Can a scanning tunneling microscope operate in air?

Yes, a scanning tunneling microscope (STM) can operate in air.

While the instrument relies on "vacuum tunneling" to function, this process can occur even when the environment surrounding the probe tip is not a vacuum. Because the spacing between the tip and the sample is extremely small—typically around five angstroms—there is very little room for gas or liquid molecules to interfere with the tunneling process.

Consequently, the STM is versatile and capable of operating in various environments, including:
* Ambient atmosphere (air)
* Water
* Insulating fluids
* Ionic solutions used in electrochemistry

Operating in these environments is often more convenient than using ultrahigh-vacuum instruments. When a high-vacuum environment is utilized, its primary purpose is to ensure the cleanliness of the sample surface rather than to improve the fundamental performance of the microscope itself.1