Reflection high-energy electron diffraction pattern calculations for Si(111)-7×7 surface

Abstract

Reflection high-energy electron diffraction (RHEED) pattern intensity calculations were performed within the kinematical approximation for the Si(111)-7×7 reconstructed surface using a structure model containing dimers, adatoms, and stacking faults (DAS) in the surface layers as proposed by Takayanagi et al. By fitting experimental RHEED pattern intensities taken with incident electron energies of 30 and 20 keV along the [1̄1̄2] azimuth, we found that the lateral and vertical positions of atoms in the first two surface layers (i.e., adatom layer and stacking fault layer) are in good agreement with that of an energy minimization calculation (EMC). The best fit to the low-order diffraction spots was obtained when all adatoms were moved out toward vacuum around 0.45 Å from bulk positions, and the average spacing between adatom layer and stacking fault layer was set at (1.23±0.04)Å. If we include the dimer layer in the calculation, using the dimer spacing given by EMC, we found that the relative calculated RHEED pattern intensities slightly deviated from the experimental RHEED patterns. This slight disagreement may be due to incorrect lateral positioning of the dimer atoms by EMC or the kinematical approximation. Also, the calculated relative RHEED pattern intensity is not very sensitive to variations in the spacing between the stacking fault and dimer layers. Finally, our results imply that the kinematical approximation can be used for analyzing the intensities of superlattice RHEED spots in some suitable RHEED patterns.