SINGLE ATOM IMAGING IN HIGH-RESOLUTION UHV ELECTRON-MICROSCOPY - BI ON SI(111) SURFACE

Bismuth (Bi) atoms are deposited on the clean Si(111) surface of the 7 x 7 structure at 550 K and the square-root 3 x square-root 3 structure is imaged by high-resolution UHV electron microscopy. In an image obtained at a particular under-focus, dark-ring images and bright-dot images appear. Each dark-ring image is surrounded by six bright-dot images. The latter is confirmed to be an image of the Si[111] atomic row and the former is due to an adsorbed Bi atom by comparing the image with multislice simulations. The image accords well with the Si-displaced model derived from transmission electron diffraction experiments. The experiment proves single atom imaging by high-resolution electron microscopy.