The specimen thickness effect upon the electron microscope image contrast transfer of amorphous objects

From experimental measurement the authors show that amorphous carbon specimens imaged by 100 keV conventional transmission electron microscopy (CTEM), with thicknesses as large as 100 nm behave like weak phase objects. The defocus of the phase transfer contrast function cannot be evaluated from the exit surface plane of the object but may be from its middle plane. A theoretical model explaining these results is propounded.