LOW-VOLTAGE SCANNING ELECTRON-MICROSCOPY OF POLYMERS

Micromorphological and microstructural characterizations of the type a nd degree of crystallinity and the relative dispersion of phases withi n polymers, as well as in the study of their surfaces and associated i nterfaces, offer a number of challenges in the field of materials scie nce of polymers. Microscopy is a natural methodology for the acquisiti on of microstructural information, but for polymers there are few stra ightforward techniques. Conventional electron microscopy methods are l imited in their ability to address fine surface details or to determin e the bulk microstructure of multicomponent polymeric materials. Somet imes these problems can be overcome, but only within the practical res trictions associated with meticulous sample preparation. An extremely promising and efficient alternative to conventional approaches is the state-of-the-art, low-voltage scanning electron microscope (LVSEM). It is demonstrated here that straightforward operation of anLVSEM equipp ed with a field emission gun (FEG) source can produce topographical co ntrast secondary electron images of polymers at substantially higher m agnifications than a conventional SEM, and with a resolution that riva ls TEM. An added advantage is the capability of being able to produce contrast based on differences in chemical composition within the sampl e. The ability to produce quality images at low accelerating beam volt ages minimizes beam damage to the sample, and affords an operating win dow (e.g. E(2)) where the sample does not build up negative charge. Th is obviates the normal requirement to coat samples with a conductive l ayer.We also describe experimental and theoretical developments that c an help us to understand the physics of interaction between low-voltag e electron beams and polymer samples. This knowledge base, along with further theoretical and instrumental development and the subsequent ap plications to polymers, promises a whole new field of electron microsc ope methodology based on the LVSEM.