Photoelectron diffraction study of the 6H-SiC(0001) √3x√3 R30° reconstruction -: art. no. 165327

We have analyzed the root 3x root 3 R30 degrees reconstruction of the Si-terminated 6H-SiC(0001) surface using high-resolution photoemission and photoelectron diffraction. We have acquired a large set of Si 2p and C 1s spectra in the form of azimuthal scans at different polar angles and photon energies. In the case of the C 1s core level we have confirmed that one of the surface components reported previously is due to surface contamination. However, in the spectrum of the contamination-free surface, reported here for the first time, we have uncovered a hitherto hidden new component and, therefore, the number of surface components remains at two. We consider different geometries for the surface reconstruction and conclude that only the Si-T-4 model is compatible with the existence of two surface components in both the Si 2p and C 1s spectra. Additionally, we show that multiple-scattering cluster diffraction (MSCD) calculations based on this model reproduce correctly all the intensity modulations. These calculations have also been used to determine the main structural parameters. We have also analyzed the data in the light of the new interpretation of the Si 2p spectrum proposed by Anisimov [Phys. Rev. B 61, 1752 (2000)]. These authors have suggested that new 2p-3p exchange interactions arising in the Mott-Hubbard ground state could completely change the spectrum of the Si adatoms. We have accordingly fitted the Si 2p spectra with a standard 2p(3/2,1/2) doublet representing the bulk component and a triplet representing the emission from the adatoms. Although these two components allow a perfect fitting of all the spectra, we have found that the intensity modulations derived with this model are in complete disagreement with the MSCD calculations, which thereby rules out this interpretation.