SYMMETRY ANALYSIS OF THE RHEED PATTERNS FROM THE SI(001)-2X1 SURFACES

Experimental and theoretical studies of the Si(001)-2 X 1 reconstructi on are reviewed. The review indicates that a technique, which is sensi tive and fast enough to detect the basic symmetry of the Si(001)-2 X 1 surface, seems still unavailable and the local density approximation (LDA) adopted in calculations makes it difficult to determine the basi c electronic property of the surface: metallic or semiconducting. The review of the distinct features of the reflection high-energy electron diffraction (RHEED) technique shows that it dearly has a role in reso lving the controversies over the Si(001)-2 X 1 reconstruction. The mul tislice formalism of Cowley and Moodie with a recently developed edge- patching method has been applied to the analyses of several experiment al RHEED patterns from the Si(001)-2 X 1 surface. The calculation resu lts reject the static buckled model for the surface. The analyses also show that the information to determine which one of three possible sy mmetrical models for the surface (namely 'inherent symmetry', 'individ ual-dimer-random-symmetry' and 'domain-random-symmetry') is closest to the true structure can be found in the experimental RHEED patterns. T he results indicate that the intensity symmetry (symmetry regarding th e intensities rather than geometrical locations of spots) of a RHEED p attern from the Si(001)-2 X 1 surface is very sensitive to the structu re variations of the surface.