Carbon-associated Si(001)-c(4×4) reconstruction dosed with hydrogen

It has recently been recognized that initial carbon (C) accommodation on Si(001)-(2×1) surfaces (less than 1 monolayer, at 600°C and using various C precursors) causes a c(4×4) surface reconstruction. In this paper we intend to determine the C lattice sites associated to this reconstruction. C 1s XPS signatures indicate a main contribution of C atoms dominantly located in substitutional subsurface sites and a weaker contribution, of 1.6 eV higher binding energy, attributed to C surface sites. C 1s X-ray photoelectron diffraction polar observations along 〈010〉 azimuths ascertain C location within the first five Si layers and the C atoms at the origin of the observed angular modulations are necessarily located from the third to fifth subsurface layers. By c(4×4) surface exposure to atomic hydrogen at room temperature, a 1×1 LEED diagram is restored. As for the Si(001)-(2×1) reconstruction, it demonstrates a break of hydrogen-saturated surface dimers. The latter may be restored by annealing but with a kinetics different from that of a simple Si dihydride desorption. These results essentially support c(4×4) reconstruction models with surface dimers including C atoms and a subsurface C-rich SinC alloy.