REAL STRUCTURE OF SURFACES AND INTERFACES

Hartmut Fuess

Materials Science, Darmstadt University of Technology, D - 64287 Darmstadt, Germany

Keywords: High resolution electron microscopy; x-ray reflectometry; nanocrystalline materials

Devices for electronic, magnetic or sensoric applications rely very often on the performance of thin films deposited by different techniques on a substrate. Ideally both substrate and film are single crystals hold together by perfect epitaxie. In most practical cases various deviations from that situation arise. The interface may exhibit signs of recrystallization or reconstruction, the film may show twinning or other imperfections. Furthermore surfaces of materials may be modified by ion implantation which gives rise to the formation of new phases as a function of penetration depth.

Suitable crystallographic tools to study the real structure of surfaces and layered materials are grazing incidence X-ray diffraction or reflectometry which are both non-destructive or high resolution electron microscopy (HREM) which does however destruct the sample.

Examples are given on the implantation of carbon ions inter steel in order to improve surface properties, or in semiconductors to produce ohmic contacts. The formation of twinning in thin films of YBCO-supraconductors on SrTiO₃ will be explained. A complete picture of the formation of the recrystallized interface in CoSi₂/Si and CoSi₂/Si_1-xGe_x/Si demonstrates the power of image simulation techniques in HREM. The technical properties of nanocrystalline particles are strongly correlated with their crystalline structure as revealed by HREM.