Electron microscope, electron source for electron microscope, and methods of operating an electron microscope

An electron source for an electron microscope, comprising:

• a cold field emitter with an emission tip;
• an extractor electrode for extracting an electron beam from the cold field emitter for propagation along an optical axis;
• a first cleaning arrangement for cleaning the emission tip by heating the emission tip;
• and
• a second cleaning arrangement for cleaning the extractor electrode by heating the extractor electrode.

A method of operating an electron microscope having an electron source with a cold field emitter, comprising:

• in a first cleaning mode, cleaning an emission tip of the cold field emitter by heating the emission tip;
• in a second cleaning mode, cleaning an extractor electrode of the electron source by heating the extractor electrode;
• and
• in an operation mode:
• extracting an electron beam from the cold field emitter for propagation along an optical axis, the electron beam being shaped by a first opening provided in the extractor electrode;
• collimating the electron beam with a condenser lens;
• and
• focusing the electron beam onto a specimen with an objective lens.