Tight-binding study of noncontact atomic force microscopy images of Si(0 0 1) surfaces

Using a silicon tip and a nanotube tip the noncontact atomic force microscopy (nc-AFM) images of Si(0 0 1) surfaces are simulated. When the silicon tip is prepared to have a sharp apex, the topmost surface atoms are found to be visible at their positions, whether the surface is chemically active or passivated. In contrast, with the nanotube tip, abnormal images including ghost atoms are frequently observed. This is because the atoms other than the apex atom participate in interaction with the surface. In order to suppress the effect of the multi-atom apex, the tip apex is required to be sharpened in the nc-AFM as well as in the scanning tunneling microscopy.