ELECTRON TRAJECTORY CALCULATION OF A STIGMATIC-FOCUS WIEN FILTER FOR ELECTRON ENERGY LOSS SPECTROSCOPY I.

Electron optical characteristics of a Wien filter with crossed electric and magnetic fields were calculated for contructing a high resolution electron energy loss spectrometer. Stigmatic focus can be achieved by a linear-gradient magnetic-field crossed with a homogeneous electric field normal to the path of incident electrons. Asymmetrical electrodes inside the tilted magnetic pole-pieces can give the fields producing stigmatic focus. Electric and magnetic fringing field distributions were calculated by the finite element methods. Electron trajectories in the Wien filter with fringing field were calculated numerically. The fringing fields cause strong deflection of electrons. However, the deflection was reduced by adjusting only the supplied currents of the magnet and voltage of electrodes or the object plane of the filter resulting in a high resolution (less than 5 mv).