Fig.1A Bulk Terminated and Reconstructed Si (001)-2 × 1 Surface. An individual silicon atom can form four bonds with neighboring atoms. In the bulk of a silicon crystal, viewed from the (001) plane, two of these bonds reach to the level below and two reach to the next level above. The top figure shows three successive planes in the bulk crystal structure (dots of different shades of red represent atoms on different levels.) Cleaving a crystal along a (001) plane leaves the surface atoms with only two bonds intact and the other two dangling. The surface atoms then swing toward neighboring atoms to form pairs, known as dimers. The bottom figure shows the same Si (001) plane reconstructed to form rows of dimers along the surface. This leaves the reconstructed surface with only two dangling bonds per dimer. At low temperatures the dimer rows buckle so that alternating atoms are slightly raised and lowered from the plane (this is shown in the varying of dot sizes.)

Fig. 1B Step Edges on the Reconstructed Si (001)-2 × 1 Surface. If a sample is imperfectly cut, then the surface will be composed of terraces. If silicon is deposited upon a clean surface, then islands may form. This figure shows the two types of step edge which border two levels, whether the top level is populated by islands or by a complete terrace. Note that consecutive levels' rows are perpendicular. Movies of terrace and island dynamics display some of the important differences between the two step edge types. The black dots represent the one level's atoms and the red dots represent the atoms on the next level up.

Copyright 1996 by the Regents of the University of Minnesota, Dept. of Physics & Astronomy. All rights reserved.