Diffuse LEED theory from surfaces partially covered with molecules. I. Calculation of the transition matrix of a molecule

Diffuse backscattering of electrons at a single crystal surface is often due to the adsorption of atoms or molecules whose presence breaks the translational symmetry of the substrate surface. Two different approaches to the diffuse LEED problem have been given. The first, due to Saldin and Pendry, considers only a single molecule adsorbed at the surface. The second, due to the present authors, considers a partially ordered overlayer of molecules and takes up the aspect of the diffuse LEED problem. The first aim of this paper is to compare both approaches. In the case of adsorbates randomly and sparsely distributed at the surface, the authors show that they are equivalent. However, each of them uses a different concept for the renormalized t-matrix of the adsorbate. The second aim of this paper is to provide a theory of multiple scattering of electrons from a molecule, from which the authors can derive a suitable expression for the t-matrix that one can readily use in the diffuse LEED theory. Application to the simple case of the CO molecule is examined here.