Scanning tunneling microscopy (STM) has provided many breakthroughs in imaging surfaces on atomic scale. Some of the most notable of these have been for the crystalline (100) surface of sillicon, which has great technological importance and also serves as the model semiconductor system for studying atomistic growth mechanisms and electronic properties. The STM image on the left reveals a Si(100) surface which is miscut by a few degrees. The surface reconstructs forming rows of sillicon atom pairs (called dimers) on terraces separated by atomic layers. Three main terraces are shown with dimers running perpendicular to the double-layer steps. The mean terrace width is approximately 4 nanometers. As the dimensions of artificially structured materials decrease (imagine, if the size of a device grown on the Si surface approaches nanometer-scale), the role of the interfaces becomes increasingly important in determining physical and electronic properties.

------ The image has been chosen for inclusion in  "Physics in the 20th Century", the commemorate issue of the centennial of American Physical Society. For details, see Phys. Rev. Lett. 84, 4546-4549 (2000).