We report on the interface between graphene and 4H-SiC͑0001͒ as investigated by scanning tunneling microscopy ͑STM͒ and low energy electron diffraction ͑LEED͒. It is characterized by the so-called ͑6 ͱ 3 ϫ 6 ͱ 3͒R30°reconstruction, whose structural properties are still controversially discussed but at the same time are crucial for the controlled growth of homogeneous high-quality large-terrace graphene surfaces. We discuss the role of three observed phases with periodicities ͑6 ͱ 3 ϫ 6 ͱ 3͒R30°, ͑6 ϫ 6͒, and ͑5 ϫ 5͒. Their LEED intensity levels and spectra strongly depend on the surface preparation procedure applied. The graphitization process imprints distinct features in the STM images as well as in the LEED spectra. The latter have the potential for an easy and practicable determination of the number of graphene layers by means of LEED.

The SiC͑111͒-͑333͒ phase was analyzed by scanning tunneling microscopy (STM), low-energy electron diffraction (LEED) holography, density functional theory (DFT), and conventional LEED. A single adatom per unit cell found in STM acts as a beam splitter for the holographic inversion of discrete LEED spot intensities. The resulting 3D image guides the detailed analyses by LEED and DFT which find a Si tetramer on a twisted Si adlayer with cloverlike rings. This twist model with one dangling bond left per unit cell represents a novel ͑n3n͒-reconstruction mechanism of group-IV (111) surfaces. [S0031-9007(97)

The preparation of hexagonal {0001} 4H and 6H silicon carbide surfaces by hydrogen plasma or etching in hydrogen flow produces highly ordered monolayers of silicon dioxide. Their structure and epitaxial relationship to the SiC substrate were analyzed by quantitative low-energy electron diffraction and Auger electron spectroscopy. The bond angles and distances retrieved agree with those of bulk SiO2. Due to the saturation of all dangling bonds the semiconductor surface is passivated and preserves its perfect order also in air. The practically ideal oxide monolayers may serve as a seed for growing epitaxial oxides with low defect density and only few structural distortions at the interface to the SiC substrate.

Promoted by Si enrichment during the formation of the reconstructed ͑ p 3 3 p 3 ͒R30 ± phase on hexagonal SiC(0001) a cubic stacking sequence develops at the surface. The reconstruction is ultimately resolved to consist of Si adatoms in T 4 sites as found by quantitative LEED crystallography. Prior to the ͑ p 3 3 p 3 ͒R30 ± phase evolution mesalike structures with various atomic periodicities are observed by STM. Smoothening of this rough and Si enriched state provides the material for the formation of the modified stacking sequence which could serve as seed for preparation of SiC polytype heterostructures. [S0031-9007(99)08644-5]