- CEM and SEM
CEM & SEM
Secondary-electron Multiplier (SEM)
is an electron multiplier / electron device intended for amplification (multiplication) of electron flows based on secondary-electron emission.
SEM is usually a part of electro-vacuum devices (Photomultipliers, Image intensifier tubes, another electron-beam transmitting devices – dissectors, image orthicons, amplifying tubes) or an independent electrovacuum device registrating particles or electromagnetic radiations.
Such detectors having no case and even input window are called open-type SEMs. They are used in equipment operating in natural vacuum conditions (at space researches), and in high-vacuum measuring devices (scanning electron microscopes, mass spectrometers etc.) at pressure levels not better than 10-3Pa.
Specific claim to open-type SEMs is the capacity of maintaining operating characteristics after the detector’s emitting areas contact with air. The above capacity is provided by protective properties of a thin (2,5-5nm) emissive oxide film (Al2O3, BeO) or aluminum CuBe alloy.