Practical Electron Microscopy and Database

Linear contrast transfer theory can be applied to weakly scattering objects, for instance thin amorphous TEM specimen, which leads only to a small phase shift on the diffracted electron wave. The diffractogram intensity is the power spectrum of the recorded image and can be given in the simple coherent form,

           D(g) ≈ |O(g)|² sin²[χ(g)] -------------------------------- [4186]

where,
         g -- Object frequency vector
         χ -- Wave aberration function
         sin²[χ(g)] -- Oscillating patterns of circular, elliptic, or hyperbolic shape (Thon rings [1])
         |O(g)|² -- Scattering power of thin amorphous objects

|O(g)|² decreases slowly towards higher spatial frequencies and is azimuthally isotropic.

[1] F.Thon and Z. Naturforsch, 21a (1966) 476.