Design of a Scanning Tunneling Microscope

Applications in nanotechnology require the use of tools that can help visualize and manipulate structures at the nanoscale. A scanning tunneling microscope (STM) is a visualization tool that utilizes the quantum mechanical phenomenon of electron tunneling to image features and structures at these small scales. Tunneling results when a metallic probe tip is brought sufficiently close to an electrically conducting, biased sample without making physical contact. A small current is drawn as electrons jump (tunnel) across the gap between the tip and the sample. This current is so small that the medium between the tip and the sample does not break down and become electrically conducting. Once a tunneling current is drawn between the tip and the sample, which are separated by a gap, feedback controls in conjunction with piezoelectric actuators adjust the gap distance in such a way as to maintain a constant tunneling current as the tip scans across the sample surface. STMs utilize this monitoring of the gap adjustment in order to produce images of the sample surface with potentially near atomic resolution. The first STM was developed by Binnig and Rohrer in 1981 and these microscopes are now commercially available. Commercial microscopes, however, are expensive, and no