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

=================================================================================

For TEM specimens that are too thick for the weak phase object approximation (WPOA ) to hold, Li and Tang [1] proposed pseudo-weak phase-object approximation. This approximation takes into account that if the specimen thickness increases beyond the limits of the WPOA validity, the lighter atoms start looking more like heavier atoms and vice versa.

[1] F. H. Li and D. Tang. Pseudo-weak-phase-object approximation in high-resolution electron microscopy I. Theory. Acta Crystallographica, A41:376–382, 1985.