Calculation of surface x-ray diffraction patterns in total external reflection conditions

Abstract

The high brilliance of the new generation of synchrotron radiation sources improves the grazing incidence x-ray diffraction techniques and leads to great advances in the determination of crystal surface structures. The evaluation of the diffraction pattern intensity can be obtained in the distorted-wave approximation introduced by Vineyard. In conditions of total reflection, typical penetration depths are about 50 Å and only the atoms in the near-surface layers interact with the electric field and produce the diffraction pattern. This model is the ground for a simulation code developed in order to calculate the diffracted peaks intensity of reconstructed and/or relaxed surfaces. An example of application, the Au (110) (1×2) reconstructed surface, is given. The intensity and the position of the diffraction peaks are determined for different values of the azimuthal angle and for different diffraction orders. The program takes into account the parameters of the beamline Advanced Line for Overlayer Interface and Surface Analysis (ALOISA) which will be available at the storage ring ELETTRA in Trieste.