SURFACE-STRUCTURE DETERMINATION USING X-RAY STANDING WAVES - A SIMPLEVIEW

In the application of x-ray standing wave (XSW) methods to the determi nation of surface structures, the experiment provides two structural p arameters: the coherent position and the coherent fraction. For simple , single-high-symmetry-site adsorption systems, the interpretation of these parameters in terms of a structural model is trivial, but in the case of lower-symmetry adsorption sites, or multiple adsorption sites (including those associated with coincidence lattice structures), the se parameters are related to spatial distribution functions through a Fourier integral. A particularly simple way of viewing this result, in terms of vector (Argand) diagrams, allows many simple cases and gener al theorems concerning the interconnection of the structure and the XS W fitting parameters to be visualized. The application of this approac h is illustrated with particular reference to recent studies of adsorp tion on FCC (111) metal surfaces, but some generalization to other sur faces is included.