The application and limitations of the edge-diffraction test for astigmatism in the electron microscope

Abstract

The ultimate resolving power of the electron microscope lies between 2 and 3 Å. In practice, astigmatism usually sets a higher limit. It is not difficult to correct astigmatism provided a sufficiently sensitive test is available. The paper analyses the edge-diffraction test quantitatively and shows that it can be used to give correction adequate for a resolving power at least as good as 10 Å without resort to photography, and below this with the help of a series of micrographs. The conditions for the successive application of the test method are specified and practical aspects of its use discussed. It is shown that the edge-diffraction fringe can also be used as a test for the adequacy of mechanical and electrical stability, etc.