Atom manipulation method to substitute individual adsorbate atoms into a Si(111)-(7 × 7) substrate at room temperature

We demonstrate a method to substitute individual adsorbate atoms into a Si(111)-(7 × 7) substrate using the tip of an atomic force microscope (AFM) at room temperature. We show that single Sn atoms diffusing within the half-unit-cells (HUCs) of the Si(111)-(7 × 7) substrate can be substituted into Si adatom sites via a close approach of the tip, whereby the intrinsic Si adatoms are ejected onto the surface of the adjacent HUCs. The Sn atom substitution sites can be precisely controlled by the approach of the AFM tip toward the surface at certain positions near the boundary of the HUCs but slightly shifted away from the HUC with the diffusing Sn atom. This manipulation method is also demonstrated to replace Si adatoms in the Si(111)-(7 × 7) surface with Pb using scanning tunneling microscopy. This method can provide a way to induce single-atom substitutional doping at certain positions from an adsorbate atom diffusing within a confined space provided by a substrate, which would allow for control of the dop...