ATOMIC-STRUCTURE OF BETA-SIC(100) SURFACES - AN AB-INITIO STUDY

We examine several different reconstructions of the beta-SiC(100) surface by the ab initio Car-Parrinello method. Our results confirm that the lowest energy c(2 X 2) reconstructed surface consists of triply bonded carbon dimers in a bridging position between neighboring underlying silicon dimers. Added hydrogen atoms bond to the carbon dimers, resulting in a lengthened double-bonded dimer, and a larger separation for the underlying silicon dimers, although those Si bonds do not disappear. The most stable structure found for the (3 X 2) reconstructed surface with a 1/3 monolayer excess of silicon is an alternate dimer row structure rather than the added dimer row model proposed by others. The energetics of various surface reactions that may be involved in growth of SiC are discussed.