STM of insulators with the probe in contact with an aqueous layer

The advent of scanning tunneling microscopy of electrical insulators and biological specimens has raised significant questions as to the mechanisms involved in image formation. We show that for successful high-resolution imaging of hydrated films of two different proteins, a water bridge can exist between the tunneling microscope probe and the sample surface. Current-probe/sample separation plots on hydrated and dehydrated protein confirm the formation of a water bridge. The practical realization of these results are discussed.