Principal trajectory and focusing properties

1 Principal trajectory and focusing properties Usually, electrostatic deflection analysers contain two regions through which the electrons pass, a field region and a field-free region. Very often the field-free region 

If the voltage U°p is kept fixed, but electrons, which have energies different from jn are considered, one has different principal trajectories. As shown in Fig. 4.5 they reach different image points which define a focal plane, and the spatial dispersion Az for electrons with energy deviation A allows the desired energy analysis. Two methods can be applied  

It depends on the geometry of the analyser (sector or 2n) and is related to the dimensions of the acceptance source volume.) The transmitted electrons are then detected by a common channeltron detector placed behind this dispersion 

Both types of detection device will be discussed in Section 4.3. 

In order to fix the principal trajectory, appropriate focusing properties of the analyser have to be selected. These properties follow from the treatment of the analyser as an electron optical device which images the source Q at the analyser entrance to the image B at the analyser exit, and a detailed treatment for a point source is given in Section 10.2. Here only the main results necessary for a basic understanding will be reproduced. 

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