Moiré patterns and other crystallinity effects in the electron microscopy of polyethylene single crystals

Abstract

Experimental. During our research on polymers we found that the crystallinity (as judged by electron diffraction) was lost by the irradiation of an electron beam intense enough to permit focusing of the picture, though the shape of the objects was not changed. Consequently, no high or medium power electron micrographs could be obtained of specimens which were still crystalline at the time the photograph was recorded. We have now overcome this difficulty by restricting the irradiation during focusing to a small area of the object with the double condenser system of the Siemens Elmiskop I. The beam intensity was then reduced and a part of the specimen not previously irradiated was brought into the beam and photographed. This technique enabled us to record crystallinity effects not previously observed. Fast working was essential as the specimens deteriorated even with the lowest intensities suitable for photography.