Current efforts to develop nanostructured materials and devices are stimulating the implementation of new experimental probes of the structure and chemical composition of solids on the atomic scale. High-resolution transmission electron microscopy (HRTEM) has been widely used in the last decades to study the structure and the properties of materials at the highest spatial resolution. More recently high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) imaging has demonstrated sub-Angstrom resolution together with high sensitivity to the chemical composition of the material allowing to study both the structure and the chemistry of interfaces at atomic resolution without the uncertainty related to the phase problem in HRTEM. Here, basic principles of HAADF imaging will be illustrated together with recent applications to the study at atomic resolution of interfaces of materials. It will be shown how HAADF can be used to probe the distribution of guest chemical species in a host matrix. Furthermore, a new approach to the simulation of HAADF images will be introduced together with a new approach to the determination of important experimental parameters as defocus values and specimen thickness.
1 Jan 2006
Volume: 51 Issue: 1 Pages: 23-32
Archives of metallurgy and materials