Electron tomography in soft materials

This review summarizes the recent advances in electron tomography (ET) and its application to polymer nanostructures. Truly quantitative three-dimensional (3D) images of polymer nanostructures can now be obtained by reducing or eliminating the missing tilt range in ET experiments. The reduction of the resulting missing wedge provides sub-nanometer resolution, which is sufficiently small for soft materials. Because soft materials often exhibit hierarchical structures, observation of a large volume with edges several micrometers in length is important to capture the structural elements on a scale larger than tens of nanometers. The introduction of scanning optics to ET has made it possible to obtain 3D data from micrometer-thick polymer specimens by using conventional electron microscopes at a relatively low accelerating voltage of 200 kV. We present some examples of the structural analysis of soft materials, such as nanostructures of self-assembled block copolymers and fuel cell electrodes.