SECONDARY-ELECTRON IMAGING OF MONOLAYER STEPS ON A CLEAN SI(111) SURFACE

Secondary electron images of monolayer steps on a 7 x 7 reconstructed Si(111) surface are shown to be observable by ultrahigh-vacuum scanning electron microscopy (UHV-SEM) with grazing incidence of the primary electron beam. With a 25 keV primary beam, clear contrast for atomic steps can be obtained at incidence angles less-than-or-equal-to 15-degrees with respect to the surface. Faint contrast for atomic steps can still be detected up to 27-degrees. The step contrast depends strongly on the orientations of the step direction relative to the primary beam incidence, indicating that the contrast is due to a geometrical effect at step edges.