Lichte’s Defocus
- Practical Electron Microscopy and Database -
- An Online Book -

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This book (Practical Electron Microscopy and Database) is a reference for TEM and SEM students, operators, engineers, technicians, managers, and researchers.
 

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Lichte defocus of least confusion minimizes contrast delocalization, however, the strong spherical aberration under this condition induces the poor point resolution and the contrast reversals in the entire frequency range, making high-resolution structure interpretation difficult.

The Lichte’s defocus of least confusion is given by,

        Lichte defocus of least confusion ----------------------- [2780a]
where,
          g -- The diffraction vector
.         λ -- The wave length,
.         Cs -- The third-order spherical aberration.

The meaning of defocus here is the Z-height (TEM specimen height) offset from standard defocus. Equation 2780a states that the imaging plane of the largest ray displacement δmax(g), inside an aperture, given by the information limit gmax  has a minimum. In this case, the respective set of rays inside the aperture gives a minimum delocalization of,

        Lichte defocus of least confusion ----------------------- [2780b]

 

 

 

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