Quantification of the information limit of transmission electron microscopes
by Juri Barthel and Andreas Thust
High-resolution transmission electron microscopes of the latest generation offer the possibility to study the atomic configuration of solid-state objects with a resolution of about 80 pm. While a lot of effort is put into improving the instrumental resolution, practical methods for the quantification of this key parameter date from the 1970s and have even come to criticism due to recently performed experiments with 80 kV accelerating voltage yielding an unexpectedly good resolution. The availability of a practicable method for the accurate quantification of the obtained resolution would therefore be highly beneficial in this field.
In the present study a highly accurate measurement method for the information limit is introduced, which is suitable for modern aberration-corrected electron microscopes. An experimental comparison with the traditionally applied Youngs fringe method yields severe discrepancies and confirms theoretical considerations according to which the Youngs fringe method does not reveal the information limit.
Complementary information on the resolution limitation of transmission electron microscopes can be obtained by the traditional Youngs fringe method and the new approach presented. The Youngs fringe method reveals a qualitative kind of net resolution limit as a result of a mixing of several accumulating effects related to the object, to the microscopes optical transfer properties, to the camera, and to environmental influences. In contrast, our new approach allows us to isolate the resolution limiting effect caused by the partial temporal coherence and thereby to quantify precisely the information limit according to its theoretical definition.
Juri Barthel and Andreas Thust: Quantification of the Information Limit of Transmission Electron Microscopes, Phys. Rev. Lett. 101 (2008) 200801.