Simulated noncontact atomic force microscopy images of Si(001) surface with silicon tip

We simulated the noncontact atomic force microscopy (nc-AFM) images of Si(001) surfaces using the Si tip based on the tight-binding model. We find that only up dimer atoms are observed slightly outside the dimer sites. This outward shift is explained based on two points. One point is that the dangling bonds on the up dimer atoms, which interact with the tip apex, are tilted outward. The other point is that the space between the adjacent dimer rows looks slightly bright on the c(4 x 2) phase since the tip located above the midpoint of the two dimer rows is subjected to attractive forces from the up dimer atoms on both sides.