Layer-by-layer atomic manipulation on Si(111)-7 × 7 surface: Surface structures and staircase conductance variation with atom removal

Si atom removal from a Si(111)-7 × 7 surface was successfully executed by allowing the biased STM tip to approach the surface to the point contact region followed by retraction to the tunneling region. This technique was found to have the capabilities of revealing: (1) the atomic structures on the newly exposed surfaces; and (2) tip-substrate current variation in relation to the Si atom removal. When the adatoms were removed, the second layer of the dimer-adatom-siacking fault (DAS) model structure appeared without reconstruction except for the relaxation of the dimer rows. When a higher biased tip (> 2 V) was used, the top three layers were removed. Clear metastable structures such as c(2 × 4) and √3 × √3 were observed in the holes, and the shape of these structures was easily changed with the expansion of the size of the hole. A staircase-shaped current drop was observed in the tip retraction process when the adatoms were removed. This is closely related to the decrease in the discrete number of Si atoms at the tip-substrate junction in an atom-by-atom manner, which shows a clear contrast to the nanowire formation in the metal surface indentation. The last drop in the current to return to the tunneling region might correspond to a junction with a single atom between the tip and the substrate, which corresponds to 4 × 10⁵Ω.