Low-angle scattering in an electron microscope: Application to polymers

Abstract

A standard unmodified three-stage electron microscope fitted with a double condenser is capable of being used as a low-angle electron diffraction camera. The first condenser is used at maximum excitation to produce a small primary source, which is then focused on the viewing screen by use of the diffraction and projector lenses; the objective lens is not energized. A greatly enlarged diffraction pattern is obtainable showing very high resolution in all parts of the pattern, in particular in the region close to the primary beam where the inherent resolution potential corresponds to several thousand angstrom units in Bragg spacing. Low-angle diffraction from specimens of stretched polyethylene have been studied and reflections corresponding to Bragg spacings of up to near 2000 å were recorded. With the aid of microscope imaging of the area of the specimen contributing to the diffraction pattern, a model for the mechanism of stretching of polyethylene is proposed.