Structural and vibrational properties of 6H-SiC(0001) surfaces studied using STM/HREELS

The structural and vibrational properties of the 6H-SiC(0001) surface have been investigated using a combined scanning tunneling microscopy (STM)/high resolution electron energy loss spectroscopy (HREELS) system. The STM was used to study the structure of the (root 3 x root 3) surface. The STM images of this surface exhibited contrast reversal between the filled and empty state images, which is inconsistent with previously proposed adatom models. In addition, the HREELS data shows no indication of H on the (root 3 x root 3) surface. Based on this and recent photoemission data, we propose a surface vacancy model for the (root 3 x root 3) surface. We have also performed the first study of the surface phonons of clean, well characterized SiC surface structures using HREELS. In order to confirm that the near surface structure and stoichiometry has no effect on the frequency of the Fuchs-KLeiwer (FK) phonon we prepared clean (root 3 x root 3) and (3 x 3) surfaces. These two surface phases have very different structures and stoichiometry. The FK phonon frequency was the same on both surfaces. Thus, we verified that the assumption made in previous studies is valid. Moreover, we found that the adsorption of 0.3 monolayers of oxygen also causes no change in the phonon frequency. (C) 1997 Elsevier Science B.V.