A photoemission investigation using synchrotron radiation of the ͑0001͒ surface of 6H-SiC is reported. The studies were concentrated on the )ϫ)-R30°and 6)ϫ6)-R30°reconstructed surfaces, but results from the chemically prepared unreconstructed 1ϫ1 surface are also presented. Core-level and valence-band spectra recorded from the 1ϫ1 surface show strong oxygen derived features. For the ) and 6) reconstructed surfaces, which were prepared by heating the 1ϫ1 surface to temperatures of ca. 950°C and 1150°C, respectively, no oxygen derived features are 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 2 p and C 1s core levels on the reconstructed surfaces. For the ) reconstruction, two surface shifted components are observed both in the Si 2 p 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) 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) diffraction pattern.

No abstract

No abstract

No abstract

Recent findings concerning primarily the √3×√3 and 6√3×6√3 reconstructed surfaces of 6H‐SiC(0001) are reviewed. First, the morphology of some different types of 6H‐SiC crystals is discussed. The scanning tunneling microscopy (STM) and atomic force microscopy (AFM) results presented show that surfaces with a morphology suitable for surface investigations can be prepared using sublimation‐ or hydrogen‐etching. Then results obtained concerning the atomic and electronic structure for the reconstructed surfaces, prepared using an ex situ method for oxide removal and in situ heating, are presented. For the √3×√3 reconstruction, recent STM and photoelectron spectroscopy (PES) data are discussed in view of available theoretical results. The STM images presented are shown to be consistent with a structural model of Si or C adatoms in threefold symmetric sites. The theoretical results favor Si adatoms in T4 sites as the optimal configuration for this reconstruction. However, the surface shifted components extracted in studies of the C 1s and Si 2p core levels and the location of a surface state band mapped out in angle resolved experiments cannot be explained using this structural model. At present, there is no structural model that satisfactorily can explain all experimental findings for the √3×√3 reconstruction. A monocrystalline graphite overlayer on top of bulk‐terminated or √3×√3‐reconstructed SiC has previously been proposed to explain the 6√3×6√3‐reconstructed surface. However, STM and PES results are presented that unambiguously show that there is no graphite on the surface when a well developed 6√3×6√3 low‐energy electron diffraction (LEED) pattern is observed. The STM images recorded during the gradual development of the 6√3×6√3 surface show growing fractions of pseudo‐periodic 6×6 and 5×5 reconstructions. These reconstructed regions dominate on the surface, but small √3×√3‐reconstructed regions are still present when a well developed 6√3×6√3 LEED pattern is observed. It is shown that the 6√3×6√3 LEED pattern can be fully explained by scattering from surfaces with a mixture of 6×6, 5×5 and √3×√3 reconstructions. Due to the complexity of the STM data, no structural model is proposed for the 6×6 and 5×5 reconstructions. STM and PES results are presented showing that graphitization of the surface is obtained only after heating at higher temperatures than that required for observing a well developed 6√3×6√3 LEED pattern. The STM images then show that the graphite appears as a monocrystalline overlayer on top of the 6×6 reconstruction and not on bulk‐terminated or √3×√3‐reconstructed SiC(0001).

No abstract

No abstract

No abstract