Breakdown of the simple kinematic approximation models in high-resolution LEED characterization of the initial growth of Si/Si(111)

We have developed a new software for spot profile analysis low energy electron diffraction experiments, which allows variation of the beam energy during a measurement. It enables following multiple diffraction peaks simultaneously. We have explored this possibility in highly accurate measurements of out-of-phase and in-phase intensity during initial growth of Si/Si(111). Under both diffraction conditions intensity oscillations have been observed, clearly demonstrating the breakdown of the usually applied simple kinematic approximation models. The effective atomic scattering factors related to atomic steps do deviate from those connected to ideal terrace sites. Our novel findings urge great caution when extracting information on the morphology of the surface either from the temporal behavior of the spot heights during growth or from the energy dependence of the central spike in the spot profile. We suggest that dynamic effects, changing upon kinetic roughening of the surface, may be important. However, additional experiments on simpler surfaces are required to fully nail down this statement.