Role of corner holes in Si(111)-7×7 structural formationstudied by ${\mathrm{HBO}}_2$smolecular irradiation and quenching

By using the characteristic of the ${\mathrm{HBO}}_2$ molecules, which initially react preferentially with the center adatoms in the unfaulted half units of the 7×7 structure, stability of corner holes in Si(111) structure was studied by scanning tunneling microscopy. The 7×7 structure began to break from the areas below step edges. Along the boundaries between 7×7 and the disordered areas including the $\sqrt{3}$×$\sqrt{3}$ phase, the structure of the corner hole in the 7×7 structure was observed to be maintained. A similar structure was also observed on a quenched Si(111) surface. The results obtained indicate that corner holes play an important role in the formation mechanism of the 7×7 structure. In fact, structures in which a dimer-adatom-stacking fault structure was considered to be formed from a corner hole were observed on a quenched Si(111) surface.