The STM was the first Scanning Probe Microscope to be developed, and it is still able to produce the highest resolution images of conducting surfaces. Invented in 1981 by Gerd Karl Binnig and Heinrich Rohrer, the STM takes advantage of the principle of quantum tunneling [1]. A voltage is applied between a sharp conducting tip (the "probe") and the surface of interest. The tip is slowly lowered toward the surface using a piezo crystal until a current begins to flow. As a distance of only one Angstrom (0.1 nm) is crossed, the number electrons passed from the probe to the surface (or vice-versa) increases by several orders of magnitude. If the current is then held constant by a feedback loop controlling the distance (constant current mode), and the height of the probe over the surface at each point is saved in a data file then an image of the electrical topography of the surface can be collected.

The early researchers at IBM noticed that the probe would sometimes pick up an atom from the surface. They soon discovered that by varying the voltage applied to the tip, it was possible to move around single atoms. By writing their company name in atoms, these researchers clearly demonstrated that nanotechnology is a real possibility [2].

References

[1] Binnig, G., et al., Surface studies by scanning tunneling microscopy, Physical Review Letters, 49 (1), p. 57-61 (5 July 1982).

[2] D.M. Eigler, E.K. Schweizer. Positioning single atoms with a scanning tunneling microscope. Nature 344, 524-526 (1990).