Atom manipulation and nanostructure engineering on III-V semiconductor surfaces
Since its implementation in the early 1990s by the pioneering research of Eigler et al., STM-based atom manipulation has been applied mainly to adsorbates on metal surfaces. We have extended this technique to III-V semiconductor materials and achieved the reversible repositioning of native In adatoms on a InAs(111)A surface grown by molecular beam epitaxy. The repositioning is realized by transferring individual atoms between the surface and the STM tip and vice versa (vertical atom manipulation). Surface-to-tip transfer is due to inelastic electron tunneling assisted by the tip-induced electric field, whereas tip-to-surface transfer is due to short-range adhesive interactions. It is feasible to create compact structures, with the adatoms occupying nearest-neighbor In vacancy sites of the reconstructed surface, or more open structures of various shape and size. Scanning tunneling spectroscopy (STS) reveals substantial electronic coupling between In adatoms next to each other yielding unoccupied quantum states delocalized along the assembled nanostructure. Our results show that the combined approach of atom manipulation and local spectroscopy is capable to explore atomic-scale quantum structures on semiconductor surfaces.
Figure:
Left panel: Constant-current STM image of a In5 chain on InAs(111)A assembled by vertical atom manipulation, the adatoms reside on In-vacancy sites of the reconstructed surface at an interatomic spacing of 8.57 Å. Right panel: STS measurements with the STM tip positioned over a discrete In adatom reveal a resonance at 0.68 V in the differential tunneling conductance (green curve) indicating an unoccupied state deriving from atomic orbital states of the In adatom. For linear InN chains (N: number of atoms) the atomic resonance is gradually shifted towards the Fermi level, which indicates an along-chain electronic coupling mediated by the semiconductor substrate.
Related publications:
