Interlayer multiple diffraction in LEED

Abstract

A new classification of interlayer multiple diffraction proceses in LEED is proposed and applied to the unperturbed surface of Ir(100)1 × 1. The method takes advantage of the fact that forward diffraction of a layer is usually strong compared with backward diffraction. Therefore only processes with one backward diffraction event are considered. As a consequence the number of forward diffractions is correlated to the number of layer distances the electron wave has propagated. So, e.g., for two forward diffractions and one backward diffraction at least two layers must be involved and the necessary minimum propagation length is two layer distances. This corresponds to a minimum penetration depth of one layer distance. The method puts all processes to the same order of expansion which require the same minimum propagation length. So an ordering with respect to the electron penetration depth results. Because of the attenuation of the electron wave, sufficiently rapid convergence is achieved which is supported by the existence of a recurrence scheme derived. With ¦ V Oi¦ = 4 eV it turns out that up to about 130 eV the main features of the I( E) spectra are reproduced by expansion orders with a minimum penetration depth of up to two interlayer distances. For higher energies higher orders become important. The method is not to compete with fast schemes of intensity calculations as, e.g., RFS. However, it allows for more detailed information about the importance of the different diffraction processes and provides a deeper understanding of LEED as a whole.