Fig. 1. Silicon (001) 2 X 1 Reconstruction with a Diffusing Dimer. As can be seen in this image (and is discussed in greater detail elsewhere) the cleaved surface reconstructs to form parallel rows. Dimer diffusion is predominately along the rows, making the system nearly one-dimensional. The movie from which this image is taken may be viewed as an animated GIF. Unlike many of our other images, this is an empty state image, so the surface rows appear dark and the troughs appear bright.