Scanning microdiffraction of polymers

Abstract

Scanning transmission electron microscopy (STEM) has been suggested to have advantages over conventional transmission electron microscopy (CTEM) for the observation of diffraction contrast features and diffraction patterns from radiation-sensitive crystalline polymers. For many applications it is desirable to obtain successive diffraction patterns from very small adjacent areas. Several microarea diffraction techniques are available using CTEM and STEM. The most useful technique is scanning microarea diffraction used in conjunction with STEM dark-field imaging. Using this technique we have obtained diffraction patterns from regions as small as 100 nm×100 nm for a 12 nm thick polyethylene single crystal. Adjacent microarea diffraction patterns can be obtained while only radiation-damaging the diffracting region. This allows mapping of the specimen crystallography on a very fine scale as well as allowing one to obtain a diffraction pattern for selecting various STEM dark-field conditions while only damaging a small portion of the specimen before the dark-field image is recorded.