Atomic-resolution three-dimensional imaging of germanium self-interstitials near a surface: Aberration-corrected transmission electron microscopy

We report the formation and direct observation of self-interstitials in surface proximity of an elemental semiconductor by exploiting subthreshold effects in a new generation of aberration-corrected transmission electron microscopes. We find that the germanium interstitial atoms reside close to hexagonal, tetragonal, and S-interstitial sites. Using phase-contrast microscopy, we demonstrate that the three-dimensional position of interstitial atoms can be determined from contrast analysis, with subnanometer precision along the electron-beam direction. Comparison with a first-principles study suggests a strong influence of the surface proximity or a positively charged interstitial. More generally, our investigation demonstrates that imaging of single atom can now be utilized to directly visualize single-defect formation and migration. These high-resolution electron microscopy studies are applicable to a wide range of materials since the reported noise level of the images even allows the detection of single-light atoms.