A type of electron microscope that is similar in
principle to the field-emission microscope, except
that a high positive voltage is applied to the metal
tip, which is surrounded by low-pressure gas rather
than a vacuum.
The image is formed in this case
by field ionization at the surface of an unheated
solid as a result of a strong electric field creating
positive ions by electron transfer from surrounding
atoms or molecules. The image is formed by ions
striking the fluorescent screen.
on the surface of the tip can be resolved and in certain
cases, adsorbed atoms may be detected.