Nano-donuts on metal surfaces

Highlights: • Observation of nano-donuts comprising of a pit surrounded by a circular ridge. • Nano-donuts originate when rare gas nano-bubbles leave the metal surface. • Nano-donuts have been observed on Au(1 1 1) and Al(1 0 0) for Ar and Ne rare gas bubbles. - Abstract: Nano-structures comprising of a pit surrounded by a circular ridge that resemble nano-donuts have been observed on flat terraces of both Au(1 1 1) and Al(1 0 0) surfaces after low energy (1.5–2 keV) rare gas (rg) ion implantation. From time lapse scanning tunneling microscopy, we demonstrate that these donuts originate from the rg bubbles that migrate out from the sub-surface region. The circular shape of the donuts is observed for both Ar and Ne bubbles. The donuts and the related nano-structures represent different stages of large time scale co-operative relaxation of Au atoms by long range elastic interaction after the rg bubbles leave the metal