Morphological Transitions in Nanoscale Patterns Produced by Concurrent Ion Sputtering and Impurity Co-deposition

We modify the theory of nanoscale patterns produced by ion bombardment with concurrent impurity deposition to take into account the effect that the near-surface impurities have on the collision cascades. As the impurity concentration is increased, the resulting theory successively yields a flat surface, a rippled surface with its wavevector along the projected direction of ion incidence, and a rippled surface with its wavevector rotated by 90 degrees. Exactly the same morphological transitions were observed in recent experiments in which silicon was bombarded with an argon ion beam and gold was co-deposited [B.~Moon et al. arXiv:1601.02534 (2016)].