redeposition of sputtered carbon material, and secondary sputtering induced by the surface impact of carbon sputterants. Results show that initially rough surface morphologies are consistently smoothened and flattened by a normal ion flux, resulting in sputtering yields that approach MD predictions. Under a highly oblique ion flux, however, the activation of multiple cooperative roughening and smoothening mechanisms at different scales lead to the formation of characteristic surface steps at the microscale, with steady-state sputtering yields that are up to an order-of-magnitude lower than MD predictions. While the observed surface features and the ensuing sputtering yield at steady-state are generally not sensitive to the initial surface morphology, the initial morphology controls the ion fluence to attain steady-state. We discuss surface design strategies to delay and abate sputtering.