Imaging Polymer Systems with High-Angle Annular Dark Field Scanning Transmission Electron Microscopy (HAADF−STEM)

We have analyzed the nanoscale organization of various polymer systems by utilizing high-angle annular dark field scanning transmission electron microscopy (HAADF−STEM). All systems under investigation are purely carbon based; in some cases staining was used for comparison with conventional transmission electron microscopy (CTEM) imaging. For contrast creation we have applied density differences rather than differences in elemental composition of the materials. Because HAADF−STEM is an incoherent imaging technique, which provides images easy to interpret due to the lack of phase contrast, the high signal-to-noise ratio and the linearity of the signal intensity, imaging artifacts are substantially reduced and additional information on the nanoscale organization of polymer materials is obtained that is not accessible by CTEM. Exemplary, we present HAADF−STEM results form four different polymer systems—a rubber blend, a carbon black filled conductive nanocomposite, a functional blend as applied for the photoactive layer of a polymer solar cell, and semicrystalline polyethylene—and discuss critically contrast origin and the advantages of HAADF−STEM imaging for morphology characterization of polymer systems.