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