Stable surface reconstructions on 6H–SiC(0001̄)

We used scanning tunneling microscopy (STM), low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) to identify and investigate stable surface reconstructions on 6H–SiC(0001̄). Starting from ex situ prepared (1×1) ordered surfaces heating of the sample in ultra-high vacuum leads to (3×3), (2×2)C and (1×1)graphitic phases with increasing temperature. The stoichiometry of the phases was determined by AES by comparison to the initial, bulk like (1×1) phase: the (3×3) structure is carbon enriched, while the (2×2)C structure reaches the bulk like stoichiometry again. The two superstructures were investigated in detail by STM revealing significant differences in structural complexity. Additional Si flux during heating produces a silicon enriched surface phase, which also exhibits (2×2) periodicity. However, this new phase, denoted as (2×2)Si, has a different surface structure than the (2×2)C phase obtained by mere heating. Apart from the different stoichiometry this is revealed by significantly different LEED intensities.