DYNAMICAL ANALYSIS OF A RHEED PATTERN FROM THE SI(111)-7X7 SURFACE

The multislice formalism of Cowley and Moodie [Acta Crystallogr. 10 (1 957) 609] with a recently developed edge-patching method has been appl ied to the analysis of an experimental RHEED (reflection high energy e lectron diffraction) pattern from the Si(111)-7 x 7 surface. Several d ata sets of atomic coordinates for the Si(111)-7 x 7 reconstruction, o ptimized by different approaches, have been evaluated based upon compa rison of visually estimated intensity ordering between the observed an d calculated patterns. The results show that compared to other data se ts, the coordinates optimized by ab initio-parallel computation appear closer to the true structure, so far as the RHEED in the current sche me can judge. The analysis also shows that the intensities of a RHEED pattern taken from the surface are highly surface sensitive. The surfa ce sensitivity extends to the whole selvage region of interest with a depth of approximately 10 angstrom. The correlation between mean inner potential V0 and the angle of incidence theta has also been investiga ted. This indicates that if the angle of incidence is measured with er rors less than +/-0.05-degrees for this specific case, V0 can be deter mined with the accuracy of approximately +/-10%, and vice versa.