The working principle of the trochoidal electron monochromator revisited

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 similar to1-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 similar to 45 meV independent of the electron energy. Further improvements are under consideration. (Int J Mass Spectrom 205 (2001) 209-226) (C) 2001 Elsevier Science B.V.