STRUCTURAL DETERMINATION OF BETA-SIC(100)-C(2X2) FROM C-1S SURFACE-CORE-EXCITON AND SI-2P ABSORPTION

The marked polarization dependences of two C-ls surface-core-exciton t ransitions-as revealed by near-edge x-ray absorption fine structure on single-domain beta-SiC(100)-c(2 X 2)-are used, together with Si-2p ab sorption and molecular orbital cluster calculations, to settle the lon g-standing controversy over the structure of this surface. The surface is terminated with staggered rows of unusual, nearly triply-bonded C dimers bridging underlayer Si dimers. Resonant valence-band photoemiss ion accompanying C-ls exciton autoionization reveals directly the elec tronic structure of the C dimers.