Cc corrector

The Cc corrector makes the chromatic aberration of the image-forming lens or the probe-forming lens to be 0 (zero) by producing a negative chromatic aberration. To produce the negative chromatic aberration, the corrector uses a quadrupole field formed by the superposition of an electrostatic field and a magnetostatic field. Multi-stage multi-poles are used to create the quadrupole field.
The cylindrically symmetric convex lens of the magnetic field type or the electric filed type, which is used for electron microscopes, always possesses a positive chromatic aberration. Thus, electrons having a lower velocity are more largely deflected toward the convergence direction (inward).
On the other hand, the quadrupole field of the Cc corrector exhibits a negative energy dispersion, which is opposite to that of the convex lens. Thus, the Cc corrector makes the electrons having a lower velocity to deflect more largely toward the divergence direction (outward). Therefore, incorporation of the Cc corrector into the convex lens system enables the positive chromatic aberration of the lens system to cancel with the negative chromatic aberration produced by the quadrupole field, making the chromatic aberration of the entire lens system of the electron microscope to be zero.

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