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

Abstract

A photoemission investigation using synchrotron radiation of the (0001) surface of 6H-SiC is reported. The studies were concentrated on the $\sqrt{3}$\ifmmode\times\else\texttimes\fi{}$\sqrt{3}$-R30\ifmmode^\circ\else\textdegree\fi{} and 6$\sqrt{3}$\ifmmode\times\else\texttimes\fi{}6$\sqrt{3}$-R30\ifmmode^\circ\else\textdegree\fi{} reconstructed surfaces, but results from the chemically prepared unreconstructed 1\ifmmode\times\else\texttimes\fi{}1 surface are also presented. Core-level and valence-band spectra recorded from the 1\ifmmode\times\else\texttimes\fi{}1 surface show strong oxygen derived features. For the $\sqrt{3}$ and 6$\sqrt{3}$ reconstructed surfaces, which were prepared by heating the 1\ifmmode\times\else\texttimes\fi{}1 surface to temperatures of ca. 950 \ifmmode^\circ\else\textdegree\fi{}C and 1150 \ifmmode^\circ\else\textdegree\fi{}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 2p and C 1s core levels on the reconstructed surfaces. For the $\sqrt{3}$ reconstruction, two surface shifted components are 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$\sqrt{3}$ 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$\sqrt{3}$ diffraction pattern. \textcopyright{} 1996 The American Physical Society.