Leed theory for incommensurate overlayers: Application to graphite on Pt(111)

A dynamical LEED analysis is applied to study the structure of incommensurate overlayers. The previously described BSN method is extended to the incommensurate case, providing an efficient theoretical scheme for calculating the required LEED beam intensities. This method is used to investigate the structure of an incommensurate graphite overlayer on the Pt(111) surface by analyzing the specular diffraction beam intensities at various angles. The measured LEED intensities are well represented by a surface model consisting of a graphite layer 3.70 ± 0.05 Å above the Pt(111) surface, supported by at least a partial layer of “intercalated” carbidic carbon atoms chemisorbed in three-fold hollow sites 1.25 ± 0.10 Å above the Pt(111) surface. A “data subdivision method” is applied in the R-factor analysis to distinguish between the different R-factor minima.