Multiple scattering effects on X-ray photoelectron diffraction from Si(111) root 3x root 3-Ag and -Sb surfaces

The effects of multiple scattering (MS) on X-ray photoelectron diffraction (XPD) from Si(111)root 3 x root 3-Ag and -Sb (referred to as root 3-Ag and -Sb) surfaces have been studied using a MS concentric-shell algorithm for sufficiently large clusters. Significant MS effects that cannot be reconciled by a kinematical treatment have been seen for the root 3-Ag surface, but not for the root 3-Sb surface. This indicates that previous XPD studies on the root 3-Ag surface were incomplete due to the failure of single scattering theory, and explains why prior XPD studies on this surface were not successful at first in predicting a presently widely accepted model. With a reliability factor analysis for MS simulations, we have shown that the root 3-Ag surface is formed in a honeycomb-chained-trimer model with its structural parameters consistent with those from other techniques.