Stable surface reconstructions on 6H-SiC(0001)

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(000 (1) over bar). Starting from ex situ prepared (1 x 1) ordered surfaces heating of the sample in ultra-high vacuum leads to (3 x 3), (2 x 2), and (1 x 1)(graphitic) phases with increasing temperature. The stoichiometry of the phases was determined by AES by comparison to the initial, bulk like (1 x 1) phase: the (3 x 3) structure is carbon enriched, while the (2 x 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 x 2) periodicity. However, this new phase, denoted as (2 x 2)(Si), has a different surface structure than the (2 x 2)(C) phase obtained by mere heating. Apart from the different stoichiometry this is revealed by significantly different LEED intensities. (C) 1999 Elsevier Science S.A. All rights reserved.