It is frequently necessary to compare experimental images obtained by high-resolution microscopy with simulated images. This is because the image detail depends so strongly on sample thickness and image defocus, neither of which can be known with precision, that in general the sample structure cannot be determined uniquely from a single image. In general, too, there are details of the sample structure which are beyond the resolution of the microscope but which still contribute to the image. The procedure adopted to resolve this difficulty is to simulate images using various defocus values, sample thicknesses and crystal structures, and find a consistent reasonable set which matches the details of the observed images over as wide a range as possible.
The software available in the facility is a package known as "JEMS"
written by Peter Stadelmann in Switzerland. This package can simulate images or
diffraction patterns (both SADP and Convergent Beam) from complex crystals with many
atoms, or from cells of material incorporating defects. It can show the results as
2-dimensional images or as linescans. It is also able to draw pictures of the crystal
structures in correct perspective. The simulated images can be exported for use in one of
the image presentation packages for
comparison with experimental images.
MIT-CMSE Electron Microscopy/tonygr@MIT.EDU
Document last reviewed September 26th. 2007.