Secondary electron multiplier (SEM) is an electronic device for amplifying the flow of electrons based on secondary electron emission.
Open SEMs are vacuum tube devices which are used for direct detection of electromagnetic radiation or particles. The device is used in facilities operating under natural vacuum conditions (in space) and in high-vacuum measuring instruments at pressures which do not normally exceed 10-3 Pa.
Depending on their design, SEMs are divided into two main groups: (1) with discrete dynode systems in which electron fluxes are multiplied on separate electrodes – dynodes, with potentials of dynodes in such SEMs increasing in a stepwise manner, and (2) with distributed (continuous) dynode systems in which electron fluxes are multiplied along the surfaces with a continuous change in potential (channel electron multiplier, microchannel plates).
Single-channel secondary electron multiplier (SEM) are reliable and effective detectors of positive and negative ions as well as electrons and photons. A glass tube with approximately 1 mm inner diameter and 2, 3, or 6 mm outer diameter is made of lead-silicate glass having a special composition. When treated accordingly, this glass exhibits properties of electrical conductivity and secondary emission. These glass surfaces can withstand multiple cycles between vacuum and atmosphere without performance degradation, which is not characteristic of SEMs with discrete copper-beryllium dinodes.
Channel SEMs have become most commonly used in quadrupole mass spectrometers and ion trap mass spectrometers; they also find many applications in magnetic sector instruments.
VTС Baspik manufactures channel-type SEM in the form of SEM-6 spiraltron.