Advances in the Transmission Electron Microscopy of Polymers

Transmission electron microscopy (TEM) of polymers involves the problem definition and methodologies associated with the microscopy of both inorganic and biological materials but cannot be categorized within either of these fields alone. On the one hand, like other synthetic materials, polymers offer the ability to control properties through synthesis and processing, and TEM is a powerful method with which to provide information within the synthesis-structure-property paradigm of materials science and engineering. The well-established techniques of bright/dark-field imaging, electron diffraction, high-resolution imaging, and analytical microscopies are thus all used to study polymers. On the other hand, the electron-specimen interactions are more like those in biological systems. Synthetic polymers and biological materials consist largely of light elements whose elastic interactions with energetic electrons are relatively weak. Generating image contrast can thus be a challenge in polymer TEM. The inelastic electron/soft material interactions are, however, relatively strong. These provide for powerful spectroscopies but also lead to radiation damage. The constraints that damage puts on imaging are far more stringent in polymers than in inorganic systems. This review highlights ongoing advances in contrast generation exploiting both elastic and inelastic electron-polymer interactions and outlines the salient issues determining the achievable spatial resolution in radiation-sensitive materials.