Figure 1

(a) Atomic force microscopy (AFM) image of Ge quantum dots grown on Si(100) patterned with 60 keV Si²⁺ ions at 1 × 10⁶ ions per spot in a square array of spots (500 nm separation). The implanted spots show up as shallow surface bumps and Ge quantum dots as the brighter spots. (b) AFM image of an area of the sample that did not undergo implantation. (c) Image acquired near the edge of the implanted region (indicated by the dotted line) showing the transition in quantum dot growth density. The shapes are distorted due to the speed of the scan. (d,e) Higher magnification images of two areas implanted with doses of 1 × 10⁶ and 1 × 10⁵ ions per spot respectively followed by Ge quantum dot growth. In (d), shallow bumps and pits (white arrows) are visible at implant sites. In (e) the bumps are smaller than in (d), no pits are visible and there is no correspondence between quantum dots and the implantation pattern. In both images the brightness and contrast in the dotted rectangle are adjusted to accentuate the features. We attribute the asymmetric shape of the surface bumps to residual astigmatism in the Si²⁺ ion beam.