Scattering of thermal atoms by disordered surfaces: II. Adsorbed defects

Abstract

We consider a periodic surface on which defects are absorbed. An incident particle is scattered by this surface and the solution of the scattering equation is given by an expansion where the term of order n gives the multiple scattering effects on n defects. The coherent peak intensities and the incoherent cross section are expressed as functions of matrix elements describing the scattering process and of the many body correlation functions of defect positions. The diffraction peak intensities of the perfect surface are modified by the presence of defects and on a flat surface they induce an increase of the small diffraction peak intensities. The incoherent cross section is periodic on the reciprocal lattice of defect sites and is reinforced around the most intense diffraction peaks. For small coverage, this cross section is equal to the product of a form factor and the Fourier transform of the two body correlation function. For a random distribution of defects, the correlation functions are constant and a measurement gives directly the form factor. For coverages near 0.5, the defects can gather in domains. In this case, one can show that an oscillation of diffraction peak heights or widths should be observed as the incident conditions vary.