Formation of $\surd $3$\times \surd $3 structure by depositing Si on Si(111)-(5$\times $2)/Au

By depositing Au on a Si(111) surface at an elevated temperature, 5$\times $2, $\surd $3$\times \surd $3, and 6$\times $6 reconstructions emerge successively as the Au coverage increases. Though great efforts have been made to identify atomic models for each reconstruction, satisfactory result is still lacking. By depositing Si on a 5$\times $2 surface, we have identified the formation of the $\surd $3$\times \surd $3 structure even there was no additional Au being deposited. This observation leads us to speculate (i) the $\surd $3$\times \surd $3 structure has a higher Si density than that of the 5$\times $2 structure, and (ii) the Au density in a single-domain $\surd $3$\times \surd $3 structure, i.e., no domain walls, is roughly equal to that in the 5$\times $2 structure.