Can a scanning tunneling microscope operate in water?

Yes, a scanning tunneling microscope (STM) can operate in water. While the instrument relies on the quantum mechanical phenomenon of tunneling to image surfaces at the atomic level, this process is not restricted to a vacuum environment.1

Because the gap between the probe tip and the sample surface is extremely small—typically around five angstroms—there is very little space for molecules to interfere with the tunneling current. Consequently, the STM can function effectively in various environments, including ambient air, insulating fluids, and the ionic solutions utilized in electrochemistry, as well as in water. Operating in these environments is often more convenient than using ultrahigh-vacuum systems, which are primarily employed to maintain sample cleanliness rather than to enable the tunneling mechanism itself.1