Anomalous patterns and nearly defect-free ripples produced by bombarding silicon and germanium with a beam of gold ions

We demonstrate that surface ripples with an exceptionally high degree of order can develop when germanium is bombarded with a broad beam of gold ions. In contrast, if silicon is sputtered with an Au- beam, patches of ripples with two distinct wave vectors can emerge. These types of order can be understood if the coupling between the surface morphology and composition is taken into account. (C) 2014 AIP Publishing LLC.