Conducting Polymer Films as EM Substrates

Abstract

The developing field of electroactive polymers, when the polymers are manipulated into thin film forms, offers potentially ideal materials for EM substrates. Mechanically, they are strong, flat, thin, and stable in the electron beam. For biological specimens, they are hydrophilic and their chemistry can be adapted to the particular specimen so the attachment can be gentle with no denaturation. They have the excellent electron optical properties of low Z, little grain, good electrical conductivity, and no observable radiation damage in the electron beam. Such films can be made fresh just prior to use to avoid contamination.Up to now, thin C films have been the best EM substrates for direct deposition of biological materials. With high vacuum evaporation of C, 20A thick films with >90% coverage of 4u windows in a holey film can be obtained. However, these films rapidly become hydrophobic by absorbing contaminants from the air and so need something like the wet-film technique or glow discharge to keep them hydrophilic. Even so, there are often hot spots of irreversible attachment of biological molecules causing distortion and even denaturation. Also, C films show a significant phase grain, presumably from C60 microcrystals.