X-ray photoelectron diffraction from (3x3) and (√3x√3)R30° (0001)_Si 6H-SiC surfaces

High-resolution (±1°) x-ray photoelectron diffraction (XPD) patterns were obtained along high symmetry azimuths of the (3 X 3) and (√3 X √3)R30° reconstructed (0001)_Si 6H-SiC surfaces. The data were compared to XPD patterns obtained from (7 X 7) Si (111) as well as to models proposed for the (3 X 3) and (√3 X √3)R30° 6H-SiC reconstructions. Forward scattering features similar to those observed from the (7 X 7) Si (111) were also observed from the (√3 X √3)R30° 6H-SiC (0001)_Si surface. Additional structures were found and attributed to the substitution of carbon atoms for silicon. Unlike (1 X 1) and (7 X 7) Si (111) surfaces, the XPD patterns of (3 X 3) and (√3 X √3)R30° SiC (0001)_Si surfaces are different which is due to the presence of an incomplete bilayer of Si on the (3 X 3) surface. The most significant difference with the Si system is the equivalence of the [1010] and [0110] azimuths in the (3 X 3) structure. These results are consistent with a faulted Si bilayer stacking sequence which was proposed based on scanning tunneling microscopy observations.