High-resolution core-level study of 6H-SiC(0001)

A photoemission investigation using synchrotron radiation of the (0001) surface of 6H-SiC is reported. The studies were concentrated on the root 3x root 3-R30 degrees and 6 root 3x6 root 3-R30 degrees reconstructed surfaces, but results from the chemically prepared unreconstructed 1x1 surface are also presented. Core-level and valence-band spectra recorded from the 1x1 surface show strong oxygen derived features. For the root 3 and 6 root 3 reconstructed surfaces, which were prepared by heating the 1x1 surface to temperatures of ca. 950 degrees C and 1150 degrees C, respectively, no oxygen derived features an detected. The core-level and valence-band spectra are found to be significantly different on these reconstructed surfaces. Recorded high-resolution core-level spectra reveal unambiguously the presence of surface shifted components in both the Si 2p and C 1s core levels on the reconstructed surfaces. For the root 3 reconstruction, two surface shifted components an observed both in the Si 2p and C 1s level. These findings cannot be explained by a structural model composed of Si or C adatoms on top of a Si-C bilayer. For the 6 root 3 reconstruction, the surface region is found to contain a considerably larger amount of carbon. This carbon is found not to be graphitic, since surface shifted C 1s components with binding energies different from the graphitic C 1s peak are observed. Clear evidence of graphitization is revealed only after heating to a higher temperature than that required for observing a well-developed 6 root 3 diffraction pattern.