Scanning Transmission Electron Microscopy Of Polymer Single Crystals

Scanning transmission electron microscopy (STEM) has several advantages over conventional transmission electron microscopy (CTEM) for studying the structure of polymer single crystals. A major limitation in the electron microscopy of polymer single crystals is the rapid loss of diffraction contrast due to destruction of crystallinity by beam-induced cross-linking and/or chain scission. Electronic signal amplification, which is inherent in the STEM image forming system, allows images to be formed at lower incident beam dosages than required for photographic recording in the CTEM. This lowers the beam damage rate and routinely permits recording of bright field, dark field, and electron diffraction sequences, or alternatively, single images at high magnification for high resolution.An SEM operated in the STEM mode at voltages in the range from 20 to 50 KV will give good images of single crystals at magnifications up to 10,000X. An STEM operated at 100 KV with cold stage techniques further improves the imaging capabilities, since beam damage is reduced by 5 to 10 times with an increase in accelerating voltage and lower sample temperatures.1