In a scanning tunneling microscope (STM) operated in ultra-high vacuum, if we place a well-prepared W tip above the Si(111)-7×7 surface at a separation of ∼1 nm and apply an appropriate voltage pulse to it, we can extract a single Si atom from a predetermined position routinely at room temperature. The extracted Si atoms are redeposited onto the surface with a certain probability, their positions always being at a fixed crystallographic site. The redeposited Si atoms can be displaced intentionally to other crystallographically equivalent sites. In case of the Si(001)-2×1 surface, usually two Si atoms forming a dimer are extracted together. For both surfaces, Si atoms at crystallographically different sites including step edges are extracted with different probabilities. The microscopic mechanisms of these processes are discussed.

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Voltage pulses applied between the tip of a scanning tunneling microscope (STM) and a crystal surface often result in extraction or deposition of single atoms or clusters of atoms on the surface. which are detected by imaging the affected area with the STM after the pulse. Here. atomic-scale displacements of the STM tip during such surface modifications. due to structural changes occurring at the tunnel junction are studied. Using this technique. it is found that for the Si(lll )7 X 7 surface and a W tip, modification during the pulse is field induced and not current induced. but that a considerable fraction of modification events occur shortly after a pulse. The ability to predict the type of modification from the direction of the tip displacement is investigated, and the applicability of this approach to high-speed nanofabrication is discussed.

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