Condensed-Matter Physics & Materials Science Seminar

Scanning transmission electron microscopy (STEM) offers many imaging modes based on both elastic and inelastic scattering of the incident electron probe. These can be used to gain complementary information about a sample and also provide insights into the image formation processes responsible for each type of image. For example, the electrons scattered through large angles into an annular dark field detector cannot also be scattered into a bright field detector. Electron energy loss spectroscopy (EELS) provides information about electrons that have undergone a range of energy losses. The elastically scattered and thermal diffuse scattered electrons form the zero loss peak (ZLP). The ZLP can be used to provide insight into the formation of images based on low-loss and core-loss events, the so called “preservation of contrast”.

In this presentation the processes contributing to the formation of atomic resolution images in the STEM will be examined. In particular we will examine image localization and contrast and the requirements for maximizing each. The relationship between images formed by core-loss EELS and ZLP will also be examined.

This research was sponsored by the Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, U.S. Department of Energy and by appointment (MPO) to the ORNL Postdoctoral Research Program administered jointly by ORNL and ORISE and by the ORNL Laboratory Directed Research and Development Program.