A new carbon rich model of the α-SiC(0001)√3x√3 surface reconstruction

This paper presents an analysis of the energetics of a few possible candidates for the structural model of the alpha-SiC(0001)root 3 x root 3 surface reconstruction. The analysis is based on quantum chemical calculations of MNDO type (AM1 parametrization). The results indicate that out of the models tested, the energetically most stable structure is made of C-6 rings bonded to the stoichiometric substrate via a 2/3 monolayer of silicon. The structure has one Si dangling bond per root 3 x root 3 surface unit cell (SUC) and as such should normally represent a conducting surface. However, instead of being exposed, the dangling bonds here are localized on the Si substrate atoms below the centers of the C-6 rings. The photoemission signal from the dangling bond states is then likely to be suppressed, thus making the surface appear semiconducting in photoemission experiments [L.I. Johansson, F. Owman, P. Martensson, Surf. Sci. 360 (1996) L478]. Moreover, the pattern of the core level shifts of the SiC(0001)root 3 x root 3 surface [L.I. Johansson, F. Owman, P. Martensson, Phys. Rev. B 53 (1996) 13793] agrees with the number of charge inequivalent Si and C atoms around the surface in the proposed model. Finally, the measured Si(LVV)/C(KLL) Auger intensity ratio of the surface at different stages of annealing [T. Tsukamoto et al., Surf Sci, 371 (1997) 316] agrees with the proposed model of the reconstruction. (C) 1998 Elsevier Science B.V. All rights reserved.