The formation and direct observation of self-interstitials in the surface region of an elemental semiconductor was studied by exploiting sub-threshold effects in a new generation of aberration-corrected transmission electron microscopes. It was found that the germanium interstitial atoms resided close to hexagonal, tetragonal and S-interstitial sites. Using phase-contrast microscopy, it was demonstrated that the three-dimensional position of interstitial atoms could be determined from contrast analysis, with sub-nanometer precision along the electron-beam direction. Comparison with a first-principles study suggested a strong influence of the surface proximity or a positively charged interstitial. More generally, the investigation demonstrated that imaging of single atom could now be utilized to directly visualize single-defect formation and migration. These high-resolution electron microscopy studies were applicable to a wide range of materials since the reported noise level of the images even permitted the detection of single-light atoms

Atomic-Resolution Three-Dimensional Imaging of Germanium Self-Interstitials Near a Surface - Aberration-Corrected Transmission Electron Microscopy. D.Alloyeau, B.Freitag, S.Dag, L.W.Wang, C.Kisielowski: Physical Review B, 2009, 80[1], 014114