a) Schematic of the self-assembled nanodot multilayers fabricated by molecular beam epitaxy. b) Bright-field TEM image of a sample with tsi=12 nm. The dark areas correspond to the Ge layers. The inset shows a high-resolution TEM of a nanodot. c) AFM image of a single Ge/Si(001) dot layer before overgrowth with Si. d) AFM image of the topmost layer of a sample with tsi=3 nm
