Reconstructed oxide structures stable in air: Silicate monolayers on hexagonal SiC surfaces

Ultrathin oxide layers on hexagonal SiC surfaces were studied using low-ene rgy electron diffraction (LEED) and Auger electron spectroscopy (AES). SiC( 0001) and SiC(000 (1) over bar). samples were ex situ prepared using therma l hydrogen etching or a microwave powered, hydrogen plasma treatment. A wel l ordered (root 3X root 3)R30 degrees reconstructed surface is observed by LEED: immediately upon introduction into vacuum. The samples contain oxygen of approximately one layer equivalent bonded to Si atoms as indicated by A ES. From a full dynamical LEED structure analysis carried out for the SiC(0 00 (1) over bar) surface the crystallographic structure is determined: The silicon oxide is arranged as a silicate (Si2O3) layer on top of the SiC sub strate, forming rings of (root 3X root 3)R30 degrees periodicity with twofo ld coordinated oxygen atoms in the topmost position. The oxygen incorporati on into the surface presumably proceeds via rapid oxidation in air of the w ell ordered topmost substrate bilayer. The extreme stability of the resulti ng surface reconstruction is caused by the absence of dangling bonds in the surface terminating silicate layer. On the SiC(0001) surface a similar sil icate type layer terminated by its oxygen atoms is found by the LEED analys is. However, the adlayer and substrate are bonded via a linear Si-O-Si bond . (C) 1999 American Vacuum Society. [S0734-2101(99)03304-7].