The structure of α′-copper phthalocyanine and its susceptibility to radiation damage

CHANGES in electron diffraction patterns are a very sensitive monitor of the radiation damage experienced by a periodic specimen under observation in an electron microscope. In the study of α ′-copper phthalocyanine reported here, we have recorded the diffraction pattern of the a * – c * plane as irradiation proceeds, and from its behaviour we have been able to confirm the structure of the undamaged crystal and put realistic limits on the electron dose allowable if molecular images of a given resolution are to be obtained. We can also confirm the suggestion of Isaacson et al. 1 that the heavily damaged material forms a regular matrix, and that this matrix has approximately the same structure as that observed in previously published molecular images of this specimen 2,3 .