napisy-gora

 

α-SDA idea

 

As seen below a small wedge (±150) is cut out from a full sphere concentric condenser. At the intersecting point of the main axis 1, the inlet axis 2 and the outlet axis 3, and in the symmetry plane of the angle α, which simultaneously is an electron optical object/image plane, a magnetic deflector is mounted, which is common to the ingoing and outgoing particles. The outlet axis 3 (along which the particles at the outlet move from the region of the concentric electrodes of the second “HDA”) and the inlet axis 2 (along which the particles at the inlet move to the region of the concentric electrodes of the first “HDA”) are both tangent to the central trajectory. The distance between the deflecting element and centre of the spherical and concentric electrodes amounts to R0/cos(α/2), where R0=(R1+R2)/2. The electron beam moves towards this element from the cathode lens along the main axis 1 perpendicularly to the symmetry plane of the angle α, providing an image being simultaneously an object of the energy filtering. The deflecting element deflects electrons by an angle π-α/2, resulting in their further propagation along the inlet axis 2. They move towards this element from the cathode lens along the main axis 1 perpendicularly to the symmetry plane of the angle α, providing an intermediate image being simultaneously an object of the energy filtering. After deflection by an angle α/2 and energy selection at the dispersion aperture, the particles turn back along the outlet axis 3 to the same deflecting element, where an energy filtered image is exactly at the location of the original object in the symmetry plane. The deflecting element deflects the charged particles again by an angle π-α/2, which leads to a total deflection angle 2π: thereby to the co-linearity of the main inlet axis 1 and the main outlet axes 4 of the α-SDA imaging energy filter.

p2 alphaSDA rys1p2 alphaSDA rys2p3 zdjęcie3

 

 
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