Tunneling Images of Atomic Steps on the Si(111)7×7 Surface

Tunneling images of single atomic steps on Si(111) have been obtained with a tunneling microscope. The 7×7 reconstruction is observed to persist essentially undistorted right up to the steps. The position of each step coincides with a 7×7 unit-mesh edge in both the upper and lower terraces adjacent to it. Asymmetry within the 7×7 unit mesh is observed and correlated with faulting of terraces adjacent to the step. The results are described by an extension of the dimer adatom stacking-fault model of Takayanagi et al.Physic