Established imaging and diffraction techniques for measuring structure of nanomaterials and soft matter do not show both good contrast and high resolution, and they can cause significant material damage. This is particularly the case for isolated nanostructures such as individual nanoparticles and ultrathin films. For example, identifying the crystallographic phase of an unknown nanoparticle of diameter < 5 nm is extremely difficult, even in the most powerful high-resolution TEMs commercially available today. The problem centers on the generation of electron scattering within small volumes. For structures in the size regime of 10 nm and smaller, electrons with energies of the order of 200 keV exhibit a mean free path for scattering that can easily approach an order of magnitude larger than the particle itself. Decreasing those energies to those typical of an SEM (~ 20 keV) decreases the mean free path to values commensurate with the particle size. As a result, more electrons will scatter, to provide the information-rich content needed to measure crystal phase, crystal orientation, defects, and internal order within nanostructures.
A fully analytical transmission-SEM, or STEM-in-SEM, would not only fuel more thorough characterization of nanoscale structures, enabling more precise process control and material reliability, but it would make available many powerful TEM-like capabilities to a large population of SEM users worldwide, in a diverse range of applications.
Present activities include novel electron detector development, interpretation of image contrast, and application to low-dimensional material systems.