ELECTRON BEAM MONOCHROMATOR AND ANALYZER

A novel type two-cascade monochromator.

Monochromic probing beam should be sufficiently intensive to provide sufficient sensitivity and rate of spectra registration of the whole electron spectrometer. In many cases there is no possibility to satisfy this requirement, when the monochromator is designed on the base of any “traditional” dispersive systems, such as hemispherical or cylindrical electrostatic deflectors. The reason for this is the influence of the beam’s space charge, and this influence leads to a well-known result: at any desirable energy spread E_m in the monochromised probing beam, its current I_m can’t exceed some certain value I_{m max} , the typical values of which lie in the range between 10^-10 and 10^-9 A if E_m =10 meV.

The new potential compresses the beam simultaneously with separating it into monokinetic components. Calculations show that this feature allows to overcome the space charge limitation of the output intensity by a factor of 2 - 3. Electron-optical test carried out with the model two-cascade monochromator (see the picture) corroborates these expectations. The overall size of the device is 200mm * 85mm * 90mm. The input and output slits are greatly variable. The monochromator works together with the primary electron gun of Pierce type.

The monochromator can be used as an analyzer. The resolution of 0.33% is easily achieved if the entrance diaphragm size is 6mm * 6.4mm. Of course, the smaller is the entrance slit, the better is the resolution.