The working principle of the trochoidal electron monochromator revisited

Abstract

On the basis of a number of different experiments employing various principles, we have demonstrated that the energy resolution of the trochoidal electron monochromator used in our laboratory the past 5 yr is not independent from the electron energy used, that is, the very high nominal-energy-resolution close-to-zero electron energy in the range of several meV deteriorates quickly with increasing electron energy reaching values of up to 100 meV at ∼1-eV electron energy. Carrying out extensive electron trajectory calculations with the Simion program, we were able to show that our variant of a trochoidal monochromator does not only operate on the trochoidal dispersion principle but also involves a retarding field component right after the dispersion region in achieving this high-energy-resolution close-to-zero energy. This retarding field is, however, weakened at higher electron energies (caused by the influence of the electron-acceleration field) leading to the decrease in energy resolution with increasing electron energy. On the basis of further simulations, we have designed and constructed a new monochromator avoiding this and other deficiencies. This new monochromator currently has an energy resolution of ∼45 meV independent of the electron energy. Further improvements are under consideration.