Formation and atomic structures of double-layer steps on Si(100) surfaces studied by scanning tunneling microscope

In this paper, we used an ultra-high-vacuum scanning tunneling microscope ( STM) to study the step structures of the Si(100) surfaces and found that do uble-layer steps can exist even at a low miscut angle (similar to 0.5 degre es) from the (100) direction. The double-layer B steps are caused by the sh rinkage of the span of the single-layer steps, and basically run in a zigza g manner with many kinks. The second layer atoms are rebonded at the step e dges, and the rebonded atoms form asymmetric dimers that make the outmost d imers on the upper terrace brighter. The asymmetric dimers propagate from t he kink site and form local c-4 x 2 structures. Their related atomic struct ure models are discussed. (C) 1999 Elsevier Science B.V. All rights reserve d.