chromatic aberration

If there is energy (wavelength) spread of the incident electron beam or the electron beam passing through a specimen, the refraction angles of these electron beams are different depending on wavelength. Thus, a blurred image is produced on the image plane. This phenomenon is called "chromatic aberration." The energy spread of the electron beam arises from instability of the accelerating voltage, the spread of the initial speed of electrons emitted from the electron gun, the Boersch effect and change of the focal length caused by fluctuations of the excitation current of the lens coils. In addition, as a specimen is thicker (～10 nm or more), energy loss of electrons (change of wavelength) due to inelastic scattering gives rise to the chromatic aberration.

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