Contributions of crystallography to materials science

The properties of materials used in various domains of science and engineering are directly correlated to the microstructure. Crystallography is devoted to the investigaton of microstructure of substances and materials by a variety of diffraction and spectroscopic methods. Several examples related to research in the department of materials science at the Technical University of Darmstadt are presented. The structure and dynamics of aromatic host molecules in catalytically active zeolites are investigated by X-ray and neutron diffraction and NMR-spectroscopy combined with inelastic neutron scattering. Surfaces and interfaces of semiconductors and thin superconducting films are studied by grazing incidence techniques. By examination of the reflectogram details on thickness, composition, surface roughness and a possible modification of these values are obtained. Transmission electron microscopy provides complementary information on the structure of interfaces, especially through the support of simulated images by a multi-slice method. Work is presented on CoSi2-films on Si and wafers of GaAs with LaB6 films. Modification of these wafers by ion mixing techniques is attempted. Furthermore, surface hardening of steel by ion implantation (carbon and nitrogen) is a way of improving tribological properties. Grazing incidence provides results on the formation of different carbides as a function of depth. Superconducting films of Bi2Sr2CaCu2O8 on SrTiO3 showed an improvement by a factor of 10 in critical current density by creating holes (Xe, Au, U-irradiation) as pinning centres. The examination by TEM revealed an amorphization of the channels with clear boundaries between the channel and nonirradiated material.