Probing the local structure and bonding at interfaces and defects using EELS in the TEM

In monolithic materials the presence of, and structure associated with, defects and grain boundaries often control the overall macroscopic properties of the bulk material, Similarly in composite materials the interfaces between the various constituents may also be property-determining Clearly it is desirable to be able to determine the structure and chemistry of such isolated, nonperiodic features using a spectroscopic technique capable of resolving chemical-state information from areas of atomic dimensions, Electron energy-loss spectroscopy (EELS) conducted in the (scanning) transmission electron microscope ((S)TEM) constitutes such a spatially resolved tool, When combined with atomic-resolution imaging and appropriate surface-sensitive spectroscopic techniques, important information about elemental distributions, local coordinations and valence states of atomic species at interfaces and defects may be derived. Examples drawn from studies of grain boundaries, interfaces in ceramic and metal matrix composites and investigations of defects in diamond are highlighted in order to illustrate this methodology.