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

Experimental and theoretical studies of the Si(001)-2 X 1 reconstruction are reviewed. The review indicates that a technique, which is sensitive 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 basic 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 resolving the controversies over the Si(001)-2 X 1 reconstruction. The multislice formalism of Cowley and Moodie with a recently developed edge-patching method has been applied to the analyses of several experimental RHEED patterns from the Si(001)-2 X 1 surface. The calculation results reject the static buckled model for the surface. The analyses also show that the information to determine which one of three possible symmetrical models for the surface (namely 'inherent symmetry', 'individual-dimer-random-symmetry' and 'domain-random-symmetry') is closest to the true structure can be found in the experimental RHEED patterns. The results indicate that the intensity symmetry (symmetry regarding the intensities rather than geometrical locations of spots) of a RHEED pattern from the Si(001)-2 X 1 surface is very sensitive to the structure variations of the surface.