TIP-SAMPLE INTERACTIONS IN THE SCANNING TUNNELING MICROSCOPE FOR ATOMIC-SCALE STRUCTURE FABRICATION

In a scanning tunneling microscope (STM) operated in ultra-high vacuum, if we place a well-prepared W tip above the Si(111)-7 x 7 surface at a separation of approximately 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 x 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.