Formation of Au–Ge nanodots by Au− ion sputtering of Ge

•Energetic Au ion sputtering of Ge single crystal at normal incidence and room temperature.•Nanodot formation studied by AFM and cross-sectional TEM.•The results are explained by the process of local melting by ion impact and subsequent re-solidification.

Energetic Au ion sputtering of crystalline Ge surface at normal incidence and room temperature can produce nanodot morphology, which has been studied by atomic force microscopy. The cross-sectional transmission electron microscopy of the dot structure reveals that the implanted Au does not form solid solution with Ge, but preferentially segregates at the top edges of the dots as well as near the amorphous/crystalline interface. The mechanism of dot formation is discussed in the light of local transient melting of the surface due to a high rate of energy deposition by the Au ions and the subsequent cooling.