The invention of the scanning tunneling microscope (STM) by Binnig and Rohrer in 1982 demonstrated an unparalleled ability to image materials at the sub-nanometer scale. The invention rapidly lead to an explosion of applications of STM in a wide variety of fields. However, imaging by an STM is essentially limited to materials which are conductive, or could be made conductive, so many materials of interest could not be imaged by STM. This limitation was removed a few years later (1985) by the invention of the atomic force microscope (AFM) by Binnig, Quate and Gerber, in which imaging is based on the response of a soft cantilever beam to the contact forces between an ultra-fine probe tip and a sample. The cantilever/probe systems could be made sensitive enough to enable the AFM to easily resolve atomic or molecular level features.
