Initial C incorporation on Si(111) studied by STM

We report the initial C incorporation on Si(111) by the C$_2 $H$_2$ deposition at 500 $^{ \circ}$C using scanning tunneling microscopy. We find that the thermally decomposed C atoms from C$_2$H$_2$ are incorporated into the sub-layer of Si(111) surface preserving $7 \times 7$ dimer-adatom-stacking fault structure. C atoms are mainly incorporated into the underneath of corner adatoms of faulted halves of Si(111) surface at 500 $^{ \circ} $C. Our experimental results are compared with the previous reports of several authors regarding the C-incorporated Si(111)-$\sqrt{3} \times \sqrt{3}$ superstructure induced by the higher C$_2$H$_2$ exposure at the similar substrate temperature range.