ANGLE-SCANNED PHOTOELECTRON DIFFRACTION: A STRUCTURAL PROBE FOR NEAR-SURFACE ATOMIC LAYERS

摘要

Electrons emitted from the core levels of a photon-irradiated crystalline sample undergo scattering by atoms in the vicinity of the emitting species. Subsequent interference phenomena between the electron wave portions propagating to the detector produce intensity modulations as a function of the direction of detection. This process constitutes the physical basis of the angle-scanned X-ray Photoelectron Diffraction (XPD) technique. The resulting modulations, properly interpreted, are rich in structural information concerning the near-surface atomic layers. In the present notes, after an introduction to the principles of XPD, some selected results in the field of chemisorption and ultrathin epitaxial films will be reported in order to outline the merits of the technique. Qualitative structural information (e.g. growth modes and lattice distortions, orientation of chemisorbed molecules) can be directly obtained from the experimental raw data without any need of theoretical simulation. On the other hand, quantitative structural parameters and chemisorption sites may be deduced by using a trial-and-error fitting procedure based on simple single-scattering models.