The group has used a Scanning Transmission Electron Microscope to study the structure and chemistry of individual grain boundaries artificially created between single crystals as well as those in polycrystalline material. Examples of microscope images are shown in Figures 1 and 2 . Figure 1 shows how the atomic structure near a grain boundary can be seen. This microscope can also be used to measure the chemical composition with near atomic resolution. The group is beginning to extend these studies to catalytic materials, like Cerium oxide, for which an electron-microscope picture is shown in Figure 3 .
Cerium oxide catalyzes reactions involving oxygen.
For example, it can be used to convert SO 2 to S, reducing acid rain, or to convert poisonous CO to harmless CO 2 . Biological contaminants, such as bacteria and viruses, may also be eliminated using this semiconducting oxide catalyst. This represents one of the great unsolved scientific problems of our age. All the high-T c superconductors are derived from antiferromagnetic insulators that contain the square planar CuO 2 lattice. A great deal of progress has been made in understanding the insulators but the physics of the superconductors is much more complex, and little consensus has been reached as to the correct physical description of this system.