Si/6H-SiC(0001): An unexpected cubic 4x3 Si phase overlayer

We investigate Si deposition on the 6H-SiC(0001) 3x3 surface reconstruction by atom-resolved scanning tunneling microscopy. Upon thermal annealing, the Si thin film forms an unexpected structure having dimer rows in a cubic 4x3 surface array. Such a 4x3 Si phase has a very open surface very likely being at the origin of the exceptionally high reactivity to oxygen of the Si/6H-SiC(0001) system. These findings are relevant in silicon carbide oxidation. (C) 2001 American Institute of Physics.